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    • 专利摘要:
    Patent specification: "Method for producing high strength steel material excellent in sulfide stress fracture resistance". a steel having a chemical composition consisting of by weight c: 0.15 to 0.65%, si: 0.05 to 0.5%, mn: 0.1 to 1.5%, cr: 0.2 to 1.5%, mo: 0.1 to 2.5%, ti: 0.005 to 0.50%, al: 0.001 to 0.50%, and optionally at least one element selected from nb: = 0 , 4%, v: = 0.5%, and b: = 0.01%, ca: = 0.005%, mg: = 0.005%, and rem: = 0.005%, and the balance being fe and impurities, where ni , p, s, neo among impurities are ni: = 0.1%, p: = 0.04%, s: = 0.01%, n: = 0.01%, and o: = 0.01% which has been hot worked to a desired shape is sequentially subjected to a step of heating the steel to a temperature exceeding the transformation point ac1 and lower than the transformation point ac3 and cooling the steel, the step of reheating the steel. to a temperature not less than transformation point ac3 and cool the steel by rapid cooling, and a step of quenching the steel to a temperature not exceeding transformation point ac1.
    公开号:BR112014019065B1
    申请号:R112014019065-8
    申请日:2013-02-26
    公开日:2019-03-26
    发明作者:Keiichi Kondo；Yuji Arai
    申请人:Nippon Steel & Sumitomo Metal Corporation；
    IPC主号:
    专利说明:

    [001] The present invention relates to a method for the production of a steel material of high strength excellent in fracture resistance by sulfide stress. More particularly, the present invention relates to a method for producing a high strength steel material excellent in sulfide stress fracture resistance, the steel material of which is especially suitable for an oil well pipe and the like such as a housing and an oil well and gas well pipe. Even more particularly, the present invention relates to a low-cost method for producing a high-strength, low-alloy steel material, which is excellent in strength and in sulfide stress fracture resistance, and from which a improvement in toughness due to refining grains from the previous austenite.
    BACKGROUND OF THE TECHNIQUE [002] As oil wells and gas wells (hereinafter, as a general term for oil wells and gas wells, referred to simply as oil wells) became deeper, steel tubes for oil wells ( hereinafter referred to as oil well tubes) must be more resistant.
    [003] To achieve this requirement, conventionally, oil well tubes of the class of 80 ksi, that is, having an elasticity limit (hereinafter abbreviated as YS) of 551 to 655 MPa (80 to 95 ksi) or well tubes of oil of the 95 ksi class, that is, having a YS of 655 to 758 MPa (95 to 110 ksi) were widely used. In addition, recently, oil well tubes in the class of 110 ksi, that is, having a YS of 758 to 862 MPa (110 to 125 ksi), and also
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    2/39 well oil tubes from the 125 ksi class, that is, having a YS of 862 to 965 MPa (125 to 140 ksi) started to be used.
    [004] In addition, oil and gas in most deep wells that have been developed recently, contain corrosive hydrogen sulfide. In such an environment, hydrogen embrittlement called sulfide stress fracture (hereinafter also referred to as SSC) occurs, and as a result the oil well tube is sometimes broken. It is widely known that with the increase in steel strength, susceptibility to SSC increases.
    [005] Therefore, when developing high-strength oil well tubes, not only does the design of the high-strength steel material need to be done, but the steel must also have SSC resistance. Especially when developing high-strength oil well tubes, preventing SSC is the big problem. Sulfide stress fracture is sometimes also referred to as sulfide stress corrosion fracture (SSCC).
    [006] As a method to prevent SSC from low-alloy oil well tubes, methods of (1) high steel purification, (2) carbide control mode, and (3) crystal grain refining have been known .
    [007] Regarding the high purification of steel, for example, Patent Documents 1 and 2 propose methods to improve resistance to SSC by restricting the sizes of nonmetallic inclusions to some specific sizes.
    [008] Regarding the mode of carbide control, for example, Patent Document 3 describes a technique in which the ratio of MC-type carbides to total carbides is 8 to 40% by weight in addition to the restriction of the total amount of carbides to 2 to 5% by mass to tremendously improve SSC resistance.
    [009] Regarding the refining of crystal grains, for example, the
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    3/39
    Patent Document 4 describes a technique a technique in which the crystal grains are made thin by performing the rapid cooling treatment twice or more on a low alloy steel to improve resistance to SSCC. Patent Document 5 also describes a technique in which crystal grains are made thin by the same treatment as in Patent Document 4 to improve toughness.
    [0010] Conventionally, when producing low alloy steel materials in the cap of seamless steel tubes for oil wells and similar tubes, to achieve strength and / or toughness properties, a quick-cooling and quenching heat treatment was often performed after the end of hot rolling such as hot pipe production. As a method for heat treatment of quick cooling and quenching of the seamless steel tube for oil well, conventionally, a so-called reheating and rapid cooling process has generally been performed, in the process of which a steel tube having been hot rolled, it is reheated in an off-line heat treatment furnace to a temperature of not less than the AC3 transformation point and is rapidly cooled, and then it is quenched to a temperature no higher than the Aci transformation point.
    [0011] However, in recent years, from the point of view of saving the process and saving energy, a process has also been carried out in which a steel pipe having been laminated is cooled quickly directly from a temperature not less than the set point. transformation Ar3 and thereafter it is tempered (a so-called direct rapid cooling process) or also a process in which a steel pipe having been hot rolled is rinsed sequentially (hereinafter referred to as specially heated further) at a temperature no lower than
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    4/39 point of transformation Ar3 and later tempered (a so-called heat treatment process on the line or rinse process on the line).
    [0012] As described in Patent Documents 4 and 5, it has been widely known that there is a close relationship between the grains of low-alloy steel anterior austenite and SSC resistance and toughness, and SSC resistance and toughness are noticeably reduced by the hardening of the grains.
    [0013] In the event that the direct blast chilling and reheating process is adopted for the purpose of process saving and energy saving, the anterior austenite grains become stale, so that sometimes it is difficult to produce a steel tube seamless in toughness and SSC resistance. The process of heat treatment in the line described above sometimes solves this problem, but it is not necessarily comparable to the process of rapid cooling and reheating.
    [0014] It is imagined that the reason for this is that in the direct quick cooling process and in the heat treatment process in the line, in the case where only the tempering is performed as post-processing heat treatment, there is no process of reverse transformation of centered body cubic structure ferrite to centered face cubic structure austenite.
    [0015] In order to solve the problem described above of crystal graining, the Patent Documents 6 and 7 propose methods in which a steel tube having been cooled quickly directly by a heat treatment in the line, respectively, is reheated and cooled quickly from a temperature not less than the Ar3 transformation point before the final temper treatment.
    [0016] In Patent Documents 4 and 5, tempering is carried out at
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    5/39 a temperature no higher than the Aci transformation point between the rapid cooling treatment and reheating several times, and in Patent Documents 6 and 7, the tempering is performed at a temperature not exceeding the Aci transformation point between the cooling treatment Rapid and reheat performed on line treatment, and Rapid cooling and reheat treatment.
    LIST OF DOCUMENTS OF THE PREVIOUS TECHNIQUE
    PATENT DOCUMENT [0017] Patent Document 1: JP2001-172739A [0018] Patent Document 2: JP2001-131698A [0019] Patent Document 3: JP2000-178682A [0020] Patent Document 4: JP59-232220A [0021] Patent Document 5: JP60-009824A [0022] Patent Document 6: JP6-220536A Patent Document 7: WO96 / 36742 DESCRIPTION OF THE INVENTION
    PROBLEMS TO BE SOLVED BY THE INVENTION [0023] By techniques to restrict the sizes of non-metallic inclusions to those specific that are proposed in Patent Documents 1 and 2, excellent resistance to SSC can be achieved. However, since the steel must be purified, the cost of production sometimes increases.
    [0024] In addition, by the technique for controlling the carbide modes that is proposed in Patent Document 3, excellent resistance to SSC can be obtained. However, Cr and Mo contents are restricted to the formation of M23C6 carbides. Therefore, the curing capacity is restricted, so that for a thick-walled material, there is a possibility of insufficient curing capacity.
    [0025] A process comprising the cooling process
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    6/39 direct or the heat treatment process in the line, and then the reheating and rapid cooling from a temperature not lower than the Ar3 transformation point before the final quenching makes the grains of the previous austenite more refined, thus improving the strength of the steel to SSC, compared to the case in which the fine quenching is carried out after direct rapid cooling or in-line treatment, or the case in which the steel tube is air-cooled once close to room temperature, and then the steel is subjected to a reheat and cool down treatment and a quench treatment.
    [0026] Even in the case where after undergoing direct direct cooling treatment or heat treatment in the line, the steel tube is reheated and cooled quickly from a temperature not lower than the Ar3 transformation point before the final tempering treatment as described above, the refining of the previous austenite grains is still insufficient compared to the case where the reheating and rapid cooling treatment is sometimes performed as proposed in Patent Documents 4 and 5.
    [0027] Therefore, by the technique in which the steel tube having been rapidly cooled directly is reheated and cooled rapidly from a temperature not lower than the Ar3 transformation point before the final temper treatment, which is technically described in Patent Document 6, sufficient SSC resistance cannot necessarily be achieved.
    [0028] Similarly, even if the steel pipe having been cooled by heat treatment in the line is reheated and cooled quickly from a temperature not lower than the Arç transformation point before the final temper treatment as proposed in Patent Document 7, a resistance sufficient SSC cannot sometimes be obtained.
    [0029] Therefore, when an attempt is made to perform the refining
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    7/39 of the crystal grains that is sufficient as a steel tube for a high-strength oil well, the reheating and rapid cooling treatment performed twice or more as described in Patent Documents 4 and 5 is significant. However, the reheat treatment performed twice or more leads to an increase in production cost.
    [0030] Patent Documents 4 and 7 propose techniques in which crystal grains are made ultrafine by increasing the rate of temperature increase at the time of reheating and rapid cooling. In the techniques, however, the apparatus must be modified on a large scale, because the heating means come to consist of induction heating or the like.
    [0031] The present invention was made in view of the above situation, and therefore an objective of the same is to provide a low cost method for the production of an excellent high strength steel material in SSC resistance. In particular, the objective of the present invention is to provide a method for the production of a high strength steel material in which the refining of the grains from the previous austenite is carried out by an economically efficient means, with which an excellent resistance to SSC and an improvement tenacity can be expected. The term high strength in the present invention means that YS is 655 MPa (95 ksi) or greater, preferably 758 MPa (110 ksi) or greater, and more preferably 862 MPa (125 ksi) or greater.
    MEANS TO SOLVE THE PROBLEMS [0032] As described above, after being subjected to the direct quick cooling treatment or the thermal treatment rapid cooling treatment on the line, the steel is also reheated to a temperature not lower than the AC3 transformation point and is cooled quickly, with which the grains of the previous austenite can be made fine. In the event that the steel having been rapidly cooled
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    8/39 is also repeatedly cooled rapidly, after the preceding rapid cooling treatment, an intermediate quench is often carried out at a temperature not exceeding the Aci transformation point. This intermediate tempering treatment has the effect of preventing delayed fracture such as the so-called seasonal fracture that occurs in rapidly cooled steel.
    [0033] However, intermediate tempering must be carried out under suitable conditions. In the case where the temperature of the intermediate temper is too low or the heating time is too short, a sufficient effect of containing the seasonal fracture cannot be achieved in some cases. Conversely, even if the temperature is not higher than the transformation point Aci, in the case where the temperature of the intermediate temper is too high or the heating time is too long, the effect of thinning the crystal grains is lost even if heating and rapid cooling is carried out after the intermediate temper treatment, and sometimes the beneficial effect of improving SSC resistance disappears.
    [0034] Consequently, the present inventors have carried out several studies in a low cost method to produce a high strength steel material by which method the steel material has a sufficient effect of containing seasonal fracture and simultaneously has an excellent resistance to SSC due to the refining of the grains from the previous austenite.
    [0035] As a result, the present inventors have discovered that if the intermediate tempering treatment, which was supposed to be carried out at a temperature not exceeding the Aci transformation point to improve the properties of the chilled steel material quickly, is performed at a temperature in the region of two phases of ferrite and austenite exceeding the transformation point Aci, the grains of the previous austenite are made remarkably thin
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    9/39 when heating and rapid cooling treatment is performed.
    [0036] Furthermore, the present inventors have obtained completely new discoveries that if the heat treatment is carried out at a temperature in the two-phase region of ferrite and austenite described above, even for a steel that has not been cooled quickly, for example, a steel that has been cooled to a cooling rate of air cooling or similar to being worked hot in a desired way, if the steel is then heated to a temperature in a suitable austenite zone and is cooled quickly, the grains of former austenite are made remarkably thin.
    [0037] The present invention was completed based on the findings described above, and involves methods for producing a high strength steel material excellent in fracture resistance by the sulfide stress described below. Hereinafter, in some cases, the methods are referred to simply as the present invention (1) through the present invention (7). Also, in some cases, the present inventions (1) to (7) are generally referred to as the present invention.
    [0038] Method for producing a high-strength steel material excellent in fracture resistance by sulfide stress, where a steel that has a chemical composition consisting, in percent by weight, of C: 0.15 to 0.65% , Si: 0.05 to 0.5%, Mn: 0.1 to 1.5%, Cr: 0.2 to 1.5%, Mo: 0.1 to 2.5%, Ti: 0.005 to 0 , 50%, Al: 0.001 to 0.50%, and the balance being Fe and impurities, where Ni, P, S, N and O among the impurities are Ni: 0.1% or less, P: 0.04% or less, S: 0.01% or less, N: 0.01% or less, and O: 0.01% or less, and which has been hot worked in a desired manner is sequentially subjected to the steps of the items [1 ] to [3] below:
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    10/39 [0039] [1] a step of heating the steel to a temperature above the transformation point Aci and lower than the transformation point Ac3 and cooling the steel;
    [0040] [2] a step of reheating the steel to a temperature not lower than the transformation point Ac 3 and cooling the steel by tempering it; and [0041] [3] a step of tempering the steel at a temperature not exceeding the Aci transformation point.
    [0042] A method for producing a high strength steel material excellent in fracture resistance by sulfide stress, where the steel having a chemical composition consisting, in mass percent, of C: 0.15 to 0.65 %, Si: 0.05 to 0.5%, Mn: 0.1 to 1.5%, Cr: 0.2 to 1.5%, Mo: 0.1 to 2.5%, Ti: 0.005 to 0.50%, Al: 0.001 to 0.50%, at least one element selected from the elements shown in (a) and (b), and the balance being Fe and impurities, where Ni, P, S, N and O impurities include Ni: 0.1% or less, P: 0.04% or less, S: 0.01% or less, N: 0.01% or less, and O: 0.01% or less, and that has been hot worked in a desired way is sequentially subjected to the steps of items [1] to [3] below:
    [0043] [1] a step of heating the steel to a temperature higher than the transformation point Aci and lower than the transformation point Ac3 and cooling the steel;
    [0044] [2] a step of reheating the steel to a temperature not lower than the transformation point Ac 3 and cooling the steel by tempering it; and [0045] [3] a step of tempering the steel at a temperature not exceeding the Aci transformation point.
    [0046] Nb: 0.4% or less, V: 0.5% or less, and B: 0.01% or less;
    [0047] Ca: 0.005% or less, Mg: 0.005% or less, and REM:
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    11/39
    0.005% or less.
    [0048] The method to produce a high strength steel material excellent in fracture resistance by sulfide stress according to items (1) or (2), where the steel having the chemical composition according to items (1) or (2) it is hot finished in a seamless steel tube and is air cooled, and subsequently it is sequentially subjected to steps [1] to [3].
    [0049] The method for producing a high strength steel material excellent in fracture resistance by sulfide stress according to items (1) and (2), here after the steel having the chemical composition according to item (1) or (2) having been finished hot in a seamless steel tube, the steel is further heated to a temperature not lower than the Ar3 transformation point not exceeding 1050Ό in the line, and after being rapidly cooled from a temperature not lower than the point transformation process Ar3, the steel is sequentially subjected to steps [1] to [3].
    [0050] The method for producing a high strength steel material excellent in fracture resistance by sulfide stress according to item (1) or (2), where after the steel having the chemical composition according to item (1) or (2) it was hot finished in a seamless steel tube, the steel is directly cooled quickly from a temperature not lower than the Ar3 transformation point, and subsequently sequentially subjected to steps [1] to [3].
    [0051] The method for producing a high strength steel material excellent in fracture resistance by sulfide stress according to item (4), where the heating in step [1] is performed by a heating device connected to a device for quick cooling of the heat treatment in the line.
    [0052] (7) The method for producing a high strength steel material excellent in sulfide stress fracture resistance
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    12/39 according to item (5), where the heating in step [1] is performed by a heating device connected to a rapid cooling device that performs direct rapid cooling.
    ADVANTAGE EFFECTS OF THE INVENTION [0053] According to the present invention, since the refining of the grains from the previous austenite can be carried out by an economically efficient means, a high strength steel material excellent in SSC resistance can be obtained at low cost. In addition, by the present invention, a seamless tube for oil well of low alloy and excellent high strength in SSC strength can be produced at relatively low cost. In addition, according to the present invention, improvement in toughness can be expected due to the refining of the grains from the previous austenite.
    MODE FOR CARRYING OUT THE INVENTION [0054] Hereinafter the requirements of the present invention are explained in detail.
    [0055] Chemical composition [0056] Initially, in item (A), an explanation is given of the chemical composition of a steel used in the production method of the present invention and the reasons why the composition range is restricted. In the explanation below, the% symbol in relation to the content of each element means percentage by mass.
    [0057] C: 0.15 to 0.65% [0058] C (Carbon) is a necessary element to increase the hardening capacity and improve the resistance. However, if the C content is less than 0.15%, the effect of increasing the hardening capacity is poor, and sufficient strength cannot be achieved. On the other hand, if the C content exceeds 0.65%, the tendency to fracture at the time of rapid cooling is notable. Therefore, the C content is 0.15% to 0.65%. The lower limit of C content is preferable
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    0.20%, more preferably 0.23%. In addition, the upper limit of the C content is preferably 0.45%, more preferably 0.30%. [0059] Si: 0.05 to 0.5% [0060] Si (Silicon) is necessary to deoxidize steel, and also has an action to increase the softening resistance of the temper and improve the resistance to SSC. For the purpose of deoxidation and improving resistance to SSC, 0.05% or more of Si must be contained. However, if Si is excessively contained, the steel is weakened, and in addition the resistance to SSC is also decreased. In particular, if the Si content exceeds 0.5%, the toughness and resistance to SSC are significantly decreased. Therefore, the Si content is 0.05 to 0.5%. The lower limit and the upper limit of the Si content are preferably 0.15% and 0.35%, respectively.
    [0061] Mn: 0.1 to 1.5% [0062] Mn (Manganese) is contained to deoxidize and desulfurize the steel. However, if the Mn content is less than 0.1%, the effects described above are poor. On the other hand, if the Mn content exceeds 1.5%, the toughness and resistance to SSC are decreased. Therefore, the Mn content is 0.1 to 1.5%. The lower limit of the Mn content is preferably 0.15%, more preferably 0.20%. In addition, the upper limit of the Mn content is preferably 0.85%, more preferably 0.55%. [0063] Cr: 0.2 to 1.5% [0064] Cr (Chromium) is an element to guarantee the hardening capacity and to improve the resistance and the resistance to SSC. However, if the Cr content is less than 0.2%, sufficient effects cannot be achieved. On the other hand, if the Cr content exceeds 1.5%, resistance to SSC is also decreased, and a decrease in toughness is also shown. Therefore, the Cr content is 0.2 to 1.5%. The lower limit of the Cr content is preferably 0.35%, and more preferably 0.45%. The upper limit of the Cr content preferably 1.28%, plus
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    14/39 preferably 1.2%.
    [0065] Mo: 0.1 to 2.5% [0066] Mo (Molybdenum) increases the hardening capacity and guarantees the resistance, and also improves the resistance to softening of the temper. Therefore, due to the Mo content, high temperature quenching can be carried out, and as a result, the carbide shape becomes spherical, and SSC resistance is improved. However, if the Mo content is less than 0.1%, these effects are poor. On the other hand, if the Mo content exceeds 2.5%, despite the fact that the cost of the raw material increases, the effects described above are sometimes saturated. Therefore, the Mo content is 0.1 to 2.5%. The lower limit of the Mo content is preferably 0.3%, more preferably 0.4%. In addition, the upper limit of the Mo content is preferably 1.5%, more preferably 1.0%.
    [0067] Ti: 0.005 to 0.50% [0068] Ti (Titanium) has an action to improve the hardening capacity by immobilizing N, which is an impurity in steel, and by making B exist in a state dissolved in steel at the time of rapid cooling. In addition, Ti has the effect of preventing the crystal grains from becoming stale and abnormal grain growth at the time of rapid cooling and from reheating by precipitation as fine carbonitrides in the process of increasing the temperature for reheating for rapid cooling. However, if the Ti content is less than 0.005%, these effects are small. On the other hand, if the Ti content exceeds 0.50%, a decrease in toughness is presented. Therefore, the Ti content is 0.005 to 0.50%. The lower limit of the Ti content is preferably 0.010%, more preferably 0.012%. In addition, the upper limit of the Ti content is preferably 0.10%, more preferably 0.030%.
    [0069] Al: 0.001 to 0.50%
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    15/39 [0070] Al (Aluminum) is an effective element for deoxidizing steel. However, if the Al content is less than 0.001%, the desired effect cannot be achieved, and if the Al content exceeds 0.50%, the amount of inclusions increases and the toughness decreases, and also the resistance to SSC is diminished by the stuttering of inclusions. Therefore, the Al content is 0.001 to 0.50%. The upper and lower limits of the Al content are preferably 0.005% and 0.05%, respectively. The Al content described above means the amount of Al sol. (Al soluble in acid).
    [0071] The chemical composition of the steel used in the production method of the present invention (specifically, the chemical composition of the steel according to the present invention (1)) consists of the elements described above and the balance being Fe and the impurities, where Ni, P , S, N and O among the impurities are Ni: 0.1% or less, P: 0.04% or less, S: 0.01% or less, N: 0.01% or less, and O: 0 , 01% or less.
    [0072] The impurities described here mean elements that come in mixed due to various factors in the production process including raw materials such as ore or scrap when steel is produced on an industrial scale, and are allowed to be contained within the range so that elements do not have an adverse influence on the present invention [0073] Below is the explanation of Ni, P, S, N and O (oxygen) in the impurities.
    [0074] Ni: 0.1% or less [0075] Ni (Nickel) decreases the resistance to SSC. In particular, if the Ni content exceeds 0.1%, the decrease in resistance to SSC is notable. Therefore, the Ni content in impurities is 0.1% or less. The NI content is preferably 0.05% or less, and more preferably 0.03% or less.
    [0076] P: 0.04% or less [0077] P (Phosphorus) secretes at the grain edge, and decreases tenacity
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    16/39 and SSC resistance. In particular, if the P content exceeds 0.04%, the decrease in toughness and resistance to SSC is remarkable. Therefore, the P content in impurities is 0.04% or less. The upper limit of the P content in the impurities is preferably 0.025%, more preferably 0.015%.
    [0078] S: 0.01% or less [0079] S (Sulfur) produces crude inclusions, and decreases toughness and resistance to SCC. In particular, if the S content exceeds 0.01%, the decrease in toughness and resistance to SSC is notable. Therefore, the S content in the impurities is 0.01% or less. The upper limit of the S content in the impurities is preferably 0.005%, more preferably 0.002%.
    [0080] N: 0.01% or less [0081] N (Nitrogen) combines with B, and avoids the advantageous effect of improving the hardening capacity of B. In addition, if N is excessively contained, N produces crude inclusions together with Al, Ti, Nb etc., and has a tendency to decrease the toughness and resistance to SSC. In particular, if the N content exceeds 0.01%, the decrease in toughness and resistance to SSC is notable. Therefore, the N content in the impurities is 0.01% or less. The upper limit of the N content in the impurities is preferably 0.005%.
    [0082] O: 0.01% or less [0083] O (Oxygen) produces inclusions together with Al, Si etc .. Due to the brutation of inclusions, the toughness and resistance to SSC are decreased. In particular, if the O content exceeds 0.01%, the decrease in toughness and resistance to SSC is notable. Therefore, the O content in impurities is 0.01% or less. The maximum limit of the O content in the impurities is preferably 0.005%.
    [0084] Another chemical composition of steel used in the production method of the present invention (specifically the composition
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    17/39 steel chemistry according to the present invention (2)) also comprises at least one element between Nb, V, B, Ca, Mg and REM (rare earth metal).
    [0085] The REM described here is a general term out of a total of 17 elements of Sc, Y and the lantanoids, and the REM content means the total content of one or more REM elements.
    [0086] Below, the explanation of the operational advantages of Nb, V, B, Ca, Mg and REM is given and the reasons why the composition range is restricted.
    [0087] Nb: 0.4% or less, V: 0.5% or less, and B: 0.01% or less [0088] All elements between Nb, V and B have an action to improve resistance to SSC. Therefore, in the event that it is desired to achieve greater resistance to SSC, these elements may be contained. Ahead Nb, V and B are explained.
    [0089] Nb: 0.4% or less [0090] Nb (Niobium) is an element that precipitates as fine carbonitrides, and has the effect of thinning the grains of the previous austenite and thus improving the resistance to SSC. Therefore, Nb can be contained as needed. However, if the Nb content exceeds 0.4%, the toughness deteriorates. Therefore, the Nb content, if contained, is 0.4% or less. The Nb content, if contained, is preferably 0.1% or less.
    [0091] On the other hand, to achieve the Nb effect described above stably, the Nb content, if contained, is preferably 0.005% or greater, and even more preferably 0.01% or greater.
    [0092] V: 0.5% or less [0093] V (Vanadium) precipitates as carbide (VC) when quenching is performed, and increases the softening resistance of the quenching, so that ο V allows quenching to be performed at high temperatures. As a result, V has the effect of improving the resistance
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    18/39 to the SSC. In addition, V has the effect of restricting the production of needle-shaped M02C, which becomes the starting point for the occurrence of SSC when the Mo content is high. In addition, as it contains V in complex with Nb, greater resistance to SSC can be achieved. Therefore, V can be contained if necessary. However, if the V content exceeds 0.5%, the toughness decreases. Therefore, the V content, if contained, is 0.5% or less. The V content, if contained, is preferably 0.2% or less.
    [0094] On the other hand, in order to stably achieve the V effect described above, the V content, if contained, is preferably 0.02% or greater. In particular, in the case where the steel contains 0.68% or more of Mo, to restrict the production of needle-shaped M02C, the amount of V described above is preferably contained complexly. [0095] B: 0.01% or less [0096] B (Boron) is an element that has the effect of increasing the hardening capacity and improving the resistance to SSC. Therefore, B can be contained if necessary. However, if the B content exceeds 0.01%, the resistance to SSC also decreases and, in addition, the toughness also decreases. Therefore, the B content, if contained, is 0.01% or less. The B content, if contained, is preferably 0.005% or less, and more preferably 0.0025% or less.
    [0097] On the other hand, in order to stably achieve the effects of B described above, the B content, if contained, is preferably 0.0001% or greater, and even more preferably 0.0005% or greater.
    [0098] However, the effects of B described above appear in the case where B exists and is dissolved in the steel. Therefore, in the case where B is contained, the chemical composition is preferably regulated so that, for example, an amount of Ti capable of immobilizing N which has a high affinity for B as nitrides is contained. [0099] (b) Ca: 0.005% or less, Mg: 0.005% or less, and REM:
    Petition 870180152726, of 11/19/2018, p. 22/50
    19/39
    0.005% or less [00100] All between Ca, Mg and REM react with the S that exists as an impurity in the steel to form sulfides, and has an action to improve the forms of inclusions and thus increase the resistance to SSC. Therefore, these elements can be contained, if necessary. However, if one of these elements is contained in more than 0.005%, resistance to SSC specifically decreases, a decrease in toughness is also presented, and defects are also likely to occur frequently on the steel surface. Therefore, the content of any element between Ca, Mg and REM, if contained, is 0.005% or less. The content of any of these elements, if contained, is preferably 0.003% or less.
    [00101] On the other hand, in order to stably achieve the effect of Ca, Mg and REM described above, the content of any of these elements, if contained, is preferably 0.001% or greater.
    [00102] As already described, REM is a general term of 17 elements between Sc, Y and lantanoids, and the REM content means the total content of one or more REM elements.
    [00103] REM is usually contained in the form of a metal misch. Therefore, REM can be added, for example, in the form of a metal misch, and it can be contained so that the amount of REM is in the range described above.
    [00104] Only one element between any one between Ca, Mg and REM can be contained, or two or more elements can be contained complexly. The total content of these elements is preferably 0.006% or less, and more preferably 0.004% or less.
    [00105] (B) Production method [00106] Next, in item (B), a detailed explanation of the method for producing a high strength steel material excellent in resistance to sulfide stress fracture of the present invention is given. 870180152726, of 11/19/2018, p. 23/50
    20/39 tion.
    [00107] In the method for producing a high strength steel material excellent in fracture resistance by sulfide stress according to the present invention, the steel having the chemical composition described in item (A) and which has been worked at hot in a desired form is sequentially subjected to the following steps: [00108] [1] A step of heating the steel to a temperature above the transformation point Aci and lower than the transformation point AC3 and cooling the steel;
    [00109] [2] A step of reheating the steel to a temperature not lower than the transformation point AC3 and quickly cooling the steel by rapid cooling; and [00110] [3] A step of tempering steel at a temperature not exceeding the Aci transformation point.
    [00111] By performing the steps of items [1] to [3] sequentially, the refining of the austenite grains above can be performed, the high strength steel material excellent in SSC resistance can be obtained at low cost, and also the improvement in toughness due to refining the previous austenite grains can be expected.
    [00112] If the steel has the chemical composition described in item (A) and was hot worked in a desired way, the production history before the performance of step [1] is not subject to any specific restriction. For example, if steel is produced by the common process in which an ingot or cast is formed after melting, and the steel is worked into a desired shape by any method such as hot rolling or hot forging, after hot work to conform to a desired shape, steel can be cooled at a low cooling rate as in air cooling, or it can be cooled at a high cooling rate as in water cooling.
    Petition 870180152726, of 11/19/2018, p. 24/50
    21/39 [00113] The reason for this is as described below. Even if any treatment is carried out after hot working to conform to a desired shape, sequentially performing steps [1] to [3] thereafter, a microstructure consisting mainly of fine tempered martensite is formed after tempering treatment at a temperature less than the Aci transformation point in step [3] has been completed.
    [00114] The heating step (1) must be formed at a temperature exceeding the transformation point Aci and lower than the transformation point Ac3. In the event that the heating temperature deviates from the temperature range described above, even if the rapid cooling heating is carried out in step [2] below, sufficient refining of the grains from the previous austenite cannot be performed in some cases.
    [00115] Step [1] does not necessarily need to be specifically restricted except that the heating is carried out at a temperature exceeding the transformation point Aci and less than the transformation point AC3, that is, at a temperature in the region of two phases of ferrite and austenite.
    [00116] Even if the heating treatment is performed under the condition that the PL value expressed by
    PL = (T + 273) x (20 + logwt) [00117] where T is the heating temperature (Ό) and t is the heating time (h), exceeds 23,500, the refining of the cooled austenite grains in the next step [ 2] tends to saturate, and the cost simply increases. Therefore, the heating treatment is preferably carried out on the condition that the PL value is 23,500 or less. Regarding the heating time, depending on the type of oven used for heating, a minus 10 seconds is desirable. In addition, cooling after the heating treatment is preferably complied with 870180152726, of 11/19/2018, p. 25/50
    22/39 air cooling.
    [00118] After step [1], the steel is subjected to a step of being reheated to a temperature not lower than the transformation point Ac3 in step [2], that is, up to a temperature in the temperature range of austenite and being cooled by rapid cooling, which the refining of austenite grains is achieved.
    [00119] If the reheat temperature in step [2] exceeds (transformation point Ac3 + 100 ° C), the grains from the previous austenite are sometimes stiffened. Therefore, the reheat temperature in step [2] is preferably (transformation point Ac3 + 100 ° C) or lower.
    [00120] The rapid cooling method does not necessarily have to be subject to any specific restrictions. A rapid water cooling method is generally used, however, as martensitic transformation occurs in the rapid cooling treatment, steel can be cooled quickly by a suitable method such as a mist cooling method.
    [00121] After step [2], the steel is subjected to a step of being tempered at a temperature not lower than the transformation point Aci in step [3], that is, at a temperature in the temperature range in which the transformation reverse in austenite does not occur, with which the high strength steel material excellent in fracture resistance by sulfide stress can be obtained. The lower limit of tempering temperature can be determined appropriately by the chemical composition of the steel and the strength required for the steel material. For example, tempering can be carried out at a higher temperature to decrease resistance and, on the other hand, at a lower temperature to increase resistance. As a method of cooling after quenching, air cooling is desirable.
    [00122] Next, the method for
    Petition 870180152726, of 11/19/2018, p. 26/50
    23/39 produce a steel material according to the present invention taking the case that a seamless steel tube is produced as an example.
    [00123] In the case where the high strength steel material excellent in sulfide stress fracture resistance is a seamless steel tube, a bar having the chemical composition described in item (A) is prepared.
    [00124] The bar can be roughened from a steel block such as a block or a plate, or it can be cast by a round CC. Needless to say, the bar can also be formed by an ingot.
    [00125] From the bar, a tube is hot rolled. In particular, initially, the bar is heated to a temperature in the temperature range at which drilling can be performed, and is subjected to a hot drilling process. The heating temperature of the bar before drilling is generally in the range of 1100 to 1300Ό.
    [00126] The means for hot drilling are not necessarily restricted. For example, a hollow shell can be obtained by the Mannesmann or similar drilling process.
    [00127] The hollow shell obtained is subjected to stretching and finishing work.
    [00128] The stretching work is a step for producing a seamless steel tube having the desired shape and size by stretching the hollow shell that was drilled by a drilling machine and adjusting the size. This step can be performed using, for example, a mandrel laminator or a mandrel laminator. In addition, finishing work can be performed using a gauge or similar meter.
    [00129] The reason for the stretching work and the wax work
    Petition 870180152726, of 11/19/2018, p. 27/50
    24/39 payment is not necessarily restricted. The finishing temperature is preferably 1100X3 or less. However, if the finishing temperature exceeds 1050Ό, a tendency for crystal grains to become inebriated is sometimes developed. Therefore, the finishing temperature in the finishing work is more preferably 1050Ό or less. At a temperature below 900Ό, the work is difficult to do due to the increase in resistance to deformation, so that the production of the tube is preferably carried out at a temperature exceeding 900 ° C.
    [00130] As shown in item (3) of the present invention, the seamless steel tube having been subjected to hot finishing work can be air-cooled in the state. The air cooling described here includes so-called natural cooling or being allowed to cool.
    [00131] Additionally, as shown in item (4) of the present invention, the seamless steel tube having undergone a hot finishing job can be further heated to a temperature not lower than the Ar3 transformation point and not more than 1050Ό on the line, and cooled rapidly from a temperature not lower than the Arç transformation point, that is, to a temperature in the austenite temperature range. In this case, since two cooling treatments including the reheating and rapid cooling treatment are carried out in the subsequent step [2], the refining of the crystal grains can be carried out.
    [00132] If the seamless steel tube is further heated to a temperature exceeding 1050Ό, the brutality of the austenite grains becomes noticeable, and even if the heating and rapid cooling treatment is carried out in the subsequent step [2], the refining the former austenite grains becomes difficult to do in some cases. The upper limit of the heating temperature
    Petition 870180152726, of 11/19/2018, p. 28/50
    Supplementary 25/39 is preferably ΊΟΟΟΌ. As a method for rapid cooling from a temperature not lower than the Ar3 transformation point, a common water cooling method is economical, however any rapid cooling method in which martensitic transformation occurs can be used and, for example, a cooling method mist spray can be used.
    [00133] In addition, as shown in item (5) of the present invention, the seamless steel tube having undergone a hot finishing job can be cooled quickly directly from a temperature not lower than the Ar3 transformation point, ie , from a temperature in the austenite temperature range. In this case, since two rapid cooling treatments including reheating of the rapid cooling are carried out in the subsequent step [2], the refining of the crystal grains can be carried out. As a method of cooling from a temperature not lower than the Ar3 transformation point, a common water cooling method is economical, however any cooling method in which the martensitic transformation occurs can be used and, for example, a mist cooling method can be used.
    [00134] In the methods described above, the seamless steel pipe having been hot worked and subsequently cooled and subjected to the stage of heating the steel to a temperature exceeding the transformation point Aci and lower than the transformation point AC3 and cooling the steel in step [1], which is a characteristic step of the present invention.
    [00135] In the explanation below, the heating performed before step [2], that is, the heating in step [1] is sometimes referred to as intermediate heat treatment.
    [00136] The intermediate heat treatment is preferably carried out by a heating device connected to an appliance for
    Petition 870180152726, of 11/19/2018, p. 29/50
    26/39 ra rapid cooling of the heat treatment in the line when the seamless steel tube having undergone the hot finishing work is further heated to a temperature not lower than the Ar3 transformation point and not more than 1050Ό in the line, quickly cooled from a temperature not lower than the transformation point Ar3, and subsequently subjected to intermediate heat treatment, as shown in item (6) of the present invention. In addition, the intermediate heat treatment is preferably carried out by a heating device connected to a rapid cooling device that performs direct rapid cooling when the seamless steel tube having undergone hot finishing work is directly cooled quickly from a temperature not lower than the Arç transformation point, and subsequently subjected to intermediate heat treatment, as shown in item (7) of the present invention. Using heating devices, a sufficient effect of restricting seasonal fracture is achieved.
    [00137] As already described, the heating conditions in step [1] need not necessarily be specifically restricted except that the heating is carried out at a temperature exceeding the transformation point Aci and less than the transformation point Ac3, that is, the a temperature in the region of two phases of ferrite and austenite.
    [00138] The seamless steel tube having been subjected to step [1] is reheated and cooled quickly in step [2], and is also quenched in step [3].
    [00139] By the methods described above, a high strength seamless steel tube can be obtained that is excellent in SSC resistance, and for which the improvement in toughness can also be expected.
    [00140] Below the present invention is explained more specifically
    Petition 870180152726, of 11/19/2018, p. 30/50
    27/39 referring to the examples. The present invention is not limited to the examples.
    EXAMPLES (Example 1) [00141] The components of each of the steels A to L having the chemical compositions given in Table 1 were regulated in a converter, and each of the steels A to L was subjected to continuous casting, with which it was A bar having a diameter of 310 mm is prepared. Table 1 additionally gives the transformation point Aci and the transformation point Ac 3 which were calculated using the formulas of Andrews [1] and [2] (KW Andrews: JISI, 203 (1965), pg. 721 - 727) described below. For each steel, Cu, W and As were not detected and a concentration of such a degree in order to exert an influence on the calculated value.
    [00142] Aci Point (° C) = 723 + 29.1 x Si - 10.7 x Mn - 16.9 x Ni + 16.9 x Cr + 6.38 x W + 290 x As ... [1 ] [00143] Point Ac 3 (° C) = 910 - 203 x C 0 · 5 + 44.7 x Si - 15.2 x Ni + 31.5 x Mo + 104 χ V +13.1 x W - (30 x Mn + 11 x Cr + 20 x Cu - 700 x P-400xAI -120 x As-400 x Ti) ... [2] [00144] where each one between C, Si, Mn, Cu, Ni, Cr, Mo, V, Ti, Al, W, As and P in the formulas signifies the mass content of that element.
    Petition 870180152726, of 11/19/2018, p. 31/50
    28/39
    co O CO CXI O LO CO CO r- σ> r- co σ> co OLO LOcoco CXI r-co CXI <co CO co CO co co co co co co r- coω CO LO coCXI σ> co co O LO CXI co Oco co LO <r- r- r- r- r- r- r- r- r- r- r- r-LOOOO) O O co CXI O co LO coco co CXI CXICXI OO O O O O O O O O ass OO O O O O O O O O D O O O O O O O O O O CXI CXI OO O OO O OO OO OO O OO O m O O O O O O O co coco r-LO σ> σ> CXICXICXI CXI CXI CXI .Ω O O O O OO O O O O z O O O O O O O O O O σ> σ> σ> LO O O O O OÇ/)'O O O O but ISI > O O O O O O O O O Φ Q_co co CXI co O CXI coLO co σ> CXI AND OOO O O O O O O O O O O O O O ωO O O O O O O O O O O O but Φ O O O O O O O O O O O O OΦLLco co LO f— CXI LO co r- CXIco LO co co coco co CXI co co co co THE CÜ ωO O O O O O O O O O O OO O O O O O O O O O O O z O O O O O O O O O O O O assCOco O O r- co co LOf— σ> co LO CXI co coco co CXI CXI CXI co Ç < O O O O O O O O O O O O ç O O O O O O O O O O O O ΦxPco co co co co co LO O O r- CXI O ANDO O O O O O O O O O O O Φ 1- O O O O O O O O O O O O assOO coσ> LO CXI σ> O co r-LO £ O r- co r- coco co r- σ> co r- σ> O O O O O O O OO O O OOco coLO CXI coOco O LO icü ι O O O O O co O O CXI O O co o »’ ω DO O O OQ_co co co co CO ANDO O O O O O O O O O O O the ω Z O O O O O O O O O O O OLD LO LO co r- co O σ> coσ> CXI O O O CXIOO OO O O O O O O O O O O O O O O O O O O O O O O O Ocn O O O O O O O O O O O O r- r- σ> σ> CXI CXI σ> co O O O OO O O O O O O O O O O O O OCL O O O O O O O O O O O O co co r- coco co COr- O LOç co O O O O O O O O O O O O coσ> σ>LO co co r- OCÕ CXI CO CXI CXI CXI co CXI CXI CXI CO CXI coO O O O O O O O O O O O co CO r- co co r- LO O σ> COr- CXI CXJ CXI CXI CXI CXI cococo CXIω O O O O O O O O O O O O o o < < m ω Q LU LL CD X - "3-1
    Petition 870180152726, of 11/19/2018, p. 32/50
    29/39 [00145] The bar was heated to 1250Ό, and was subsequently hot worked and finished in a seamless steel tube having a desired shape. In particular, the bar having been heated to 1250Ό was initially drilled using a Mannesmann drilling rig to obtain a hollow shell. Then the hollow shell was subjected to stretching work using a mandrel laminator and finishing work using a stretch reduction laminator, and was finished in a seamless steel tube having an outside diameter of 244.48 mm, a wall thickness of 13.84 mm, and a length of 12 m. The finishing temperature in the diameter reduction work using the diameter reduction laminator was around 950Ό in all cases.
    [00146] The seamless steel tube having been finished in order to have the dimensions described above was cooled under the conditions given in Table 2.
    [00147] The ILQ in Table 2 indicates that the finished seamless steel tube was further heated under the conditions of 950Ό x 10 min on the line, and was quickly cooled by water cooling. DQ indicates that the seamless steel tube has been water-cooled from a temperature of not less than 900Ό, which is the temperature not less than the Ar3 transformation point, without being further heated, and has been directly cooled quickly. AR indicates that the seamless steel tube has been air-cooled to room temperature.
    [00148] The seamless steel tube thus obtained was cut into pieces, and was subjected to intermediate heat treatment experimentally under the conditions given in Table 2. The cooling after the intermediate heat treatment was air cooled. The symbol in the intermediate heat treatment in Table 2 indicates that the intermediate heat treatment has not been carried out.
    [00149] From the steel tube having been air-cooled after treatment
    Petition 870180152726, of 11/19/2018, p. 33/50
    30/39 intermediate thermal, a specimen was cut to measure hardness, and Rockwell C hardness (hereinafter abbreviated as HRC) was measured. HRC measurement was made from the point of view of assessing resistance to seasonal fracture. If HRC is 41 or less, especially 40 or less, it can be judged that the occurrence of seasonal fracture can be suppressed. For the AR seamless steel tube, that is, the steel tube that has been air-cooled to room temperature after being finished, the seasonal fracture will not occur because the steel tube has not been cooled quickly. Therefore, for the steel tube subjected to intermediate heat treatment, the HRC measurement was omitted.
    [00150] Next, the steel tube, having been air-cooled after heat treatment, was subjected to heating and rapid cooling experimentally in step [2], in which the steel tube was heated to 920Ό for 20 minutes and was cooled quickly . Regarding heating and rapid cooling, for steel tubes using steels A to F and L, the steel tube was cooled quickly by being immersed in a tank or was cooled quickly using a water jet, and for tubes steel using G to K steels, the steel tube was cooled by spraying water mist.
    [00151] After reheating and rapid cooling, the grain size of the previous austenite was examined. That is, a specimen was cut from the reheated steel tube and cooled rapidly so that its cross section perpendicular to the direction of the tube length (direction of production of the tube) is the surface to be examined, and was fitted into a resin. Therefore, the edge of the anterior austenite grain was revealed by the Bechet-Beaujard method, in which the test specimen was corroded by a saturated aqueous solution of picric acid, and the grain size of the anterior austenite was examined in accordance with ASTM E112. -10.
    [00152] Table 2 gives additionally to HRC in the event that the tu
    Petition 870180152726, of 11/19/2018, p. 34/50
    31/39 bo of steel was air-cooled after the intermediate heat treatment and the result of measuring the grain size of the previous austenite after reheating and rapid cooling. In Table 2, for ease of description, the HRC described above was described as HRC after the intermediate heat treatment.
    Table 2
    Test n 5 Steel Cooling condition Intermediate heat treatment HRC after Intermediate heat treatment Grain size of previous austenite after reheating and rapid coolingTemperatureheating (° C) Warm-up time (min) ValuePL 1 THE ILQ 760 60 20660 20.3 10.0 Example ofInvention 2 THE ILQ 780 60 21060 24.4 10.6 3 THE ILQ 800 30 21137 24.7 10.1 4 THE ILQ 720 * 30 19561 30.0 8.4 Comparative example 5 THE ILQ 740 * 30 19955 26.1 8.5 6 THE AIR - * - - - 8.4 7 B ILQ 780 30 20743 24.5 10.3 Example ofInvention 8 B DQ 780 30 20743 25.2 10.4 9 B AIR 780 60 20660 - 10.4 10 B IL 550 * 30 16212 40.8 8.8 Comparative example 11 B DQ 550 * 30 16212 40.7 9.1 12 B AIR - * - - - 8.3 13 Ç ILQ 760 180 21153 20.0 10.4 Example ofInvention 14 Ç ILQ 780 30 20743 24.6 10.3 15 Ç ILQ 780 180 21562 23.8 10.4 16 Ç ILQ 800 180 21972 23.4 10.3 17 Ç ILQ 830 120 22392 28.5 10.0 18 Ç ILQ 740 * 30 19955 22.4 8.4 Ex. Comp. 19 D ILQ 760 30 20349 18.3 10.0 Example ofInvention 20 D ILQ 760 180 21153 17.2 10.2 21 D ILQ 780 30 20743 22.4 10.5 22 D ILQ 780 180 21562 24.1 10.3
    Petition 870180152726, of 11/19/2018, p. 35/50
    32/39
    23 D ILQ 830 90 22254 30.3 10.024 D DQ 780 30 20743 22.2 10.425 D ILQ 650 * 30 18182 39.1 8.8 Ex. Comp. 26 AND ILQ 760 30 20349 16.6 10.027 AND ILQ 760 60 20660 16.3 10.1 Example of the invention 28 AND ILQ 760 180 21153 15.3 10.5 29 AND ILQ 780 180 21562 19.5 10.5 30 AND DQ 780 30 20743 17.1 10.331 AND DQ 710 * 180 20129 21.8 8.3 Example- 32 AND ILQ 710 * 300 20347 20.1 8.3 parative 33 F ILQ 770 50 20777 17.0 9.7 Example of 34 F AIR 770 50 20777 17.2 9.6 invention 35 F ILQ 600 30 17197 30.4 8.3 Ex. Comp. 36 G ILQ 760 60 20660 20.0 10.137 G ILQ 760 180 21153 20.5 10.538 G ILQ 780 180 21562 21.1 10.539 G DQ 800 30 21137 24.3 10.340 H AIR 760 60 20660 19.5 10.241 H AIR 760 180 21153 19.2 10.5 Example of 42 H AIR 780 30 20743 20.4 10.5 invention 43 I AIR 760 60 20660 22.5 10.844 I AIR 780 30 20743 23.8 10.845 J AIR 780 30 20743 25.5 11.146 K AIR 780 30 20743 26.5 11.247 L AIR 810 60 21660 24.0 9.5PL = [T + 273) x (20 + ogiot)[where T is the heating temperature (° C) and t is the heating time cement (h)] in the intermediate heat treatment column indicates that the intermediate heat treatment has not been carried out of in the HRC column after the intermediate heat treatment indicates that the HRC measurement was not performed gives. * indicates that the conditions do not satisfy those defined by the present invention.
    [00153] Table 2 clearly shows that, regardless of the cooling conditions of the seamless steel tube, in testing modalities of examples of the present invention in which the
    Petition 870180152726, of 11/19/2018, p. 36/50
    33/39 steel was cooled after being heated to a temperature above the transformation point Aci and lower than the transformation point Ac3 as defined in the present invention, that is, to a temperature in the region of two phases of ferrite and austenite, the Grain size of the previous austenite after reheating and rapid cooling was 9.5 in test n ° 47 even in the case of the rawest grains, and in most cases, it was 10 or more, indicating fine grains.
    [00154] While the grain size of the previous austenite in tests numbers 9, 34, and 40 to 47 of the example modalities of the present invention were 9.5 to 11.2, the grain size of the previous austenite in tests no 05 6 and 12 of comparative examples were 8.4 and 8.3 respectively. It is apparent that even in the case where the seamless steel tube is air-cooled and is not cooled quickly after finishing work, if the steel tube is produced by the method according to the present invention, excellent refinement can be achieved .
    [00155] Furthermore, in the embodiments of the examples of the present invention, the HRC in the case where the steel tube was air-cooled after the intermediate heat treatment was 30.3 or less, so that seasonal fracture will not occur.
    [00156] In contrast, in the tests of the comparative examples in which the steel pipe was cooled after being heated to a temperature no higher than the transformation point Aci deviating from the condition defined in the present invention, the grain size of the previous austenite after reheating and rapid cooling were at most 9.1 (test number 11), and the grains were crude compared to the exemplary modalities of the present invention.
    [00157] As described above, it is apparent that by submitting the steel, which has the chemical composition defined in the present invention and has been hot worked in a desired way, to the steps [1]
    Petition 870180152726, of 11/19/2018, p. 37/50
    34/39 and [2] defined in the present invention sequentially, that is, cooling the steel that has been heated to a temperature exceeding the transformation point Aci and lower than the transformation point AC3 and then reheating the steel to a temperature not lower than the transformation point AC3 and cooling the same rapidly, the grains of the previous austenite can be made fine. By refining the grains from the previous austenite, the improvement in SSC resistance and toughness can be improved.
    Example 2 [00158] To confirm the improvement in SSC resistance due to the refining of the grains from the previous austenite, whose improvement was achieved by the method of the present invention, some of the steel tubes subjected to the reheating and rapid cooling described above (example 1) were tempered in step [3]. The quenching was carried out by heating the steel tube to a temperature of 650 to 710 ° C for 30 to 60 minutes so that the YS is adjusted to about 655 to 862 MPa (95 to 125 ksi), and cooling after the quench was air-cooled.
    [00159] Table 3 gives the specific tempering conditions together with the cooling conditions after the finishing work of the seamless steel tube and the grain size of the previous austenite after reheating and rapid cooling. The test numbers in Table 3 correspond to the test numbers in Table 2 described above (example 1). In addition, the letters a to d attached to tests number 7 and 8 are marks meaning that the quenching conditions have been changed.
    [00160] From each of the hardened steel tubes, a specimen to measure the hardness was cut to measure the HRC.
    [00161] In addition, from the steel tube, a round bar specimen specified in Method A of NACE TM0177, whose specimen has a parallel part having an external diameter of 6.35 mm
    Petition 870180152726, of 11/19/2018, p. 38/50
    35/39 and a length of 25.4 mm, was cut so that its longitudinal direction is the direction of the length of the steel tube (direction of production of the tube), and the tensile properties at room temperature were examined. Based on the results of this examination, the constant load test specified in Method A of NACE TM0177 was conducted to examine resistance to SSC.
    [00162] As a test solution for examining resistance to SSC, an aqueous solution of 0.5% acetic acid + 5% sodium chloride was used. While the 0.1 MPa hydrogen sulfide gas was fed into this solution, a voltage of 90% of the YS actually measured (hereinafter referred to as 90% AYS) or a voltage of 85% of the nominal limit value YS (hereinafter referred to as 85% SMYS) was imposed, with which the constant load test was conducted.
    [00163] Specifically, in tests Nos 1 to 5, 14, 21, 23, 26, 38, 42, and 44 to 47 given in Table 3. The constant load test was conducted by the imposition of AYS 90%. Furthermore, in tests Nos 7a to 12 and 33 to 35, the constant load test was conducted by the imposition of 645 MPa and 85% of SMYS considering the resistance level as the 110 ksi class in which YS is 758 to 862 Mpa (110 to 125 ksi) from the result of the examination of the tensile properties. In each of the tests, the resistance to SSC was evaluated by the shortest break time, making the number of tests 2 or 3. When the break did not occur in the 720 hour test, the constant load test was discontinued at that moment.
    [00164] Table 3 gives the results of HRC exams, tensile properties, and SSC resistance. The shortest break time> 720 in the SSC resistance column in Table 3 indicates that all specimens were not broken in the 720 hour test. In the case described above, in Table 3, the O mark was described in the judgment column considering resistance to SSC as being excellent.
    Petition 870180152726, of 11/19/2018, p. 39/50
    36/39 lens. On the other hand, in the case where the break time is no longer than 720 hours, the x mark was described in the judgment column considering the resistance to SSC as being poor.
    Petition 870180152726, of 11/19/2018, p. 40/50
    37/39 co ro ω .ω co
    Example of the invention Comparative example Example of the invention Comparative example SSC resistance judgment O O O X X O O O O O O O O X X X Shortest breakthrough time (h) ___________ > 720 > 720 > 720 286.3 330 > 720 > 720 > 720 > 720 > 720 > 720 > 720 > 720 231 368 479.6 Charging voltage 90% AYS 90% AYS 90% AYS 90% AYS 90% AYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS 85% SMYS Traction properties YR (%) 90.5 91.2 91.2 88.5 89.2 91.4 90.9 91.8 92.3 91.8 91.4 91.7 90.6 90.0 90.1 89.1 TS (MPa) Moo oo 879 904 878 873 867 921 916 934 853 887 55 885 893 904 895 YS (MPa) o o oo CM O OO M-CM OO LU 779 792 OO CO oo 841 863 783 oõ 835 801 804 814 798 HRC r <CM r <CM 28.4 27.2 26.9 27.4 27.3 28.7 29.3 27.6 hr <CM 29.7 27.6 28.3 29.9 26.8 Hardening Warm-up time(min) LO LO LO Μ - LO Μ - LO Μ - CO LO Μ - LO Μ - CO The co the CO LO Μ - CO CO CO CO Heating temperaturerç) _______ 705 705 705 705 705 710 ooz OOZ ooz 705 705 ooz 705 710 705 710 Grain size of previous austenite after reheating and rapid cooling O o 10.6 O Moo 8.5 10.3 10.3 10.3 10.3 10.4 10.4 10.4 10.4 OO oo σΓ 8.3 Cooling condition ILQ ILQ ILQ ILQ ILQ ILQ ILQ ILQ ILQ DQ DQ DQ AIRDQ AIR O o < < < < < < QC QC QC QC QC QC QC QC QC QC QC Test No.CM COLO CÜ h- _Q h- The h- Ό h- CÜ oo _Q OO O ooOCM
    Petition 870180152726, of 11/19/2018, p. 41/50
    38/39
    Example of the inventionEx. Comp. Example of the invention > 720 in the SSC resistance column indicates that none of the specimens was broken in the 720 hour test.o was described in the judgment column, considering SSC resistance to be excellent. On the other hand, in the case where the rupture time is no more than 720 hours, the x mark was described in the judgment column considering the resistance to SSC as being poor.* indicates that the conditions do not satisfy those defined by the present invention. O O O O O O X O O O O O O > 720 > 720 > 720 > 720 > 720 > 720 205 > 720 > 720 > 720 > 720 > 720 > 720 90% AYS SAV% 06 SAV% 06 SAV% 06 85% SMYS 85% SMYS 85% SMYS SAV% 06 SAV% 06 SAV% 06 SAV% 06 SAV% 06 SAV% 06 90.8 87.2 89.0 87.6 92.0 91.2 OO oo oo 55 90.0 96.1 92.0 94.1 89.0 861 829 oo CM OO 832 862 865 912 907 932 933 939 943 790 782 723 737 729 793 789 810 826 839 897 863 887 703 27.0 23.5 24.1 25.0 26.3 25.8 27.0 28.5 29.1 29.9 29.7 30.5 23.0 CO CO CO CO CO LO CO CO CO CO CO CO CO 705 705 705 695 680 685 650 700 705 690 710 705 700 10.3 10.5 O o O o 9.7 9.6 8.3 10.5 10.5 OO oCM ~ 9.5 ILQ ILQ ILQ ILQ ILQ AIR ILQ ILQ AIR AIR AIR AIR AIR ω α α LLI LL LL LL ω X _1CM CO CM CO CM POO item CO LO CO OO CO44 LO CO 47
    Petition 870180152726, of 11/19/2018, p. 42/50
    39/39 [00165] Table 3 evidently shows that by subjecting the steel, in which the refining of the austenite grains above is achieved by the sequential performance of the steps [1] and [2] defined in the present invention, to the tempering treatment in the step [3], excellent resistance to SSC can be achieved.
    INDUSTRIAL APPLICABILITY [00166] According to the present invention, since the refining of the grains from the previous austenite can be carried out by an economically efficient means, a high strength steel material excellent in SSC resistance can be obtained at a low cost . In addition, by the present invention, a seamless, low-alloy, high-strength seamless oil well pipe in SSC resistance can be produced at relatively low cost. In addition, in accordance with the present invention, improvement in toughness due to refining of the austenite grains above can be expected.
    权利要求:
    Claims (7)
    [1]
    [1] a step of heating the steel to a temperature that exceeds the transformation point Aci and lower than the transformation point Ac3 and cooling the steel;
    1. Method for the production of a resistant steel material with fracture resistance by sulfide stress, characterized by the fact that the steel has a chemical composition consisting of, in percentage by mass, C: 0.15 to 0.65%, Si: 0.05 to 0.5%, Mn: 0.1 to 1.5%, Cr: 0.2 to 1.5%, Mo: 0.1 to 2.5%, Ti: 0.005 to 0, 50%, Al: 0.001 to 0.50%, and the balance of Fe and impurities, where Ni, P, S, N and O between impurities are Ni: 0.1% or less, P: 0.04 % or less, S: 0.01% or less, N: 0.005% or less, and O: 0.01% or less, and which has been hot worked in a desired manner is sequentially subjected to steps [1] to [3] below:
    [2]
    [2] a step of reheating the steel to a temperature not lower than the transformation point AC3 and quickly cooling the steel by tempering it; and [3] a step of tempering the steel at a temperature not exceeding the transformation point Aci;
    (a) Nb: 0.4% or less, V: 0.5% or less, and B: 0.01% or less;
    (b) Ca: 0.005% or less, Mg: 0.005% or less, and REM: 0.005% or less.
    2/3 [1] a step of heating the steel to a temperature exceeding the transformation point Aci and lower than the AC3 point and cooling the steel;
    2. Method for the production of a resistant steel material with resistance to fracture by sulfide stress, characterized by the fact that the steel that has a chemical composition consisting of, in percentage by mass, C: 0.15 to 0.65% , Si: 0.05 to 0.5%, Mn: 0.1 to 1.5%, Cr: 0.2 to 1.5%, Mo: 0.1 to 2.5%, Ti: 0.005 to 0 , 50%, Al: 0.001 to 0.50%, at least one element selected from the elements shown in (a) and (b), and the balance being Fe and impurities, where Ni, P, S, N and O impurities are Ni: 0.1% or less, P: 0.04% or less, S: 0.01% or less, N: 0.005% or less, and O: 0.01% or less, and that has been hot worked in a desired way is sequentially subjected to the steps [1] to [3] below:
    Petition 870180152726, of 11/19/2018, p. 44/50
    [2] a step of reheating the steel to a temperature not lower than the transformation point AC3 and quickly cooling the steel by tempering it; and [3] a step of tempering the steel at a temperature not exceeding the Aci transformation point.
    [3]
    3/3 chemical composition, as defined in claim 1 or 2, having been finished hot in a seamless steel tube, the steel is quickly cooled directly from a temperature not lower than the Ar3 transformation point, and subsequently subjected to the steps from [1] to [3].
    3. Method for producing a resistant steel material with sulfide stress fracture resistance, according to claim 1 or 2, characterized by the fact that the steel having the chemical composition, as defined in claim 1 or 2, is finished hot in a seamless steel tube and cooled by air, and subsequently sequentially subjected to steps [1] to [3].
    [4]
    4. Method for producing a resistant steel material with sulfide stress fracture resistance, according to claim 1 or 2, characterized by the fact that after the steel having the chemical composition, as defined in claim 1 or 2, having been hot finished in a seamless steel tube, the steel is further heated to a temperature not lower than the Ar3 transformation point and not more than 1050Ό in the line, and after being rapidly cooled to a temperature not lower than the transformation point Ar3, the steel is sequentially subjected to steps from [1] to [3].
    [5]
    5. Method for producing a resistant steel material with fracture resistance by sulfide stress, according to claim 1 or 2, characterized by the fact that after the steel having the
    Petition 870180152726, of 11/19/2018, p. 45/50
    [6]
    6. Method for producing a resistant steel material with fracture resistance by sulfide stress, according to claim 4, characterized by the fact that the heating in step [1] is performed by a heating device connected to a device for quick cooling of the heat treatment in the line.
    [7]
    7. Method for producing a resistant steel material with fracture resistance by sulfide stress, according to claim 5, characterized by the fact that the heating in step [1] is carried out by a heating device connected to a device rapid cooling system that performs direct rapid cooling.
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    同族专利:
    公开号 | 公开日
    CN104039989A|2014-09-10|
    US10287645B2|2019-05-14|
    CA2849287A1|2013-09-12|
    WO2013133076A1|2013-09-12|
    EP2824198A1|2015-01-14|
    UA112792C2|2016-10-25|
    JP5387799B1|2014-01-15|
    SA113340364B1|2015-07-22|
    ES2755750T3|2020-04-23|
    EP2824198A4|2015-12-30|
    EP2824198B1|2019-09-18|
    AR090243A1|2014-10-29|
    CN104039989B|2015-11-25|
    MX2014009157A|2014-10-13|
    MX371103B|2020-01-17|
    EA201491650A1|2015-01-30|
    AU2013228617B2|2015-07-30|
    EP2824198B8|2020-04-15|
    EA025503B1|2016-12-30|
    AU2013228617A1|2014-04-17|
    JPWO2013133076A1|2015-07-30|
    IN2014DN03395A|2015-06-26|
    US20150041030A1|2015-02-12|
    CA2849287C|2016-11-29|
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    法律状态:
    2018-03-13| B06T| Formal requirements before examination [chapter 6.20 patent gazette]|
    2018-08-21| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2019-02-12| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2019-03-26| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 26/02/2013, OBSERVADAS AS CONDICOES LEGAIS. |
    2019-11-26| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2012049970|2012-03-07|
    JP2012-049970|2012-03-07|
    PCT/JP2013/054866|WO2013133076A1|2012-03-07|2013-02-26|Method for producing high-strength steel material having excellent sulfide stress cracking resistance|
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