Bake-hardenable cold rolled steel sheet with superior strength and aging resistance, gal-vannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel shee

A technology of bake hardening and aging resistance, which is applied in the manufacture of cold-rolled steel sheets, galvanized layer diffusion annealed steel sheets, and high-strength cold-rolled steel sheets. Problems such as secondary processing embrittlement deterioration

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

Problems solved by technology

Whereas in the case of batch annealing, because P-added aluminum deoxidized steel is cooled at a relatively fast rate, it is easy to ensure bake hardenability, but there is a problem that formability is deteriorated because of rapid heating and a short annealing process
[0029] In the above method, although the addition of boron (B) is about 5ppm, and it is expected that boron can improve the resistance to secondary processing embrittlement, the excessively high P content limits the improvement of secondary embrittlement resistance by adding B Effect
[0030] In addition, if an excessive amount of B is added to the steel to improve the secondary processing embrittlement resistance, the secondary processing embrittlement resistance 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 and aging resistance, gal-vannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel shee
  • Bake-hardenable cold rolled steel sheet with superior strength and aging resistance, gal-vannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel shee
  • Bake-hardenable cold rolled steel sheet with superior strength and aging resistance, gal-vannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel shee

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Embodiment

[0162] After the steel slabs having the compositions shown in Table 1 were hot-rolled at a finishing delivery side temperature of 900-910°C to form hot-rolled steel sheets, the hot-rolled steel sheets were coiled at a coiling temperature of 610-630°C. Then, the hot-rolled steel sheet is cold-rolled at a reduction ratio of 75-78%, followed by continuous annealing at an annealing temperature of 800-820°C. The annealed cold-rolled steel sheet is hot-dipped at 450-470°C, and then subjected to diffusion annealing of the galvanized layer at 500-530°C, and then leveled at a leveling compression ratio of about 1.5%. After that, the BH value, aging index (AI), grain size, and ductile-brittle transition temperature (DBTT) at a drawing ratio of 2.0 (for evaluating secondary working embrittlement) of the final steel sheets were measured. The results of these assays are shown in Table 2. In addition, the amount of solute carbon in the crystal grains was measured for No. 6 steel of the pre...

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Abstract

A bake-hardenable cold rolled steel sheet with high strength and superior aging resistance used for outer panels of an automobile body, a galvannealed steel sheet using the cold-rolled steel sheet, and a method for manufacturing the cold-rolled steel sheet are disclosed. The steel sheet comprises, by weight%, C: 0.0016-0.0025%, Si: 0.02% or less, Mn: 0.2-1.2%, P: 0.05-0.11%, S: 0.01% or less, Sol. Al: 0.08-0.12%, N: 0.0025% or less, Ti: 0-0.003%, Nb: 0.003-0.011%, Mo: 0.01-0.1%, B: 0.0005-0.0015%, the balance of Fe and other unavoidable impurities. The steel sheet has 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 as an outer panel of a vehicle body, 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 specifically, the present invention relates to a high-strength cold-rolled steel sheet having excellent bake hardenability, room-temperature aging resistance, and secondary work embrittlement resistance, and a galvanized layer diffusion annealing treatment of the cold-rolled steel sheet A steel plate, and a method for manufacturing the cold-rolled steel plate. 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 outer panels. [0003] For cold-rolled steel sheets used for body panels, excellent properties are required in term...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D8/02
CPCC22C38/04C21D8/0236C21D9/46C21D9/56C22C38/06C22C38/12C21D8/02
Inventor 韩成豪
Owner 浦项股份有限公司
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