Cast steel and casting mold

Abstract

By limiting steel compositions with respect to special components and controlling contents of Ti, Zr and S in a steel to a suitable range, fine Ti and Zr sulfides are generated so that a cast steel having excellent internal quality and machinability after casting can be ensured. Then, by casting this cast steel a mold having excellent machinability, whose internal quality as cast is comparable to that of a forged steel product, can be produced. Therefore, the mold of the present invention can be widely applied to use, which severely requires excellent surface properties in products for deep-engraving in which a worked surface reaches the internal portion of the section material or for finishing.

What is claimed is:  
     
         1 . A cast steel having excellent internal quality and machinability after casting, characterized by comprising: 
 by mass %, C: 0.02-0.45%, Si: 0.1-2.5%, Mn: 0.1-2.5%, P: 0.10% or less, S: 0.02-0.60%, N: 0.020% or less, and Al: 0.001-0.03% and further comprising one or two of Ti: 0.05-0.25% and Zr: 0.05-0.50, and the remnants Fe and impurities, and also characterized in that effective Ti equivalent weight (Ti *) given by the following expression (1) satisfies a relation given by the following expression (2) and said cast steel contains sulfide containing one or more of Ti and Zr, and which is used as cast.    Ti*=Ti+0.53×Zr−3.4×N  (1) Ti*/S≧1.5  (2)    
     
     
         2 . A cast steel having excellent internal quality and machinability after casting, according to  claim 1 , characterized in that in place of a part of Fe, one or two or more elements selected from groups consisting of, by mass %, Cr: 0.2-9.0%, Ni: 0.2-2.0%, Mo: 0.05-2.0% and V: 0.01-1.5% be contained.  
     
     
         3 . A cast steel having excellent internal quality and machinability after casting, according to  claim 1 , characterized in that in place of a part of Fe, one or two elements selected from groups consisting of, by mass %, Cu: 0.1-3.0% and 0 (oxygen): 0.005-0.020% be contained.  
     
     
         4 . A cast steel having excellent internal quality and machinability after casting, according to  claim 1 , characterized in that in place of a part of Fe, one or two or more elements selected from groups consisting of, by mass %, Cr: 0.2-9.0%, Ni: 0.2-2.0%, Mo: 0.05-2.0% and V: 0.01-1.5% be contained, and one or two elements selected from groups consisting of, by mass %, Cu: 0.1-3.0% and 0 (oxygen): 0.005-0.020% be contained.  
     
     
         5 . A mold produced by casting said cast steel according to  claim 1 .  
     
     
         6 . A mold produced by casting said cast steel according to  claim 2 .  
     
     
         7 . A mold produced by casting said cast steel according to  claim 3 .  
     
     
         8 . A mold produced by casting said cast steel according to  claim 4.