阅读说明：本技术 一种刀具用高碳高铬马氏体不锈钢及其制备方法 (High-carbon high-chromium martensitic stainless steel for cutter and preparation method thereof ) 是由 石全强 段文峰 史显波 严伟 李艳芬 王威 单以银 于 2020-10-22 设计创作，主要内容包括：本发明涉及一种刀具用高碳高铬马氏体不锈钢及其制备方法,属于材料技术领域。以重量百分比计,该高碳高铬马氏体不锈钢的化学成分为：C:0.90～1.20％,Cr:14.0～16.0％,Co:1.0～2.0％,Mo:0.5～1.5％,V:0.20～0.40％,Mn:0.2～0.6％,La:0.001～0.01％,P<0.01％,S<0.01％,余量为铁。该高碳高铬马氏体不锈钢的制备方法为：配料→熔炼→浇注成型→锻造和热加工→冷加工和热处理。本发明通过优化材料中的稀土元素含量,抑制一次碳化物的粗化,促进碳化物的均匀分布,通过改进热处理工艺,控制基体中马氏体和奥氏体的含量,获得材料强度和韧性的最佳搭配。(The invention relates to high-carbon high-chromium martensitic stainless steel for a cutter and a preparation method thereof, belonging to the technical field of materials. The high-carbon high-chromium martensitic stainless steel comprises the following chemical components in percentage by weight: 0.90-1.20% of C, 14.0-16.0% of Cr, 1.0-2.0% of Co, 0.5-1.5% of Mo, 0.20-0.40% of V, 0.2-0.6% of Mn, 0.001-0.01% of La, 0.01% of P, 0.01% of S and the balance of iron. The preparation method of the high-carbon high-chromium martensitic stainless steel comprises the following steps: batching → smelting → casting molding → forging and hot working → cold working and heat treatment. According to the invention, the content of rare earth elements in the material is optimized, coarsening of primary carbides is inhibited, uniform distribution of the carbides is promoted, and the contents of martensite and austenite in the matrix are controlled by improving a heat treatment process, so that the optimal matching of the strength and the toughness of the material is obtained.)

1. The high-carbon high-chromium martensitic stainless steel for the cutter is characterized by comprising the following chemical components in percentage by weight: 0.90-1.20% of C, 14.0-16.0% of Cr, 1.0-2.0% of Co, 0.5-1.5% of Mo, 0.20-0.40% of V, 0.2-0.6% of Mn, 0.001-0.01% of La, 0.01% of P, 0.01% of S and the balance of iron.

2. The martensitic stainless steel with high carbon and high chromium for cutting tools according to claim 1, wherein La is preferably 0.002-0.006.

3. A preparation method of the high-carbon high-chromium martensitic stainless steel for the cutting tool as set forth in any one of claims 1 to 2, characterized by comprising the steps of:

(1) mixing the chemical components in proportion, and smelting and pouring to obtain a steel ingot;

(2) forging the obtained steel ingot in an austenite single-phase region;

(3) and (3) rolling the forged steel ingot under control: firstly, carrying out primary rolling in a recrystallization zone, controlling the rolling temperature to be 1100-1200 ℃, controlling the reduction of each pass of rolling to be 10-20% and the total reduction to be 75-85%, and carrying out air cooling to room temperature after hot rolling;

(4) cold rolling the hot-rolled plate;

(5) and carrying out heat treatment after cold rolling.

4. The method for preparing a high-carbon high-chromium martensitic stainless steel for cutting tools as claimed in claim 3, wherein in the step (2), the forging process comprises: the initial forging temperature is 1150-1200 ℃, the forging ratio is more than 8, and the forging is carried out by air cooling to the room temperature.

5. The method for preparing the high-carbon high-chromium martensitic stainless steel for the cutter according to claim 3, wherein in the step (4), the cold rolling process comprises the following steps: and (3) annealing in the middle pass at the annealing temperature of 880 +/-20 ℃ when the reduction of each pass is less than 10%, and cooling the furnace to room temperature after heat preservation for 60-120 min.

6. The method for preparing a high-carbon high-chromium martensitic stainless steel for cutting tools as claimed in claim 3, wherein in the step (5), the heat treatment process comprises: firstly, preserving heat at 11050 +/-20 ℃ for 20-40 min, then carrying out oil quenching to room temperature, then carrying out deep cooling in a liquid nitrogen environment for 30-60 min, then carrying out air cooling to room temperature, finally preserving heat at 150-250 ℃ for 120-240 min, and then carrying out air cooling to room temperature.

7. The method for preparing the high-carbon high-chromium martensitic stainless steel for the cutter according to claim 6, wherein the volume content of austenite in the high-carbon high-chromium martensitic stainless steel for the cutter after heat treatment is 5-10%, the yield strength is more than 1800MPa, the tensile strength is more than 2300MPa, and the Rockwell hardness HRC is more than 60.

Technical Field

The invention relates to high-carbon high-chromium martensitic stainless steel for a cutter and a preparation method thereof, belonging to the technical field of materials.

Background

In order to ensure the sharpness and the durability of the cutter, high-carbon high-chromium martensitic stainless steel with high hardness and excellent wear resistance is generally selected as a raw material, at present, martensitic stainless steel with different carbon and chromium contents is selected according to the grade of the cutter product, and the high-carbon high-chromium martensitic stainless steel with the HRC hardness of more than 60 is generally selected as a material for high-grade cutter products. At present, the price difference of high-grade, medium-grade and low-grade products in the international cutter market is 10:5:1, wherein German and Swiss products monopolize the high-grade cutter market, and Japanese high-grade and low-grade products keep stronger competitiveness in Asia regions.

The contents of carbon and chromium in the martensitic stainless steel used by the cutting tool in China at present are respectively lower than 0.5 wt% and 15 wt%, such as: 20Cr13, 30Cr13, 40Cr13 and other martensitic stainless steels, and meanwhile, some manufacturers adopt traditional carbon steels, and compared with the materials used for the cutter with the international known brand, the materials have great quality difference, so that the added value of the cutter product is lower. The HRC hardness of the high-carbon high-chromium martensitic stainless steel used by TWIN and ZWILLING Pro series cutters of German famous cutter brand is more than 60, the cutting performance of the cutters is outstanding, and the high-carbon high-chromium martensitic stainless steel has good corrosion resistance, so that the high-carbon high-chromium martensitic stainless steel gains wide attention in the cutter industry. The production process of the high-carbon high-chromium martensitic stainless steel used as the raw material of the high-grade cutter is complex, the requirements on technology and equipment are strict, only high-grade stainless steel of departments can be produced in domestic large and medium specialized steel plants at present, the quality of the high-carbon high-chromium martensitic stainless steel produced by domestic enterprises is unstable, and the core preparation technology of the high-carbon high-chromium martensitic stainless steel is not mastered yet. The high-carbon high-chromium martensite stainless steel used by the high-grade cutter is imported from developed countries basically, the supply of the stainless steel material of the high-grade cutter is strictly controlled abroad, and the steel leftover materials of the branded product produced by incoming materials must be completely returned, so that the high-grade cutter market in China is monopolized by the products in the developed countries at present, and the development of the cutter industry in China on the international market is severely restricted. However, because the demand of the steel for the cutter is relatively small and the requirement of the raw material is special, the research and development work of new materials in the domestic cutter industry is always in a cold-falling state, and particularly the research and development of high-quality high-carbon high-chromium cutter materials are more limited. Therefore, the development of the high-carbon high-chromium martensitic stainless steel for strengthening high-grade cutters has important significance.

Disclosure of Invention

The invention aims to provide high-carbon high-chromium martensitic stainless steel for a cutter and a preparation method thereof.

The technical scheme of the invention is as follows:

the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following chemical components in percentage by weight: 0.90-1.20% of C, 14.0-16.0% of Cr, 1.0-2.0% of Co, 0.5-1.5% of Mo, 0.20-0.40% of V, 0.2-0.6% of Mn, 0.001-0.01% of La, 0.01% of P, 0.01% of S and the balance of iron.

The high-carbon high-chromium martensitic stainless steel for the cutter is preferably La of 0.002-0.006.

The preparation method of the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following steps:

(1) mixing the chemical components in proportion, and smelting and pouring to obtain a steel ingot;

(2) forging the obtained steel ingot in an austenite single-phase region;

(3) and (3) rolling the forged steel ingot under control: firstly, carrying out primary rolling in a recrystallization zone, controlling the rolling temperature to be 1100-1200 ℃, controlling the reduction of each pass of rolling to be 10-20% and the total reduction to be 75-85%, and carrying out air cooling to room temperature after hot rolling;

(4) cold rolling the hot-rolled plate;

(5) and carrying out heat treatment after cold rolling.

The preparation method of the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following steps in the step (2): the initial forging temperature is 1150-1200 ℃, the forging ratio is more than 8, and the forging is carried out by air cooling to the room temperature.

The preparation method of the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following steps of (4): and (3) annealing in the middle pass at the annealing temperature of 880 +/-20 ℃ when the reduction of each pass is less than 10%, and cooling the furnace to room temperature after heat preservation for 60-120 min.

The preparation method of the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following heat treatment process in step (5): firstly, preserving heat at 11050 +/-20 ℃ for 20-40 min, then carrying out oil quenching to room temperature, then carrying out deep cooling in a liquid nitrogen environment for 30-60 min, then carrying out air cooling to room temperature, finally preserving heat at 150-250 ℃ for 120-240 min, and then carrying out air cooling to room temperature.

According to the preparation method of the high-carbon high-chromium martensitic stainless steel for the cutter, in the high-carbon high-chromium martensitic stainless steel for the cutter after heat treatment, the volume content of austenite is 5-10%, the yield strength is more than 1800MPa, the tensile strength is more than 2300MPa, and the Rockwell hardness HRC is more than 60.

The design concept of the present invention is two-fold, as follows:

1) adding a certain content of rare earth elements: la which is compounded and added in the high-carbon high-chromium martensite stainless steel for the cutter and accounts for 0.002 wt% -0.006 wt% plays two roles: 1) the method has the advantages that the method plays the roles of refining crystal grains, increasing nucleation positions of coarse precipitation phases of primary carbides and improving distribution of secondary carbides, and increases the nucleation positions of the primary carbides in the metal pouring and solidifying process through heterogeneous nucleation of rare earth La, so that growth and coarsening of the primary carbides are inhibited, uniform distribution of the carbides is realized, and the toughness of the material is improved; 2) the rare earth can react with oxygen in the molten steel preferentially to generate oxides, and then the oxides float on the molten steel, so that the oxygen content in the material can be reduced, and the content of the oxide inclusions can be reduced.

2) Innovation of a heat treatment system: the carbon content in the high-carbon high-chromium stainless steel is 0.9-1.2 wt%, and the carbon is an element for strongly expanding an austenite phase region, so that the martensite transformation end temperature M of the material_fLower than room temperature, so that a large amount of austenite remains in the material matrix during oil quenching in normalizing, thereby making it difficult to ensure the hardness, wear resistance, service life, etc. of the material. The invention adopts cryogenic heat treatment in a liquid nitrogen environment after normalizing, promotes a large amount of residual austenite in the material to be transformed into martensite, and avoids the adverse factors of metal fragmentation and the like caused by volume change due to the structure transformation of unstable residual austenite. Meanwhile, the liquid nitrogen temperature can reach 196 ℃ below zero, the ultra-low temperature can transfer the transport energy of metal atoms, the diffusion among the atoms is hindered, and the bonding force among the atoms is improved, so that the toughness of the material is further improved. Through heat treatment, the contents of martensite and austenite are adjusted, so that the volume content of the austenite in the steel is controlled to be between 5 and 10 percent, the structures of low-temperature tempered martensite and a certain amount of residual austenite are obtained, and the good toughness of the steel is ensured.

The content ranges of the main elements in the invention are explained as follows:

c: carbon is an austenite forming element, and can enlarge austenite phase region, reduce ferrite phase region, and inhibitFormation of high temperature ferrite in steel. Carbon forms M with alloying elements Cr, V, etc₂₃C₆The type and MX type carbides are separated out at interfaces such as a prior austenite crystal boundary, a lath boundary and the like, and are used for pinning dislocation, hindering interface movement and providing a precipitation strengthening effect. However, carbon is an element which is easily diffused, and when the content is too high, the carbide is easily coarsened to lower the structural stability of the heat-resistant steel, so the content of carbon in the steel of the present invention is controlled as follows: 0.90 wt% -1.20 wt%.

Cr: chromium is the primary element determining the corrosion resistance of stainless steels, and when a sufficient amount of chromium is present in the steel, it forms in an oxidizing medium₂O₃Is a stable surface protective film of the substrate. In addition, chromium can effectively improve the pitting potential value of steel and reduce the susceptibility of steel to pitting corrosion. When the chromium content is less than 12 wt%, the corrosion resistance of the steel is drastically reduced. However, too high a chromium content in the steel will reduce the thermal conductivity of the steel, increase the stable ferrite content in the steel under quenching and tempering conditions, reduce the hardness and tensile strength of the steel, and significantly reduce the martensitic transformation temperature. In addition, when the chromium content is higher than 18 wt%, the steel cannot obtain a stable pure austenite phase region at high temperature, so the chromium content in the invention is controlled as follows: 14.0 wt% -16.0 wt%.

Co: cobalt is basically and completely dissolved in a matrix to play a role in solid solution strengthening, does not form carbide, and more particularly forms a synergistic effect with Mo to promote Ni₃Mo、Fe₂Precipitation of Mo and the like. The cobalt can inhibit the recovery of a wrong substructure in martensite, provide more nucleation sites for a later precipitated phase and promote the precipitation strengthening effect. The cobalt is selected to be 1.0 wt% -2.0 wt% according to the balance effect of cobalt on ferrite forming elements and the influence of cobalt on precipitation effect.

Mo: molybdenum is a ferrite-forming element and has a capacity corresponding to chromium. In martensitic stainless steel, molybdenum can improve the corrosion resistance of stainless steel in a reducing medium, enhance the performances of resisting electric corrosion, chloride ion corrosion and the like, and improve the corrosion resistance of steel in organic acid. In addition, after molybdenum is added into the Fe-Cr alloy, the passivation stability and the pitting corrosion resistance of the alloy are greatly improved, and the capacity of the molybdenum is 3.3 times that of the chromium in this respect. Generally, the content of molybdenum in martensitic stainless steel is 1.5 wt% or less, and too high content of Mo promotes high-temperature ferrite formation, causing adverse effects, so the content of molybdenum in the steel of the present invention is controlled as follows: 0.5 wt% to 1.5 wt%.

V: vanadium is a strong carbide forming element, forms a nano-scale precipitated phase with carbon and nitrogen in steel, and pins dislocation. Carbon is fixed and alloy elements such as chromium are diffused from the matrix to the carbide to cause aging, thereby improving the heat strength. When the vanadium content is lower, fine carbides are not easy to be fully formed, the effect of pinning dislocation cannot be achieved, and when the vanadium content is higher, the steel is embrittled, so the vanadium content in the steel is controlled as follows: 0.20 wt% -0.40 wt%.

Mn: manganese is an austenite forming element and a stabilizing element, and can remarkably reduce the austenite forming temperature A of steel_C1Point and martensite formation temperature M_SThe hardenability of the alloy steel is improved, and the formation of delta ferrite is suppressed. However, when the manganese content is excessively increased, segregation is easily generated in the steel, so that local transformation occurs to form new austenite grains, thereby deteriorating the performance. And manganese is easy to form MnS inclusion with sulfur in steel, and the volume fraction of the inclusion is increased to reduce the impact toughness of the steel, so the content of manganese in the steel is controlled as follows: 0.2 wt% -0.6 wt%.

Rare earth: the steel contains a certain amount of rare earth, so that the plasticity and toughness of the steel can be obviously improved, and the transverse performance and low-temperature toughness of the steel are improved. The rare earth has the functions of purifying molten steel, modifying and mixing impurities and microalloying, and is beneficial to improving the cold stamping formability and the corrosion resistance of steel. When the content of the rare earth La in the steel exceeds 0.002 wt%, the initiation and the propagation of contact fatigue cracks of the steel can be delayed, and meanwhile, the contact fatigue penetration angle and the penetration depth are obviously reduced. However, when the content exceeds 0.01 wt%, a large block-like rare earth inclusion is formed, which seriously deteriorates the properties of the material. Therefore, the La content in the steel is optimally controlled as follows: 0.002 wt% -0.006 wt%.

S, P: respectively, the main inclusion forming elements and the harmful elements in the steel. Sulphur has a very adverse effect on crack formation and propagation of the impact toughness of the steel, at the same time as the creep properties of the steel are impaired. The phosphorus sharply raises the ductile-brittle transition temperature of the steel and increases the cold brittleness of the steel, so the content control of the sulfur and the phosphorus in the steel is very strict: s is less than 0.01 wt% and P is less than 0.01 wt%.

The heat treatment system of the present invention is explained as follows:

the normalizing temperature and the heat preservation time of the invention are as follows: the purpose of normalizing is to eliminate coarse primary carbides in the original structure, to solutionize them into the matrix in the austenitized state, and during subsequent tempering, M₂₃C₆And MX carbide can be separated out at interfaces such as a prior austenite crystal boundary, a lath boundary and the like, so that the precipitation strengthening effect is achieved, and meanwhile, the proper grain size is obtained by adjusting the normalizing temperature. When the steel of the present invention is normalized at a temperature lower than 1030 ℃, the carbide is not sufficiently dissolved, and the precipitation strengthening effect cannot be sufficiently exerted. When the temperature is higher than 1080 ℃, a coarse structure is obtained due to rapid growth of crystal grains, and the impact toughness of the steel is rapidly reduced. Therefore, the normalizing system is selected to be 1050 +/-20 ℃ for 30-60 min and austempering.

The deep cooling process and the heat preservation time thereof are as follows: because the martensite transformation final temperature of the material is lower than room temperature, a cryogenic treatment process is added in the traditional heat treatment system of the steel for the cutter, the further transformation of the residual austenite in the material to martensite is promoted, and meanwhile, the bonding force between the atomic levels of the material can be promoted at the ultralow temperature provided by the liquid nitrogen environment. Therefore, the cryogenic cooling process of the steel is carried out in a liquid nitrogen environment, and the steel is cooled to room temperature after heat preservation for 30-60 min.

The low-temperature tempering temperature and the heat preservation time of the invention are as follows: after quenching and low-temperature tempering, the material can obtain cryptocrystalline tempered martensite and uniformly distributed granular carbide structures, has high hardness and wear resistance, and simultaneously obviously reduces the quenching stress and brittleness of the material. In addition, the internal stress of quenching is reduced after low-temperature tempering, the strength and the plasticity of the material are further improved, and the excellent comprehensive mechanical property is kept. Therefore, the tempering system of the steel is selected to be that the temperature is kept between 150 ℃ and 250 ℃ for 120min to 240min and then the steel is cooled to the room temperature by air.

The invention has the advantages and beneficial effects that:

1. the invention creatively adds a certain content of rare earth elements into the high-carbon high-chromium martensitic stainless steel for the cutter, and plays the roles of refining crystal grains and increasing nucleation positions of primary carbides to inhibit coarsening of the carbides by optimizing the content of the rare earth elements in the material, thereby promoting uniform distribution of the carbides, and simultaneously playing the roles of purifying and smelting and reducing the content of inclusions.

2. According to the invention, a liquid nitrogen cryogenic treatment technology is innovatively added between the traditional normalizing and tempering heat treatment regimes, and by improving the heat treatment process, the martensite phase transformation of the residual austenite in the steel is promoted, the contents of martensite and austenite in the matrix are controlled, the internal stress is eliminated, the bonding force between atoms is improved, the hardness and strength of the cutter are improved, the optimal matching of the material strength and toughness is obtained, the sharpness and durability of the cutter are greatly improved, and the service life of the cutter is prolonged.

Drawings

FIG. 1 is a schematic metallographic structure of example 1.

FIG. 2 is a schematic metallographic structure of comparative example 1.

FIG. 3 is a schematic representation of the carbide distribution of example 1.

FIG. 4 is a schematic view of carbide distribution in comparative example 1.

Detailed Description

The following examples further illustrate the invention but are not intended to limit the invention thereto. The steels in the examples and the steels in the comparative examples are processed into standard tensile test samples after smelting, hot working and heat treatment, and then mechanical properties are tested.

The preparation process of the high-carbon high-chromium martensitic stainless steel comprises the following steps: material preparation → smelting → casting molding → forging and hot working → cold working and heat treatment, and the following method is adopted in the embodiments 1-5, and the specific steps are as follows:

(1) mixing the chemical components according to the proportion, and smelting and pouring to obtain a steel ingot;

(2) forging the obtained steel ingot in an austenite single-phase region: the initial forging temperature is 1150-1200 ℃ (1155 ℃, 1168 ℃, 1194 ℃, 1184 ℃ and 1172 ℃ in the embodiments 1-5), the forging ratio is more than 8 (8.4, 9.1, 8.2, 10.4 and 9.3 in the embodiments 1-5), and the forging is carried out and then air cooling is carried out to the room temperature;

(3) and (3) rolling the forged steel ingot under control: firstly, carrying out primary rolling in a recrystallization zone, wherein the rolling temperature is 1100-1200 ℃ (1108 ℃, 1186 ℃, 1125 ℃, 1149 ℃ and 1165 ℃ in examples 1-5), the reduction of each pass of rolling is controlled to be 10-20%, the total reduction is controlled to be 75-85% (75.4%, 80.4%, 77.2%, 84.6% and 82.7% in examples 1-5), and the steel is air-cooled to room temperature after hot rolling;

(4) the hot-rolled plate is cold-rolled, the reduction per pass is less than 10% (7.1%, 5.6%, 6.8%, 9.5% and 7.5% in examples 1 to 5), intermediate-pass annealing is carried out, the annealing temperature is 880 +/-20 ℃ (881 ℃, 863 ℃, 873 ℃, 895 ℃ and 883 ℃ in examples 1 to 5), the temperature is kept for 60-120 min (62 min, 115min, 91min, 75min and 105min in examples 1 to 5), and then the furnace is cooled to room temperature.

(5) The heat treatment process after cold rolling comprises the following steps: firstly, keeping the temperature of 1050 +/-20 ℃ (1035 ℃, 1060 ℃, 1051 ℃, 1069 ℃ and 1045 ℃ in examples 1 to 5 respectively) for 20-40 min (21 min, 30min, 25min, 38min and 31min in examples 1 to 5 respectively), then carrying out oil quenching to the room temperature, then carrying out deep cooling for 30-60 min (31 min, 58min, 44min, 51min and 36min in examples 1 to 5 respectively) in a liquid nitrogen environment, then carrying out air cooling to the room temperature, finally keeping the temperature of 150-250 ℃ (246 ℃, 200 ℃, 155 ℃, 176 ℃ and 228 ℃ in examples 1 to 5 respectively) for 120-240 min (235 min, 120min, 181min, 148min and 207min in examples 1 to 5 respectively) and then carrying out air cooling to the room temperature.

The invention is explained in more detail below with reference to the figures and examples.

Example 1

In the embodiment, the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following chemical components in percentage by weight: 0.92% of C, 14.43% of Cr, 1.21% of Co, 0.63% of Mo, 0.23% of V, 0.25% of Mn, 25ppm of La, 55ppm of S, 80ppm of P and the balance of iron.

Example 2

In the embodiment, the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following chemical components in percentage by weight: 1.06% of C, 15.08% of Cr, 1.52% of Co, 1.04% of Mo, 0.29% of V, 0.41% of Mn, 41ppm of La, 50ppm of S, 75ppm of P and the balance of iron.

Example 3

In the embodiment, the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following chemical components in percentage by weight: 0.97% of C, 14.97% of Cr, 1.37% of Co, 0.84% of Mo, 0.27% of V, 0.37% of Mn, 34ppm of La, 59ppm of S, 71ppm of P and the balance of iron.

Example 4

In the embodiment, the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following chemical components in percentage by weight: 1.18% of C, 15.94% of Cr, 1.92% of Co, 1.48% of Mo, 0.37% of V, 0.58% of Mn, 58ppm of La, 52ppm of S, 81ppm of P and the balance of iron.

Example 5

In the embodiment, the high-carbon high-chromium martensitic stainless steel for the cutter comprises the following chemical components in percentage by weight: 1.11% of C, 15.45% of Cr, 1.67% of Co, 1.25% of Mo, 0.34% of V, 0.48% of Mn, 46ppm of La, 56ppm of S, 74ppm of P and the balance of iron.

Comparative example 1

In the comparative example, no La rare earth element is added to the chemical components of the high-carbon high-chromium martensitic stainless steel for the cutter, the other chemical components are completely the same as those in example 1, and the smelting method and the heat treatment process are the same as those in examples 1 to 5.

As shown in FIGS. 1 to 4, compared with example 1, it can be seen that the grain size of the material is larger and reaches 20 μm because a certain content of rare earth is not added in comparative example 1, and the size of primary carbides in the steel is relatively larger and the maximum size reaches 8 μm because the nucleation positions increased by heterogeneous nucleation of the rare earth are not present, and the yield strength, tensile strength and HRC hardness of the material are relatively lower.

Comparative example 2

In the comparative example, the smelting method and chemical components of the high-carbon high-chromium martensitic stainless steel for the cutter are completely the same as those in the example 2, and the heat treatment process comprises the following steps: keeping the temperature of 1060 ℃ for 30min, then oil quenching to room temperature, keeping the temperature of 200 ℃ for 120min, and then air cooling to room temperature.

As shown in Table 1, in comparative example 2, since the cryogenic heat treatment system in a liquid nitrogen environment was not employed, the austenite content in the steel reached 35%, resulting in lower yield strength, tensile strength and HRC hardness of the material, and reduced tool life.

The mechanical properties, HRC hardness and austenite content of the examples and comparative examples are shown in Table 1.

TABLE 1

As can be seen from Table 1, the La rare earth with a certain content is added into the steel, the nucleation position of the primary carbide is increased in the ingot casting solidification process, the coarsening of the carbide is inhibited, the uniform distribution of the carbide is promoted, the inclusion content in the steel is reduced, and the purification smelting effect is achieved; then the traditional heat treatment process is broken through, a cryogenic treatment process in a liquid nitrogen environment is added between the traditional normalizing and tempering heat treatment systems, the further transformation of residual austenite in the steel to martensite is promoted, the tensile strength and the hardness of the steel are improved, and therefore the high-carbon high-chromium martensitic stainless steel for the cutter with excellent obdurability matching is obtained.

As shown in FIG. 1, as can be seen from the schematic microstructure of example 1 of the present invention, the average grain size of the steel is 9.5 μm, which is relatively small due to the addition of the rare earth element.

As shown in FIG. 2, as can be seen from the schematic microstructure of comparative example 1 of the present invention, the average grain size of the steel was 20 μm, and the average grain size of the steel was relatively large.

As shown in FIG. 3, it can be seen from the schematic microstructure of the carbide of example 1 of the present invention that the carbide is uniformly distributed in the steel without the primary carbides having a relatively large size.

As shown in FIG. 4, it can be seen from the schematic microstructure of the carbide of comparative example 1 of the present invention that there are densely distributed primary carbides in the steel, in which the maximum size reaches 8 μm and the carbide distribution is not uniform.

The embodiment results show that the invention optimizes and controls the nucleation quantity and distribution of primary carbides by adding a certain content of rare earth element La, purifies the content of inclusions in steel, reduces the austenite content in the steel by optimizing the heat treatment process, and improves the strength and hardness of the steel. In the high-carbon high-chromium martensitic stainless steel for the cutter after heat treatment, the volume content of austenite is 5-10%, the yield strength is over 1800MPa (preferably 1820-1930 MPa), the tensile strength is over 2300MPa (preferably 2340-2450 MPa), and the Rockwell hardness HRC is over 60 (preferably 60.2-62.5).

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.