The effect of single and double austenitization temperatures on the microstructure, mechanical properties, and pitting corrosion of AISI 431 electron beam welds

The relative effects of single austenitization (SA) and double austenitization (DA) temperatures on the microstructure, mechanical properties, and pitting corrosion 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 1000 and 1050 degrees C and double austenitizing at 1050 and 1000 degrees C and air cooling followed by double tempering, i.e. tempering at both 670 and 600 degrees C. The prior austenite grain size increased with an increase in austenitizing temperature from 1000 to 1050 degrees C. Grain refinement resulted after DA. Parent metal grain size was coarser as compared to grain size in the weld zone in the respective conditions. Retained austenite content increased after DA. Undissolved carbides were observed in welds and parent metal austenitized up to 1000 degrees C and they dissolved at austenitizing temperature >= 1050 degrees C. DA treatment resulted in the dissolution of most of the carbides. Coarsening of martensite laths was observed after tempering. DA after double tempering resulted in optimum mechanical properties, i.e. strength, hardness, and toughness. The pitting resistance of the DA-treated samples showed a considerable improvement over those obtained by either of the two SA treatments followed by double tempered conditions.