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Galvannealed sheet steel and process for production thereof

A technology of hot-dip galvanized steel sheet and manufacturing method, applied in hot-dip galvanizing process, metal material coating process, coating and other directions, can solve the problems of non-disclosure, uneven trace components, difficult countermeasures, etc., and achieve coating properties Excellent, good looking results

Active Publication Date: 2008-04-16
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Many of these unevennesses are caused by the unevenness of the oxide film of the plated original plate, the unevenness of trace components, etc. in many cases, but basically the cause is difficult to identify, and the fundamental countermeasures are in a difficult situation.
In the documents cited above, there is no disclosure of guidelines for obtaining an extremely good appearance that is allowable even for the automotive exterior panel application targeted by the present invention.

Method used

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  • Galvannealed sheet steel and process for production thereof
  • Galvannealed sheet steel and process for production thereof
  • Galvannealed sheet steel and process for production thereof

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1～13、 and comparative example 1～11

[0055] Table 1 shows the composition of the annealed very low carbon steel sheets used in the tests. After pretreatment according to the conditions shown in Table 2, in the plating bath shown in Table 3 by electroplating (bath temperature 60 ° C, current density 30A / dm 2 ) for pre-plating Ni.

[0056] Then, at 3% H 2 +N 2 In the atmosphere, heat up to 450°C at a heating rate of 50°C / sec, immediately dip in a hot-dip galvanizing bath kept at 450°C, keep for 3 seconds and then wipe to adjust the weight per unit surface area of ​​the coating, just after wiping Alloying is carried out at the specified heating rate, temperature, and soaking time. With regard to cooling, rapid cooling was performed at 20°C / sec after slow cooling at 2°C / sec for 10 seconds. Then, temper rolling was performed at a reduction ratio of 0.5%.

[0057] Samples were produced under various conditions (Ni pre-deposition amount, Al concentration in the plating bath, alloying conditions) shown in Table 4. ...

Embodiment 14～22 and comparative example 12、13

[0086] Table 7 shows the composition of the annealed very low carbon steel sheets used in the tests. After pretreatment using the conditions shown in Table 2, electroplating was carried out in the plating bath shown in Table 3 (bath temperature 60°C, current density 30A / dm 2 ) for pre-plating Ni.

[0087] Then, at 4% H 2 +N 2 Heated to 455°C at a heating rate of 50°C / sec in an atmosphere, immediately immersed in a hot-dip galvanizing bath kept at 450°C, kept for 2.5 seconds and then wiped to adjust the weight per unit surface area of ​​the coating. Immediately after wiping, use After heating up at 50°C / sec and holding for 4 seconds, rapid cooling was performed at 50°C / sec. Thereafter, temper rolling was performed at a reduction rate of 0.5%.

Embodiment 19～25 and comparative example 15～17

[0106] Using the cold-rolled and annealed original plate shown in Table 1, after performing the pretreatment shown in Table 2, in the plating bath shown in Table 3, electroplating (bath temperature 60 ° C, current density 30A / dm 2 ) for pre-plating Ni. Then, at 3% H 2 +N 2 In the atmosphere, heat up to 460°C at a heating rate of 50°C / s, immediately dip in a hot-dip galvanizing bath kept at 455°C, keep for 3 seconds and then wipe to adjust the weight per unit surface area of ​​the coating. The weight per unit surface area of ​​the coating is 60g / m 2 . Then heat alloying treatment is performed under predetermined conditions. Cooling after heating was performed at 2°C / s for 10 seconds, followed by rapid cooling at 20°C / s. Then, temper rolling was performed at a reduction ratio of 0.5%. In addition, the samples used for observing the interface alloy layer were dipped in a hot-dip galvanizing bath, held for 3 seconds, and then rapidly cooled.

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Abstract

The invention aims at providing galvannealed sheet steel excellent in corrosion resistance, workability, coatability and appearance and a process for the production thereof. The invention relates to a process for the production of galvannealed sheet steel which comprises subjecting an ultra low carbon steel sheet to surface cleaning and preplating with nickel, heating the resulting sheet rapidly either in the absence of oxygen or in a reducing atmosphere to a sheet temperature of 430 to 500 DEG C at a temperature rise rate of 30 DEG C / sec or above, plating the sheet in a plating bath of molten Zn, wiping the resulting sheet, heating the sheet rapidly to 470 to 600 DEG C at a temperature rise rate of 30 DEG C / sec or above, and then cooling the sheet either without soaking or after soaking for less than 15 seconds. The galvannealed steel sheet produced by the process is composed of an ultra low carbon steel sheet and a galvannealed layer formed on at least one side of the sheet which layer comprises by mass Fe: 8 to 13 %, Ni: 0.05 to 1.0%, and Al: 0.15 to 1.5% with the balance being Zn and unavoidable impurities, and has an Al / Ni ratio of 0.5 to 5.0, the mean thickness of G layer present on the interface of basis steel being 1 m or below and the dispersion of the thickness falling within +- 0.3 m.

Description

technical field [0001] The present invention relates to an alloyed hot-dip galvanized steel sheet which is excellent in corrosion resistance, workability, and paintability and uses an ultra-low carbon steel sheet as the original sheet and a manufacturing method thereof. In addition, the present invention also relates to a method for producing a hot-dip galvanized steel sheet with an extremely good appearance. Background technique [0002] Conventionally, galvannealed steel sheets have been known as steel sheets for automobiles and constructions excellent in coating film adhesion and corrosion resistance after coating. In recent years, since deep drawability is required for automotive applications, alloyed hot-dip galvanized steel sheets made of ultra-low carbon steel sheets have been widely used. In this case, the corrosion resistance in the bare state and the corrosion resistance of the scratched part of the coating cannot necessarily be said to be sufficient. In addition...

Claims

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Application Information

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IPC IPC(8): C23C2/02C23C2/06C23C2/28
Inventor 石塚清和西村一实菊池郁夫宫坂明博
Owner NIPPON STEEL CORP
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