Improvement of strength-ductility balance of SAE 304 stainless steel by asymmetric cross rolling

Abstract

In the current research, a new technique, namely, asymmetric cross rolling used for enhancement of strength-ductility balance of SAE 304 stainless steel sheet. The microstructural evolution, texture, and mechanical properties of processed samples investigated. The strain-induced martensite fraction for the samples after 20% (34.67%), 30% (38.37%), and even 40% (40.27%) asymmetric cross cold rolling were lower than that for 10% (41.45%) deformed sample. This interesting result was due to the formation of new grains through dynamic recrystallization (DRX) after 20%, 30%, and 40% thickness reductions. The combination of asymmetric and cross cold rolling generated additional stored energy leading to the generation of recrystallized grains with the average grain size of 545 nm. The intensity of the Copper texture component along the τ-fiber reduced when the sample rolled along the transverse direction, i.e., during 20% and 40% deformation. After 30% deformation, the Brass/Copper texture ratio remarkably decreased to 0.78, which was related to the occurrence of DRX and the creation of new grains with Cube and Goss orientation. Increasing the volume fraction of martensite after 30% deformation was 10.7%, while that for 40% rolled sample decreased to 5.9%. The yield and ultimate tensile strength of 40% rolled sample was 1196.1 MPa and 1219.1 MPa, respectively, which was approximately 5.8 and 1.9 times higher than that of the initial sample, also the total elongation was high (21.1%). The 40% deformed sample exhibited enhanced strength-ductility balance. The hardness of RD–TD plane in the solution-treated sample was the minimum; however, this plane had the maximum hardness for the deformed stainless steel sheets due to the presence of stronger γ-fiber in the processed samples. By an increment of the rolling strain, the size and depth of the dimples slightly decreased but the fracture mode is still ductile. Interestingly, the number of interconnected voids remarkably reduced in the fracture surface of the 20% rolled steel.