CN106893947B - A kind of preparation method for the bearing steel being resistant to 400 degree of high temperature - Google Patents

Abstract

The invention belongs to the development field of high-temperature bearing steel, and mainly relates to a preparation method of bearing steel which can withstand a high temperature of 400 degrees. The bearing is made of steel and can be used at a high temperature not exceeding 400°C. The high-temperature bearing steel of the present invention is double-vacuum smelted by vacuum induction furnace and vacuum electroslag remelting, and the composition is 4.50-5.28% Cr, 3.75-4.10% Mo, 0.56-0.80% V, 0.30-0.34% Mn, 0.21-0.26% Ni , 0.20-0.29% Si. The heat treatment process is as follows: heating the bearing steel to 800-870°C for heat preservation, cooling to 700-800°C for isothermal annealing, and then slowly cooling to room temperature; heating to 1050-1070°C for solid solution, oil quenching after heat preservation; and then heating to 510-550°C Tempering at ℃ for 2 to 2.5 hours, and tempering three times according to this process. The new high-temperature bearing steel designed by the present invention reduces the vanadium content to make the carbides fine and dispersed, which can reduce the source of fatigue cracks and further improve the hardness. application under conditions.

Description

A kind of preparation method of bearing steel that can withstand high temperature of 400 degrees

technical field

The invention belongs to the technical field of composition development and heat treatment process of high-temperature bearing steel, and mainly relates to composition development and heat treatment process of a novel high-temperature bearing steel.

Background technique

High temperature bearing steel is mainly used in main shaft bearings in aero-engines, used in aircraft or rockets. The higher the hardness value of the bearing, the better the fatigue life of the bearing and the longer the service time. With the current development of gas turbines, higher hardness is required at high temperatures to meet the long-term work of gas turbines. Therefore, it is necessary to improve the room temperature hardness and high temperature hardness of bearing steel. The steel grades and international, American and domestic standards of the widely used high-temperature bearing steels are shown in Table 1. Among them, M50 (equivalent to domestic 8Cr4Mo4V) is the most widely used high-temperature bearing steel at home and abroad. It is mainly used for gas turbine main shaft bearings. Below 315°C. According to the American high-speed steel standard, its chemical composition characteristics are: 0.78~0.88wt.%C, 3.75~4.50wt.%Cr, 3.90~4.75wt.%Mo, 0.80~1.25wt.%V, 0.10~0.15wt.% Ni, 0.15-0.45wt.% Mn, 0.20-0.60wt.% Si, P≤0.03wt.%, S≤0.03wt.%. The heat treatment process of M50 steel is generally as follows: preheat the steel at 732-843 °C, then heat it to 1104 °C in a salt bath furnace, keep it for at least 5 minutes, and then oil quench it to 100-200 °C, and cool it to room temperature after oil extraction. Reheat to 538°C and temper three times for 2 hours each time. Finally, ledeburite steel is obtained. In the A600.13324 high-speed steel American standard, it is stipulated that the room temperature hardness of M50 bearing steel shall not be lower than 61HRC. In the use standard of bearing steel, the hardness of bearing steel shall not be lower than 58HRC or 652HV at the service temperature. The higher the value, the better the wear resistance. There are large irregular carbides on the working surface or subsurface of the bearing steel with the above-mentioned composition content and the above-mentioned heat treatment method, mainly primary carbides containing V and Mo, which are easy to become the starting point of fatigue spalling during service. After heat treatment, M50 steel has a room temperature hardness of 61-63 HRC.

Table 1 Chemical composition of high temperature bearing steel in international, American and Chinese standards

The improvement of high temperature bearing steel such as M50 has the following related inventions. Patent CN104313294A is an invention of a heat treatment method for improving the dimensional stability of Cr4Mo4V steel. The steel composition is the same as that of M50 steel. The heat treatment is heating to 1065-1090 ° C, holding for 30-55 minutes, and cooling to 50-200 ° C with nitrogen gas oil after being released from the furnace; At 535-545°C, keep warm for 2-2.5 hours, and temper three times. It is characterized in that: additional tempering at 520±5°C for 4-4.5 hours after rough grinding; additional tempering at 250±5°C after fine grinding for 8-10 hours. After treatment, its dimensional stability has been improved. The average dimensional change rate of the finished ferrule after storage is 1.33×10 ^-5 , and the maximum dimensional change rate is 2.67×10 ^-5 . Patent CN104294031A improves the problem of large deformation and taper through high-pressure gas quenching process. The process is to preheat and heat-preserve the high-temperature bearing steel ferrule in a vacuum environment. The two preheating temperatures and times are: 650°C, 30min; Quenching with high-pressure nitrogen gas, and then tempering at 540 ° C for 2 to 2.5 hours, a total of 3 times. Its hardness after high temperature tempering is 61.5 ~ 62HRC.

In addition, there are many studies on the surface hardening treatment of high temperature bearing steel at home and abroad, the most extensive of which is the carburizing and nitriding treatment of M50 steel and improved M50NiL steel, such as in the patent US6966954B2. Among them, the M50NiL steel composition is to reduce the C content and increase the Ni content on the basis of M50, so as to achieve the surface heat treatment conditions of high temperature carburizing or nitriding. The chemical composition of its M50NiL is 0.11～0.15wt.%C, 4.00～4.25wt.%Cr, 4.00～4.50wt.%Mo, 1.13～1.33wt.%V, 3.20～3.60wt.%Ni, 0.15～0.35wt .% Mn, 0.10～0.25wt.% Si, P≤0.015wt.%, S≤0.010wt.%, Co≤0.25%, W≤0.25wt.%, Cu≤0.1wt.%, and the rest is Fe. At high temperature, the surface is carbonitrided, and the thickness of the carburized layer is 0.002-0.014 inches, which greatly improves the surface hardness, which can reach 72HRC.

The detection of high-temperature bearings that failed after service found that large, irregular-shaped, and unevenly distributed primary carbides were found on the working surface or sub-surface of the bearing, which caused the generation and expansion of fatigue cracks and seriously affected the service life of the bearing steel. . The shape and distribution of carbides are determined by the composition and heat treatment process of the steel. Therefore, the present invention has developed a high-temperature bearing steel with a new composition system and its corresponding heat treatment process, which can significantly reduce the precipitation of large primary carbides, but at the same time Maintain high room temperature and high temperature hardness, which can improve the high temperature service life of the bearing.

Contents of the invention

In order to solve the above-mentioned technical problems, the object of the present invention is to disclose a high-temperature bearing steel with a new composition and a corresponding manufacturing process, so as to reduce the size of carbides, obtain evenly distributed carbide particles and higher hardness values, and improve bearing service life of steel.

The technical solution adopted in the present invention is: a new type of high-temperature bearing steel composition design and heat treatment method, while significantly reducing the content of V elements that form primary carbides, the content of other alloy components and the corresponding heat treatment process are optimized to ensure that the bearing steel Excellent room temperature and high temperature hardness, refined carbide size, fine and dispersed distribution to improve service life. In terms of composition design of the new high-temperature bearing steel, the high-temperature bearing steel is Mo-based bearing steel in composition, and its preparation process is as follows:

(1) Steel smelting: suitable for double vacuum smelting in vacuum induction furnace and vacuum electroslag remelting. The composition is different from the high-temperature bearing steel currently used. The mass fraction of carbon ranges from 0.75 to 0.90wt.%, and the mass fraction of nitrogen element ranges from 0.005 to 0.012wt.%. The alloy elements contained are Cr, Mo, V, Mn, Ni, Si, the range of mass fraction content is 4.50～5.28wt.%Cr, 3.75～4.10wt.%Mo, 0.56～0.80wt.%V, 0.30～0.34wt.%Mn, 0.21～0.26wt. %Ni, 0.20～0.29wt.%Si, the mass fraction content of other elements is controlled at Ti≤0.005wt.%, P≤0.01wt.%, S≤0.008wt.%, O≤0.0009wt.%, the rest is Fe and Unavoidable impurities.

(2) Solidification, hot forging/hot rolling process: the molten steel obtained from the above smelting is continuously cast or die-cast to obtain a billet or ingot, and after solidification, it is preheated at 750-850°C for 10min-20min, and heated to 1050°C-1150°C. Hot forging or hot rolling into rods with a diameter of not less than 15mm, the final forging or final rolling temperature is not lower than 900°C, and the furnace or ash cools to room temperature after forging.

(3) Heat treatment process:

The above-mentioned forged or rolled materials are sequentially subjected to three heat treatment processes of isothermal annealing, high-temperature solid solution and oil quenching, and high-temperature tempering to obtain the required properties. In the first step of isothermal annealing, heat the bearing steel to 800-870°C, keep it warm for 4-6 hours, then cool it to 700-800°C at a cooling rate of 3-10°C/min, hold it for 4-6 hours, and then cool it at 20-30°C Cool slowly at a cooling rate of 600-670°C per hour, and then cool to room temperature with the furnace; the second step is to heat the steel piece cooled to room temperature to 750-850°C for 30-50 minutes, and then heat it at 10-20°C/ Heating at a speed of 1050-1060°C at a minimum speed of 30-50 minutes; oil cooling to 100-200°C after being out of the furnace, and then air-cooling to room temperature; the third step is to temper the cooled bearing steel at 520-550°C for 2~ After 2.5 hours, air cool to room temperature and temper three times. After treatment, its hardness reaches 62-65HRC, and its Vickers hardness at a high temperature of 400°C reaches above 658HV, which is equivalent to a Rockwell hardness above 58HRC, which can well meet the requirements of working in an environment of 400°C.

It is also possible to change the steel piece obtained by isothermal annealing in the first step above to heating to 750-850°C for 30-50 minutes in the second step, then heating to 1070°C at a speed of 10-20°C/min, and holding for 30-50 minutes ;Oil cooled to 100-200°C after being released from the furnace, and air-cooled to room temperature after the oil is released; the third step is to temper the cooled bearing steel at 510-550°C for 2-2.5 hours, then air-cool to room temperature, and temper three times in total . After treatment, its hardness reaches 63-66HRC, and its Vickers hardness at a high temperature of 400°C reaches above 660HV, which can well meet the requirements of working in an environment of 400°C.

The method of the invention can be used in the manufacture of steel for the main shaft bearing of the aircraft engine, improves the hardness value of the bearing at room temperature and working temperature, and makes the carbide fine and dispersed to reduce the generation of cracks, and can prolong the service time of the bearing.

Description of drawings

Figure 1 is the SEM structure diagram after heat treatment, (a) is the structure picture of steel A after solution treatment at 1060°C and tempered three times at 540°C, (b) steel B is solution treated at 1050°C, and tempered at 540°C Tissue picture after tempering three times.

Figure 2 is the metallographic diagram under the light microscope after heat treatment, (a) steel A after solid solution at 1070 °C, tempered three times at 540 °C, (b) steel B after solid solution at 1050 °C, tempered three times at 540 °C Organize pictures.

Detailed ways

Example:

Specific embodiments of the present invention are given below and described in conjunction with the appended tables.

The composition is shown in Table 1 and Table 2. It is smelted by vacuum induction furnace and vacuum electroslag remelting double vacuum, then forged into a rod with a diameter of 25mm, and cut into small pieces with a thickness of 15mm. Experiments are performed in groups. After heat preservation at 850°C and isothermal annealing at 750°C, the bearing steel was cooled to 650°C at a rate of 20°C to 30°C/min, then slowly cooled to room temperature, and heated at each solution temperature for 30 minutes according to the experimental scheme shown in Table 3. Cool the oil out of the furnace to between 100 and 200°C, and then air cool the oil out to room temperature. In order to prevent cracking, temper it below 300°C in time. Put the bearing steel cooled to room temperature into the tempering furnace, and perform high-temperature tempering according to the temperature shown in Table 3. The tempering time is 2 to 2.5 hours, and the tempering is 3 times in total. Go to the next step. The Rockwell hardness of the final sample is measured, and the high-temperature hardness measurement is carried out on the sample with an ideal hardness value. The measurement temperature is 400°C. The corresponding heat treatment processes and the measured hardness values are shown in Table 3 and Table 4. Among them, the hardness values of A1, A2, A5～A24, B4～B21 steels at room temperature all exceeded 60HRC, meeting the requirements for the use of high temperature bearing steels, A6～A9, A12, A13, A18～A22, B6, B7, B11, The hardness values of samples B12, B18, and B19 all exceeded 63HRC, exceeding the maximum hardness value of M50 bearing steel at room temperature. For the hardness measurement value at 400°C, it can be seen that the high-temperature hardness of samples A6~A9, A12~A15, A18~A22, B5~B7, B10~B14, and B17~B20 all exceeded 658HV or 58HRC, fully meeting the use requirements . Figure 1 is the SEM structure diagram after heat treatment, and Figure 2 is the metallographic diagram under the light microscope after heat treatment. It can be seen from the figure that the carbide particles of this material are fine, the largest size is not more than 4 μm, and they are dispersed in the tempering horse. Between the slats.

The chemical composition (wt%) of table 1 invention steel A

The chemical composition (wt%) of table 2 invention steel B

Table 3A Hardness values of steel after different heat treatment processes

Table 4B Hardness values of steel after different heat treatment processes

Claims (2)

1. a kind of preparation method for the bearing steel being resistant to 400 degree of high temperature, it is characterised in that preparation process is：

(1) smelting of steel：Suitable for vaccum sensitive stove and the double vacuum metlings of vacuum electroslag remelting；Composition quality fraction range is：C 0.75~0.90wt.%, N 0.005~0.012wt.%, Cr 4.50~5.28wt.%, Mo 3.75~4.10wt.%, V 0.56~0.80wt.%, Mn 0.30~0.34wt.%, Ni 0.21~0.26wt.%, Si 0.20~0.29wt.%, Ti≤ 0.005wt.%, P≤0.01wt.%, S≤0.008wt.%, O≤0.0009wt.%, remaining for Fe and inevitably it is miscellaneous Matter；

(2) solidification, hot forging/hot rolling technology：Above-mentioned smelting is obtained into molten steel, steel billet or steel ingot are obtained by continuous casting or molding, solidified 10min~20min is preheated at 750~850 DEG C afterwards, is heated to 1050 DEG C~1150 DEG C, hot forging or hot rolling are not less than for diameter The bar of 15mm, finish-forging or finishing temperature are not less than 900 DEG C, and furnace cooling or ash cooling are to room temperature after forging；

(3) heat treatment process：Above-mentioned forging material or stocking are passed through into isothermal annealing, high temperature solid solution and oil quenching, high tempering successively Three heat treatment procedures obtain required performance；Bearing steel is heated to 800~870 DEG C when first step isothermal annealing, heat preservation 4~ Then 6h is as cold as 700~800 DEG C, 4~6h of isothermal with 3~10 DEG C/min cooling rates again, after with the cooling rate slow cooling of 20~30 DEG C/h extremely 600~670 DEG C, then with being furnace-cooled to room temperature；Second step be by the steel part for being cooled to room temperature be heated to 750~850 DEG C preheating 30~ 50min, then 1050~1060 DEG C are heated to 10~20 DEG C/min speed, keep the temperature 30~50min；After coming out of the stove oil cooling to 100~ 200 DEG C, then it is air-cooled to room temperature；Third step is to be tempered bearing steel after cooling 2~2.5 hours between 520~550 DEG C, After be air-cooled to room temperature, altogether tempering three times；Its hardness reaches 62-65HRC after processing, and the Vickers hardness at 400 DEG C of high temperature reaches To 658HV or more, it is equivalent to Rockwell hardness 58HRC or more, can meet well and work in 400 DEG C of environment.

2. a kind of preparation method for the bearing steel being resistant to 400 degree of high temperature, it is characterised in that preparation process is：

(1) smelting of steel：Suitable for vaccum sensitive stove and the double vacuum metlings of vacuum electroslag remelting；Composition quality fraction range is：C 0.75~0.90wt.%, N 0.005~0.012wt.%, Cr 4.50~5.28wt.%, Mo 3.75~4.10wt.%, V 0.56~0.80wt.%, Mn 0.30~0.34wt.%, Ni 0.21~0.26wt.%, Si 0.20~0.29wt.%, Ti≤ 0.005wt.%, P≤0.01wt.%, S≤0.008wt.%, O≤0.0009wt.%, remaining for Fe and inevitably it is miscellaneous Matter；

(2) solidification, hot forging/hot rolling technology：Above-mentioned smelting is obtained into molten steel, steel billet or steel ingot are obtained by continuous casting or molding, solidified 10min~20min is preheated at 750~850 DEG C afterwards, is heated to 1050 DEG C~1150 DEG C, hot forging or hot rolling are not less than for diameter The bar of 15mm, finish-forging or finishing temperature are not less than 900 DEG C, and furnace cooling or ash cooling are to room temperature after forging；

(3) heat treatment process：Above-mentioned forging material or stocking are passed through into isothermal annealing, high temperature solid solution and oil quenching, high tempering successively Three heat treatment procedures obtain required performance；Bearing steel is heated to 800~870 DEG C when first step isothermal annealing, heat preservation 4~ Then 6h is as cold as 700~800 DEG C, 4~6h of isothermal with 3~10 DEG C/min cooling rates again, after with the cooling rate slow cooling of 20~30 DEG C/h extremely 600~670 DEG C, then with being furnace-cooled to room temperature；Second step be by the steel part for being cooled to room temperature be heated to 750~850 DEG C preheating 30~ 50min, then 1070 DEG C are heated to 10~20 DEG C/min speed, keep the temperature 30~50min；Oil cooling is to 100~200 DEG C after coming out of the stove, Then it is air-cooled to room temperature；Third step is to be tempered bearing steel after cooling 2~2.5 hours between 510~550 DEG C, rear air-cooled To room temperature, it is tempered altogether three times；Room temperature hardness that treated can reach 63-66HRC, and the Vickers hardness at 400 DEG C of high temperature reaches To 660HV or more, it can meet well and work in 400 DEG C of environment.