Metallographic examination of Cryogenically treated steel weldments

Abstract

Introduction: Materials are made suitable to the requirements by subjecting them to various treatment process. Weldments, due to their heterogeneous nature, are generally treated prior to and after the welding process. Deep Cryogenic processing is a one-time, homogenous process that provides significant extension in the performance and productive life of various metallic components from brake rotors, gears, engines, machine parts, machine tools and gun barrels with more and more applications being discovered every day. The metallurgy behind cryogenic processing of high carbon steel is that it creates a large amount of fine or small carbides that precipitate uniformly throughout the lattice structure, resulting in close and fine grain structures [1,2]. This greatly improves the wear properties of metal. The martensitic phase transformation creates a metallurgically improved and stabilized alloy. Barron [3] has also attributed the improvement of the wear resistance of these tools to grain refinement besides the transformation of the retained austenite into martensite. He verified that this new mechanism would be time and temperature dependent as the tools would have to stay a long period (8 h or more of soaking) at cryogenic temperatures. Hence the deep cryogenic treatment with a larger soaking time would bring out an enhancement in mechanical properties which may be due to phase transformation or /and grain refinement. This investigation thus metallographically analyzes the behavior of steel weldments under deep cryogenic treatment.