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    • 专利摘要:
    Summary Drawn heat-treated stable row for high-strength spring use provided containing, in mass% C: 0.67% to less than 0.9%, Si: 2.0 to 3%, Mn: 0.5 to 1.2%, Cr: 1 , 3 to 2.5%, N: 0.003 to 0.007%, and Al: 0.0005% to 0.003%, with a content of Si and Cr satisfying the following terms: 0.3 ° As Si-Cr1, 2%, and with a balance of iron and unavoidable impurities, P: 0,025% or less, and S: 0,025% or less, in addition with a content of undissolved spherical carbides with a circle equivalent diameter of less than 0,2 μm, in addition with a content of a metal structure, at least residual austenite in volume mats of Over 6% to 15%, with a previous austenite particle size number # 10 or more, and with an undissolved content of spherical carbides with a circle equivalent diameter of less than 0.2 μm.
    公开号:SE537538C2
    申请号:SE1250810
    申请日:2011-07-05
    公开日:2015-06-09
    发明作者:Masayuki Hashimura；Tetsushi Chida
    申请人:Nippon Steel Corp；
    IPC主号:
    专利说明:

    [1] The present invention relates to drawn heat-treated steel wire, for high-strength spring use, which can be used as a material for high-strength springs, made by cold winding, and to the preferred steel wire.
    [2] Springs used for motor vehicle engines, clutches, etc. need to offer more advanced performance and higher durability to cope with the trend towards lighter weight and higher performance of motor vehicles. For this reason, the material of the springs, that is to say, drawn heat-treated steel line for high-half-spring use, also needs to have a high material-half strength. Usually in the manufacture of such small, high-strength springs, the material has the drawn heat-treated steel line for high-strength spring use, toughened to give higher material strength, in the drawn heat-treated steel line for high-strength spring use, which then forms a coil spring. In addition, stress-relieving glazing or other heat treatment and nitriding is performed to obtain a finished coil spring. For this reason, the drawn heat-treated steel line, for high-strength spring use, not only needs to have high half-strength, but also sufficiently high machining ability so that it is not broken during cold winding and to steam softening by annealing, nitriding and other heat treatment, after sawing, aft have resistance to heat-related softening.
    [3] A fjacler needs to have good fatigue properties, therefore the drawn heat-treated steel row intended for high-strength spring use is used, t material, which is further nitrided or ball-bombed to increase the hardness of the surface layer of the spring. The durability of a spring includes fatigue properties and a resilience property. The fatigue properties are affected by the surface hardness. 1 The resilience property (the property of the spring resulting in plastic deformation in the load direction during use) is greatly affected, not only by the surface hardness, but also the hardness of the base material in the spring. For this reason, the surface hardness after nitriding and resistance to heat-related softening on the inside, where nitrogen is not introduced by nitriding, are important in the stable line, for high-strength spring use.
    [4] In addition, in the case of spring production by cold winding, oiling, induction hardening treatment, etc., where rapid heating and rapid cooling are used in the manufacture of the material of the drawn heat-treated steel wire, can be used for spring strength spring use. For this reason, the drawn heat-treated steel row can be reduced to a high austenite grain size, so that a spring with excellent fracture properties can be obtained. However, if the drawn heat-treated stable row has high half-strength spring use Mr hagre half-strength, in cold winding, fractures can occur and the spring shape may not be formed.
    [5] To deal with the problem, some of the inventors suggested that the carbides should be controlled, which makes the previous austenite finer, in this way both the strength and cold winding capacity (PLT 1) of the drawn heat-treated steel row can be achieved, for high-strength spring use. Furthermore, the inventors endangered the control of residual austenite and residual carbides, the dyeing of previous austenite, the ability to achieve both strength and cold winding shape (PLT 2 to PLT 4), in the drawn heat-treated steel row, for pasture spring spring breathing. In particular, the starting points are suppressed for fractures caused by the formation of coarse oxides and carbides, and the distribution of fine carbides of cementite which are required to ensure that the strength becomes uniform in order to vaporize the fatigue properties and machinability of the drawn heat treated stable line for pasture spring use.
    [6] PLT 2 focuses on the fact that the areas of sparsely distributed spherical carbides, with a circle equivalent diameter cm 2 μm or more, in the areas of sparse distribution of fine spherical carbides (in particular, cementite), affect the dynamic properties and define it. omeadet. 2
    [7] PLT 3 and PLT 4 note the effect of precipitation of fine carbides due to the addition of the alloying substance V, and limit the nitrogen (N) content to suppress undissolved spherical carbides. Legend has it that they use the effect of precipitation of carbides, nitrides, and carbon nitrides of V to enable the hardening of the steel bar to cure, at the annealing temperature or the hardening of the surface layer during nitriding. In addition, they also have the effect of vaporizing the coarseness of the austenite grain size, due to the formation of precipitate. The effect of the addition of V is remark value. Despite this, undissolved spherical carbides or nitrides are easily formed, so even if nitrogen (NJ) is suppressed, precipitation control needs to be done precisely.
    [8] DartOr compares PLT 4 quantitatively undissolved spherical carbides and precipitated carbides and defines the amount to obtain as much precipitated V carbides as possible, which affects the final spring performance. In particular, PLT 4 proposes to vague the precipitation of V carbides in the electrolytic reading, at constant potential, and compares the amount with the amount V passing through the filter (the amount of precipitated V).
    [9] PLT 1: Japanese Patent Publication (A) No. 2002-180198 PLT 2: Japanese Patent Publication (A) No. 2006-183137 PLT 3: Japanese Patent Publication (A) No. 2006-342400 PLT 4: International Publication WO2007 / 114491 Summary of the Invention Technical Problem
    [10] In recent years, surface hardening by nitriding has become a conventional method, in order to increase the durability of high-strength springs. Furthermore, increasing the nitriding depth and shortening the nitriding time, by increasing the treatment temperature, have been studied. For this reason, the features 3 heat-treated steel row, for high-strength springs, need further improved resistance to heat-related softening.
    [11] The above conventional drawn heat-treated steel row, for high-strength spring use, ensures a certain degree of uniform dispersion of fine carbides for improved fatigue properties and machining ability. But in order to improve resistance to heat-related softening, further spreading is necessary. In particular, the addition of V, proposed PLT 3 and PLT 4, has to a large extent the effect of hardening the steel row at the annealing temperature, hardening the surface layer at nitriding, and refining the austenite. ErneHeald, the control of the nitrogen content (N) is not simple. As a result, coarse carbides, nitrides, and carbon nitrides fall out, causing fatigue durability to deteriorate.
    [12] PLT 3 adds Nb and Ti, with the effect of capturing Excess Nitrogen (N), as a mill. Even if additives Ors control of appropriate amount N is still not easy. PLT 4 takes samples of remaining undissolved spherical carbides, obtained as a result, and compares with the dissolved carbides. DariOr PLT4 does not proactively control the uniform distribution of fine carbides.
    [14] Furthermore, as described in PLT 3 and PLT 4, in order to obtain excellent tensile strength and hardness and excellent machining ability, the size of the undissolved spherical carbides in the steel should be Refl. Effective size is preferably 0.1 μm or less. If the size is Over 1 pm, the contribution to hall strength and 4 processing capacity is lost and only a combination of the deformation properties is obtained. For that reason, the grain density of unplastic spherical carbides with a circle equivalent diameter of 0.2 μm or more becomes an important indicator. Therefore, it is an object of the present invention not to permit the occurrence of unloaded spherical carbides having a circle equivalent diameter of 0.2 .mu.m or more, when improving the shape of the rigid spring half-spring spring.
    [15] The inventors conducted intensive research to solve the above problems and obtained as a result the following discoveries: (a) They discovered again by carefully controlling the content of C, Si, Mn, and Cr in the stable line, to vaporize the formation of spherical carbides and by assimilating residual austenite, even without the addition of alloying elements such as V, the drawn heat-treated steel line for haghail strength spring use has improved half-strength and cold-winding shape compared to conventional steel wire.
    [16] (B) It was also discovered that by adding both Cr and Si in appropriate amounts to the steel row, the formation of unplastic spherical carbides and the softening on sliding or nitriding after winding is vaporized, and in addition, better hardness of the nitrated layer can be achieved. viii saga, in order to increase the strength of the fatigue properties, the addition of Cr is effective, but Cr is a substance which leaves uncharged spherical carbides, which have a negative effect on the cold winding shape. For that reason, the amount of added Cr behaved limited. The inventions also noted that Si vaporizes the growth of undissolved spherical carbides and the formation of cementite. The inventors discovered that if Si was added together with Okad addition of Cr, then the half-strength of the drawn heat-treated staldrad Oka. Quantitatively, it is sufficient to add a large amount of both Si and Cr, since the ratio between them controls the difference in the amount of added Si and the amount of added Cr, the viii saga, (Si-Cr)%.
    [17] (C) It was further discovered that by heating the gate to 1250 ° C or more, it is possible for Ora Cr and other alloying elements in the steel material to be uniformly dispersed and to vaporize the formation of coarse unplastic spherical carbides and also Ora fine carbides uniformly dispersed.
    [18] (D) Furthermore, it was discovered that the addition of V has a detrimental effect on p'a. the mechanical properties and fatigue strength of the stable row, for spring use.
    [19] From these facts the inventors discovered that it is possible to vaporize the coarsening of undissolved spherical carbides, by not adding V, or by adding an extremely small amount, and further, as explained above, controlling the amount Cr I in equilibrium with the amount Si .
    [20] Has means "undissolved spherical carbides" undissolved carbides with a ratio between the maximum size (longest size) and the minimum size (shortest size) (side ratio) of 2 or less. In fact, "carbides" and "spherical carbides" are also undissolved. These are also called "undissolved carbides" and "undissolved spherical carbides" even though they are synonymous. Although they are synonymous, they are also called "undissolved carbides" and "undissolved spherical carbides", respectively, to emphasize.
    [21] [121] (1) Preferred form line for high strength spring application, can be characterized by content in mass of, C: 0.67% fill 0.9%, Si: 2.0 to 3.5%, Mn: 0.5 to 1.2 %, Cr: 1.3 to 2.5%, N: 0.003 to 0.007%, and Al: 0.0005% to 0.003 with Si and Cr having the following expression: 0.3% 5Si-Cr5.1,2%, with balance of iron and unavoidable impurities, wherein P and S are impurities comprising P: 0.025% or less and S: 0.025% or less, and further, wherein a circle equivalent diameter for undissolved spherical carbides is less than 0.2 μm. (2) Preferred formulations for high-strength spring use, as set forth in (1), therefor can be drawn by content in mass%, of one or more of, 0.03 to 0.10%, Nb: 0.015% or less, Mo: 0.05 to 0.30%, 0.05 to 0.30%, Mg: 0.002% or less, Ca: 0.002 `) / 0 or less, and Zr: 0.003% or less, when V is 1.4%. 5.Cri-V52.6% and 0.70% 5Mn-FV51.3%, and, when containing Mo and W, 0.05% 5Mo + WQ, 5% is satisfied. (3) Drawn heat-treated stable row for high-strength spring use, can be drawn content in mass% of .7 C: 0.67% to 0.9%, Si: 2.0 to 3.5%, Mn: 0.5 to 1.2% , Cr: 1.3 to 2.5%, N: 0.003 to 0.007%, and Al: 0.0005% to 0.003%, Si and Cr having the following expression: 0.3% 5_Si-Cr51.2%, and with balance of jam and unavoidable impurities, with P and S as impurities comprising P: 0.025% or less and S: 0.025% or less, and further, with a metal structure comprising at least residual austenite of a volume mat of Over 6% to 15%, with a previous austenite particle size number # 10 or more, and further wherein a circle equivalent diameter for undissolved spherical carbides is less than 0.2 μm. (4) Drawn heat-treated steel line for high-strength spring use, according to (3), can be characterized by content in mass%, of one or more of, V: 0.03 to 0.10%, Nb: 0.015% or less Mo: 0.05 to 0.30%, W: 0.05 to 0.30% Mg: 0.002% or less, Ca: 0.002% or less, and Zr: 0.003% or less, when V is content, 1.4% 5Cr + V52.6% and 0.70% 5Mn + V.5.1, 3%, and, when containing Mo and W, 0.05% 5..Mo + W50.5% is satisfied. 8 (5) Drawn heat-treated steel line for high-strength spring use, according to (3) or (4), characterized in that the drawn heat-treated steel line, for high-strength spring use, has a tensile strength 2100 to 2400 MPa. (6) Drawn heat-treated steel line for high-strength spring use, according to any one of (3) to (5), characterized in that the drawn heat-treated steel line, for high-strength spring use, has a yield strength of 1600 to 1980 MPa. (7) Drawn heat-treated steel line for high-strength spring use, according to any one of (3) to (6), characterized in that the drawn heat-treated steel line, for high-strength spring use, has a surface hardness of HV750 or more according to the Vickers scale, and internal hardness or more gentle nitration at 500 ° C for 1 hour. (8) Production Procedure for Prefabricated Structural and High Strength Spring Use Can be characterized in that a good content in mass%, C: 0.67% to 0.9%, Si: 2.0 to 3.5 ° A), Mn: 0.5 to 1.2 %, Cr: 1.3 to 2.5%, N: 0.003 to 0.007%, and Al: 0.0005% to 0.003%, with Si and Cr satisfying the following expression: 0.3% 5Si-Cr51.2% , with a balance of iron and unavoidable impurities, with P and S as impurities comprising P: 0,025% or less and S: 0,025% or less, the goat being heated to 1250 ° C or more, then the goat is hot-rolled to produce a rolling stock and heating of the rolling stock to 1200 ° C or 30 more, with subsequent hot rolling for the manufacture of a lined steel line. (9) Production process for the preferred structure spring strength application according to (8), characterized in that the goth also contains, in mass%, one or more of 9 0,03 to 0,10%, NO: 0,015% or less Mo: 0,05 to 0.30%, 0.05 to 0.30% Mg: 0.002% or less, Ca: 0.002% or less, and Zr: 0.003% or less, when content of V is 1.4% .5.Cr + V5 .2,6 ° A) and 0,70% .5..Mn + W,1,3%, and, 10 for Mo and W content, 0,05 To 5M0 + VV50, Production ProcedureContracted for high-strength spring application, can be further illustrated by heating the Treatments shaped according to (8) or (9), to 900 ° C or more, after which it is patented at 600 ° C or less.
    [22] According to the three-pronged invention, in particular, the drawn heat-treated stable line, for high-strength spring application, with a high surface layer hardness and an inner hardness, and also high-strength spring with excellent durability, can be obtained due to the excellent cold winding shape and resistance to resistance. 500 ° C for 1 hour. The contribution to industry is an extreme start.
    [23] FIG. 1 is a photomicrograph of the metal structure showing an example of spherical carbides, in the drawn heat treated steel row, for high strength spring application, in the present invention. Undissolved spherical carbides are seen at the tips of the arrows in the figure.
    [24] Generally, a rolled spring roll is manufactured as follows: Of course, the manufacture of springs is not limited to the described process. This describes only one example.
    [25] Thereafter, the spring is machined by cold winding for improved strength and nitriding for improved surface hardness. PA sá satt is a "feather" manufactured as a final product. First, the chemical composition of the drawn heat-treated steel row, for high-strength spring use, in the present invention and its material, that is, the preferred steel spring, for high-strength spring use, will be explained. Has "%" in the chemical composition means mass%, unless otherwise indicated.
    [26] C: 0.67% to less than 0.9% C is an important substance which has a strong effect on the strength of the steel material and C also contributes to the formation of residual austenite. In the present invention, the lower limit of the amount C has been set to 0.67% or more to obtain sufficient strength. To increase the strength, the amount C is 0.70% or more, preferably 0.75% or more.
    [27] Si: 2.0 to 3.5% Si is an important substance for improving the food condition against heat-related softening of the steel and the resilience properties have the spring. To obtain these effects, 2.0% or more Si is needed. Furthermore, Si is effective for spheroidization and refinement of the cementite. To vaporize the formation of coarse spherical carbides, 2.1% or more of Si is preferably added. To increase the inner hardness, after nitriding and other treatments, to make the surface layer harder, 2.2% or more of Si was preferably added. Furthermore, from the balance sheet with Cr, Si is more advantageously set at 2.3% or more. Si is sometimes set to 3.0% or more.
    [28] Mn: 0.5 to 1.2% 12 Mn is a substance that is important for increasing the slackening ability and for stably securing the amount of residual austenite. In the present invention, Mn has been added in 0.5% or more, more preferably 0.65% or more, even more preferably 0.70% or more, to increase the yield strength of the steel and to secure residual austenite.
    [29] Cr: 1.3 to 2.5% Cr is a substance which is effective in improving the slackening ability and the resistance to heat-related softening. To obtain these effects, 1.3% or more Cr needs to be added. When nitriding, it is possible to make the hardened layer obtained by nitriding thicker by adding Cr. More than 1.5% of Cr is preferably added, to provide curing by nitration and softening resistance at the nitration temperature. More dangerously, 1.7% or more of Cr.
    [30] N: 0.003 to 0.007% N is a substance which forms nitrides with Al etc. included as the purification steel, in the present invention. To use fine nitrides and fine residual austenite, 0.003% or more of N should be included. On the other hand, if the amount N is exaggerated, the color rough nitrides and cold winding shape and fatigue properties decrease. Daft- ar den Owe gransen gets the amount N made 0.007% or less. Furthermore, taking into account the conditions for heat treatment, etc., the amount N is dangerously 0.0000% or less. 13
    [31] P: 0.025% or less P is a contaminant. P causes the steel to harden, form segregations, and cause proliferation, it said (hire limit of P is seen to be 0.025% or less. 5 Furthermore, P, as segregated at previous austenite grain boundaries, causes toughness and resistance to delayed fractures, etc. to decrease, said the Owe limit for the amount of P is preferably set at 0.015% or less.In addition, the amount of P is preferably limited to less than 0.010% when the yield strength of the steel line exceeds 2150 MPa.
    [32] S: 0.025% or less S is also a panty liner. If S is present in steel, it causes the steel to crack, see the upper limit for the amount of S seen at 0.025% or less. To dampen the effect of S, the addition of Mn is effective. Nevertheless, MnS is an inclusion. Especially in the star of high-strength, MnS sometimes becomes the beginning of crime. Therefore, in order to vaporize the incidence of fractures, the upper limit of the amount of S has preferably been set at 0.015% or less. Furthermore, the amount S is preferably limited to less than 0.01%, when the yield strength of the drawn heat-treated steel row, for high-strength spring use, will exceed 2150 MPa.
    [33] Al: 0.0005 to 0.003% Al is a deoxidizing agent. It interferes with the formation of oxides. If hard oxides are formed, the fatigue durability decreases. Especially if Al is added in Overflode, the fatigue strength varies and the stability is impaired, in high strength springs. If the amount of Al exceeds 0.003%, the incidence of fractures due to inclusions becomes larger, so the amount of Al is limited to 0.003% or less in the drawn heat-treated steel for high-strength spring use, in the present invention. The greater the spruce value of the quantity Al al is preferably 0.0028%, the more preferred 0.0025%.
    [34] [0034] On the other hand, if the amount of Al becomes less than 0.0005%, silicon-based hard oxides are easily formed. For that reason, the amount of Al is 0.0005% or more. The lower limit for the amount of Al is preferably 0.0007%, more preferably 0.0008%, even more preferably 0.001% or more. 14
    [35] Most recently, the standpoint of the present invention, that is, the relationship between Si and Cr, will be explained. It is already possible that both Si and Cr are important for increased strength in spring numbers.
    [36] 0.3% 5Si-Cr 1.2% If the amount of Si exceeds the prescribed amount, the propagation becomes extreme and the processing capacity during winding is reduced. Not only that but 10 decalcification in the Transition process becomes startling. For this reason, the surface layer hardness becomes lower and the durability decreases, in the final spring product. Furthermore, stripped parts are formed randomly, which is affected by the duration of the half-strength, of the manufactured spring. When the quantity Si is less than the prescribed quantity, the half-strength decreases. Furthermore, the forgiveness property is insufficient. It ors accuse clearly in the hardness after nitriding. Sufficient hardness can not be ensured either at the surface layer or inside.
    [37] Given this, the ratio of Si to Cr, in the cementite, steel is important. That is to say, Si is a substance which destabilizes cementite. If a large amount of Cr is added or other substances which stabilize cementite on heating, it has the effect that the formation of a solid load of cementite is promoted. Therefore, the amount of undissolved spherical carbides becomes larger and the processing capacity decreases remarkably, while the amount of Si is small, regardless of whether a large amount of Cr is added. The inventors discovered that it is possible to use the difference between the Si content (mass%) and the Cr content (mass%) in the steel, that is to say, the Si-Cr amount, as a carpet stack. That is, when the value of Si-Cr is less than 0.3%, the amount of Cr becomes relatively rigid and undissolved spherical carbides remain light. On the other hand, if Si-Cr is over 1.2%, Si becomes relatively superfluous, which causes spreading, decalcification or other problems. Daric5r the value of Si-Cr should be set to 0.3 to 1.2%.
    [38] In order to vaporize the formation of carbides, a large amount of Si-Cr allows undissolved carbides to be suppressed, but industrially, if Si is present in too large an amount, the thickness of the hardened layer by nitriding becomes slightly thin. For this reason, Si-Cr is preferably 50.9%, more preferably Si-Cr is 50.75%, in view of the behavior having undissolved spherical carbides and the hardened layer formed by nitration. Furthermore, with the intention of reducing the amount of Cr and reducing the residual occurrence of undissolved spherical carbides, respectively, the lower limit is advantageously 0.35% 5Si-Cr, more advantageously 0.4% Si-Cr.
    [39] Most recently, the selectively added chemical composition will be explained.
    [40] V: 0.03 to 0.10% V is a substance which forms nitrides, carbides, and carbon nitrides. Fine V nitrides, carbides, and carbon nitrides with a circle equivalent diameter of less than 0.2 microns are effective RN staining of residual austenite. Furthermore, these can also be used for hardening the surface layer by nitriding. On the other hand, it is necessary to precisely control the precipitation, as undissolved carbides and nitrides are still formed, even if nitrogen (N) is suppressed. For that reason, according to the present invention, V is not intentionally added. To obtain such an effect, a fine amount of V can be added. To obtain the effect, V should be added in 0.03% or more, preferably 0.035% or more, more advantageously 0.04% or more.
    [41] On the other hand, with the addition of more than 0.10%, coarse spherical carbides are formed and the cold winding force and spring fatigue properties are compromised. Therefore, the V content must be set to 0.1% or less. Furthermore, by adding V, pre-drawing, an subcooled structure is easily formed which causes cracks and fractures during drawing. For this reason, the upper limit is that the quantity V is preferably set at 0.09 `) / 0 or less, more preferably 0.08% or less, most preferably 0.05% or less. In particular, in the case of the addition of a small amount of Nb, the amount of addition of V is preferably set to 0.05% or less. Furthermore, V is a substance which strongly affects the formation of residual austenite in the same way as Mn, so the amount of V must be carefully controlled together with the amount Mn,
    [42] Nb: 0.015% or less Nb is a substance which forms nitrides, carbides and carbon nitrides in st51. These precipitates are sometimes used to control the austenite grain size, etc. But at the same time, the excessive addition gives reduced ductility and results in cracks forming more easily during rolling and hot forming. For this reason, Excessive addition of Nb should be avoided.
    [43] Nb was allowed for the purpose of controlling the quantity N. The precipitates are not used directly to control the quality. Valve springs and other springs are manufactured by slackening, tempering, then cold winding, but at that time, dissolved suffocating color deformation prevents and reduces the stress limit. For this reason, the cold winding stock is mixed. Therefore, the effect is by adding Nb and forming nitrides at high temperature, that the dissolved nitrogen matrix decreases and the cold winding capacity is improved.
    [44] Furthermore, the addition of a small amount of Nb is also effective in vaporizing V and other undissolved spherical carbides involved as unavoidable impurities. Is a substance which is effective in improving the resistance to heat-related softening during nitriding and the hardness of the outermost layer. However, if the amount of added V becomes larger, V-nitrides, V-carbides, and V-carbon nitrides are often not sufficiently low, even in patenting, slackening and other heatings, as Ors to obtain an austenite phase, for the manufacture of drawn heat-treated steel for high-strength spring use. spherical carbides of V wax from the nuclei of the V-based nitrides, formed at the time of normal high temperature. As a result, undissolved spherical carbides remain and the winding shape accumulates. For this reason, it is necessary to vaporize the amount of added V when undissolved spherical carbides are suppressed. In the present invention, V was not a necessary substance.
    [45] In contrast, Nb nitrides form at a higher temperature than V. For this reason, Nb suppresses the formation of V nitrides in the steelmaking process. The viii saga, Nb forms nitrides in the high temperature region, where V dissolves and does not form nitrides, Furthermore, at high temperatures where V nitrides are formed, Nb consumes nitrogen, so that the formation of V nitrides is justified, even on cooling. For this reason, the addition of a small amount of Nb is particularly effective in vaporizing undissolved spherical carbides and securing the winding capacity when adding a large amount of V.
    [46] If the amount of Nb added is greater than 0.015%, the hot ductility is impaired and defects and other problems during rolling appear more easily. For this reason, the amount of Nb added is set to 0.015% or less, three times 0.010% or less, more preferred 0.005% or less, most preferred less than 0.001%.
    [47] 1.4% 5_Cr + V 2.6% In the present invention, V is not intentionally added. However, as explained above, the addition of a small amount of V effect on the refinement of the former austenite and the formation of residual austenite. By carefully controlling the sum of the amount of Cr and V added with respect to V, it is possible to increase the hall strength to increase the surface layer hardness after nitriding and that the inner hardness is suitable for high half-strength springs.
    [48] Cr and V are both substances which prevent softening on heating by glowcigning or nitriding etc. performed after spring winding, the viii saga partly so-called heat-related resistance to softening. In particular, nitriding causes nitrides to precipitate at the nitrided part of the surface layer, thereby improving the surface hardness and increasing the nitriding effect. Furthermore, even at the inside, where nitriding does not spread, carbide probes are steamed. On the other hand, Cr and V! Ada are the substances that facilitate the formation of undissolved spherical carbides. Cr is dissolved in the cementite to increase the resistance, so that the dissolution of the cementite vaporizes the heating step for dissolving the cementite (heating at the time of patenting and heating at the time of slackening), often remaining as undissolved spherical carbides. Furthermore, V also6 has a dissolution temperature for the precipitates, which is higher than the A3 point for steel, so V remains! All as undissolved spherical carbides.
    [49] If the total content of Cr and V, i.e. CNN, is less than 1.4%, the surface hardness of the high-strength spring decreases below HV750 and the inner-half strength decreases below HV570. For that reason, Cr + V is preferably 1.4% or more. Furthermore, 1.5% or more is preferable. On the other hand, Excessive additive leaves 18 Cr + V, of more than 2.6%, large amounts of undissolved steric carbides, which leads to a reduction in the winding capacity. DartOr, 2.6% is set to the Upper border. Furthermore, Cr + V is preferably 2% or less, more preferably 1.8% or less. 0.7% 5.Mn + V% Mn and V are the substances which improve the leaching capacity and which also have a large effect on the formation of residual austenite. If the amount Mn is greater than the prescribed amount, the amount of residual austenite increases. has the sum of both Mn and V, which occur as unavoidable contaminants, a direct effect on the behavior of 10 austenite, It is not only the working capacity that is affected, but also the yield strength is strongly affected. Adequate durability can not be ensured. [00511Therefore, it is the total. the content of Mn and V, the viii saga Mn + V, juice to 0.7 to 1.3% in the present invention To ensure a volume mat of Over 6% of residual austenite, the lower limit for Mn + V must be set to 00% or more. As a result, transformation-induced plasticity causes the toughness to improve and mitigates the cold winding shape, however, the upper limit of Mn + V must be set to 1.3% or less, for aft Ora residual austenitic volume of 15%. el laughs less. Due to this, the formation of processing-induced martensite, as a result of the impact field during cold winding, is suppressed and local propagation can be prevented. Mo: 0.05 to 0.30 ° A Mo is a substance which improves the quenching capacity. Furthermore, Mo is also extremely effective in improving the resistance to heat-related softening. In particular in the present invention, 0.05% or more of Mo is added to further improve the resistance to heat-related softening.More is a substance which forms Mo-based carbides steel.The temperature at which the Mo-based carbides precipitate is lower than the temperature at which V-carbides etc. precipitate. This is because the addition of a suitable amount of Mo is also effective in producing carbide coarsening. Addition of 0.10% or more of Ma is preferable. However, when the amount of Mo is added is more than 0.30%, a supercooled structure is easily formed. , 19 for hot rolling, and patenting for drawing, etc. Therefore, in order to vaporize the formation of a supercooled structure, causing cracking or breaking of wire during drawing, the maximum limit of the amount Mo is set to 0.30% or less, f 0.25% or less. Furthermore, if the amount of Mo is large, in the case of patenting, the time until the end of the perlite transition becomes longer, so the amount of Mo is preferably reduced to 0.20 ') / 0 or less.
    [54] In particular, W: 0.05 to 0.30% W, like Mo, is a substance which is effective in improving the slackening ability and the resistance to heat-related softening and is a substance which precipitates in the steel as carbides, In particular in the present invention added 0.05% or more W to improve the resistance to heat-related softening.
    [55] On the other hand, when W is present in OverflOd, a supercooled structure is formed which causes cracking or fractures during drawing, so that the amount W must be juiceed to 0.30% or less.
    [56] In addition, in view of the simplicity of heat treatment, etc., the amount W is preferably 0.1 to 0.2%, more preferably 0.13 to 0.18%.
    [57] 0.05% .5_Mo-i-VV _ 0.5% Mo and W are the substances which are effective in improving the resistance to heat-related softening. If added in combination with each other, the growth of carbides is vaporized and the resistance to heat-related softening can be remarkably improved with the addition of only Mo or W. In particular, to improve the resistance to heat-related softening when heated to 500 ° C, the Mo + must be set. to 0.05% or more, preferably 0.15% or more.
    [58] Most recently, Mg, Ca, and Zr will be explained.
    [59] With the addition of more than 0.001%, however, it is black for Mg to remain in the molten steel, there is an effect of the oxide composition and the amount of emerging oxides which form the basis for fatigue becomes larger, so 0.002% Mg is the Upper the border. Therefore, the upper limit of the amount of added Mg was set to 0.002 ° / 0, preferably 0.0015% or less. Furthermore, when it comes to spring steel compared to other steel for construction use, the amount of added S is suppressed, considering the yield, etc., is 0.001% or less is preferable. Furthermore, when used for high strength valve springs, the containment probability is high, so Mg has the effect of improving the corrosion resistance and the resistance to postpone fracture prevention rolling cracks due to the effect of the distribution of MnS etc. Added by so many small amounts. the range 0.0002 to 0.001 is preferred.
    [60] Ca: 0.002% or less Ca is after oxide and sulfide-forming substance. In spring figures Or Ca, said that MnS becomes spherical and thereby vaporizes the extent of MnS, which serves as the initiating place for fatigue and other fractures, which makes MnS harmless. The effect is similar to the effect of Mg. Addition of 0.0002% or more is preferable. Furthermore, not only is the yield poor, although more than 0.002% is added, but oxides and CaS and other sulfides are also formed and problems in manufacturing and assembling the spring fatigue durability properties fall, so the amount was set to 0.002% or less. In view of the amount added, in which the probability of containment is high when used for high-strength valve, the advantageous amount is preferably 0.0015% or less, more preferably 0.001%.
    [61] Zr: 0.003% or less Zr is an oxide, sulfide, and nitride-forming moiety. In spring numbers, the oxides are finely distributed, and on the same salt as with Mg they form nuclei for precipitation of MnS, and can then sail Ora MnS finely distributed. As a result, it is possible to improve the fatigue durability and further increase the ductility in order to thereby improve the winding capacity. Preferably 0.0002% or more is added. Furthermore, even if more than 0.003% is added, not only the yield is added, but oxides and ZrN, ZrS, and other nitrides and sulfides are formed and problems in the production or degradation of the spring durability properties are folanied, so the amount is set to 0.003% or less. The amount added is preferably 0.0025% or less. In addition, Zr has the effect of improving the winding capacity by controlling the sulphides, so the additive is advantageous for high strength valve springs, but Mr to minimize the effect of inclusions, suppression to 0.0015% or less is preferable.
    [62] Notes that the above voluntarily added chemical compositions, if containing small amounts, do not detract from the effect of the stable radical comprising the basic chemical composition of the present invention.
    [63] The metal structure of the housing structure, for high-strength spring use in the present invention, is to be explained.
    [64] Undissolved spherical carbides Undissolved spherical carbides play an important role in ensuring the half-strength of the stable line for high-strength spring use. On the other hand, the presence of undissolved spherical carbides causes the winding stomach to constrict. Furthermore, coarse carbides also cause the fatigue properties to deteriorate. It is necessary to vaporize undissolved spherical carbides on winding and after final nitriding to create a uniform distribution of fine carbides to solve the problem of the present invention.
    [65] The stable line for high-strength spring use in the present invention has a long size of undissolved spherical carbides of 0.2 μm or less which is suppressed during roughening. The undissolved spherical carbides are already present after the rolling of the wire rod Wet wants to say the treaties are shaped).
    [66] The Strength in the Stable Row for High Resilience Spring Use In the present invention, Oker is further increased by the addition of C, the fill of Mn and Cr, the further addition of Mo, W, and other so-called alloying elements. When large amounts of C and in particular Cr and other alloying substances, which form nitrides, carbides, and carbon nitrides, are added, spherical cementite carbides and alloy-based carbides remain in the steel. Spherical cementite carbide and alloy-based carbides are undissolved spherical carbides that do not dissolve in the steel during heating during hot rolling.
    [67] Note that in the present invention, both spherical alloy-based carbides and spherical cementite carbides will be referred to as spherical carbides. In the steel there are nal-shaped carbides corresponding to the nal-shaped structure of tempered martensite, but these nal-shaped carbides are not included in the spherical carbides in the present invention. Squeegee-shaped carbides are not present immediately after slackening but fall out during the rolling process. The 23 tempered martensite structure is a structure suitable for achieving both strength and toughness and machining ability. Nalform is in a sense the ideal form for carbides.
    [68] Strictly speaking, the machining mold can also be assembled if carbides with a proportion of 2 or more (nal-shaped carbides) are coarse. But in fact, needle-shaped carbides become coarse when the annealing temperature is high or when the retention time during annealing is extremely long. The effect of the performance is because the strength and hardness become insufficient. Problems arise in other areas with undissolved spherical carbides. Coarse-grained nal-shaped carbides are not formed in the 2100 MPa or so strong steel row, included in the present invention. Therefore, nal-shaped carbides are not included in the present invention. As explained above, the precipitated carbides are normally undissolved, but in the present invention the term "unresolved" has been added. This only emphasizes their unresolved character. In the present invention, "undissolved spherical carbides" and "spherical carbides" are synonymous.
    [69] Unresolved carbide carbide can be observed with a microscope microscope (SEM) by adhering a sample obtained from a preferred stable or drawn heat-treated stable, for high-strength spring application, to mirror gloss and etching the sample by picral or electrolytic etching. Furthermore, spherical carbides can be observed by model procedure by transmission electron microscopy (TEM).
    [70] Figure 1 shows an example of a structural SEM image of a pray after electrolytic sketching. In the structural picture In Figure 1 it is observed that the matrix of the steel has two types of structures, that is to say saga, squeegee-shaped structures and spherical structures. Among these are the needle-shaped structures of annealed martensite formed by toughening. On the other hand, the spherical structures are carbides 1 which have taken their spherical shape in that they have not been dissolved in the steel by additionally being made spherical by toughening by annealing in oil or induction hardening treatment (undissolved spherical carbides) due to heating by hot rolling. Spherical carbides can be observed at the front of the arrow in Figure 1. 24
    [71] Undissolved spherical carbides with a circle equivalent diameter of less than 0.2 .mu.m In the present invention, undissolved spherical carbides affect the properties of the drawn heat-treated steel row for high-strength spring application and are controlled in size as follows: Note that compared to prior art. Spherical carbides are further defined to achieve higher performance and machining ability in the present invention. Spherical carbides with a circle equivalent diameter of less than 0.2 .mu.m are extremely effective in maintaining the strength and resistance to heat-related softening of the steel.
    [72] In contrast, spherical carbides with a circle equivalent diameter of 0.2 μm or more do not contribute to improving the strength and resistance to heat-related softening and the degree of cold winding capacity. For this reason, the present invention is characterized by not allowing the formation of spherical carbides with a circle equivalent diameter of 0.2 μm or more.
    [73] Here, the process of feeding the circle equivalent diameter and density of the present spherical carbides will be explained. A sample that has tags from the stable line, for high-strength spring application, is polished and electrolytically etched. Note that the observed area is randomly selected near the center of the radius of the heat-treated rolling bar (steel bar), that is to say, the so-called "1 / 2R-dough", to eliminate special conditions such as decarburization and segregation in the middle. . Furthermore, the feed area is 300 pm2 or more. In electrolytic sketching, the surface of the sample is corroded by electrolysis in an electrolytic cluster (a mixture of acetylacetone 10 mass%, tetamethylammonium chloride 1 mass%, and an equilibrium of 5 methyl alcohol) where the sample is used as anode and platinum as cathode and has a current potential generator. used. The potential becomes constant at a potential that is suitable for the sample in the range -50 to -200 mV vs SCE. It is preferred that the potential be constant at -100 mV vs SCE, Mr st6ltrAden in the present invention.
    [74] The amount of current used can be determined by the total surface area of the sample x 0.133 [c / cm 2]. Note that not only the polished surface but also the surface of the sample embedded in resin is added to the total surface area of the sample.
    [75] After that, the sample is observed with SEM and a structural image of the spherical carbides is tagged. In the SEM, the structure of the spherical carbides is relatively white, and has a proportion (partial proportion) of largest size (Ong size) and a minimum size (short size) of 2 or smaller, spherical carbides. The magnification of the image taken with SEM is X1000 or more, with X5000 to X20000 to be preferred. As feed positions, the solids were selected at a thickness of about 0.5 to 1 mm from the surface of the roll wire, the segregated center portions being avoided. The SEM structure image was processed with image processing to feed the smallest size (short size) and largest size (size) of the spherical carbides observed in the feed area and the circle equivalent diameter is calculated. The circle equivalent diameter is the diameter near the area, calculated by image processing, of an undissolved carbide in an area Mare converted to a circle with the same area.
    [76] The metal structure of the drawn high-strength spring application and drawn heat-treated strong 26 The metal structure of the drawn heat-treated steel line for high-strength spring use, according to the present invention, comprises volume mat Over 6% to 15% of residual austenite and a balance of anlOpt martensite. Fine inclusions are allowed. The "fine inclusions" are oxides and sulfides. The oxides are deoxidation products of Al and Si etc., the sulfides corresponding to MnS, CaS, etc.
    [77] The previous austenite grain size in the structure is # 10 or more, with the circle equivalent diameter of the spherical carbides being less than 0.2 μm.
    [78] Previous austenite grain size number: # 10 or more The structure which has been heat treated for high strength fiber use in the present invention is comprised mainly of tempered martensite. Previous austenite grain size has a large effect on the 20 properties. That is, the fatigue properties and formability are improved due to the refinement of the previous austenite grain size as an effect of grain size reduction. In the present invention, the former austenite grain size is made # 10, in order to achieve sufficient fatigue properties and formability.
    [79] Refining of prior austenite is particularly effective in improving the properties of the heat treated steel for high strength spring use. The previous austenitic grain size number is preferably made # 11, more preferred # 12. To refine the grain size of previous austenite, it is effective to reduce the heating temperature during slackening. Note that "previous austenite grain size number" is based on JIS G 0551. If slackening is performed by reducing the heating temperature and shortening the time, the previous austenite grain size can be refined, but unreasonably low temperature and short treatment time not only increases the amount of undissolved spherical carbides, but results 27 sometimes also in unsatisfactory austenite transformation per se and slackening in tv6 phases. Conversely, the formability and fatigue properties are sometimes reduced. For that reason, # 13.5 is usually the upper limit.
    [80] Residual austenite: Over 6% to 15% (unit by volume) The microstructure which is heat treated for high strength spring application includes after toughening, tempered martensite, residual austenite, and a small volume fraction of inclusions (the precipitates described are also included). Residual austenite is effective in improving cold winding capacity. The volume unit of residual austenite is made 6%, preferably 7% or more, more preferably 8% or more, to secure the cold winding capacity, in the present invention.
    [81] On the other hand, if residual austenite exceeds the volume content by 15%, martensite, which is formed as a result of work-induced conversion, causes the cold winding properties to decrease. Therefore, the volume mat of residual austenite is set at 15% or less, preferably 14% or less, more preferably 12% or less.
    [82] Note that residual austenite is softer than annealed martensite, which reduces the yield strength. Furthermore, the transformation-induced plasticity is used to improve the formability, which contributes remarkably to improve the cold formability. On the other hand, residual austenite often remains in the segregated parts, former austenite basket boundaries, and areas clamped by the hanging grains, so that martensite which is formed by work-induced phase transformation (work-induced martensite) becomes the starting point for crime. Furthermore, if residual austenite increases, anlOpt martensite decreases proportionally.
    [83] For this reason, previous decrease in strength and cold winding ability, due to residual austenite, has been considered a problem. But in 28 high-strength steel radar of over 2000 MPa, the amount is added C, Si, Mn, Cr, etc. storm which makes the use of residual austenite extremely effective to improve cold winding capacity. Furthermore, flight high performance spring machining technology has made it possible to vaporize the deterioration of the formability properties even if parts with high hardness are formed locally due to the formation of machining induced martensite in forming the spring.
    [84] Most recently, the mechanical properties of the drawn heat-treated steel row for high-strength spring use will be explained.
    [85] Therefore, it is necessary to set the tensile limits for materials of the drawn heat-treated wire, for high-strength spring respiration, in order to increase the half-strength of the spring and improve the fatigue properties. Furthermore, cold-winding capacity is required in order for the drawn heat-treated steel row, for high-strength spring use, to be able to be processed into the desired shape, so the upper limit for the stretch limit must be limited.
    [86] Stretch limit: 2100 to 2400 MPa If the Preferred heat-treated stable line, for high-hill spring application, hardened at the surface by nitriding, etc., has a large tensile limit, it is possible to improve the fatigue properties and the resilience property of the spring. In the present invention, the tensile strength of the drawn heat-treated stable row for high-strength spring use is made 2100 MPa or more, to improve the fatigue properties and resilience properties of the spring.
    [87] [0087] On the other hand, if the drawn heat-treated steel row for high-strength spring use has too large a stretch limit, the cold-winding shape decreases so that the stretch limit is set to 2400 MPa or less.
    [88] Strain boundary (if tensile strength cannot be observed, indicates 0.2% test stress): 1600 to 1980 MPa the present invention means the tensile strength or tensile point of drawn heat-treated steel line, For high-strength spring use, the highest tensile strength when a tensile point is seen on the stress curve -axial tensile strength test and 0.2% shows tension when no tensile point is visible. In order to ensure the strength and resilience of the spring, which is elastically deformed by repeated tensioning, increased tensile strength is preferred. In order to increase the yield strength of the spring, it is preferable to increase the yield strength of the material that is to say drawn heat-treated steel row, for high-strength spring use.
    [89] [0089] On the other hand, with the drawn heat-treated steel line for high-strength ladder use, there is a great deal of scrutiny, and the cold-winding shape is sometimes cherry-picked. For this purpose, the heat-treated steel line for high-strength spring use preferably has a tensile strength of 1600 MPa or more, in order to ensure the strength and resilience of the spring.
    [90] To provide further higher durability, 1700 MPa or more is preferable.
    [91] Vickers hardness after nitration by maintaining at 500 ° C for 1 hour: Surface hardness HV .750, inner hardness HVa570 A high-strength spring is improved in surface layer hardness during nitration, whereby the inside is softened. For example, in the case of gas nitriding at 500 ° C, it was black to evaporate the softening of the inside of the drawn heat-treated steel row, for high-strength spring application, when the conventional heating temperature becomes 500 ° C. The drawn heat-treated stable line for high-strength spring use, in the present invention, has excellent resistance to heat-related softening and enables the cause of the spring fatigue properties and the resilience property after heating at 500 ° C.
    [92] The surface layer hardness is added to the micro Vickers hardness at a depth of 50 to 100 μm from the surface layer with the Vickers hardness 750 or more. If the Vickers hardness is 750 or more, the surface layer hardness becomes insufficient and fatigue durability is also impaired, which means that the residual stress after the ball bombing is not sufficiently reduced. Preferably, the surface layer hardness is 780 or more.
    [93] On the other hand, the inner hardness is sometimes measured. The Vickers hardness is sometimes measured during slackening, when the temperature at the surface layer of the steel row is higher than inside, which means that feeding of the inner hardness is preferably Ors at a position 500 m deep from the surface. In order to ensure the yield strength and yield properties, the Vickers hardness after heat treatment maintaining the range at 500 ° C for 1 hour shall be 570 or more. Furthermore, 575 or more are the Lecture.
    [94] Furthermore, the surface layer of the drawn heat-treated steel row for high-strength spring use is used as material for high-strength springs, hardened by ball bombardment, nitriding, etc. The inner hardness will vary depending on the nitriding temperature during actual production of a spring.
    [95] Note that when drawn heat-treated stable wire for high-strength spring use, in the three-pronged invention, is used as a material for producing high-strength spring, it is cold-wound and nitrided. For this reason, residual austenite decreases somewhat, at a depth of 500 μm from the surface of the high-strength spring, compared with the material for the drawn heat-treated steel for high-strength spring use.
    [96] Most recently, the process for producing the drawn heat-treated steel frame for high-strength spring application, the present invention, will be explained. A steel grade adapted according to the chemical composition of the trout is rolled to produce a steel roll of reduced size. Furthermore, the roll assembly is heated, after which it is hot-rolled for all obtained contracts designed for 25 high-strength spring application. The preferred steel wire for high strength spring application is patented, shaped and also slipped to make the hard surface soft. Thereafter, the draft line is drawn, slacks and antps to produce the drawn heat-treated steel line for high-strength fiader application. "Patenting involved heat treatment to lubricate the structure of the steel after hot rolling ferrite and perlite and ors for softening the steel wire pre-coating. After drawing, antifouling in oil, induction hardening treatment, and toughening are carried out to adjust the steel wire structure and properties. 32
    [97] The method of preventing spheronization of spherical carbides is important in the production of the preferred designs for high strength spring use in the present invention.
    [98] In particular, when the content of C and Cr Ai-Mgt, in the present invention, it is extremely important to heat the goat or rolling stock sufficiently for pre-rolling at that stage and to simplify precipitation inside the steel and to dissolve the internal coarse carbides (alloy carbides). and cementites) and the Ora material is homogeneous. In order to prevent the formation of coarse carbides, coarse carbides which are formed by the goth or whey must be dissolved in the steel. Furthermore, it is nOcIvAndigt to create uniform spreading steel. For this reason, Cikad heating temperature is preferred.
    [99] [0099] Darr & Ar gOten or the roll made foist after casting at a heating temperature of 1250 ° C or more. As a result, it is possible to dissolve the 15 undissolved spherical carbides sufficiently. For this reason, the heating temperature and the heating time are insufficient during the heating after subsequent rolling, patenting and quenching, so undissolved spherical carbides remain overnight, but in order to allow sufficient dissolution from the beginning, the dimensions of the vessels may be insoluble. The heating temperature of the GO should be 1270 ° C or more.
    [100] Thereafter, the roll blank, which has been manufactured by rolling the cast iron, is further hot-rolled (the roll is rolled) to make the preferred steel for high-strength spring use. At this time, the heating temperature of the roll is set to 1200 ° C or more. Preferably, the heating temperature of the roll blank should be set to 1250 ° C or more.
    [101] In the above procedure, it is necessary to reduce the size in order to avoid coarseness in order to vapor coagulation of undissolved spherical carbides has the stable line after heat treatment of the undissolved spherical carbides, which are presently preferred Wet will say, after vaistra greatly reduced or if, for example, undissolved carbides are present.
    [102] After rolling tags appeared in a spool and air cooler according to conventional method. For this reason, the microstructure of the preferred staltra (staltra after rolling of rolling) usually comprises ferrite and perlite or perlite with a high perlite structure fraction, since the amount C is high. Undissolved spherical carbides are present in the base material.
    [103] Unread spherical carbides can be observed by observing a polished and etched detection sample by SEM. Undissolved carbides can be clearly distinguished from laminar cementite contained in the perlite structure because the base material is spherical. Of course, the size can also be fed.
    [104] After hot rolling, the preferred steel row is patented for spring use.
    [105] The slackening after drawing is carried out by heating to a temperature of A3 point or more. To promote the dissolution of carbides, it is advisable to increase the heating temperature at slackening. Upon slackening, the heating rate was set three times to 10 ° C / sec or more and the retention time at the temperature of the A3 point or more is preferably to 1 min to 5 min, to vaporize the growth of carbides. In order to dampen the grain growth of austenite, it is advisable to shorten the retention time. To promote slackening and martensite transformation, the cooling rate should preferably be 50 ° C / sec to 100 ° C.
    [106] The refrigerant in the quenching process is preferably set to 100 ° C or less, more preferably a low temperature of 80 ° C or less, to accurately control the amount of residual austenite. The coolant temperature is 40 ° C or more in the present invention. The choice of coolant is not particularly limited as long as it is an oil, after water-soluble quencher or other coolant that promotes quenching. Furthermore, the cooling time can be shortened in the same way as for oil opening and induction hardening treatment. It is preferable to avoid prolonged retention time at low temperature to greatly reduce residual austenite and lower the refrigerant temperature to 30 ° C or less. That is to say, it is preferable that the slacking is completed within 5 minutes.
    [107] [0107] After slackening, tempering is performed. Fertilization suppresses the growth of carbides, so it is preferable that the heating rate is 10 ° C / sec or more and that the retention time is 15 minutes or less. The retention temperature varies due to the chemical composition and the target for the half strength, but the material is usually maintained at 400 to 500 ° C.
    [108] The designs designed for high strength spring use are cold wound to be processed into the desired spring shape, freed from stress and nitrided and ball bombing to manufacture the spring.
    [109] The cold-wound steel row is reheated by stress-relieving glocigning, nitriding, etc. At this time, the inside is softened, which means that the performance of the spring decreases. In particular, in the present invention, sufficient hardness is preserved even if nitration is carried out at a high temperature of about 500 ° C. As a result, it is possible to increase the micro Vickers hardness at a depth of 500 microns from the surface layer of high-strength springs HV575 or more, for the designs designed for high-strength spring application. Note that the micro Vickers hardness is fed at a depth of 500 μm from the surface layer of spring to evaluate Vickers hardness of the base material which is not affected by nitriding and ball bombing during curing. Example
    [110] Steel with the chemical composition shown in Tables 1-1 to 1-4 is smeared in a 10 kg vacuum malting furnace and cast to obtain a cast or roll blank. These vacuum narrow materials were hot pressed up to 08 mm. Thereafter, the materials which are hot pressed up to 8 mm were heated at 1270 ° Cx4 hours. Furthermore, a portion of the sample is refined in a 250 ton converter, continuously cast to prepare the cast, then heated at 1270 ° Cx4 hours or more, then made into roll rolls. with a cross-section of 160 mmx160 mm. These are further rolled to obtain 1) 8 mm of rolled wire. The heating temperature of the roll blank for rolling was set to 1200 ° C or more. [0111] A diameter of 8 mm of the preferred steel wire (rolled wire) is preferably The heating temperature at patenting is preferably 900 ° C or more so sufficient raising of carbides etc. is achieved.Patenting is performed by heating at 930 ° C then the sample is fed into a flowing bath at 600 ° C. patenting, the steel wire drawn is allowed to obtain a 4 mm diameter drawn wire rod, on this juice by heating the grit at a high temperature after which the temperature in the rolling process e, patenting, and slackening As high as possible, it is possible to vaporize the growth of undisturbed spherical carbides and keep the dimensions down to 0.2 μm or less. 36
    [112] In order to adapt the stretch limit of the patented and drawn staltraden, the staltraden is hardened to manufacture the preferred staltrad for spring use. Note that the sample that broke during drawing was not toughened. Tough curing was done by heating the drawn stable at a heating rate of 10 ° C / sec or more at 950 ° C or 1100 ° C (temperature at A3 point or more), maintaining at the top of the heating temperature for 4 minutes to 5 minutes, then placing the steel in a room temperature water tank said that the cooling rate will be 50 ° C in sec or more and the cooling Ors to 100 ° C or less.
    [113] The results of the evaluation show the state of wire breakage, previous austenite grain size number, residual austenite quantity (vol%), circle equivalent diameter and density of carbide presence, yield strength, sample stress 0.2%, saving bending angle, average discharge strength, Vickers hardness strength.
    [114] A sample taken from the obtained heat-treated steel-treated steel row for fiader use, evaluated for previous austenite grain size, volume fraction of residual austenite, and carbides, then the sample for tensile test, bending test of the spar, and micro Vickers hardness test. Note that the fatigue properties were evaluated by simulating treatment and production of the spring (hereinafter, referred to as "feather production and treatment") including gas nitriding, simulating nitriding on a spring after processing (500 ° C, 60 minutes), ball bombing (diameter of cut tad 0 , 6 mm, 20 minutes), and long-term de-stressing treatment (180 00, 20 minutes).
    [115] Previous austenite grain size numbers were measured based on JIS G 0551. The circle equivalent density and density of the carbides were measured by using an electronically etched sample to obtain a SEM structural image, and by analyzing the image. Furthermore, the volume mat of residual austenite is fed by the magnetic feeding method.
    [116] The fatigue test is a Nakamura type of rotary bending fatigue test (fatigue test bending through two-point skid weight and turning the motor to apply compressive and tensile stress to the surface of the wire). The maximum loading force was added to the average fatigue strength for 10 samples, having a life of 7 cycles or more with a probability of 50% or more. The bending test at the spar is a test for evaluating the cold winding shape and is performed as follows.
    [117] A punch 2 with an angle of the tip shown in Figure 2 on 10 was used to provide a notch (notch) of a maximum depth of 30 μm in a specimen. Note that as shown in Figure 3, the notch 4 is provided at a steering angle in the longitudinal to longitudinal direction in the middle of the test piece 3 in the longitudinal direction. Then, as shown in Fig. 4 from the opposite side of the notch 4, a punch 5 was used to apply a load P of a highest tensile strength stress through a load applying device 6 and the specimen was deformed by three-point bending. Note that the cracking radius r of the tip of 38 load breathing device 6 was made 4.0 mm, the difference L between reinforcements being made L .--. 2r-F3D. Where D is the diameter of the specimen.
    [118] The bending deformation was applied to the aft part with the spar brats.
    [119] Micro Vickers hardness after nitriding was evaluated at a depth of 500 μm or more from the surface layer because the inner hardness was defined as "nitrated layer hardness of micro Vickers hardness at a depth of 50 μm from the surface layer. The feed weight was 10 grams.
    [120] The results of these tests are shown in Tables 1-5 to 1-8. Note that in Tables 1-5 to 1-8, the metal structure includes residual austenite (y) and annealed martensite as well as certain inclusions. Furthermore, jams and unavoidable hazardous impurities were the weight of the chemical compositions.
    [121] Examples 1 to 47, in the present invention, show all the cold winding capacity, i.e., the bending angle of the spare, of a good 28 ° or more and are an excellent indication of spring half strength, i.e., Nakamura type of rotary bending fatigue strength (from here and there). simply referred to as the "fatigue strength" and an excellent indication of the resilience and resistance to heat-related softening, that is, the nitride layer hardness.
    [122] Further examples 48 and 49 are examples where the amount of added C is outside the range of the claims. If the quantity C is added Above the prescribed quantity (cf. Example 48), the unloaded spherical carbides become stiffer and 39 accumulation of the cold winding shape and the bending angle of the spar are indicated. On the other hand, if C is present in a smaller amount than the prescribed amount (comparative example 49), the toughening property is impaired, which means that sufficient half-strength cannot be ensured. In particular, the inner hardness after nitriding and spring spring strength (Nakamura type of rotary bending fatigue strength) and the resilience property (internal hardness after nitriding) become lower.
    [123] Comparative Examples 50 and 51 are examples where the amount of Si added is outside the range of the claims. If the quantity Si Exceeds the prescribed quantity 10, the matrix is propagated and the working capacity is collected, that is to say, the bending angle of the savings is law. On the other hand, if Si occurs to a lesser extent than prescribed, the toughening properties merge, which means that sufficient half-strength cannot be ensured after heating by nitration. In particular, the inner hardness after nitriding and the hardness of the nitrated layer become law.
    [124] Comparative Examples 52 and 53 are examples where the amount of added Mn is outside the prescribed range in the claims. If Mn is present in a large amount in the prescribed interval, the residual austenite becomes coarser, the yield strength decreases, and the fatigue strength (Nakamura-type rotating bending fatigue strength) is subordinate. On the other hand, when Mn is present in a smaller quantity than the prescribed quantity, the residual austenite decreases too much and the working capacity is reduced, which has the consequence that the bending angle of the spare decreases.
    [125] Comparative Examples 54 and 55 are examples where the amount of Cr added is outside the range of the claims. If the amount Cr exceeds the prescribed interval, cementite and even when heating the goth or rolling stock to high temperature, toughening, etc., increase undissolved carbides and the working capacity of the spring is greatly reduced. For this reason, the bending angle of the spar decreases. On the other hand, if Cr is present in a smaller amount than the prescribed amount, the steel softens during heat treatment during nitration, etc., and the so-called resistance to heat-related softening becomes insufficient, which causes the hardness of the nitrated layer to decrease.
    [126] Comparative Examples 56, 57, and 58 are examples where the amount of Mo, W, and Mo + W added is greater than the range of claims. If the quantities Mo and W exceed the prescribed quantities, a supercooled structure of martensite, bainite etc. is formed, during rolling and cooling and after patenting and other heat treatment which has to MO that the wire is broken during transport or during the drawing process, and that the feed test cannot be performed .
    [127] Comparative Example 59 is an example of Excessive addition of V. V is a substance which forms carbides in the steel. Excessive addition causes undissolved carbides 10 to form around the V, the machining ability is impaired and the bending angle of the spare decreases. Comparative Examples 60 and 61 show the amount N of Excessive compared to the range of claims. The Excessive amount N increases the temperature for the formation of nitrides and carbon nitrides of V, Nb, etc. and causes the coarse formation of carbides and other precipitates such as In addition, nitrides, carbon nitrides and carbides dissolve incompletely and a large amount of coarse undissolved spherical carbides remain after repeated heating, as is used in the present invention.As a result, the working capacity is compromised. ,
    [129] Comparative Examples 62 and 63 are examples where the amount of Nb added is outside the range of the claims. If Nb exceeds the prescribed quantity, the hot formability is remarkably black, a number of surface cracks occurred in the rolled material, occurred sharply during drawing, and after feeding tests could not be performed,
    [130] Comparative Example 64 is the case where the sum of the amounts added Mn and V is more than the range according to the present invention. The amount of residual austenite staltraden then becomes greater than the prescribed cairn. In the bending test of the spar, the hardness of the part decreases with the spar to ft * of stress-induced phase transformation and the machining capacity decreases. This is an example where the bending angle of the savings decreases. Repeating ourselves, V is not added in the present invention, but sometimes V is included as an inevitable contaminant, which means that V cannot be declared irrelevant. 41
    [131] Comparative Example 65 is the case where the sum of the amounts added Mn and V is lower than the range of the present invention. The amount of residual austenite is less than the optimal range, which means that the working capacity of the saving bend angle decreases.
    [132] Comparative Example 66 is the case where the sum of the amounts of Cr added and V is greater than the content explained in the present invention. Undissolved spherical carbides remain in Excessive quantity and machining capacity, that is, the bending angle of the spar decreases.
    [133] Comparative Example 67 is the case where the sum of the amount of Cr and V added is less than the range explained in the present invention. The machining ability is excellent, but the inner hardness after nitriding and the hardness of the nitrided layer are insufficient and the performance of the spring is insufficient.
    [134] Comparative Examples 68 to 70 are cases where the difference between the amount of Si and the amount of Cr ([Si%] - [Cr%]) differs from the content of the claims and the amount of Cr is greater than the amount of Si. If the amount Cr is Exaggerated in relation to the amount Si, undissolved spherical carbides remain and the working capacity is reduced, ie the bending angle of the saving decreases.
    [135] In the same way, comparative examples 71 and 72 are cases where the difference between the amount Si and the amount Cr ([Si ° / 0] - [Cr%]) is greater than the upper limit of the range in the claims. The quantity Si is very Exaggerated in relation to the quantity Cr. In these cases, the charred layer of the rolled material of the rolled material grows strongly and cannot be removed to a sufficient extent by surface shaving in a small amount. For this reason, the fatigue strength (Nakamura type of rotary flexural fatigue strength) was irrelevant.
    [138] Comparative Examples 73 and 74 are Example 1 and Example 23, respectively, of the invention, in which the steel is rolled at the heating temperature of the rolling stock 1100 ° C. At the beginning of the rolling, undissolved spherical carbides remain. The effects remain so that the working capacity is finally concentrated, that is to say the bending angle of the saving decreases. 42
    [137] Examples 101 to 109 are examples of the invention of drawn stalls of Examples 1 to 5 and 20 to 23 of the invention. Comparative Examples 110 and 111 are Examples 101 and 106 of the invention, where the heating temperature of the roll is 1100 ° C.
    [139] Table 1-2 Chemical compositions (mass%) ...
    [141] Table 1-4Chemical Compositions (Mass%) 0.76 2.4P.074 '0.00, 14 ", 0.4". E% • 0.0034, 0047 2. Ei% 02.5; '0.0253. 10, 0.78 2 1 3. 4 L 0 0 LL, 0.023, pc) •; 2 4: 3: 3 6. P,: 337, e .- x J3% 2 360 ', 00330, - -3 3 1,0, .30% 313.06016,03: 12 0.000: 3. 1) 0'1 ri 00% 3% 3 0.00 03 0.000.6 0.0.301, '3022: 0 0 ,: 0.56% 0.27 -7-77,. 5S,. 0.00: 16 U 0C x 023_0.0042%. 0013 0.00 3.4 3 0..60341_0, -10 0,00 0.12 13.003, S0,03% 0 „003, _0,1510,".:. 6 6.0044 5, r.) 70.11.0, opo, 0,00330e, i0.00 € 0.13% n. c) co4 0.44% 0.2S 0.23 1 0.31% 1. & 80.56 1 0.27) 48 HAARD hardness nitrated layer itnn j W - Inner hardness after nitriding (Hy) Nakamura type of rotating bend (HPa) Spirbiijning degrees (degrees) Yield ratio (%) 0.2% test pan - "Draghill fatness (MPa) Restauetenite (vol%). (3: 1 Previous aue e itcornator lek (74) Proximal spherical carbide diameter rn Tradbrott etc. no abnormitst] lacquering temperature Patenting temperature) Valeamnestemperature -t Good for all inv, ex Hardness ho s nitrated layer (lW) Inner hardness after nitrarcing (HIT) Nakamura type of rotating bending (mPa) Saving bending degrees (degrees) Yield ratio (%) 0% 2% sample aghHallfastness (MPa) Residual austenite (vol%) Previous austenitic grain history Maximum spherical k bite diameter MNMM (x ... CC. M -, 7- • H 7-) N - ■, C) 0 • C- C) Cr; CC, M CCN N CC-CC C7.1 Tradbrott etc.
    [147] 1 spherical carbides 2 punch 10 3 test piece 4 spare feeder 6 stand used for load P load L distance between supports 0 bending angle of the spare 52
    权利要求:
    Claims (1)
    [1]
    1. € a A, -; ., '.) 1 , -' 4 * -4 ........ L .__ .. k. 1i.sV - ---- -, t -, '-'- e ----- - --- ----- - - ------- - -J --- - - - -,
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    引用文献:
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    JP4555768B2|2004-11-30|2010-10-06|新日本製鐵株式会社|Steel wire for high strength spring|
    JP4478072B2|2005-06-09|2010-06-09|新日本製鐵株式会社|High strength spring steel|
    JP4486040B2|2005-12-20|2010-06-23|株式会社神戸製鋼所|Steel wire for cold forming springs with excellent cold cutability and fatigue characteristics and manufacturing method thereof|
    WO2007114490A1|2006-03-31|2007-10-11|Nippon Steel Corporation|Heat-treatment steel for high-strength spring|
    JP4868935B2|2006-05-11|2012-02-01|株式会社神戸製鋼所|High strength spring steel wire with excellent sag resistance|MX339397B|2011-08-18|2016-05-25|Nippon Steel & Sumitomo Metal Corp|Spring steel and spring.|
    JP2016014169A|2014-07-01|2016-01-28|株式会社神戸製鋼所|Wire rod for steel wire and steel wire|
    KR102326352B1|2014-09-04|2021-11-15|티센크룹 페던 운트 스타빌리자토렌 게엠베하|Method for producing cold-formed steel springs|
    JP6453138B2|2015-03-31|2019-01-16|株式会社神戸製鋼所|Heat-treated steel wire with excellent bending workability|
    WO2018211779A1|2017-05-19|2018-11-22|住友電気工業株式会社|Oil tempered wire|
    WO2019010661A1|2017-07-13|2019-01-17|田圣林|High toughness and high strength corrosion resistant spring|
    KR20200121874A|2018-03-29|2020-10-26|닛폰세이테츠 가부시키가이샤|Hot stamp molded body|
    WO2020233872A1|2019-05-20|2020-11-26|Nv Bekaert Sa|Method of making a spring core for a mattress or for seating products|
    法律状态:
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    优先权:
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