Effect of cryogenic temperature on strain and plastic deformation evolution in impacted fractures of high manganese austenitic steel using neutron Bragg-edge imaging and electron back scattering diffraction

Jiang, L.*; Wang, H. H.*; Xu, P. G.   ; Su, Y. H.  ; Shinohara, Takenao   ; Wang, Y. W.*

High manganese austenitic steels as a cryogenic structural material are widely applied in the pressurized storage infrastructures for storing and transporting liquefied natural gas (LNG), liquefied hydrogen (LH). Considering that cryogenic impact toughness is important in predicting the service performance of high manganese austenitic steel, it is critical for analyzing residual strain and plastic deformation evolution in impacted fractures and for deeply understanding the deformation and fracture mechanisms. Here, the strain and plastic deformation evolution of impacted fractures in high manganese steel (24Mn-4Cr-0.4C-0.3Cu) were comparably investigated by neutron Bragg-edge transmission (BET) imaging and electron back scattering diffraction (EBSD) at various cryogenic temperatures. The BET results show that the residual strain 111 is negative and 200 is positive in the region with large plastic deformation near the fracture. However, 111 and 200 in the region far away from the fracture show similar distribution in the V-notched impact sample at the same temperature. With the decrease of impact temperature, the high broadening area of Bragg-edge width near the fracture gradually decreased, revealing that the local plastic strain during cryogenic impact deformation in the corresponding area decreased, which is primarily consistent in the change trend of impact toughness value obtained at various temperatures. EBSD results show evident difference in the local distribution density of 111 and 200-oriented grains in the region near the fracture after cryogenic impacting. It is suggested that the steel texture is a primary reason for clarifying the different distribution features of 111 and 200 in the region near the cryogenic impact fracture.