Effect of W, Mo and V on the Various Properties of High-C, High-Cr Die Steel (SKD 1)

Abstract

High-C, high-Cr cold die steel (SKD 1) is widely used for punching dies and appreciated as an abr asion-resisting and a material non-deformable due to heat treatment. Lately, necessity for promoting productivity of motor or transformer core materials due to increased demands needs to further improve die life of this steel. Based on the above reason, the effect of W, Mo and V was investigated on such various properties of SKD 1, which contained the behavior of hardness, micro-structure, hardenability, distortion ratio due to heat treatment, toughness and wear resistance. Main results obtained were as follows:
(1) By addition of Mo and W to SKD 1, as-quenched hardness was increased at lower temperatures and decreased at higher temperatures. On the other hand, the addition of V showed the inverse effect.
(2) The addition of W, Mo and V increased the resistance to temper-softening of quenched specimens. This effect was in the following order: Mo>W>V.
(3) Hardenability of SKD 1 was improved by addition of these alloying elements, but the effect of Mo was much remarkable.
(4) V-contained specimens were comparatively insensitive to changes of distortion ratios due to quenching temperature.
(5) Decomposition of retained austenite due to tempering appeared in one or two stages, influenced by chemical composition of specimens. By observation on the dilatation of specimens, it was deduced that the addition of W developed the decomposition of retained austenite in the first stage of tempering, and the combined addition of Mo and V depressed this tendency.
(6) Wear resistance was improved by addition of W, Mo and V, but especially the effect was the strongest with W and the weakest with Mo.