Development of delayed cracking evaluation method for meta-stable austenitic stainless steels

Meta-stable austenitic stainless steel can be susceptible to delayed cracking after forming processes. Conventionally, multi-stage circular-cup tests have been used to evaluate delayed cracking of austenitic stainless steels, which are often affected by the edge state of a circular blank. In this paper, a new method of evaluation for delayed cracking based on a square-cup test is proposed to overcome the limitation of the conventional test method. Several stainless steel grades were formed by square dies with various corner radii and the propagation time of delayed cracking was measured on each sample. A square blank rotated 45 degrees from the punch shape can make an excessive compression forming mode as in a multi-stage cupping test. Forming limit strain to avoid delayed cracking on each stainless steel grade can also be derived by combination of experiments and FE simulations.