Development of Microstructural Heterogeneity in 304 LN Austenitic Stainless Steel: Effect of Temperature and Strain

• Published in: Journal of materials engineering and performance 2022-11, Vol.31 (11), p.9050-9059
• Main Authors: Kundu, Amrita, Field, David P., Chandra Chakraborti, Pravash, Raut, Parvej
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Engineering Design; Materials Science; Quality Control; Reliability; Safety and Risk; Technical Article; Tribology
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-022-06946-7

The grain scale dynamic interaction of dislocations with the deformation induced martensites and twins, improving the strength, ductility and formability, in 304 LN austenitic stainless steel was examined at 28 and 350 °C through microstructure mapping using electron back scatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) during interrupted tensile tests. Greater deformation induced martensites and twins form at 28 than 350 °C in the grains having higher Schmid factors. The larger geometrically necessary dislocation (GND) density, measured by EBSD, validates the excellent balance of strength and ductility at 28 than 350 °C. The rate of increase of GND density with strains and temperatures is not singular and can be explained by higher strain hardening, low dislocation cross-slip and dynamic recovery. The heterogeneity in GND distribution is greater at 28 °C due to presence of martensite, twins, refinement of the co-planar slip band spacings and formation of shear bands, fragmenting the grains with strains improving the work hardening. Finer austenite grains sustain larger GND density with temperatures and strains. Thus, GNDs are responsible for forest hardening (dissipative strain gradient strengthening) and generation of back stress (energetic strengthening) more at 28 than at 350 °C.