Defects such as valleys, scratches, and cracks on the surface of the parts that are microscopically uneven are prone to stress concentration under the action of alternating loads, and the machine tool generates and aggravates fatigue cracks, resulting in fatigue damage to the parts.
The chilled layer on the surface of the part can hinder the appearance or expansion of cracks and improve the fatigue strength of the part. Machine tool but the chill layer is too deep or too hard, the machine tool is prone to small cracks and peeling, but will reduce the fatigue strength, so the degree of chill and the depth of the chill layer should be appropriate.
When the residual tensile stress of the surface layer and the tensile stress generated by the working load are superimposed on the strength of the material, fatigue cracks will occur on the surface of the machine tool parts and the fatigue strength will be reduced. The residual compressive stress of the surface layer of the machine tool parts can offset the tensile stress imposed by the working load, delay the expansion of fatigue cracks, and improve the fatigue strength of the parts. Therefore, for machine tool parts working under alternating loads, the surface of the machine tool generally needs to have a high residual compressive stress.
Effects on Surface Corrosion
The surface of the part with a large surface roughness value has a larger contact area with the corrosive medium, and the more corrosive gas or liquid adsorbed on the surface, it is easy to cause chemical corrosion. At the same time, the corrosive medium is easy to accumulate in the valley, and electrochemical corrosion occurs between the peaks and valleys, causing electrochemical corrosion. The deeper the valley, the more serious the corrosion.
The residual stress on the surface of the parts will cause stress corrosion under the working stress state. If there are cracks, it will increase the sensitivity of stress corrosion, so it will reduce the corrosion resistance of the parts.