The precipitation behavior and its effect on mechanical properties of cold-rolled super-ferritic stainless steels during high-temperature annealing

The precipitation behavior, microstructure evolution and mechanical properties of a cold-rolled 27.6Cr-3.7Mo-2Ni ferritic stainless steel during high temperature annealing treatment were investigated. Experimental results demonstrated that the cold rolled microstructure was characterized by orientation-dependent heterogeneity, and many shear bands were found in the <111>//ND (normal direction) orientation grains. The elongated deformation microstructure gradually changed into equiaxed grains and three kinds of interphases including sigma-phase, chi-phase and Laves phase were observed as the annealing temperature increased from 850 to 1000 degrees C. After annealing below 1000 degrees C, the alpha-phase and chi-phase were observed to be located at grain boundaries, near the TiN particles as well as along with shear bands in grains, whereas the Laves phase distributed dispersedly in grains. After annealing at 1000 degrees C, both the sigma-phase and chi-phase were almost completely dissolved, while the nanoscale Laves phases at grain boundaries were dominant. The grain boundary Laves phase precipitation at high temperature was attributed to the Nb segregation induced by cold rolling deformation. The sigma-phase precipitation kinetics was calculated based the Johnsone-Mehle-Avrami equation, and the fastest precipitation kinetics appeared at 850 degrees C with the activation energy of similar to 176.7 kJ$mol(-1). The Vickers hardness, ultimate tensile strength and yield strength values decreased while the elongation value increased with increasing annealing temperature. The breakage pattern transformed from brittle to ductile fracture as the annealing temperature increases from 850 to 1000 degrees C. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The study investigated the precipitation behavior, microstructure evolution, and mechanical properties of a cold-rolled 27.6Cr-3.7Mo-2Ni ferritic stainless steel during high temperature annealing treatment. It was found that different interphases precipitated with increasing annealing temperature, leading to changes in hardness, ultimate tensile strength, yield strength, and fracture pattern.