CN114603079A

CN114603079A - Carbide refining method for flat-bottom bearing ring

Info

Publication number: CN114603079A
Application number: CN202210231831.4A
Authority: CN
Inventors: 王建国; 刘�东; 杨艳慧
Original assignee: Northwestern Polytechnical University
Current assignee: Anhui Hanzheng Bearing Technology Co ltd
Priority date: 2022-03-10
Filing date: 2022-03-10
Publication date: 2022-06-10
Anticipated expiration: 2042-03-10
Also published as: CN114603079B

Abstract

The invention discloses a method for refining carbides of a flat-bottom bearing ring, relates to the field of refining all carbides of a bearing, and particularly relates to a method for refining carbides of a flat-bottom bearing ring, which comprises the following steps: heating a bearing bar, performing cross rolling perforated pipe type forging, performing air cooling after forging the bearing bar into a pipe, preserving heat for 1-3 h, and then cooling the pipe to room temperature in a furnace; cutting the cross-piercing tube by cutting at room temperature, and performing axial closed rolling forming forging on the cut sample at room temperature to obtain a semi-finished product of the bearing ring; and processing the semi-finished product of the bearing ring obtained after the axial closed rolling forming forging to the required size to form a flat-bottom bearing ring finished product. In the step of pipe forming, the annealing replaces the original cooling mode, so that the hardness is reduced, the cutting performance is improved, the structure is adjusted, and the preparation is made for the next room temperature cutting. Compared with the traditional processing flow, the process saves the annealing process after forging, reduces the heating times, reduces the cost and saves the time.

Description

Carbide refining method for flat-bottom bearing ring

Technical Field

The invention relates to the field of refining all carbides of bearing rings, in particular to a method for refining carbides of a flat-bottom bearing ring.

Background

The bearing has very wide application in the fields of high-grade car manufacturing, heavy equipment and other heavy equipment and the fields of high-speed rail transportation, wind power generation, aerospace and other emerging industries, is one of the most important key basic parts of a machine, and is called as a joint of high-end equipment. There are two main forms of bearing failure: dominant contact fatigue failures and secondary wear failures. Bearings typically operate in harsh environments of repeated cyclic contact fatigue stress and sliding wear and are required to withstand static and cyclic loads, and bearings having high frictional wear resistance, plastic deformation resistance, high rotational and dimensional accuracy and simultaneously having long service life and high reliability are required. With the rapid development of China, more and higher requirements are made on bearings. As a raw material for bearing fabrication, the performance requirements for the required bearing steel have also increased. Therefore, the improvement of the quality of the bearing steel is an urgent need for the development of the bearing industry in China.

Through the development of years, bearing steel has formed various series such as high-carbon chromium bearing steel, high-temperature bearing steel and the like. The bearing steel yield of China is explosively increased in recent years, and the gap between the bearing steel quality and the foreign developed countries is also reduced. By introducing foreign advanced equipment and learning production technology, the production level is greatly improved, and the quality of bearings produced by some enterprises is close to the international quality standard. The certification of international famous bearing companies such as FAG, SKF, NSK, Timken and the like is obtained in sequence by multiple production enterprises such as Xingchen special steel, Beiman special steel, Bao steel special steel and the like, and becomes a material supplier of the enterprises. In terms of production level and quality of the whole industry, China has a certain gap with the international advanced level. Compared with the quality of foreign bearing steel products, carbide is a more prominent problem.

The quality evaluation factors of the bearing steel are mainly two, one is the purity of the bearing steel, and the other is the carbide in the bearing steel. An important factor in determining high quality bearing steel is the uniformity of carbides in the bearing steel, mainly the uniformity of the shape, distribution and size of carbides in the steel. Because of the advantages of high-carbon chromium bearing steel in the aspects of comprehensive performance, price and the like, the high-carbon chromium bearing steel becomes the steel grade with the largest use amount in bearing steel. The high-carbon chromium bearing steel belongs to hypereutectoid steel and has a considerable amount of carbides, and the particle size and the distribution state of the carbides have important influence on the wear resistance and the fatigue life of the bearing.

The main causes of bearing failure are fatigue and wear, while carbide shape and distribution are important contributors to bearing life. The carbides are hard and brittle and large particles of carbides can cause stress concentrations under the service conditions of the bearing steel. When the stress concentration exceeds the strength of the material, the defects of fatigue spalling, microcracks and the like can appear, the use of the bearing is influenced, the service life of the bearing is reduced, and even the bearing directly fails.

Carbides are mainly classified into liquated carbides, ribbon-like carbides, and network carbides. Among the three carbides of high carbon chromium bearing steel, carbide liquation is the most harmful one. Firstly, because the liquated carbide has large particles and high hardness and brittleness, the surface layer is easy to peel off, and the abrasion of the bearing can be accelerated in the using process; secondly, the liquated carbide is a root cause for generating fatigue cracks in the crystal grains, so that the fatigue life of the bearing part is greatly reduced, and the damage to the bearing is equivalent to that of the brittle inclusions in the steel; meanwhile, when the bearing part is subjected to heat treatment, it is a fuse causing the generation of quench cracks. The harm of the banded carbides to the bearing steel is mainly shown in the following steps: in the quenching and heating process of the bearing steel, the band-shaped structure can increase the overheating sensitivity of the steel and is easy to crack; the microhardness difference between the high-carbon band and the low-carbon band is increased, so that the contact fatigue life is reduced, and the size stability of a finished part is influenced by the nonuniformity of the components and the performance; when the bearing steel is annealed, a uniform pearlite structure is difficult to obtain due to the influence of the zonal carbides; the structure and hardness of the bearing steel may also become non-uniform after quenching due to the presence of band-shaped carbides. The existence of the net-shaped carbide has two main hazards to the bearing steel: (1) cracks occur when the bearing steel is subjected to a grinding process. (2) When the network structure is serious, the network structure is difficult to remove when being subjected to spheroidizing annealing treatment, and even the network structure is remained in a quenching structure to generate cracks; even if no cracks are generated during quenching, the net-like carbides will be the origin of fatigue cracks during later use. In the hypereutectoid steel, a large amount of carbides exist necessarily, particularly, network carbides, and the problem of the shape and distribution of the carbides is solved in the production process. At present, with the application of advanced smelting equipment and process level, the problems of liquation and banding of carbide are basically eliminated, and the problem that the level of reticular carbide exceeds the standard is still outstanding, which is a common problem encountered by domestic bearing steel manufacturers at present.

Aiming at the problem that the level of the current reticular carbide generally exceeds the standard, more researches are carried out at home and abroad, and certain achievements are obtained. By way of summary, the main measures currently used to avoid the generation of a network are: (1) controlling the content of Cr and other elements in the bearing steel within a certain horizontal interval; (2) the segregation degree of the steel is reduced as much as possible, and the segregation degree is reduced to the minimum as much as possible; (3) taking a measure of low-temperature finish rolling in the rolling process; (4) finishing rolling at high temperature, and then performing quick cooling; (5) if the net carbon is severe, a normalizing treatment can be adopted. The normalizing process can effectively improve the net carbon degree, but the adoption of the process not only leads the increase of working procedures to be complicated, but also causes the problem of uneven carbide granularity, so that enterprises basically do not adopt the process any more. In order to ensure that carbides in bearing steel are uniformly and finely distributed, a form of matching forging and heat treatment is mostly adopted, and at present, two schemes are mainly adopted: the first solution is to control the cooling rate after forging the bearing ring. The proposal is that the forged steel is rapidly cooled and rapidly passes through a carbide precipitation temperature interval, thereby strongly inhibiting the precipitation of carbides and improving the distribution condition of the carbides.

A bearing ring structure fine homogenization rolling control and cooling control method is researched in 2013 by Qiandongsheng, and the specific process comprises the following steps:

forging the ring blank at 950-1050 ℃.

And rolling into bearing ring under the conditions of deformation amount controlled at 30-60%, deformation speed controlled at 1.1-1.5m/s and deformation temperature controlled at 800-850 deg.c.

Thirdly, the hot-rolled bearing ring is immersed into cooling water of 60-80 ℃ to be cooled to 400-500 ℃, and then the hot-rolled bearing ring is taken out and is cooled to room temperature by using a fan to blow air.

The second solution is to add a heat treatment process after forging, and to control the process parameters, cooling mode or perform multiple heat treatments to obtain uniformly distributed fine carbides.

A forging and cold control process for manufacturing a bearing ring by GCr15 in the Reynolds construction in 2010 is researched, and the specific flow is as follows: finishing finish forging at the temperature of 850-.

When the cooling rate is controlled after forging, the cooling method and the cooling medium are required, and the practicability is limited to a certain extent. When the mode of increasing the heat treatment flow after forging is adopted, the efficiency is reduced, the cost is improved, the energy consumption is increased, and the period is prolonged due to the increase of the number of fire. The heat treatment method and medium are also limited.

Disclosure of Invention

In order to solve the problems, the invention provides a method for refining the carbide of the flat-bottom bearing ring, which adopts the heat treatment and forging process with less fire number and short period, improves the efficiency, reduces the energy consumption, shortens the period, adopts a reasonable heat treatment process, is easy to operate and reduces the requirements on a cooling mode and a cooling medium.

The invention discloses a method for refining carbides of a flat-bottom bearing ring, which comprises the following steps of:

firstly, heating a bearing bar to 950-1050 ℃, performing cross rolling perforated pipe type forging, after forging the bearing bar into a pipe, air-cooling to 750-850 ℃, preserving heat for 1-3 h, and then cooling the pipe to room temperature in a furnace;

secondly, cutting the cross-rolled perforated pipe at room temperature, and performing axial closed rolling forming forging on the cut sample at room temperature to obtain a semi-finished bearing ring;

and thirdly, processing the semi-finished product of the bearing ring obtained after the axial closed type rolling forming forging to the required size to form a flat bottom type bearing ring finished product.

Preferably, the skew-piercing tube forging of the bar in the first step is specifically: the method comprises the steps of placing a bar and a top on a cross rolling puncher, adjusting the distance between rollers, the distance between guide plates, the forward extension amount of the top and the reduction amount of the top, driving the bar to rotate forward under the rotation of the rollers, and enabling the top to penetrate through a bar core in the forward process of the bar so that the bar is deformed into a seamless pipe.

Preferably, in the skew rolling perforation tube type forging of the bar, the distance of a roller is 55-60mm, the distance of a guide plate is 50-55mm, the forward extension of a vertex angle is 5-30mm, the reduction is 10-15%, and the diameter of a top is 30-6-mm.

Preferably, the axial closed type rolling forming forging is carried out on the sample in the second step, and the method specifically comprises the following steps: fixing the cut sample on a lower die, embedding a bulge for rolling a groove with a required shape on the sample on the working surface of an upper die facing the sample, wherein the bulge is connected with the upper die in a rolling manner, the lower die continuously rotates at a certain angular speed, the upper die keeps a certain inclination angle and continuously descends at a certain speed, and the ratio of the sample height before the upper die is forged to the sample height after the upper die is the axial deformation degree.

Preferably, in the second step, the sample is axially closed rolled, formed and forged, the axial deformation degree is 40-60%, the feeding speed of the upper die is 5-7mm/s, and the angular speed of the lower die is 0.8-1.2 rad/s.

Or preferably, the bearing bar is a GCr15 bearing bar.

In the step of pipe forming, the annealing replaces the original cooling mode, so that the hardness is reduced, the cutting performance is improved, the structure is adjusted, and the preparation is made for the next room temperature cutting. Compared with the traditional processing flow, the process saves the annealing process after forging, reduces the heating times, reduces the cost and saves the time.

The invention uses axial closed rolling forming forging, on the basis of ensuring the basic molding of the ferrule, and with large deformation, breaks crystal grains and large carbide blocks, plays the roles of refining the crystal grains and uniformly distributing the carbide, improves the properties of the product such as strength, hardness, contact fatigue and the like, and prolongs the service life. The size of the ring is basically formed after the axial closed type rolling forming forging, the ring can be put into use only by simple processing, the workload of lathes is reduced, and the cost and the time are reduced.

The whole process of the invention can be completed by only one fire, compared with the traditional processing flow, the invention greatly reduces the energy consumption and shortens the period in the aspect of heat treatment. Furnace cooling and air cooling are adopted in the whole heat treatment process, requirements on cooling media and cooling modes are low, operation is convenient, and practicability is high.

Drawings

FIG. 1 is a schematic view of a bearing bar after it has been swaged into a tube by cross rolling a perforated tube.

Fig. 2 is a schematic view of a tube cut.

Fig. 3 is a schematic diagram of the structure of the sample after cutting.

FIG. 4 is a schematic diagram of a semi-finished bearing ring formed by axially closed rolling and forging a sample.

FIG. 5 is a schematic view of the heat treatment of the present invention.

Figure 6 is a metallographic picture at 200 x magnification of GCr15 bearing steel without the treatment according to the invention.

Figure 7 is a metallographic picture at 200 x magnification of GCr15 bearing steel after treatment according to the invention.

FIG. 8 is a schematic cross-sectional view of an upper mold during axial closed-type roll forming forging.

Detailed Description

The invention discloses a carbide refining method for a flat-bottom bearing ring, which comprises the following steps:

secondly, cutting the cross-piercing tube by cutting at room temperature, and performing axial closed rolling forming forging on the cut sample at room temperature to obtain a semi-finished product of the bearing ring;

The first step of performing skew rolling perforation tube type forging on the bar specifically comprises the following steps: the method comprises the steps of placing a bar and a top on a cross rolling puncher, adjusting the distance between rollers, the distance between guide plates, the forward extension amount of the top and the reduction amount of the top, driving the bar to rotate forward under the rotation of the rollers, and enabling the top to penetrate through a bar core in the forward process of the bar so that the bar is deformed into a seamless pipe.

In the process of carrying out skew rolling perforation tube type forging on the bar, the distance between rollers is 55-60mm, the distance between guide plates is 50-55mm, the forward extension of the vertex angle is 5-30mm, the reduction is 10-15%, and the diameter of the top is 30-6-mm.

In the second step, the axial closed rolling forming forging of the sample specifically comprises the following steps: fixing the cut sample on a lower die, embedding a bulge for rolling a groove with a required shape on the sample on the working surface of an upper die facing the sample, wherein the bulge is connected with the upper die in a rolling manner, the lower die continuously rotates at a certain angular speed, the upper die keeps a certain inclination angle and continuously descends at a certain speed, and the ratio of the sample height before the upper die is forged to the sample height after the upper die is the axial deformation degree. The position of the bulge is determined by the shape and the position of the groove on the sample, and the effect of the bulge is mainly that the mold is in rolling contact, so that the service life of the mold is prolonged.

In the second step, the sample is axially rolled and forged in a closed type, the axial deformation degree is 40-60%, the feeding speed of an upper die is 5-7mm/s, and the angular speed of a lower die is 0.8-1.2 rad/s.

The bearing bar is GCr15 bearing bar.

Example (c):

the material is spheroidizing annealed GCr15 bearing steel bar with the diameter of 65mm and the length of 180 mm. And (3) performing cross rolling on the punched pipe at 1000 ℃ to form a pipe, then performing air cooling to 820 ℃, preserving heat for 2 hours, and then performing furnace cooling to room temperature. Cutting at room temperature and performing axial closed rolling forming forging.

The forging parameters of the cross-rolled perforated pipe are as follows: the forging temperature is 1000 ℃, the roller distance is 57mm, the guide plate distance is 63mm, the front extension of the top is 30mm, the reduction is 12%, and the diameter of the top is 35 mm.

The axial closed type rolling forming forging technological parameters are as follows: the axial deformation degree is 55 percent, the feeding speed of the upper die is 6mm/s, and the angular speed of the lower die is 1.1 rad/s.

Core samples of the blank before and after the axial closed type rolling forming forging are taken for metallographic observation, and metallographic pictures are shown in fig. 6 and 7.

The experimental comparison chart shows that: as can be seen from FIG. 6, the samples which are not treated by the method have large carbides, the maximum size of the samples reaches 25 mu m, and the large carbides are distributed in a chain shape, so that the product performance is seriously influenced. The carbides in the sample of FIG. 7 treated by the method are small in size, the sizes are below 7 mu m, the carbides are distributed in a dispersed manner, and the carbides are not distributed in a chain shape. The material performance is improved.

Claims

1. A method for refining carbides of a flat-bottom bearing ring is characterized by comprising the following steps of:

2. The method for refining the carbide of the flat-bottom bearing ring according to claim 1, wherein the step of performing cross-piercing tube forging on the bar in the first step comprises the following steps: placing the bar and the top on a cross rolling piercing mill, adjusting the distance of a roller, the distance of a guide plate, the forward extension amount and the reduction amount of the top, and driving the bar to rotate and advance under the rotation of the roller;

during the forward process of the bar, the top penetrates through the core of the bar, so that the bar is deformed into a seamless pipe.

3. The method for refining the carbide of the flat-bottom bearing ring according to claim 2, wherein in the skew rolling and piercing tube type forging of the bar, the distance between the rollers is 55 to 60mm, the distance between the guide plates is 50 to 55mm, the forward extension at the apex angle is 5 to 30mm, the reduction is 10 to 15%, and the diameter of the plug is 30 to 60 mm.

4. The method for refining the carbide of the flat-bottom bearing ring according to claim 2, wherein the step of forging the sample by axial closed-type rolling forming comprises the following steps: fixing the cut sample on a lower die, embedding a bulge for rolling a groove with a required shape on the sample on the working surface of an upper die facing the sample, wherein the bulge is connected with the upper die in a rolling manner, the lower die continuously rotates at a certain angular speed, the upper die keeps a certain inclination angle and continuously descends at a certain speed, and the ratio of the sample height before the upper die is forged to the sample height after the upper die is the axial deformation degree.

5. The method for refining the carbide of the flat-bottom bearing ring according to claim 4, wherein in the second step of forging the sample by axial closed-type rolling, the axial deformation degree is 40-60%, the feeding speed of the upper die is 5-7mm/s, and the angular speed of the lower die is 0.8-1.2 rad/s.

6. The method of carbide refinement of a flat bottom bearing ring according to any one of claims 1 to 5, characterized in that said bearing bar is a GCr15 bearing bar.