JPH05140717A - Manufacture of galvannealed steel sheet - Google Patents

Abstract

PURPOSE:To securely execute alloying treatment by previously applying Fe-C-S composite plating to the surface of a steel sheet, then applying galvanizing and thereafter executing heating and alloying treatment. CONSTITUTION:The surface of a steel sheet contg. 0.02 to 0.05% P and/or 0.03 to 3% Si and/or 0.1 to 3% Mn is applied with Fe-C-S composite plating and is then galvanized, and thereafter, alloying is executed in heating. Thus, its plating wettability is improved, 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 as follows: normal cold-rolled steel sheet or hot-rolled steel sheet is heated in an oxidizing or non-oxidizing atmosphere, stains such as oil adhering to the surface are burned off, and then the surface is cleaned 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 Fe
Since it is controlled by the diffusion rate of aluminum, the speed varies depending on the steel type, and the line speed is changed or the Al concentration in the plating bath is adjusted as a method of coping with it, but this causes a decrease in operating efficiency and quality variations. There is a disadvantage. Also,
P-added steel, which is used as a high-strength steel sheet, has a significantly low Fe diffusion rate, which causes serious production problems. On the other hand, in the Si-added steel that is implemented as a high-strength steel plate, the Si in the steel is
When the content is high, Si oxide is generated on the surface of the steel sheet, which impedes the wettability with molten zinc, and even if the Si content in the steel is low, it causes a reduction in the rate of hydriding. 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-mentioned problems, and is characterized by a novel plating method for further enhancing the effect of pre-plating before hot dipping.

[0004]

Means for Solving the Problems The present invention is as follows: (1) Fe-C-S composite plating is applied to the surface of a steel sheet in advance,
Then, a hot dip galvanized coating is applied, followed by a heat alloying treatment. A method for producing an alloyed hot dip galvanized steel sheet (2) P0.02 to 0.5% and / or Si0.0
Fe-C-S composite plating is applied to the surface of a steel sheet containing 3 to 3% and / or 0.1 to 3% of Mn, and then hot dip galvanizing is applied, followed by heat alloying. Method for producing galvanized steel sheet (3) Using an acidic plating bath containing one or two or more Fe ² + ions and 0.01 to 20 g / l polysulfone, an organic compound containing S such as a sulfide derivative,
Plating is carried out, It is a manufacturing method of Fe-C-S compound plating according to claim 1 or 2 characterized by things.

[0005]

The Fe-C-S composite plating layer refers to a plating layer having a structure in which carbonaceous and S-based substances are alloyed, mixed, or occluded in Fe. An example of an electroplating method is shown below as a method for forming the Fe—C—S composite plating layer. If necessary, after degreasing and pickling the steel plate in the usual way,
The solution was introduced into a bath containing 0.01 to 10 g / l of polysulfone in an aqueous solution of ferrous sulfate and / or ferrous chloride, and a steel sheet was used as a cathode to obtain a current density of 30 to 300 A / dm ² ,
By performing electrolytic treatment for 1 to 30 seconds, polysulfone, which is a C and S substance, in the Fe plating layer has a C.
0 to 1% and 0.01 to 0.5% of S are codeposited. Then, when the temperature is raised to 500 to 700 ° C. in a non-oxidizing furnace, and is held at 500 to 800 ° C. in a reducing furnace for heat treatment, the Fe plating layer is recrystallized and polysulfone is decomposed to form Fe—C—. The S composite plating layer is formed. In the absence of carbonaceous matter and sulfuraceous matter, the Fe plating layer recrystallizes to form crystal grains similar to those of the base steel sheet, but through the grain boundaries, Mn, Si, P, and Elements such as Al easily diffuse to the surface of the Fe plating layer. These trap elements have a significant effect on the subsequent alloying reaction, but their surface concentration differs depending on the steel type, and therefore the alloying rate differs. For this reason, the effect of leveling the surface concentration of the trap element was insufficient in Fe pre-plating. On the other hand, F
In the e-C-S composite plating, amorphous-like fine crystals are generated in the recrystallization process, and clear grain boundaries are not observed. Further, C and S diffuse faster in the grains than P, Si, and Mn, and are likely to be concentrated at grain boundaries and surfaces. Therefore, the diffusion of the trap element to the plating layer surface is significantly suppressed, and even if the steel types are different, the surface concentration is leveled,
A nearly 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. In addition, also in the case of Si and Mn-added steel, the formation of oxides of Si and Mn is suppressed by the same effect, the wettability with molten zinc and the plating adhesion are improved, and the alloy acceleration can be promoted.

Next, a plating method of Fe-C-S composite plating will be described. First, a method by electroplating is used. An aqueous solution of ferrous sulfate and / or ferrous chloride is used as an anionic surfactant and a cationic interface containing polysulfone, a sulfide derivative and S as C and S components. Using an acidic plating bath containing 0.01 to 20 g / l of one or more of an activator, a nonionic surfactant and a zwitterionic surfactant, electrolytic treatment is performed using a steel sheet as a cathode. These C and S substances have high adsorbability at active points due to the action of polar groups such as sulfone groups, sulfide groups, ether groups and amine groups, so they are easily and uniformly contained in Fe plating. It

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 groups and / or their derivatives (carboxylic acids, sulfur
Acid, phosphoric acid or other functional group, salt, ester) n = 1 to 2000 These compounds are linear compounds such as polysulfone.
May also be crown ether or sorbita monolaurate
A cyclic compound such as a sulfone derivative of
A linear or cyclic mixture such as amine sulfone may be used. Concrete
For example,

[0008]

[Chemical 1]

Sulfide RSR 'R, R' = alkyl, H

[0010]

[Chemical 2]

[0011]

[Chemical 3]

[0012]

[Chemical 4]

[0013]

[Chemical 5]

・ Thiourea SC (NH₂)₂  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
If the content exceeds C, the content of C and S will be saturated, and the dissolution in the plating bath will occur.
Limited by the solution. The above additives are mixed alone or in combination of two or more.
It can also be used together. Fe²+ Especially the ion concentration
Although not limited, usually 10 to 150 g / l
In the range, the target plating is optimal considering the current efficiency.
The matter can be adopted. In addition, Na +, K +, NH_Four
+, Mg²+ Adding extraneous salts such as ions to the bath
It is effective for increasing the electrical conductivity. Depending on the purpose,
Then Ni, Co, Cr, Mn, Cu, Cd, Sn, P
Add a small amount of ions such as b to reduce the third component in the plating layer.
The effect is essentially the same even if the amount of eutectoid is used.

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. When it is 30 A / dm ² or less, it takes time to obtain a sufficient amount of Fe—C—S plating 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 ° C is suitable. The plating amount is 0.2 to 10
Apply g / m ² plating. If the plating amount is less than 0.2 g / m ² , the effect is small, and if it exceeds 10 g / m ² , the effect is almost the same and the cost is disadvantageous. Therefore, 10 g / m ² or less is preferable. The amount of C in the Fe-C-S plating is preferably 0.01% or more and 1.0% or less. If the amount of C 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 peels off in the furnace, which is not preferable. The amount of S in the Fe-C-S plating is 0.001.
% Or more and 0.5% or less is preferable. When the S content is less than 0.005%, the effect on the alloying reaction is small, and the content of 0.
If it exceeds 5%, the plating layer becomes fragile 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 C, S-containing substance of the Fe-C-S composite plating layer is hot-dipped in the 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. Fe-C-S composite plating is Fe,
The physical vapor deposition method targeting C and S, and the chemical vapor deposition method of decomposing and depositing by using a vaporizable Fe salt and an organic vapor can also be applied. The mechanism of action of the Fe-C-S composite plating in these methods will be the same as above and will be obvious. Fe-C of the present invention
The thickness of the -N composite plating layer is preferably 0.2 to 10 g / m ² . If it is less than 0.2 g / m ² , the effect is unclear, and if it is more than 10 g / m ² , the effect is almost unchanged and the cost is disadvantageous.

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—C—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 -C-S composite plating, the effect is insufficient. In the Mn-added steel, a steel sheet having a Mn content of 0.1 to 3% has an effect of improving wettability with molten zinc, an effect of promoting alloying,
Greatly improves the plating adhesion. If it is less than 0.2%, it is not different from that of ordinary steel, and if it exceeds 3% Mn, Fe-C- of the present invention.
Even with S composite plating, the effect is insufficient. Even if two or more of these elements are added, the effect range of each element is the same as above. The hot-dip galvanizing bath of the galvannealed steel sheet usually contains 0 to 0.15% Al.
In addition, Pb, Cd, Sb, and Sn may be present in a small amount, and Ni, Mn, and T may be added for the purpose of quality improvement.
Although a small amount of i, Zr, Mg, Ca, Li, lanthanide, etc. may be added, essentially all of the method of the present invention is applicable when the alloying step is performed. In Fe-C-S composite plating, other elements such as Ni, Zn, Mn, Cu, P, B, O, N, Cl,
Even if a small amount of H, Na, etc. is mixed, it is essentially the same as the present invention.

[0018]

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, and Tables 1A and 1
B, Table 1C, and Table 1D show pre-plating conditions. After performing this pre-plating, 650 ° C. at the outlet of the direct-heating non-oxidizing furnace of the continuous hot dip galvanizing equipment pretreatment furnace.
(Plate temperature), heat treatment was carried out at 750 to 800 ° C. for 30 seconds in a reduction heat treatment furnace, 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.

[0019]

[Table 1]

[0020]

[Table 2A]

[0021]

[Table 2B]

[0022]

[Table 2C]

[0023]

[Table 2D]

[0024]

[Table 3A]

[0025]

[Table 3B]

[0026]

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 carried out with almost no change in the alloying treatment conditions (temperature, time) depending on the steel type, 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 steel sheet surface to Fe—C—S composite plating in advance, then hot-dip galvanizing, and then heat-alloying. 2. P0.02-0.5% and / or S
Fe—C—S composite plating is applied to the surface of the steel sheet containing i0.03 to 3% and / or Mn of 0.1 to 3%, and then hot dip galvanizing is applied, followed by heat alloying treatment. A method for manufacturing a galvannealed steel sheet. 3. Fe ² + ions and 0.01 to 20 g /
Fe-C-S according to claim 1 or 2, wherein the S-containing organic compound such as polysulfone and sulfide derivative of 1 is plated using an acidic plating bath containing one or more kinds. Composite plating manufacturing method.