Hot-rolled steel sheet and method for producing the same

Abstract

A hot-rolled steel sheet according to the present embodiment has a chemical composition containing, in mass %: C: 0.07 to 0.30%, Si: more than 1.0 to 2.8%, Mn: 2.0 to 3.5%, P: 0.030% or less, S: 0.010% or less, Al: 0.01 to less than 1.0%, N: 0.01% or less, O: 0.01% or less, and one or more types selected from the group consisting of Sb, Sn and Te in a total amount of 0.03 to 0.30%, with a balance being Fe and impurities, and satisfying Formula (1). The micro-structure of the hot-rolled steel sheet includes ferrite and pearlite in a total amount of 50 area % or more. The tensile strength of the hot-rolled steel sheet is 900 MPa or less. Si+Mn≥3.20  (1) Where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1).

1 . A hot-rolled steel sheet having a chemical composition consisting of, in mass %:
 C: 0.07 to 0.30%,   Si: more than 1.0 to 2.8%,   Mn: 2.0 to 3.5%,   P: 0.030% or less,   S: 0.010% or less,   Al: 0.01 to less than 1.0%,   N: 0.01% or less,   O: 0.01% or less,   Sb: 0.03 to 0.30%,   Ti: 0 to 0.15%,   V: 0 to 0.30%,   Nb: 0 to 0.15%,   Cr: 0 to 1.0%,   Ni: 0 to 1.0%,   Mo: 0 to 1.0%,   W: 0 to 1.0%,   B: 0 to 0.010%,   Cu: 0 to 0.50%,   Sn: 0 to 0.30%,   Bi: 0 to 0.30%,   Se: 0 to 0.30%,   Te: 0 to 0.30%,   Ge: 0 to 0.30%,   As: 0 to 0.30%,   Ca: 0 to 0.50%,   Mg: 0 to 0.50%,   Zr: 0 to 0.50%,   Hf: 0 to 0.50%, and   rare earth metal: 0 to 0.50%,   with a balance being Fe and impurities, and satisfying Formula (1):
   Si+Mn≥3.20  (1)
 
 where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1). 
   
     
     
         2 . The hot-rolled steel sheet according to  claim 1 , containing, in mass %, one or more types of element selected from a group consisting of:
 Ti: 0.005 to 0.15%,   V: 0.001 to 0.30%, and   Nb: 0.005 to 0.15%.   
     
     
         3 . The hot-rolled steel sheet according to  claim 1 , containing, in mass %, one or more types of element selected from a group consisting of:
 Cr: 0.10 to 1.0%,   Ni: 0.10 to 1.0%,   Mo: 0.01 to 1.0%,   W: 0.01 to 1.0%, and   B: 0.0001 to 0.010%.   
     
     
         4 . The hot-rolled steel sheet according to  claim 1 , containing, in mass %,
 Cu: 0.10 to 0.50%.   
     
     
         5 . The hot-rolled steel sheet according to  claim 1 , containing, in mass %,
 one or more types of element selected from a group consisting of Sn, Bi, Se, Te, Ge and As in a total amount of 0.0001 to 0.30%.   
     
     
         6 . The hot-rolled steel sheet according to  claim 1 , containing, in mass %,
 one or more types of element selected from a group consisting of Ca, Mg, Zr, Hf and rare earth metal in a total amount of 0.0001 to 0.50%.   
     
     
         7 . The hot-rolled steel sheet according to  claim 1 , comprising:
 an Sb concentrated layer having a thickness of 0.5 μm or more between a surface and scale.   
     
     
         8 . The hot-rolled steel sheet according to  claim 1 , wherein:
 in a micro-structure of the hot-rolled steel sheet, a total area fraction of ferrite and pearlite is 75% or more; and   a tensile strength of the hot-rolled steel sheet is 800 MPa or less.   
     
     
         9 . The hot-rolled steel sheet according to  claim 1 , wherein:
 in a micro-structure of the hot-rolled steel sheet, a total area fraction of bainite and martensite is 75% or more; and   a tensile strength of the hot-rolled steel sheet is 900 MPa or more.   
     
     
         10 . The hot-rolled steel sheet according to  claim 1 , wherein:
 in a micro-structure of the hot-rolled steel sheet, a total area fraction of bainite and martensite is 75% or more; and   a tensile strength of the hot-rolled steel sheet is 800 MPa or less.   
     
     
         11 . The hot-rolled steel sheet according to  claim 1 , wherein:
 a thickness of an internal oxidized layer of the hot-rolled steel sheet is 5 μm or less.   
     
     
         12 . The hot-rolled steel sheet according to  claim 8 , wherein:
 a scale thickness on a surface of the hot-rolled steel sheet is 10 μm or less.   
     
     
         13 . The hot-rolled steel sheet according to  claim 8 , wherein:
 a decarburization layer thickness in an outer layer of the hot-rolled steel sheet is 20 μm or less.   
     
     
         14 . The hot-rolled steel sheet according to  claim 9 , wherein:
 a scale thickness on a surface of the hot-rolled steel sheet is 7 μm or less.   
     
     
         15 . A production method for producing a hot-rolled steel sheet comprising:
 a process of preparing a steel material having a chemical composition consisting of, in mass %:   
       C: 0.07 to 0.30%, 
       Si: more than 1.0 to 2.8%, 
       Mn: 2.0 to 3.5%, 
       P: 0.030% or less, 
       S: 0.010% or less, 
       Al: 0.01 to less than 1.0%, 
       N: 0.01% or less, 
       O: 0.01% or less, 
       Sb: 0.03 to 0.30%, 
       Ti: 0 to 0.15%, 
       V: 0 to 0.30%, 
       Nb: 0 to 0.15%, 
       Cr: 0 to 1.0%, 
       Ni: 0 to 1.0%, 
       Mo: 0 to 1.0%, 
       W: 0 to 1.0%, 
       B: 0 to 0.010%, 
       Cu: 0 to 0.50%, 
       Sn: 0 to 0.30%, 
       Bi: 0 to 0.30%, 
       Se: 0 to 0.30%, 
       Te: 0 to 0.30%, 
       Ge: 0 to 0.30%, 
       As: 0 to 0.30%, 
       Ca: 0 to 0.50%, 
       Mg: 0 to 0.50%, 
       Zr: 0 to 0.50%, 
       Hf: 0 to 0.50%, and 
       rare earth metal: 0 to 0.50%, 
       with a balance being Fe and impurities, and satisfying Formula (1):
   Si+Mn≥3.20  (1)
 
 where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1), 
 a process of heating the steel material to 1100 to 1350° C., and thereafter performing hot rolling of the steel material so as to form a steel sheet; and 
 
       a process of coiling the steel sheet at a temperature of 600 to 750° C.,
 wherein in a micro-structure of the hot-rolled steel sheet, a total area fraction of ferrite and pearlite is 75% or more; and a tensile strength of the hot-rolled steel sheet is 800 MPa or less. 
 
     
     
         16 . A production method for producing a hot-rolled steel sheet comprising:
 a preparation process of preparing a steel material having a chemical composition consisting of, in mass %:   
       C: 0.07 to 0.30%, 
       Si: more than 1.0 to 2.8%, 
       Mn: 2.0 to 3.5%, 
       P: 0.030% or less, 
       S: 0.010% or less, 
       Al: 0.01 to less than 1.0%, 
       N: 0.01% or less, 
       O: 0.01% or less, 
       Sb: 0.03 to 0.30%, 
       Ti: 0 to 0.15%, 
       V: 0 to 0.30%, 
       Nb: 0 to 0.15%, 
       Cr: 0 to 1.0%, 
       Ni: 0 to 1.0%, 
       Mo: 0 to 1.0%, 
       W: 0 to 1.0%, 
       B: 0 to 0.010%, 
       Cu: 0 to 0.50%, 
       Sn: 0 to 0.30%, 
       Bi: 0 to 0.30%, 
       Se: 0 to 0.30%, 
       Te: 0 to 0.30%, 
       Ge: 0 to 0.30%, 
       As: 0 to 0.30%, 
       Ca: 0 to 0.50%, 
       Mg: 0 to 0.50%, 
       Zr: 0 to 0.50%, 
       Hf: 0 to 0.50%, and 
       rare earth metal: 0 to 0.50%, 
       with a balance being Fe and impurities, and satisfying Formula (1):
   Si+Mn≥3.20  (1)
 
 where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1), 
 a hot rolling process of heating the steel material to 1100 to 1350° C., and thereafter performing hot rolling of the steel material so as to form a steel sheet, and cooling the steel sheet to a coiling temperature; and 
 a process of coiling the steel sheet after the cooling, at a temperature of 150 to 600° C., 
 wherein in a micro-structure of the hot-rolled steel sheet, a total area fraction of bainite and martensite is 75% or more; and a tensile strength of the hot-rolled steel sheet is 900 MPa or more. 
 
     
     
         17 . A production method for producing a hot-rolled steel sheet comprising:
 a process of preparing a steel material having a chemical composition consisting of, in mass %:   
       C: 0.07 to 0.30%, 
       Si: more than 1.0 to 2.8%, 
       Mn: 2.0 to 3.5%, 
       P: 0.030% or less, 
       S: 0.010% or less, 
       Al: 0.01 to less than 1.0%, 
       N: 0.01% or less, 
       O: 0.01% or less, 
       Sb: 0.03 to 0.30%, 
       Ti: 0 to 0.15%, 
       V: 0 to 0.30%, 
       Nb: 0 to 0.15%, 
       Cr: 0 to 1.0%, 
       Ni: 0 to 1.0%, 
       Mo: 0 to 1.0%, 
       W: 0 to 1.0%, 
       B: 0 to 0.010%, 
       Cu: 0 to 0.50%, 
       Sn: 0 to 0.30%, 
       Bi: 0 to 0.30%, 
       Se: 0 to 0.30%, 
       Te: 0 to 0.30%, 
       Ge: 0 to 0.30%, 
       As: 0 to 0.30%, 
       Ca: 0 to 0.50%, 
       Mg: 0 to 0.50%, 
       Zr: 0 to 0.50%, 
       Hf: 0 to 0.50%, and 
       rare earth metal: 0 to 0.50%, 
       with a balance being Fe and impurities, and satisfying Formula (1):
   Si+Mn≥3.20  (1)
 
 where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1), 
 a process of heating the steel material to 1100 to 1350° C., and thereafter performing hot rolling of the steel material so as to form a steel sheet; 
 a process of coiling the steel sheet at a temperature of 150 to 600° C.; and 
 a process of tempering the steel sheet after coiling, at a temperature of 550° C. or more, 
 wherein in a micro-structure of the hot-rolled steel sheet, a total area fraction of bainite and martensite is 75% or more; and a tensile strength of the hot-rolled steel sheet is 800 MPa or less. 
 
     
     
         18 . The hot-rolled steel sheet according to  claim 10 , wherein a scale thickness on a surface of the hot-rolled steel sheet is 7 μm or less.