Bake-hardenable cold rolled steel sheet with superior strength, galvannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel sheet

A technology for baking hardened and cold-rolled steel sheets, applied in the fields of diffusion annealed galvanized steel sheets, cold-rolled steel sheets, and high-strength cold-rolled steel sheets, which can solve problems such as limitations and poor performance

Active Publication Date: 2008-11-19
浦项股份有限公司
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0029] In the above method, although the addition amount of boron (B) is about 5ppm, and it is expected that boron can improve the secondary processing embrittlement resistance, but too high P content limits the effect of improving DBTT by adding B
[0030] In addition, if an excessive amount of B is added to the steel to improve the secondary processing embrittlement resistance, the performance of the steel will be deteriorated due to the high B content
Therefore, there is a certain limit to the amount of B added to the steel

Method used

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  • Bake-hardenable cold rolled steel sheet with superior strength, galvannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel sheet
  • Bake-hardenable cold rolled steel sheet with superior strength, galvannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel sheet
  • Bake-hardenable cold rolled steel sheet with superior strength, galvannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel sheet

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Experimental program
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Effect test

Embodiment 1

[0200] After the steel slabs having the compositions shown in Table 1 were hot-rolled to form hot-rolled steel sheets, the hot-rolled steel sheets were subjected to hot coiling, cold rolling, and continuous annealing under the conditions listed in Table 2. Then, the annealed cold-rolled steel sheet is subjected to a galvanized layer diffusion annealing treatment at 450° C., and then leveled at a leveling reduction ratio of about 1.5%. After that, the BH value, aging index (AI), grain size and ductility-brittle transition temperature (DBTT) at 2.0 drawing ratio (drawingratio) of the final steel plate were measured (in order to evaluate secondary processing embrittlement), the results of these measurements Shown in Table 2.

[0201] In addition, after annealing, observe the microstructure of No. 4 steel of the present invention with a microscope magnified 200 times, the results are shown in Image 6 middle.

[0202] In addition, the DBTT of steel No. 6 according to the inventi...

Embodiment 2

[0226] After the steel slabs having the compositions shown in Table 3 were hot-rolled to form hot-rolled steel sheets, the hot-rolled steel sheets were coiled, cold-rolled, and continuously annealed under the conditions listed in Table 4. Then, the annealed cold-rolled steel sheet is subjected to a galvanized layer diffusion annealing treatment at 450° C., and then leveled at a leveling reduction ratio of about 1.5%. After that, the BH value, aging index (AI) and grain size of the final steel sheets were measured, and the results of these measurements are shown in Table 4.

[0227] Table 3 lists the compositions of the steel sheets of the present invention and comparative steel sheets produced under strict control of C, Ti, soluble Al and Mo. In Table 3, steel Nos. 15-30 are steels of the present invention, and steel Nos. 21-26 are comparative steels.

[0228] Table 4 lists the manufacturing conditions and steel sheet properties using steel slabs having the compositions shown...

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Abstract

A cold-rolled steel sheet for outer panels and the like of an automobile body, a galvannealed steel sheet using the cold-rolled steel sheet, and a method for manufacturing the same are disclosed. It is an object of the present invention to provide a high strength cold-rolled steel sheet, which has superior bake hardenability, aging resistance at room temperature and secondary work embrittlement resistance, and a method for manufacturing the same. The steel sheet has a grain size of ASTM No. of 9 or more after annealing, a BH of 30 MPa or more, an AI of 30 MPa or less, and a tensile strength of 340-390 MPa through appropriate control of solute elements in steel by addition of a small amount of Ti, addition of Al and Mo, and control of manufacturing conditions, and refinement of crystal grains after annealing. The cold-rolled steel sheet and the galvannealed steel sheet produced using the cold-rolled steel sheet have the superior bake hardenability, aging resistance at room temperature, and secondary work embrittlement resistance.

Description

technical field [0001] The present invention relates to a cold-rolled steel sheet used for exterior parts of a vehicle body, etc., a galvannealed steel sheet using the galvanized layer of the cold-rolled steel sheet, and a method for manufacturing the cold-rolled steel sheet. More particularly, the present invention relates to a high-strength cold-rolled steel sheet that is bake hardenable and has excellent aging resistance, a steel sheet that is diffusion-annealed using a galvanized layer of the cold-rolled steel sheet, and a steel sheet of the cold-rolled steel sheet Production method. Background technique [0002] In order to improve fuel efficiency and reduce the weight of automobiles, there is an increasing demand for high-strength steel sheets for vehicle bodies to improve dent resistance and reduce thickness of exterior parts. [0003] Cold-rolled steel sheets used for exterior parts of vehicle bodies are required to have excellent properties in terms of tensile stre...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D8/02
CPCC21D6/005C21D8/0205C21D9/46C22C38/04C22C38/06C22C38/12C22C38/14
Inventor 韩成豪
Owner 浦项股份有限公司
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