Surface alloying of iron by laser melting: microstructure and mechanical properties

Abstract

Superficial laser induced melting produces non-equilibrium phases without changing the microstructure of the bulk and therefore alters specimen properties. Nitrided steels are of interest in a wide range oftechnological applications because of increased hardness and corrosion resistance as well as interesting magnetic and electrical properties. The aim of the present study was to determine the influence of nitride coatings (y’-Fe4N, ε-Fe3–2N, α″′-Fe8N, BN, AlN, and Cr2N) on the superficial alloying, microstructure, and microhardness of Armco iron melted with a continuous CO2 laser beam at a power level of 400 W Depending onmelting conditions as well as thickness and chemical composition of the coating, ferrite, martensite, austenite, γ’, or ε phases are detected at the surface of laser alloyed iron using Mossbauer spectroscopy, X-ray diffraction, and optical microscopy. The microhardness can be considerably increased depending on the microstructure and residual stresses in the surface layers.