Effect of combined addition of N and C on high-temperature deformation behavior of UNS S32101 type lean duplex stainless steels

Abstract In this paper, hot deformation behavior of Febalance-21Cr-4.5Mn-1.5Ni-0.3Mo-0.225N (in wt%) duplex stainless steel (UNS S32101 type DSS) and modified S32101 DSS containing 0.165 wt% N and 0.107 wt% C was investigated through hot compression tests in the temperature range of 800–1000 °C. As a result, it was found that (C+N)-added S32101 was more resistant to high-temperature cracking than normal S32101 containing only N. The hot deformation cracking was initiated at the precipitates formed at the ferrite–austenite interphase boundary, and the main precipitate of (C+N)-added S32101 was Cr23C6, and that of normal S32101 was Cr2N. TEM analyses on the precipitates formed at the ferrite–austenite interphase boundary revealed that obvious crystallographic orientation was not developed at both Cr2N–ferrite and Cr2N–austenite interfaces for normal S32101 DSS. In contrary, for (C+N)-added S32101 DSS, it was found that Cr23C6 was fully-coherent to the austenite phase. Thus, it is considered that this coherent Cr23C6 precipitation in the (C+N)-added S32101 DSS contributed to superior resistance to the high-temperature cracking.