Abstract
High temperature deformability and fracture behavior of deformation-processed high nitrogen high carbon Fe-Cr-Mn-Ni stainless steel rods were studied. The effective fracture elongation increased rapidly from 1000 °C, and reached high values (>45%) at 1100–1200 °C, accompanied by strain softening and stress serrations, supporting periodic dynamic recrystallization (DRX). Dynamically recrystallized grains were observed close to the fracture surface, suggesting that active DRX worked until its fracture. Pre-deformation-annealing of Fe-Cr-Mn-Ni stainless steel rods at 1200 °C was found to deteriorate in deformability above 1000 °C, while it enhanced ductility below 950 °C. Pre-deformation annealing had a negative effect on the deformability above 1000 °C due to the reduction of driving forces for DRX, but it exhibited a beneficial effect on the ductility at lower temperatures because of the ease of slip in large-grained structures. The fracture surface at 1250 °C exhibited intergranular fractures due to partial melting at grain boundaries, supported by the thermodynamic calculation of the solidus temperature of Fe-Cr-Mn-Ni austenite stainless steel. In this study, effective fracture elongation, defined based on the assumption that the effective gage length decreases with straining, was found to be an accurate measure of hot deformability.
Highlights
Development of high-nitrogen high-manganese stainless steels containing no or little nickel have been driven by high and unstable nickel prices [1]
Pre-deformation annealing had a negative effect on the deformability above 1000 ◦ C due to the reduction of driving forces for DRX, but it exhibited a beneficial effect on the ductility at lower temperatures because of the ease of slip in large-grained structures
In the groove-rolled Fe-Cr-Mn-Ni rod of the present study, as-cast ingots were homogenized at 1080 °C, at which the Cr2N phase was fully dissolved into the γ matrix ingots were homogenized at 1080 ◦ C, at which the Cr2 N phase was fully dissolved into the γ matrix quickly because of the lower-volume fraction (3% at 800 °C) of Cr2N (Figure 3), and instability at high quickly because of the lower-volume fraction (3% at 800 ◦ C) of Cr2 N (Figure 3), and instability at temperatures
Summary
Development of high-nitrogen high-manganese stainless steels containing no or little nickel have been driven by high and unstable nickel prices [1]. Mn and nitrogen has been proven to be successful in the production of austenitic stainless steels. In addition to stabilizing austenitic structures, nitrogen is known to reduce the stacking fault energy of austenitic stainless steels, resulting in a number of beneficial effects such as enhanced strength, fatigue resistance, and impact and fracture resistances [1,2,3,4,5]. High-nitrogen, high-carbon Fe-Cr-Mn-Ni stainless steels with high Cr contents are known to have thermal stability due to their high temperature oxidation and wear resistances [1,7]
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