2014 Volume 55 Issue 637 Pages 132-136
Recently, high-strength steels with over 1500 MPa in tensile strength have been manufactured by hot stamping. To decrease their coefficient of friction, the effects of die surface coating on such a parameter were investigated. The Five kinds of die coated with TiN, TiCN, CrN, TiAlN, and DLC-Si were used. The experimental tests were carried out under a dry condition using a simulation testing machine developed by the authors, and the coefficient of friction for a drawing stroke was measured. The coefficient of friction of the noncoated die increased abruptly with a stroke of 5 mm. On the other hand, the coefficients of friction of the hard-coated dies gradually increased by 10 mm. At a stroke of over 10 mm, the coefficients of friction of the noncoated and hard-coated dies finally approached 0.52. From the results of the surface analyses, the adhesion of aluminum on the die surface was observed.
