JPH0238549A - Manufacturing method of alloyed hot-dip galvanized steel sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet, and more specifically, the present invention relates to a method for manufacturing an alloyed hot-dip galvanized steel sheet, and more specifically, the alloyed layer has a beautiful surface appearance without micro-irregularities or streaks. The present invention relates to a method for producing uniformly alloyed hot-dip galvanized steel sheet.

(Prior Art) Alloyed hot-dip galvanized steel sheets are widely used as exterior materials for automobiles, home appliances, etc. because they not only have excellent corrosion resistance but also excellent paint finish appearance and paint film adhesion. Darning alloyed hot-dip galvanized steel sheets are usually produced by heating (annealing) and reducing cold-rolled steel sheets, then immersing them in a hot-dip galvanizing bath to plate them, and then heating them at a material temperature of 250 to 750°C to remove Fe. −
It is manufactured by performing a so-called alloying process to form an alloy layer by causing interdiffusion of Zn.

Incidentally, in recent years, hot-dip galvanized steel sheets have also come to be required to have various properties. For example, rust-proof steel sheets for automobiles can be molded more severely than conventional products, or in response to the demand for lighter car bodies, we are developing rust-proof steel sheets that are thinner than conventional products but have the same or higher strength. A high-strength product that provides the desired properties is desired. In order to meet the requirements for galvanizing, Ti is added to ultra-low carbon steel as the base plated steel sheet.
, Nb, etc. added, as well as Si, Mn,
Materials to which one or more alloying elements such as Al1 and Cr are added have come to be used. In particular, for products that require a high degree of deep drawability, steel sheets to which solid solution C is fixed by adding T (so-called 5-labilized steel) are used.
e I), among which I added Ti to the ultra-low carbon network.
P steel (Interstitial Free steel) is attracting attention as a base material for alloyed hot-dip galvanized steel sheets.

However, steel sheets containing metals such as Af, Si, Mn, and Ti as mentioned above may have surface concentration of these elements, segregation of surface inclusions, surface oxidation, and locally uneven surface grain size. It tends to fluctuate easily. In other words, the surface of the steel sheet is exposed to the above-mentioned defects due to its interfacial energy during manufacturing processes such as copper manufacturing, continuous casting, hot rolling, and cold rolling, as well as during the heating, reduction, and cooling processes in hot-dip galvanizing lines. Although uniformity inevitably occurs, ■, Si,
Steel sheets containing Mn, Ti, etc. tend to further promote this non-uniformity.

It is known that if a steel sheet with such localized surface non-uniformity is alloyed after hot-dip galvanizing, microscopic unevenness patterns are likely to occur in the alloyed layer, and in severe cases, white streaks or visible streaks may appear. Uneven streaks called black streaks occur.

The reason why an uneven pattern occurs in the alloyed layer is that Zn--Fe alloying progresses at a non-uniform rate depending on the surface position in the non-uniform portion.

On the other hand, the progress of non-uniform alloying caused by such non-uniformity on the surface of the steel sheet is due to the effective Al concentration in the molten zinc bath (i.e., the total Al2 concentration in the bath minus the Fe concentration), It responds sensitively to changes in various plating operating conditions, such as bath temperature, temperature at which the steel plate enters the bath, and heat patterns such as heating, reduction, and cooling. For this purpose, go to 1. ．． Si
It is extremely difficult to rapidly and stably produce an alloyed hot-dip galvanized steel sheet with a beautiful appearance from a steel sheet containing metals such as , , Mn, and Ti. In addition, since the non-uniformity of the steel sheet surface varies due to differences in steel types and variations in steel manufacturing and hot rolling conditions, the production of alloyed hot-dip galvanized steel sheets with a beautiful appearance is extremely unstable, resulting in poor manufacturing efficiency and yield. is extremely low.

Furthermore, the production of alloyed hot-dip galvanized steel sheets also uses plating equipment that produces regular galvanized steel sheets, and the hot-dip galvanizing bath contains a small amount of 8! (0 to effective at 2 concentrations
．． 0.05 to 0.20%). In this bath! The higher the concentration, the better the workability of the plating film, but if the concentration is low, alloying will proceed at an uneven rate depending on the surface position in the subsequent alloying process, and the uneven pattern will appear in the alloyed layer. It is known that this is more likely to occur. That is,
If an attempt is made to improve the workability of a plating film, there is a problem in that uneven patterns are likely to occur.

In addition, as a method of manufacturing an alloyed hot-dip galvanized steel sheet by subjecting the surface of the steel sheet to base coating treatment in advance, then hot-dip galvanizing, and then heat diffusion alloying treatment, there is a method disclosed in JP-A-57-76.
There are methods disclosed in Japanese Patent Application Laid-open No. 176, Japanese Patent Application Laid-open No. 58-120771, and Japanese Patent Application Laid-Open No. 58-120772. However, these methods are intended to improve the adhesion and corrosion resistance of the plating film, and are intended to improve the adhesion and corrosion resistance of the plating film. It is not intended to suppress the uneven pattern.

(Problem to be Solved by the Invention) The problem to be solved by the present invention is to solve the problem of steel sheets having unevenness such as concentration of components such as Af, Si, Mn, and Ti and segregation of inclusions on the surface.
Alternatively, to provide a method for stably manufacturing an alloyed hot-dip galvanized steel sheet having an alloyed layer free from microscopic irregularities (streaks) and a beautiful surface even if variations occur in plating operating conditions, etc. It is in.

(Means for Solving the Problems) The present inventors have proposed that by applying an Fe-based coating containing metalloid elements such as P, B, and S to a certain thickness on the surface of a steel sheet prior to hot-dip galvanizing, the surface of the steel sheet can be Various experiments have shown that an alloyed layer without microscopic irregularities or streaks can be obtained even if there is non-uniformity such as concentration of ingredients or segregation of inclusions, or variations in plating operating conditions. The findings from the results led to the present invention.

The gist of the present invention is that ``one of P, B, and S is applied to the surface of the steel plate.
After applying a Fe-based coating containing a total of 0.001 to 30.0 wt% of one or more species and a coating weight of 0.01 to 10 g/m, hot-dip galvanizing is performed by heating, reduction, and cooling treatment. "A method for producing an alloyed hot-dip galvanized steel sheet" which comprises performing a heat diffusion alloying treatment.

In the method for producing an alloyed hot-dip galvanized steel sheet of the present invention, the base steel sheet includes A1 killed steel, S-eyed steel, slow aging steel for drawing (RBII), Si-Mn-added high-strength steel, and Ti alone. Alternatively, various types of steel can be used, such as ultra-low carbon Ti-added steel in which one or more of Ti, B, Nb, etc. are added. Among these, the method of the present invention is extremely effective for steel plates made of ultra-low carbon Ti-added steel (Ti-containing IFm), which is fragile and has a non-uniform surface using conventional methods.

(Function) Hereinafter, the method for producing an alloyed hot-dip galvanized steel sheet of the present invention will be described in detail.

A feature of the present invention is that when hot-dip galvanizing is performed after heating, reducing and cooling a steel sheet to be plated, and then thermal diffusion alloying treatment is performed to produce an alloyed hot-dip galvanized steel sheet, before the heat treatment. A total of 0.001 to 30 of one or more of P, B, and S on the surface of the steel plate to be plated.
．． The purpose is to apply a Fe-based coating containing 0 wt% and having a coating amount of 0.01 to Log/m2.

By applying a Fe-based coating containing one or more of P, B, and S, it can be used even on steel sheets with uneven surface elements such as elemental concentration or inclusion breakage, or changes in plating operating conditions. Although it is not theoretically clear why the alloyed layer does not have an uneven pattern in the subsequent alloying treatment, the Fe-based coating layer containing the semimetal is likely to have uneven elemental concentration on the surface. It is presumed that this is because the metalloid and the element that segregates on the surface form a stable compound that acts as a diffusion barrier for the metal.

Note that the Fe-based coating containing one or more of P, B, and S mentioned above refers to pure Fe or Fe-based coating containing Z as a main component.
n, Mn, Mg, W, Mo, Ni, Go,
Cr, Cu, Ti, ■, SnX Sb, AsX
Pb, In, , Ca, , Ba, Sr, , Si, 82, G
It contains one or more elements selected from e, Se, GaXHg, Ag, AuXB1, etc. Even if one or more of these elements are contained, the effects of the present invention will not be particularly impaired as long as the amount is 10 wt% or less.

The reason why the content of P, B, and S in the above Fe-based coating is set to 0.001 to 30.0 wt% in total of one or more types is that if it is less than O,001 wt%, it is heated and reduced in the hot-dip plating line. This is because during the cooling process, transmission of non-uniformity such as element concentration and segregation on the steel sheet surface occurs through diffusion, creating an uneven pattern in the alloyed layer. This is because the effect of preventing the progress of Zn--Fe alloying is saturated, and the manufacturing cost increases, making it uneconomical. A desirable content is 0.01 to 10 t%.

The reason why the amount of Fe-based coating is set to 0.01 to 10 g/m2 is that if the amount of adhesion is less than 0.01 g/m, it will be difficult to uniformly apply Fe-based coating to the surface of the steel plate to be plated.
This is because uneven patterns are likely to occur in the alloyed layer, and 10 g
Zn-Pe is non-uniform even when coated over / m2
This is because the effect of preventing the progress of alloying is saturated and only the plating cost increases, which is economically unfavorable. The desired coverage is 0.5-5 g/m''.

In the present invention, the Pe-based coating can be formed by electroplating, electroless plating, ion plating, vacuum evaporation,
It can be carried out by various methods such as sputtering method. Among these, electroplating method and electroless plating method are
This method is advantageous in carrying out the present invention because it is possible to uniformly plate the entire surface of the copper strip and to perform stable and high-speed processing. Also, P, B and S
Pulse plating is also effective in increasing the efficiency of semimetal deposition.

When applying the Fe-based film by electroplating or electroless plating, a sulfate bath, a chloride bath, or the like containing a metalloid element and Pa ions can be used. The metalloid element can be added to the plating bath in the following form.

When the metalloid is P, it is in the form of phosphorous acid, hypophosphorous acid or its salts, when it is B, it is in the form of sodium metaborate, thorium boron, dimethylamineporane, trimethylamineborane, etc., and when it is S can be added in the form of thiocyanate.

Further, the Fe-based coating treatment may be performed in-line before heating of the hot-dip galvanizing equipment, or may be performed on a line separate from the hot-dip plating line.

In-line processing is cheaper in manufacturing cost. F
When applying e-based coating, it is desirable to clean and activate the surface of the steel plate by performing known degreasing treatment or acid activation treatment, but if you select the appropriate cleaning method depending on the cleanliness of the steel plate surface good.

The surface of the alloyed hot-dip galvanized steel sheet produced by the method of the present invention is further coated with Fe-based, Fe-Zn-based, Fe-Mn-based, F
Electrodeposition coating defects can be suppressed by providing an upper layer of e-5n, re-Zn-3n, Fe-Ni, or the like. Additionally, fingerprint resistance can be improved by chromate treatment and clear organic resin coating.

Next, the present invention will be further explained by examples.

(Example) Steel having the chemical composition shown in Table 1 was melted and hot-rolled in a conventional manner to obtain a hot-rolled steel plate having a thickness of 4 mm. Next, cold rolling was performed to produce a cold rolled steel plate with a thickness of 0.8 mm.

This cold-rolled steel plate was used as a base material, and after being subjected to degreasing treatment and acid activation treatment, an Fe-based coating was applied to the surface. For Fe-based coating, prepare the sulfate baths or chloride baths shown in Table 2 (bath a) to (bath e), and prepare (bath b), (bath C), and (bath e).
, was carried out by electroplating at a current density of 1 to 20 OA/dm'', and (bath A) and (bath d) were carried out by chemical plating.

The S content was adjusted by the Na)IzPO□ concentration, the S content was adjusted by the sodium metaborate concentration or DMAB (dimethylamine borane) concentration, and the S content was adjusted by the potassium thiocyanate concentration. Furthermore, the amount of adhesion was adjusted by the immersion time in the chemical plating method, and by the current application time in the electroplating method.

Table 3 shows the steel type and plating bath of the cold-rolled steel sheets used, as well as the amount of adhesion and the content of P, B, and S in the Fe-based film.

The steel plate coated with the Fe-based film was subsequently annealed under the following conditions, and then subjected to hot-dip galvanizing treatment and thermal diffusion alloying treatment to produce an alloyed hot-dip galvanized steel plate.

(Annealing treatment conditions) Heating rate: 15°C/sec, heating temperature and holding time: 8
20°C x 30 seconds, ■2 concentration of furnace atmosphere gas: 25~
75% (hot-dip galvanizing treatment conditions) ^l concentration in Zn plating bath: o, 16%, Fe concentration:
0.02%, bath temperature: 465°C1 plating immersion time: 2 seconds, Zn' coating amount 60-70 g/m2 on two sides (thermal diffusion alloying treatment conditions) 450-650°CXl0-1000 seconds Obtained alloy The appearance of the alloyed layer of the hot-dip galvanized steel sheet was visually inspected and examined. The results are shown in Table 3.

The × marks in the table indicate the appearance results of alloyed hot-dip galvanized steel sheets obtained by conventional manufacturing methods, Δ marks are slightly better than this, O marks are also good, and ◎ marks are also significantly better. Good.

(Hereinafter, blank space) As is clear from Table 3, the alloyed hot-dip galvanized steel sheets (test Nos. 4 to 23) produced by the method of the present invention are alloyed with no microscopic irregularities or streaks. It has layers and has a beautiful appearance.

On the other hand, alloyed hot-dip galvanized steel sheet (Test No. 1) manufactured by the conventional method without Fe-based coating treatment
The alloyed layer has microscopic irregularities and streaks, and the appearance is significantly inferior. In addition, alloyed hot-dip galvanized steel sheets (No. 2 and N
o, 3), although the surface appearance was slightly improved compared to the conventional alloyed hot-dip galvanized steel sheet, the effect of the Fe-based coating was small, and the alloyed hot-dip galvanized steel sheet obtained by the method of the present invention It is inferior compared to

In addition, various tests were conducted on the alloyed hot-dip galvanized steel sheets (test Nos. 4 to 23) produced by the method of the present invention, such as a cylindrical drawing test, a "Bee-Toy" hat forming test, and a "Bee-Toy" test. , good ml powdering properties were exhibited for all deformations.

(Effects of the Invention) As explained above, according to the method of the present invention, Δ! , S
Even if the steel plate has non-uniformities such as concentration of components such as L, Mn, and Ti or segregation of inclusions, or changes in plating operating conditions, etc., it is possible to create an alloyed layer without microscopic irregularities or streaks. It is possible to stably produce alloyed hot-dip galvanized steel sheets with beautiful surfaces.

Claims (1)

[Claims] The surface of the steel plate contains a total of 0.001 to 30.0 wt% of one or more of P, B, and S, and the amount of adhesion is 0.
After applying a Fe-based coating of 01 to 10 g/m^2, heating and
1. A method for producing an alloyed hot-dip galvanized steel sheet, which comprises performing hot-dip galvanizing through reduction and cooling treatment, and then performing heat-diffusion alloying treatment.