Patent ID: 8052808
Filing Date: 2011-11-08
Classification: C21D

Abstract:
1. A hot rolled steel sheet comprising Fe and: 0.010 to 0.05 percent by mass carbon (C); 0.5 to 2.5 percent by mass silicon (Si); 2.5 to 3.5 percent by mass manganese (Mn); 0.01 to 0.1 percent by mass aluminum (Al); 0.30 percent by mass or less titanium (Ti); 0.3 percent by mass or less nickel (Ni); 0.008 percent by mass or less nitrogen (N); and 0.005 percent by mass or less sulfur (S), wherein the contents of C, Ti, N, and S satisfy following condition (1): the contents of Si and Mn satisfy following condition (2): wherein [C] represents a content of C in percent by mass, [Ti] represents a content of Ti in percent by mass, [N] represents a content of N in percent by mass, [S] represents a content of S in percent by mass, [Si] represents a content of Si in percent by mass, and [Mn] represents a content of Mn in percent by mass, wherein the hot rolled steel sheet has a microstructure comprising: an area percentage of bainitic ferrite of 90 percent by area or more; an area percentage of martensite of 5 percent by area or less; and an area percentage of bainite of 5 percent by area or less, based on the area of an observed field, and wherein a tensile strength of the steel is 980 MPa or higher; a hole expansion ratio λ of the steel is 70% or more; and a value of a tensile strength of the steel (MPa)×a hole expansion ratio λ of the steel (%) is equal to or larger than 81,804 MPa·%.