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

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 [mu]m from the surface.

Description

technical field [0001] The present invention relates to a hot-rolled steel sheet and a manufacturing method thereof, more specifically, to a high-strength hot-rolled steel sheet with excellent surface quality and a manufacturing method thereof, wherein the hot-rolled steel sheet is used as a galvanized steel sheet (hot-dip galvanized steel sheet ( hot galvanizediron, HGI)) base steel plate. Background technique [0002] A high-strength galvanized steel sheet (hot-dip galvanized iron (HGI)) using a high-strength hot-rolled steel sheet as a base steel sheet is widely used as a frame material and the like. [0003] As the high-strength hot-rolled steel sheet as the base steel sheet of the high-strength galvanized steel sheet, a steel grade containing Nb is generally used. [0004] The high-strength hot-rolled steel sheet is usually produced by heating a steel slab containing Nb, hot-rolling it in the austenite region of Ar3 or higher, and then coiling it. [0005] However, as...

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Problems solved by technology

[0005] However, as described above, when a slab containing Nb is hot-rolled in the austenite region of Ar3 or higher, there is a problem that Nb delays recrystallization during hot rolling and increases the rolling load of finish rolling, thereby roughening the roll surface. Lead to poor passability and surface defects of the steel plate, especially defects such as sand-type scale

[0007] However, the above-mentioned prior art cannot be regarded as a fundamental solution because it causes problems such as poor passability of hot-rolled sheets and frequent dimensional changes.

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