High-hardness and high-corrosion-resistance martensitic stainless steel as well as preparation method and application thereof

Abstract

The invention discloses high-hardness and high-corrosion-resistance martensitic stainless steel, a preparation method and application, and relates to the technical field of steel smelting, and the high-hardness and high-corrosion-resistance martensitic stainless steel comprises the following chemical components in percentage by weight: 0.15-0.23% of C; 0.15% to 0.30% of Si; 0.30% to 0.60% of Mn; less than 0.020% of P; less than 0.010% of S; cr: 12.5%-13.5%; 1.5% to 2.5% of Ni; 1.8% to 2.4% of Mo; 0.10% to 0.20% of N; less than 0.008% of B, and the balance Fe and impurities. According to the high-hardness and high-corrosion-resistance martensitic stainless steel, the preparation method and the application, the martensitic stainless steel has high hardness and high corrosion resistance, the martensitic stainless steel contains Mn, Mo, N and B alloy elements, the hardness of the martensitic stainless steel is increased, meanwhile, the hardness of the martensitic stainless steel can be reduced through the adopted annealing process, high-precision machining is facilitated, and the service life of the martensitic stainless steel is prolonged. The pin can be used for more than 168 hours in a 5% NaCl salt spray test, can be used for a data transmission connector pin for a 5G communication base station, is long in service life, and is suitable for manufacturing a structural member and a bearing member in an atmospheric environment.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and in particular to a high-hardness and high-corrosion-resistant martensitic stainless steel, a preparation method and an application thereof. Background Art

[0002] It is a martensitic stainless steel with good corrosion resistance in the atmosphere and high-temperature water vapor. It also has sufficient corrosion resistance in fresh water, seawater, salt solutions with a temperature not exceeding 30 degrees, food media, and low-concentration organic acids. However, it generally does not withstand more than 24 hours in a 5% NaCl salt spray test.

[0003] According to the invention patent application with publication number CN108396232A and publication date August 14, 2018, medium-carbon martensitic stainless steel and its preparation method are disclosed, belonging to the field of iron and steel metallurgy. The invention addresses the poor corrosion resistance of medium-carbon martensitic stainless steel and the existing need to add the precious metal molybdenum to improve its corrosion resistance. The technical solution provides medium-carbon martensitic stainless steel with the following chemical composition by weight: C: 0.26-0.45%, Si ≤ 1.0%, Mn: 0.1-2.0%, P ≤ 0.035%, S ≤ 0.020%, Ni: 0.1-2.0%, Cr: 14.5-18.0%, Cu: 0.05-0.50%, V: 0.05-0.5%, Al ≤ 0.03%, N: 0.002-0.08%, and the balance being Fe. The main technical effect is that the medium-carbon martensitic stainless steel has excellent comprehensive mechanical properties and good salt spray corrosion resistance.

[0004] In special environments, especially for 5G communication base stations, the working conditions of the data transmission connector pins are open atmosphere (high temperature, cold, rain and snow, etc.), and the performance requirements are: easy to connect, not easy to wear and long working life. Therefore, the pins are required to have high corrosion resistance and high hardness. Conventional It is unable to meet the requirements of high corrosion resistance and high hardness. Therefore, a high hardness and high corrosion resistance martensitic stainless steel is proposed to solve the problems in the existing technology. In special environments, the problem of being unable to meet the requirements of high corrosion resistance and high hardness. Summary of the Invention

[0005] The purpose of the present invention is to provide a high hardness and high corrosion resistance martensitic stainless steel, a preparation method and application thereof, in order to solve the problems in the prior art. In special environments, the problem of being unable to meet the requirements of high corrosion resistance and high hardness.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A high-hardness and high-corrosion-resistant martensitic stainless steel, the chemical composition of which is expressed by weight percentage as follows: C: 0.15%-0.23%; Si: 0.15%-0.30%; Mn: 0.30%-0.60%; P: <0.020%; S: <0.010%; Cr: 12.5%-13.5%; Ni: 1.5%-2.5%; Mo: 1.8%-2.4%; N: 0.10%-0.20%; B: <0.008%, and the balance is Fe and impurities.

[0007] Preferably, the phosphorus content also includes a mass percentage range, P: P < 0.007%.

[0008] Preferably, the sulfur element also includes a mass percentage range, S: S<0.003%.

[0009] A preparation method using the above-mentioned high-hardness and high-corrosion-resistant martensitic stainless steel comprises the following steps: Vacuum smelting, electroslag remelting, forging, rolling, annealing processes and drawing.

[0010] Preferably, the annealing process includes: Place the martensitic stainless steel to be drawn into the heating furnace and close the furnace door; Set the annealing temperature to 730-750℃, the heating rate to 150-200℃ / h, heat up, keep warm for 4-5h, then cool in the heating furnace, control the cooling rate to 25-30℃ / h, and the furnace cooling time to 20-24h; After cooling in the furnace for 20-24 hours, set the annealing temperature to 640-660℃ again, and heat up at a rate of 150-200℃ / h. Heat for 4-5 hours, then cool in the heating furnace, control the cooling rate to 25-30℃ / h, and the furnace cooling time is 20-24 hours.

[0011] Preferably, after quenching at 1150° C. and tempering at 200° C., the high-hardness and high-corrosion-resistant martensitic stainless steel has a hardness HV1 of 520-550, a yield strength of ≥1100 MPa, and a tensile strength of ≥1700 MPa.

[0012] Preferably, the high-hardness and high-corrosion-resistant martensitic stainless steel has a hardness HV1 of 280-300 after the annealing process.

[0013] A martensitic stainless steel product prepared according to the above preparation method is used in the field of data transmission connector pins for 5G communication base stations.

[0014] In the above technical solution, the present invention provides a high-hardness and high-corrosion-resistant martensitic stainless steel, a preparation method and an application thereof, which have the following beneficial effects: The invention provides a martensitic stainless steel adopting a Fe-Cr-Ni-Mo alloy system. On the basis of strictly controlling the content of S and P elements, Mn, Mo, N, and B alloy elements are added, so that the martensitic stainless steel has both high hardness and high corrosion resistance. The content of Mn, Mo, N, and B alloy elements increases the hardness of the martensitic stainless steel. At the same time, the annealing process adopted can reduce the hardness of the martensitic stainless steel provided by the invention, which is convenient for high-precision machining and can achieve >168 hours in a 5% NaCl salt spray test. It can be used for data transmission connector pins for 5G communication base stations, has a long service life, and is suitable for manufacturing structural parts and bearing parts in atmospheric environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0016] Figure 1 This is the annealed metallographic image of the martensitic stainless steel provided in an embodiment of the present invention when the diameter is 3 mm. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0018] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained by those skilled in the art through conventional or commercial channels unless otherwise specified.

[0019] See also Figure 1 , a high hardness and high corrosion resistance martensitic stainless steel, the chemical composition is expressed by weight percentage: C: 0.15%-0.23%; Si: 0.15%-0.30%; Mn: 0.30%-0.60%; P: <0.020%; S: <0.010%; Cr: 12.5%-13.5%; Ni: 1.5%-2.5%; Mo: 1.8%-2.4%; N: 0.10%-0.20%; B: <0.008%, the balance is Fe and impurities.

[0020] The first embodiment of the martensitic stainless steel provided by the present invention has the following chemical composition by weight: C: 0.16%; Si: 0.25%; Mn: 0.55%; P: 0.0058%; S: 0.0025%; Cr: 13.1%; Ni: 1.92%; Mo: 2.1%; N: 0.12%; B: 0.0035%. The remainder is Fe and impurities.

[0021] The second embodiment of the martensitic stainless steel provided by the present invention has the following chemical composition by weight: C: 0.22%; Si: 0.26%; Mn: 0.54%; P: 0.003%; S: 0.0025%; Cr: 13.2%; Ni: 1.94%; Mo: 2.0%; N: 0.185%; B: 0.0040%. The balance is Fe and impurities.

[0022] The third embodiment of the martensitic stainless steel provided by the present invention has the following chemical composition by weight: C: 0.16%; Si: 0.23%; Mn: 0.52%; P: 0.0047%; S: 0.0013%; Cr: 13.3%; Ni: 2.4%; Mo: 2.35%; N: 0.196%; B: 0.0041%. The remainder is Fe and impurities.

[0023] The fourth embodiment of the martensitic stainless steel provided by the present invention has the following chemical composition by weight: C: 0.23%; Si: 0.26%; Mn: 0.54%; P: 0.0019%; S: 0.009%; Cr: 12.8%; Ni: 1.58%; Mo: 1.85%; N: 0.11%; B: 0.0043%. The remainder is Fe and impurities.

[0024] The fifth embodiment of the martensitic stainless steel provided by the present invention has the following chemical composition by weight: C: 0.192%; Si: 0.16%; Mn: 0.48%; P: 0.001%; S: 0.0029%; Cr: 13.3%; Ni: 2.42%; Mo: 1.88%; N: 0.14%; B: 0.0078%. The remainder is Fe and impurities.

[0025] The sixth embodiment of the martensitic stainless steel provided by the present invention has the following chemical composition by weight: C: 0.151%; Si: 0.17%; Mn: 0.28%; P: 0.006%; S: 0.001%; Cr: 13.4%; Ni: 2.45%; Mo: 1.86%; N: 0.15%; B: 0.0022%. The remainder is Fe and impurities.

[0026] The functions of the components contained in the martensitic stainless steel provided in the embodiments of the present invention are briefly described as follows: C is an austenite forming element and martensite structure is obtained after quenching. C combines with Cr to form , precipitates along the grain boundaries, causing a decrease in the Cr content at the grain boundaries and resulting in intergranular corrosion. Therefore, to ensure appropriate hardness, the C content is controlled below 0.23%. As a preferred embodiment provided by the present invention, C: ≤ 0.020%.

[0027] Si inhibits bubble formation, reduces oxygen content in molten steel, and avoids porosity defects in ingots. Si can enhance corrosion resistance and oxidation resistance. Si can promote the surface of stainless steel Small amounts of Si can enhance resistance to pitting and stress corrosion cracking, particularly in acidic or chloride environments, by forming a denser passive film. Si also strengthens solid solution and improves stability. However, Si can form low-melting-point eutectics, increasing hot crack susceptibility, so its effects should be considered in alloy design. In the examples provided herein, Si is present in an amount of 0.15% to 0.30%.

[0028] The addition of Mn is beneficial to deoxidation and desulfurization. Mn acts as a deoxidizer during the steelmaking process, combining with oxygen to form MnO, reducing oxide inclusions in the steel and improving the purity of the steel. Mn combines with S to form MnS, preventing sulfur and iron from forming low-melting-point FeS, thereby reducing thermal brittleness during hot working and improving processing performance. Mn can slightly improve hardenability, especially when it co-exists with Cr and Mo, which can promote a deeper hardened layer and make it easier for thick interface materials to form a uniform martensitic structure during quenching. Mo is usually added in an amount between 0.3% and 1.5%. Excessive addition may lead to an increase in residual austenite, reducing hardness and strength. It has a potential negative impact on corrosion resistance. As an embodiment provided by the present invention, Mn: 0.30%-0.60%.

[0029] The effect of P on stainless steel is similar to that of S. Although its content in the alloy is very small, its harmful effects cannot be underestimated. P mainly forms a low-melting-point eutectic with Ni in the alloy, segregating at grain boundaries, widening the semi-molten zone and increasing the tendency to crack. Therefore, the P content in stainless steel must be controlled. In the embodiment provided by the present invention, P is less than 0.020%. In the preferred embodiment provided by the present invention, P is less than 0.010%.

[0030] Ni's solid solution strengthening effect can increase the strength of steel. As an austenite-forming element, Ni can expand the austenite phase region, resulting in a martensitic structure after quenching. Ni helps to improve the plasticity and toughness of steel, especially significantly improving the low-temperature toughness of steel. However, when the Ni content is too high, the steel loses its hardenability. As an embodiment provided by the present invention, Ni: 1.5%-2.5%.

[0031] Cr is the main element for rust prevention of stainless steel. Stainless steel generally contains at least 10.5% by mass of Cr element. It forms an anti-oxidation and anti-corrosion protective layer on the surface of the base material, which makes the stainless steel have basic corrosion resistance. As a ferrite-forming element, Cr can promote the formation and residue of ferrite in martensitic stainless steel, reduce the austenite phase region in the phase diagram, and when the content is too much, it may even cause the steel to be unable to obtain martensitic structure when cooled from a high temperature. As a carbide-forming element, Cr has a strong affinity with C and can form chromium-rich carbides that precipitate and reduce the corrosion resistance of martensitic stainless steel. In addition, Cr can also form nitrides with N, which can produce medium-temperature temper brittleness in steels with a higher N content. As an embodiment provided by the present invention, Cr: 12.5%-13.5%.

[0032] Mo is mainly used for anti-oxidation and anti-corrosion in stainless steel. Adding Mo to stainless steel can improve the material's resistance to pitting corrosion, crevice corrosion and sulfide stress cracking. In addition, when Mo is added to martensitic stainless steel to form carbides, the steel will undergo secondary hardening, thereby increasing the strength of the steel. The Mo element can inhibit the addition of carbon and nitrogen compounds, which are not conducive to the hot processing of the material. As a ferrite-forming element, Mo will promote the formation and residue of ferrite in martensitic stainless steel, impairing the plasticity and toughness of the steel. As an embodiment provided by the present invention, Mo: 1.8%-2.4%, as a preferred embodiment provided by the present invention, the Mo content is 2.1%.

[0033] N improves the corrosion resistance of stainless steel. Nitrogen and chromium work synergistically to promote the formation of a dense passivation film, especially in a chloride ion-containing environment (such as the marine atmosphere or chemical environment), which can delay pitting and stress corrosion cracking. Nitrogen can inhibit the precipitation of chromium carbide. At high temperatures, nitrogen preferentially competes with carbon to bind to chromium, reducing the precipitation of chromium carbide and thus reducing the tendency of intergranular corrosion. N can enhance the mechanical properties in stainless steel. As an interstitial atom, nitrogen is dissolved in the martensite lattice and significantly improves the strength and hardness of the material by hindering dislocation movement. Nitrogen can inhibit the coarsening of austenite grains at high temperatures. Indirectly refine the martensite structure after quenching and improve the comprehensive mechanical properties of the material. As an embodiment provided by the present invention, N: 0.10%-0.20%.

[0034] B improves hot workability in stainless steel. Boron is concentrated at the grain boundaries and combines with impurities such as oxygen and sulfur to reduce low-melting point compounds at the grain boundaries and reduce crack sensitivity during hot working. Trace amounts of boron in stainless steel can delay dynamic recrystallization and optimize thermal deformation capacity, making it particularly suitable for large deformation processing. B also optimizes mechanical properties. Trace amounts of boron are solid-dissolved in the matrix, slightly improving strength, but its main function is still to regulate grain boundaries. The optimal boron content is extremely low, and excessive amounts will lead to the precipitation of brittle borides. As an embodiment provided by the present invention, B is less than 0.008%.

[0035] The martensitic stainless steel provided in the embodiments of the present invention has an excessively high hardness after annealing when using conventional annealing methods. This easily damages high-precision processing equipment during high-precision processing, and therefore cannot be used for high-precision processing. To this end, a preparation method using the above-mentioned high-hardness and high-corrosion-resistant martensitic stainless steel is proposed.

[0036] A preparation method using the above-mentioned high-hardness and high-corrosion-resistant martensitic stainless steel comprises the following steps: Vacuum smelting, electroslag remelting, forging, rolling, annealing processes and drawing.

[0037] As a further embodiment provided by the present invention, the annealing process includes: Place the martensitic stainless steel to be drawn into the heating furnace and close the furnace door; Set the annealing temperature to 730-750℃, the heating rate to 150-200℃ / h, heat up, keep warm for 4-5h, then cool in the heating furnace, control the cooling rate to 25-30℃ / h, and the furnace cooling time to 20-24h; After cooling in the furnace for 20-24 hours, set the annealing temperature to 640-660℃ again, and heat up at a rate of 150-200℃ / h. Heat for 4-5 hours, then cool in the heating furnace, control the cooling rate to 25-30℃ / h, and the furnace cooling time is 20-24 hours.

[0038] After annealing, it is drawn into stainless steel filaments with a diameter of 0.8 mm, which are used in data transmission connector pins for 5G communication base stations.

[0039] It should be noted that the high-hardness and high-corrosion-resistant martensitic stainless steel provided in the embodiments of the present invention can be prepared by conventional steelmaking methods.

[0040] The martensitic stainless steel provided in an embodiment of the present invention is applied to data transmission connector pins for 5G communication base stations. It can resist corrosion for a long time when exposed to the atmospheric environment, has high hardness, and does not require frequent replacement.

[0041] The martensitic stainless steel provided in the embodiment of the present invention has a hardness HV1 of 520-550, a yield strength of ≥1100 MPa, and a tensile strength of ≥1700 MPa after quenching at 1150° C. and tempering at 200° C.

[0042] The martensitic stainless steel provided in the embodiment of the present invention has a corrosion resistance time of at least 168 hours in a 5% NaCl salt spray test after quenching at 1150° C. and tempering at 200° C.

[0043] It should be pointed out that the 5% NaCl salt spray test is a conventional salt spray test method.

[0044] The invention provides a martensitic stainless steel adopting a Fe-Cr-Ni-Mo alloy system. On the basis of strictly controlling the content of S and P elements, Mn, Mo, N, and B alloy elements are added, so that the martensitic stainless steel has both high hardness and high corrosion resistance. The content of Mn, Mo, N, and B alloy elements increases the hardness of the martensitic stainless steel. At the same time, the annealing process adopted can reduce the hardness of the martensitic stainless steel provided by the invention, which is convenient for high-precision machining and can achieve >168 hours in a 5% NaCl salt spray test. It can be used for data transmission connector pins for 5G communication base stations, has a long service life, and is suitable for manufacturing structural parts and bearing parts in atmospheric environments.

[0045] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A high hardness and high corrosion resistance martensitic stainless steel, characterized in that: Chemical composition expressed in weight percentage: C: 0.15%-0.23%; Si: 0.15%-0.30%; Mn: 0.30%-0.60%; P: <0.020%; S: <0.010%; Cr: 12.5%-13.5%; Ni: 1.5%-2.5%; Mo: 1.8%-2.4%; N: 0.10%-0.20%; B: <0.008%, the balance is Fe and impurities.

2. The high hardness and high corrosion resistance martensitic stainless steel according to claim 1, characterized in that: The phosphorus content also includes a mass percentage range, P: P < 0.007%.

3. The high hardness and high corrosion resistance martensitic stainless steel according to claim 1, characterized in that: The sulfur element also includes a mass percentage range, S: S<0.003%.

4. A method for preparing the high-hardness and high-corrosion-resistant martensitic stainless steel according to any one of claims 1 to 3, characterized in that: The following steps are involved: Vacuum smelting, electroslag remelting, forging, rolling, annealing processes and drawing.

5. The annealing method of high hardness and high corrosion resistance martensitic stainless steel according to claim 4, characterized in that: The annealing process includes: Place the martensitic stainless steel to be drawn into the heating furnace and close the furnace door; Set the annealing temperature to 730-750℃, the heating rate to 150-200℃ / h, heat up, keep warm for 4-5h, then cool in the heating furnace, control the cooling rate to 25-30℃ / h, and the furnace cooling time to 20-24h; After cooling in the furnace for 20-24 hours, set the annealing temperature to 640-660℃ again, and heat up at a rate of 150-200℃ / h. Heat for 4-5 hours, then cool in the heating furnace, control the cooling rate to 25-30℃ / h, and the furnace cooling time is 20-24 hours.

6. The method for preparing martensitic stainless steel according to any one of claims 4 to 5, characterized in that: After quenching at 1150° C. and tempering at 200° C., the high-hardness and high-corrosion-resistant martensitic stainless steel has a hardness HV1 of 520-550, a yield strength of ≥1100 MPa, and a tensile strength of ≥1700 MPa.

7. The method for preparing martensitic stainless steel according to any one of claims 4 to 5, characterized in that: The high-hardness and high-corrosion-resistant martensitic stainless steel has a hardness HV1 of 280-300 after the annealing process.

8. Application of a martensitic stainless steel product prepared according to the preparation method according to any one of claims 4-5 in the field of data transmission connector pins for 5G communication base stations.

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