Influence of microshot peening on surface layer characteristics of structural steel

The influence of microshot peening on the surface layer characteristics of the structural steel was investigated. Shot peening is one of the surface treatments and it is a mechanical surface treatment widely used in automotive industry to enhance fatigue life and surface layer characteristics of mechanical parts. In this process, the surface is collided repeatedly with small spherical media called shot, making overlapping indentations on the surface. Thus, the surface layer characteristics of mechanical parts such as gear and spring can be greatly improved by shot peening. In a conventional shot peening process, particle used for shot peening consists of small spheres. It is made of high carbon cast steel and the diameter is in the range from 0.6 to 2.0 mm. More recently, a new type of particle has been developed to enhance peening effect. The new media, called fine-particle or microshot, is smaller and harder than the conventional one. They are made of cemented carbide or amorphous alloy and those diameters are in the range from 0.03 to 0.15 mm. The aim of this paper is to present the enhanced peening effect for the structural steel using microshot. Surface roughness, compressive residual stress, hardness and wear resistance in the peened workpieces were measured. The effect of processing temperature on the surface layer characteristics was also examined. The use of hard microshot such as cemented carbide and amorphous alloy was found to cause a significantly enhanced peening effect for the structural steel. It was also found that the surface of the workpiece peened by microshot was sufficient for wear resistance.