Examination of the effect of Shot-Peening Conditions on the Improvement of Fatigue Reliability of Meatl-Molded Austempered Ductile Iron.

Abstract

An examination of the effect of shot-peening (SP) conditions on the improvement of fatigue reliability of metal-molded ADI was performed with a mesoscopic observation of fracture morphology. The main results obtained were as follows: (1) The 106 endurance limit could be improved with an increase of SP strength, but the endurance limit of 1.0mmA-Sp material was as high as that of 0.8-SP material. On the other hand, the 2×107 endurance limit as not improved with SP treatment. (2) The origin of fatigue cracks of metal-molded ADI as not the pores, since the cooling rate of metal-molded ADI was slower than that of sand-molded ADI. (3) The origin of fatigue cracks was transferred from the surface to the inside with an increase of SP strength, due to the effect of compressive residual stress induced by SP treatment. (4) Although the depth affected by SP treatment of 1.0-SP material was greater than that of 0.8-SP material. The influence of SP strength on the endurance limit of metal-molded ADI was only effective up to 0.8-SP strength because of the existence of a stress gradient.