Correlation of austenite stability and ductile-to-brittle transition behavior of high-nitrogen 18Cr–10Mn austenitic steels

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 528; no. 24; pp. 7257 - 7266
• Main Authors: Hwang, Byoungchul, Lee, Tae-Ho, Park, Seong-Jun, Oh, Chang-Seok, Kim, Sung-Joon
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.09.2011; Elsevier
• Subjects: Applied sciences; Austenite; Austenite stability; Austenitic stainless steels; Brittle fracture; Correlation; Cross-disciplinary physics: materials science; rheology; Deformation; Deformation, plasticity, and creep; Deformation-induced martensite; Ductile brittle transition; Ductile-to-brittle transition; Exact sciences and technology; Fractures; High-nitrogen austenitic steels; Martensitic transformations; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Stability; Structural steels; Treatment of materials and its effects on microstructure and properties; Ductile-to-brittle transition; High-nitrogen austenitic steels; Austenite stability; Deformation-induced martensite; Brittle fracture; Slip plane; Mechanical properties; Empirical relation; Displacement(deformation); Plastic deformation; Secondary martensite; EBSD; Brittle-ductile transitions; High nitrogen steels; Crack propagation; Fracture toughness; Ductile brittle transition; Localized deformation; Transmission electron microscopy; Charpy impact test; Metastable state; High nitrogen steel; Martensitic transformation; Fractography
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.06.025

► In high-nitrogen austenitic steels, ductile-to-brittle transition occurs. ► Some metastable austenites in the steels are transformed to α′-martensite. ► Deformation-induced martensite transformation decreases low-temperature toughness. ► Reduction of austenite stability increases ductile-to-brittle transition temperature. Ductile-to-brittle transition behavior of high-nitrogen 18Cr–10Mn austenitic steels containing different contents of Ni, Mo, Cu as well as nitrogen is discussed in terms of austenite stability and associated deformation-induced martensitic transformation (DIMT). Electron back-scattered diffraction and transmission electron microscopy analyses of cross-sectional area of the Charpy impact specimens fractured at −196 °C indicated that the brittle fracture planes were almost parallel to one of {1 1 1} slip planes and some metastable austenites near the fracture surface were transformed to α′-martensite by localized plastic deformation occurring during crack propagation. Quantitative evaluation of deformation-induced martensite together with characteristics of true stress–strain and load–displacement curves obtained from tensile and Charpy impact tests, respectively, supported that DIMT might take place in high-nitrogen austenitic steels with relatively low austenite stability. The occurrence of DIMT decreased low-temperature toughness and thus increased largely ductile-to-brittle transition temperature (DBTT), as compared to that predicted by empirical equations strongly depending on nitrogen content. As a result, the increased DBTT could be reasonably correlated with austenite stability against DIMT.