Hot-rolled steel sheet

Abstract

A hot-rolled steel sheet includes a predetermined chemical composition, and a structure which includes, by area ratio, ferrite and bainite in a range of 75% to 95% in total, and martensite in a range of 5% to 20%, in which in the structure, in a case where a boundary having an orientation difference of equal to or greater than 15° is set as a grain boundary, and an area which is surrounded by the grain boundary, and has an equivalent circle diameter of equal to or greater than 0.3 μm is defined as a grain, the ratio of the grains having an intragranular orientation difference in a range of 5° to 14° is, by area ratio, in a range of 10% to 60%.

1 . A hot-rolled steel sheet comprising, as a chemical composition, by mass %,
 C: 0.04% to 0.18%,   Si: 0.10% to 1.70%,   Mn: 0.50% to 3.00%,   Al: 0.010% to 1.00%,   B: 0% to 0.005%,   Cr: 0% to 1.0%,   Mo: 0% to 1.0%,   Cu: 0% to 2.0%,   Ni: 0% to 2.0%,   Mg: 0% to 0.05%,   REM: 0% to 0.05%,   Ca: 0% to 0.05%,   Zr: 0% to 0.05%,   P: limited to equal to or less than 0.050%,   S: limited to equal to or less than 0.010%, and   N: limited to equal to or less than 0.0060%, with the remainder including Fe and impurities;   wherein a structure includes, by area ratio, a ferrite and a bainite in a range of 75% to 95% in total, and a martensite in a range of 5% to 20%, and   wherein in the structure, in a case where a boundary having an orientation difference of equal to or greater than 15° is defined as a grain boundary, and an area which is surrounded by the grain boundary and has an equivalent circle diameter of equal to or greater than 0.3 μm is defined as a grain, the ratio of the grains having an intragranular orientation difference in a range of 5° to 14° is, by area ratio, in a range of 10% to 60%.   
     
     
         2 . The hot-rolled steel sheet according to  claim 1 ,
 wherein a tensile strength is equal to or greater than 590 MPa, and a product of the tensile strength and a limit forming height in a saddle type stretch flange test is equal to or greater than 19500 mm·MPa.   
     
     
         3 . The hot-rolled steel sheet according to  claim 1  or  2 ,
 wherein the chemical composition contains, by mass %, 
 
       one or more selected from the group consisting of:
 B: 0.0001% to 0.005%, 
 Cr: 0.01% to 1.0%, 
 Mo: 0.01% to 1.0%, 
 Cu: 0.01% to 2.0%, and 
 Ni: 0.01% to 2.0%. 
 
     
     
         4 . The hot-rolled steel sheet according to  claim 1  or  2 ,
 wherein the chemical composition contains, by mass %, one or more selected from the group consisting of: 
 Mg: 0.0001% to 0.05%, 
 REM: 0.0001% to 0.05%, 
 Ca: 0.0001% to 0.05%, and 
 Zr: 0.0001% to 0.05%. 
 
     
     
         5 . The hot-rolled steel sheet according to  claim 3 ,
 wherein the chemical composition contains, by mass %, one or more selected from the group consisting of:   Mg: 0.0001% to 0.05%,   REM: 0.0001% to 0.05%,   Ca: 0.0001% to 0.05%, and   Zr: 0.0001% to 0.05%.