Hot rolled steel sheet for square column for building structural members

Patent metadata

Field	Value
Publication number	US-9708680-B2
Application number	US-201214391899-A
Country	US
Kind code	B2
Filing date	Apr 12, 2012
Priority date	Apr 12, 2012
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

Abstract

A hot rolled steel sheet for a square column for building structural members, the hot rolled steel sheet having a composition of, in terms of % by mass,
C: 0.07 to 0.18%, Mn: 0.3 to 1.5%, P: 0.03% or less, S: 0.015% or less, N: 0.006% or less, Al: 0.01 to 0.06%,

and the balance being Fe and unavoidable impurities, and having a microstructure that includes a primary phase constituted of ferrite and a second phase constituted of pearlite or pearlite and bainite, wherein a second phase frequency defined by equation (1) below is 0.20 to 0.42 and a mean crystal grain diameter of the primary phase and the second phase together is 7 to 15 μm

Second phase frequency=(Number of second phase grains intersecting line segments of particular length)/(Number of primary phase grains and second phase grains intersecting line segments of particular length)  (1).

First claim

The invention claimed is:

1. A hot rolled steel sheet for a square column for building structural members, the hot rolled steel sheet having a composition of, in terms of % by mass,
C: 0.07 to 0.17%, Mn: 0.3 to 1.5%,
P: 0.03% or less, S: 0.015% or less,
Al: 0.01 to 0.06%, N: 0.006% or less,
and the balance being Fe and unavoidable impurities, and having a microstructure that includes a primary phase constituted of ferrite and a second phase constituted of pearlite or pearlite and bainite, wherein a second phase frequency defined by equation (1) below is 0.20 to 0.42 and a mean crystal grain diameter of the primary phase and the second phase together is 7 to 15 μm
Second phase frequency=(Number of second phase grains intersecting line segments of a length)/(Number of primary phase grains and second phase grains intersecting line segments of the same length)  (1).

2. The hot rolled steel sheet according to claim 1 , wherein the composition further comprises Si: less than 0.4% by mass.

3. The hot rolled steel sheet according to claim 1 , wherein the composition further comprises at least one selected from Nb: 0.015% or less, Ti: 0.030% or less, and V: 0.070% or less in terms of % by mass.

4. The hot rolled steel sheet according to claim 1 , wherein the composition further comprises B: 0.008% by mass or less.

5. A square column for building structural members, manufactured by cold-forming a raw material which is the hot rolled steel sheet according to claim 1 .

6. The hot rolled steel sheet according to claim 2 , wherein the composition further comprises at least one selected from Nb: 0.015% or less, Ti: 0.030% or less, and V: 0.070% or less in terms of % by mass.

7. The hot rolled steel sheet according to claim 2 , wherein the composition further comprises B: 0.008% by mass or less.

8. The hot rolled steel sheet according to claim 3 , wherein the composition further comprises B: 0.008% by mass or less.

9. The hot rolled steel sheet according to claim 6 , wherein the composition further comprises B: 0.008% by mass or less.

Assignees

• Kami Chikara
• Tamura Yuta
• Tamai Takato
• Kawamura Shuji
• Jfe Steel Corp

Inventors

• Kami Chikara
• Tamura Yuta
• Tamai Takato
• Kawamura Shuji

Classifications

• C22C38/002

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

• C22C38/02

  containing silicon · CPC title

• C21D8/0226

  Hot rolling · CPC title

• C21D2211/005

  Ferrite · CPC title

• C21D6/008

  containing Si · CPC title