Abstract: An alloy steel having the capability of retaining high hardness at elevated temperature for a prolonged time is suitable for use as a high speed tool steel. The alloy steel comprises in % by weight: 0.7-1.4 C; less than 1 Mn; less than 0.04 P; up to 0.7 Si; 3-6 Cr; 4-12 Mo; less than 0.5 Co; 0.5-2.25 V; 1-7 W; up to 1.25 Al; at least one of 0.04-2.5 Nb; 0.025-2.5 Zr; 0.08-4.75 Ta and 0.005-0.7 Ti; balance substantially Fe. The alloy may also have an S content of 0.036-0.300; Mn of 0.30-1.35 and may optionally be treated when in a liquid state with up to 0.05 of Mg or Ca.

Abstract: A modified H-13 hot work die steel in which impact toughness and thermal fatigue resistance is greatly improved. The steel consists of in weight %:______________________________________ Carbon (C): 0.34-0.40, Manganese (Mn): 0.25-0.45, Silicon (Si): 0.85-1.15, Chromium (Cr): 5.00-5.40, Nickel (Ni): 0.30 max, Molybdenum (Mo): 1.20-1.50, Vanadium (V): 0.31-0.52, Niobium (Nb): 0.02-0.09, Iron (Fe) and Incidental impurities: Balance ______________________________________The steel also preferably includes about 0.01-0.20 weight % titanium (Ti) and is preferably subjected to premium quality treatment, including remelting and homogenization, either thermal or mechanical (by hot working).