Steel holder block for plastic molding

Abstract

A manufacturing mold base for plastic injection molds is formed from a martensitic stainless steel alloy comprising: about 0.03%-0.06% by weight C, about 1.0%-1.6% by weight Mn, about 0.01%-0.03% by weight P, about 0.06%-0.3% by weight S, about 0.25%-1.0% by weight Si, about 12.0%-14.0% by weight Cr, about 0.5%-1.3% by weight Cu, about 0.01%-0.1% by weight V, about 0.02%-0.08% by weight N, with the balance being Fe with trace amounts of ordinarily present elements.

What is claimed is:  
     
         1 . A manufacturing mold base for plastic injection molds having sufficient dimensional stability that at least two opposing surfaces remain substantially parallel during formation of the base and formation and any subsequent heat treating of a major cavity in the base, the base having suitable ductility and breakout resistance for repeatable formation of one or more apertures in the mold without breakout, which apertures render the base suitable for use as a mold base, and further having suitable corrosion resistance and weldability for use as a mold base, the base being formed from a martensitic stainless steel alloy comprising: 
 about 0.03%-0.06% by weight C;    about 1.0%-1.6% by weight Mn;    about 0.01%-0.03% by weight P;    about 0.06%-0.3% by weight S;    about 0.25%-1.0% by weight Si;    about 12.0%-14.0% by weight Cr;    about 0.5%-1.3% by weight Cu;    about 0.01%-0.1% by weight V;    about 0.02%-0.08% by weight N; and    the balance being Fe with trace amounts of ordinarily present elements.    
     
     
         2 . The mold base of  claim 1 , wherein said alloy has a 2% yield strength of at least 115 ksi and an ultimate tensile strength of at least 145 ksi.  
     
     
         3 . The mold base of  claim 1 , wherein said alloy has an elongation in two inches of 14% and a reduction in area of 35%.  
     
     
         4 . The mold base of  claim 1 , wherein said alloy has a hardness within the range of 32 to 36 HRC.  
     
     
         5 . The mold base of  claim 1 , wherein said alloy is normalized to provide more uniform alloy microstructure.  
     
     
         6 . The mold base of  claim 1 , wherein said alloy comprises a maximum of 10% by volume ferrite phase.  
     
     
         7 . A martensitic tool steel alloy for use in the manufacture of plastic injection mold base components, said alloy is comprised of about 1.0%-1.6% by weight Mn, about 0.01%-0.03% by weight P, about 0.25%-1.0% by weight Si, about 0.5%-1.3% by weight Cu, about 0.01%-0.1% by weight V, about 0.02%-0.08% by weight N, a maximum of 0.06% by weight C, a maximum of 14.0% by weight Cr, a maximum of 0.3% by weight S and the balance being Fe with residual impurities wherein said alloy comprises a hardness within the range of 32 to 36 HRC.  
     
     
         8 . The alloy of  claim 7 , wherein said alloy comprises a 2% yield strength of at least 115 ksi and an ultimate tensile strength of at least 145 ksi.  
     
     
         9 . The alloy of  claim 7 , wherein said alloy comprises an elongation in two inches of 14% and a reduction in area of 35%.  
     
     
         10 . The alloy of  claim 7 , wherein said alloy is normalized to provide more uniform alloy microstructure.  
     
     
         11 . A mold base made of the alloy of  claim 7 .  
     
     
         12 . A process of manufacturing a mold base for plastic injection molds, said process comprising the steps of: 
 heat treating a steel alloy comprising about 1.0%-1.6% by weight Mn, about 0.01%-0.03% by weight P, about 0.25%-1.0% by weight Si, about 0.5%-1.3% by weight Cu, about 0.01%-0.1% by weight V, about 0.02%-0.08% by weight N, about 0.03%-0.06% by weight C, about 12.0%-14.0% by weight Cr, about 0.06%-0.3% by weight S and the balance being Fe with residual impurities, at a temperature not lower than 2150° F.;    hot working said steel alloy within the temperature range of about 1700-2150° F.;    cooling said steel alloy by free air cooling to room temperature; and    forming a mold base from said alloy for use in plastic injection molding.    
     
     
         13 . The process of  claim 12 , wherein said step of hot working said steel alloy comprises the steps of rolling or forging said steel alloy.  
     
     
         14 . The process of  claim 13 , further comprising hot leveling said steel alloy after finalizing said rolling or forging.  
     
     
         15 . The process of  claim 12 , further comprising the step of a stress relieving treatment performed in a temperature range of 450-650° F.  
     
     
         16 . The process of  claim 12 , further comprising the step of aging said steel alloy at a temperature range of 700-900° F. to raise the HRC-hardness value of said alloy by 4 to 6 hardness units.  
     
     
         17 . A mold base formed by the process of claim  12 .