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

Patent metadata

Field	Value
Publication number	US-9499873-B2
Application number	US-201314422496-A
Country	US
Kind code	B2
Filing date	Dec 3, 2013
Priority date	Dec 28, 2012
Publication date	Nov 22, 2016
Grant date	Nov 22, 2016

Abstract

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/mm 2 , a tensile strength is 780 to 940 N/mm 2 , 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.

First claim

The invention claimed is:

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/mm 2 ,
a tensile strength is 780 to 940 N/mm 2 ,
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 1

β=0.65×C 1/2 ×(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.

2. The steel plate according to claim 1 , wherein the chemical composition includes, in terms of mass %:
Mn—: 0.7 to 1.2%;
Ni—: 0.8 to 2.5%;
Cr—: 0.5 to 1.0%;
Mo—: 0.35 to 0.75%;
V—: 0.02 to 0.05%;
Al—: 0.04 to 0.08%; and
Cu—: 0.2 to 0.7%.

3. The steel plate according to claim 1 , wherein the plate thickness of the steel plate is 50 to 150 mm.

4. The steel plate according to claim 1 , wherein
when a stress relief annealing is performed on the steel plate with a holding temperature of 560° C., a holding time of h hours defined by Expression 3 and Expression 4, a rate of temperature increase within a temperature range of 425° C. or more of 55° C./hour or less, and a rate of temperature decrease within the temperature range of 425° C. or more of 55° C./hour or less, a Charpy absorbed energy at −40° C. is 100 J or more,
when t≧ 50, h=t/ 25  Expression 3,

when t<50, h=2  Expression 4, and

t indicates the plate thickness of the steel plate in terms of mm and h indicates the holding time in unit of hour.

5. The steel plate according to claim 2 , wherein the plate thickness of the steel plate is 50 to 150 mm.

6. The steel plate according to claim 1 , wherein the chemical composition includes, in terms of mass %:
Mn: 0.5 to 0.88%.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Saitoh Naoki
• Sawamura Mitsuru
• Kurebayashi Katsumi
• Takahashi Yasunori
• Miyake Takumi

Classifications

• C22C38/42

  with copper · CPC title

• C22C38/46

  with vanadium · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/54

  with boron · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title