Solid stabilizer, steel material for solid stabilizer, and manufacturing method of solid stabilizer

Abstract

A steel material for a solid stabilizer which has high bendability, high hardenability, and high quenching crack resistance, a solid stabilizer having high strength, and a manufacturing method of the solid stabilizer. The steel material for the solid stabilizer contains, in mass %, 0.24 to 0.40% of C, 0.15 to 0.40% of Si, 0.50 to 1.20% of Mn, 0.03% or less of P, 0.30% or less of Cr, 0.01 to 0.03% of Ti, and 0.0010 to 0.0030% of B. The steel material for the solid stabilizer satisfies a condition of formula (1) below. Hardness in a radial center portion of the steel material for the solid stabilizer after tempering is 400 HV or more, and a martensite ratio in the radial center portion after the tempering is 80% or more. 1.24<(2C+0.1Si+0.4Mn+0.4Cr)×{1+(1.5B−300B2)×240}<1.7   (1) It is an object to provide a steel material for a solid stabilizer which has high bendability, high hardenability, and high quenching crack resistance, a solid stabilizer having high strength, and a manufacturing method of the solid stabilizer. The steel material for the solid stabilizer contains, in mass %, 0.24 to 0.40% of C, 0.15 to 0.40% of Si, 0.50 to 1.20% of Mn, 0.03% or less of P, 0.30% or less of Cr, 0.01 to 0.03% of Ti, and 0.0010 to 0.0030% of B. The steel material for the solid stabilizer satisfies a condition of formula (1) below. Hardness in a radial center portion of the steel material for the solid stabilizer after tempering is 400 HV or more, and a martensite ratio in the radial center portion after the tempering is 80% or more. 1.24<(2C+0.1Si+0.4Mn+0.4Cr)×{1+(1.5B−300B 2 )×240}<1.7   (1)

1 . A solid stabilizer fabricated by cold forming, quenching, and tempering a steel material for the solid stabilizer, the solid stabilizer characterized in that
 the steel material for the solid stabilizer contains, in mass %, 0.24 to 0.40% of C, 0.15 to 0.40% of Si, 0.50 to 1.20% of Mn, 0.03% or less of P, 0.30% or less of Cr, 0.01 to 0.03% of Ti, and 0.0010 to 0.0030% of B, and satisfies a condition of formula (1) below,   remainder of the steel material for the solid stabilizer is formed of Fe and an unavoidable impurity, and   hardness in a radial center portion of the solid stabilizer after the tempering is 400 HV or more, and a martensite ratio in the radial center portion of the solid stabilizer after the tempering is 80% or more.
   1.24<(2C+0.1Si+0.4Mn+0.4Cr)×{1+(1.5B−300B 2 )×240}<1.7   (1)
 
   
     
     
         2 . The solid stabilizer according to  claim 1 , wherein a lower limit of the C is 0.25%, an upper limit of the Mn is 1.00%, and a lower limit of the formula (1) is 1.4. 
     
     
         3 . The solid stabilizer according to  claim 1 , wherein
 a condition of formula (2) below is satisfied.
   (Si/C)<1.5   (2)
 
   
     
     
         4 . The solid stabilizer according to  claim 1 , wherein
 after the tempering, tensile strength is 1,200 MPa or more, 0.2% proof stress is 1,100 MPa or more, and an impact value at room temperature is 70 J/cm 2  or more.   
     
     
         5 . A steel material for a solid stabilizer, containing, in mass %, 0.24 to 0.40% of C, 0.15 to 0.40% of Si, 0.50 to 1.20% of Mn, 0.03% or less of P, 0.30% or less of Cr, 0.01 to 0.03% of Ti, and 0.0010 to 0.0030% of B, and satisfying a condition of formula (1) below, wherein
 remainder of the steel material for the solid stabilizer is formed of Fe and an unavoidable impurity, and   in finish rolling, the steel material for the solid stabilizer is rolled at a heating temperature of 1,000° C. or less, and hardness of the steel material for the solid stabilizer after the rolling is 200 HV or less.
   1.24<(2C+0.15Si+0.4Mn+0.4Cr)×{1+(1.5B−300B 2 )×240}<1.7   (1)
 
   
     
     
         6 . The steel material for the solid stabilizer according to  claim 5 , wherein
 a lower limit of the C is 0.25%, an upper limit of the Mn is 1.00%, and a lower limit of the formula (1) is 1.4.   
     
     
         7 . The steel material for the solid stabilizer according to  claim 5 , wherein
 a condition of formula (2) below is satisfied.
   (Si/C)<1.5   (2)
 
   
     
     
         8 . A method for manufacturing a solid stabilizer, comprising:
 a forming step of cold bending a steel material for the solid stabilizer that contains, in mass %, 0.24 to 0.40% of C, 0.15 to 0.40% of Si, 0.50 to 1.20% of Mn, 0.03% or less of P, 0.30% or less of Cr, 0.01 to 0.03% of Ti, and 0.0010 to 0.0030% of 13, and that satisfies a condition of formula (1) below, wherein   remainder of the steel material for the solid stabilizer is formed of Fe and an unavoidable impurity, and   in finish rolling, the steel material for the solid stabilizer is rolled at a heating temperature of 1,000° C. or less, and hardness of the steel material for the solid stabilizer after the rolling is 200 HV or less, the method further comprising:   a quenching step of quenching the steel material for the solid stabilizer after the forming; and   a tempering step of tempering the steel material for the solid stabilizer after the quenching.
   1.24<(2C+0.1Si+0.4Mn+0.4Cr)×{1+(1.5B−300B 2 )×240}<1.7   (1)
 
   
     
     
         9 . The method for manufacturing the solid stabilizer according to  claim 8 , wherein
 a lower limit of the C is 0.25%, an upper limit of the Mn is 1.00%, and a lower limit of the formula (1) is 1.4.   
     
     
         10 . The method for manufacturing the solid stabilizer according to  claim 8 , wherein
 a condition of formula (2) below is satisfied.
   (Si/C)<1.5   (2)
 
   
     
     
         11 . The solid stabilizer according to  claim 2 , wherein
 a condition of formula (2) below is satisfied.
   (Si/C)<1.5   (2)
 
   
     
     
         12 . The solid stabilizer according to  claim 2 , wherein
 after the tempering, tensile strength is 1,200 MPa or more, 0.2% proof stress is 1,100 MPa or more, and an impact value at room temperature is 70 J/cm 2  or more.   
     
     
         13 . The solid stabilizer according to  claim 3 , wherein
 after the tempering, tensile strength is 1,200 MPa or more, 0.2% proof stress is 1,100 MPa or more, and an impact value at room temperature is 70 J/cm 2  or more.   
     
     
         14 . The solid stabilizer according to  claim 11 , wherein
 after the tempering, tensile strength is 1,200 MPa or more, 0.2% proof stress is 1,100 MPa or more, and an impact value at room temperature is 70 J/cm 2  or more.   
     
     
         15 . The steel material for the solid stabilizer according to  claim 6 , wherein
 a condition of formula (2) below is satisfied.
   (Si/C)<1.5   (2)
 
   
     
     
         16 . The method for manufacturing the solid stabilizer according to  claim 9 , wherein
 a condition of formula (2) below is satisfied.
   (Si/C)<1.5   (2)