1997 Volume 83 Issue 5 Pages 335-340
To improve the stretch-flangeability of a high strength TRIP-aided dual-phase (TDP) sheet steel, the effects of forming temperature, forming rate and clearance on the stretch-flangeability were investigated. Warm hole-punching at 150-200°C and successive warm hole-expanding at about 150°C increased considerably the stretch-flangeability. The warm hole-punching minimized void initiation at matrix/second phase interface, work hardening and a depth of damage layer at hole surface by suppressing the strain-induced transformation in an early stage. Also, it increased the volume fraction of untransformed retained austenite, which contributes to large stretch-flangeability. The warm hole-expanding improved the localized ductility due to the transformation induced plasticity. When a clearance between punch and die was about 10%, the largest stretch-flangeability was obtained with the minimum surface damage on hole-punching. Punching rate influenced hardly upon the stretch-flangeability, although it did somewhat on surface damage.
