HOT ROLLED STEEL PLATE FOR ELECTRIC RESISTANCE WELDED STEEL PIPE HAVING EXCELLENT WELDABILITY, AND MANUFACTURING METHOD THEREOF

• US 20190323103A1
• Filed: 11/29/2017
• Published: 10/24/2019
• Est. Priority Date: 12/19/2016
• Status: Active Grant

• Current Assignee: POSCO Co. Ltd. (Posco Holdings Incorporated)
• Original Assignee: Posco Holdings Incorporated
• Inventors: SEO, Seok-Jong, NA, Hyun-Taek
• Granted Patent: US 11,535,907 B2
• Time in Patent Office: Days
• CPC Class Codes: B21B 3/02 Rolling special iron alloys , e.g. stainless steel
• CPC Class Codes: B21B 37/74 Temperature control, e.g. by cooling or heating the rolls or the product B21B37/32, B21B37/44 take precedence
• CPC Class Codes: B23K 11/0873 of the longitudinal seam of tubes
• CPC Class Codes: B23K 11/16 taking account of the properties of the material to be welded
• CPC Class Codes: B23K 2101/06 Tubes
• CPC Class Codes: B23K 2101/18 Sheet panels
• CPC Class Codes: B23K 2103/04 Steel or steel alloys
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 6/002 containing Cr C21D6/004 takes precedence
• CPC Class Codes: C21D 6/005 containing Mn
• CPC Class Codes: C21D 6/008 containing Si
• CPC Class Codes: C21D 8/0205 of ferrous alloys
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 8/105 of ferrous alloys
• CPC Class Codes: C21D 9/08 for tubular bodies or pipes
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 : containing silicon
• CPC Class Codes: C22C 38/04 : containing manganese
• CPC Class Codes: C22C 38/06 : containing aluminium
• CPC Class Codes: C22C 38/24 : with vanadium
• CPC Class Codes: C22C 38/26 : with niobium or tantalum
• CPC Class Codes: C22C 38/28 : with titanium or zirconium
• CPC Class Codes: C22C 38/38 : with more than 1.5% by weight of manganese

Abstract

Provided is a steel used for chassis parts, etc. of an automobile and, more specifically, to a hot rolled steel plate for an electric resistance welded steel pipe, which shows an excellent weldability in electric resistance welding, and a manufacturing method thereof.

Claims

1. A hot rolled steel plate for an electric resistance welded steel pipe having excellent weldability, comprising, by wt %:

carbon (C);

0.05 to 0.14%, silicon (Si);

0.1 to 1.0%, manganese (Mn);

0.8 to 1.8%, phosphorus (P);

0.001 to 0.02%, sulfur (S);

0.001 to 0.01%, aluminum (Al);

0.1 to 0.3%, chromium (Cr);

0.3 to 1.0%, titanium (Ti);

0.01 to 0.05%, niobium (Nb);

0.025% or less, vanadium (V);

0.035% or less, nitrogen (N);

0.001 to 0.01%, and the balance of iron (Fe) and inevitable impurities,

wherein Mn and Si satisfy the following Relational Expression 1, a microstructure comprises a mixture of martensite and bainite phases together with a ferrite phase as a matrix structure, and the following Relational Expression 2 is satisfied,

4<

Mn/Si<

12 

 

[Relational Expression 1]

where, Mn and Si refers to a weight content of each element,

SSG_M+B/(M+B+SSG_M+B)≥

0.6 

 

[Relational Expression 2]

where, M refers to a martensite phase, B refers to a bainite phase, and SSG_M+B refers to a hard phase in which the B and M phases exist together in a single grain, that is, a structure in which the M phase exists around a grain boundary, and the B phase exists in a central region, and each phase refers to an area fraction (%).

2. The hot rolled steel plate for an electric resistance welded steel pipe having excellent weldability of claim 1, wherein the ferrite phase comprises an area fraction of 60 to 85%.

3. The hot rolled steel plate for an electric resistance welded steel pipe having excellent weldability of claim 1, wherein the hot rolled steel plate has tensile strength of 590 MPa or more and a yield ratio (YR=YS/TS) of 0.8 or less.

4. The hot rolled steel plate for an electric resistance welded steel pipe having excellent weldability of claim 1, wherein the hot rolled steel plate has a Vickers hardness difference (Δ

Hv) between a weld heat affected zone formed at the time of electric resistance welding and a base material is 30 or less.

7. An electric resistance welded steel pipe having excellent expandability, manufactured by electric resistance welding the hot rolled steel plate of claim 1.

5. A manufacturing method of a hot rolled steel plate for an electric resistance steel pipe having excellent weldability comprising steps of:

reheating steel slab including by wt %;

carbon (C);

0.05 to 0.14%, silicon (Si);

0.1 to 1.0%, manganese (Mn);

0.8 to 1.8%, phosphorus (P);

0.001 to 0.02%, sulfur (S);

0.001 to 0.01%, aluminum (Al);

0.1 to 0.3%, chromium (Cr);

0.3 to 1.0%, titanium (Ti);

0.01 to 0.05%, niobium (Nb);

0.025% or less, vanadium (V);

0.035% or less, nitrogen (N);

0.001 to 0.01%, and the balance of iron (Fe) and inevitable impurities, Mn and Si satisfying the following Relational Expression 1, to a temperature within a range of 1180 to 1300°

C.;

finish hot rolling the reheated steel slab at a temperature equal to or higher than Ar3 to manufacture a hot rolled steel plate;

first cooling the hot rolled steel plate to a temperature within a range of 550 to 750°

C. at a cooling rate of 20°

C./s or higher;

second cooling the hot rolled steel plate at a cooling rate of 0.05 to 2.0°

C./s within a range satisfying the following Relational Expression 3 after the first cooling;

third cooling the hot rolled steel plate at a cooling rate of 20°

C./s or higher to a temperature within a range of room temperature to 400°

C. after the second cooling; and

coiling the hot rolled steel plate after the third cooling,

4<

Mn/Si<

12 

 

[Relational Expression 1]

where, Mn and Si refer to a weight content of each element,

|t−

ta|≤

2

(ta=252+(109[C])+(10.2[Mn])+(22.81[Cr])−

(3.46[Si])−

(5.41[Al])−

(0.87 Temp)+(0.00068 Temp̂

2), where, t refers to a retention time (sec) of the second cooling (extreme slow cooling zone), ta refers to a retention time (sec) of the second cooling (extreme slow cooling zone) for securing an optimal phase fraction, and Temp refers to an intermediate temperature of the second cooling(extreme slow cooling zone), and a temperature at a middle point between a second cooling starting point and an stop point, where each alloy composition refers to a weight content.

6. The manufacturing method of a hot rolled steel plate for an electric resistance welded steel pipe having excellent weldability of claim 5, further comprising a step of pickling the coiled hot rolled steel plate and then greasing.