The effects of ausforming on variant selection of martensite in Cr-Mo steel

Abstract

The effects of ausforming on variant selection of martensite in Cr-Mo steel were investigated. The non-ausformed martensite and martensite ausformed at 850°C and 750°C were analyzed. Blocks were elongated in a single direction in the non-ausformed martensite specimens, however, blocks were elongated in multiple directions in ausformed martensite specimens. EBSD analyses indicated that non-ausformed martensite specimens contained only a single packet in a single γ, but that ausformed martensite specimens contained four packets in a single γ. The sizes of the blocks and packets decreased with ausforming. In situ observations revealed that blocks were formed only from γ grain boundaries in non-ausformed martensite specimens. In contrast, in the ausformed γ grains, sub-grain boundaries were observed, and martensite blocks were formed from γ grain boundaries as well as sub-grain boundaries. The blocks were not developed parallel to the slip band. The elongation of the blocks was stopped at sub-grain boundaries; as a result, packet size was considered to be smaller.