PURPOSE:To provide the titled tool steel having long service life and excellent resistance to heat crack and seizure under severe repeated thermal shock conditions by use of a composition consisting of each specific amount of C, Si, Mn, Cr, W, Mo, V, N, or further, Ni, Co, and the remaining Fe with accompanying impurities. CONSTITUTION:The titled tool steel consists of C: 0.2-0.35%, Si0.7%, Mn 1.2%, Cr: 4.5-6.5%, single or combined W and Mo (1/2W+Mo): 0.6-1.95%, V: 0.2-1.1%, N: 0.025-0.15%, or further Ni: 0.3-1.2%, or Co: 0.3-3.2%, and the remaining Fe with accompanying impurities. When the above is used as hot working tools such as metal mold for die casting, metal mold for hot forging, etc., crack development is controlled and long service life is ensured even under severe thermal stress acting conditions such as spray quenching on die surface.
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