MICROSTRUCTUR AND MICROHARDNESS OF LASER CLADDING Ni BASED ON COLD ROLLED STEEL

Abstract

A study is reported of the laser cladding of a nominal composition of Ni 5 wt% Al on coldrolled low carbon steel (0.16 wt% C), using a high power continuous CO2 laser. The severerolled microstructure of steel was changed considerably at the heat affected zones under allspecific energies. The cladded coatings showed the presence of ɣ solid solution and β(NiAlFe) phases. Sound metallurgical bonding with absence of porosity and cracks wasobserved between the substrate and the clad coat at specific energy higher than 80 J/mm2.The ferrite and pearlite microstructure of the substrate was changed to martensite at the regionadjacent to the clad interface. It followed by large grains of austenite/ferrite and pearlite(grain growth zone), fine grains of austenite/ferrite and pearlite (recrystallization zone) andvery small zone of relatively small change of cold structure (recovery zone). The last zonewas confirmed by micro hardness as a recovery zone.This investigation confirms clearly the possibility of formation different structures of graingrowth, recrystallization and recovery at the laser heat affected cold rolled low carbon steel.The observed results suggest the developing of a new technique to obtain tentativefunctionally graded material.