Hot-rolled steel sheet for high strength galvanized steel sheet, having excellent surface quality, and method for producing same

Patent metadata

Field	Value
Publication number	US-10351927-B2
Application number	US-201415533609-A
Country	US
Kind code	B2
Filing date	Dec 24, 2014
Priority date	Dec 22, 2014
Publication date	Jul 16, 2019
Grant date	Jul 16, 2019

Abstract

The present invention relates to a hot-rolled steel sheet for a high strength galvanized steel sheet, having excellent surface quality, and a method for producing the same, the hot-rolled steel sheet comprising, by weight %: C: 0.05 to 0.15%, Si: 0.03 to 0.10%, Mn: 0.7 to 1.39%, P: 0.001 to 0.05%, S: 0.001 to 0.03%, Al: 0.002 to 0.035%, and the remainder being Fe and unavoidable impurities. The weight ratio of Mn/Si is 15 to 25, the weight ratio of C/Si is 1 to 5, and the weight ratio of Si/P is 3 to 10. The hot-rolled steel sheet has a microstructure consisting of, in area fraction, 10 to 40% of bainite, 20 to 30% of pearlite and 40 to 60% of ferrite, and includes a ternary eutectic compound of FeO, Fe2SiO4 and Fe3(PO)4 formed within 50 μm from the surface.

First claim

The invention claimed is:

1. A high-strength hot-rolled steel sheet having excellent surface quality characterized in that it comprises, by weight %, C: 0.05 to 0.15%, Si: 0.03 to 0.10%, Mn: 0.7 to 1.39%, P: 0.001 to 0.05%, S: 0.001 to 0.03%, Al: 0.002 to 0.035%, the remainder Fe and other unavoidable impurities, wherein the weight ratio of Mn/Si is 15 to 25, the weight ratio of C/Si is 1 to 5, and the weight ratio of Si/P is 3 to 10, a microstructure consists of, in an area fraction, 10 to 40% of bainite, 20 to 30% of pearlite and 40% to 60% of ferrite, and a ternary eutectic compound of FeO, Fe 2 SiO 4 and Fe 3 (PO 4 ) 2 is formed within 50 μm from the surface of the steel sheet.

2. The high-strength hot-rolled steel sheet having excellent surface quality according to claim 1 , characterized in that said steel sheet further comprises, by weight %, one or two or more selected from the group consisting of N: 0.01% or less (excluding 0), Ti: 0.02% or less (excluding 0), Cu: 0.05% or less (excluding 0), Ni: 0.08% or less (excluding 0), Cr: 0.10% or less (excluding 0), V: 0.01% or less (excluding 0) and Mo: 0.03% or less (excluding 0).

3. The high-strength hot-rolled steel sheet having excellent surface quality according to claim 1 , characterized in that the number of sand type scales having a point shape formed on both surfaces of said steel sheet is an average of 0.1 pieces/m 3 or less.

4. The high-strength hot-rolled steel sheet having excellent surface quality according to claim 1 , characterized in that said steel sheet comprises a zinc plated layer formed on the steel sheet.

5. The high-strength hot-rolled steel sheet having excellent surface quality according to claim 1 , characterized in that said steel sheet has a tensile strength of 490 to 650 MPa, a yield strength of 366 to 600 MPa, and an elongation of 16 to 30%.

6. A method for producing a high-strength hot-rolled steel sheet having excellent surface quality, comprising steps of
heating a slab comprising, by weight %, C: 0.05 to 0.15%, Si: 0.03 to 0.10%, Mn: 0.7 to 1.39%, P: 0.001 to 0.05%, S: 0.001 to 0.03%, Al: 0.002 to 0.035%, the remainder Fe and other unavoidable impurities at 1000 to 1250.degree. C., wherein the weight ratio of Mn/Si is 15 to 25 and the weight ratio of C/Si is 1 to 5 and the weight ratio of Si/P is 3 to 10;
rough rolling the heated slab at 990 to 1090° C. to obtain a bar;
finish rolling said bar at a finish rolling temperature of 810 to 910° C. to obtain a hot-rolled steel sheet; and
coiling said hot-rolled steel sheet at a coiling temperature of 510 to 610° C.,
wherein a microstructure consists of, in an area fraction, 10 to 40% of bainite, 20 to 30% of pearlite and 40% to 60% of ferrite, and a ternary eutectic compound of FeO, Fe 7 SiO 4 and Fe 3 (PO 4 ) 2 is formed within 50 μm from the surface of the steel sheet.

7. The method for producing a high-strength hot-rolled steel sheet having excellent surface quality according to claim 6 , characterized in that said slab further comprises, by weight %, one or two or more selected from the group consisting of N: 0.01% or less (excluding 0), Ti: 0.02% or less (excluding 0), Cu: 0.05% or less (excluding 0), Ni: 0.08% or less (excluding 0), Cr: 0.10% or less (excluding 0), V: 0.01% or less (excluding 0) and Mo: 0.03% or less (excluding 0).

8. The method for producing a high-strength hot-rolled steel sheet having excellent surface quality according to claim 6 , characterized in that said coiling temperature is 550 to 570° C.

9. The method for producing a high-strength hot-rolled steel sheet having excellent surface quality according to claim 6 , further comprising a step of forming a zinc plated layer on the steel sheet after said coiling step.

Assignees

• Posco

Inventors

• Kwak Hyo Jung
• Kim Young-Ha
• Seo Seok Jong

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C22C38/04 Primary

  containing manganese · CPC title

• C22C38/26

  with niobium or tantalum · CPC title

• C22C38/001

  containing N · CPC title

• Y10T428/12799

  Next to Fe-base component [e.g., galvanized] · CPC title