An Experimental Investigation on Rate Sensitivity of Fracture-Mechanical Characteristics in 304 Austenitic Stainless Steel under Bending Deformation

摘要

It is considered that the martensitic transformation in austenitic stainless steel is responsible for its high fracture toughness. A mechanism for fracture mechanical characteristics in the steel at higher rate of deformation might become quite complicated because a quick temperature rise may suppress the martensitic transformation as well as thermal softening. An investigation on fracture-mechanical characteristics of austenitic stainless steel at the higher rate and its rate sensitivity is indispensable. Recently, J -integral of 304 austenitic stainless steel is determined by three-point bending tests at various deflection rates. However, the tests carried out on small specimens might derive some errors for its evaluation because the plane strain condition is not ensured for J -integral. Additionally, the validity of the measured J -integral is not confirmed by other fracture parameters and it is obvious that measured value does not become a critical value of J -integral. In this study, J -integral of the steel is evaluated at different deflection rate by three-point bending tests on larger specimens. As a result, a higher value of J -integral is obtained compared with previous investigation on smaller specimens at the same normalized deflection rate. Additionally, the results indicates that the relationship between value of J -integral and normalized deflection rate is roughly a linear function in a semi-logarithmic plot in the range of normalized deflection rate from 4×10~(?4) to 10.5/s. The obtained values of the stretch zone width (SZW) are suitable for observation of a positive rate sensitivity of J -integral. Thus, the validity of the results for J -integral is confirmed.