Hot dip galvanized high strength steel sheet having excellent plating adhesion and hole expansibility, and its production method

A high-strength steel plate, hot-dip galvanizing technology, applied in hot-dip galvanizing process, manufacturing tools, coatings, etc., can solve the problems of production line stop, production load reduction, low yield and so on

Inactive Publication Date: 2007-02-07
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in the case of high-temperature annealed materials and high-strength steel sheets used to manufacture the above-mentioned hot-dip galvanized steel sheets, the yield is low due to high-temperature annealing. In the case of ordering/production, there is a problem that the production is concentrated on the hot-dip galvanizing line with its own annealing furnace, which cannot be dealt with
[0005] On the other hand, although the u...

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0039] After melting and casting steel having the composition shown in Table 1 in a vacuum melting furnace, the steel slab thus obtained is reheated to 1,200°C, and then finished rolling at a temperature of 880°C in hot rolling to produce a hot-rolled steel sheet , cooled, coiled at a coiling temperature of 600° C., and then subjected to a coiling heat treatment maintained at this temperature for 1 hour. The obtained hot-rolled steel sheet was ground to remove scale, cold-rolled at a reduction ratio of 70%, and then heated to a temperature of 770° C. using a continuous annealing simulator, and kept at that temperature for 74 seconds. annealing. Next, it cooled to 450 degreeC at 10 degreeC / s, and manufactured the galvanized steel sheet by the two manufacturing methods described below, ie, the conventional method and the method of this invention.

[0040] (1) Conventional method

[0041] After the above-mentioned cooling to 450°C, hot-dip galvanizing at a temperature of 500°C ...

Embodiment 2

[0070] A, I, and P steels in the composition ranges of the present invention described in Table 1 were melted and cast in a vacuum melting furnace, and the steel slabs thus obtained were reheated to 1200° C., and then finished rolling at a temperature of 880° C. in hot rolling. After being made into a hot-rolled steel sheet, it was cooled, coiled at a coiling temperature of 600° C., and then subjected to a coiling heat treatment maintained at this temperature for 1 hour. The obtained hot-rolled steel sheet was descaled by grinding, cold-rolled at a reduction ratio of 70%, and then heated to a temperature of 770° C. using a continuous annealing simulator, and kept at that temperature for 74 seconds. Annealing, cooling to 450°C at 10°C / s, followed by overaging treatment at 400°C for 180 seconds, and then the following 5 experiments were performed on the steel plate cooled to the martensitic transformation point or below .

[0071] Experiment 1 (example of the present invention)...

Embodiment 3

[0081] After melting and casting steel having the composition shown in Table 5 in a vacuum melting furnace, the steel slab thus obtained was reheated to 1200°C, and then finished rolling at a temperature of 880°C in hot rolling to produce a hot-rolled steel sheet , cooled, coiled at a coiling temperature of 600°C, and then the coiling heat treatment held at this temperature for 1 hour was reproduced. The obtained hot-rolled steel sheet was descaled by grinding, cold-rolled at a reduction ratio of 70%, and then heated to a temperature of 770° C. using a continuous annealing simulator, and kept at that temperature for 74 seconds. annealing. Next, it was cooled to 450° C. at 10° C. / s, and a galvanized steel sheet was produced by two production methods described below, that is, the conventional method and the method of the present invention.

[0082] (1) Conventional method

[0083] After the above-mentioned cooling up to 450°C, hot-dip galvanizing at a temperature of 500°C with...

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PUM

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Abstract

The present invention provides hot dip galvanized high strength steel sheet excellent in plating adhesion and hole expandability and a method of production of the same, that is, hot dip galvanization steel sheet excellent in plating adhesion and hole expandability containing, by mass%, C: 0.08 to 0.35%, Si: 1.0% or less, Mn: 0.8 to 3.5%, P: 0.03% or less, S: 0.03% or less, Al: 0.25 to 1.8%, Mo: 0.05 to 0.35%, and N: 0.010% or less and having a balance of Fe and unavoidable impurities, said hot dip galvanized high strength steel characterized in that the steel sheet has a metal structure having ferrite, bainite, by area percent, 0.5% to 10% of tempered martensite, and, by volume percent, 5% or more of residual austenite, and a method of production comprising annealing by a continuous annealing process at 680 to 930 DEG C in temperature, then cooling to the martensite transformation point or less, then hot dip galvanizing the steel during which heating the steel to 250 to 600 DEG C, then hot dip galvanizing it.

Description

technical field [0001] The present invention relates to a hot-dip galvanized high-strength steel sheet excellent in coating adhesion and hole expandability and a manufacturing method thereof. Background technique [0002] In recent years, the fuel efficiency of automobiles has been improved, and the demand for weight reduction of the vehicle body has been increasing. In order to achieve weight reduction, there is an increasing demand for high-strength steel sheets with excellent tensile strength and yield strength. However, forming such a high-strength steel sheet becomes difficult as the strength increases, and in particular, the elongation of the steel material decreases. In response to this, recently, TRIP steel (high retained austenitic steel) having both high strength and elongation has been gradually used for structural members of automobiles. [0003] However, since the conventional TRIP steel contains more than 1% of Si, there is a problem that it is difficult to un...

Claims

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Application Information

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IPC IPC(8): C22C38/00C22C38/12C22C38/58C21D9/46C23C2/02C23C2/06C23C2/26C23C2/28
Inventor 谷口裕一松村贤一郎服部俊树加藤敏
Owner NIPPON STEEL CORP
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