MICROSTRUCTURAL EVOLUTION DURING SOLIDIFICATION OF AUSTENITIC STAINLESS-STEEL WELD METALS - A COLOR METALLOGRAPHIC AND ELECTRON-MICROPROBE ANALYSIS STUDY

Structural evolution during solidification of austenitic stainless ste el welds plays a crucial role in solidification cracking and microsegr egation. Currently, there is no unambiguous method available to study the solidification mechanism in detail. The present investigation was undertaken to explore the potential of color metallography for reveali ng solidification structures. Weld composition was altered by adding v arying amounts of nitrogen such that its location with respect to the phase diagram is moved in a specified direction. The controlled variat ions in the solidification mechanism thus brought about were studied m etallographically, using Beraha's etchant and electron microprobe anal ysis. Metallographic studies complemented by electron probe microanaly sis demonstrated color metallography to be a highly useful, simple, an d reliable technique for revealing solidification structures. Color et ching enables the quantitative estimation of high-temperature phases i n the ferritic-austenitic mode of solidification. It also reveals the three-phase reaction mechanism in the (L + delta + gamma) region in de tail. Ln fully austenitic structures, color etching reveals the growth patterns of cell structures and the effective interface area where im purities are expected to segregate. (C) Elsevier Science Inc., 1997.