The effect of aging on heat-resistant cast stainless steels

The effect of aging on four heat-resistant cast stainless steels heat treated for various durations at 820 °C was investigated and is described in this paper. The steels were examined in terms of their microstructure and mechanical properties. Microstructural characterization of the steels revealed complex microstructures with a large number of carbide precipitates in an austenitic matrix. The as-cast materials contained carbides as clusters or networks, which were almost fully dispersed in the specimens aged for 1200 h. The σ-phase was identified in each steel grade after only 100 h of aging, although in an austenitic-ferritic grade, it was identified already in the as-cast condition. Impact toughness results revealed the embrittlement of each studied steel grade after only 100 h of aging at 820 °C. The hardness values for the steels increased slightly and almost linearly with increase in the aging time. The results of this study indicate that the formation of the σ-phase is primarily responsible for the observed embrittlement, while the increase in hardness may be explained by the formation of the σ-phase and the dispersion of the carbides. These results are presented and discussed in this paper.