Laser metal deposition of high Cr white iron powder: The effect of pre-heat and laser scan speed on microstructure

Abstract

High Cr white irons are commonly used in a wear resistant parts. Using high Cr white iron as a deposited material presents opportunities in repair, fabrication of high wear resistant parts, and surface coating with superior wear resistance. The aim of this paper was to investigate the effect of substrate pre-heat and laser scan speed on the microstructure and hardness of laser metal deposited high Cr white iron. Controlling the key processing parameters plays a crucial role to achieve a crack free deposited layer with a refined microstructure. Especially, with the high hardness and brittle properties of high Cr white irons, any rise in tensile residual stress may produce micro-cracks in the clad layer. The crack sensitivity, microstructure, elemental composition, phases, and microhardness were analyzed. Interestingly, no micro-cracking was observed in the clad layer for all combinations of substrate pre-heat temperatures and laser scan speeds. The general structure formed was a dendritic primary austenite in a matrix of M7C3 carbide eutectic. A very fine microstructure was achieved for high scan speeds and lower pre-heat temperatures, due to the very rapid cooling rates. The hardness associated with the very fine microstructure was 635 HV.