CN113201698A

CN113201698A - High-temperature bearing steel and clean and uniform preparation method thereof

Info

Publication number: CN113201698A
Application number: CN202110486187.0A
Authority: CN
Inventors: 杨卯生; 李建新; 童锐; 孙勇; 毕明龙; 颜家森; 赵开礼; 郭军; 刘璐; 罗志强; 于安乐
Original assignee: Central Iron and Steel Research Institute
Current assignee: Central Iron and Steel Research Institute
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2021-08-03
Anticipated expiration: 2041-04-30
Also published as: CN113201698B

Abstract

A high-temperature bearing steel and a clean and uniform preparation method thereof belong to the technical field of alloy steel. The high-temperature bearing steel comprises the following chemical components in percentage by mass: c: 0.80-0.85%, Mn: less than or equal to 0.35 percent, Si: less than or equal to 0.25 percent, Cr: 4.00-4.25%, Mo: 4.00-4.50%, V: 0.90-1.10%, Ni: less than or equal to 0.15%, W: less than or equal to 0.25 percent, Nb: less than or equal to 0.040%, Al: less than or equal to 0.010 percent, Ca: less than or equal to 0.001 percent, Ti: less than or equal to 0.0040 percent, O: less than or equal to 0.0007 percent, N: less than or equal to 0.0020%, H: less than or equal to 0.001 percent, and the balance of Fe and inevitable impurities. The process comprises the steps of raw material preparation → vacuum induction furnace pouring electrode bar → air cooling → car light → vacuum consumable remelting → steel ingot annealing car light → forging → rolling into material → annealing. The high-strength wear-resistant steel has the advantages of high strength, high hardness, wear resistance, high rotary bending fatigue limit strength, excellent fatigue performance and good size stability at room temperature and 300 ℃.

Description

High-temperature bearing steel and clean and uniform preparation method thereof

Technical Field

The invention belongs to the technical field of alloy steel, and particularly relates to high-temperature bearing steel and a clean and uniform preparation method thereof, so that the steel has excellent fatigue performance.

Background

The high-performance bearing is used as a key component of a transmission system of aerospace, high-speed trains, traffic vehicles, metallurgy and engineering machinery, is a limiting factor of the performance, service life and reliability of the whole machine, and influences the stability and safety of the whole machine. With the increase of the transmission energy, the rotating speed, the temperature and the service life are increased, and the bearing is required to have higher bearing capacity, namely the bearing steel has high strength at room temperature and high temperature and is super-hardened on the surface; the bearing can continuously, stably and reliably work in high-bearing, high-speed and high-temperature states, and the high reliability, long service life and high stability of the bearing steel in the high-bearing and high-temperature states are very important.

High-temperature bearing steel is a typical high-temperature martensitic bearing steel as a high hardenability steel, and the hot hardness of the high-temperature bearing steel depends on carbides such as molybdenum carbide. During the austenitizing process of the heat treatment, about 3 to 4 mass percent of Mo-rich type M2C, V-rich type MC and Cr-rich type M6C are not dissolved. The steel is quenched to room temperature, tempered at 550 ℃, tempered at-75 ℃ and again tempered at 550 ℃ to form a microstructure consisting of undissolved carbides, martensite and less than about 10% of retained austenite. The secondary hardening is carried out by tempering for 2 hours at 540-550 ℃ and then air cooling to room temperature. The fatigue life of high temperature bearing steel increases with increasing hardness. If the low-temperature treatment is not carried out, the austenite content is reduced by repeated tempering treatment, the tempering temperature is 550 ℃, the air cooling is carried out to the room temperature, and the residual austenite content of the high-temperature bearing steel is reduced to be below 4 percent, so that the dimensional stability is improved and the toughness is enhanced in the using process. The maximum temperature at which M50 can be continuously used was 300 ℃. Hardness is a critical factor, and even when operating at ambient temperatures, contact fatigue life increases as hardness increases above 54HRC, whereas M50 is typically hardened to at least 58 HRC. Since M50 has a high rolling contact fatigue life.

The requirements of the U.S. and euro-state high temperature bearing steel standards or specifications are increasingly common in steel grade level, metallurgical quality and dimensional accuracy thereof. The high-cleanliness homogenization preparation process is adopted, the sizes, the quantity and the distribution of inclusions and carbides are controlled, and the contact fatigue life and the bending fatigue limit strength of the steel are obviously improved. The aviation or automobile bearing is made of high-temperature bearing steel, the cleanliness and the surface hardness of the bearing steel are high, and the structure uniformity and the fatigue resistance performance are good. Although the standards in the united states and europe are different in terms of high performance bearing materials, the choice of bearing materials also varies. It is well known that the metallurgical quality and the fine structure significantly affect the reliability and safety of high-performance bearings such as aerospace and the like. As for bearings on engines and transmission systems in China, high-temperature bearing steel such as 8Cr4Mo4V, W9Cr4V2Mo, G13Cr4Mo4Ni4V and the like is widely selected due to the limitation of temperature conditions of service environments. In addition, the bearings are different in use conditions at home and abroad, for example, compared with the domestic high-temperature bearing, the domestic high-temperature bearing has more rigorous and complex service environment, and has the influence effects of longer running time, larger temperature change, system environment and the like. Higher and more comprehensive performance and quality requirements are put forward for high-temperature bearing steel. In the aerospace service process, the contact fatigue performance and the bending fatigue performance of the high-temperature bearing steel are more important based on the good technological properties and mechanical properties of the bearing steel. The mechanical property and the fatigue property of the high-temperature bearing steel are tested in China, and the bending and contact fatigue properties of the high-temperature bearing steel are analyzed. But the comprehensive mechanical property and excellent fatigue property obtained based on component and process optimization are not reported.

Disclosure of Invention

The invention aims to provide high-temperature bearing steel and a clean and uniform preparation method thereof, wherein the high-temperature bearing steel bears load, is stable in size and has excellent fatigue performance. Through the precise control of chemical component design and proportion, the control of high purity, high uniformity and grain refinement process technology, and the corresponding optimal heat treatment process, the steel obtains good matching of high strength, high surface hardness, dimensional stability, ultra-long contact fatigue life and higher bending fatigue strength.

The idea of the technical scheme adopted by the invention is as follows:

the steel high-temperature bearing steel comprises the following chemical components in percentage by mass: c: 0.80-0.85%, Mn: less than or equal to 0.35 percent, Si: less than or equal to 0.25 percent, Cr: 4.00-4.25%, Mo: 4.00-4.50%, V: 0.90-1.10%, Ni: less than or equal to 0.15%, W: less than or equal to 0.25 percent, Nb: less than or equal to 0.040%, Al: less than or equal to 0.010 percent, Ca: less than or equal to 0.001 percent, Ti: less than or equal to 0.0040 percent, O: less than or equal to 0.0007 percent, N: less than or equal to 0.0020%, H: less than or equal to 0.001 percent, and the balance of Fe and inevitable impurities. Wherein 10C/(V + Mo + Cr) is 0.8-0.9. The functions and the proportion of the elements are as follows:

the C element is the main alloy element of the invention steel, and is the main solid solution strengthening and carbide forming element. C forms carbide with Cr, Mo, V and other elements to raise the hardness and antiwear performance of steel. In order to ensure enough hardness and abrasion resistance, the content of C is required to be more than 0.80 percent; however, too much C forms eutectic carbides and degrades the mechanical properties and corrosion resistance of the steel, and the upper limit of the C content present in the steel does not exceed 0.85%.

Si and Mn: the carburized layer is easily oxidized, the toughness of the carburized layer is reduced, and the contact fatigue strength of the bearing is reduced. Although Si has the functions of tempering resistance and matrix strengthening, in order to ensure the toughness of the bearing steel infiltration layer, the contents of Si and Mn are controlled to be below 0.35 percent.

The Cr element is the main alloy element of the steel, can effectively improve the hardenability of the steel and form stable carbide. The strength and wear resistance are improved, and the rolling contact fatigue life is further improved, but the excessive addition of Cr causes the residual austenite and ferrite and the net-shaped M in the steel₂₃C₆Carbides reduce the hardness and corrosion resistance of the steel. Therefore, the Cr content should be controlled within the range of 4.00-4.25%.

Mo is the main alloy element of the steel, can effectively improve the hardenability of the steel, form stable carbide and improve the heat resistance and the tempering resistance of the steel. Enlarging the passivation range and increasing the corrosion resistance. Mo is solid-solution strengthened on the one hand, and dispersion strengthened on the other hand. M alloyed by Mo₂The X phase has extremely high stability and slows down the formation of M₂₃C₆The tempering stability of the steel is improved by the carbide process. Below 0.30%, the above-mentioned effect is not significant; too high Mo will cause the toughness of steel to decrease, the content is not more than 4.50%, Mo is a ferrite stabilizing element which can promote the formation of grain boundary ferrite film and reduce the thermoplasticity and toughness. Therefore, the Mo content is limited to 4.00-4.50%.

The V element is the main alloy element of the steel, the capability of forming MC carbide is improved, fine dispersion carbide formed by combining with C can prevent crystal grains from growing up during heating, and the effects of fine grain strengthening and precipitation strengthening are achieved, so that the wear resistance and the fatigue resistance of the steel can be improved at the same time. The content of V is lower than 0.90 percent, and the effect is not obvious; the content of V is higher than 1.10%, large-particle primary carbide is formed, and the fatigue property of steel is reduced. Therefore, the addition range of V is controlled to be 0.90-1.10%.

V, Nb, it is advantageous to form fine, uniform and very stable (V, Nb) C complex carbides by carburization, thereby achieving high hardness. Mo, V and Nb have the functions of refining crystal grains and improving the strength, and fine, uniform and stable (V, Nb) C carbonitride is formed at high temperature, so that carbide in large-ingot steel can be refined, the growth of the crystal grains in the large-ingot processing process can be inhibited, the strength of the steel can be improved, and the fatigue performance of the steel can be improved. Excessive V, Nb alloying elements will form large grain primary carbides, affecting the toughness of the steel. The Nb element is controlled within 0.04 percent.

P, S, [ O ], [ N ], [ H ]: reaching a certain amount of the above elements will reduce the toughness and fatigue properties of the bearing steel. P, S form micro segregation when molten steel is solidified, and the micro segregation will concentrate at grain boundaries when heated at a temperature after austenite, thereby increasing the brittleness of steel. The [ O ] element is easy to form oxide inclusion and obviously affects the fatigue performance of the bearing steel, and the [ N ] and [ H ] elements are easy to segregate in the grain boundary, thereby reducing the contact fatigue performance of the steel. Therefore, the steel controls [ N ] + [ O ] + [ H ] + P + S to be less than or equal to 0.0090%, As + Sn + Sb + Pb + Bi to be less than or equal to 0.010%, and the size of the unchanged clamping impurities is not more than 6 mu m; the size of carbide is not more than 30 μm, the grain size is finer than 8 grades, and the residual austenite is less than 2%.

The steel is suitable for parts bearing high temperature of 300 ℃ and resisting fatigue, and the adopted materials are required to have good high-temperature performance matching, higher carburized surface hardness and good fatigue performance; the tensile strength Rm of the steel at room temperature is not less than 2600MPa, the tensile strength Rm at 300 ℃ is not less than 2200MPa, the surface hardness at room temperature is not less than 62HRC, and the high-temperature hardness at 300 ℃ is not less than 58 HRC.

The steel is suitable for manufacturing parts with stable dimension required in the service process. The stress and the cycle number are 10 under 4000MPa within the temperature range of 20-100 DEG C⁹The sample size change rate was less than 0.01%.

The steel is mainly suitable for parts requiring fatigue resistance in a long-term service process. The contact fatigue life reaches 10 under the stress of 5000MPa⁸(ii) a Number of cycles 10⁷The lower bending fatigue limit strength is not less than 1000 MPa.

The clean uniform preparation process of the high-temperature bearing steel comprises the following steps: raw material preparation → vacuum induction furnace pouring electrode rod → air cooling → polishing → vacuum consumable remelting → ingot annealing polishing → forging → rolling finished material → annealing. The method comprises the steps of controlling harmful elements by adopting raw materials, and adopting a high-purity smelting method of vacuum induction and vacuum consumable pair or a high-purity smelting method of vacuum induction, electroslag remelting and vacuum consumable pair; the technical parameters controlled in the process steps are as follows: carrying out high-temperature diffusion treatment on the consumable ingot, wherein the temperature range is 1160-1210 ℃, and the heating and heat preservation time is 30-60 hours; after the consumable ingot is diffused at high temperature, the consumable ingot is firstly subjected to more than two times of upsetting-drawing homogenization deformation and cogging by a quick forging machine, and the forging or rolling temperature is controlled within the range of 1100-1160 ℃. The final forging or rolling temperature is controlled within the range of 850-900 ℃. The design idea of the process is as follows:

(l) Through Cr-Ni-Mo component design, ultrapure smelting and hot working process optimization, the control range of the main components of the steel (C: 0.80-0.85%, Cr: 4.00-4.25%, Mo: 4.00-4.50%, V: 0.90-1.10%); the inlet temperature of the vacuum consumable cooling water is less than or equal to 30 ℃. Setting the melting speed to 3-6kg/min by vacuum consumable; the forging temperature is 1100-1160 ℃, and a heat treatment system is adopted: the strength and the hardness of the bearing steel are improved by quenching at 1090-1110 ℃, cold treatment at minus 73 ℃ and tempering at 550 ℃.

(2) 0.01-0.04% of trace element Nb alloy element is added into large-ingot high-temperature bearing steel, and is supplemented with 1160-1210 ℃ high-temperature diffusion, more than two times of upsetting and drawing and forging processing technologies, so that the size of carbide is ensured to be smaller than 30 mu m, the grain size of austenite is ensured to be larger than 8 grades, and the strength, toughness and fatigue property of the steel are improved;

(3) adopting ultra-pure smelting (the vacuum degree of vacuum induction smelting is less than or equal to 5Pa, and the vacuum degree of vacuum consumable working is less than or equal to 0.4Pa), and controlling oxygen, nitrogen, hydrogen and impurity elements in steel to ensure that the size of impurities is not more than 6 mu m; the dimensional stability, the shock resistance and the fatigue performance of the steel are improved. The key point of the invention is based on the designed material component control range, the metallurgical quality control and the organic combination of smelting, hot working and heat treatment processes, and the invention is characterized by the stable control of the aspects of fine and uniform material structure, stability, material hardness and strength and the like, thereby improving the contact fatigue performance and the rotary bending fatigue performance. As a result, the high hardness and the high strength are obtained, and simultaneously, the contact and bending fatigue performances of the bearing steel are obviously improved, so that the steel has excellent fatigue failure resistance in the service process.

The invention adopts raw material control harmful elements and a high-purity smelting method of vacuum induction and vacuum self-consumption two-in-one or vacuum induction, electroslag remelting and vacuum self-consumption three-in-one, and ensures that the size of the inclusions is not more than 6 mu m; carrying out high-temperature diffusion treatment on the consumable ingot, wherein the temperature range is 1160-1210 ℃, and the heating and heat preservation time is not less than 30 hours; after the consumable ingot is diffused at high temperature, firstly, the consumable ingot is subjected to upsetting-drawing homogenization deformation for more than two times through a quick forging machine and cogging, products such as bars and the like with various specifications are forged and rolled, the forging (rolling) temperature is controlled within the range of 1100-1160 ℃, and the uniformity of the bearing steel is ensured by ingot forming process control and forging deformation process optimization; the niobium and vanadium are added in a composite way to disperse and separate out an MC second phase in different temperature ranges, and the size of carbide is controlled within 30 mu m, as shown in figure 1. The final forging (rolling) temperature is controlled within the range of 850-900 ℃ to ensure that the grain size is above 8 grade, as shown in figure 2; the amount of retained austenite is controlled, the surface hardness of the steel is improved, and the dimensional stability of the material is ensured. Compared with the prior art, the steel has the advantages of bearing fatigue load, stable size, high bending fatigue strength limit and long contact fatigue life. The steel of the invention has less residual austenite, fine crystal grain, fine structure and greatly improved strength and fatigue performance, thereby ensuring the long service life of the high-temperature bearing.

Compared with the prior art, the invention has the advantages of high strength at room temperature and 300 ℃, high hardness, wear resistance, high rotary bending fatigue limit strength, excellent fatigue performance, good dimensional stability and good matching of process adaptability.

Drawings

FIG. 1 is a metallographic photograph of a high-temperature bearing steel structure.

FIG. 2 is a metallographic photograph (5 μm) of a high-temperature bearing steel structure.

FIG. 3 is a grain size diagram of high temperature bearing steel. Quenching temperature: crystal size at 1100 ℃: and 9.5 grade.

FIG. 4 is a grain size diagram of high temperature bearing steel. Quenching temperature: grain size at 1110 ℃: and 9 stages.

Detailed Description

According to the designed chemical composition range, 4 furnaces (numbers 1-4) of the invention steel are smelted on a 1-ton vacuum induction furnace and a vacuum consumable furnace, in addition, 3 groups of Cr-Mo-V comparison steels (numbers 5-7) have specific chemical compositions shown in Table 1, and the P, S element content of the invention steel is obviously lower than that of the comparison steels. The invention relates to a method for preparing steel by double vacuum smelting, casting into ingots, and finally forging and rolling into phi 120 and phi 80 bar stocks through high temperature diffusion, upsetting-drawing deformation and forging cogging. The invention steel and the comparison steel are processed into a standard room temperature tensile sample, a Charpy notch impact sample, a hardness sample, a metallographic sample, a rolling contact fatigue sample and a spin bending fatigue sample. The steel of the invention and the comparative steel adopt a heat treatment system: carrying out oil quenching at 1090 ℃, deep cooling, tempering at 550 ℃, grinding and polishing a sample for determining the grain size, corroding by a saturated picric acid aqueous solution, and measuring by using a line cutting method, wherein the scales of carbides and inclusions are determined by using a scanning electron microscope and an image analyzer.

The results of the tests of strength, hardness, inclusions, carbides, and grain size of the inventive steel and the comparative steel are shown in Table 2. As can be seen from Table 2, the tensile strength of the inventive steel is not less than 2600MPa, the impact energy is not less than 12J, which is significantly higher than that of the comparative steel; the grain size of the invented steel is above 8 grade, and reaches 9 grade, while the grain size of the comparative steel is about 7 grade. The steel of the invention has high cleanliness, the maximum size of inclusions is not more than 6 mu m, carbides are distributed in a dispersion way, the maximum size of the carbides is not more than 30 mu m, the steel is obviously superior to the comparative steel, the temperature is reduced to 1090 ℃ for oil cooling, and finally the steel is tempered at 550 ℃ for 2 hours and then air cooled, and the surface hardness test of a sample is carried out. The hardness of the samples of the invention steel and the comparative steel is different, and the surface hardness of the invention steel is more than HRC62 and is higher than that of the comparative steel.

TABLE 1 chemical composition (%) balance Fe for inventive steels and comparative steels

TABLE 2 Strength, toughness, hardness, inclusions, carbides, grain size of inventive steels and comparative steels

After the retained austenite of the invention steel and the comparative steel samples is measured, the retained austenite amount of the invention steel is not more than 2 percent and is obviously lower than that of the comparative steel, and the table 3 shows.

Grinding the rolling contact fatigue sample after the carburizing heat treatment to a final size, measuring the contact fatigue life on a rolling contact fatigue tester, setting the stress to be 5GPa, grinding the rolling contact fatigue sample after the carburizing heat treatment to a final size, measuring on a rotary bending fatigue tester, and carrying out a rotary bending fatigue test on the invention steel and the comparison steel according to GB 4337-84. The speed of the experiment was 5000rpm, and the number of specimens was 22. Fatigue test for failure of sample or up to 10⁷Until the next time. The fatigue limit of the steel is measured by adopting a lifting method to represent the bending fatigue resistance of the steel, the test results of the rotary bending and contact fatigue resistance are shown in the table 3, and the rated contact fatigue life (L) of the steel is shown in the table₁₀) Is about 4 times of the comparison steel and is obviously higher than the comparison steel. The rotary bending fatigue limit of the steel is more than 1000MPa and is obviously higher than that of the comparative steel.

The dimensional stability of the material is measured on a contact fatigue test sample under the conditions of the cyclic stress of 4000MPa and the cycle number of 10⁹Under the condition of (1), measuring the dimensional change delta L of the raceway on a sample, wherein the diameter Lo of the sample is 10mm, the dimensional stability is represented by the ratio of the dimensional change delta L of the raceway to the diameter Lo of the sample, the calculation is shown in formula 1, and the test result is shown in Table 3.

The result shows that the dimensional stability of the steel is not more than 0.010 percent and is obviously better than that of the comparative steel.

TABLE 3 residual austenite, dimensional stability, rotary bending strength, contact fatigue life of inventive steels and comparative steels

As can be seen from tables 2 and 3, the steel is compared with comparative steel. The inventive steel exhibits good dimensional stability, its ultra-long contact fatigue life and excellent resistance to rotary bending fatigue.

Claims

1. The high-temperature bearing steel is characterized by comprising the following chemical components in percentage by mass: c: 0.80-0.85%, Mn: less than or equal to 0.35 percent, Si: less than or equal to 0.25 percent, Cr: 4.00-4.25%, Mo: 4.00-4.50%, V: 0.90-1.10%, Ni: less than or equal to 0.15%, W: less than or equal to 0.25 percent, Nb: less than or equal to 0.040%, Al: less than or equal to 0.010 percent, Ca: less than or equal to 0.001 percent, Ti: less than or equal to 0.0040 percent, O: less than or equal to 0.0007 percent, N: less than or equal to 0.0020%, H: less than or equal to 0.001 percent, and the balance of Fe and inevitable impurities. Wherein 10C/(V + Mo + Cr) is 0.8-0.9.

2. A high-temperature bearing steel As claimed in claim 1, wherein the steel has a control [ N ] + [ O ] + [ H ] + P + S of 0.0090% or less, As + Sn + Sb + Pb + Bi of 0.010% or less, Ti of 0.0040% or less, and a non-deformed inclusion dimension of 6 μm or less; the size of carbide is not more than 30 μm, the grain size is finer than 8 grades, and the residual austenite is less than 2%.

3. A high-temperature bearing steel as claimed in claim 1, wherein the steel has a controlled room-temperature tensile strength Rm of 2600MPa or more, a controlled 300-temperature tensile strength Rm of 2200MPa or more, a controlled room-temperature surface hardness of 62HRC or more, and a controlled 300-temperature high-temperature hardness of 58HRC or more.

4. A high temperature bearing steel as claimed in claim 1, wherein; the steel is suitable for parts with stable size in the service process; the stress and the cycle number are 10 under 4000MPa within the range of 20-100 DEG C⁹The sample size change rate was less than 0.01%.

5. High strength and toughness bearing steel as claimed in claim 1, wherein the steel is suitable for use in components requiring fatigue resistance during long-term service. The contact fatigue life reaches 10 under the stress of 5000MPa⁸(ii) a Number of cycles 10⁷The lower bending fatigue limit strength is not less than 1000 MPa.

6. A clean and uniform preparation method of the high-temperature bearing steel as claimed in claim 1, which is characterized in that raw materials are adopted to control harmful elements, and a high-purity smelting method combining vacuum induction and vacuum self-consumption or combining vacuum induction, electroslag remelting and vacuum self-consumption is adopted, wherein the vacuum degree of vacuum induction smelting is less than or equal to 5Pa, and the vacuum degree of vacuum self-consumption working is less than or equal to 0.4 Pa; the technical steps and the controlled technical parameters are as follows: carrying out high-temperature diffusion treatment on the consumable ingot, wherein the temperature range is 1160-1210 ℃, and the heating and heat preservation time is 30-60 hours; after the consumable ingot is diffused at high temperature, the consumable ingot is firstly subjected to more than two times of upsetting-drawing homogenization deformation and cogging by a quick forging machine, and the forging or rolling temperature is controlled within the range of 1100-1160 ℃. The final forging or rolling temperature is controlled within the range of 850-900 ℃.