Influence of austenitizing temperature on microstructure and mechanical properties of AISI 431 martensitic stainless steel electron beam welds

The relative effects of various austenitizing temperatures on microstructure and mechanical properties of electron beam welds of AISI 431 martensitic stainless steel were studied. The post-weld heat treatments consist of austenitizing the weld samples for 1 h at various temperatures, i.e., at 950 degrees C, 1000 degrees C, 1050 degrees C, 1100 degrees C and at 1150 degrees C and air cooling followed by double tempering, i.e., tempering at 670 + 600 degrees C. In the as-welded condition the microstructure contains dendritic structure with ferrite network and retained austenite in a matrix of un-tempered martensite. The prior austenite grain size increased with increase in austenitizing temperature. Parent metal grain size was coarser as compared to grain size in the weld zone in respective conditions. Retained austenite content increased with increase in the austenitizing temperature. Presence of undissolved carbides was observed in welds and parent metal austenitized up to 1000 degrees C and they dissolved at austenitizing temperature >= 1050 degrees C. Coarsening of martensite laths was observed after tempering. The martensite laths were coarser in the samples subjected to higher austenitizing temperatures. Optimum mechanical properties, i.e., strength, hardness and toughness were observed when austenitized between 1050 degrees C and 1100 degrees C followed by tempering. Austenitizing at 1150 degrees C and tempering resulted in inferior mechanical properties. The mechanism for the observed trends is discussed in relation to the microstructure, fracture features and mechanical properties. (c) 2008 Elsevier Ltd. All rights reserved.