Heat treatment of high-speed steel to improve the distribution of carbides

Conclusions

• 1. It was found that heat treatment affects the distribution and shape of eutectic carbides in high-speed steels.

• 2. It is possible to modify the eutectic network by two methods: a) high-temperature heating, which induces coalescence of the eutectic carbides; b) multiple heating at a temperature 30–40°C above Ac₁, which induces changes in the carbide phase.

• 3. High-temperature heating with subsequent normal annealing (850–900°C) is suitable for cast tools 40–100 mm in diameter and for ingots subjected to low degrees of reduction, particularly in manufacturing forged discs.

• 4. Multiple heating at temperatures somewhat above Ac₁ does not eliminate the eutectic network in cast steel but produces more complete dissolution and some refining of the carbides during subsequent forging. This produces thin carbide bands in the forged steel without affecting its red hardness or susceptibility to grain growth (quenching temperature of 1290°C for R18 steel). This treatment is effective for small castings or bars with a little-deformed eutectic network which are subjected to further forging or rolling with substantial degrees of reduction.