JPS58177446A - Manufacture of steel plate plated with alloy by hot dipping and provided with superior corrosion resistance and coatability - Google Patents

Abstract

PURPOSE:To considerably enhance the corrosion resistance, workability and coatability of a steel plate, by plating the surface of the plate with a Zn-Al-Si- Mg alloy having a specified composition by hot dipping. CONSTITUTION:In the manufacture of a one-side hot dipped steel plate for a car member or an external material for household electric appliances, one side of a steel plate is covered with a masking agent, and the plate is dipped in a molten Zn alloy bath consisting of 3-40% Al, 0.05-2.0% Mg, 0.005-0.1 time as much Si as Al, <0.02% Pb and the balance Zn to carry out hot dipping at 480-680 deg.C bath temp. The amount of the Zn alloy stuck by the hot dipping is controlled to <=30g/m<2>, and by apraying cooling water or the like, the Zn alloy layer is solidified by rapid cooling. The plate is then heated to 550-900 deg.C in a heating furnace to alloy the layer with the surface of the plate. Materials used in the hot dipping vessel are made of Cr cast steel or stainless cast steel to prevent corrosion. A hot dipped steel plate with superior corrosion resistance, workability and coatability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a Zn-based hot alloy plated steel sheet, and
The present invention relates to a method for producing a hot alloy coated steel sheet on which a g-alloy coating layer is formed.

Traditionally, the main uses of hot-dip galvanized steel sheets were building materials such as airplanes and walls, and colored galvanized iron sheets for building materials, but in recent years, they have diversified and are now being used for automobile parts and exterior materials for home appliances. Along with this, for example, 30? ~
There is a growing demand for materials that have a high degree of corrosion resistance even with a relatively low basis weight of (one piece [W) or less] and have excellent workability and paintability.

Generally speaking, in the case of hot-dipped steel sheets, A1-plated steel sheets and Zn-Al plated steel sheets are well known as having excellent corrosion resistance.
There are alloy plated steel sheets.

Since the former is made by plating industrial fishing line AI onto a steel plate, the surface of the plating layer is covered with pure AIK, and exhibits superior corrosion resistance than za-plated steel plate. However, since there is a hard (and brittle) Fe-Al alloy layer of 6 to 8 μm at the boundary between the steel substrate and the plating layer, when strong processing is performed, the plating layer may crack or peel, resulting in poor workability compared to Zn plating. It is significantly inferior to steel plate, and if cracks occur in the processed part, it does not have sacrificial corrosion protection like Za, so it tends to corrode the steel base at the boundary of wet corrosion, and if cracks occur, it has better corrosion resistance than Zn-plated steel plate. It has the disadvantage of being rather inferior in terms of strength.For this reason, it has not been suitable for use as exterior materials for automobile parts or home appliances that require high-strength processing.

On the other hand, the latter Zn-Al alloy plated steel sheet has the above A1
Some plated steel sheets have improved workability and sacrificial corrosion protection. For example, Zn-AI of Special Publication No. 56-44143
-8i alloy plated steel sheet. This steel [)! AIV
5~24%tWj LeZll-Al BathKSiv
It is plated by adding □ to the extent that it can be solved.
3i Since the formation of the Fe-Al alloy layer is suppressed compared to K, it has better workability, and since it is Zn-based, it has a greater sacrificial anticorrosion effect, and since it contains Alt, its corrosion resistance is higher than that of hot-dip galvanized steel sheets. Are better.

However, upon investigation of this Zn-AI-Si alloy plated steel sheet, there are various difficulties in using it for automobile parts and household appliance parts.

One of them is that the corrosion of zinc in the plating layer is extremely severe in a wet corrosion environment. That is, in the case of this steel sheet, the corrosion loss over time is small, but numerous pitting corrosion occurs, and although it appears to have excellent corrosion resistance, it is not actually excellent. This can be determined from the two-layer -A1;4 phase diagram, when the matte layer solidifies, and the composition is eutectic and eutectoid of KZn phase (β), Al phase (α), and β+α. It is thought that a complex structure is formed in which phases with different potentials coexist, and in a wet corrosion environment, a local battery is formed and the Zn phase (Cl) with a low potential is preferentially corroded, causing pitting corrosion.

Another difficulty is the problem of blistering of the paint film when it is painted. In other words, if the product is used for a long period of time after painting, the paint film is likely to blister over time (also, paint film blister is likely to occur when the usage environment is harsh).

The present invention is based on AI-plated steel sheets and Mu-AI, which are conventionally considered to have particularly excellent corrosion resistance among hot-dip galvanized steel sheets.
Point K11 that the series alloy mating steel sheet has the drawback as mentioned above.
The objective is to obtain a hot-dip galvanized steel sheet that combines only the advantages of both steel sheets.

The present inventors have investigated the high corrosion resistance of AI-plated steel sheets and the Zs-Al
It combines the workability and sacrificial fat eating properties of alloy-plated steel sheets,
To produce a hot-dip galvanized steel sheet that is free from pitting corrosion and coating film damage (after various studies, Zn-AI-Si alloy K
Adding a certain amount of Mg and also keeping the amount of Kpb below a certain level improves corrosion resistance by 3 to 5 times, and there is a significant difference in the occurrence of pitting corrosion and coating blistering, and even with a light basis weight, corrosion resistance and workability of ilI & It has also been found that a hot-dipped steel plate with excellent paintability can be obtained.

As a result of detailed study, we found that AI-plated steel sheet and Zn-A
To obtain a hot-dip plated steel plate that has all the advantages of l-based alloy plated steel plate and is free from pitting corrosion and paint blistering, K is Al: 3 to 3.
40%, average: o, os~2.0%, 8! :A1% 0.
Using a bath consisting of 0.005 to 0.1 times, Pb: 0.02% or less, balance Zn and inevitable impurities, bath temperature 480 to 6
It was confirmed that plating at 80C is sufficient.

The reasons for limiting the bath according to the present invention will be described below.

(1) Aluminum AI has excellent corrosion resistance, and although it is an electrochemically less base metal than ZnK, it is active, so it resists atmospheric oxygen, moisture,
Or it is easily oxidized when placed in an oxidizing atmosphere,
Forms oxides on the surface. Therefore, in the case of Zn-A1 alloy, the corrosion potential is reversed with respect to Zn, and Zn often becomes an anode and is eluted. Therefore, if there is a large amount of AI (corrosion resistance improves, but the sacrificial anticorrosion effect due to Zn decreases. Therefore, the amount of AI added needs to be determined taking into account this improvement in corrosion resistance and the decrease in the sacrificial anticorrosion effect. Result 3~
It was confirmed that 40% is preferable.

(2) Magnesium Mg is effective in improving corrosion resistance, and it was confirmed that it is significantly effective in improving pitting corrosion of Zr*-AI alloy plated steel sheets and in improving coating film roughness when painted. When investigating the amount of Mg added and its effect on improving pitting corrosion and coating blistering, it was found that the effect was significantly more effective than 0.05% Mg and increased with the amount added. However, it has been found that when the content exceeds 2.0%, the matte layer becomes hard and brittle, tends to cause scratches, and reduces workability. Therefore, it was confirmed that the most effective addition of Mg is 0.05 to 2.0% in terms of the relationship between corrosion resistance and workability.

This improvement in corrosion resistance by MgK is thought to be due to the concentration of M in the surface layer of the plating layer. In other words, as mentioned above (Zn
- In the case of AI-based alloy plated steel sheets, the plating layer is Zn phase (
It consists of multiple phases with different potentials: β), AI phase (α), β+α eutectic, and eutectoid, but when Mg was added, the concentration distribution of Mg was investigated. It is mainly distributed in the α and β grain boundaries, eutectic parts, and eutectoid parts, and is further distributed more in the surface layer than in the lower layer of the plating layer.

Therefore, when such concentration occurs, the difference in potential between each phase becomes smaller, so the difference in corrosion potential between each phase becomes smaller, which is thought to improve pitting corrosion and paint film damage.

(3) Silicon suppresses the formation of a hard and brittle Fe-Al alloy layer and improves the workability of the plating layer. Therefore, the amount added is in a relative relationship with the amount of AI in the bath, and if the amount added is small compared to the amount of AI, the growth of the alloy layer will be promoted. On the other hand, if the amount added is too large, a dross-like substance consisting of Zn-AI-8i-F@ floats to the bath surface, making plating work difficult and adhering to the surface of the K111 product, impairing its appearance. Therefore, the amount of Si added was set to 0.005 to 0.1 times the amount of AI in the bath.

(4) Lead Pb is generally contained in Zn ingots as an unavoidable impurity, and even in electrolytic zinc ingots produced by electrolytic method, 0.
The content is less than 0.03%, and distilled zinc ingots produced by a distillation method may contain about 1%. This PB does not dissolve in solid solution in Zn or Al, but concentrates at grain boundaries and phase boundaries during solidification of the plating layer, forming local batteries and causing local corrosion or partial corrosion along grain boundaries and phase boundaries. .

As a result of examining the corrosion effect of Pb in a Zn-AI-Si-Mg bath, it was found that if the amount of Pb exceeded 0.02%, it could not be reduced even if ceramic was added. Proceeds significantly along the grain boundaries, and in a simple processing test (bending test for 2), there were cases where the plating layer was partially dulled.Therefore, the amount of PB was set to 0.02% or less.

Is the present invention a Znn pace containing the above-mentioned ingredients? Using this method, a steel plate is attached at a bath temperature of 480 to 680C. Since this bath temperature is high when the amount of AI is small, it promotes the formation of an alloy layer, so the bath temperature is set to be high (corresponding to the amount of AI) within the above range.

In the present invention, there are no particular limitations on the steel type of the original sheet to be plated, the pretreatment in the plating process, the adjustment of the coating amount, and the post-treatment. In other words, the plated original plate can be made of conventionally commonly used materials such as rimmed steel, guild steel, and high-strength steel, and the steel plate surface can be pretreated using known methods such as in-line annealing heat reduction method and pre-annealing heat reduction method. Just clean it and adjust the board temperature to around the bath temperature. In terms of quality, the gas squeezing method is preferable for adjusting the amount of adhesion, but the roll squeezing method can also be used. Further, as for post-treatment, if the formation of spangles is not desirable in terms of appearance, Z-nimized formation by spraying water droplets or alloying treatment by heating through a heating furnace may be performed.

However, in the case of the present invention, since the AI in the bath is as high as 3 to 40%, the metallurgy and other equipment immersed in the bath are severely corroded. Therefore, in the case of a low Al side column with A13 to 25%, Cr
Steel whose main components are 2O~30% and Ni1O~30%/
Thread hook type cast steel and more, 1i5AI@bath place f
It is preferable to use chromium-based cast iron whose main components are 02 to 6% K, 3 to 2.0% CrO, and 2% or less Si.

Examples Rimmed steel, Killed steel (Cr-Ti system) and high tensile strength;
EXAMPLE 4 (Si-Mn-based) green-cold-rolled steel sheets were plated using a non-oxidation furnace type continuous hot-dip plating apparatus.

Figure 1 shows the plate temperature of each steel in the pretreatment process. The atmospheric gas in the annealing reduction furnace was AX gas (Hz 7 s%
, N325%) was used.

Table 1 Steel type and pretreatment conditions and lIl! Table 2 shows the relationship between plating bath composition and bath temperature, and Table 4 shows the individual bath compositions.

Table 2 Plating bath composition and bath temperature Adjustment of deposition amount was performed by gas squeezing method using combustion exhaust gas, and after adjustment of deposition amount, air cooling, forced cooling by water S* mist injection, and alloying treatment in a heating furnace were performed. Regular spangles, minimized spangles, and alloyed plated steel sheets were produced respectively. Table 3 shows the post-treatment conditions.

Table 3 Post-treatment methods and conditions Next, the following performance tests were conducted on the products manufactured as described above.

(1) Workability of the plating layer 2 was bent to investigate the occurrence of peeling (adhesion) of the plating layer and the occurrence of cranking or powdering.

0...No peeling 0...Slight peeling Δ・
(2) Corrosion Resistance In a salt spray test according to JIS Z2371, we investigated the time (Hr) until red rust occurs on a flat plate by 5% of the total area and the corrosion weight loss <W> after 10 days. Next, a bent version of 2 was subjected to the above test, and the occurrence of rust was investigated after 10 days.

(3) II Moisture test The test piece was left in a humid atmosphere at a humidity of 9g% and a temperature of 70C', and then 2 was bent and cellophane tape peeling test V was performed to determine whether the plating layer was wet (time to sip and The situation of pitting corrosion was confirmed.

(4) Paintability test pieces were treated with a commercially available chemical conversion treatment solution for aluminum (Alodine #1
000) t' for 5 seconds at 65C, and then an epoxy thermosetting primer was applied to a dry film thickness of 41111 mm, and then an acrylic thermosetting roof coating paint was similarly applied to 12 μm to form a coated board t'. Next, cross-cut processing and 21-fold processing were performed on the adjusted 6, and a salt spray test was conducted.
I went for 720 hours. The evaluation was based on the condition of paint film blistering based on the following criteria.

O...No abnormality ○-...Some occurrence Δ...
- Significant occurrence ×... Significant occurrence Table 4 summarizes these test results in relation to the manufacturing conditions.

Table 4 Examples (r!') *Intergranular Corrosion According to Table 4, cranks do not occur in both regular spangle products and double-mized spangle products when Mg is added and Pb t' is reduced to 0.02% or less. The alloyed product also has fewer boundaries.

In addition, the corrosion resistance is better than A1 plated steel sheet at A125-40% by increasing - and lowering Kpb within the scope of the present invention (
In addition, the material according to the present invention has less corrosion loss (and has excellent corrosion resistance after bending.Of course, the corrosion resistance of the material according to the present invention is higher than that of the electrical Zn with the same coating amount).
Superior to galvanized steel.

Furthermore, the humidity 1RWli which had a problem in the past! The problems of pitting corrosion and paint blistering under atmospheric conditions have been significantly improved.

In addition, in the bath of /f67.8.12.13 in Table 4.

Before plating, a clay-based slurry V was applied to one side of the steel plate for masking, and then plating was performed to produce a single-sided plated product.The weldability of the product was investigated, but no problems were found.

As described above, the present invention combines the high corrosion resistance of A1 steel sheets with the workability and sacrificial corrosion resistance of Zn-AI alloy plated steel sheets.
It is possible to obtain a melt-alloy plated steel plate with improved membrane blistering, and it is the first product of lid products with a high degree of corrosion resistance, workability, and paintability in recent years! It can be fully loaded.

A point worth mentioning is that the products obtained by the present invention have significantly higher torsion and heat resistance of the above-mentioned characteristics than ordinary fused 1-lead steel sheets. In other words, the heat resistance temperature of conventional general hot-dip galvanized steel sheets was 1-3250°C or less, but as the amount of Al increases, the heat-resistant temperature increases to 280-350°C. Therefore, it is convenient to use the conventional Sa1 galvanized steel sheet, and it can be used as a material for exhaust gas (low-temperature wet corrosion) of a vehicle, and as a material for a low-temperature combustor. Also, due to its high corrosion resistance, it can also be used for various purposes such as fuel injection.

Continuation of page 1 0 shots clear person Yasushi Miyoshi 2-1-17 Sakurajima, Konohana-ku, Osaka City No. 1 Nisshin Steel Co., Ltd. Hanshin Manufacturing Inside the office

Claims (7)

[Claims] (1) In a method for manufacturing a molten alloy plated steel sheet, in which the steel sheet is pretreated and then immersed in an alloy plating bath for plating, and the coating amount is then controlled, the alloy plating bath has an AI of 3 to 3.
40%, 0.05 to 2. ．． 0%, Si:A1% o
, oos ~ 0.1 times, Pb: 0.02% or less, balance Zn
and unavoidable impurities, bath temperature 480~
A method for producing a hot-melt alloy plated steel sheet with excellent corrosion resistance and paintability, characterized by plating with 680C. (2) The method for manufacturing a hot-melt alloy plated steel sheet according to claim 1, characterized in that the amount of adhesion is controlled to 30 f/d or less. (3) Melting according to claim 1 or 2, characterized in that after controlling the amount of adhesion and when the plating layer is not solidified, droplets of water or an aqueous solution are injected onto the plating layer to rapidly solidify it. Method for producing alloy plated steel sheets. (4) After controlling the amount of adhesion, pass through a heating furnace to 550 to 90
Claim 1 or 2 states that heating at 0C for 2 to 30 seconds to alloy the plating layer results in mold.
A method for producing a hot-melt alloy coated steel sheet as described in 2. (5) The method for manufacturing a hot-melt alloy plated steel sheet according to claim 1, characterized in that one side of the steel sheet is covered with an osking agent and then plated. (6) When the AI% in the bath is 3 to 25%, the main component is Cr: 20 to 30% as the mating equipment used in the bath.
, a method for producing a hot alloy plated steel sheet according to claim 1, characterized in that a steel plate made of stainless thread hook steel containing 10 to 30% Ni is used. (7) When the AI% of Rakuchu is 25 to 40%, the main component is C: 2 to 6% Cr as the plating equipment used in the bath.
2. The method for manufacturing a molten alloy coated steel sheet according to claim 1, characterized in that a chromium-based cast iron having a Si content of 0.3 to 2.0% and a Si content of less than 2% is used.