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Hot-rolled steel sheet, method for production thereof and molded article formed from hot-rolled steel sheet

A technology of hot-rolled steel plate and manufacturing method, which is applied in the direction of manufacturing tools, heat treatment furnaces, heat treatment equipment, etc., and can solve problems such as non-existent stable manufacturing

Inactive Publication Date: 2008-03-26
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, there is no technology for stably producing steel sheets satisfying these characteristics in the industry

Method used

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  • Hot-rolled steel sheet, method for production thereof and molded article formed from hot-rolled steel sheet
  • Hot-rolled steel sheet, method for production thereof and molded article formed from hot-rolled steel sheet

Examples

Experimental program
Comparison scheme
Effect test

no. 1 example

[0155] First, a first example in which strain age hardening characteristics are studied will be described.

[0156] After smelting molten steel with the composition shown in Table 1 (the balance is Fe and impurities) and making a steel slab, the steel slab was heated to 1250°C and hot rolled under the conditions shown in Table 2 to produce A hot-rolled steel strip (hot-rolled sheet) with a plate thickness of 3.0 mm. Except for the sample designation J, the quenching final temperature is the same as CT. For the obtained hot-rolled steel strip (hot-rolled sheet), the microstructure, solid solution C content, tensile properties, and strain-age hardening properties were determined by the following procedures.

[0157] (1) Microstructure

[0158] A test piece was selected from the obtained steel strip, and the microstructure was photographed using an optical microscope or a scanning electron microscope for a cross section (L cross section) parallel to the rolling direction. Then...

no. 2 example

[0181] Next, a second embodiment will be described. Here, attention is also paid to fatigue properties in addition to strain age hardening properties.

[0182] After smelting molten steel with the composition shown in Table 4 (the balance is Fe and impurities), and making a steel slab, the steel slab was heated to 1200°C, and hot rolled under the conditions shown in Table 5, thereby producing A hot-rolled steel strip (hot-rolled sheet) with a plate thickness of 3.0 mm. For the obtained hot-rolled steel strip (hot-rolled sheet), the microstructure, solid solution C content, tensile properties, strain age hardening properties, main phase ferrite phase hardness after strain aging, and fatigue properties were determined. (1) microstructure, (2) solid solution C content, (3) tensile properties, and (4) strain age hardening properties were solved in the same manner as in the first example. Each hardness and fatigue properties were obtained as follows.

[0183] (5) Hardness

[01...

no. 3 example

[0204] The smelted composition contains C: 0.1%, Si: 0.01%, Mn: 2.2%, P: 0.012%, S: 0.005%, Al: 0.045%, N: 0.003%, and the balance is composed of Fe and impurities After forming the molten steel and making it into a steel slab, the steel slab was heated to 1250° C. and hot-rolled under the conditions shown in Table 7 to make a hot-rolled steel strip (hot-rolled plate) with a thickness of 2.0 mm. . Ar of the steel 3 The phase transition point is 701°C. FT is 800°C (ie Ar 3 Phase transition point + about 100°C), quench stop temperature and CT are 180°C (Ms point is 429°C).

[0205] In addition, sample symbol 3P was subjected to a low-temperature tempering treatment under the conditions in Table 7 after coil winding. And sample No. 3I is intentionally slow-cooled for a short time in the bainite nose region (about 500°C) to generate a small amount of bainite.

[0206] The results are shown in Table 8.

[0207] Table 7

[0208] try

Sample

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Abstract

A hot-rolled steel sheet which comprises 0.01 to 0.2% by mass of C, 2.0% by mass or less of Si and 3.0% by mass or less of Mn and has a martensite phase as the main phase and a ferrite phase as a second phase, the ferrite phase containing ferrite having a grain size of 20 [mu]m or less in such an amount that the area ratio of ferrite becomes 1 to 30% (inclusive) and also containing 0.01% by mass or more of solid solution carbon. The steel sheet has excellent press workability, and exhibits excellent strain ageing property, that is, can be markedly increased in its tensile strength by a heat treatment, after press forming, at a temperature around that for a conventional baking finish, and thus can be suitably used as a steel sheet for an automobile. Further, fatigue characteristics after the strain ageing treatment are improved by hardening the ferrite phase.

Description

technical field [0001] The present invention relates to a hot-rolled steel sheet and a manufacturing method thereof. The hot-rolled steel sheet of the present invention is suitable for a hot-rolled steel sheet for automobiles requiring press workability such as bendability and stretch-flangeability. The hot-rolled steel sheet of the present invention is particularly suitable for applications requiring excellent strain age hardening properties (strain aging property) or better fatigue properties (fatigue strength: fatigue strength). [0002] Here, the strain age hardening property referred to herein refers to a property in which tensile strength is increased by heat treatment after press forming. In addition, in the present invention, "excellent strain age hardening properties" refers to the case of having strain age hardening properties of ΔTS of 100 MPa or more. Here, ΔTS is defined as: the increase in the tensile strength (tensile strength) of the strain age hardening trea...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/06C22C38/14C21D9/46
Inventor 星亨松冈才二
Owner JFE STEEL CORP
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