JPS58189363A - Manufacture of steel plate coated with alloyed zinc by galvanization - Google Patents

Abstract

PURPOSE:To uniformalize the thickness of each of layers formed by galvanization and to enhance the surface appearance, corrosion resistance and weldability, by dipping a steel plate in a Zn bath contg. specified amounts of Al, Mg and Pb to carry out galvanization at a specified temp., introducing the plate into a heating furnance when the resulting layers are in a melted or half-melted state, and heating the plate under specified conditions. CONSTITUTION:A steel plate is dipped in a Zn bath consisting of, by weight, 0.3-5% Al, 0.01-2% Mg, <0.01% Pb and the balance Zn with inevitable impurities to carry out galvanization at 450-480 deg.C bath temp., and the thickness of each of the resulting layers is adjusted to <=30g/m<2> by a gas blowing method. When the layers are in a melted or half-melted state, the plate is introduced into a heating furnace kept at 550-1,200 deg.C atmospheric temp., and it is heated for 2-30sec to accelerate the mutual diffusion of Fe in the plate and Zn in the layers. By the diffusion the layers are partially alloyed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an alloyed galvanized steel sheet using a hot-dip coating method with excellent properties and weldability.

In general, electrogalvanized steel sheets have better workability than hot-dip galvanized steel sheets because they do not undergo rapid thermal history during the manufacturing process.
In addition, the surface is fine and has no irregularities such as spandal or serpentine patterns, so it has an excellent appearance, and the plating is thin and uniform throughout, making it suitable for welding or press processing. However, conventional electrolytic galvanized steel sheets were intended to contain only zinc, and because the plating thickness was thin, their corrosion resistance was poor, and they were also expensive, so they were not used much in automobiles or home appliances, and were inexpensive. Hot-dip galvanized steel sheets with good corrosion resistance have been used.

However, in recent years, research into electrolytic zinc alloy plating has been actively conducted, and various highly corrosion-resistant electrostrictive i-alloy mated steel sheets have been developed.This, along with improving the corrosion resistance of automobiles and home appliances, has led to the development of cold-rolled steel sheets and hot-dip galvanized steel sheets. It is being used in large quantities instead of.

For this reason, various countermeasures have been taken for hot-dip galvanized steel sheets with high corrosion resistance electrolytic galvanized steel sheets in mind. One of them is to introduce the plated layer into a heating furnace after hot-dip plating.
This is a method in which Fe is alloyed and applied to an alloyed galvanized steel sheet. With this method, spangles and serpentine patterns do not occur, resulting in a lil-dense appearance and improved paintability. Weldability is also improved due to the inclusion of yrFe.However, the corrosion resistance and workability of the plated layer are worse than those of hot-dip galvanized steel sheets, and these are major obstacles in competing with electrolytic zinc alloy coated steel sheets. It becomes.

For example, in the case of highly corrosion-resistant electrolytic zinc alloy coated steel sheets, the time required for red rust to occur in a salt spray test is approximately 200 hours at a coating weight of about 2OL, or for alloyed galvanized steel sheets at a coating weight of 30 to 60 I/-. It is extremely short, only 24 hours long.

The 1st layer can be easily bent or pressed to prevent peeling, stiffness, and powdering (powdering phenomenon).
The corrosion resistance of the processed part will be significantly reduced.

It is known that the peeling and powdering of the plating on this alloyed galvanized steel sheet is largely dependent on the plating thickness and heating conditions, and in order to prevent these, the plating thickness must be thin and the heating conditions The amount of Fe in the plating layer depends on the thickness of the plating layer.
It is said that it is important to have a moderate content of 514u. And the conventional plating thickness is 451/
wl has been considered a safe target value, and efforts have been made to accurately control it toward that target value. However, AI' is 0.1
In the case of a zinc bath containing 5 to 0.20%, there is a control problem in that the plating thickness changes due to slight fluctuations in AI% or bath temperature, so it is difficult to accurately control the target value.

Therefore, the inventors of the present invention conducted extensive studies in an attempt to obtain a @gold galvanized steel sheet that is more similar to a highly corrosion-resistant electrolytic zinc alloy coated steel sheet.
Corrosion resistance is improved by using a bath with gχ added and the impurity Pb below a certain level, and the plating thickness can be adjusted to 30~30 or less in terms of coating weight, improving workability. It has been found that if the layer is introduced into a molten or semi-molten state into a sharpening furnace and subjected to at least partial alloying, the thickness of the layer becomes uniform throughout, and a uniform and dense appearance can be obtained.

That is, the present invention is a steel plate with AI0.30 to 5.0%, Mg
0.01-2.0%, Pb O, 01% or less, balance Zn
and unavoidable impurities at a bath temperature of 450℃.
After plating with ~480U, the plating thickness is V- by gas squeezing method.
Then, when the plating layer is in a molten or semi-molten state, the atmosphere is il! Summer 550-1200t
- Zr* It is characterized by promoting interdiffusion and partially (at least partially) alloying the plating layer.

In the present invention, the problem of workability of the copper plate remains, but this problem can be solved by separately performing an overaging treatment or by using a non-aging copper plate.

The present invention 94 will be explained in detail below.

In the case of the present invention, first, a cold rolled steel sheet is subjected to pretreatment N'2 to obtain surface and mit'v metal suitable conditions. There are no particular limitations on the pretreatment (it can be done by any known method. For example, when performing the non-oxidizing furnace method or the oxidizing furnace method, the steel plate is heated to 550 to 620 C in a heating zone and the surface After degreasing and cleaning and preheating the steel plate, it was heated in a reduction furnace for 68 hours.
It is heated to 0 to 690C for reduction and annealing, and then adjusted to the appropriate degree of plating.

The pretreated steel plate is then immersed in a bath having the above composition, and the bath temperature is 45%.
Plate at 0 to 480C. The reason for limiting the bath temperature in this way is that if the alloy layer develops during fitting, the flow of the plating layer, which is performed later in the heating furnace prior to alloying, will be incomplete, making it impossible to obtain a smooth and dense surface. .

After plating, the plating thickness is adjusted by the gas squeezing method after rising from the bath. In this case, the plating thickness is 309/rr on one side under conventional gas throttling conditions. It can be adjusted as below. Also, one side that is the guarantee side should be set to 30 or less, and the other side should be
309/rr? More than f, for example 901! It is also possible to make the thickness slightly different from β.

Furthermore, it has been confirmed that it is also possible to apply a slurry-like masking substance made of a clay composition to one side of the shoulder plate before pretreatment, and then apply it to one side of the steel plate.

Steel plates whose plating thickness is adjusted by pressure in this manner do not melt the plating layer [--When in a semi-molten state, the steel plate is introduced into a heating furnace and the plating layer is alloyed. The alloy layer of the plating layer on the steel sheet that enters the heating furnace is not developed and is in a molten or semi-molten state, so reflow occurs in the furnace before it becomes a base metal, and the surface of the plating layer becomes smooth. and the thickness is uniform throughout. In addition, in the case of differential thickness plating, only the thinner side of the plate is t-alloyed, and the thicker side is formed with η-Zm phase or β-
It is also possible to leave the Zn phase remaining.

Alloying treatment in a heating furnace is performed at ambient temperature [550 to 1200
C for 2 to 30 seconds to alloy the entire plating layer or partially alloy it. In the case of partial alloying, the surface structure of the plating layer mainly consists of η-Zn phase and β-Zn phase, and spangles are generated after passing through a heating furnace. For this reason, when the plating layer is in an unsolidified state, it is removed from the heating furnace and sprayed with droplets of water or an aqueous solution such as an inorganic salt to minimize or erase the spa/glue.

Next, the reason for limiting the bath composition will be described.

(1) Al Al is added to improve the fluidity of the bath to make it thinner and to improve its corrosion resistance. In the case of the present invention, the plating thickness is targeted to be 301/d or less in terms of deposition amount, compared to the conventional 45 or more. Therefore, it is necessary to improve the fluidity of the bath so that the amount of adhesion can be reduced by 30% or more under the same bath temperature and gas restriction conditions.

Therefore, K is 0.3% for A1, compared to about 0.2% in the conventional case.
It was necessary to do more than Kj.

The fluidity of the bath increases as the amount of A1 added increases, and the corrosion resistance also improves to L5 to 2.0 times that of conventional products at 5%. Since AI has the effect of suppressing the growth of the alloy layer, if the amount added is large, only partial alloying will occur even when heated, and the η-Zn phase and β-Zn phase will remain on the surface of the plating layer. , prevents peeling of the plating layer and pulverization.

However, if AI#i+Ik exceeds 5% Y, the surface of the alloy layer becomes rough and the growth of the dissimilar alloy layer also increases to +a, resulting in a quality disadvantage compared to electroplated steel sheets. Based on Kosai I et al., AI was set at 0.30 to 5%.

(2) Mg Mg is added for the purpose of improving the corrosion resistance of the plating layer, and the corrosion resistance becomes noticeable when the amount added is around 0.01%, and thereafter improves as the amount increases. However, if it exceeds 2.0%, the surface 1fi of the miteru layer becomes wrinkled, and the surface 1jK of the miter layer 1jK is formed as a black Mg# compound. Furthermore, if the amount of Mg added is too large, the surface of the bath is easily oxidized and becomes a large amount of dross, resulting in a decrease in Mg yield.

As a result, the bath composition fluctuates rapidly, making it difficult to control the bath composition and reducing work efficiency. Therefore, the lower limit of Mg is 0.
01%, and the upper limit was 2.0%.

(31Pb Pb is unavoidably carved into the zinc base metal due to its manufacturing method, and 1
! It may be present at a high concentration of less than 0.003% in the case of electrolytic zinc produced by the solution method, and around 1% in the case of constant distillation zinc produced by the distillation method. When the mating layer solidifies, this Pb precipitates in large quantities at the grain boundaries and forms local cell noise with areas with less Pb, reducing corrosion resistance.

Zn-AI-Mg alloy bath K
%, corrosion resistance will not improve even if Mg is added, and (
In a K-moist environment, corrosion along grain boundaries progresses significantly,
The plating layer will be partially peeled off by a simple bending process such as bending 2. For this reason, pb was set to 0.01% or less.

EXAMPLE An unannealed rimmed cold-rolled steel plate (thickness: 0.6 mm) was plated and alloyed using a non-oxidizing furnace type continuous hot-dipping apparatus incorporating a heating furnace for alloying.

For plating, the plate is heated to 600 CK in a non-oxidizing furnace, then annealed and reduced in a reduction annealing furnace using AX gas (75% Hz - 25% N2) at a plate temperature of 700 r, and then cooled to approximately the same temperature as the plating bath and exposed to the atmosphere. (It was done by immersing it in a mitsuba with the composition shown in Table 1.)

After plating, the plating thickness was adjusted by a gas squeezing method using combustion exhaust gas, and while the plating layer was in a molten state, it was introduced into a heating furnace, heated under the conditions shown in Table 1, and alloyed.

In addition, the plating bath was conducted at a constant temperature of 460C at 11 degrees.
The gas throttling conditions for adjusting the plating thickness were the conventional bath (Zn -0,
15% AI) K: was set to 301//n/ (one side), and the conditions were the same for all.

The obtained alloyed galvanized steel sheet and highly corrosion-resistant electrolytic zinc alloy plating f! The following test was performed on @4 fN (Zn-Ni alloy electroplated copper plate).

(1) Resistance to powdering of the plating layer (resistance to powdering) 2 is bent, unbended and inspected for powdered ridges on the inner side of the bend.

A: No abnormality, B: Slight occurrence, C: Significant occurrence (2)
Corrosion Resistance 1) Salt Spray Test The time required for red rust to occur on 5% and 30% of the entire surface of the flat part and 2) The time required for red rust to occur on the bent part was measured in a salt spray test according to JIS Z2371.

H) Wet test 2 was bent and placed in a humid S@ atmosphere of 98% humidity and 70C, and a sellotape peel test was performed to measure the time until peeling of the plating layer occurred.

The results of this test are shown together with the bath composition and heating conditions.

As is clear from Table 1, when plating with the bath having the composition of the present invention, an extremely thin basis weight can be obtained even though the gas restriction conditions are the same as in the conventional bath.

Moreover, this thin coating property becomes more noticeable as the amount of A1 added increases.

The appearance of the products in the present invention is good, with smooth surfaces being obtained in all cases, and those heated under moderate heating conditions and mild pressure (Mus. 2.3 and 8) having metallic luster.

Powdering of the plating layer did not occur at all as a result of the thin coating weight, which was significantly improved over the conventional product (410).

In addition, corrosion resistance is significantly improved compared to conventional products, and the amount of AI is increased.
The effect of adding Mg is clearly visible. Furthermore, in the case of A611 with a high Pb%, it occurs in a short time in a humid atmosphere, but in the case of the present invention, it is good. and (A62.3.8 of the present invention has a η-Zn phase on the surface of the mesh layer,
Or, the β-Zn phase is present [7], but it is good, and the effect of reducing Pb is manifested.

As described above, according to the present invention, it is possible to make the coating weight thinner without changing the conventional gas squeezing conditions and conditions, and it is possible to completely prevent powdering of the matte layer due to processing. It has corrosion resistance equal to or higher than that of highly corrosion-resistant electrolytic zinc alloy plated steel sheets, and the surface appearance is smooth and dense because the matte layer is reflowed in a heating furnace. Therefore, weldability is good,
In addition, it has a moderate surface roughness of 5, so it has good paintability (,
Since the smooth K plating layer is uniform throughout, press workability is also good. Therefore, when used as a member for automobiles or home appliances, it has the advantage of being comparable in quality to 5 corrosion-resistant electrolytic zinc alloy plated steel sheets and being cheaper in price.

patent applicant Nisshin Steel Co., Ltd. agent Mitsuru Shindo Continuation of page 1 0 shots Akira Yasushi Miyoshi 2-1-17 Sakurajima, Konohana-ku, Osaka City No. 1 Nissin Steel Co., Ltd. Hanshin Works Inside 0 shots Toshio Yoshimoto 2-1-17 Sakurajima, Konohana-ku, Osaka City No. 1 Nisshin Steel Co., Ltd. Hanshin Manufacturing Inside the office

Claims (5)

[Claims] (1) When manufacturing an alloyed galvanized steel sheet by heating after hot-dipping, the steel sheet is heated to an AIo of 30 to 5.0.
%, Mg 0.01-2.0%, Pb O, 01% or less, residual @Zn and unavoidable impurities.After plating at a bath temperature of 450-480C, the plating thickness was determined by gas squeezing method. After that, when the plating layer is in a molten or semi-molten state, the plating layer is introduced into a heating furnace with an ambient temperature of 550 to 1200C and heated for 2 to 30 seconds to promote Fe-Zn interdiffusion in the plating layer. A method for manufacturing an alloyed galvanized steel sheet, characterized by partially alloying. (2) The method for manufacturing an alloyed galvanized steel sheet according to claim 1, characterized in that the plating thickness is adjusted to 309/d or less on one side. (3) The plating thickness on both sides is different, and one side is 30mm thick.
The method for manufacturing an alloyed galvanized steel sheet according to claim 1, characterized in that the differential thickness of the galvanized steel sheet is spliced to 9/sl or less and the other side to 309/w or more. (4) Mask one side of the steel plate, immerse it in a bath, plate only the other side, and adjust the plating thickness! A method for manufacturing an alloyed galvanized steel sheet according to claim 1 or 3, characterized in that: (5) After the plating layer is partially alloyed in a heating furnace, when the plating layer is not solidified, water or water droplets of an aqueous solution are sprayed from the heating furnace at 94 VC to rapidly solidify the plating layer. A method for producing an alloyed galvanized steel sheet according to item 1.