Hot-rolled steel sheet and method for producing the same

Abstract

A hot-rolled steel sheet according to the present embodiment has a chemical composition containing, in mass %: C: 0.07 to 0.30%, Si: more than 1.0 to 2.8%, Mn: 2.0 to 3.5%, P: 0.030% or less, S: 0.010% or less, Al: 0.01 to less than 1.0%, N: 0.01% or less, O: 0.01% or less, and one or more types selected from the group consisting of Sb, Sn and Te in a total amount of 0.03 to 0.30%, with a balance being Fe and impurities, and satisfying Formula (1). The micro-structure of the hot-rolled steel sheet includes ferrite and pearlite in a total amount of 50 area % or more. The tensile strength of the hot-rolled steel sheet is 900 MPa or less.Si+Mn≥3.20  (1)Where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1).

Description

TECHNICAL FIELD[0001]The present invention relates to a hot-rolled steel sheet and a method for producing the hot-rolled steel sheet.BACKGROUND ART[0002]In order to compatibly achieve both collision safety and a reduction in weight of automobiles, the application of high strength steel sheets to automobiles is progressing. A high strength steel sheet contains a large amount of alloying elements to increase strength. In particular, a high strength steel sheet having a tensile strength of 980 MPa or more contains a large amount of Si and Mn.[0003]A high strength steel sheet is usually produced by the following method. First, a slab is hot rolled to produce a hot-rolled steel sheet, which is then coiled in a coil shape. Next, the hot-rolled steel sheet is pickled, cold-rolled, and annealed.[0004]The temperature of the hot-rolled steel sheet when being coiled into a coil shape (hereunder, referred to as “coiling temperature”) may be raised to enhance the cold workability of the hot-roll...

AI Technical Summary

Benefits of technology

The present invention relates to a hot-rolled steel sheet that has reduced internal oxidation and scale formation. The technical effect of this innovation is to improve the quality of the steel sheet and enhance its performance in various applications.

Problems solved by technology

The internal oxidized layer reduces the surface properties, formability and weldability of the steel sheet after cold rolling (cold-rolled steel sheet).

The scale reduces the surface properties, formability and weldability of the steel sheet.

However, if the internal oxidized layer or the scale is thick, an excessive workload is applied in the pickling treatment for the hot-rolled steel sheet.

Furthermore, the internal oxidized layer or the scale peel off during forming of the cold-rolled steel sheet, and cause surface defects such as indentation defects.

Therefore, an internal oxidized layer is liable to arise in a hot-rolled steel sheet in which the content of Si and Mn is high.

Scale is similarly liable to become thick on a hot-rolled steel sheet having a high Si and Mn content.

If the coiling temperature is raised in order to enhance the cold workability of the hot-rolled steel sheet as described above, an internal oxidized layer is more liable to arise, and is liable to be thick.

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