Effect of the Conditions of Laser Hardening on the Initiation and Propagation of Fatigue Cracks in Notched Specimens

Abstract

UDC 620.194 Laser hardening is widely used for the strengthening of elements of machines and mechanisms, first of all, in order to enhance their surface hardness, wear resistance, and resistance to fatigue fracture. The effect of laser heating on changes in the structure and properties of metals and alloys was studied mainly on smooth specimens and specimens with smooth notches or fillet junctions. At the same time, the efficiency of laser hardening of articles with acute notches or cracks has seldom been considered [1, 2]. In this case, laser hardening does not always lead to the desired results because, as a rule, a clearly pronounced structural inhomogeneity appears in the zone of stress concentration, and, hence, the fatigue characteristics of an article depend on the spatial location of the crack tip with respect to locally hardened metal and the residual thermal stresses arising in the course of hardening. In the present work, we consider the effect of laser hardening on the time to fatigue crack initiation in specimens with acute notches and on the rate of crack growth depending on its location relative to the zones of hardened low-alloy chromium-molybdenum-vanadium steel.