Hot work tool steel and mold member excellent resistance to melting loss

Abstract

A hot work tool steel having a chemical composition in wt %: C: 0.10 to 0.35%, Si: less than 0.80%, Mn: 3.0% or less, Cr: 2.0% or more and less than 7.0%, N: more than 0.05% and 0.50% or less, O: 0.0100% or less, P: 0.050% or less, Al: 0.050% or less, with the proviso that ½W+Mo: 0.3 to 5.0%, C+N: 0.20 to 0.60% and C/N: 6 or less, and the balance: substantially Fe, and optionally V: 0.01 to 0.5%. The hot work tool steel exhibits excellent resistance to melting, while retaining good toughness and good resistance to heat checking.

1 . A hot work tool steel excellent in resistance to melting loss, having a composition in mass %: C, 0.10 to 0.35%, Si: less than 0.80%, Mn: 3.0% or less, Cr: 2.0% or more and less than 7.0%, ½W+Mo: 0.3 to 5.0%, N: more than 0.05% and 0.50% or less, C+N: 0.20 to 0.60% (with a proviso that C/N: 6 or less), O: 0.0100% or less, P: 0.050% or less, Al: 0.050% or less, and the balance: substantially Fe.  
   
   
       2 . The hot work tool steel according to  claim 1 , further containing, in mass %, V: 0.01% or more and 0.3% or less.  
   
   
       3 .- 7 . (canceled)  
   
   
       8 . The hot work tool steel according to  claim 1 , further containing, in mass %, 
 at least one of Ni: 2.0% or less and Co: 5.0% or less;    at least one of Ti: 1.0% or less, Ta: 1.0% or less, B: 0.010% or less, and Cu: 1.0% or less; and    at least one of S: 0.050% or less, Ca: 0.0100% or less, Se: 0.0100% or less, Te: 0.0100% or less, Zr: 0.0100% or less, Mg: 0.0100% or less, and Y: 0.100% or less.    
   
   
       9 . The hot work tool steel according to  claim 2 , further containing, in mass %, 
 at least one of Ni: 2.0% or less and Co: 5.0% or less;    at least one of Ti: 1.0% or less, Ta: 1.0% or less, B: 0.010% or less, and Cu: 1.0% or less; and    at least one of S: 0.050% or less, Ca: 0.0100% or less, Se: 0.0100% or less, Te: 0.0100% or less, Zr: 0.0100% or less, Mg: 0.0100% or less, and Y: 0.100% or less.    
   
   
       10 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 1 .  
   
   
       11 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 2 .  
   
   
       12 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 8 .  
   
   
       13 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 9 .  
   
   
       14 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 1  and having a surface layer which has, because of modification thereof by a surface treatment, a higher resistance to Al-melting loss than that of a base metal.  
   
   
       15 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 2  and having a surface layer which has, because of modification thereof by a surface treatment, a higher resistance to Al-melting loss than that of a base metal.  
   
   
       16 . A mold member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 8  and having a surface layer which has, because of modification thereof by a surface treatment, a higher resistance to Al-melting loss than that of a base metal.  
   
   
       17 . A mole member excellent in resistance to melting loss, the mold member being formed of the hot work tool steel according to  claim 9  and having a surface layer which has, because of modification thereof by a surface treatment, a higher resistance to Al-melting loss than that of a base metal.