Hot rolled bar or hot rolled wire rod, component, and manufacturing method of hot rolled bar or hot rolled wire rod

Abstract

The present invention adopts a hot rolled bar or hot rolled wire rod including a chemical composition including, by mass %, C: 0.05 to 0.30%, Si: 0.30 to 0.60%, Mn: 0.40 to 1.0%, S: 0.008 to less than 0.040%, Cr: 1.60 to 2.00%, Mo: 0.1% or less, Al: 0.025 to 0.05%, N: 0.010 to 0.025%, Ti: 0.003% or less, Bi: 0.0001 to 0.0050%, and a remainder including Fe and impurities, in which amounts of P and O in the impurities are respectively P: 0.025% or less and O: 0.002% or less; in which a microstructure includes ferrite-pearlite or ferrite-pearlite-bainite, and an Expression (1) is satisfied. 1.70≤Cr+2×Mo≤2.10  (1)

1 . A hot rolled bar or hot rolled wire rod comprising:
 a chemical composition including, by mass %,
 C: 0.05 to 0.30%, 
 Si: 0.30 to 0.60%, 
 Mn: 0.40 to 1.0%, 
 S: 0.008 to less than 0.040%, 
 Cr: 1.60 to 2.00%, 
 Mo: 0 to 0.1% or less, 
 Al: 0.025 to 0.05%, 
 N: 0.010 to 0.025%, 
 Ti: 0 to 0.003%, 
 Bi: 0.0001 to 0.0050%, 
   and a remainder including Fe and impurities,
 wherein amounts of P and O in the impurities are respectively 
 P: 0.025% or less, and 
 O: 0.002% or less; 
   wherein a microstructure includes ferrite-pearlite or ferrite-pearlite-bainite, and an Expression (1) is satisfied,
   1.70≤Cr+2×Mo≤2.10  (1),
 
   where, an element symbol in the Expression (1) represents an amount of a corresponding element (mass %).   
     
     
         2 . The hot rolled bar or hot rolled wire rod according to  claim 1 , comprising, instead of a part of Fe, by mass %,
 Nb: 0.08% or less.   
     
     
         3 . The hot rolled bar or hot rolled wire rod according to  claim 1 , comprising, instead of a part of Fe,
 one or more elements selected from Cu: 0.40% or less and Ni: 0.80% or less.   
     
     
         4 . A component obtained by cutting the hot rolled bar or hot rolled wire rod according to  claim 1 . 
     
     
         5 . A manufacturing method of a hot rolled bar or hot rolled wire rod, comprising:
 manufacturing a slab including a chemical composition according to  claim 1  by continuous casting or ingot casting,
 wherein a ratio of Mn contents (Mn max /Mn) satisfies an Expression (2); and 
   hot rolling the slab,
   Mn max /Mn<2.4  (2),
 
   where, in the Expression (2), the Mn max  represents a Mn content in a space between primary arms of a dendrite and the Mn represents a Mn content in a steel (mass %).   
     
     
         6 . The hot rolled bar or hot rolled wire rod according to  claim 2 , comprising, instead of a part of Fe,
 one or more elements selected from Cu: 0.40% or less and Ni: 0.80% or less.   
     
     
         7 . A component obtained by cutting the hot rolled bar or hot rolled wire rod according to  claim 2 . 
     
     
         8 . A component obtained by cutting the hot rolled bar or hot rolled wire rod according to  claim 3 . 
     
     
         9 . A component obtained by cutting the hot rolled bar or hot rolled wire rod according to  claim 6 . 
     
     
         10 . A manufacturing method of a hot rolled bar or hot rolled wire rod, comprising:
 manufacturing a slab including a chemical composition according to  claim 2  by continuous casting or ingot casting,
 wherein a ratio of Mn contents (Mn max /Mn) satisfies an Expression (2); and 
   hot rolling the slab,
   Mn max /Mn<2.4  (2),
 
   where, in the Expression (2), the Mn max  represents a Mn content in a space between primary arms of a dendrite and the Mn represents a Mn content in a steel (mass %).   
     
     
         11 . A manufacturing method of a hot rolled bar or hot rolled wire rod, comprising:
 manufacturing a slab including a chemical composition according to  claim 3  by continuous casting or ingot casting,
 wherein a ratio of Mn contents (Mn max /Mn) satisfies an Expression (2); and 
   hot rolling the slab,
   Mn max /Mn<2.4  (2),
 
   where, in the Expression (2), the Mn max  represents a Mn content in a space between primary arms of a dendrite and the Mn represents a Mn content in a steel (mass %).   
     
     
         12 . A manufacturing method of a hot rolled bar or hot rolled wire rod, comprising:
 manufacturing a slab including a chemical composition according to  claim 6  by continuous casting or ingot casting,
 wherein a ratio of Mn contents (Mn max /Mn) satisfies an Expression (2); and 
   hot rolling the slab,
   Mn max /Mn<2.4  (2),
 
   where, in the Expression (2), the Mn max  represents a Mn content in a space between primary arms of a dendrite and the Mn represents a Mn content in a steel (mass %).