Manufacturing method of steel component and steel component

Abstract

A manufacturing method of a steel component includes: heating a steel sheet in a carburizing atmosphere to form a carburized layer on a surface of the steel sheet, the steel sheet having: a chemical composition represented by: in mass %, C: 0.0005 to 0.1%; Si: 0.01 to 2.0%; Mn: 0.05 to 3.0%; Al: 0.9% or less; P: 0.05% or less; S: 0.01% or less; Ti: 0.0 to 0.2%; Nb: 0.0 to 0.1%; Cr: 0 to 2%; Mo: 0.0 to 0.2%; B: 0.000 to 0.005%; and the balance: Fe and impurities; and a steel structure represented by ferrite with an area fraction of 70% or more; and forming the steel sheet by using metal dies, and performing quenching on the steel sheet in a state of housing the steel sheet in the metal dies to transform the carburized layer into martensite and make a part of the steel sheet on the further inside than the carburized layer to be a steel structure represented by ferrite with an area fraction of 50% or more.

1 . A manufacturing method of a steel component, comprising:
 heating a steel sheet in a carburizing atmosphere to form a carburized layer on a surface of the steel sheet, the steel sheet having:   a chemical composition represented by:   in mass %,   C: 0.0005 to 0.1%;   Si: 0.01 to 2.0%;   Mn: 0.05 to 3.0%;   Al: 0.9% or less;   P: 0.05% or less;   S: 0.01% or less;   Ti: 0.0 to 0.2%;   Nb: 0.0 to 0.1%;   Cr: 0 to 2%;   Mo: 0.0 to 0.2%;   B: 0.000 to 0.005%; and   the balance: Fe and impurities; and   a steel structure represented by   ferrite with an area fraction of 70% or more; and   forming the steel sheet by using metal dies, and performing quenching on the steel sheet in a state of housing the steel sheet in the metal dies to transform the carburized layer into martensite and make a part of the steel sheet on the further inside than the carburized layer to be a steel structure represented by ferrite with an area fraction of 50% or more.   
     
     
         2 . The manufacturing method of the steel component according to  claim 1 , wherein
 in the formation of the carburized layer on the surface of the steel sheet, the steel sheet is subjected to soaking at a temperature of 820° C. or more.   
     
     
         3 . The manufacturing method of the steel component according to  claim 2 , wherein
 in the formation of the carburized layer on the surface of the steel sheet, the steel sheet is subjected to soaking for one hour or more.   
     
     
         4 . The manufacturing method of the steel component according to  claim 3 , further comprising
 performing working on the steel sheet at an equivalent strain of less than 5% or 20% or more, before the formation of the carburized layer on the surface of the steel sheet.   
     
     
         5 - 7 . (canceled) 
     
     
         8 . The manufacturing method of the steel component according to  claim 2 , further comprising
 performing working on the steel sheet at an equivalent strain of less than 5% or 20% or more, before the formation of the carburized layer on the surface of the steel sheet.   
     
     
         9 . The manufacturing method of the steel component according to  claim 1 , wherein
 in the formation of the carburized layer on the surface of the steel sheet, the steel sheet is subjected to soaking for one hour or more.   
     
     
         10 . The manufacturing method of the steel component according to  claim 9 , further comprising
 performing working on the steel sheet at an equivalent strain of less than 5% or 20% or more, before the formation of the carburized layer on the surface of the steel sheet.   
     
     
         11 . The manufacturing method of the steel component according to  claim 1 , further comprising
 performing working on the steel sheet at an equivalent strain of less than 5% or 20% or more, before the formation of the carburized layer on the surface of the steel sheet.   
     
     
         12 . A steel component, comprising:
 a base material having:   a chemical composition represented by:   in mass %,   C: 0.0005 to 0.1%;   Si: 0.01 to 2.0%;   Mn: 0.05 to 3.0%;   Al: 0.9% or less;   P: 0.05% or less;   S: 0.01% or less;   Ti: 0.0 to 0.2%;   Nb: 0.0 to 0.1%;   Cr: 0 to 2%;   Mo: 0.0 to 0.2%;   B: 0.000 to 0.005%; and   the balance: Fe and impurities; and   a steel structure represented by in an area fraction,   ferrite: 50% or more; and   a carburized layer made of martensite and existing on a surface of the base material.   
     
     
         13 . The steel component according to  claim 12 , wherein:
 the carburized layer made of the martensite contains C of 0.5 to 0.9% in mass %; and   in a range of t/4 to 3t/4 from a surface of the steel component when a thickness of the steel component is set to t, a total area fraction of ferrite grains each having a grain diameter of 200 μm or more in terms of a circle-equivalent diameter is 5% or less.   
     
     
         14 . The steel component according to  claim 13 , wherein
 an effective case depth is 0.05 to 0.5 mm.   
     
     
         15 . The steel component according to  claim 12 , wherein
 an effective case depth is 0.05 to 0.5 mm.