" IMPROVING THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SOME HIGHLY ALLOYED CAST TOOL STEELS °

Abstract

The main problem of near-net shape cast tooling is the bad toughness due to the relatively coarse structure and the presence of eutectic brittle carbide network . To overcome this problem , special standard tool steels with high amount of austenitic stabilizing elements such as chromium + carbon and cobalt + tungsten were selected to produce austenite + carbide in as cast condition in order to eliminate the risk of martensitic transformation during intensive secondary cooling in oil bath immediately after pouring in V-shape Cu-water cooled mould.

Prespherodization heat treatment at different temperatures was applied to improve the carbide morphology in cast structures of these steels.

Traditional hardening of high speed ( TS-1 & TS-2 ) and cold work ( TS-3 & TS-4 ) cast steels showed severe deterioration in carbide morphology and increased noncoherency with the matrix. In this case , skeleton brittle carbide morphologies were detected in steels ( TS-1 and TS-2 ) , and rossetta noncoherent carbides were also observed in steels ( TS-3 & TS-4 ).

Excellent modification in carbide morphology was detected when cold work cast steels ( TS-3 & TS-4 ) were spherodized at 1230°C for section sizes between 15 and 30 mm.