Comparison of Heat Treatment Response of Wrought and Sintered BT1 Grade High Speed Steel

A comparison was made of the secondary hardening characteristics of a conventionally wrought and two batches of directly sintered BT1 high speed steel. Minor differences in hardness between the types were observed after austenitizing between 1050 and 1280°C and tempering from 400 to 600°C. The recommended hardening temperature for BT1 was considered too high in at least two types by as much as 30 K. The wrought material had the finest microstructure throughout, e.g. 8 μm grain diameter for 1200°C austenitization treatment. Considerable grain refinement, however, was achieved in both directly sintered products by a post-sinter transformation anneal. The grain size after quenching was 2–3 times smaller than for the as-sintered, e.g. 15 and 19 μm compared to 46 and 36 μm respectively for the same austenitization temperature. PM/0331