Process for preparing high carbon martensitic stainless steel

Abstract

To provide a preparation process for obtaining a high-carbon martensitic stainless steel exhibiting characteristics such as improved wear resistance and corrosion resistance.SOLUTION: A process for preparing a high-carbon martensitic stainless steel comprises the steps of: preparing a steel composition comprising 1.7-1.9 wt.% of C, 17-18 wt.% of Cr, 1.6-2.0 wt.% of Mo, 2.9-3.5 wt.% of V, 0.40-0.60 wt.% of Nb, and Fe as a main constituent; melting the steel composition; transferring the molten steel composition to a die casting mold; demolding the steel composition at a temperature in a range of 850-950°C followed by forced air cooling; preparing the demolded steel composition for open die forging; and subjecting the steel composition to open die forging, subjecting the steel composition to anti-flaking heat treatment, followed by hardening and tempering to obtain the high carbon martensitic stainless steel.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a process for preparing high-carbon martensitic stainless steel.

Background Art

[0002] Martensitic stainless steel usually has a carbon content of 0.1 wt% to 1.2 wt%. Generally, high-carbon martensitic stainless steel containing up to 1.2 wt% carbon is produced via conventional ingot casting and forging or rolling. However, to achieve higher strength levels and high corrosion and wear resistance according to application requirements, a carbon content of up to 1.8 wt% is required. When the conventional ingot casting method is used to produce this high-carbon martensitic stainless steel, the resulting steel exhibits microstructural inhomogeneities in the form of chromium carbide banding and grain boundary segregation, rendering the process unsuitable.

[0003] In this case, powder metallurgy is employed to produce high-carbon martensitic stainless steel without the above-mentioned inhomogeneities in the microstructure. However, the process is very expensive compared to the conventional ingot casting method. Therefore, the use of powder metallurgy is limited.

Summary of the Invention

[0004] A process for preparing high-carbon martensitic stainless steel is disclosed. The process for preparing high-carbon martensitic stainless steel comprises the steps of: preparing a steel composition containing 1.7 to 1.9 wt% C, 17 to 18 wt% Cr, 1.6 to 2.0 wt% Mo, 2.9 to 3.5 wt% V, 0.40 to 0.60 wt% Nb, and Fe as the main component; melting the steel composition; transferring the molten steel composition to a die-casting mold; demolding the steel composition at a temperature in the range of 850 to 950°C and then forcibly cooling it by air; preparing the steel composition for free forging; and performing free forging on the steel composition, subjecting the steel composition to a delamination prevention heat treatment, and then hardening and tempering to obtain high-carbon martensitic stainless steel. [Brief explanation of the drawing]

[0005] [Figure 1A] This figure shows a 1x image of the microstructure of a high-carbon martensitic stainless steel prepared according to the embodiments of this disclosure. [Figure 1B] This figure shows a 3x magnified image of the microstructure of a high-carbon martensitic stainless steel prepared according to the embodiments of this disclosure. [Figure 2A] This figure shows the microstructure of conventional high-carbon martensitic stainless steel. [Figure 2B] This figure shows the microstructure of a high-carbon martensitic stainless steel prepared according to the embodiments of this disclosure. [Figure 3A] This figure shows the black phase (stainless steel matrix) and white phase (carbides) in the microstructure of conventional high-carbon martensitic stainless steel. [Figure 3B] This figure shows the black phase (stainless steel matrix) and white phase (carbides) in the microstructure of high-carbon martensitic stainless steel prepared according to embodiments of this disclosure. [Figure 4A] This figure shows the primary and secondary carbides in the SEM-EDAX microstructure of conventional high-carbon martensitic stainless steel. [Figure 4B]This figure shows the primary and secondary carbides in the SEM-EDAX microstructure of high-carbon martensitic stainless steel prepared according to embodiments of this disclosure. [Figure 5A] This figure shows a comparison of the average carbide diameter (equivalent to a circle diameter) in conventional high-carbon martensitic stainless steels. [Figure 5B] This figure shows a comparison of the average carbide diameter (equivalent to a circle diameter) in high-carbon martensitic stainless steel prepared according to embodiments of this disclosure. [Figure 6A] This figure shows a comparison of the nearest neighbor distances for carbides in conventional high-carbon martensitic stainless steel. [Figure 6B] This figure shows a comparison of the nearest neighbor distances of carbides in high-carbon martensitic stainless steel prepared according to embodiments of this disclosure. [Figure 7A] This figure shows a comparison of the aspect ratios of carbides in conventional high-carbon martensitic stainless steel. [Figure 7B] This figure shows a comparison of the aspect ratios of carbides in high-carbon martensitic stainless steel prepared according to embodiments of this disclosure. [Figure 8] This figure shows a comparison of the impact strength of conventional high-carbon martensitic stainless steel and high-carbon martensitic stainless steel prepared according to embodiments of the present disclosure. [Figure 9] This figure shows a comparison of the wear resistance of conventional high-carbon martensitic stainless steel and high-carbon martensitic stainless steel prepared according to embodiments of the present disclosure. [Figure 10] This figure shows a comparison of the stress corrosion resistance of conventional high-carbon martensitic stainless steel and high-carbon martensitic stainless steel prepared according to embodiments of the present disclosure. [Figure 11] This figure shows the effect of demolding at various temperatures followed by forced air cooling on the microstructure of high-carbon martensitic stainless steel prepared according to embodiments of this disclosure. [Modes for carrying out the invention]

[0006] Embodiments are referenced herein and specific terminology is used to illustrate them, for the purpose of facilitating understanding of the principles of this disclosure. Nevertheless, the scope of this disclosure is not limited thereto, and any modifications and further variations of the compositions and methods disclosed, as well as any further applications of the principles of this disclosure to this disclosure, should be considered as those that a person skilled in the art would ordinarily conceive of in relation to this disclosure.

[0007] Those skilled in the art will understand that the above general description and the following detailed description are illustrative and explanatory of the disclosure and do not limit it.

[0008] Throughout this specification, any reference to “one embodiment,” “embodiment,” or similar wording means that a particular configuration, structure, or feature described in relation to that embodiment is included in at least one embodiment of this disclosure. Therefore, throughout this specification, any occurrence of the phrases “in one embodiment,” “in an embodiment,” or similar wording may, but not necessarily, all refer to the same embodiment.

[0009] The terms “comprise,” “comprising,” or any other variation thereof, are intended to encompass non-exclusive inclusion, meaning that a process or method that includes a list of steps may include other steps that are not explicitly listed in or are inherent in the process or method, rather than including only those steps, and are not intended to be interpreted as “consisting of only.”

[0010] Similarly, the terms "having" and "including," and their grammatical variations, are non-restrictive so as not to exclude other items that could be substituted or added to the listed items.

[0011] Unless otherwise noted, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described herein. All publications mentioned herein are incorporated herein by reference.

[0012] The term "primary carbide" mainly refers to M7C3 carbide composed of liquid metal of carbon (C) in the martensite-based matrix of steel and metals (M) such as iron (Fe), chromium (Cr), vanadium (V), niobium (Nb), molybdenum (Mo), etc., and contains Cr with a molar fraction of 40 - 70% and other elements such as V, Mo, Fe, etc. with a molar fraction of 0.5 - 20% in the martensite-based matrix of steel.

[0013] The term "secondary carbide" mainly refers to MC6 carbide precipitated from austenite of C in the martensite-based matrix of steel and M such as Fe, Cr, V, Nb, Mo, etc., and contains Cr with a molar fraction of 50 - 90% and other elements such as V, Mo, Fe, etc. with a molar fraction of 0.5 - 20% in the martensite-based matrix of steel. 23 The term "specific metal carbide" mainly refers to carbide composed of liquid metal of C in the martensite-based matrix of steel and M such as Fe, Cr, V, Nb, Mo, etc., and contains either Nb with a molar fraction of 40 - 70% (referred to as "niobium-rich carbide") or V with a molar fraction of 40 - 90% (referred to as "vanadium-rich carbide") and trace amounts of other metals such as Cr, Fe, etc. up to a molar fraction of 10% in the martensite-based matrix of steel.

[0014] The term "specific metal carbide" mainly refers to carbide composed of liquid metal of C in the martensite-based matrix of steel and M such as Fe, Cr, V, Nb, Mo, etc., and contains either Nb with a molar fraction of 40 - 70% (referred to as "niobium-rich carbide") or V with a molar fraction of 40 - 90% (referred to as "vanadium-rich carbide") and trace amounts of other metals such as Cr, Fe, etc. up to a molar fraction of 10% in the martensite-based matrix of steel.

[0015] This disclosure relates, in its broadest sense, to a process for preparing high-carbon martensitic stainless steel. The process for preparing the high-carbon martensitic stainless steel comprises the steps of: preparing a steel composition containing 1.7 to 1.9 wt% C, 17 to 18 wt% Cr, 1.6 to 2.0 wt% Mo, 2.9 to 3.5 wt% V, 0.40 to 0.60 wt% Nb, and Fe as the main component; melting the steel composition; transferring the molten steel composition to a die-casting mold; demolding the steel composition at a temperature in the range of 850 to 950°C and then forcibly cooling it by air; preparing the steel composition for free forging; and performing free forging on the steel composition, subjecting the steel composition to a delamination prevention heat treatment, and then hardening and tempering to obtain high-carbon martensitic stainless steel.

[0016] The inventors have found that both the disclosed composition and process are important for achieving high-carbon martensitic stainless steel with improved malleability, corrosion resistance, and wear resistance.

[0017] The melting of the steel composition is carried out using any well-known apparatus. In the embodiment, the melting is carried out in an induction furnace at a temperature in the range of 1470 to 1520°C for a time in the range of 60 to 90 minutes.

[0018] After melting, the molten composition is transferred into the die-casting mold using any known method. In the embodiment, the transfer is performed using an injection ladle at a uniform injection rate.

[0019] In the embodiment, the steel composition is cooled to a temperature in the range of 850-950°C within 5 minutes in a die-casting mold. Demolding is performed at a temperature in the range of 850-950°C. After demolding, the resulting steel composition is subjected to forced air cooling using any known means, such as direct forced air cooling or indirect forced air cooling. The inventors have found that demolding at a temperature in the range of 850-950°C before forced air cooling inhibits the formation of secondary carbides.

[0020] After forced air cooling, the material is prepared for free forging using known means. In some embodiments, the material is prepared by heating it to a temperature in the range of 1100 to 1200°C, with immersion for 30 to 50 minutes per inch at a minimum forging temperature of 950°C. In some embodiments, the material is prepared by heating it to a temperature of 1120 to 1150°C, with immersion for 30 to 50 minutes per inch at a minimum forging temperature of 950°C.

[0021] In the next step, a delamination prevention treatment is performed to diffuse hydrogen from the steel material. The delamination prevention treatment is performed by known means, which involves heating the steel composition below the lower critical temperature (AC1), followed by sufficient immersion to allow hydrogen to diffuse from the steel material. In some embodiments, the delamination prevention heat treatment is performed at a temperature of 760-800°C for a period of 15-25 hours. In some embodiments, the delamination prevention heat treatment is performed at a temperature of 760-780°C for a period of 18-20 hours.

[0022] In some embodiments, curing is performed using known means at a temperature in the range of 1080–1130°C for immersion time of 30–60 minutes / inch. In some embodiments, curing is performed at a temperature in the range of 1110–1130°C for immersion time of 30–60 minutes / inch. In some embodiments, after curing, the steel composition is quenched in oil. Any known oil can be used for quenching the steel material.

[0023] In some embodiments, the quenched steel composition is tempered using known methods at a temperature of 320–370°C at a rate of 60–90 minutes per inch. In some embodiments, the quenched steel composition is tempered at a temperature of 350–370°C at a rate of 60–90 minutes per inch. The tempered steel composition is then formed into the final product.

[0024] This disclosure also relates to high-carbon martensitic stainless steel obtained using the disclosed process. This high-carbon martensitic stainless steel contains 1.7 to 1.9 wt% C, 17 to 18 wt% Cr, 1.6 to 2.0 wt% Mo, 2.9 to 3.5 wt% V, 0.40 to 0.60 wt% Nb, and Fe as the main component. Furthermore, the high-carbon martensitic stainless steel has a microstructure composed of 15 to 30 volume% primary carbides and less than 2 volume% secondary carbides.

[0025] In this embodiment, the microstructure of the high-carbon martensitic stainless steel is predominantly martensitic.

[0026] The high-carbon martensitic stainless steel of this disclosure contains primary carbides of uniform size and uniformly distributed within the microstructure of the steel material. Figures 1A and 1B show the distribution of primary carbides within the microstructure of high-carbon martensitic stainless steel prepared according to embodiments of this disclosure.

[0027] In some embodiments, the microstructure includes primary carbides having an average carbide diameter (equivalent circle diameter) in the range of 10 to 30 microns, with distances between consecutive (or nearest) primary carbides in the range of 0.4 to 0.6 microns. In some embodiments, the microstructure includes primary carbides having an average carbide diameter of about 17.19 microns, with distances between consecutive primary carbides of 0.51 microns. In some embodiments, the carbides in the disclosed high-carbon martensitic stainless steel have an average aspect ratio in the range of 1 to 2. In some embodiments, the carbides have an average aspect ratio of 1.9.

[0028] In some embodiments, the microstructure of the high-carbon martensitic stainless steel includes primary carbides in the range of 20-30 volume%. In some embodiments, the microstructure of the high-carbon martensitic stainless steel includes secondary carbides in an amount of less than 1 volume%. In some embodiments, the microstructure of the high-carbon martensitic stainless steel includes specific metal carbides in the range of 1-5 volume%. In some embodiments, the microstructure of the steel includes specific metal carbides in the range of 2-4 volume%. The specific metal carbides improve the wear resistance of the disclosed high-carbon martensitic stainless steel.

[0029] In some embodiments, the high-carbon martensitic stainless steel contains C in an amount ranging from 1.80 to 1.90% by weight. In some embodiments, the high-carbon martensitic stainless steel contains C in an amount of 1.8% by weight.

[0030] In some embodiments, the high-carbon martensitic stainless steel contains Cr in an amount ranging from 17.0 to 17.5% by weight. In some embodiments, the high-carbon martensitic stainless steel contains Cr in an amount of 17% by weight.

[0031] In some embodiments, the high-carbon martensitic stainless steel contains Mo in an amount ranging from 1.90 to 2.0 wt%. In some embodiments, the high-carbon martensitic stainless steel contains Mo in an amount of 2 wt%. Alloying of Nb and Mo at the disclosed percentages reduces primary carbide formation by half and contributes to increasing the malleability of the disclosed high-carbon martensitic stainless steel.

[0032] In some embodiments, the high-carbon martensitic stainless steel contains V in an amount ranging from 3.1 to 3.20% by weight. In some embodiments, the high-carbon martensitic stainless steel contains V in an amount of 3.2% by weight.

[0033] In some embodiments, the high-carbon martensitic stainless steel contains Nb in an amount ranging from 0.45 to 0.50% by weight. In some embodiments, the high-carbon martensitic stainless steel contains Nb in an amount of 0.5% by weight.

[0034] High-carbon martensitic stainless steel contains trace amounts of nickel (Ni). In some embodiments, the high-carbon martensitic stainless steel contains up to 0.50% by weight of Ni. In some embodiments, the high-carbon martensitic stainless steel contains 0.20% by weight of Ni.

[0035] In some embodiments, the high-carbon martensitic stainless steel contains silicon (Si) in an amount ranging from 0.30 to 0.60 wt%. In some embodiments, the high-carbon martensitic stainless steel contains Si in an amount of 0.36 wt%.

[0036] High-carbon martensitic stainless steel contains trace amounts of tungsten (W). In some embodiments, the high-carbon martensitic stainless steel contains up to 0.07% by weight of W. In some embodiments, the high-carbon martensitic stainless steel contains 0.01% by weight of W.

[0037] In some embodiments, the high-carbon martensitic stainless steel contains manganese (Mn) in an amount ranging from 0.40 to 0.60 wt%. In some embodiments, the high-carbon martensitic stainless steel contains Mn in an amount of 0.45 wt%.

[0038] In some embodiments, the disclosed high-carbon martensitic stainless steel has a hardness in the range of 53 to 57 HRC. In some embodiments, the high-carbon martensitic stainless steel has a hardness of 55 to 57 HRC. In some embodiments, the high-carbon martensitic stainless steel has a hardness of 55 HRC.

[0039] In this embodiment, the high-carbon martensitic stainless steel has a load of 18-24 J / mm². 2 It has a Charpy impact strength in the range of 20-21 J / mm². In some embodiments, high-carbon martensitic stainless steel has a Charpy impact strength in the range of 20-21 J / mm². 2 It has a Charpy impact strength of 20 J / mm². In some embodiments, high-carbon martensitic stainless steel has a Charpy impact strength of 20 J / mm². 2 It has a Charpy impact strength of [value missing].

[0040] In some embodiments, high-carbon martensitic stainless steel exhibits corrosion resistance for a period of 200 to 300 hours before failure under a tensile load condition of 350 MPa in an H2S atmosphere according to NACE0177-201. In some embodiments, high-carbon martensitic stainless steel exhibits corrosion resistance for a period of 220 to 280 hours before failure under a tensile load condition of 350 MPa in an H2S atmosphere according to NACE0177-201. In some embodiments, high-carbon martensitic stainless steel exhibits corrosion resistance for a period of 220 hours before failure under a tensile load condition of 350 MPa in an H2S atmosphere according to NACE0177-201.

[0041] In the embodiment, high-carbon martensitic stainless steel measured 200-280 mm when subjected to a 45 N load with alumina abrasive for 30 minutes. 3 It has a wear mass loss in the range of . In some embodiments, high-carbon martensitic stainless steel has a wear mass loss of 260-280 mm when measured over 30 minutes under a load of 45 N with alumina abrasive. 3 It has a wear mass loss of 260 mm when measured over 30 minutes under a load of 45 N with alumina abrasive. In some embodiments, high-carbon martensitic stainless steel has a wear mass loss of 260 mm when measured over 30 minutes. 3 It has wear mass loss. [Examples]

[0042] To allow for a deeper understanding of the present invention, the following examples are described. These examples are for illustrative purposes only, and the exact compositions, preparation methods, and embodiments described are not limitations of the present invention, and any obvious modifications will be apparent to those skilled in the art.

[0043] Methods for characterizing high-carbon martensitic stainless steel formed using embodiments of the processes described in the claims are also described herein.

[0044] Example 1: Comparison of exemplary high-carbon martensitic stainless steel with conventional high-carbon steel having a similar composition High-carbon martensitic stainless steel (INV1) prepared according to embodiments of this disclosure was compared with high-carbon martensitic stainless steel (CR4) prepared using a conventional ingot casting method.

[0045] INV1 and CR4 had a composition containing Fe and other untested metals, as well as the following elements in the amounts listed below. [Table 1]

[0046] Process used to prepare INV1: The steel composition was prepared according to the composition listed in Table 1 above. The steel composition was melted at 1520°C. After melting, the molten steel composition was transferred to a die-casting mold at a temperature of 1470°C and then demolded. Demolding of the steel composition was performed at a temperature of 950°C, followed by forced air cooling using direct forced air cooling. The demolded steel composition was prepared for free forging at a temperature of 1150°C with a minimum forging temperature of 950°C for a time of 50 minutes / inch. In the next step, the steel composition was free forged. The forged steel composition was subjected to a delamination prevention heat treatment at a temperature of 760-780°C for a time ranging from 18 to 20 hours. The resulting steel composition was hardened at a temperature of 1120°C with a time of 60 minutes / inch. After hardening, the steel composition was rapidly cooled in oil. The rapidly cooled steel material was tempered at a temperature of 370°C for 90 minutes per inch to obtain high-carbon martensitic stainless steel. This tempered steel composition is then formed into the final product.

[0047] The process used to prepare CR4: CR4 was prepared using a conventional ingot casting method.

[0048] Evaluation of primary, secondary, and specific metal carbides in CR4 and INV1: CR4 and INV1 were evaluated, and the percentages of primary carbides, secondary carbides, and specific metal carbides were calculated.

[0049] Characterization methods: Multiple microstructure images were recorded at various magnifications using a duert microscope and processed with image processing software (Biowizard software) to estimate the total percentage of carbides (primary carbides, secondary carbides, and specific metal carbides). EDAX (energy-dispersive X-ray) mapping was performed using a JEOL scanning electron microscope to evaluate the chemical composition of each carbide. Based on the chemical composition of each carbide, primary carbides, secondary carbides, and specific metal carbides were identified.

[0050] Figures 2A and 2B show the microstructures of CR4 and INV1, respectively. Figures 3A and 3B show the black phase (stainless steel matrix) and white phase (carbides) within the microstructures of CR4 and INV1, respectively. Figures 4A and 4B show the primary and secondary carbides within the SEM-EDAX microstructures of CR4 and INV1, respectively.

[0051] The percentages of primary carbides, secondary carbides, and specific metal carbides within the microstructure of both CR4 and INV1 are summarized in Table 2 below. [Table 2]

[0052] Figures 5, 6, and 7 show the equivalent circle diameter, nearest neighbor distance, and aspect ratio of primary carbides within the microstructures of CR4 and INV1, respectively. The characteristics of primary carbides within the microstructures of both CR4 and INV1 are summarized in Table 3 below. [Table 3]

[0053] Both INV1 and CR4 were tested to evaluate their impact strength, abrasion resistance, and corrosion resistance. Characterization method used: 1. Impact strength: The impact strength of the steel material was evaluated by performing a Charpy impact test, specifically a Charpy V-notch test (IS code 1757), under the following conditions. Notch: None Temperature: 24℃ 2. Abrasion resistance: The wear resistance of the steel material was evaluated by performing a rubber wheel abrasion test (ASTM G65) under a load of 45N for 30 minutes. 3. Stress corrosion test: Vulnerability to stress corrosion was measured according to NACE0177-2016 under the following conditions. H2S 200ml / min / lit 5% NaCl + 0.5% glacial acetic acid pH: 2.7 Load: 25-45% UTS Temperature: 24℃

[0054] Results and Discussion: Figure 8 shows a comparison of the impact strength of CR4 and INV1. INV1 was found to have approximately 155% higher impact strength compared to CR4. Figure 9 shows a comparison of the wear resistance of CR4 and INV1. INV1 was found to have approximately 47% higher wear resistance compared to CR4. Figure 10 shows a comparison of the corrosion resistance of CR4 and INV1. INV1 was found to have approximately 400% higher stress corrosion resistance compared to CR4.

[0055] Example 2: Effect of demolding steel compositions at various temperatures on the microstructure of steel materials The effect of demolding a steel composition at temperatures above 850°C on the microstructure of the steel was investigated by performing the demolding process at 900°C, 400°C, and room temperature, followed by forced cooling. Three sets of experiments were conducted using the process of Example 1, varying the temperature at which the demolding was performed.

[0056] Results and Discussion: Figure 11 shows the effect of demolding steel compositions at various temperatures on the microstructure of high-carbon martensitic stainless steel.

[0057] It was confirmed that demolding at temperatures higher than 850°C resulted in a uniform distribution of carbides from the core to the surface of the cast steel. On the other hand, demolding at lower temperatures of 400°C or room temperature resulted in non-uniform and aggregated carbide precipitation from the surface to the core. [Industrial applicability]

[0058] The disclosed process for preparing high-carbon martensitic stainless steel allows for control over the amount and distribution of carbides within the steel matrix. The disclosed process can be performed using existing ingot casting equipment and systems.

[0059] The high-carbon martensitic stainless steel obtained using the disclosed process exhibits the necessary toughness (impact strength) for dynamic applications, as well as improved wear resistance and corrosion resistance compared to stainless steel obtained using well-known and expensive methods such as powder metallurgy. Furthermore, the high-carbon martensitic stainless steel obtained using the disclosed process exhibits significantly improved malleability compared to high-carbon martensitic stainless steel processed by conventional ingot casting methods that involve forging or rolling.

Claims

1. A process for preparing a high-carbon martensitic stainless steel, comprising: preparing a steel composition containing 1.7 to 1.9% by mass of C, 17 to 18% by mass of Cr, 1.6 to 2.0% by mass of Mo, 2.9 to 3.5% by mass of V, 0.40 to 0.60% by mass of Nb, with the balance being Fe and inevitable impurities; melting the steel composition; transferring the molten steel composition to a die-casting mold; releasing the steel composition from the mold at a temperature in the range of 850 to 950 °C and then subjecting it to forced air cooling; heating and raising the temperature of the released steel composition to prepare the released steel composition for open forging and performing open forging on the steel composition; performing a hydrogen diffusion heat treatment on the forged steel composition at a temperature below the lower critical temperature (AC1) to diffuse hydrogen, and then hardening it at a temperature in the range of 1080 to 1130 °C, and obtaining the high-carbon martensitic stainless steel by quenching and tempering; A process comprising the above steps.

2. The process according to claim 1, wherein the step of melting the steel composition is carried out at a temperature in the range of 1470 to 1520 °C for a time in the range of 60 to 90 minutes.

3. The process according to claim 1, wherein before release, the steel composition is cooled to a temperature in the range of 850 to 950 °C within 5 minutes in the die-casting mold.

4. The process according to claim 1, wherein the released steel composition is subjected to homogenization heat treatment at a rate of 30 to 50 minutes per inch of the dominant cross-section of the steel composition, and the material is heated to a temperature in the range of 1100 to 1200 °C to be prepared for open forging, and then forged at a temperature of 950 °C or higher.

5. The process according to claim 1, wherein the anti-peeling heat treatment is carried out at a temperature in the range of 760 to 800 °C for a time in the range of 15 to 25 hours.

6. The process according to claim 1, wherein the hardening step is carried out by subjecting the dominant cross-section of the steel composition to homogenization heat treatment at a rate of 30 to 60 minutes per inch.

7. The process according to claim 1, wherein the quenched steel composition is tempered at a temperature in the range of 320 to 370 °C at a rate of 60 to 90 minutes per inch of the dominant cross-section of the steel composition.

8. The process according to claim 1, wherein the quenching is carried out in oil.

9. The process according to claim 1, wherein the steel composition contains a maximum of 0.50% by weight of Ni.

10. The process according to claim 1, wherein the steel composition contains W up to 0.07% by weight.

11. The process according to claim 1, wherein the steel composition contains Si in an amount in the range of 0.30 to 0.60% by weight.

Images