Variation in the surface properties of high chromium iron components due to laser irradiation and shot blasting

Abstract

Mainly tensile residual stresses are generated at the surface of cast and heat-treated high chromium iron due to laser action. Here, maximum residual stresses were noted at the edge of the melt zone, whereas they occurred in the central portion in the hardened (without fusion) zone. The highest residual stresses are generated in the hardened zone, such that σx = 2140 and 450 N/mm2 in the cast and heat-treated irons respectively. Laser hardening of heat-treated iron produces a large number of cracks, these being accompanied by a reduced residual stresses level. Preheating to 400°C with an optimum hardened zone structure enables cracking to be avoided. The subsequent effect from a shot stream forms cold work hardened layers in which the tensile stresses are altered to compressive stresses. The hardened layers depth and residual stresses distribution type along the surface of blades used in shot blasters is determined by the shot attack angle.