Investigation on the Effects of Sheet Thickness and Deformation Temperature on the Forming Limits of Boron Steel 22MnB5

To study the effects of temperature and thickness on forming limits of boron steel 22MnB5, Nakajima tests have been performed for the steels with thickness of 1.0mm and 1.4mm at 600℃ and 700℃, respectively. The forming limit curve (FLC) of the steel at 700℃ is higher than that at 600℃, and the FLC of the steel with 1.4mm is higher than that of the steel with 1.0mm. With increasing the forming temperature, the strain rate sensitive exponent m increases, and it results in a longer Swift’s diffuse instability phase and greater limit strains. The effect of thickness on yield path is different from the case at room temperature, due to the half angle of pointed Vertex, θ₀, which increases with increasing of the thickness, and then the limit strains increase.