Factors affecting rolling mill bearing life and control methods:

Early failure of rolling bearing forms, mainly broken, plastic deformation, wear, corrosion and fatigue, under normal conditions, mainly contact fatigue. Bearing parts failure in addition to service conditions, mainly by the hardness of steel, strength, toughness, wear resistance, corrosion resistance and oil-free bearing bushing stress state constraints. Factors affecting the performance and status of the main bronze-based bearings and control methods:

1. Martensite in hardened steel:

When the original structure of high-carbon chrome steel is granular pearlite, the carbon content of quenched martensitic steel obviously affects the mechanical properties of steel under the condition of low temperature tempering of self-lubricating hardened steel sleeve. The strength and toughness are about 0.5%, the contact fatigue life is about 0.55%, and the anti-crush ability is about 0.42%. When the carbon content of the quenched martensitic steel of GCr15 steel is 0.5% ~ 0.56%, the highest anti-failure ability can be obtained The comprehensive mechanical properties.

It should be noted that the martensite obtained in this case is cryptocrystalline martensite and the measured carbon content is the average carbon content. In fact, the carbon content in the martensite is not uniform in the micro-region, the carbon concentration around the carbide is higher than the part away from the ferritic carbide, and thus they start to undergo martensitic transformation at different temperatures, Thereby inhibiting the growth of martensite grains and microscopic appearance of a cryptocrystalline martensite. It can avoid high-carbon steel quenching prone to micro-cracks, and its sub-structure of high strength and toughness of the dislocation-like lath martensite. Therefore, it is only possible for the bearing parts to obtain the matrix with the best anti-failure ability when the medium-carbon cryptocrystalline martensite is obtained when the high-carbon steel is quenched.

2. Hardened steel in the retained austenite:

High-carbon chromium steel, after normal quenching, may contain 8% ~ 20% Ar (retained austenite). Ar bearing parts in the pros and cons, in order to pros and cons, Ar content should be appropriate. As the amount of Ar is mainly related to the austenitizing condition of quenching and heating, the amount of Ar affects the amount of carbon and the amount of undissolved carbides of quenched martensite, and it is difficult to accurately reflect the influence of the amount of Ar on the mechanical properties. To this end, the fixed austenitic conditions, the use of austenitic body thermal stabilization process to obtain different Ar content, studied the quenching low temperature tempering Ar content of GCr15 steel hardness and contact fatigue life. With the increase of austenite content, both the hardness and the contact fatigue life increase with the increase of the austenite content, and then decrease with the increase of the peak value. However, the peak Ar content is different and the peak value of hardness appears at about 17% Ar, while the contact fatigue life The peak appears at about 9%. When the test load decreases, the effect of increasing Ar content on contact fatigue life decreases. This is because when the amount of Ar is small, the effect on the strength reduction is small, and the effect of toughening is obvious. The reason is that when the load is small, a small deformation of Ar occurs, which not only reduces the stress peak but also strengthens the deformed Ar processing and stress-strain induced martensitic transformation. However, if the load is large, large plastic deformation of Ar and the substrate will locally produce stress concentration and rupture, thus reducing the life expectancy. It should be noted that the beneficial effect of Ar must be under Ar steady state, if the spontaneous transformation to martensite, the toughness of steel will be sharply reduced and embrittled.

3. Hardened steel in the undissolved carbide:

The amount, morphology, size and distribution of undissolved carbides in hardened steel are influenced not only by the chemical composition of the steel and the original microstructure before quenching but also by the austenitizing conditions, Impact study less. Carbide is a hard and brittle phase, in addition to the beneficial effects of wear resistance, bearing will (especially non-spherical carbides) and the matrix caused by stress concentration and the resulting cracks, which will reduce the toughness and fatigue resistance. In addition to its effect on the properties of steel, quenched and undissolved carbides also affect the carbon content and Ar content and distribution of the quenched martensite, which has an additional effect on the properties of the steel. In order to reveal the effect of undissolved carbides on performance, different steels with different carbon content were used, after quenching, the martensite carbon content and Ar content were the same but the content of undissolved carbides was different. After being tempered at 150 ℃, Due to the same carbon content of martensite and higher hardness, a small increase of undissolved carbides has little effect on the increase of hardness, and the collapse load reflecting the strength and toughness decreases, while the stress fatigue-sensitive contact fatigue life Obvious reduction. Therefore, excessive quenching undissolved carbide mechanical properties of steel and failure resistance is harmful. Properly reducing the carbon content of bearing steel is one of the ways to improve the service life of parts.

In addition to the number of quenched undissolved carbides on the material properties, the size, morphology, distribution also affect the material properties. In order to avoid the hazards of undissolved carbides in the bearing steel, it is required that the amount of undissolved carbides be small (small number), small (small size), uniform (small and small in size and evenly distributed), round spherical). It should be noted that a small amount of undissolved carbides is necessary after quenching of bearing steel, not only to maintain sufficient wear resistance, but also to obtain fine grain cryptocrystalline martensite. Valve import pump industrial washing machine

Residual stress after quenching and tempering:

Bearing parts after quenching and tempering, still has a greater internal stress. Residual internal stress in the parts of the two advantages and disadvantages. Steel after heat treatment, with the surface residual compressive stress increases, the fatigue strength of steel increases, whereas the surface residual stress is tensile stress, then the fatigue strength of steel decreases. This is because fatigue failure occurs when the parts are subjected to excessive tensile stress, when the surface has a larger compressive stress residual, it will offset the same value of the tensile stress, leaving the actual value of steel tensile stress decreases, the fatigue strength The ultimate value increases. When there is a large residual tensile stress on the surface, it will be superimposed with the tensile stress to be applied, so that the actual tensile stress of the steel increases obviously, even if the fatigue strength limit decreases. Therefore, the bearing parts after quenching and tempering surface residual large compressive stress, but also to improve the service life of the measures (of course, excessive residual stress may cause deformation or even cracking, should be given sufficient attention).

5 steel impurity content:

Impurities in steel, including non-metallic inclusions and harmful elements (acid soluble) content, their performance on steel tend to be mutually reinforcing, as the higher the oxygen content, the more oxide inclusions. Impurities in steel on the mechanical properties and anti-failure ability of parts and impurity type, nature, quantity, size and shape, but usually have to reduce the toughness, ductility and fatigue life.

As the inclusion size increases, the fatigue strength decreases, and the higher the tensile strength of steel, the lower the trend of increase. Oxygen content in steel increased (oxide inclusions increased), bending fatigue and contact fatigue life under high stress also will be reduced. Therefore, it is necessary to reduce the oxygen content of manufacturing steel for bearing parts that work under high stress. Some studies have shown that MnS inclusions in steel, due to their ellipsoid shape, can encroach on the more damaging oxide inclusions, so they have less or possibly a reduced beneficial effect on fatigue life reduction and are therefore wide controllable.