Experimental Determination and Theoretical Prediction of Limiting Strains for ASS 316L at Hot Forming Conditions

In the present work, the austenitic stainless steel 316L is used for determining the forming limit diagrams (FLDs) at hot forming conditions. Firstly, the theoretical prediction of flow stress was done using Johnson-Cook and modified Zerilli-Armstrong (m-ZA) constitutive equations at three test temperatures (750, 825 and 900 degrees C). It was found that the m-ZA model displayed better predictability of flow stress. Additionally, Hill 1948 and Barlat 1989 yielding functions have been formulated, and it was found that Barlat 1989 displays better-yielding behavior predictability at all considered temperatures. Further, the Nakazima test has been used to find the experimental FLD. The limiting strains of the material displayed an improvement of approximately 57% with an increase in temperature from 750 degrees C to 900 degrees C. The Marciniak-Kuczynski (M-K) model has been used for theoretical prediction of FLD and it was found that the combination of Barlat 1989 function with m-ZA model displayed the best FLD prediction ability at all the considered temperatures with an error of approximately 5%. Further, the limiting dome height, surface strain and thickness distribution have been found at all the testing temperatures. The fractographic study revealed a ductile type of failure for all the specimens at all the temperatures.