• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The present invention relates to a process for the manufacturing of a forming tool which comprises: providing a base steel for the forming tool; and a clad steel of defined chemical composition; depositing by laser cladding the clad steel onto at least part of the surface of the base steel for the forming tool, obtaining a coating with presence of retained austenite; finish machining in soft condition of the resulting piece; and cryogenic treatment to transform the retained austenite into martensite and increase the hardness of the generated coating. The invention also relates to the forming tool with improved hardness and wear resistance, obtained by the process of the invention.
    公开号:EP3698902A1
    申请号:EP17811342.9
    申请日:2017-10-19
    公开日:2020-08-26
    发明作者:Garikoitz ARTOLA；Maider MURO；Carlos Soriano Reyes；Josu LEUNDA ARRIZABALAGA
    申请人:Casa Maristas Azterlan；Fundacion Tekniker；
    IPC主号:B22F3-00
    专利说明:
    [0001] The present invention is related to an improved process for manufacturing a forming tool with increased hardness and high wear resistance. The invention also relates to the forming tool obtained by the said process. BACKGROUND OF THE INVENTION
    [0002] Forming tools for deformation processes, such as forging, rolling, powder pressing (powder metallurgy), coining or stamping are usually manufactured in steel grades known as "tool steels". "Tool steels" are versatile materials that are well-adapted for manufacturing tools for use in deformation processes. Tool steels can reach a particularly high hardness when they are heat treated in order to resist wear damage and are available for several grades, adapted to specific applications, such as punching, dies or cutting.
    [0003] The regular manufacturing route to produce forming tools is to carry out first a rough machining of a tool steel in state of supply, in low hardness conditions (annealed) until a geometry is achieved, which is close to the desired final geometry of the forming tool to be obtained. Secondly a hardening heat treatment is applied (by quench and tempering or by solution annealing and hardening) so that the high working hardness of the tool is achieved; and finally the tool steel is mechanized until the final geometry of the forming tool is achieved. That is, conventionally, it is necessary to carry out a finish machining operation of the forming tool after the hardening heat treatment, due to the distortions and surface oxidation that occur during the heat treatment.
    [0004] At the level of the microstructural characteristics, some specific tool steels retain some austenite after quench and tempering, and to transform this retained austenite into martensite several tempering treatments and/or criogenic treatments can be carried out. Usually these treatments are applied to the whole of the forming tool since they show retained austenite in all their volume. The microstructural change caused during the heat treatment induces significant dimensional distortions since the volume occupied by the martensitic microstructure is slightly larger than that of the austenite which it replaces. To correct the volumetric distortions caused during heat treatment and achieve the final desired dimensions of the forming tool, very expensive finish machining operations are needed.
    [0005] The chip removal finish machining operations of high hardness materials, such as tool steels, are very demanding processes in terms of cutting conditions, due to the high friction and cutting forces involved. Dimensional accuracy is also difficult to achieve since the elastic deformations generated during machining must be properly handled. In general, as the material hardness increases, the machining costs increase as consequence of the strategies to compensate the stresses, the wear and the deformations involved during the chip removal finish machining operations.
    [0006] In view of the state of the art there is the need of providing an alternative process for manufacturing high hardness forming tools which overcomes at least part of the disadvantages above mentioned. DETAILED DESCRIPTION OF THE INVENTION
    [0007] The present inventors have now discovered that it is possible to manufacture a forming tool according to an alternative process which significantly reduces or even avoids, surface oxidation and large deformations of the forming tool, reducing the intensity of the finish machining operation and allowing the use of cheaper base steels for the tool steel. An additional advantage of this novel process is the overall lowering of the manufacturing costs.
    [0008] The process, hereinafter referred to as the process of the invention comprises the following steps:a) Providing a base steel for the forming tool; b) Depositing by laser cladding a clad steel onto at least part of the surface of the base steel for the forming tool, obtaining a cladded piece with presence of retained austenite in the coating, c) Carrying out a finish machining operation of the piece obtained in previous step b), d) Applying a cryogenic treatment to the piece obtained in previous step c), obtaining a forming tool.
    [0009] The base steel for the forming tool provided in step a) is obtained by rough machining a base steel for the forming tool in state of supply or delivery, until a geometry is achieved close to the desired final geometry of the forming tool to be manufactured. The base steels for the forming tool which can be used are well known materials; they can be of ferritic, perlitic, bainitic, martensitic nature or a mixture thereof.
    [0010] According to a particular embodiment the base steel for the forming tool is the standard DIN 1.2709, DIN 1.2379, DIN 1.7225, or DIN 1.0503.
    [0011] The base steel for the forming tool provided in step a) has preferably a hardness equal or greater than 30 HRC. According to another preferred embodiment the base steel for the forming tool has a hardness equal or lower than 52 HRC. In a particular embodiment, the hardness is between 30 and 52 HRC. Illustrative examples of the hardness of the base steel for the forming tool are 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 HRC. In a further preferred embodiment, the hardness is between 44 and 46, more preferably 45 HRC.
    [0012] The process of the invention comprises also providing a clad steel which chemical composition is selected to promote austenite retention in the coating obtained from the same in step b) of the process. The skilled person knows the chemical elements and their relative percentage in the composition which provide a coating with retained austenite, and there is no particular limitation about it. In a particular embodiment the clad steel chemical composition comprises: C (0.25-1.60%), Mn (<2.50%), Ni (0.50-5.00%), N (0.01-0.30%), in weight % in respect of the total weight of the composition, wherein Mn + Ni (<5.0%).
    [0013] In a preferred embodiment the clad steel chemical composition comprises, in weight % in respect of the total weight of the composition:C (0.25-1.60%), Mn (<2.50%), Ni (0.50-5.00%), N (0.01-0.30%), Si (<1.5 %), P (<0.02%), S (<0.01 %), Cr (2.0-10.0%), Mo (0.10-3.0%), V (0.1-1.0%), Fe (balanced %) and unspecified other elements (each <0.1% and total <0.3%), wherein Mn + Ni (<5.0%).
    [0014] In another preferred embodiment the clad steel chemical composition comprises in weight % in respect of the total weight of the composition:C (0.25-0.8%), Mn (<1.0%), Ni (1.00-4.00%), N (0.01-0.30%), Si (<1.5%), P (<0.02%), S (<0.01%), Cr (2.0-8.0%), Mo (0.20-1.70%), V (0.5-1.0%), Fe (balanced %) and unspecified other elements (each <0.1% and total <0.3%), wherein Mn + Ni (<4.0%).
    [0015] In a further preferred embodiment the clad steel chemical composition comprises the following: C (0.29-0.35%), Mn (0.20-0.4%), Ni (2.00-3.00%), N (0.01-0.1%), Si (<1.00%), P (<0.014%), S (<0.006%), Cr (6.5-7.5%), Mo (1.2-1.5%), V (0.5-1.0%), the rest Fe and unspecified other elements (each <0.1% and total <0.3%).
    [0016] The process of the invention comprises depositing by laser cladding said clad steel with suitable chemical composition onto at least part of the surface of the base steel for the forming tool obtaining a cladded piece with presence of retained austenite in the coating. The depositing by laser cladding can be done on one or more areas of the surface of the base steel for the forming tool.
    [0017] The content of retained austenite in the coating obtained in step b) is comprised between 2% and 18% (in volume in respect of the total volume of the coating). In a particular embodiment the amount of retained austenite is between 2% and 10%. In another particular embodiment is between 2% and 8%, and preferably between 2% and 6%.
    [0018] The coating obtained in b) has a thickness which may vary within a broad range. According to a particular embodiment the thickness is between 1 to 20 mm, preferably between 2 and 5 mm. According to another particular embodiment the thickness is between 1 and 15 mm. Further illustrative non-limiting examples of thicknesses are 3 mm, 4 mm, 6 mm, 7 mm, 8 mm, 9 mm and 10 mm.
    [0019] The coating obtained in b) usually has a hardness which is higher than the hardness of the base steel for the forming tool. Usually the hardness is between 48 and 58 HRC, preferably between 50 and 54 HRC. In a particular embodiment the coating with retained austenite obtained in b) has a hardness between 50 and 57 HRC, for example, 51 HRC, or 52HRC, or 53 HRC or 56 HRC.
    [0020] The presence of retained austenite is deliberately caused, presenting advantages in respect of the reduction of the risk of cracking of the coating carried out by lase cladding, since the austenite stands better the thermal stress caused by the laser cladding process, and the resulting hardness of the coating obtained in b) ranges between 48 and 58 HRC. Accordingly thereafter, the finish machining in soft condition step c) can be carried out, which results in an advantage for the finish machining process itself.
    [0021] The finish machining step c) is performed in any conventional manner, such as milling and/or turning operations.
    [0022] Thereafter, in step d) a cryogenic treatment is applied at a temperature equal or lower than -150ºC, preferably lower than -160ºC, and more preferably between -170 ºC and -180 ºC, so that the retained austenite is transformed into martensite. After this treatment the resulting coating achieves a final hardness which is usually comprised between 54 and 60 HRC. The amount of retained austenite is reduced in the resulting coating to a value comprised between 0 and 5%. In a particular embodiment the amount is reduced to a value between 0 and 3%, preferably between 0 and 2%, more preferably between 0 and 1%.
    [0023] The process of the invention presents the advantage that the cryogenic treatment does not cause significant dimensional distortions of the tool, since the only dimensional relevant variations, due to the transformation of the retained austenite into martensite, affect at most the 18% of the microstructure of the coating of the cladded piece obtained in b).
    [0024] Later, after the application of the criogenic treatment it results advantageous to be able to avoid carrying out an additional step of finish machining of the forming tool.
    [0025] The hardness of the coating of the forming tool obtained in step d) is between 54 and 60 HRC, preferably between 56 and 60, more preferably 58 and 60, for example 59 HRC.
    [0026] In another aspect the invention relates to a forming tool obtained by the process of the invention as previously disclosed.
    [0027] The forming tools that are obtained are suitable for forging, rolling, powder pressing (powder metallurgy), coining or stamping processes. The forming tool of the invention is characterized in that the hardness of the coating obtained by laser cladding, and after the application of the criogenic treatment, is greater than the hardness of the coating obtained by laser cladding without criogenic treatment, and this value is greater than the one that the starting base steel for the forming tool presents.
    [0028] The process and the forming tool of the present invention are illustrated below by means of reference examples which are presented only in an illustrative manner and it is not intended that they limit the present invention in any way. EXAMPLES
    [0029] The clad steel that was used presented the following chemical composition: C-0.34%, Si-1.01%, Mn-0.23%, P-0.011%, S-0.005%, Cr-7.51 %, Mo-1.44%, Ni-2.02%, V-0.94%, N-0.03%, Fe in balance. Example 1:
    [0030] A standard steel DIN 1.7225 with a hardness of 34-38 HRC in quenched and tempered state was submitted to machining to generate a base steel for the forming tool. Thereafter, a coating of about 4 mm thickness, a hardness of 53 HRC and 8% of retained austenite was deposited by laser cladding onto the surface of the base steel. Then a finish machining by end milling was performed with a machining depth of about 1 mm.
    [0031] After finish machining, a cryogenic treatment was applied in a cryogenic processing chamber during 19 hours with a minimum temperature of -175ºC (98K). Before removing the sample from the cryogenic chamber, the temperature was raised to 50ºC in order to avoid condensation humidity.
    [0032] After the cryogenic treatment, the hardness of the cryogenized coating had increased up to 57 HRC. The content of retained austenite had dropped below 3% in example 1. Example 2:
    [0033] A standard steel DIN 1.2709 age hardened, with a hardness of 49-50 HRC was submitted to rough machining to generate a base steel for the forming tool. Thereafter, a coating of about 4 mm thickness, a hardness of 53 HRC and 8% of retained austenite was deposited by laser cladding onto the surface of the base steel.. A conventional finish machining by end milling was performed with a machining depth of about 1 mm was performed.
    [0034] After the finish machining, a cryogenic treatment is applied in a cryogenic processing chamber during 19 hours with a minimum temperature of -175ºC (98K). Before removing the sample from the processing chamber, the temperature was raised to 50ºC in order to avoid condensation humidity.
    [0035] After the cryogenic treatment, the hardness of the cryogenized coating had increased up to 57 HRC. The content of retained austenite had dropped below 3% in example 2.
    [0036] These examples showed that the cryogenic treatment triggered the transformation of the retained austenite in martensite, increasing the hardness of the cryogenized coating of the forming tool
    权利要求:
    Claims (14)
    [0001] A process for the manufacturing of a forming tool which comprises the following steps:
    a) Providing a base steel for the forming tool;
    b) Depositing by laser cladding a clad steel onto at least part of the surface of the base steel for the forming tool, obtaining a cladded piece with presence of retained austenite in the coating,
    c) Carrying out a finish machining operation of the piece obtained in previous step b),
    d) Applying a cryogenic treatment to the piece obtained in previous step c).
    [0002] Process according to claim 1, wherein the base steel for the forming tool provided in step a) has hardness equal or superior to 30 HRC.
    [0003] Process according to claim 1 or 2, wherein the clad steel presents a chemical composition suitable to promote austenite retention.
    [0004] Process according to claim 3, wherein the clad steel chemical composition comprises, in weight % in respect of the total weight of the composition:C (0.25-1.60%), Mn (<2.50%), Ni (0.50-5.00%), N (0.01-0.30%), Si (<1.5 %), P (<0.02%), S (<0.01%), Cr (2.0-10.0%), Mo (0.10-3.0%), V (0.1-1.0%), Fe (balanced %) and unspecified other elements (each <0.1% and total <0.3%), wherein Mn + Ni (<5.0%),
    [0005] Process according to claim 4, wherein the clad steel chemical composition comprises in weight % in respect of the total weight of the composition:C (0.25-0.8%), Mn (<1.0%), Ni (1.00-4.00%), N (0.01-0.30%), Si (<1.5%), P (<0.02%), S (<0.01 %), Cr (2.0-8.0%), Mo (0.20-1.70%), V (0.5-1.0%), Fe (balanced %) and unspecified other elements (each <0.1% and total <0.3%), wherein Mn + Ni (<4.0%).
    [0006] Process according to claim 5, wherein the clad steel chemical composition comprises the following: C (0.29-0.35%), Mn (0.20-0.4%), Ni (2.00-3.00%), N (0.01-0.1%), Si (<1.00%), P (<0.014%), S (<0.006%), Cr (6.5-7.5%), Mo (1.2-1.5%), V (0.5-1.0%), the rest Fe and unspecified other elements (each <0.1% and total <0.3%).
    [0007] Process according to any one of claims 1 to 6, wherein the coating obtained by deposition by laser cladding presents between 2% and 18% in volume of retained austenite and preferably between 2% and 6%.
    [0008] Process according to claim 7, wherein the coating obtained by deposition by laser cladding presents a thickness between 1 to 20 mm and preferably between 2 and 5 mm.
    [0009] Process according to claim 7 or 8, wherein the coating obtained by deposition by laser cladding presents a hardness between 48 to 58, and preferably 50 to 54 HRC.
    [0010] Process according to any one of claims 1 to 9, wherein the finish machining operation is milling and/or turning.
    [0011] Process according to any one of claims 1 to 10, wherein the cryogenic treatment is carried out at a temperature equal or lower than -150 ºC.
    [0012] Process according to any one of claims 1 to 11, wherein the coating of the forming tool obtained in step d) has a hardness between 54 to 60 HRC.
    [0013] Process according to claim 12, wherein the coating of the forming tool obtained in step d) presents an amount of retained austenite between 0 to 5% and preferably between 0 to 1%.
    [0014] A forming tool obtained by the process according to any one of previous claims.
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    同族专利:
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