Abstract
Recently, the difficulty in improving in hot- and warm-forging die life is an important problem because of the reduction in forging process cost. The major factor affecting die life is wearing. To solve the problem posed by wearing, some types of surface treatment are applied to dies. The most popular surface treatment is nitride treatment. Now the use of a hard coating to deal with high bearing stress has been increasing. To evaluate these different surface treatments, pin-on-disk and Ogoshi wearing tests are normally used as general tests. However, they can not deal with hot- and warm-forging conditions. Thus, we developed a new die damage test that simulated the actual forging process reported in our previous paper. In this study, we investigated the effect of surface treatment on the wearing of a die prepared by hot and warm forging, using our new test. We confirmed that a nitride layer improves wearing resistance because of the wearing rate reduction effect of the nitride layer. Thus, if the nitride layer used is sufficiently, wearing resistance will be good. The effect was excellent for hot-forging die steel that had a relatively low strength at high temperature. In the case of matrix high-speed tool steel that had an initially high hardness and a relatively high softening resistance, the effect of hard coating was excellent.
