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Abstract

Steel useful for the manufacture of molds for the injection molding of plastics, the chemical composition of which includes, by weight: 0.03%.ltoreq.C.ltoreq.0.25%, 0%.ltoreq.Si.ltoreq.0.2%, 0%.ltoreq.Mn.ltoreq.0.9%, 1.5%.ltoreq.Ni.ltoreq.5%, 0%.ltoreq.Cr.ltoreq.18%, 0.05%.ltoreq.Mo+W/2.ltoreq.1%, 0%.ltoreq.S.ltoreq.0.3%, at least one element chosen from Al and Cu in contents of between 0.5% and 3%, optionally 0.0005%.ltoreq.B.ltoreq.0.015%, optionally at least one element taken from V, Nb, Zr, Ta and Ti, in contents of between 0% and 0.3%, optionally at least one element taken from Pb, Se, Te and Bi, in contents of between 0% and 0.3%, the remainder being iron and impurities resulting from the processing, especially nitrogen; the chemical composition additionally satisfying the relations: Kth=3.8.times.C+9.8.times.Si+3.3.times.Mn+2.4.times.Ni+.alpha..times.Cr+1.4.times.(Mo+W/2).ltoreq.15, with .alpha.=1.4 if Cr<8% and .alpha.=0 if Cr.gtoreq.8%; Tr=3.8.times.C+1.07.times.Mn+0.7.times.Ni+0.57.times.Cr+1.58.times.(Mo+W/2)+kB.gtoreq.3.1 with kB=0.8 if B is between 0.0005% and 0.015% and kB=0 if not; if Cr.ltoreq.5%, Kth/Tr.ltoreq.3. Steel block of hardness greater than 350 BH and welding wire.

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First Claim