High-strength quenched and tempered silver bright steel for nuclear fasteners and preparation method of high-strength quenched and tempered silver bright steel

Abstract

The invention relates to the technical field of forging, in particular to high-strength quenched and tempered silver bright steel for nuclear fasteners and a preparation method of the high-strength quenched and tempered silver bright steel. Comprising the following steps that S1, alloy steel raw materials are smelted in an electric furnace, then a deoxidizing agent is added for refining and impurity removal, vacuum degassing, cooling and discharging are conducted, and alloy steel liquid is obtained; s2, the molten alloy steel is subjected to casting treatment, rolling treatment and cooling in sequence, and basic quenched and tempered silver bright steel is obtained; s3, the surface of the basic quenched and tempered silver bright steel is pretreated, then heat treatment is conducted, and quenched and tempered silver bright steel A is obtained; s4, the surface of the quenched and tempered silver bright steel A is subjected to plasma electrolysis pre-boriding treatment, pre-boriding heat treatment, cooling and discharging, and quenched and tempered silver bright steel B is obtained; s5, the surface of the quenched and tempered silver bright steel B is subjected to boron-chromium co-permeation treatment, boron-chromium co-permeation heat treatment, cooling and discharging; therefore, the high-strength quenched and tempered silver bright steel for the nuclear energy fastener is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of forging, in particular to a high-strength quenched and tempered silver bright steel for nuclear energy fasteners and a preparation method thereof. Background Art

[0002] With the continuous development of nuclear energy technology and the expansion of its application field, the performance requirements for nuclear energy equipment and its components are also increasing. As an indispensable component of nuclear energy equipment, the quality of fasteners is directly related to the safety and reliability of the entire equipment. In the existing technology, the heat treatment process during the preparation process is not perfect enough, resulting in unstable performance, internal defects, and reduced dimensional accuracy of the prepared silver-bright steel, which leads to insufficient strength and instability during use; at the same time, the silver-bright steel has not been surface-treated, resulting in damaged surface quality, oxidation, rust and other phenomena on the surface of the steel, reducing the overall mechanical properties and stability, and limiting the application of silver-bright steel.

[0003] In summary, it is of great significance to prepare a high-strength quenched and tempered silver bright steel for nuclear energy fasteners. Summary of the invention

[0004] The object of the present invention is to provide a high-strength quenched and tempered silver bright steel for nuclear energy fasteners and a preparation method thereof, so as to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners comprises the following steps: S1: The alloy steel raw material is smelted in an electric furnace, and then a deoxidizer is added for refining and impurity removal, vacuum degassing, cooling, and unloading to obtain alloy steel liquid; S2: Casting, rolling and cooling the alloy steel liquid in sequence to obtain basic quenched and tempered silver bright steel; S3: pre-treating the surface of the basic quenched and tempered silver bright steel, and then performing heat treatment to obtain quenched and tempered silver bright steel A; S4: subjecting the surface of the quenched and tempered silver bright steel A to a plasma electrolytic pre-boronization treatment and a pre-boronization heat treatment, cooling, and taking out of the furnace to obtain a quenched and tempered silver bright steel B; S5: subjecting the surface of the quenched and tempered silver bright steel B to boron-chromium co-penetration treatment, boron-chromium co-penetration heat treatment, cooling, and taking out of the furnace to obtain high-strength quenched and tempered silver bright steel.

[0006] More optimally, the composition of the basic quenched and tempered silver bright steel includes the following elements, by mass percentage: 0.37%~0.44% carbon, 0.17%~0.37% silicon, 0.5%~0.8% manganese, 0.6%~0.9% chromium, 0.15%~0.25% molybdenum, 1.25%~1.65% nickel, copper ≤0.20%, and the rest is iron and unavoidable impurities ≤0.03%.

[0007] More optimally, in S1, the temperature of the smelting treatment is 1600~1650℃; the temperature of the refining and impurity removal is 1550~1600℃; the specific process parameters of the vacuum degassing are: setting the vacuum degree to 55~65Pa, the time is 15~20min, introducing argon to break the air, and soft blowing treatment for 10~15min.

[0008] More optimally, the deoxidizer comprises silicon carbide and ferromanganese alloy in a mass ratio of 1:1.2-1.8; the amount of the deoxidizer added accounts for 0.2-0.3wt% of the alloy steel liquid.

[0009] More optimally, deoxidizers are added during refining and impurity removal, which can effectively remove oxygen, carbon and other non-metallic inclusions in the molten steel. These inclusions will reduce the mechanical properties and corrosion resistance of the steel. Through refining and impurity removal, the purity of the steel can be significantly improved, thereby improving its overall performance. Defects such as pores and cracks in the steel can be reduced after treatment with deoxidizers, and the mechanical properties of the steel can be improved; after refining and impurity removal with deoxidizers, the molten steel is more uniform, which is conducive to subsequent casting, rolling and other processing processes. Uniform steel quality can reduce deformation and cracking during processing, and improve the yield rate and product quality. In addition, the addition of deoxidizers can also enhance the corrosion resistance of steel and extend its service life.

[0010] More optimally, in S2, the temperature of the casting process is 1550-1600°C; the temperature of the rolling process is 1100-1150°C, the reduction is 50-60 mm, and the rolling acceleration is 1.0-1.5 m / s 2 .

[0011] More optimally, in S3, the pretreatment process is specifically as follows: soaking the basic quenched and tempered silver bright steel in the mixed solution for 10 to 30 minutes, washing with water, and drying with nitrogen; The heat treatment process is specifically as follows: after the pretreatment is completed, water quenching is performed at 850-900°C for 15-45 minutes, oil cooling is performed to room temperature, and then high temperature tempering is performed at 550-650°C for 100-140 minutes; The mixed liquid raw materials include the following components: by mass, 5-6 parts of potassium permanganate, 10-12 parts of sodium hydroxide, 5-6 parts of potassium nitrate, and 76-80 parts of deionized water.

[0012] More optimally, in S4, the process of the plasma electrolytic pre-boronizing treatment is specifically as follows: setting the shot peening particle size between 100 and 200 μm, subjecting the quenched and tempered silver bright steel A to shot peening pretreatment for 15 to 30 minutes, introducing boron trifluoride as a boron source, and subjecting the quenched and tempered silver bright steel A to plasma boronizing treatment at 550 to 600° C. for 30 to 60 minutes in a hydrogen and nitrogen atmosphere; The process of the pre-boronizing heat treatment is specifically as follows: after the plasma electrolytic pre-boronizing treatment is completed, oil quenching is performed at 1000-1050° C. for 15-45 minutes, water cooling is performed to room temperature, and tempering is performed twice at 600-650° C.

[0013] Among them, plasma electrolytic pre-boronization treatment is first carried out on the surface, which can form a layer of boride on the surface and form micropores on the surface. This structure helps to form a more uniform and dense boride layer in the subsequent co-infiltration process, thereby improving wear resistance, high-temperature oxidation resistance and coating durability. The thickness of the boride layer should not be too high. Too high thickness will make it difficult to form micropores, thus affecting subsequent operations; in addition, the boride layer can also improve the hardness and corrosion resistance of the material.

[0014] More optimally, in S5, the boron-chromium co-diffusion treatment process is specifically as follows: adding 60-70wt% of the co-diffusion agent to the quenched and tempered silver bright steel B, drying at 100-300°C, and then increasing the temperature to 450-550°C and introducing nitrogen at 0.02-0.04MPa for pressure relief operation; The process of the borochromizing heat treatment is specifically as follows: after the borochromizing treatment is completed, the steel is oil quenched and kept warm at 700-750° C. for 1-2 hours, air-cooled, and tempered at 600-650° C. for 30-60 minutes.

[0015] Among them, the boron-chromium co-diffusion treatment after the plasma electrolytic pre-borization treatment can improve the surface hardness of the material and form a dense protective layer, thereby improving the corrosion resistance of the material and improving the surface quality; during the co-diffusion treatment, the boron element can penetrate into the surface of the material and form a microporous structure. In further processing, a more uniform and dense diffusion layer is formed to optimize the microstructure and performance of the material; in addition, chromium and boron elements can form a stable oxide layer at high temperature, which can effectively prevent oxygen from further diffusing into the material, thereby significantly improving the material's resistance to high-temperature oxidation.

[0016] In a further scheme, a boron-chromium co-diffusion heat treatment is carried out after the boron-chromium co-diffusion treatment, which can reduce the stress in the diffusion layer, inhibit the formation of hard and brittle phases, improve the stability of the diffusion layer, and prevent the cracking of the inner boronized layer; in addition, it can also improve the surface hardness, wear resistance, thermal stability and corrosion resistance of the material.

[0017] More optimally, the co-infiltration agent raw materials include the following components: by mass, 15 to 20 parts of anhydrous borax, 3 to 5 parts of potassium fluoroborate, 1 to 2 parts of potassium fluorotitanate, 30 to 40 parts of iron boride, 30 to 40 parts of chromium trioxide, and 6 to 10 parts of metal oxides; the metal oxides include cerium oxide and lanthanum oxide in a mass ratio of 2 to 2.5:1.

[0018] More optimally, a method for preparing high-strength quenched and tempered silver-bright steel for nuclear energy fasteners is used to prepare high-strength quenched and tempered silver-bright steel.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. In the scheme, by adding deoxidizer for refining and impurity removal, the purity of steel can be significantly improved; defects such as pores and cracks in steel can be reduced, and the mechanical properties of steel can be improved; the corrosion resistance of steel can also be enhanced and its service life can be extended.

[0020] 2. In the scheme, plasma electrolysis pre-boronization treatment is first carried out to form a boride layer with a microporous structure, which is conducive to the subsequent co-boronization to form a uniform and dense boride layer, enhance wear resistance, high temperature oxidation resistance, coating durability, hardness and corrosion resistance, but the thickness of the boride layer needs to be moderate to prevent affecting the operation.

[0021] 3. In the scheme, the material surface hardness and corrosion resistance are enhanced by plasma electrolytic pre-boronization treatment and then boron-chromium co-diffusion treatment. The chromium-boron oxide layer improves the resistance to high-temperature oxidation and effectively prevents oxygen infiltration. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be noted that the following parts are by mass, and the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions, and illustratively include: in the following embodiments, the specification of silicon carbide is 500nm, the product number is YM-SiC-500Y, purchased from Yumu (Ningbo) New Materials Co., Ltd.; manganese iron alloy was purchased from Anyang Yuchengxin Ferroalloy Co., Ltd.

[0024] In the following scheme, the composition of the quenched and tempered silver bright steel A includes the following elements, by mass percentage: 0.4% carbon, 0.27% silicon, 0.65% manganese, 0.75% chromium, 0.2% molybdenum, 1.45% nickel, 0.15% copper, and the rest is iron and unavoidable impurities 0.03%.

[0025] The raw materials of the co-infiltration agent include the following components: by mass, 17 parts of anhydrous borax, 4 parts of potassium fluoroborate, 1 part of potassium fluorotitanate, 35 parts of iron boride, 35 parts of chromium trioxide, and 8 parts of metal oxides; the metal oxides include cerium oxide and lanthanum oxide in a mass ratio of 2.3:1.

[0026] Example 1: A method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners, comprising the following steps: S1: The alloy steel raw material is smelted in an electric furnace at 1625°C, 0.25wt% deoxidizer is added, the mass ratio of silicon carbide and ferromanganese alloy in the deoxidizer is 1:1.5, and refined and impurity-removed at 1575°C, the vacuum degree is set to 60Pa for vacuum degassing for 18min, argon gas is introduced to break the air, soft blowing treatment is performed for 12min, cooling and furnace removal are performed to obtain alloy steel liquid; S2: Cast the alloy steel liquid at 1575℃ and set the rolling acceleration to 1.2m / s 2 , rolling treatment was carried out at 1125°C with a reduction of 55 mm, and cooling was performed to obtain basic quenched and tempered silver bright steel; S3: The basic quenched and tempered silver bright steel is placed in a mixed solution (5.5 parts of potassium permanganate, 11 parts of sodium hydroxide, 5.5 parts of potassium nitrate, and 78 parts of deionized water) and soaked for 15 minutes, washed with water, dried by nitrogen, quenched in water at 875°C for 30 minutes, cooled to room temperature with oil, and then tempered at 600°C for 120 minutes, cooled, and taken out of the furnace to obtain quenched and tempered silver bright steel A; S4: The shot peening particle size is set at 150 μm, and the quenched and tempered silver bright steel A is shot peened for 23 minutes, and boron trifluoride is introduced as a boron source. In a hydrogen and nitrogen atmosphere, the steel is plasma boronized at 575°C for 45 minutes. After the plasma electrolytic pre-boronization treatment is completed, the steel is oil quenched at 1025°C for 30 minutes, water-cooled to room temperature, tempered twice at 630°C, cooled, and discharged from the furnace to obtain the quenched and tempered silver bright steel B; S5: Add 65wt% of the co-infiltration agent to the quenched and tempered silver bright steel B, dry it at 200℃, then increase the temperature and introduce nitrogen at 0.03MPa at 500℃ to discharge the pressure; oil quench at 730℃ for 1.5 hours, air cool, temper at 630℃ for 45min, cool and take out of the furnace to obtain the quenched and tempered silver bright steel.

[0027] Embodiment 2: A method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners, comprising the following steps: S1: The alloy steel raw material is smelted in an electric furnace at 1625°C, 0.25wt% deoxidizer is added, the mass ratio of silicon carbide and ferromanganese alloy in the deoxidizer is 1:1.5, and refined and impurity-removed at 1575°C, the vacuum degree is set to 60Pa for vacuum degassing for 18min, argon gas is introduced to break the air, soft blowing treatment is performed for 12min, cooling and furnace removal are performed to obtain alloy steel liquid; S2: Cast the alloy steel liquid at 1575℃ and set the rolling acceleration to 1.2m / s 2 , rolling treatment was carried out at 1125°C with a reduction of 55 mm, and cooling was performed to obtain basic quenched and tempered silver bright steel; S3: The basic quenched and tempered silver bright steel is placed in a mixed solution (5.5 parts of potassium permanganate, 11 parts of sodium hydroxide, 5.5 parts of potassium nitrate, and 78 parts of deionized water) and soaked for 15 minutes, washed with water, dried by passing nitrogen, quenched with water at 850°C for 15 minutes, cooled to room temperature with oil, and then tempered at 550°C for 100 minutes, cooled, and taken out of the furnace to obtain quenched and tempered silver bright steel A; S4: The shot peening particle size is set at 100 μm, and the quenched and tempered silver bright steel A is shot peened for 15 minutes, and boron trifluoride is introduced as a boron source. In a hydrogen and nitrogen atmosphere, the steel is plasma boronized at 575°C for 45 minutes. After the plasma electrolytic pre-boronization treatment is completed, the steel is oil quenched at 1025°C for 30 minutes, water-cooled to room temperature, tempered twice at 630°C, cooled, and discharged from the furnace to obtain the quenched and tempered silver bright steel B; S5: Add 60wt% of the co-infiltration agent to the quenched and tempered silver bright steel B, dry it at 100°C, then increase the temperature and introduce nitrogen at 0.02MPa at 450°C for pressure relief operation; oil quench at 700°C for 1 hour, air cool, temper at 600°C for 30min, cool and take out of the furnace to obtain the quenched and tempered silver bright steel.

[0028] Embodiment 3: A method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners, comprising the following steps: S1: The alloy steel raw material is smelted in an electric furnace at 1625°C, 0.25wt% deoxidizer is added, the mass ratio of silicon carbide and ferromanganese alloy in the deoxidizer is 1:1.5, and refined and impurity-removed at 1575°C, the vacuum degree is set to 60Pa for vacuum degassing for 18min, argon gas is introduced to break the air, soft blowing treatment is performed for 12min, cooling and furnace removal are performed to obtain alloy steel liquid; S2: Cast the alloy steel liquid at 1575℃ and set the rolling acceleration to 1.2m / s 2 , rolling treatment was carried out at 1125°C with a reduction of 55 mm, and cooling was performed to obtain basic quenched and tempered silver bright steel; S3: The basic quenched and tempered silver bright steel is placed in a mixed solution (5.5 parts of potassium permanganate, 11 parts of sodium hydroxide, 5.5 parts of potassium nitrate, and 78 parts of deionized water) and soaked for 15 minutes, washed with water, dried by nitrogen, quenched in water at 900°C for 45 minutes, cooled to room temperature with oil, and then high-temperature tempered at 650°C for 140 minutes, cooled, and taken out of the furnace to obtain quenched and tempered silver bright steel A; S4: The shot peening particle size is set at 200 μm, and the quenched and tempered silver bright steel A is shot peened for 30 minutes, and boron trifluoride is introduced as a boron source. In a hydrogen and nitrogen atmosphere, the steel is plasma boronized at 575°C for 45 minutes. After the plasma electrolytic pre-boronization treatment is completed, the steel is oil quenched at 1025°C for 30 minutes, water-cooled to room temperature, tempered twice at 630°C, cooled, and discharged from the furnace to obtain the quenched and tempered silver bright steel B; S5: Add 70wt% of the co-infiltration agent to the quenched and tempered silver bright steel B, dry it at 300°C, then increase the temperature and introduce nitrogen at 0.04MPa at 550°C for pressure relief operation; oil quench at 750°C for 2 hours, air cool, temper at 650°C for 60min, cool and take out of the furnace to obtain the quenched and tempered silver bright steel.

[0029] Comparative Example 1: Based on Example 1, the plasma electrolysis pre-boronization treatment time was extended, and the other processes remained unchanged, specifically: S4: setting the shot peening particle size at 300 μm, subjecting the quenched and tempered silver bright steel A to shot peening pretreatment for 2 hours, introducing boron trifluoride as a boron source, and subjecting the steel to plasma boronization treatment at 575° C. for 3 hours in a hydrogen and nitrogen atmosphere. After the plasma electrolytic pre-boronization treatment is completed, the steel is oil quenched at 1025° C. for 30 minutes, water-cooled to room temperature, tempered twice at 630° C., cooled, and discharged from the furnace to obtain the quenched and tempered silver bright steel B; S5: Add 65wt% of the co-infiltration agent to the quenched and tempered silver bright steel B, dry it at 200℃, then increase the temperature and introduce nitrogen at 0.03MPa at 500℃ to discharge the pressure; oil quench at 730℃ for 1.5 hours, air cool, temper at 630℃ for 45min, cool and take out of the furnace to obtain the quenched and tempered silver bright steel.

[0030] Comparative Example 2: Based on Example 1, plasma electrolysis pre-boronization treatment is not performed, only boron-chromium co-diffusion treatment is performed, and the other processes remain unchanged, specifically: S1: The alloy steel raw material is smelted in an electric furnace at 1625°C, 0.25wt% deoxidizer is added, the mass ratio of silicon carbide and ferromanganese alloy in the deoxidizer is 1:1.5, and refined and impurity-removed at 1575°C, the vacuum degree is set to 60Pa for vacuum degassing for 18min, argon gas is introduced to break the air, soft blowing treatment is performed for 12min, cooling and furnace removal are performed to obtain alloy steel liquid; S2: Cast the alloy steel liquid at 1575℃ and set the rolling acceleration to 1.2m / s2 , rolling treatment was carried out at 1125°C with a reduction of 55 mm, and cooling was performed to obtain basic quenched and tempered silver bright steel; S3: The basic quenched and tempered silver bright steel is placed in a mixed solution (5.5 parts of potassium permanganate, 11 parts of sodium hydroxide, 5.5 parts of potassium nitrate, and 78 parts of deionized water) and soaked for 15 minutes, washed with water, dried by nitrogen, quenched in water at 875°C for 30 minutes, cooled to room temperature with oil, and then tempered at 600°C for 120 minutes, cooled, and taken out of the furnace to obtain quenched and tempered silver bright steel A; S4: 65wt% of the co-infiltration agent was added to the quenched and tempered silver bright steel A, and the steel was dried at 200°C. The temperature was then increased and nitrogen was introduced at 0.03MPa at 500°C for pressure relief operation. The steel was oil quenched and kept at 730°C for 4 hours, air-cooled, tempered at 630°C for 45 minutes, cooled, and discharged from the furnace to obtain the quenched and tempered silver bright steel.

[0031] Comparative Example 3: Based on Example 1, after the boron-chromium co-penetration treatment, no boron-chromium co-penetration heat treatment is performed, and the other processes remain unchanged, specifically: S5: 65wt% of the co-infiltration agent is added to the quenched and tempered silver bright steel B, and the steel is dried at 200°C. The temperature is then increased, and nitrogen is introduced at 0.03MPa at 500°C for pressure relief operation. The steel is cooled and taken out of the furnace to obtain the quenched and tempered silver bright steel.

[0032] Comparative Example 4: Based on Example 1, the heat treatment process was changed, and the other processes remained unchanged, specifically: S1: The alloy steel raw material is smelted in an electric furnace at 1625°C, 0.25wt% deoxidizer is added, the mass ratio of silicon carbide and ferromanganese alloy in the deoxidizer is 1:1.5, and refined and impurity-removed at 1575°C, the vacuum degree is set to 60Pa for vacuum degassing for 18min, argon gas is introduced to break the air, soft blowing treatment is performed for 12min, cooling and furnace removal are performed to obtain alloy steel liquid; S2: Cast the alloy steel liquid at 1575℃ and set the rolling acceleration to 1.2m / s 2 , rolling treatment was carried out at 1125°C with a reduction of 55 mm, and cooling was performed to obtain basic quenched and tempered silver bright steel; S3: The basic quenched and tempered silver bright steel is placed in a mixed solution (5.5 parts of potassium permanganate, 11 parts of sodium hydroxide, 5.5 parts of potassium nitrate, and 78 parts of deionized water) and soaked for 15 minutes, washed with water, dried by nitrogen, quenched with water at 600°C for 10 minutes, cooled with oil to room temperature, and then tempered at 500°C for 30 minutes, cooled, and taken out of the furnace to obtain quenched and tempered silver bright steel A; S4: The shot peening particle size is set between 150 μm, the quenched and tempered silver bright steel A is shot peened for 23 minutes, boron trifluoride is introduced as a boron source, and plasma boronization is performed at 575°C for 45 minutes in a hydrogen and nitrogen atmosphere. After the plasma electrolytic pre-boronization treatment is completed, oil quenching is performed at 1025°C for 30 minutes, water-cooled to room temperature, tempered twice at 630°C, cooled, and discharged from the furnace to obtain quenched and tempered silver bright steel B; S5: Add 65wt% of the co-infiltration agent to the quenched and tempered silver bright steel B, dry it at 200℃, then increase the temperature and introduce nitrogen at 0.03MPa at 500℃ to discharge the pressure; oil quench at 730℃ for 1.5 hours, air cool, temper at 630℃ for 45min, cool and take out of the furnace to obtain the quenched and tempered silver bright steel.

[0033] Comparative Example 5: Based on Example 1, after the plasma electrolysis pre-boronization treatment, no pre-boronization heat treatment is performed, and the other processes remain unchanged, specifically: S4: setting the shot peening particle size to between 150 μm, subjecting the quenched and tempered silver bright steel A to shot peening pretreatment for 23 min, introducing boron trifluoride as a boron source, subjecting the quenched and tempered silver bright steel A to plasma boronization treatment at 575° C. for 45 min in a hydrogen and nitrogen atmosphere, cooling, and removing from the furnace to obtain the quenched and tempered silver bright steel B; S5: Add 65wt% of the co-infiltration agent to the quenched and tempered silver bright steel B, dry it at 200℃, then increase the temperature and introduce nitrogen at 0.03MPa at 500℃ to discharge the pressure; oil quench at 730℃ for 1.5 hours, air cool, temper at 630℃ for 45min, cool and take out of the furnace to obtain the quenched and tempered silver bright steel.

[0034] Testing experiment: The high-strength quenched and tempered silver-bright steel for nuclear energy fasteners prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was subjected to the following performance tests: (1) Tensile strength test: The quenched and tempered silver-bright steel prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was subjected to performance test with reference to GB / T 228.1; (2) Vickers hardness test: The quenched and tempered silver-bright steel prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was subjected to performance test with reference to GB / T 230.1 using a hardness tester.

[0035] Examples tensile strength Vickers hardness (MPa) (HV) Example 1 1540 2490 Example 2 1520 2471 Example 3 1527 2463 Comparative Example 1 1403 2273 Comparative Example 2 1439 2310 Comparative Example 3 1466 2388 Comparative Example 4 1475 2362 Comparative Example 5 1490 2391 Table 1 Result analysis: According to the data analysis in Table 1, it can be seen that the present invention improves the purity of steel, reduces defects, improves mechanical properties, enhances corrosion resistance, and prolongs service life by adding a deoxidizer for refining and removing impurities; forms a boride layer and a microporous structure through plasma electrolysis pre-boronization, promotes the formation of a uniform and dense boride layer, and enhances wear resistance, high-temperature oxidation resistance, durability, hardness, and corrosion resistance, but the thickness of the boride layer needs to be controlled; the surface hardness and corrosion resistance can be significantly improved by borochromium co-diffusion treatment combined with plasma electrolysis pre-boronization, and the chromium-boron oxide layer enhances high-temperature oxidation resistance and prevents oxygen penetration; the internal stress is reduced by heat treatment after borochromium co-diffusion, the formation of hard and brittle phases is inhibited, the stability of the boride layer is enhanced, cracking is prevented, and the surface hardness, wear resistance, thermal stability, and corrosion resistance are improved.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners, characterized in that: The following steps are involved: S1: The alloy steel raw material is smelted in an electric furnace, and then a deoxidizer is added for refining and impurity removal, vacuum degassing, cooling, and unloading to obtain alloy steel liquid; S2: Casting, rolling and cooling the alloy steel liquid in sequence to obtain basic quenched and tempered silver bright steel; S3: pre-treating the surface of the basic quenched and tempered silver bright steel, and then performing heat treatment to obtain quenched and tempered silver bright steel A; S4: subjecting the surface of the quenched and tempered silver bright steel A to a plasma electrolytic pre-boronization treatment and a pre-boronization heat treatment, cooling, and taking out of the furnace to obtain a quenched and tempered silver bright steel B; S5: subjecting the surface of the quenched and tempered silver bright steel B to boron-chromium co-penetration treatment, boron-chromium co-penetration heat treatment, cooling, and taking out of the furnace to obtain high-strength quenched and tempered silver bright steel.

2. The method for preparing a high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: The composition of the basic quenched and tempered silver bright steel includes the following elements, calculated by mass percentage: 0.37% to 0.44% carbon, 0.17% to 0.37% silicon, 0.5% to 0.8% manganese, 0.6% to 0.9% chromium, 0.15% to 0.25% molybdenum, 1.25% to 1.65% nickel, copper ≤0.20%, and the rest is iron and unavoidable impurities ≤0.03%.

3. The method for preparing a high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: In S1, the temperature of the smelting treatment is 1600~1650℃; the temperature of the refining and impurity removal is 1550~1600℃; the specific process parameters of the vacuum degassing are: setting the vacuum degree to 55~65Pa, the time is 15~20min, introducing argon to break the air, and soft blowing treatment for 10~15min.

4. The method for preparing a high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: The deoxidizer comprises silicon carbide and ferromanganese alloy in a mass ratio of 1:1.2-1.8; the amount of the deoxidizer added accounts for 0.2-0.3wt% of the alloy steel liquid.

5. The method for preparing a high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: In S2, the casting temperature is 1550-1600°C; the rolling temperature is 1100-1150°C, the reduction is 50-60 mm, and the rolling acceleration is 1.0-1.5 m / s 2 .

6. The method for preparing a high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: In S3, the pretreatment process is specifically as follows: soaking the basic quenched and tempered silver bright steel in the mixed solution for 10 to 30 minutes, washing with water, and drying with nitrogen; The heat treatment process is specifically as follows: after the pretreatment is completed, water quenching is performed at 850-900°C for 15-45 minutes, oil cooling is performed to room temperature, and then high temperature tempering is performed at 550-650°C for 100-140 minutes; The mixed liquid raw materials include the following components: by mass, 5-6 parts of potassium permanganate, 10-12 parts of sodium hydroxide, 5-6 parts of potassium nitrate, and 76-80 parts of deionized water.

7. The method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: In S4, the process of the plasma electrolytic pre-boronizing treatment is specifically as follows: setting the shot peening particle size between 100 and 200 μm, subjecting the quenched and tempered silver bright steel A to shot peening pre-treatment for 15 to 30 minutes, introducing boron trifluoride as a boron source, and subjecting the steel to plasma boronizing treatment at 550 to 600° C. for 30 to 60 minutes in a hydrogen and nitrogen atmosphere; The process of the pre-boronizing heat treatment is specifically as follows: after the plasma electrolytic pre-boronizing treatment is completed, oil quenching is performed at 1000-1050° C. for 15-45 minutes, water cooling is performed to room temperature, and tempering is performed twice at 600-650° C.

8. The method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 1, characterized in that: In S5, the boron-chromium co-diffusion treatment process is specifically as follows: adding 60-70wt% of the co-diffusion agent to the quenched and tempered silver bright steel B, drying at 100-300°C, and then increasing the temperature to 450-550°C and introducing nitrogen at 0.02-0.04MPa for pressure relief operation; The process of the borochromizing heat treatment is specifically as follows: after the borochromizing treatment is completed, the steel is oil quenched and kept warm at 700-750° C. for 1-2 hours, air-cooled, and tempered at 600-650° C. for 30-60 minutes.

9. The method for preparing high-strength quenched and tempered silver bright steel for nuclear energy fasteners according to claim 8, characterized in that: The co-infiltration agent raw materials include the following components: by mass, 15 to 20 parts of anhydrous borax, 3 to 5 parts of potassium fluoroborate, 1 to 2 parts of potassium fluorotitanate, 30 to 40 parts of iron boride, 30 to 40 parts of chromium trioxide, and 6 to 10 parts of metal oxides; the metal oxides include cerium oxide and lanthanum oxide in a mass ratio of 2 to 2.5:

1.

10. High-strength quenched and tempered silver-bright steel prepared according to the method for preparing high-strength quenched and tempered silver-bright steel for nuclear energy fasteners according to any one of claims 1 to 9.