1. Martensite in oil-free bearing hardened steel
Original arrangement of high carbon chromium steel: granular pearlite
Quenching + low temperature tempering: the carbon content of quenched martensite M, obviously high load bearing bearing affects the mechanical function of steel
GCr15 steel quenched M with a carbon content of 0.5% to 0.56% can achieve the strongest generalized mechanical function of failure resistance.
M: Cryptocrystalline martensite, the measured carbon content is the uniform carbon content of the sliding bearing.
2. Retained austenite in oil-free bearing hardened steel
After normal quenching, high carbon chromium steel can contain 8% to 20% Ar (retained austenite).
Ar in bearing parts has advantages and disadvantages, and the Ar content should be appropriate.
Hardness and touch fatigue life are added accordingly. If it spontaneously transforms into martensite, it will decrease after reaching the peak. The beneficial effect of Ar must be that when Ar is stable, the resistance of steel will drop sharply. Brittle.
When the shaft receives a small load: Ar undergoes a small amount of deformation, which not only reduces the stress peak, but also strengthens the deformed Ar processing and stress-strain induced martensite transformation. The increase in the amount of Ar reduces the impact on the fatigue life of the touch. When the shaft receives a large load: the larger plastic deformation of Ar and the partial stress concentration of the matrix will break, thereby reducing the life.
3. Residual stress after quenching and tempering of oil-free bearings
The increase of the residual compressive stress on the surface increases the fatigue strength (excessive residual stress may cause deformation of the parts). When the residual internal stress on the surface is tensile stress, the fatigue strength decreases.
After the bearing parts are quenched and tempered at low temperature, they still have a large internal stress.
4. Undissolved carbides in quenched steel
The amount, trace, size, and dispersion of undissolved carbides in quenched steel are affected by the chemical composition of the steel and the original arrangement before quenching and are affected by the austenitizing conditions.
When loaded (especially the carbide is non-spherical) and the matrix causes stress to gather and cracks, which will reduce the resistance and fatigue resistance.
Quenching undissolved carbides affect the function of steel
Affect the carbon content and Ar content and dispersion of the quenched martensite, thereby having an additional impact on the function of the steel.
Excessive quenching of undissolved carbides is harmful to the generalized mechanical function and failure resistance of steel.
After the bearing steel is quenched, there are a few undissolved carbides which are necessary for wear resistance to obtain fine-grained cryptocrystalline martensite. It requires less undissolved carbides (small number), small (small scale), and uniformity (the difference in size is small, And evenly distributed), round (each carbide is spherical).
Appropriately reducing the carbon content of bearing steel is one of the ways to improve the service life of parts.
5. Impurity content of oil-free bearing steel
Impurities: non-metallic impurities (acid-soluble) harmful elements such as the higher the oxygen content, it is necessary to reduce the oxygen content of the steel used. Exception: the more oxide impurities the impurity in the steel has the effect on the mechanical function and the anti-failure ability of the parts The impact is related to the type, nature, quantity, size and shape of impurities. Generally, it has the effect of reducing resistance, plasticity and fatigue life. As for bearing parts operating under high stress, the MnS dopants in steel can be wrapped due to the shape of an ellipsoid. The more harmful oxides doping has little effect on the reduction of fatigue life and may even be beneficial.