Raw material for high-strength steel plate, high-strength steel plate, and manufacturing method thereof

Abstract

The present invention provides a high-strength steel sheet having a tensile strength of 980 MPa or more and a TS-El balance of 30,000 MPa% or more, which has excellent surface quality and formability by improving internal quality such as slab surface quality and segregation during casting . The high-strength steel plate has the following composition: when 1.1≤(Ti+Mn 1 / 2 / 400) / (0.01+5N)≤6.0 ​​contains C: 0.08 to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al : 1.5% or less, Ti: 0.010 to 0.300% or less, and N: 0.0020 to 0.0100% or less, the high-strength steel sheet has a structure including retained austenite phase and ferrite phase, wherein the retained austenite phase The ratio γMn / αMn of the average Mn concentration (γMn) to the average Mn concentration (αMn) of the ferrite phase is 1.5 or more.

Description

technical field [0001] The present invention relates to a high-strength steel sheet excellent in surface quality and a balance between strength and ductility, which is used in applications requiring both high strength and high formability, such as steel sheets for automobiles or structural materials, construction machinery, and pipes, and the production of the same. High-strength steel sheets are preferred intermediate products, and methods for their manufacture. Background technique [0002] For steel used in fields such as steel sheets for automobiles, structural materials, construction machinery, and pipes, in order to maintain the function of the steel product itself and protect people inside the steel structure against external impacts and loads, material, requiring high strength. Especially in recent years, from the viewpoint of reducing the environmental load and reducing the cost, it is required to reduce the weight of the steel plate, so it is necessary to maintain...

AI Technical Summary

Problems solved by technology

However, in this method, the thickness of the solidified shell (shell) becomes thinner due to slow cooling, and the extent of the convex phenomenon in which the shell expands outward due to the pressure of molten steel becomes serious, thereby causing longitudinal cracks and subsurface cracks. The resulting deterioration of surface quality, as well as the deterioration of materials such as ductility and tensile flangeability caused by local hard parts caused by internal cracks and severe center segregation

In addition, since it is subjected to strain while maintaining a high temperature for a long time, elements added for precipitation strengthening of the final product such as Ti, Nb, and V are significantly coarsened in the slab, even in the heating furnace during subsequent hot rolling. It cannot be fully dissolved, so there is a disadvantage that the amount of precipitation strengthening decreases.

In addition, in order to completely solidify in the continuous casting machine, it is necessary to slow down the casting speed (Vc), which will reduce the manufacturing efficiency

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