Factors affecting bearing life and its control

China Bearing Network believes that the early failure modes of rolling bearings mainly include: cracking, plastic deformation, wear, corrosion and fatigue. Under normal conditions, it is mainly contact fatigue. Main intrinsic influencing factors: hardness, strength, toughness, wear resistance, corrosion resistance, internal stress state (outside service conditions).

1. Martensite in hardened steel
High carbon chromium steel original structure: granular pearlite
Quenching + low temperature tempering: quenching martensite M carbon content, which obviously affects the mechanical properties of steel
The carbon content of GCr15 steel quenching M is 0.5% to 0.56%, and the comprehensive mechanical properties with the strongest failure resistance can be obtained.
M: cryptocrystalline martensite, the measured carbon content is the average carbon content.

2. Retained austenite in hardened steel
High carbon chromium steel may contain 8% to 20% Ar (residual austenite) after normal quenching.
The Ar in the bearing parts has advantages and disadvantages, and the Ar content should be appropriate.
The hardness and contact fatigue life of Ar%↑ increase with the peak value, and then the beneficial effect of reducing Ar must be under the stable state of Ar. If it is spontaneously transformed into martensite, the toughness of steel will be drastically reduced. And embrittlement.
When the load of the bearing is small: Ar is slightly deformed, which reduces the stress peak, and strengthens the deformed Ar processing and stress-strain induced martensite transformation. The influence of the increased amount of Ar on the contact fatigue life is reduced. When the load is large: the large plastic deformation of Ar and the local body will locally cause stress concentration and break, thus reducing the life.

3. Undissolved carbides in hardened steel
The amount, morphology, size and distribution of undissolved carbides in hardened steel are affected by the austenitizing conditions due to the chemical composition of the steel and the original microstructure before quenching.
When the load (especially the carbide is non-spherical) and the matrix cause stress concentration and cracks, the toughness and fatigue resistance are lowered.
Quenching of undissolved carbides affects the properties of steel
Affects the carbon content and Ar content and distribution of quenched martensite, which has an additional effect on the properties of steel.
Excessive quenching of undissolved carbides is detrimental to the overall mechanical properties and failure resistance of the steel.
A small amount of undissolved carbides after quenching of the bearing steel is necessary for wear resistance. Fine grained cryptocrystalline martensite is required. The amount of undissolved carbides is small (small quantity), small (small size), and uniform (the sizes are very small, And evenly distributed), round (each carbide is spherical).
Properly reducing the carbon content of bearing steel is one of the ways to improve the service life of parts.

4. Residual stress after quenching and tempering
After quenching and low temperature tempering, the bearing parts still have large internal stress.
When the surface residual compressive stress increases, the fatigue strength increases (excessive residual stress may cause deformation of the part). When the residual internal stress is tensile stress, the fatigue strength is lowered.

5. Impurity content of steel
Impurities: non-metallic inclusions harmful elements (acid soluble), such as the higher the oxygen content, the more oxide inclusions, the influence of impurities in the steel on the mechanical properties and the failure resistance of the parts and the type, nature, quantity and size of the impurities and The shape is usually related to the reduction of toughness, plasticity and fatigue life. For bearing parts working under high stress, the oxygen content of the steel must be reduced. The MnS inclusions in the steel can be wrapped in an ellipsoid shape. Large oxide inclusions have little or even beneficial effect on fatigue life reduction.https://www.supplyforever.com/

High carbon chromium bearing steel

      What are the grades, uses and characteristics of high carbon chromium bearing steels? The bearing network will be introduced in detail for everyone.

       High carbon chromium bearing steels have high contact fatigue strength and wear resistance. Many grades are fully hardened steels such as GCr15 GCr15SiMn, GCr15SiMo, and GCr18Mo. However, since some bearings require good toughness in the core and high hardness on the surface, a hardened bearing steel such as GCr4 has been developed.

       1 GCr15 (fully hardened steel) GCr15 is a typical steel grade of high carbon chromium bearing steel, which has high hardness, wear resistance and contact fatigue strength after quenching and tempering. Its hot workability and workability are good, the hardenability is moderate, but the weldability is poor. GCr15 has a large white point sensitivity, but this defect can be eliminated in bearings that are vacuum degassed. It is used to manufacture rolling bearing rings with wall thickness ≤12mm and diameter ≤250mm, or to manufacture cones, cylinders, spherical rollers and all sizes of needles with diameter ≤22mm. It can also be used to make molds, gauges and woodworking tools as well as mechanical parts with high elastic limit and high fatigue strength.

       2 GCr15SiMn (highly hardened steel) improves the content of silicon and manganese on the basis of GCr15 steel, so the hardenability, elastic limit and wear resistance are better than GCr15. The rolling bearing parts produced therefrom should not be used above 180 °C. It is used for the manufacture of rolling bearing rings with wall thickness >12mm, outer diameter >120mm, steel balls with diameter >50mm and cones, cylinders, spherical rollers and all sizes of needles with diameter >22mm. Other uses are the same as GCr15.

       3 GCr15SiMo (highly hardened steel) increases the silicon content based on GCr15 and adds molybdenum. It has high hardenability, good wear resistance, high fatigue strength and good overall performance. It is suitable for the manufacture of rolling bearing rings and steel balls, rollers and the like in a large size range.

       4 GCr18Mo (high-hardenable steel) adds molybdenum with a mass fraction of 0.15%~0.25% on the basis of GCr15, and increases the content of each, so the hardenability and wear resistance are improved. The lower bainite austempering can be performed to achieve hardness and wear resistance similar to martensite quenching, and the impact, fracture toughness and flexural strength of the steel are improved, thereby improving the overall mechanical properties and life of the steel. A rolling bearing ring with a wall thickness of up to 20 mm can be produced, and the size range of the rolling bearing member is also expanded.

       5 GCr4 (restricted hardened steel) GCr4 is a low-hardenability rolling bearing steel. It has the properties of GCr15 fully hardened bearing steel and low carbon alloy carburized steel after being heated by volumetric tip and surface quenched and tempered. After quenching, the surface hardness is high, the surface resistance is good, the fatigue resistance is good, the core hardness is only 35~40HRC, and the toughness is good and impact resistant. It is mainly used to manufacture rolling bearing rings and rollers of various sizes and loads.https://www.supplyforever.com/