Overlapping tracks processed by TIG melting TiC preplaced powder on low alloy steel surfaces

Abstract

An overlapping composite track coating was produced on a steel surface by preplacing a 0·5 mm thick layer of TiC powder and then melting using a tungsten inert gas torch of constant energy input. The influence of the overlapping operation on preheating of the substrate, the dissolution of TiC particulates and the subsequent depth and hardness of the composite layer was analysed. The melt microstructure consisted of both undissolved and partially dissolved TiC particulates, together with a variety of morphologies and sizes of TiC particles precipitated during solidification. Preheating, resulting from the overlapping operation, occurred, producing additional melting of the TiC particulates and deeper melt depths but with a reduced volume fraction of TiC precipitates in the subsequent tracks. A maximum hardness of over 800 HV was developed in the composite layer. The high hardness was unevenly distributed in tracks melted at the initial and final stages, while it varied across the melt depths in other tracks.