Bulk steel for the production of injection moulds for plastic material or for the production of pieces for working metals

Abstract

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=1.8×C+1.1×Mn+0.7×Ni+0.6×Cr+1.6×Mo*+K wherein K=0 if the steel does not contain boron and K=0.5 if the steel contains boron; Dr=54×C 0.25 +24.5×(Mo*+3×V*) 0.30 +1.58×Mn+0.74×Ni+1.8×Si+12.5×(Cr) 0.20 ; U=1600×C+100×(0.25×Cr+Mo*+4.5×V*); R=3.8×C+10×Si+3.3×Mn+2.4×Ni+1.4×(Cr+Mo*); Mo*+3×V*≧0.4%; Mo*=Mo+W/2; V*=V+Nb/2+Ta/4 and B≧⅓×K 1 +0.5 wherein K 1 =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) 2 +283)))}.

1 . Steel block for the manufacture of moulds for the injection moulding of plastics material or the moulding of metals 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 at all points is between 430 HB and 530 HB and of which the chemical composition of the steel comprises, in % by weight: 
         0.180%≦C≦0.400% 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% boron in a content of between 0.0005% and 0.015%,    optionally one or more elements from among sulphur, selenium and tellurium, the sum of contents of these elements being less than or equal to 0.2%,    optionally one or more elements from among lead and bismuth, the sum of contents of these elements being less than or equal to 0.2%,    optionally calcium in a content of less than or equal to 0.1%,    the remainder being iron and impurities resulting from production, the copper being an impurity, the chemical composition also satisfying the following equations:     3.2≦Tr≦9 85≦Dr≦95 U/Dr≦10.0 Mo*+3×V*≧0.4%   in which, for contents expressed in %:       Tr= 1.8×C+1.1×Mn+0.7×Ni+0.6×Cr+1.6×Mo*+K   wherein K=0 if the steel does not contain boron and K=0.5 if the steel contains boron       Dr= 54×C 0.25 +24.5×(Mo*+3×V*) 0.30 +1.58×Mn+0.74×Ni+1.8×Si+12.5×(Cr) 0.20   U=1600×C+100×(0.25×Cr+Mo*+4.5×V*) R=3.8×C+10×Si+3.3×Mn+2.4×Ni+1.4×(Cr+Mo*) Mo*=Mo+W/2 V*=V+Nb/2+Ta/4   the contents of boron, aluminium, titanium, zirconium and nitrogen, expressed in thousandths of % by weight, being such that:            B   ≥         1   3     ×   K1     +   0.5             wherein       K 1=Min ( I*;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) 2 +283)))}.   
     
     
         2 . Steel block according to  claim 1 , of which the chemical composition is such that 
         R>11 
     
     
         3 . Steel block according to  claim 1 , characterised in that 
         R≦2.7× Tr   
     
     
         4 . Steel block according to any of  claim 1 , characterised in that the silicon content is strictly less than 0.45% by weight and the carbon content less than or equal to 0.35% by weight.  
     
     
         5 . Steel block according to  claim 1 , characterised in that R/(2.7×Tr)≦0.90.  
     
     
         6 . Steel block according to  claim 5;  characterised in that R/(2.7×Tr)≦0.80.  
     
     
         7 . Steel block according to any of  claim 1 , characterised in that U/Dr<9.0.  
     
     
         8 . Steel block according to  claim 7 , characterised in that the composition is such that: 
         0.230%≦C≦0.350% Si≦0.30% 0.1%≦Mn≦1.8% Ni≦2% 0.2%≦Cr≦3% Mo+W/2≦2.5% V+Nb/2+Ta/4≦0.3% Mo*+3×V*≧0.8% 
     
     
         9 . Steel block according to  claim 8 , characterised in that its composition is such that: 
         0.240%≦C≦0.320% Si≦0.15% 0.1%≦Mn≦1.6% Ni≦2% 0.2%≦Cr≦2.5% 0.3%≦Mo+W/2≦2.5% V+Nb/2+Ta/4≦0.3% Mo*+3×V*≧1.2% 
     
     
         10 . Steel block according to  claim 8 , characterised in that Tr>4.5.  
     
     
         11 . Steel mould part machined in a block according to any of  claim 1 , of which at least a portion of the surface is hardened by nitriding and of which the hardness at all points is between 430 HB and 530 HB.