A Study on Surface Durability of Plasma Case-Hardened Sintered Powder Metal Rollers. Influences of Shot Velocity and Peening Time on Surface Durability.

Abstract

The purpose of this study is to investigate the influence of shot peening on surface durability of sintered powder metal rollers under a sliding-rolling contact condition. The compressive residual stress, the hardness and the surface roughness of the rollers increased and the pores near the surface of those were deformed by the shot peening. The failure mode of the rollers was mainly spalling. The failure depth agreed almost with the depth where the amplitude A(τyz/HV) of the ratio of the orthogonal shear stress to Vickers hardness became maximum. The surface durabilities of the shot-peened rollers were lower than that of the unpeened roller in these experiments. While, the spalling cracks propagated from the sharp notches of the pores deformed by the shot peening. In addition, it can be considered that the shear stress below the contact surface of the shot-peened rollers increases, since the increase of the surface roughness by the shot peening results into the increase of the frictional force between the rollers. Therefore, it could follows from this that the mild shot peening without sharp deformed pore and too large surface roughness should be selected in order to improve the surface durability of the sintered rollers.