Abstract: Wear of trimming dies deteriorates the edge quality of DP980 steel sheets, reducing their formability. As such, wear-resistant die materials with higher hardness and toughness and protected by wear-resistant coatings are being developed. In this research, the reciprocating sliding tests were performed to evaluate the tribological performances of D2 (11.8%Cr, 61HRC), Carmo (4.5%Cr, 58HRC), Caldie (5.0%Cr, 61HRC), and TiCN coated Caldie samples in contact with a DP980 steel counterface. Uncoated Caldie exhibited higher wear resistance than D2 and Carmo due to its finer carbide size, which includes carbides smaller than 0.2μm uniformly distributed in the prior austenite grains. TiCN improved the wear resistance and run-in COF of the Caldie during the sliding wear test. Trimming tests were performed to study the damage mechanisms of the tools during the actual trimming operations which consisted of impact damage in addition to sliding wear damage. White-light optical interferometry supported by large depth-of-field optical microscopy and SEM identified the trim die wear mechanisms on the sliding planes of the upper and lower dies after 40,000 trimming cycles revealing the differences of the wear characteristics between the upper and lower dies. The damage features at the contact surfaces of the lower dies (D2 and TiCN coated Caldie) were affected by impact stresses that caused both chipping of the trim edge of D2, and partial removal of the protective coatings on the trim edge of TiCN coated Caldie.
Authors: Z. Cui, A. Rose, D.E. Green, J. Tjong, and A.T. Alpas
Keywords: Die wear; Trimming; PVD coating; AHSS; Reciprocating sliding