High strength steel product with improved formability and steel manufacturing process

a technology of high strength steel and manufacturing process, applied in the field of high strength steel products, can solve the problems of material becoming harder, increasing the difficulty of further thickness reduction by rolling, and increasing the difficulty of material shaping

US20050199319A1Inactive Publication Date: 2005-09-15ALGOMA STEEL
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Patent Information

Authority / Receiving Office
US · United States
Patent Type
Applications(United States)
Current Assignee / Owner
Publication Date
2005-09-15
Estimated Expiration
Not applicable · inactive patent

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Abstract

A process and apparatus are disclosed for manufacturing high strength low alloy (HSLA) flat rolled steel products having high yield strength and formability. A preferred process comprises the formation of an as-cast product; reducing the thickness of the as cast product in a roughing mill; holding the temperature of the rough-reduced product at a temperature sufficient to permit substantially complete recrystallization of austenite grains in the rough-reduced product; followed by a final reduction step in a hot rolling strip mill. In this process, there is little or no precipitation of microalloy until after the material passes through the strip mill and therefore the material being rolled is relatively soft compared to known processes. Therefore, less power is required to roll the material to its final dimensions, with a corresponding improvement in dimensional control. The material produced according to this process has a strength of at least about 70 ksi, more preferably at least about 80 ksi, and a formability as measured by n-value within the range of from about 0.1 to about 0.15.
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Description

FIELD OF THE INVENTION

[0001] The present invention relates to high strength steel products, and more particularly to high strength low alloy (HSLA) flat rolled steel products having high yield strength and formability. The invention also relates to manufacturing processes for producing flat rolled steel products having high yield strength and formability. BACKGROUND OF THE INVENTION

[0002] Most HSLA steels are produced in conventional processes where molten steel from a basic oxygen furnace (BOF) or an electric arc furnace (EAF) is cast, cooled, reheated and reduced in thickness while still hot in a rolling mill. The rolling mill reduces the thickness of the slab to produce thin gauge steel sheet or strip material having high strength characteristics. Some HSLA steels are produced by modern thin-slab or medium-slab casting processes in which slabs of steel, still hot from the caster, are transferred directly to a reheating or equalizing furnace prior to thickness reduction in the h...

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Embodiment Construction

[0026] The process according to the present invention preferably utilizes many of the same process steps and apparatus as modern thin slab and medium slab processes for producing flat rolled steel products. Typical processes of this type utilize a furnace to produce molten steel, at least a portion of which may comprise scrap material. The molten steel is cast, preferably on a continuous basis, to produce a slab having a thickness of from about 30 to about 200 mm. According to the present invention, It is preferred that the hot as-cast slab is directly charged into a reheating or equalizing furnace to prevent excessive cooling. However, the process of the invention is also compatible with processes in which the as-cast slab is allowed to cool before further processing.

[0027] A preferred process and apparatus according to the present invention are schematically illustrated in FIG. 1. As in known thin slab and medium slab casting processes, molten steel 10 is produced in a furnace (n...