A high strength steel excellent in uniform elongation properties and method of manufacturing the same

A technology for uniformly elongated, high-strength steel plates, used in manufacturing tools, temperature control, heat treatment process control, etc.

A technology for uniformly elongated, high-strength steel plates, used in manufacturing tools, temperature control, heat treatment process control, etc.

CN1970812AInactive Publication Date: 2007-05-30JFE STEEL CORP +1
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Examples

Experimental program
Comparison scheme
Effect test

Embodiment

[0096] Steel slabs having the chemical compositions shown in Table 1 were heated to different temperatures, and the heated slabs were hot-rolled to obtain hot-rolled steel sheets each having a thickness of 2.0 mm. During the hot-rolled steel plate manufacturing process, the heating temperature, finish rolling temperature, cooling rate and coiling temperature are changed. Samples were prepared from hot-rolled steel sheets after pickling. In order to obtain the hole expansion ratio λ that provides the standard of tensile flanging, 130mm is cut out from the steel plate 2 A steel sample of the size of , and then drill a 10mmФ hole on the sample. Then when the crack penetrates the steel plate, a 60-degree conical drill bit is pushed upward from below, and the hole diameter d is measured. The expansion ratio λ[%] can be calculated by the following formula:

[0097] λ(%)=100·(d-10) / 10

[0098]The mechanical properties of the steel plate are obtained by taking out the JIS 5 tensil...

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Abstract

The present invention is intended to provide a high strength steel sheet having a strength not lower than 780 MPa and exhibiting a high yield ratio, an excellent balance between the strength and the uniform elongation, and a good plating property in addition to a good balance between the strength and the stretch flangeability. The present invention provides a high strength steel, comprising 0.05 to 0.25 % of C, less than 0.5 % of Si, 0.5 to 3.0 % of Mn, not more than 0.06. % of P, not more than 0.01 % of S, 0.50 to 3.0 % of Sol. A1, not more than 0.02 % of N, 0.1 to 0.8 % of Mo, 0.02 to 0.40 % of Ti, and the balance of iron and unavoidable impurities, wherein the steel has a structure formed of at least three phases including a bainite phase, and a retained austenite phase in addition to a ferrite phase having a composite carbide containing Ti and Mo dispersed and precipitated therein, wherein the total volume of the ferrite phase and the bainite phase is not smaller than 80%, the volume of the bainite phase is 5% to 60%, and the volume of the retained austenite phase is 3 to 20%.

Description

technical field [0001] The present invention relates to a high-strength steel plate having a strength of not less than 780 MPa and an excellent balance between strength (TS) and uniform elongation (U·EL). The steel sheet is suitable as a raw material for members subjected to processing such as press forming, bending, or stretch flanging. Background technique [0002] As concerns about environmental issues increase, efforts are being made to reduce the weight of components by increasing their strength or reducing their thickness. Moreover, with the expansion of the application field of high-strength steel sheets, press forming is more and more widely used in complex processes, even for processing high-strength steel sheets, which increases the demand for materials with high strength and excellent processability . [0003] Especially in the automotive field, high-strength steel sheets are required to have not only a balance of strength and stretch flangeability but also vari...

Claims

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Application Information

Patent Timeline
30 May 2007
Publication
CN1970812A
IPC
C22C38/14; C21D8/02; C21D11/00; B21B37/74; B21D5/00
CPC
C21D8/0226; C22C38/14; C22C38/06; C22C38/04; C22C38/12
Inventors
横田毅; 小林聪雄