Effect of restoration on hot ductility of high alloy and duplex stainless steels

Abstract

The effect of restoration on the hot ductility of two high alloy austenitic stainless steels and one ferritic–austenitic stainless steel was investigated by means of hot rolling and stress relaxation testing. Cracking tendency was assessed on the basis of the length of the cracks formed. It was found that the recrystallisation kinetics of the high alloy steels is relatively slow, so only partial softening can occur between rolling passes. In the ferritic–austenitic steel the restoration is fairly fast, so softening can be completed between hot rolling passes. The cracking tendency of the steels in the as cast condition increases with increasing pass strain and temperature, but it is negligible in rolling of the steels in the as wrought condition and also minimal in rolling of the as cast steels when using a small strain of 0.1 in the first pass. On the basis of these results, it can be concluded that the cracking problems in these steels are present in the cast structure only. The hot ductility of even partially recrystallised material is perfectly adequate. Hot ductility improves nearly independently of the degree of static recrystallisation, which indicates that ductility is controlled mainly by the grain or phase sizes, not by recrystallisation itself.