The tension compression fatigue fracture morphology of low alloy HT250 with different surface roughness is shown in the figure.
Figure (a) (b) shows the 30x morphology of tension compression fatigue fracture surface of low alloy HT250 with different surface roughness. It can be seen from the figure that the fatigue fracture surface of two different surface roughness is black, rough, and there is no obvious light source area and propagation area. In figure (a) (b), obvious river patterns and fatigue cracks can also be seen (solid frame in the figure). Figure (c) (d) shows 500X morphology of tension compression fatigue fracture of low alloy HT250 with different surface roughness. It can be seen from the figure that there are obvious tearing edges and smooth cleavage surfaces (solid line arrow in the figure). Figure (E) (f) shows 1000x morphology of tension compression fatigue fracture of low alloy HT250 with different surface roughness. It can be seen from the figure, Fatigue bands appear on tension compression fatigue fracture surfaces of two different surface roughness (solid frame in the figure).
It can be seen from the figure that the surface roughness value Ra of low alloy HT250 is 0.3-2.5 μ M, different surface roughness has no significant effect on the tensile compressive fatigue results of low alloy HT250. This shows that the surface roughness of gray cast iron sample is ra = 0.3-2.5 μ M, the surface roughness has no obvious effect on the tensile compressive fatigue test results of gray cast iron, and its fatigue strength mainly depends on the material itself. In order to speed up the test progress, the working section of gray cast iron fatigue test samples in the later stage does not need sandpaper grinding, and the original surface can be used.