Effects of deformation-induced martensite and grain size on ductile-to-brittle transition behavior of austenitic 18Cr-10Mn-N stainless steels |
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Authors: | Byoungchul Hwang Tae-Ho Lee Sung-Joon Kim |
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Affiliation: | (1) Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784, Korea;(2) Materials Science and Engineering Department, Pohang University of Science and Technology, Pohang, Korea;(3) Sheet Products & Process Research Group, Technical Research Laboratories, POSCO, Pohang, 790-785, Korea; |
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Abstract: | Effects of deformation-induced martensite and grain size on ductile-to-brittle transition behavior of austenitic 18Cr-10Mn-(0.3∼0.6)N stainless steels with different alloying elements were investigated by means of Charpy impact tests and microstructural analyses. The steels all exhibited ductile-to-brittle transition behavior due to unusual brittle fracture at low temperatures despite having a face-centered cubic structure. The ductileto-brittle transition temperature (DBTT) obtained from Chapry impact tests did not coincide with that predicted by an empirical equation depending on N content in austenitic Cr-Mn-N stainless steels. Furthermore, a decrease of grain size was not effective in terms of lowering DBTT. Electron back-scattered diffraction and transmission electron microscopy analyses of the cross-sectional area of the fracture surface showed that some austenites with lower stability could be transformed to α’-martensite by localized plastic deformation near the fracture surface. Based on these results, it was suggested that when austenitic 18Cr-10Mn-N stainless steels have limited Ni, Mo, and N content, the deterioration of austenite stability promotes the formation of deformation-induced martensite and thus increases DBTT by substantially decreasing low-temperature toughness. |
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