2018 Volume 59 Issue 694 Pages 221-227
The effects of hot trimming conditions on the sheared-edge quality and mechanical properties in hot stamping of ultra-high strength steel parts were examined. In hot stamping, the temperature of the parts rapidly drops during stamping, and the subsequent trimming operation is greatly influenced by the temperature. The sheared-edge quality was high above the temperature at which the martensitic transformation starts for a comparatively small clearance. The trimming temperature had a great influence on the occurrence of delayed fracture, whereas the clearance had no influence. In hot trimming, delayed fracture was prevented by decreasing the tensile residual stress and hardness near the sheared edge. The static and fatigue strengths of the parts are reduced by delayed cracks and hydrogen embrittlement, whereas the fatigue limit is unaffected. In hot trimming of thin sheets, delayed fracture tends to occur as a result of a large temperature drop.
