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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AI-Extracted 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 countermeasure...

Method used

According to the present invention, the alloyed hot-dip galvanized steel sheet with excellent corrosion resistance, workability, and paintability can be obtained by using the ultra-low carbon steel sheet mainly used in automobile applications as the original sheet, which is industrially The use value is great. In addition, according to the present invention, it is possible to obtain a method for producing a galvannealed steel sheet with an extremely good appearance that is also applicable to automobile outer panels and the like.

[0032] The present invention is characterized in that the average thickness of the Γ layer of the substrate iron interface is 1 μm or less, and its deviation is within ± 0.3 μm. Here, as a method for measuring the thickness of the Γ layer, any of the following methods may be used, for example, the current stripping method in which the Γ layer is quantified by constant current electrolysis after dissolving the part ...

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.

Application Domain

Hot-dipping/immersion processes

Technology Topic

Rise rateHot-dip galvanization +8

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Examples

Experimental program(3)
Comparison scheme(2)

Example

[0054] (Examples 1-13 and Comparative Examples 1-11)

[0055] Table 1 shows the composition of the annealed very low carbon steel sheet used in the test. After pre-treatment according to 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 ) Pre-plating Ni.

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

[0057] The samples were produced under the various conditions shown in Table 4 (Ni pre-deposition amount, Al concentration of the plating bath, alloying conditions). In addition, the weight per unit surface area of the coating is 50g/m 2.

[0058] The results of measuring the composition of the coating layer and the thickness of the Γ layer using the samples in Table 4 are shown in Table 5. Dissolve the plating layer with hydrochloric acid and find the concentration of each component. In addition, for the Γ layer, 10 points were measured by the electrolytic peeling method, and the average value, the maximum value, and the minimum value were determined. Regarding the deviation of the Γ layer, any difference between the maximum value-the average value and the average value-the minimum value exceeds 0.3 μm, it is marked as "×".

[0059] Table 6 shows the performance evaluation results. The performance evaluation was performed as follows.

[0060] (1) Appearance of the plating layer: Visual observation was performed, and the evaluation was "○" if there were no defects such as non-plating, the evaluation was "△" if there were defects, and the evaluation was "×" if the non-plating defects were serious.

[0061] (2) Processability (pulverization): Using a sample coated with rust preventive oil, press a cylinder of Ф40mm (deep drawing) under the condition of a drawing ratio of 2.2, and peel off the side with tape. According to the blackening Degree to be evaluated. A degree of blackening of 0 to less than 20% was evaluated as "○", a degree of from 20% to less than 30% was evaluated as "△", and a degree of 30% or more was evaluated as "x".

[0062] (3) Workability (slidability): Using samples coated with rust preventive oil, a flat continuous sliding test was performed. The continuous sliding was performed 5 times under a pressing load of 500 kgf, and the friction coefficient of the fifth time was used for evaluation. A friction coefficient of less than 0.15 was evaluated as "○", a friction coefficient of 0.15 to less than 0.2 was evaluated as "△", and a friction coefficient of 0.2 or more was evaluated as "×".

[0063] (4) Corrosion resistance (red rust resistance of the scratched part of the coating): Tri-cation chemical conversion treatment for automobiles is performed on the steel plate sample ※1 , Cationic electrodeposition coating ※2 After (20μm), peel off the coating film in a strip of 5mm×50mm to expose the coated surface, and conduct a corrosion cycle test ※3. The appearance after 10 days was used for evaluation. No rust or only yellow rust was evaluated as "○", red rust less than 20% was evaluated as "△", and red rust was 20% or more as "x".

[0064] (5) Corrosion resistance (perforation resistance): After smoothing the sample that has been folded (ビ一ド付) U-shaped bending and punching, it is masked by 40mm×40mm, and the three-cation chemical conversion treatment for automobiles is implemented. ※1 , Cationic electrodeposition coating ※2 (20μm). The curved plate and the flat plate were aligned with a 0.5mm spacer, and the unpainted part with the shield removed became the inner-inner, and the car body hemming model was produced. Corrosion cycle test on this sample ※3. The appearance after 30 days was used for evaluation. The evaluation of red rust less than 20% was "○", the evaluation of red rust of 20% to less than 50% was "△", and the evaluation of red rust of 50% or more was "×".

[0065] (6) Paintability: Tri-cation chemical conversion treatment for automobiles is performed on steel plate samples ※1 , Cationic electrodeposition coating ※2. Electrodeposition coating was carried out under the conditions of voltage 220V, upslope 0.5 minutes, and energized for a total of 3 minutes. The number of abnormal parts such as discharge traces in the test piece (70×150mm) was counted, and no abnormality was evaluated as " ○", the evaluation of 1 to less than 3 abnormal sites was "△", and the evaluation of 3 or more abnormal sites was "×".

[0066] ※1: SD5000 manufactured by Japan's ペイソト company;

[0067] ※2: PN120M made by Japan's ペイソト company;

[0068] ※3: SST (6 hours)  dry at 50℃ 45% RH (3 hours)  wet at 50 ℃ 95% RH (14 hours)  dry at 50 ℃ 45% RH (1 hour).

[0069] Table 1 Test steel

[0070] Composition (mass%)

[0071] Table 2 Pre-treatment conditions

[0072]

[0073] Table 3 Plating solution for pre-plating Ni

[0074] Ingredients

[0075] Table 4 Sample manufacturing conditions

[0076]

[0077] 7

[0078] Table 5 The composition of the coating layer and the thickness of the Г layer of the test materials

[0079] No

[0080]

[0081] Table 6 Performance evaluation results

[0082]

[0083] 3

[0084] As shown above, samples within the scope of the present invention have obtained excellent characteristics.

Example

[0085] (Examples 14-22 and Comparative Examples 12 and 13)

[0086] Table 7 shows the composition of the annealed very low carbon steel sheet used in the test. After pretreatment under 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 ) Pre-plating Ni.

[0087] Then, at 4%H 2 +N 2 Heated to 455°C at a temperature increase rate of 50°C/sec in the atmosphere, immediately immersed in a hot-dip galvanizing bath at 450°C for 2.5 seconds, then wiped to adjust the weight of the coating per unit surface area, just after wiping The temperature was raised at 50°C/sec, and after being maintained for 4 seconds, it was rapidly cooled at 50°C/sec. Then, temper rolling with a reduction ratio of 0.5% was performed.

Example

[0105](Examples 19-25 and Comparative Examples 15-17)

[0106] Using the cold-rolled and annealed original plates shown in Table 1, after the pretreatment shown in Table 2, they were electroplated in the plating bath shown in Table 3 (bath temperature 60°C, current density 30A/dm 2 ) Pre-plating Ni. Then, at 3% H 2 +N 2 In the atmosphere, heat to 460°C at a temperature increase rate of 50°C/sec. Immediately immerse in a hot-dip galvanizing bath kept at 455°C for 3 seconds and 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 carried out under prescribed conditions. The cooling after heating is performed by slow cooling of 2° C./sec for 10 seconds, and then rapid cooling is performed at 20° C./sec. Then, temper rolling with a reduction ratio of 0.5% was performed. In addition, the sample used for observing the interface alloy layer was immersed in a hot-dip galvanizing bath, kept for 3 seconds and then rapidly cooled.

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Classification and recommendation of technical efficacy words

Excellent paintability
good looking

Base film for MLCC ceramic green sheet carrier, method for producing same, and carrier film

ActiveCN112143013AExcellent paintability

Owner:ZHEJIANG JIEMEI ELECTRONICS & TECH

Galvannealed sheet steel and process for production thereof

AI-Extracted Technical Summary

Problems solved by technology

Method used

Abstract

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Examples

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Example

Example

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Description & Claims & Application Information

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