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High-strength steel sheets and processes for production of the same

A high-strength steel plate and a manufacturing method technology, applied in the direction of manufacturing tools, furnace types, furnaces, etc., can solve the problems of insufficient elongation, poor ductility, insufficient tensile flanging, etc., and achieve excellent elongation and tensile flanging. Excellent edge properties, elongation and stretch flanging properties, and excellent extrusion formability.

Inactive Publication Date: 2009-06-17
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the elongation EL (%) is less than 8%, and the ductility is poor
[0008] However, since the steel sheet produced by the steelmaking method disclosed in Patent Document 4 has a relatively high cooling stop temperature in the steelmaking process, a large amount of bainite is precipitated and a large amount of retained austenite remains, so the ductility is excellent, but the tensile strength is high. Insufficient flanging
The steelmaking method of Patent Document 4 cannot produce a steel sheet having excellent elongation and tensile flanging properties

Method used

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  • High-strength steel sheets and processes for production of the same
  • High-strength steel sheets and processes for production of the same
  • High-strength steel sheets and processes for production of the same

Examples

Experimental program
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Effect test

Embodiment 1

[0083] Steel slabs having chemical compositions shown in the following Table 1 were melted, and each steel slab was heated to about 1000-1100° C., hot rolled under the conditions of the following Table 2, or further subjected to preliminary annealing to produce raw steel sheets. The average cooling rate after hot rolling was 50° C. / sec. A microstructure observation test piece was extracted from each raw material steel plate, the microstructure was observed with a microscope, and the microscopic microstructure photograph after etchant corrosion was image-analyzed to measure the space factor of bainite. Table 1 shows the values ​​of the Ac3 point and the Ms point calculated from the components using a known calculation formula and is also used as a reference. In addition, the organizational observation results are shown in combination with Table 2. Then, the final annealing (two-phase domain annealing) and tempering were performed on each of the obtained original steel sheets u...

Embodiment 2

[0130] Hereinafter, the operation and effect of the high-strength steel sheet and its manufacturing method according to the present embodiment will be described using examples.

[0131] First, a method for producing a test steel plate tested in this example will be described. In this example, tests were carried out on steel slabs having component compositions represented by steel symbols A to Y having the component compositions shown in Table 5. As shown in Tables 6 and 7, steel slabs composed of these components A to Y were made into 56 test steel plates in which the hot rolling conditions, pre-annealing conditions, annealing process and tempering process were changed, and the tensile strength of these test steel plates was measured. Strength, ductility, tensile flanging and other properties. B, C, E, F, I, J, L, and N to Y in the steel slabs of the component compositions of A to Y are steel slabs of the component compositions corresponding to the examples of the embodiment....

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Abstract

A high strength steel sheet with both excellent elongation and stretch-flanging performance is provided. The high strength steel sheet of the present invention comprises, in percent by mass, C: 0.05 to 0.3%, Si: 0.01 to 3.0%, Mn: 0.5 to 3.0%, Al: 0.01 to 0.1%, and Fe and inevitable impurities as the remainder, and has a structure mainly composed of tempered martensite and annealed bainite. The space factor of the tempered martensite is 50 to 95%, the space factor of the annealed bainite is 5 to 30%, and the mean grain size of the tempered martensite is 10 [mu]m or smaller in terms of the equivalent of a circle diameter. The steel sheet has a tensile strength of 590 MPa or higher. The high strength steel sheet of the present invention has a space factor of the martensite phase which is a main component of the metal structure is 80% or higher; the mean grain size of the martensite phase is 10 [mu]m or smaller in terms of the equivalent of a circle diameter; in the martensite phase, the space factor of the martensite phase having a grain size of 10 [mu]m or larger in terms of the equivalent of a circle diameter is 15% or lower; and the space factor of the retained austenite phase in the metal structure is 3% or lower. The high strength steel sheet of the present invention is a dual phase steel sheet mainly composed of a ferrite phase and martensite, and the space factor of the ferrite phase is 5 to 30%, and the space factor of the martensite phase is 50 to 95%. Moreover, the ferrite phase is annealed martensite.

Description

technical field [0001] The present invention relates to a high-strength steel sheet which requires high extrudability typified by steel sheets for automobiles, and particularly a combination of elongation and stretch flanging, and a method for producing the high-strength steel sheet. Background technique [0002] In general, high-strength steel sheets used for extrusion molding are used in industrial products such as automobiles, electrical equipment, and industrial equipment. High-strength steel sheets are used for lightweight industrial products, so it goes without saying that high strength is required, but it is also necessary to be able to form various shapes of products. For this reason, high-strength steel sheets are required to have excellent extrudability. In order to meet this demand, a high-strength steel sheet that is excellent in elongation and stretch flanging properties required to improve extrusion formability is required. [0003] As a steel having these ch...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/06C22C38/58C21D9/46
CPCC21D1/25C21D6/005C21D9/46C21D2211/005C21D2211/008C22C38/02C22C38/04C22C38/06C22C38/12C22C38/14
Inventor 齐藤贤司增田智一三浦正明向井阳一池田周之
Owner KOBE STEEL LTD
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