Fracture Characteristics of Super Duplex Stainless Steel after Hot Tensile Testing

Abstract

Abstract This study’s temperature range of hot tensile testing is 1000–1200 °C, which is consistent with ordinary industrial hot working temperatures. The fractography of super duplex stainless steel S32750 after hot tensile testing is investigated with Optical Microscopy and Scanning Electron Microscopy, and Electron Back-scatter Diffraction and Transmission Electron Microscopy study hot deformation behaviors of the necking area. The results reveal that ~1050–1150 °C is the optimal hot working temperature range regarding hot ductility and cracking sensitivity. The micro-voids nucleate at the ferrite-austenite interphase boundaries following the Kurdjumov-Sachs (K-S) or Nishiyama-Wasserman (N-W) orientation relationship at 1000 °C. Therefore, a quasi-cleavage fracture forms along the interphase boundaries. At the temperature range 1050–1150 °C, a uniform distribution of fracture surface is formed, and the highest Reduction in Area appears at 1150 °C. Dynamic phase transformation occurs with the formation of secondary austenite at ferrite grain boundaries at 1200 °C, which results in an intergranular fracture surface morphology.