Cold-rolled steel sheet, electrolytic zinc-coated cold-rolled steel sheet, hot-dip zinc-coated cold-rolled steel sheet, alloyed hot-dip zinc-coated cold-rolled steel sheet, and methods for producing said steel sheets

Abstract

A cold-rolled steel sheet which contains, in mass%, 0.0005 to 0.0045% of C, 0.80 to 2.50% of Mn, 0.002 to 0.150% of Ti and 0.0005 to 0.01% of B, fulfills the requirement represented by formula (1), and also contains iron and unavoidable impurities as a remainder, wherein the random strength ratio (A) in the (332) <110> orientation is 3 or less and each of the random strength ratio (B) in the (557)<9 16 5> orientation and the random strength ratio (C) in the(111)<112> orientation is 7 or more as measured at a position corresponding to one-fourth of the thickness of the steel sheet, and the requirements represented by the formulae ( (B) / (A) >= 5) and ( (B) > (C) ) are fulfilled.

Description

technical field [0001] The present invention relates to cold-rolled steel sheets excellent in rigidity and deep drawability, zinc-based electroplated cold-rolled steel sheets, hot-dip galvanized cold-rolled steel sheets, alloyed hot-dip galvanized cold-rolled steel sheets, and methods for producing them. Background technique [0002] In the automotive field, from the viewpoint of improving fuel consumption, there is an increasing demand for lightweight car bodies, and from the viewpoint of ensuring crash safety, various high-strength steel sheets are used in automotive parts. However, the Young's modulus does not change even when the yield strength and tensile strength of the steel are increased by strengthening mechanisms such as structure strengthening and fine-graining effect. Therefore, when the thickness of the steel plate is reduced for weight reduction, the rigidity of the member decreases, making it difficult to reduce the thickness of the steel plate. [0003] On t...

AI Technical Summary

Problems solved by technology

However, since the {112} orientation significantly reduces the r value in the rolling direction and the transverse direction, there is a problem that the deep drawability is significantly deteriorated.

In addition, the Young's modulus in the rolled 45° direction is lower than that of ordinary steel plates, so there is a problem that it can only be applied to unidirectional long parts such as frame parts, and cannot be applied to panel parts, which require Components with Young's modulus in multiple directions such as torsional rigidity

However, the technique described in Patent Document 8 has a problem of high load on the rolling mill, such as performing rolling with a total reduction of 85% or more in the temperature range of Ar3 to Ar3+150°C.

In addition, in Patent Document 8, the Young's modulus in the 45° direction is not necessarily high, and the well-developed crystal orientation is not appropriate, so it is impossible to obtain remarkable rigidity.

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