CN109266825B

CN109266825B - Long-life double-refining heat treatment process for high-carbon chromium bearing steel

Info

Publication number: CN109266825B
Application number: CN201811321639.4A
Authority: CN
Inventors: 曹文全; 俞峰; 许达; 徐海峰
Original assignee: Central Iron and Steel Research Institute
Current assignee: Central Iron and Steel Research Institute
Priority date: 2018-11-07
Filing date: 2018-11-07
Publication date: 2020-03-20
Anticipated expiration: 2038-11-07
Also published as: CN109266825A

Abstract

Long-life double-thin high-carbon chromium bearing steelA heat treatment process, belonging to the technical field of material heat treatment. The method comprises the following steps: the heat treatment material is high-carbon chromium bearing steel GCr15, spheroidizing annealing heat treatment, primary quenching heat treatment, primary tempering heat treatment, secondary quenching heat treatment, tertiary quenching heat treatment and secondary tempering heat treatment. The advantages that the high-carbon chromium bearing steel GCr15 can obtain a matrix structure with the grain size less than or equal to 10 grade and residual carbide with the maximum grain size less than or equal to 2 mu m after the heat treatment, and the contact fatigue life L₁₀≥5×10⁷Next, the process is carried out.

Description

Long-life double-refining heat treatment process for high-carbon chromium bearing steel

Technical Field

The invention belongs to the technical field of material heat treatment, and particularly relates to a long-service-life double-refining heat treatment process for high-carbon chromium bearing steel.

Background

The high-carbon chromium bearing steel GCr15 is widely applied to parts such as inner and outer races and rolling bodies of rolling bearings for various mechanical equipment, and the metallurgical quality and the performance after heat treatment directly determine the service performance, the service life, the reliability and the like of the bearings and even a main machine. With the development of high-end manufacturing industry, the high-speed precision machine tool main shaft bearing, the wind driven generator main shaft bearing, the high-speed railway axle box bearing and the like all require ultra-long service life and high reliability, and the high-carbon chromium bearing steel used is required to have 10⁷And the second or more ultra-long contact fatigue life.

At present, after the high-carbon chromium bearing steel GCr15 produced by adopting the vacuum degassing process is subjected to conventional quenching and tempering heat treatment, the contact fatigue rated fatigue life L under the high stress load of 4.5GPa₁₀Usually in the range of 0.5X 10⁶ sub-1.0X 10⁷Cannot meet the high-end equipment 10⁷And the service life is prolonged for more than the second time. Research shows that the contact fatigue life L of the high-carbon chromium bearing steel₁₀At 10⁷The next or less, contact fatigue life L is determined by contact fatigue fracture dominated by non-metallic inclusions in steel₁₀Up to 10⁷The residual carbides and the matrix structure in the steel play a decisive role in the next ultra-long life stage. The refinement of the residual carbide can reduce stress concentration and reduce the generation of fatigue initial cracks; the refinement of the matrix structure (crystal grains) can improve the toughness of the steel and prevent the steel from being damagedOr slow the propagation of fatigue cracks, thereby achieving an ultra-long fatigue life.

And a great deal of research work is carried out on the aspects of improving the purity of the high-carbon chromium bearing steel GCr15 and controlling non-metallic inclusions at home and abroad. Meanwhile, the method for refining the grain size of the high-carbon chromium bearing steel and prolonging the fatigue life of the bearing steel through secondary quenching, surface shot blasting and the like is also researched. However, there is no report on a method for improving the fatigue life of high-carbon chromium bearing steel by simultaneously refining the grain size and residual carbides.

Disclosure of Invention

The invention aims to provide a long-life double-refinement heat treatment process for high-carbon chromium bearing steel, which enables the contact fatigue rated fatigue life L of the high-carbon chromium bearing steel GCr15 to be under a high-stress load of 4.5GPa₁₀Up to 1.0 × 10⁷The above steps are repeated.

The present invention provides a double refining heat treatment process, i.e. refining grains and residual carbides simultaneously, thereby obtaining an ultra-long contact fatigue life. The specific steps and the technical parameters of the control are as follows:

heat treatment of the material: the high-carbon chromium bearing steel GCr15 meets the requirement of GB/T18254-2016 standard.

Spheroidizing annealing heat treatment: and (3) putting the high-carbon chromium bearing steel GCr15 steel into an annealing furnace, heating to 790-810 ℃, keeping the temperature for 2-4 hours, reducing the temperature to 745 ℃ at 15 ℃/h, reducing the temperature to 680 ℃ at 5 ℃/h, and then cooling in air.

First quenching heat treatment: and (3) placing the spheroidizing annealed high-carbon chromium bearing steel GCr15 steel component into a quenching furnace, heating to 830-850 ℃, keeping the temperature for 30-60 minutes, and then quenching in oil at 30-80 ℃.

First tempering heat treatment: and (3) putting the part subjected to the first quenching into a tempering furnace, heating to 160-180 ℃, keeping the temperature for 2-4 h, tempering, and cooling in air after tempering.

And (3) secondary quenching heat treatment: and (3) putting the part after the first tempering into a quenching furnace, heating to 850-870 ℃, keeping the temperature for 30-60 minutes, and then quenching in oil at 30-80 ℃.

And (3) quenching heat treatment for the third time: and cleaning and drying the parts subjected to the first secondary quenching, then putting the parts into a quenching furnace again, heating the parts to 830-850 ℃, keeping the temperature for 30-60 minutes, and then quenching the parts in oil at the temperature of 30-80 ℃.

And (3) second tempering heat treatment: and (3) putting the part subjected to the third quenching into a tempering furnace, heating to 160-180 ℃, keeping the temperature for 2-4 hours, tempering, and cooling in air after tempering.

After the heat treatment, the high-carbon chromium bearing steel GCr15 can obtain a matrix structure with the grain size less than or equal to 10 grade and residual carbide with the maximum grain size less than or equal to 2 mu m, and has the contact fatigue life L₁₀≥5×10⁷Next, the process is carried out.

The invention has the advantages that the structure grain size and the residual carbide grain size of the high-carbon chromium bearing steel are subjected to double refinement through a multiple quenching and tempering heat treatment process, so that the high-carbon chromium bearing steel has ultra-long contact fatigue life and high reliability.

Drawings

FIG. 1 is a graph of a double-refining quenching and tempering heat treatment process.

FIG. 2 is a graph of a conventional quenching and tempering heat treatment process.

FIG. 3 is a photograph showing the grain size after heat treatment (double refining heat treatment).

FIG. 4 is a photograph showing the grain size after heat treatment (conventional heat treatment).

Fig. 5 is a photograph of grain size residual carbides after heat treatment (double refining heat treatment).

FIG. 6 is a photograph showing grain size residual carbides after heat treatment (conventional heat treatment).

FIG. 7 is a graph of contact fatigue life P-N.

Detailed Description

The chemical composition of the high carbon chromium bearing steel GCr15 used in the specific implementation is shown in Table 1.

Firstly, spheroidizing annealing GCr15 steel, heating to 805 ℃, preserving heat for 3h, reducing the temperature to 745 ℃ at 15 ℃/h, reducing the temperature to 680 ℃ at 5 ℃/h, and then cooling in air. And processing the spheroidizing annealed bar into a thrust piece sample with the diameter of 52mm (outer circle) multiplied by 20mm (inner circle) multiplied by 5mm (height). And selecting 20 GCr15 thrust piece samples to carry out double-thinning heat treatment.

Firstly, placing a spheroidizing annealed GCr15 thrust piece sample into a quenching furnace, heating to 840 ℃, preserving heat for 30 minutes, then placing the sample into oil at 30 ℃ and carrying out primary quenching heat treatment; putting the sample subjected to the first quenching into a tempering furnace, heating to 170 ℃, keeping the temperature for 3 hours, then air-cooling, and carrying out first tempering heat treatment; putting the sample after the first tempering into a quenching furnace, heating to 860 ℃, preserving heat for 30 minutes, and then putting the sample into oil at 30 ℃ for second quenching heat treatment; cleaning and drying the sample after the second quenching, putting the sample into a quenching furnace again, heating the sample to 840 ℃, preserving the heat for 30 minutes, and then putting the sample into oil at 30 ℃ for third quenching heat treatment; and finally, placing the sample subjected to the third quenching into a tempering furnace, heating to 170 ℃, keeping the temperature for 3 hours, air-cooling, and performing second tempering. The specific process is shown in figure 1.

And another 20 GCr15 thrust piece samples are taken and treated according to the conventional quenching and tempering heat treatment process of GCr15, and the specific process is shown in figure 2. And grinding the samples treated by the two heat treatment processes, and then performing a contact fatigue test. Contact fatigue test conditions: the maximum contact stress is 4.5GPa, the rotation speed of a testing machine is 1500rpm, the testing temperature is 25 ℃, the lubricating medium 4010 lubricating oil and the test steel ball GCr 15.

The grain size of the high-carbon chromium bearing steel GCr15 after double-refining heat treatment is 10-grade, and a typical metallographic photograph is shown in FIG. 3 (a). The grain size after the conventional heat treatment is grade 8, and a typical metallographic photograph is shown in fig. 4 (b). The grain size of the high-carbon chromium bearing steel GCr15 is obviously refined by double-refining heat treatment.

The maximum grain size of the residual carbides of the high-carbon chromium bearing steel GCr15 after double-refining heat treatment is 1.56 μm, the number of carbides per square micron is 0.046, and a typical scanning electron micrograph is shown in figure 5 (a). The maximum grain size of the carbide after the traditional heat treatment is 2.68 μm, and simultaneously, adherent carbides exist, the maximum grain size reaches more than 5 μm, the number of the carbides per square micron is 0.375, and a typical scanning electron micrograph is shown in figure 6 (b). The grain size of the residual carbide of the high-carbon chromium bearing steel GCr15 is obviously refined and the quantity is also obviously reduced by double refining heat treatment.

The results of the contact fatigue life test of the high carbon chromium bearing steel GCr15 after heat treatment are shown in Table 2 and FIG. 5. The test shows that: rated contact fatigue life L after double-refining heat treatment₁₀Up to 5.90X 10⁷Sub, median life L₅₀Up to 12.65X 10⁷Second, the slope parameter was 2.47. Contact fatigue rated life L after conventional heat treatment₁₀Is 1.07X 10⁷Sub, median life L₅₀Is 3.34 × 10⁷Second, the slope parameter is 1.66. Contact fatigue life L of GCr15 after double refining heat treatment₁₀And L₅₀About 5 times and 4 times after conventional heat treatment, respectively. The slope parameter double-refining process is also larger than the traditional process, which shows that the double-refining process also has higher reliability.

TABLE 1 chemical composition/wt.% of test steels, balance Fe

TABLE 2 contact fatigue life after Heat treatment

Claims

1. A long-life double-refining heat treatment process for high-carbon chromium bearing steel is characterized by comprising the following specific steps and controlled technical parameters:

(1) heat treatment of the material: the high-carbon chromium bearing steel GCr15 meets the standard requirement of GB/T18254-2016;

(2) spheroidizing annealing heat treatment: placing the GCr15 steel of the high-carbon chromium bearing steel into an annealing furnace, heating to 790-810 ℃, preserving heat for 2-4 hours, reducing the temperature to 745 ℃ at 15 ℃/h, reducing the temperature to 680 ℃ at 5 ℃/h, and then cooling in air;

(3) carrying out quenching and tempering heat treatment according to the following sequence:

heating temperature of the first quenching is 830-850 ℃, preserving heat for 30-60 minutes, and then performing oil quenching at 30-80 ℃;

tempering and heating for the first time at 160-180 ℃, keeping the temperature for 2-4 h, and then air cooling;

heating temperature of the second quenching is 850-870 ℃, and after heat preservation is carried out for 30-60 minutes, oil quenching is carried out at 30-80 ℃;

carrying out oil quenching at 30-80 ℃ after the third quenching heating temperature is 830-850 ℃ and the heat preservation is 30-60 minutes;

tempering and heating at 160-180 ℃ for the second time, keeping the temperature for 2-4 h, and then air cooling;

after the heat treatment, the high-carbon chromium bearing steel GCr15 obtains a matrix structure with the grain size less than or equal to 10 grade and residual carbide with the maximum grain size less than or equal to 2 mu m, and the contact fatigue life L₁₀≥5×10⁷Next, the process is carried out.