JPH05140719A - Manufacture of galvannealed steel sheet - Google Patents

Abstract

PURPOSE:To securely execute alloying treatment by previously applying Fe-S composite plating to the surface of a steel sheet, then applying galvanizing thereto and thereafter executing heating and alloying treatment. CONSTITUTION:The surface of a steel sheet contg. 0.02 to 0.5% P and/or 0.03 to 3% Si and/or 0.1 to 3% Mn is applied with Fe-S composite plating and is then galvanized, and thereafter, alloying treatment is executed in heating. Thus, the alloying rates of various steel sheets with different alloying reaction rates are equalized, the industrial manufacture is facilitated and the alloying rates can be promoted particularly to the kinds of steel late in alloying reaction such as P-added steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a galvannealed steel sheet, which improves the coating wettability and equalizes the alloying rates of various steel sheets having different alloying reaction rates, thereby achieving industrial production. The purpose is to facilitate the process and to accelerate the alloying rate of steels such as P-added steels, which have a particularly slow alloying reaction.

[0002]

[Prior Art and Problems] Alloyed hot-dip galvanized steel sheet is F
It has a Zn-Fe alloy composition containing 6 to 18% of e and is excellent in coating corrosion resistance, press formability, and weldability, and thus is a material used in a wide range of industrial fields such as automobiles, home appliances, and building materials. The manufacturing method is usually to heat the cold-rolled steel sheet or hot-rolled steel sheet in an oxidizing or non-oxidizing atmosphere to burn off dirt such as oil adhering to the surface, and then clean the surface in a reducing atmosphere. After that, hot-dip galvanizing is performed, and then Fe is diffused from the base iron into the plated layer by heat treatment to alloy it. The alloying reaction is F
Since it is governed by the diffusion rate of e, the speed varies depending on the steel type, and the line speed is changed and the Al concentration in the plating bath is adjusted as a countermeasure to deal with it, but it causes a decrease in operating efficiency and quality variations. There are disadvantages. Further, P-added steel, which is implemented as a high-strength steel sheet, has a remarkably slow Fe diffusion rate, resulting in serious production failure. on the other hand,
In the Si-added steel that is implemented as a high-strength steel sheet, if the Si content in the steel is high, Si oxide is generated on the steel sheet surface,
This impedes the wettability with molten zinc, and even if the Si content in the steel is low, the alloying rate is reduced. As a solution to this problem, it has been disclosed that the surface of the steel sheet is plated with Fe prior to plating (Japanese Patent Laid-Open No. 59-23858). However, the effect is insufficient, and the present invention proposes a method for improving it. To do.

[0003]

The present invention has been made in order to advantageously solve the above problems, and is characterized by a novel plating method that further enhances the effect of pre-plating before hot dipping.

[0004]

MEANS FOR SOLVING THE PROBLEMS The present invention is: (1) Alloying and melting characterized in that the surface of a steel sheet is previously subjected to Fe-S composite plating, and then hot dip galvanizing is applied, followed by heat alloying treatment. Method for producing zinc-based plated steel sheet (2) P 0.02 to 0.5% and / or Si 0.
Fe-S composite plating is applied to the surface of a steel plate containing 03 to 3% and / or 0.1 to 3% of Mn, and then hot dip galvanizing is applied, followed by heat alloying treatment. Method for producing zinc-based plated steel sheet (3) Plating using an acidic plating bath containing one or two or more Fe2 + ions and 0.01 to 20 g / l of an organic compound containing S such as polysulfone and sulfide derivative The method for producing Fe—S composite plating according to claim (1) or (2), characterized in that.

[0005]

The Fe-S composite plating layer refers to a plating layer having a structure in which an S-based substance is alloyed, mixed, or occluded in Fe. An example of an electroplating method is shown below as a method of forming the Fe-S composite plating layer. If necessary, the steel sheet is degreased and pickled by a conventional method, and then 0.01 to 10 polysulfone is added to an aqueous solution of ferrous sulfate and / or ferrous chloride.
It was introduced into a bath containing g / l, and the current density was 3 with the steel plate as the cathode.
By performing electrolytic treatment at 0 to 300 A / dm ² for 0.1 to 30 seconds, polysulfone as an S substance is co-deposited as 0.01 to 1% as S in the Fe plating layer. Then, the temperature is raised to 500 to 700 ° C. in the mineralization furnace and 500 to 700 in the reduction furnace.
When heat treatment is performed while holding at 800 ° C, the Fe plating layer is recrystallized and polysulfone is decomposed to produce Fe-S.
A composite plating layer is formed. When no S component is present, the Fe plating layer recrystallizes to form crystal grains similar to those of the base steel sheet, but through the grain boundaries, Mn and S of the base steel sheet are passed.
Elements such as i, P and Al easily diffuse to the surface of the Fe plating layer. These trap elements have a significant influence on the subsequent alloying reaction, but their surface concentration differs depending on the steel type, and therefore the alloying rate differs from each other. For this reason, the effect of leveling the surface concentration of the trap element was insufficient in Fe pre-plating.

On the other hand, in Fe--S composite plating,
Amorphous fine crystals are generated during the recrystallization process, and no clear grain boundaries are observed. In addition, S is the diffusion in the grains is P,
Compared to Si and Mn, it is faster and easily concentrated on the grain boundaries and the surface. Therefore, the diffusion of the trap element to the surface of the plating layer is remarkably suppressed, the surface concentration is leveled even if the steel type is different, and a substantially constant alloying reaction rate is achieved. Even in the P-added steel, the surface concentration of P is suppressed and the alloying rate can be promoted to a level close to that of ordinary steel. Also,
Even in the case of Si and Mn-added steel, Si and Mn have similar effects.
The formation of oxides is suppressed, the wettability with molten zinc and the plating adhesion are improved, and the alloying rate can be accelerated.

Next, the plating method of Fe-S composite plating will be described. First, the method by electroplating,
Anionic surfactants, cationic surfactants, nonionic surfactants, zwitterionic interfaces containing polysulfone, sulfide derivatives and S as S components in aqueous solutions of ferrous sulfate and / or ferrous chloride One or two activators
Using an acidic plating bath containing 0.01 to 20 g / l of seeds or more, electrolytic treatment is performed using a steel sheet as a cathode. These S
Since the substance of mass has a high adsorptivity to active points due to the action of polar groups such as sulfone group, sulfide group, ether group and amine group, it is easily and uniformly contained in Fe plating.

These additives are generally R²-X- (R¹-Y) n-R³  And / or R²-(R¹-X) n-R³  Indicates a compound represented by. Here, X, Y: O (ether group), S (sulfide group), SO
₂(Sulfone group), NH, NR (amine group), NR₂+
(Ammonium group) R¹: Alkylene group and / or R², R³: H, alkyl group, phenyl, naphthyl, etc.
Aryl group and / or its derivatives (carboxylic acid, sulfuric acid,
Functional groups such as phosphoric acid, salts, esters) n = 1 to 2000 These compounds are chain compounds like polysulfone.
May also be crown ether or sorbita monolaurate
A cyclic compound such as a sulfone derivative of
A linear / cyclic mixed compound such as amine sulfone may be used.
To give a specific example,

[0009]

[Chemical 1]

.Sulfide RSR 'R, R': alkyl, H

[0011]

[0012]

[0013]

[Chemical 2]

[0014]

[Chemical 3]

Thiourea SC (NH ₂ ) ₂ thiocyanate KSCN, NH ₄ SCN, etc. The addition amount of these additives in the plating bath is 0.0
1 to 20 g / l is a preferable range. 0.01 g / l
Below the level, almost no effect is observed. 20g / l
When the content exceeds S, the S content is saturated, and the solubility in the plating bath is restricted. The above additives may be used alone or in combination of two or more. The Fe2 + ion concentration is not particularly limited, but usually, it is in the range of 10 to 150 g / l, and the optimum conditions can be adopted for the target plating in consideration of the current efficiency. Furthermore, Na +, K +, NH 4 +,
The addition of extraneous salts such as Mg2 + ions is effective in increasing the electrical conductivity of the bath. Note that, depending on the purpose, even if a small amount of ions such as Ni, Co, Cr, Mn, Cu, Cd, Sn, and Pb are added to cause a small amount of the third component to eutectoid in the plating layer, the effect of the present invention is essential. Does not change to

Next, the plating conditions will be described. It is preferable to plate the steel sheet at a current density of 30 A / dm ² or more. If it is 30 A / dm ² or less, it takes a long time to obtain a sufficient Fe—S plating amount for improving alloying, which is not industrial. The flow velocity of the plating solution is 10 to 200 m / min as the relative velocity to the steel strip, and the plating temperature is 40 to 70.
℃ is suitable. The plating amount is 0.2 to 10 g /
Apply m ² plating. If the plating amount is less than 0.2 g / m ² , the effect is small, and if it is more than 10 g / m ² , the effect is almost unchanged and the cost is disadvantageous.
It is preferably g / m ² or less. In addition, S during Fe-S plating
The amount is preferably 0.01% or more and 1.0% or less.
If the S content is less than 0.01%, the effect on the alloying reaction is small, and if it exceeds 1.0, the plating layer becomes brittle and tends to peel off in the furnace, which is not preferable. If necessary, the steel sheet may be degreased and pickled by a conventional method before plating. It is also possible to add the sulfide fine particles as they are or together with the above-mentioned surfactant.

Next, examples of modes other than the above will be shown. The electroplating method may be performed immediately before the hot dipping method. After electroplating, if necessary, flux may be applied and heated to 400 to 500 ° C. to lead to a hot dip plating bath, or directly to the hot dip bath at room temperature and heated in the bath for plating. In this case, the S-containing substance of the Fe-S composite plating layer is hot-deposited in an undecomposed or partially-decomposed state, but it has a sufficient suppressing effect on the diffusion of the trap element in the hot-dip plating bath. The Fe-S composite plating can also be applied by a physical vapor deposition method using Fe and S as targets, and a chemical vapor deposition method in which vaporizable Fe salt and organic vapor are used for decomposition and deposition. The mechanism of action of Fe-S composite plating in these methods will be the same as above and will be obvious. The Fe-S composite plating layer of the present invention preferably has a thickness of 0.2 to 10 g / m ² . 0.2 g / m ²
If it is less than 10 g, the effect is unclear, and if it exceeds 10 g / m ² , the effect is almost unchanged and it is disadvantageous in terms of cost.

In the P-added steel, a steel sheet having a P content of 0.02 to 0.5% has a large alloying promoting effect. 0.02%
If it is less than 0.5%, it is not different from ordinary steel, and if it exceeds 0.5% P, the effect is insufficient even with the Fe-S composite plating of the present invention. In the Si-added steel, a steel sheet having a Si content of 0.2 to 3% has a large effect of improving wettability with molten zinc, an effect of promoting alloying, and an effect of improving plating adhesion. If it is less than 0.2%, it is the same as ordinary steel, and if it exceeds 3% Si, Fe- of the present invention is used.
Even with S composite plating, the effect is insufficient. Mn
In the added steel, a steel sheet having a Mn content of 0.1 to 3% has a large effect of improving wettability with molten zinc, an effect of promoting alloying, and an effect of improving plating adhesion. If it is less than 0.2%, it is not different from ordinary steel, and if it exceeds 3% Mn, the effect is insufficient even with the Fe-S composite plating of the present invention. These elements are 2
Even if more than one kind is added, the effect range of each element is the same as above. The hot dip galvanizing bath of the alloyed hot-dip galvanized steel sheet usually contains 0 to 0.15% of Al.
b, Cd, Sb, Sn may be present in a small amount, and for the purpose of quality improvement, Ni, Mn, Ti, Zr, M
Although a small amount of g, Ca, Li, lanthanide, etc. may be added, the method of the present invention is essentially completely applicable when an alloying process is performed. Fe-S
In complex plating, other elements such as Ni, Zn,
Even if a small amount of Mn, Cu, P, B, O, C, N, Cl, H, Na, etc. is mixed, it is essentially the same as the present invention.

[0019]

EXAMPLES Next, examples of the present invention will be given together with comparative examples. 1) Table 1 shows the chemical composition of each steel sheet. In addition, Table 2A, Table 2B, Table 2C, and Table 2D are pre-plating conditions. After plating under such pre-plating conditions, 650 ° C. (plate temperature) on the outlet side of the direct-heating non-oxidizing furnace of the continuous hot dip galvanizing equipment pretreatment furnace, and 750 on the reduction heat treatment furnace.
Heat treatment was performed at ˜800 ° C. for 30 seconds, and then it was introduced into a zinc-based plating bath for plating. 2) The plated steel sheet was alloyed as shown in Tables 3A and 3B. The alloying was carried out with the temperature of the direct-fired heating furnace kept constant at 950 ° C. and the temperature of the heat-retaining furnace kept constant at 650 ° C., respectively. In this case, the higher the stripping speed is, the faster the alloying speed is, which means that the alloying treatment can be performed in a shorter time.

[0020]

[Table 1]

[0021]

[Table 2A]

[0022]

[Table 2B]

[0023]

[Table 2C]

[0024]

[Table 2D]

[0025]

[Table 3A]

[0026]

[Table 3B]

[0027]

As described above, according to the present invention, the alloying treatment can be performed in a short time, and the productivity can be improved accordingly.
By doing so, the alloying treatment can be performed with almost no change in the alloying treatment conditions (temperature, time) depending on the type of steel, which is industrially stable and can be reliably performed. Further, the alloying treatment time can be shortened, the productivity can be improved accordingly, and the excellent effects such as the wettability with molten zinc and the plating adhesion can be improved.

Claims (3)

[Claims] 1. A method for producing an alloyed hot-dip galvanized steel sheet, which comprises subjecting a surface of a steel sheet to Fe-S composite plating in advance, then hot-dip galvanizing, and then heat alloying treatment. 2. P 0.02-0.5% and / or Si 0.03-3% and / or Mn 0.1-3%.
A method for producing an alloyed hot dip galvanized steel sheet, which comprises performing Fe-S composite plating on the surface of the steel sheet to be contained, then hot dip galvanizing plating, and then heat alloying treatment. 3. Fe2 + ions and 0.01 to 20 g /
The Fe according to claim (1) or (2), characterized in that an S-containing organic compound such as polysulfone or sulfide derivative of 1 is plated using an acidic plating bath containing one or more kinds. -S composite plating manufacturing method