HOT ROLLED STEEL PLATE FOR ELECTRIC RESISTANCE WELDED STEEL PIPE HAVING EXCELLENT WELDABILITY, AND MANUFACTURING METHOD THEREOF
First Claim
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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,
SSGM+B/(M+B+SSGM+B)≥
0.6
[Relational Expression 2]where, M refers to a martensite phase, B refers to a bainite phase, and SSGM+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 (%).
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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.
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Citations
7 Claims
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1. A hot rolled steel plate for an electric resistance welded steel pipe having excellent weldability, comprising, by wt %:
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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,
SSGM+B/(M+B+SSGM+B)≥
0.6
[Relational Expression 2]where, M refers to a martensite phase, B refers to a bainite phase, and SSGM+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 (%). - View Dependent Claims (2, 3, 4, 7)
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5. A manufacturing method of a hot rolled steel plate for an electric resistance steel pipe having excellent weldability comprising steps of:
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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; andcoiling 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. - View Dependent Claims (6)
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Specification