The effect of laser energy density on the microstructure, residual stress and phase composition of H13 steel treated by laser surface melting

Abstract

The effect of laser energy density on the microstructure, residual stress and phase composition were investigated of H13 steel treated by laser surface melting. The microstructure in the molten zone (MZ) displays a hypoeutectic microstructure consisting of fine lath martensite, retained austenite, carbides; the hardened zone (HZ) consists of lath martensite, retained austenite and carbides; the heat-affected zone (HAZ) consists of ferrite, a few lath martensite, retained austenite, and many undissolved carbides. Increasing laser energy density, the microstructure of the MZ is coarsened, and the lath martensite decreases. Moreover, the minimum micro-strain (0.179) appears at the bottom of the MZ, and the maximum one appears at the top of the MZ (0.371). When the laser energy density is 110 J/mm2, the ferrite in the HZ completely transformed into austenite, but there is a few undissolved carbides. Residual compressive stress of the HZ increases with the increasing laser energy density. The maximum residual compressive stress of 1403.4 MPa can be achieved when the energy density is 120 J/mm2.