Comparison of forming and fracture limits of cold rolled high-strength austenitic stainless steels

Forming and fracture limits of two metastable AISI 301LN high-strength austenitic stainless steels were studied. One of the alloys was cold rolled for additional strengthening. Hydraulic bulge testing was employed in the stretch forming experiments. Marciniak-type in-plane tests and tensile tests were carried out to study the limit strains in the deep drawing region. Laser-marked grids were used to measure the surface strains. In stretch forming both alloys failed by fracture, showing no signs of local necking. In the deep drawing region both failed by local necking and the fracture direction was inclined to the rolling direction. The forming limit could be predicted by Hill's criterion for the non-cold rolled alloy. For the cold rolled alloy the forming limits in the deep drawing region were much lower, indicating a rather flat forming limit curve.