At present, automobiles are developing towards light weight, comfort, solidity, high power, compact structure, durability, good acceleration performance and high reliability. In addition, due to the advancement of electronic control technology, automobiles are also developing in the direction of practical performance such as low energy consumption, simplicity and convenience, and strong operability. Therefore, as an important part of automobile support, rolling bearings must adapt to this trend.
During the service process of the automobile bearing, the rolling element and the surface of the ferrule must bear a lot of pressure on the unit area, which can be up to 5000N/mm2 by calculation. In addition to rolling and sliding during the operation of the bearing, in addition to being subjected to high frequency, alternating In addition to the contact stress, it is also affected by centrifugal force.
According to literature records, the main failure modes of automobile bearings are spalling, pitting, adhesion, strain, fracture, loss of precision, excessive vibration and noise, etc. Therefore, the performance of bearing steel has the following requirements:
①High purity.
② low oxygen content.
③High hardness and wear resistance.
④Good dimensional stability.
⑤ Sufficient compressive strength and deformation resistance.
⑥Good process performance.
Bearing steel is one of the important special steel varieties. Its quality and performance largely reflect the metallurgical level of a country. Automobile bearing steel accounts for about 40 percent of the annual output of bearing steel, and the amount is very large.
The life and reliability of automotive bearings are of course related to the initial design, processing, lubrication, installation and maintenance, but raw materials are the key.
It can be seen from the above that among the major components of the automobile bearing assembly, except that the cage is changed from the original stamping steel to the popular nylon material (such as injection-molded PA66 plus 30 percent GF) and the seals are more often made of rubber materials ( In addition to ACM plus SPCC, NBR plus SUS430), the rolling elements and inner and outer rings of automobile bearings in my country are widely used in such high-carbon chromium-containing bearing steels containing wC=0.95 percent 1.05 percent , wCr=1.40 percent 1.65 percent , In order to improve the hardenability to meet the needs of changes in the wall thickness of the parts, increasing the Mo content can develop a series of high hardenability high carbon chromium bearing steels:
For example, 100Cr6, 100CrMo in Germany, SKF2, SKF3 in Sweden, 52100.3, 52100.4 in the United States, SUJ2, SUJ3, SUJ4, SUJ5 in Japan, etc., are suitable for martensitic quenching, and also suitable for bainite quenching of ultra-thick-wall bearing parts , there are slight differences in the chemical composition between them, in fact, these steel grades can be regarded as variants of GCr15.
Although its variety is relatively simple, it is also the most demanding variety in structural steel (gear steel, bearing steel, spring steel, non-quenched and tempered steel, cold heading steel).
The most critical thing is to improve the purity of steel and strictly reduce the content of trace elements such as O, S, Ca, N, Ti, etc., and to control the defects that may be caused in the process of metallurgical products including smelting, casting, rolling, forging, etc. Smelting processes such as vacuum degassing, electroslag remelting, and out-of-furnace refining are adopted.
It is an indisputable fact in the industry that reducing the oxygen content can significantly prolong the fatigue life of the bearing. The following figure shows the relationship between the oxygen content and the relative life of the bearing. In the national standard GB/T 18254-2002, the O content of high carbon chromium bearing steel is clearly stipulated: die casting steel Less than or equal to 15ppm, continuous casting steel Less than or equal to 12ppm, and in actual production with the development of metallurgical equipment and technology The control is more stringent , the lowest level can reach 5ppm.
In addition, the standard or technical agreement has relevant restrictions on the smelting method, non-metallic inclusions, segregation, decarburization layer, low magnification structure, microstructure, carbide inhomogeneity, surface quality, dimensional tolerance, etc. And bearing manufacturers must strictly test and manage when steel enters and leaves the factory.
It should be added that, in addition to the vast majority of rolling bearings, only the crankshaft bearing bush, connecting rod bush, piston bushing, guide seat for shock absorber, gearbox reverse gear bushing, etc. are sliding bearings, which do not involve Heat treatment is mainly formed by powder metallurgy sintering plus rolling. The material is generally made of steel with wC Less than or equal to 0.15 percent on the back (such as 08Al), and the main bush is an alloy layer (such as Al-Sn20Cu or common tin-based, lead-based, copper-based or aluminum-based bearing alloys).
