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Abstract

Steel for the manufacture of molds, and especially of molds for injection molding of plastics, whose chemical composition comprises, by weight: 0.17%.ltoreq.C.ltoreq.0.27%, 0%.ltoreq.Si.ltoreq.0.5%, 0%.ltoreq.Mn.ltoreq.2%, 0%.ltoreq.Ni.ltoreq.2%, 0%.ltoreq.Cr.ltoreq.3%, 0%.ltoreq.Mo+W/2.ltoreq.1.5%, 0%.ltoreq.V+Nb/2+Ta/4.ltoreq.0.5%, 0.002%.ltoreq.B.ltoreq.0.015%, 0.005%.ltoreq.Al.ltoreq.0.2%, optionally at least one element taken from sulfur, selenium and tellurium, the sum of the contents of these elements being smaller than or equal to 0.2% optionally at least one element taken from titanium and zirconium, in contents such that the sum of the titanium content and of half the zirconium content is smaller than or equal to 0.3%, optionally at least one element taken from lead and bismuth, the sum of the contents of these elements being smaller than or equal to 0.2%, optionally calcium in a content lower than or equal to 0.1%, the remainder being iron and impurities resulting from the production, the chemical composition additionally satisfying the following relationships: Cr+3.times.(Mo+W/2)+10.times.(V+Nb/2+Ta/4).gtoreq.2.1, Mo+W/2>0.7% if Cr.ltoreq.1.5%, Qu=3.8.times.C+1.1.times.Mn+0.7.times.Ni+0.6.times.Cr+1.6.times.(Mo+W/2)+0.6.gtoreq.3, R=3.8.times.C+10.times.Si+3.3.times.Mn+2.4.times.Ni+1.4.times.(Cr+Mo+W/2).ltoreq.11.

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First Claim