Steel plate having yield strength of 670 to 870 N/mm²and tensile strength of 780 to 940 N/mm²

摘要

In a steel plate according to the present invention, a chemical composition is within a predetermined range, an α value is 0.13 to 1.0 mass %, a β value is 8.45 to 15.2, an yield strength is 670 to 870 N/mm2, a tensile strength is 780 to 940 N/mm2, an average grain size at ½t of the steel plate is 35 μm or less, and a plate thickness is 25 to 200 mm. In the steel plate according to the present invention, in a case where SR is performed on the steel, a charpy absorbed energy at −40° C. in an area in which SR is performed may be 100 J or more.

主权项

1. A steel plate having a chemical composition comprising, in terms of mass %:
C—: 0.07 to 0.10%; Si—: 0.01 to 0.10%; Mn—: 0.5 to 1.5%; Ni—: 0.5 to 3.5%; Cr—: 0.1 to 1.5%; Mo—: 0.1 to 1.0%; V—: 0.005 to 0.070%; Al—: 0.01 to 0.10%; B—: 0.0005 to 0.0020%; N—: 0.002 to 0.010%; P—: 0.006% or less; S—: 0.003% or less; Cu—: 0 to 1%; Nb—: 0 to 0.05%; Ti—: 0 to 0.020%; Ca—: 0 to 0.0030%; Mg—: 0 to 0.0030%; REM-: 0 to 0.0030%; and the remainder including Fe and impurities,
wherein an α value defined by Expression 1 is 0.13 to 1.0 mass %, a β value defined by Expression 2 is 8.45 to 15.2, a yield strength is 670 to 870 N/mm2, a tensile strength is 780 to 940 N/mm2, a grain is defined as an area surrounded by a boundary in which a misorientation is 30° or more and which is identified by performing an orientation analysis using an electron beam backscatter diffraction pattern analysis method, a grain size is defined as an equivalent circle diameter of the grain, an average grain size is defined as a grain size at which a cumulative frequency is 90% when a frequency distribution of the grain size is cumulated from a small grain size side, the average grain size at mid-thickness of the steel plate is 35 μm or less, and a plate thickness is 25 to 200 mm, and
wherein
α=C+6×Si+100×P  Expression 1β=0.65×C1/2×(1+0.64×Si)×(1+4.10×Mn)×(1+0.27×Cu)×(1+0.52×Ni)×(1+2.33×Cr)×(1+3.14×Mo)  Expression 2, and C, Si, P, Mn, Cu, Ni, Cr, and Mo indicate the amounts of C, Si, P, Mn, Cu, Ni, Cr, and Mo in terms of mass %, respectively.