Hot-deformation-induced structural and mechanical properties of Ce-modified SAF 2507 super duplex stainless steel
Tian Zhou, Yi Xiong, Xiao-qin Zha, Yun Yue, Yan Lu, Tiantian He, Fengzhang Ren, Ekta Rani, Harishchandra Singh, Jukka Kömi, Marko Huttula, Wei Cao
Abstract
A typical rare-earth element modified Ce-SAF 2507 super duplex stainless steel was isothermally hot-compressed to reach superior mechanic properties over its pristine and peers. Mechanical, macro- and micro-structural evolutions subjected to hot-modification were studied in detail toward an optimal hot working for the Ce-SAF2507. A dynamic softening phenomenon shows that the increase of hot deformation temperature and decrease of the strain rate were dominated by the dynamic recovery of ferrite at a high strain rate and low deformation temperature. The same phenomenon at a low strain rate but high deformation temperature was ruled by the dynamic recrystallization of austenite. These two processes determined significant phase transformations from austenite to ferrite under higher deformation temperature and strain rate. A hot deformation activation energy Q ∼406 kJ mol−1 was obtained through a unified strain-compensated constitutive equation for Ce-SAF2507. Quantitative grain size refinements further proved the above mechanisms deduced from mechanical and microscopic observations, while structure induced changes of mechanical properties were crosschecked with the microhardness. Insights of microstructure also demonstrated the existences of the Cr2N in both phases, grain boundaries, and α/γ interface. The overall deformation dynamics was explicated based on the structural and quantitative results.