Steel for machine structural use having improved machinability

Abstract

Disclosed is a steel for machine structural use which is usable instead of Pb (lead) free-machining steel, has no adverse effect on environment, and can be stably machined. This steel for machine structural use comprises by mass carbon (C): 0.10 to 0.60%, silicon (Si): 0.05 to 1.0%, manganese (Mn): 0.3 to 2.0%, sulfur (S): 0.02 to 0.25%, aluminum (Al): 0.002 to 0.030%, and calcium (Ca): 0.0005 to 0.01%, with the balance consisting of iron (Fe) and unavoidable impurities, the steel satisfying Ca/Al ratio=0.1 to 1.0 in terms of % by mass ratio.

1 . A steel for machine structural use having improved machinability, said steel comprising by mass 
 carbon (C): 0.10 to 0.60%,    silicon (Si): 0.05 to 1.0%,    manganese (Mn): 0.3 to 2.0%,    sulfur (S): 0.02 to 0.25%,    aluminum (Al): 0.002 to 0.030%, and    calcium (Ca): 0.0005 to 0.01%,    the balance consisting of iron (Fe) and unavoidable impurities, said steel having a Ca/Al ratio of 0.1 to 1.0 in terms of % by mass ratio.    
     
     
         2 . A steel for machine structural use having improved machinability, said steel comprising by mass 
 carbon (C): 0.10 to 0.60%,    silicon (Si): 0.05 to 1.0%,    manganese (Mn): 0.3 to 2.0%,    sulfur (S): 0.02 to 0.25%,    aluminum (Al): 0.002 to 0.030%,    chromium (Cr): 0.1 to 2.5%, and    calcium (Ca): 0.0005 to 0.01%,    the balance consisting of iron (Fe) and unavoidable impurities, said steel having a Ca/Al ratio of 0.1 to 1.0 in terms of % by mass ratio.    
     
     
         3 . The steel for machine structural use according to  claim 1 , which further comprises one or more selected from the group consisting of, by mass, nickel (Ni): 0.1 to 2.5%, molybdenum (O): 0.05 to 1.50%, vanadium (V): 0.01 to 0.50%, titanium (Ti): 0.01 to 0.50%, niobium (Nb): 0.001 to 0.30%, and boron (B): 0.0003 to 0.005%.  
     
     
         4 . The steel for machine structural use according to  claim 2 , which further comprises one or more selected from the group consisting of, by mass, nickel (Ni): 0.1 to 2.5%, molybdenum (Mo): 0.05 to 1.50%, vanadium (V): 0.01 to 0.50%, titanium (Ti): 0.01 to 0.50%, niobium (Nb): 0.001 to 0.30%, and boron (B): 0.0003 to 0.005%.  
     
     
         5 . The steel for machine structural use according to  claim 1 , wherein said steel contains an oxide, and the content of Al 2 O 3  in the oxide is not more than 90% by mass on average.  
     
     
         6 . The steel for machine structural use according to  claim 2 , wherein said steel contains an oxide, and the content of Al 2 O 3  in the oxide is not more than 90% by mass on average.  
     
     
         7 . The steel for machine structural use according to  claim 3 , wherein said steel contains an oxide, and the content of Al 2 O 3  in the oxide is not more than 90% by mass on average.  
     
     
         8 . The steel for machine structural use according to  claim 4 , wherein said steel contains an oxide, and the content of Al 2 O 3  in the oxide is not more than 90% by mass on average.