SKF researchers will crack the development process is divided into the following phases:
The first stage, the cracks began to expand. The critical stress intensity of the high-speed steel can be changed by heat treatment, but the absolute value of the range is not large, ~ 5MPa/m2.
The second stage is crack propagation. High-speed steel of the crack propagation velocity is also similar, as in the 10Mpa/m2 case, approximately 5 × 10-6mm / cycle. Speed ??but with larger toughness of the steel can slow down the crack extension.
The third stage, the crack is expanding rapidly. When the cracks reach this stage, the bearings will soon fail.
(3) Surface treatment processes
According to the research and analysis on the fracture toughness and other relations and material crack development process, we can see that dn value and the existence of circumferential stress, the surface treatment of high-speed steel and low carbon content of high-speed steel hardening depth of surface the change has important significance. , SKF has developed a surface treatment process can enhance the surface hardness and compressive stresses. Has the following characteristics: surface treatment of the material has good resistance to fatigue crack resistance, the second phase, the lower rate of expansion of existing cracks and hardening caused by lack of or low carbon content of the core material fracture toughness values ??higher.
SKF developed such a surface processing method including:
(1) quenching less than the ordinary high-speed steel using laser, electron beam or induction hardening methods such as local heat treatment, surface hardened layer. It should be pointed out that the lack of quenching in order to improve the fracture toughness.
(2) Chemical treatment methods, the surface hardened layer. This method includes the carbon or nitrogen to penetrate into the microstructure of common high-speed steel, or a small degree of change of carbon content.