| 摘要 |
Steel blocks for the manufacture of moulds for the injection moulding of plastics material or for the manufacture of metal-working parts having a thickness greater than 20 mm, of which the structure is completely martensitic or martensito-bainitic, of which the hardness is between 430 HB and 530 HB and of which the chemical composition comprises, in % by weight: 0.180%<=C<=0.40%; Si<=0.8%; Mn<=2.5%; Ni<=3%; Cr<=3.5%; Mo+W/2<=2.8%; V+Nb/2+Ta/4<=0.5%; Al<=0.4%; Ti+Zr/2<=0.1%; 0.0005%<B<0.015%; S+Se+Te<0.2%; Pb+Bi<0.2%; Ca<0.1%, the remainder being iron and impurities resulting from production, the chemical composition also satisfying the following equations: 3.2<=Tr<=9; 85<=Dr<=95; U/Dr <=10.0, wherein Tr=1.8xC+1.1xMn+0.7xNi+0.6xCr+1.6xMo*+K wherein K=0 if the steel does not contain boron and K=0.5 if the steel contains boron; Dr=54xC<SUP>0.25</SUP>+24.5x(Mo*+3xV*)<SUP>0.30</SUP>+1.58xMn+0.74xNi+1.8xSi+12.5x(Cr)<SUP>0.20</SUP>; U=1600xC+100x(0.25xCr+Mo*+4.5xV*); R=3.8xC+10xSi+3.3xMn+2.4xNi+1.4x(Cr+Mo*); Mo*+3xV*>=0.4%; Mo*=Mo+W/2; V*=V+Nb/2+Ta/4 and B>=1/3xK<SUB>1</SUB>+0.5 wherein K<SUB>1</SUB>=Min (I*;J*); I*=Max (O;I); J*=Max (O;J); I=Min (N; N-0.29(Ti+Zr/2-5)); J=Min (N;0.5(N-0.52 Al+{square root}{square root over ((N-0.52Al)<SUP>2</SUP>+283)))}. |
