1998 Volume 84 Issue 1 Pages 79-84
The life of dies for cold working was markedly decreased by increasing stress applied to the edge of die; because the strength of materials for works was increased. It was found from an investigation of fractured waste dies which were used at high stress that fracture of dies originated at coarse primary rod-like carbides. It was confirmed that fatigue life of dies used at high stress could be evaluated with tension-compression fatigue test whose frequency was equivalent to that of practical dies. The effect of primary carbide on the fatigue life of JIS SKD11 die steels was studied on the basis of tension-compression fatigue test results. The fatigue life, N, at stress of 1.65GPa which is similar to stress applied to the edge of die decreased with an increase in the maximum width, W, of primary carbide following the equation : N=103.12-0.08W. Voids already initiated at interfaces between coarse primary carbides and matrix at extream low stress (plastic strain) of 0.3GPa (0.001%) in tensile tests.
Voids were generated at all of coarse carbides more than 8μm of width and seldom at carbides less than 2μm. Thus, it is important that coarse primary carbides corresponding to latent crack are reduced to life of dies for cold working.
