Steel sheet

Patent metadata

Field	Value
Publication number	US-2016076123-A1
Application number	US-201414785788-A
Country	US
Kind code	A1
Filing date	Apr 24, 2014
Priority date	Apr 25, 2013
Publication date	Mar 17, 2016
Grant date	—

Abstract

A steel sheet according to the present invention includes a predetermined chemical composition, in which amounts of each elements by mass % in the chemical composition satisfy both of expression “0.3000≦{Ca/40.88+(REM/140)/2}/(S/32.07)” and expression “Ca≦0.0058−0.0050×C”, and a number density of carbonitrides including Ti which exists independently and has a long side of 5 μm or more is limited to 5 pieces/mm 2 or less.

First claim

1 . A steel sheet, wherein
a chemical composition comprises, by mass %: C: more than 0.25% and less than 0.50%; Si: 0.10% to 0.60%; Mn: 0.40% to 0.90%; Al: 0.003% to 0.070%; Ca: 0.0005% to 0.0040%; REM: 0.0003% to 0.0050%; Cu: 0% to 0.05%; Nb: 0% to 0.05%; V: 0% to 0.05%; Mo: 0% to 0.05%; Ni: 0% to 0.05%; Cr: 0% to 0.50%; B: 0% to 0.0050%; P: limited to 0.020% or less; S: limited to 0.0070% or less; Ti: limited to 0.050% or less; O: limited to 0.0040% or less; N: limited to 0.0075% or less; and remainder including iron and impurity, amounts of each elements by mass % in the chemical composition satisfy both of expression 1 and expression 2, a number density of carbonitrides including Ti which exists independently and has a long side of 5 μm or more is limited to 5 pieces/mm2 or less,
0.3000≦{Ca/40.88+(REM/140)/2}/(S/32.07):  expression 1, and

Ca≦0.0058−0.0050× C:   expression 2.

2 . The steel sheet according to claim 1 , wherein
the chemical composition further comprises one or more of, by mass %: Cu: 0.01% to 0.05%; Nb: 0.01% to 0.05%; V: 0.01% to 0.05%; Mo: 0.01% to 0.05%; Ni: 0.01% to 0.05%; Cr: 0.01% to 0.50%; and B: 0.0010% to 0.0050%.

3 . The steel sheet according to claim 1 , wherein
the steel sheet further includes a composite inclusion which includes Al, Ca, O, S, and REM, and an inclusion in which the carbonitride including Ti is adhered on the composite inclusion.

4 . The steel sheet according to claim 1 , wherein
the amounts of the each elements by mass % in the chemical composition satisfy expression 3,
18×(REM/140)−O/16≧0:  expression 3.

5 . The steel sheet according to claim 3 , wherein
the amounts of the each elements by mass % in the chemical composition satisfy expression 4,
18×(REM/140)−O/16≧0:  expression 4.

6 . The steel sheet according to claim 2 , wherein
the steel sheet further includes a composite inclusion which includes Al, Ca, O, S, and REM, and an inclusion in which the carbonitride including Ti is adhered on the composite inclusion.

7 . The steel sheet according to claim 2 , wherein
the amounts of the each elements by mass % in the chemical composition satisfy expression 3,
18×(REM/140)−O/16≧0:  expression 3.

8 . The steel sheet according to claim 6 , wherein
the amounts of the each elements by mass % in the chemical composition satisfy expression 4,
18×(REM/140)−O/16≧0:  expression 4.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Morohoshi Takashi
• Aramaki Takashi
• Zeze Masafumi

Classifications

• C22C38/54

  with boron · CPC title

• C22C38/50 Primary

  with titanium or zirconium · CPC title

• C21D9/46

  for sheet metals · CPC title

• C21C7/068

  Decarburising · CPC title

• C21C7/06

  Deoxidising, e.g. killing · CPC title