High-Temperature Deformability of a Fe-Cr-Mn-Ni Austenite Stainless Steel with High Nitrogen and High Carbon Contents

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.

Recycling Zr-Nb-Sn-Fe Scrap in Casting of Nuclear-Grade Alloy Ingots and Its Effects on Mechanical Performance and Integrity

“…4. The higher oxygen content revealed by EDS spectra from crack initiation site suggests that the higher oxygen content due to the reduction of Fe 2 O 3 by Zr and dissolution of oxygen into matrix is responsible for the low deformability It is interesting to note that the strength increases with increasing fraction of scrap, which can be attributed to the increase of oxygen content [11], [12]. The ductility decreased slightly with increase of scrap fraction.…”

“…Oxide contamination of scrap may increase the oxide content in newly cast alloy after remelting, which may deteriorate the properties. Some scrap cake was mixed with Fe 2 O 3 particle to investigate the possible inclusion of iron oxide from steel storage containers during storage and handling of scrap [11]. In order to investigate the possible effects of impurities introduced from the scrap, some model alloys without scrap addition were cast with the intentional addition Fe and Fe 2 O 3 to simulate and examine the most probable impurities of Fe and O.…”

“…The addition oxygen is known to increase the stability of hexagonal α phase, causing the reduction of the thickness due to enhanced nucleation of α phase [8]- [10]. Interstitial atoms such as oxygen [8]- [10] and carbon [11], [12] are known to increase the strength of Ti and Zr, but it decreases the deformability and ductility if the oxygen content exceeds 1800 ppm [13]- [15].…”

Mechanical Performance and Microstructural Evolution of (NiCo)75Cr17Fe8Cx (x = 0~0.83) Medium Entropy Alloys at Room and Cryogenic Temperatures

“…The grain size including twin boundaries was measured to be 11.3 μm, 6.4 μm and 1.9 μm for three alloys, respectively. The decrease of grain size with increase of carbon content in (NiCo)75Cr17Fe8Cx MEAs is attributed to grain boundary pinning effect of carbide particles [25][26][27]. A higher dislocation storage and the lower recovery due to carbon atoms and carbides may have contributed to grain size refinement [27].…”

“…Klimova et al [25] found that the solubility of interstitial carbon in fcc solid solution increases with a decrease of Cr content. The decrease of Cr content from 20 at.% to 6.3 at.% was reported to increase the carbon solubility from 0.36 at.% to 1.61 at.% in CoCr x FeMnNi (x = 1, 0.25) at 1000 • C. Carbon atoms are also known to strengthen the steels [26] and HEAs [25,27,28] through solution strengthening, precipitation and/or grain-size strengthening. In this study, mechanical properties and microstructural evolution of non-equiatomic quaternary Alloy-600-type CoNiCrFe with and/or without carbon addition at room and cryogenic temperatures were studied.…”