Factors Affecting Roller Bearing Life and Its Control
The early failure modes of the Roller Bearing are: rupture, plastic deformation, wear, corrosion, fatigue under normal conditions are mainly contact fatigue main internal factors: hardness, strength, toughness, abrasion resistance, corrosion resistance, internal stress state Outside of service conditions)
1. martensite in hardened steel
High-carbon chrome steel Original organization: granular pearlite
Quenching + low temperature tempering: quenched martensite M carbon content, significantly affect the mechanical properties of steel
GCr15 steel quenching M carbon content of 0.5% to 0.56% can get the strongest anti-failure ability of the comprehensive mechanical properties.
M: cryptocrystalline martensite, measured carbon content is the average carbon content.
2. Residual austenite in hardened steel
High-carbon chrome steel after normal quenching, can contain 8% to 20% Ar (residual austenite).
Ar parts of the Roller Bearing parts have advantages and disadvantages, Ar content should be appropriate.
Ar% ↑ hardness, contact fatigue life are increased, to reach the peak and then reduce the beneficial role of Ar must be in Ar stable state, if the spontaneous conversion to martensite, will significantly reduce the toughness of steel And brittle.
When the Roller Bearing load is small: Ar occurs a small amount of deformation, both the reduction of the stress peak, but also to the deformation of the Ar processing and stress-induced martensitic transformation induced martensitic transformation, Ar increased the impact of contact fatigue life When the load is larger: Ar larger plastic deformation and the base will produce localized stress concentration and rupture, so that life is reduced
3. Uncrystallized carbides in hardened steel
The number, shape, size and distribution of undissolved carbides in the quenched steel are affected by the austenitizing conditions by the chemical composition of the steel and the influence of the original structure before quenching.
When the load (especially carbide is non-spherical) and the matrix caused by stress concentration and cracks, which will reduce the toughness and fatigue resistance.
Effect of Quenched Unsaturated Carbide on Steel
Affect the quenched martensite carbon content and Ar content and distribution, which has an additional impact on the performance of steel.
Quenching the undissolved carbides too much is harmful to the comprehensive mechanical properties and failure resistance of the steel.
Roller Bearing steel quenching after a small amount of undissolved carbides is necessary to wear fine grain fine crystal stealth martensite requirements of less dissolved carbide less (small number), small (small size), uniform (size difference between each other is very small, And evenly distributed), round (each carbide is spherical).
Properly reduce the carbon content of Roller Bearing steel is one of the ways to improve the service life of parts.
4. Residual stress after quenching and tempering
Roller Bearing parts after quenching low temperature tempering, still has a large internal stress.
The residual stress is increased and the fatigue strength increases (the excess residual stress may cause the deformation of the part). When the residual stress is tensile stress, the fatigue strength is reduced.
5. Impurity content of steel
Impurities: non-metallic inclusions harmful elements (acid soluble) such as the higher the oxygen content, the more impurities in the steel impurities in the mechanical properties and resistance to the impact of the impact of impurities and impurity type, nature, quantity, size and The shape of the relevant usually have to reduce the toughness, plasticity and fatigue life of the role of the Roller Bearing parts for high stress work must reduce the oxygen content of steel manufacturing exception: steel in the MnS inclusions due to the shape of the ellipsoid can be wrapped harm Large oxide inclusions may or may not be beneficial to reduce fatigue life.
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