Some analysis on stress and strain limit for necking and fracture during forming of some HSLA steel sheets

This paper deals with the development of stress based forming limit diagram and fracture limit diagram from the experimentally determined strain values for different stress or strain ratios for three HSLA steel sheets, namely HSLA steel sheet with 1.6 mm thickness, microalloyed steel sheet of 1.2 mm thickness and carbon–manganese steel sheet of 1.4 mm thickness. Here, the forming and fracture behaviour of the above steels have been related with the mechanical properties and microstructure of steels. It is observed that carbon–manganese steel shows better formability in tension–tension and plane strain regions. The carbon–manganese steel, which exhibits high normal anisotropy and pancake type of microstructure, is highly found suitable for drawing operation. A good correlation between the void size and the strain ratios derived from Mohrʹs circle to the mean strain, namely (γ12/ɛm, γ23/ɛm and γ13/ɛm) have been found from the present investigation.