抄録
Deep dent defects on the automobile parts produced by hot die forging have become problems because the dents were disadvantageous to the strength of these parts. The dents may have been probably caused by scales of hot billets. The behaviour of these thick scales in hot die forging was experimentally analyzed in this paper. The dents gradually grew bigger and changed the shapes every forging shot before the scales periodically transferred to the workpiece. The deep dent defects frequently formed at the part of the workpiece with large plastic deformation. Additionally, it was found the scales consisted of the oxide/non-oxide layers derived from the hot billet materials by microscope observation and electron probe micro analysis. It was estimated that the thicker scales were formed by layered pick-up and adhesion under severe tribological conditions. Adjusting preform shape and controlling lubrication were proposed to decrease the defects.
