Microstructures and Mechanical Properties of Sintered and Hot-Forged High-Carbon High-Vanadium Tool Steels

Abstract

Microstructures of steel powders containing 3.79 to 6.62% C, 16.48 to 37.55% V and 1% Cr, atomized by spraying water or argon gas, have been investigated. Vanadium carbides are uniformly distributed in the powders containing up to 5% C and 25% V. However, coarse spheroidal vanadium carbides are distributed with more than 5% C and 25% V.
Tool steels containing 3.4 to 4.4% C, 14 to 18% V, 2.7 to 3.2% Cr, 2.3 to 4.1% Mo, 4.7 to 9.7% W and 6.3 to 8.6% Co have been made by sintering water-atomized alloy powders in a vacuum and hot-forging to investigate their microstructures, heat-treatment, and mechanical properties. It is observed that fine vanadium carbides, the total volume per cent of which is about 40%, are uniformly distributed. Grinding is relatively easy in the tool steels as well as in the conventional high speed steel bar stock of JIS SKH 57. Furthermore, it is concluded that the tool steels hardened by quenching and tempering have a high hardness, high transverse rupture strength, and high notch-toughness because of the uniform distribution of fine carbides. Their cutting tool life is also greatly increased.