Martensitic precipitation hardening stainless steel and preparation method thereof

Abstract

The martensitic precipitation hardening stainless steel comprises the following components in percentage by mass: 14.2%-15.2% of Cr, 6.0%-6.8% of Ni, 0.65%-0.75% of Mo, 1.40%-1.65% of Cu, 0.3%-0.6% of Nb, 0.01%-0.04% of Al, 0.015%-0.020% of N, less than or equal to 0.05% of C, less than or equal to 0.60% of Si, less than or equal to 0.70% of Mn, less than or equal to 0.008% of P, less than or equal to 0.002% of S and the balance of Fe and other inevitable impurities. According to the martensitic precipitation hardening stainless steel and the preparation method thereof, on the basis of existing martensitic precipitation hardening stainless steel, the content of Cr, Ni, Cu and other elements is adjusted, a proper amount of Mo element is added, a precipitated phase rich in Mo and Cu elements is evenly precipitated during precipitation hardening treatment of the martensitic precipitation hardening stainless steel, a matrix is strengthened, and the plasticity of the material is improved on the premise that the hardness is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel production, and more specifically to a martensitic precipitation hardening stainless steel and a preparation method thereof. Background Art

[0002] Precipitation hardening stainless steel is a type of high-strength stainless steel that is made by adding different types and quantities of strengthening elements to the chemical composition of stainless steel, and precipitating different types and quantities of carbides, nitrides, carbonitrides and intermetallic compounds through the precipitation hardening process, which not only improves the strength of the steel but also maintains sufficient toughness. It is referred to as PH steel. Precipitation hardening stainless steel has both high strength and sufficient toughness, and is widely used in cutting-edge and civilian industries, such as aerospace, petrochemicals, medical equipment and marine engineering.

[0003] Precipitation hardening stainless steel can be divided into three categories according to the metallographic structure of its matrix: martensitic, semi-austenitic and austenitic. At present, martensitic precipitation hardening stainless steel uses 05Cr17Ni4Cu4Nb, which contains elements such as chromium, nickel, copper and niobium. However, it is difficult to ensure the hardness of 05Cr17Ni4Cu4Nb stainless steel during deep cold forming, thus limiting its application in some occasions that require complex cold forming processes. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a martensitic precipitation hardening stainless steel and a preparation method thereof, so as to improve the plasticity of the material while ensuring the hardness.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0006] A martensitic precipitation hardening stainless steel comprises the following components in the following mass percentages: Cr: 14.2% to 15.2%, Ni: 6.0% to 6.8%, Mo: 0.65% to 0.75%, Cu: 1.40% to 1.65%, Nb: 0.3% to 0.6%, Al: 0.01% to 0.04%, N: 0.015% to 0.020%, C: ≤0.05%, Si: ≤0.60%, Mn: ≤0.70%, P: ≤0.008%, S: ≤0.002%, and the rest is Fe and other inevitable impurities.

[0007] To further optimize the technical solution, the precipitation hardening stainless steel includes the following components in the following mass percentages: Cr: 14.37%, Ni: 6.73%, Mo: 0.70%, Cu: 1.42%, Nb: 0.32%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

[0008] To further optimize the technical solution, the precipitation hardening stainless steel includes the following components in the following mass percentages: Cr: 14.25%, Ni: 6.63%, Mo: 0.69%, Cu: 1.43%, Nb: 0.33%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

[0009] To further optimize the technical solution, the precipitation hardening stainless steel includes the following components in the following mass percentages: Cr: 14.27%, Ni: 6.53%, Mo: 0.68%, Cu: 1.40%, Nb: 0.25%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

[0010] A method for preparing martensitic precipitation hardened stainless steel, characterized in that it comprises the following steps:

[0011] S1. According to the mass percentage of precipitation hardening stainless steel components, pure iron Fe, metal molybdenum Mo, metal chromium Cr, metal nickel Ni, electrolytic manganese Mn, and metal copper Cu are added. The raw materials other than metal manganese Mn and electrolytic copper Cu are added into a vacuum induction furnace according to the percentage content for electric heating. The remaining raw materials other than metal manganese and electrolytic copper are added while the material is low-powered; when the temperature of the molten steel reaches 1550℃~1570℃, refining begins, and metal silicon and aluminum particles are added for deoxidation. After refining for ≥20min, the composition is fine-tuned according to the content of each element in the steel, and preparation for tapping begins. Metal manganese and electrolytic copper are added before tapping. The tapping temperature is 1560℃~1570℃. At this temperature, electrodes are cast and the electrodes are remelted into steel ingots through electroslag;

[0012] S2. The electroslag ingot is kept at 1140-1180°C for 3h before forging, the intermediate billet is heated to 1120-1150°C for 1-1.5h, and then forged;

[0013] S3. The billet is rolled into a finished product, and then subjected to solution and aging heat treatment, wherein the rolling temperature is 1120-1150°C, the solution temperature is 1020-1040°C, the solution is kept for 1 hour, and water-cooled to room temperature; the aging heat treatment temperature is 540-610°C, then kept for 4 hours, and air-cooled to obtain precipitation hardened stainless steel.

[0014] To further optimize the technical solution, in step S1, the raw materials are electrically heated when they are added to 20% to 35% of the volume of the vacuum induction furnace.

[0015] To further optimize the technical solution, in step S1, the vacuum degree of the vacuum induction furnace during the refining period is ≤5Pa.

[0016] To further optimize the technical solution, in step S2, when the electrode is forged and blanked, the starting forging temperature is ≥1000°C, and the final forging temperature is ≥800°C.

[0017] To further optimize the technical solution, in step S3, when rolling the blank, the starting rolling temperature is ≥1000°C, and the final rolling temperature is ≥800°C.

[0018] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0019] The present invention provides a martensitic precipitation hardening stainless steel and a preparation method thereof. On the basis of existing martensitic precipitation hardening stainless steel, the contents of elements such as Cr, Ni and Cu are adjusted, and an appropriate amount of Mo element is added, so that during precipitation hardening treatment, a precipitation phase rich in Mo and Cu elements is uniformly precipitated to strengthen the matrix, and the plasticity of the material is improved while ensuring the hardness.

[0020] The present invention adopts a smelting method of vacuum induction + electroslag remelting during the production process to ensure the purity of the steel, while reducing the tendency of component segregation in the steel, and ensuring that a uniform precipitated phase is obtained after subsequent processing and heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of the present invention;

[0022] Figure 2 It is the metallographic structure diagram 100X of the present invention;

[0023] Figure 3 This is the metallographic structure diagram 500X of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] A martensitic precipitation hardening stainless steel comprises the following components in the following mass percentages: Cr: 14.2% to 15.2%, Ni: 6.0% to 6.8%, Mo: 0.65% to 0.75%, Cu: 1.40% to 1.65%, Nb: 0.3% to 0.6%, Al: 0.01% to 0.04%, N: 0.015% to 0.020%, C: ≤0.05%, Si: ≤0.60%, Mn: ≤0.70%, P: ≤0.008%, S: ≤0.002%, and the rest is Fe and other inevitable impurities.

[0026] The role of chromium Cr in this steel is to improve the corrosion resistance of stainless steel. A thin and stable chromium-rich oxide film is formed on the surface to prevent the penetration and oxidation of oxygen atoms, reduce the starting temperature of martensitic transformation, and improve hardenability. In combination with nickel, a complete martensitic structure can be obtained through solid solution and quenching treatment.

[0027] The role of nickel Ni in this steel is to expand the austenite phase region, increase the Ni equivalent, reduce the ferrite content in the steel, increase the residual austenite content, and refine the grains.

[0028] Molybdenum Mo in this steel can precipitate molybdenum-rich phases along the austenite grain boundaries at the initial stage of aging, which can improve the strength of the steel while avoiding intergranular fracture and improving the toughness of the steel.

[0029] Copper Cu is the main element for precipitation strengthening during the aging process of this steel. During the aging heat treatment process, it forms a nano-sized second phase strengthening matrix with precipitation strengthening elements such as Nb and Ni, thereby greatly improving the strength of the steel.

[0030] A method for preparing martensitic precipitation hardening stainless steel, combined with Figure 1 As shown, it includes the following steps:

[0031] S1. According to the mass percentage of precipitation hardening stainless steel components, pure iron Fe, metal molybdenum Mo, metal chromium Cr, metal nickel Ni, electrolytic manganese Mn, and metal copper Cu are added. The other raw materials except metal manganese Mn and electrolytic copper Cu are added into the vacuum induction furnace according to the percentage content. When the raw materials are added to 20% to 35% of the volume of the vacuum induction furnace, electric heating is performed, and the remaining raw materials except metal manganese and electrolytic copper are added while the material is low-powered. When the temperature of the molten steel reaches 1550°C to 1570°C, refining begins, and metal silicon and aluminum particles are added for deoxidation. The vacuum degree of the vacuum induction furnace during the refining period is ≤5Pa. After refining for ≥20min, the composition is finely adjusted according to the content of each element in the steel, and preparation for tapping begins. Metal manganese and electrolytic copper are added before tapping. The tapping temperature is 1560°C to 1570°C. At this temperature, electrodes are cast and the electrodes are remelted into steel ingots through electroslag.

[0032] S2. Keep the electroslag ingot at 1140-1180°C for 3 hours before forging, heat the intermediate billet to 1120-1150°C, keep it for 1-1.5 hours, and then forge the billet; wherein, the starting forging temperature is ≥1000°C, and the final forging temperature is ≥800°C.

[0033] S3. Roll the blank into finished product, and then carry out solution and aging heat treatment, wherein the rolling temperature is 1120-1150°C, the start rolling temperature is ≥1000°C, and the final rolling temperature is ≥800°C; the solution temperature is 1020-1040°C, and after solution, it is kept warm for 1 hour and cooled to room temperature by water; the aging heat treatment temperature is 540-610°C, and then kept warm for 4 hours and air cooled to obtain precipitation hardened stainless steel. The metallographic structure diagram 100X and the metallographic structure diagram 500X of the present invention are respectively as shown in Figure 2 and Figure 3 shown.

[0034] Example 1

[0035] The present embodiment provides a precipitation hardened stainless steel, comprising the following components in the following mass percentages: Cr: 14.37%, Ni: 6.73%, Mo: 0.70%, Cu: 1.42%, Nb: 0.32%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

[0036] According to the mass percentage of the above components, pure iron, metallic molybdenum, metallic chromium, metallic nickel, electrolytic manganese, metallic copper, etc. are added. When the other raw materials except electrolytic manganese and metallic copper are added into the vacuum induction furnace to 30% of its volume, it is electrically heated. While the material is reduced to a low power of 100KW, the remaining raw materials except metallic manganese and electrolytic copper are added; when the temperature of the molten steel reaches 1550℃, refining begins.

[0037] The vacuum degree during the refining period is ≤5Pa, the refining holding time is ≥20min, the temperature during the refining period is 1560℃, the composition is fine-tuned according to the content of each element in the steel, and preparation for steelmaking begins. Metal manganese and electrolytic copper are added before steelmaking, and the electrodes are cast into electrodes at a temperature of 1565℃, and then the electrodes are remelted into ingots through electroslag.

[0038] The electroslag ingot is kept at 1160°C for 3 hours, and then forged, the intermediate billet is heated to 1135°C and kept for 1.5 hours; wherein the start forging temperature is ≥1000°C, and the final forging temperature is ≥800°C, to obtain a billet;

[0039] The above-mentioned billet is rolled into a finished product, and then subjected to solution and aging heat treatment, wherein the rolling temperature is 1135°C, the starting rolling temperature is ≥1000°C, and the final rolling temperature is ≥800°C; the solution temperature is 1030°C, kept for 1 hour, cooled to room temperature by water, and the aging heat treatment temperature is 550°C, kept for 4 hours, and air cooled. The precipitation hardening stainless steel with the furnace number of 2KD71172 is obtained.

[0040] Example 2

[0041] The present embodiment provides a precipitation hardened stainless steel, comprising the following components in the following mass percentages: Cr: 14.25%, Ni: 6.63%, Mo: 0.69%, Cu: 1.43%, Nb: 0.33%, Al: 0.02%, and the rest being Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

[0042] According to the mass percentage of the above components, pure iron, metallic molybdenum, metallic chromium, metallic nickel, electrolytic manganese and metallic copper are added, and the raw materials other than electrolytic manganese and metallic copper are added to the vacuum induction furnace to 30% of its volume, and then electrically heated, and the remaining raw materials except metallic manganese and electrolytic copper are added while the material is oxidized at a low power of 100KW; when the temperature of the molten steel reaches 1550℃, refining is started;

[0043] The vacuum degree during the refining period is ≤5Pa, the refining holding time is ≥20min, the temperature during the refining period is 1560℃, the composition is fine-tuned according to the content of each element in the steel, and preparation for steelmaking begins. Metal manganese and electrolytic copper are added before steelmaking, and the electrodes are cast into electrodes at a temperature of 1565℃, and then the electrodes are remelted into ingots through electroslag.

[0044] The electroslag ingot is kept at 1160°C for 3 hours, and then forged, the intermediate billet is heated to 1135°C and kept for 1.5 hours; wherein the start forging temperature is ≥1000°C, and the final forging temperature is ≥800°C, to obtain a billet;

[0045] The above-mentioned billet is rolled into a finished product, and then subjected to solution and aging heat treatment, wherein the rolling temperature is 1135°C, the starting rolling temperature is ≥1000°C, and the final rolling temperature is ≥800°C; the solution temperature is 1030°C, kept for 1 hour, cooled to room temperature by water, and the aging heat treatment temperature is 595°C, kept for 4 hours, and air cooled. The precipitation hardening stainless steel with the furnace number of 2KD71085 is obtained.

[0046] Example 3

[0047] The present embodiment provides a precipitation hardened stainless steel, comprising the following components in the following mass percentages: Cr: 14.27%, Ni: 6.53%, Mo: 0.68%, Cu: 1.40%, Nb: 0.25%, Al: 0.02%, and the rest being Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

[0048] According to the mass percentage of the above components, pure iron, metallic molybdenum, metallic chromium, metallic nickel, electrolytic manganese and metallic copper are added, and the raw materials other than electrolytic manganese and metallic copper are added to the vacuum induction furnace to 30% of its volume, and then electrically heated, and the remaining raw materials except metallic manganese and electrolytic copper are added while the material is oxidized at a low power of 100KW; when the temperature of the molten steel reaches 1550℃, refining is started;

[0049] The vacuum degree during the refining period is ≤5Pa, the refining holding time is ≥20min, the temperature during the refining period is 1560℃, the composition is fine-tuned according to the content of each element in the steel, and preparation for steelmaking begins. Metal manganese and electrolytic copper are added before steelmaking, and the electrodes are cast into electrodes at a temperature of 1565℃, and then the electrodes are remelted into ingots through electroslag.

[0050] The electroslag ingot is kept at 1160°C for 3 hours, and then forged, the intermediate billet is heated to 1135°C and kept for 1.5 hours; wherein the start forging temperature is ≥1000°C, and the final forging temperature is ≥800°C, to obtain a billet;

[0051] The above-mentioned billet is rolled into a finished product, and then subjected to solution and aging heat treatment, wherein the rolling temperature is 1135°C, the starting rolling temperature is ≥1000°C, and the final rolling temperature is ≥800°C; the solution temperature is 1030°C, kept for 1 hour, cooled to room temperature by water, and the aging heat treatment temperature is 605°C, kept for 4 hours, and air cooled. The precipitation hardening stainless steel with the furnace number of 2KD10280 is obtained.

[0052] Comparative Example 1

[0053] The chemical composition mass percentage of precipitation hardening stainless steel S17400 of the American ASTMA564 standard is as follows:

[0054] Table 1 Chemical composition (wt%)

[0055]

[0056] The manufacturing process is as follows: vacuum induction furnace casting electrode → electroslag remelting → rapid forging to open the blank → hot rolling to form the product → solution treatment → aging → polishing.

[0057] Among them, the solid solution of the above steel is 1040°C, kept warm for 1 hour, and water cooled; the aging heat treatment system is 550°C, kept warm for 4 hours, and air cooled; and it can be obtained.

[0058] Comparative Example 2

[0059] The chemical composition mass percentage of precipitation hardening stainless steel S17400 of the American ASTMA564 standard is as follows:

[0060] Table 2 Chemical composition (wt%)

[0061]

[0062] The manufacturing process is as follows: vacuum induction furnace casting electrode → electroslag remelting → rapid forging to open the blank → hot rolling to form the product → solution treatment → aging → polishing.

[0063] Among them, the solid solution of the above steel is 1040℃, kept warm for 1h, and water cooled; the aging heat treatment system is 595℃, kept warm for 4h, and air cooled; it can be obtained.

[0064] The test results are shown in Table 3:

[0065] Table 3 Chemical composition (wt%) (the balance in the table is Fe and other unavoidable impurities)

[0066]

[0067] Table 4 Mechanical properties

[0068]

[0069] It can be seen from Table 4 that by conducting multiple batches of trial production on Examples 1-3, the mechanical properties after solution + aging are shown in Table 4. The tensile strengths obtained by the aging system from 550°C to 605°C for 4h are 1135MPa, 1040MPa, and 1013MPa, respectively, and the hardnesses are 333HBW, 312HBW, and 309HBW, respectively, all showing a trend of gradually decreasing with increasing aging temperature. Under the same heat treatment conditions, the strength and hardness can basically meet the performance requirements corresponding to S17400 in ASTM 5643, and the impact performance is far superior to the US standard S17400.

Claims

1. A martensitic precipitation hardening stainless steel, characterized in that: The present invention comprises the following components in the following mass percentages: Cr: 14.2% to 15.2%, Ni: 6.0% to 6.8%, Mo: 0.65% to 0.75%, Cu: 1.40% to 1.65%, Nb: 0.3% to 0.6%, Al: 0.01% to 0.04%, N: 0.015% to 0.020%, C: ≤0.05%, Si: ≤0.60%, Mn: ≤0.70%, P: ≤0.008%, S: ≤0.002%, and the rest are Fe and other inevitable impurities.

2. The martensitic precipitation hardening stainless steel according to claim 1, characterized in that: The precipitation hardening stainless steel comprises the following components in the following mass percentages: Cr: 14.37%, Ni: 6.73%, Mo: 0.70%, Cu: 1.42%, Nb: 0.32%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

3. The martensitic precipitation hardening stainless steel according to claim 1, characterized in that: The precipitation hardening stainless steel comprises the following components in the following mass percentages: Cr: 14.25%, Ni: 6.63%, Mo: 0.69%, Cu: 1.43%, Nb: 0.33%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

4. The martensitic precipitation hardening stainless steel according to claim 1, characterized in that: The precipitation hardening stainless steel comprises the following components in the following mass percentages: Cr: 14.27%, Ni: 6.53%, Mo: 0.68%, Cu: 1.40%, Nb: 0.25%, Al: 0.02%, and the rest are Fe and other inevitable impurities such as C, P, S, Si, H, O, and N.

5. A method for preparing martensitic precipitation hardening stainless steel according to any one of claims 1 to 4, characterized in that: It includes the following steps: S1. According to the mass percentage of precipitation hardening stainless steel components, pure iron Fe, metal molybdenum Mo, metal chromium Cr, metal nickel Ni, electrolytic manganese Mn, and metal copper Cu are added. The raw materials other than metal manganese Mn and electrolytic copper Cu are added into a vacuum induction furnace according to the percentage content for electric heating. The remaining raw materials other than metal manganese and electrolytic copper are added while the material is low-powered; when the temperature of the molten steel reaches 1550℃~1570℃, refining begins, and metal silicon and aluminum particles are added for deoxidation. After refining for ≥20min, the composition is fine-tuned according to the content of each element in the steel, and preparation for tapping begins. Metal manganese and electrolytic copper are added before tapping. The tapping temperature is 1560℃~1570℃. At this temperature, electrodes are cast and the electrodes are remelted into steel ingots through electroslag; S2. The electroslag ingot is kept at 1140-1180°C for 3h before forging, the intermediate billet is heated to 1120-1150°C for 1-1.5h, and then forged; S3. The billet is rolled into a finished product, and then subjected to solution and aging heat treatment, wherein the rolling temperature is 1120-1150°C, the solution temperature is 1020-1040°C, the solution is kept for 1 hour, and water-cooled to room temperature; the aging heat treatment temperature is 540-610°C, then kept for 4 hours, and air-cooled to obtain precipitation hardened stainless steel.

6. The method for preparing martensitic precipitation hardening stainless steel according to claim 5, characterized in that: In the step S1, the raw materials are electrically heated when they are added to 20% to 35% of the volume of the vacuum induction furnace.

7. The method for preparing martensitic precipitation hardening stainless steel according to claim 5, characterized in that: In the step S1, the vacuum degree of the vacuum induction furnace during the refining period is ≤5Pa.

8. The method for preparing martensitic precipitation hardening stainless steel according to claim 5, characterized in that: In the step S2, when the electrode is forged, the starting forging temperature is ≥1000°C and the final forging temperature is ≥800°C.

9. The method for preparing martensitic precipitation hardening stainless steel according to claim 5, characterized in that: In the step S3, when rolling the blank, the starting rolling temperature is ≥1000°C, and the final rolling temperature is ≥800°C.

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