JPH01159360A - Hot dip coating method - Google Patents

Abstract

PURPOSE:To inexpensively and easily execute hot dip coating while preventing deterioration of the material quality of a steel sheet on which a metallic layer of a low m. p. is previously coated by subjecting said steel sheet to hot dip coating and maintaining the temp. of the steel sheet at the temp. below the m. p. of the hot dip coating metal during this time. CONSTITUTION:The steel strip 2 un-coiled from a payoff reel 1 is brought into contact with a roll coater 4 which is kept immersed in a plating bath 3 heated by a heater 8 and is thereby subjected to the hot dip coating. After the plating deposition is adjusted by a gas blowing nozzle 5, the steel strip is taken up on a tension roll 6 to form a coil 7. The metal of the m. p. lower than the m. p. of the hot dip coating metal is previously coated on the above- mentioned steel strip 2 prior to the hot dip coating of the steel strip 2 in the above-mentioned hot dip coating. Furthermore, the plating is executed while a cooling gas is ejected from nozzles 9 to maintain the temp. of the steel 2 at the temp. below the m. p. of the hot dip coating metal, more preferably <=300 deg.C after the coating of the above mentioned metal before the end of the hot dip coating. The deterioration ot the material quality of the steel strip is thereby prevented and the thick plating with good adhesiveness is enabled.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to various automobiles having various mechanical characteristics,
This relates to the production of rust-proof steel sheets for home appliances.

[Conventional technology]

Many types of rust-proof steel sheets are being manufactured in response to the strengthening of anti-corrosion measures for automobiles and other products in recent years. Broadly speaking, these can be classified into plated steel sheets and organic coated steel sheets in which an organic coating is applied using a pretreated or plated steel sheet as a base material.
Plated steel plates cover both types and form the basis of rust-proof steel plates. These plated steel sheets can be classified according to the type of plated metal, composition, and structure of the plating layer, and many types of plated steel sheets are actually commercially available and are used as base materials for organic coated steel sheets.

These various types of plated steel sheets can be classified into two types depending on the manufacturing method. Namely, there is a hot-dip plating method in which plating metal is brought into contact with a steel plate as a base material in a molten state, and an electroplating method is in which the plating metal is electrically deposited on the surface of a base metal plate. For the former, the Sendzimir method currently used in large-scale industrial production is the Sendzimir method, which removes oils and fats from the surface of steel sheets, removes scales, and removes both crystals from steel sheets.
This is a method in which a steel plate is heated to 800°C and then immersed in a molten zinc bath at about 460°C at a high temperature of about 500°C for plating. The galvannealing method, which promotes the alloying reaction between zinc and base iron to form an alloy layer up to the surface, involves the step of further heating the steel plate to 450 to 550°C.

Therefore, from the perspective of heat treatment of steel sheets, this process is so-called continuous annealing.On the other hand, compared to the continuous annealing technology developed in recent years for automobile thin sheet manufacturing, it is
This is a process that essentially makes it impossible to apply modern continuous annealing metallurgy techniques such as rapid cooling to 50°C and overaging treatment at 300 to 350°C. For this reason, it is difficult to produce steel sheets with good formability by hot-dip plating, and methods such as adding pre-annealing or post-annealing or using expensive ultra-low carbon steel as the material are used. It is also extremely difficult to manufacture bake-hardenable steel sheets and dual-face high-strength steel sheets. In recent years, so-called single-sided galvanized steel sheets, in which only one side of the steel sheet is plated, have been developed.In this case, instead of immersing the steel sheet in a molten metal bath, plating is performed using a roll coater or an electromagnetic pump.
The molten metal is supplied so that it contacts only one side of the steel plate, but the basic heat treatment cycle is the same as double-sided plating.

On the other hand, with the electroplating method, metal is electrically plated on an annealed steel sheet at room temperature, so there are no problems with building up the steel material as with the hot-dip plating method, but the manufacturing cost increases, especially when the amount of plating is large. High levels are said to be fatal. For example, it is disclosed in JP-A-59-162294 that Ni, Co, Cu, and Fe plating is applied and the upper layer is plated with zinc or the like by melting, but this method improves the corrosion resistance of the plated steel sheet. This is accompanied by the above-mentioned difficulties.

[Problem that the invention seeks to solve]

The present invention solves the above-mentioned problems in forming steel sheet materials using the hot-dip plating method, and utilizes the advantages of the hot-dip plating method, which is inexpensive and can easily be thickened, to economically provide various material properties. This makes it possible to manufacture rust-proof steel sheets.

[Means for solving problems]

The problem with material build-up in the hot-dip plating method is that, as mentioned above, it is necessary to heat and cool the steel plate in order to plate the molten metal, and this heat treatment cycle is compatible with modern continuous annealing metallurgy technology for thin sheets. First, it is necessary to constrain the various heat treatment cycles required to create various material properties. Furthermore, when a steel plate is immersed in a molten metal bath without being heated, the plated metal and the steel plate do not adhere to each other and separate, resulting in what is called "unplated" state. For this reason, the inventors of the present invention have made numerous attempts to find a method for forming a plating layer with sufficient adhesion between the hot-dip plated metal and the base steel sheet without applying any heat treatment to the steel sheet for plating. As a result, if a steel plate is coated in advance with a metal layer having a lower melting point than the hot-dip plated metal, the temperature of the steel plate is suppressed to a low temperature below the melting point of the hot-dip plated metal from the time the metal layer is coated until the hot-dip plating is completed. The inventors have also discovered that it is possible to hot-dip a plating layer with sufficient adhesion. That is, when a steel plate having a pre-coated metal layer is brought into contact with a molten plated metal, the pre-coated metal having a melting point lower than the temperature of the plated metal instantly melts, and atoms rapidly diffuse between the plated metal and the molten plated metal. plating occurs without raising the temperature of the steel sheet. In addition, if a steel plate is coated with a metal layer in advance and a plated metal molten at a temperature higher than the melting point of the metal layer is brought into contact with this, there is no need to preheat the steel plate before plating, and even during or after plating. We have discovered that it is possible to form a plating layer with sufficient adhesion without the need to raise the temperature of the steel plate.

If the hot-dip metal is mainly composed of zinc, such as zinc, an alloy of zinc and iron, or an alloy of zinc and aluminum, the metal to be coated in advance may be zinc, tin, lead, aluminum, etc., or an alloy thereof. Sufficient plating layer adhesion can be obtained as long as the melting point is equal to or lower than that of the upper layer metal, or the hot-dip plated upper layer metal is melted at a temperature higher than the melting point of the pre-coated metal. in this case,
For example, if the plated metal melted at 450 to 900°C is brought into contact with the steel plate for a short time on one side at a time or on both sides at the same time using a single-sided roll coater as in the single-sided galvanizing manufacturing method, the entire plate, apart from the outermost surface of the steel plate, can be coated. The temperature rise is slight, and thermal history that would affect the material and properties of the annealed steel sheet can be avoided. At this time, the material properties of the steel plate hardly change unless the temperature exceeds 300°C. The amount of metal to be coated in advance is not limited as long as the surface of the steel plate is coated with the metal, but from economical considerations it is 30 t/
rrl or less, preferably 0.005 f/m' or more from the viewpoint of coverage.

In this way, the present invention coats the surface of a steel plate with a metal layer having a low melting point in advance, and plated the plated metal melted at a temperature higher than the melting point of the metal while suppressing the temperature of the steel plate below a temperature that does not affect the material quality. This relates to a method for manufacturing plated steel sheets, which is characterized by the following: This method prevents the material properties of the steel sheets from changing during the plating process, and can be used as a plating base sheet for processing, bake hardenability, and dual-face steel rings. By using , it is possible to obtain various material properties even though it is a hot-dip coated steel sheet, and it is possible to coat the hot-dip coated steel sheet with thick coating as a metal layer by, for example, electroplating, vapor deposition plating, thermal spray plating, hot-dip plating, etc. Seshime,
Next, a plating metal melted at a temperature higher than the melting point of the metal constituting the metal layer is plated on the top layer. When the metal layer is formed by the above-mentioned electroplating etc., its surface is then heated to a temperature higher than the melting point of the metal constituting the metal layer. When plating is applied, there is almost no generation of oxides or the like that would adversely affect adhesion, and hot-dip plating can be applied as is.

The reason why the upper layer is plated with a plating metal melted at a temperature higher than the melting point of the father ligand coating metal is to melt a portion of the lower layer and integrate it with the upper layer plating in order to improve plating adhesion. During such hot-dip plating, as mentioned above, the steel plate temperature is suppressed to below a temperature that does not affect the material quality, and the plating methods include immersion in a plating bath, roll coater 1 electromagnetic pump, etc. There is a method in which a part of the bath surface is raised by such methods, and a steel plate is passed through the raised bath in contact with the raised bath. Even if hot-dip plating is carried out while suppressing the steel plate temperature to 300°C or less, prolonged coating may have a negative effect on the material. For example, if the steel plate temperature is 300°C, it will take less than 10 seconds, and if the steel plate temperature is 250°C, 60
If the temperature is 200°C, it is preferably 600 seconds or less. Therefore, for example, it is preferable to cool by blowing gas immediately after plating. Also, the melting point of the pre-coated metal is 3
It can be said that the temperature is preferably 00°C or lower.

[Example] Examples of the present invention will be described below. In each case, a steel strip after non-hot dipping was plated on one side using a single roll coater as shown in FIG.

That is, a steel strip 2, which has been plated by non-hot-dip plating on both sides of a copper strip coil rewound from a payoff reel 1, is placed on the surface of a plating bath 3 melted at a temperature higher than the melting point of the plated metal. The lower part is immersed and rotates in synchronization with the threading speed.
It also rotates in the plate passing direction and lifts the bath 3 metal with the rolls 4.

One side of the steel strip 2 is plated in contact with a roll, then gas is sprayed with a gas injection nozzle 5 to control the amount of plating to a predetermined amount, and the copper strip coil 7 is wound onto a tension reel 6 and hot-dipped again on one side. is attached to the payoff reel 2, and hot-dip plating is applied to the other side. In the figure, 8 is a heater that heats the bath 3, and 9 is a cooling gas jet nozzle that cools the steel strip 2.

Example-1 After degreasing and cleaning a cold-rolled steel plate with a thickness of 0.4 m, one side was 1/rr? Electroplated tin of 46% by the method shown in Figure 1.
Each side was plated with 402/- of hot dip zinc at 0°C. In the case of heat treatment, the steel plate temperature rose to a maximum of 180° C. for 5 seconds. The adhesion of the galvanized steel sheet was good, and a fully hard-tempered hot-dip galvanized steel sheet was obtained without any softening of strength.

Example-2 A cold-rolled steel sheet for processing with a thickness of 0.8fi was passed through an electrogalvanizing line to obtain a piece of WJ5f/lt? After plating with zinc, apply molten zinc at 460°C to 90°C on one side using the method shown in Figure 1.
PIT was plated one by one. Maximum steel plate temperature rise is 73℃ x 5
The processing time was within seconds, and a thick galvanized steel sheet with good adhesion was obtained.

Example 3 The same galvanized steel sheet as in Example 2 above was coated with 65% zinc containing 5% Fe, which was melted at 810°C by the method shown in Figure 1.
? /rr? Plated one by one. Maximum steel plate temperature is 210℃×
It rose within 5 seconds. Is the basis weight 65 f/rr? Despite the thick iron and zinc alloy plating, no powdering occurred and the workability was good.

Example-4 A 100 kg class high-strength steel plate with a thickness of 1.4 m was passed through an electrogalvanizing line and one side was coated with 39/lr. After plating with zinc, Fe was melted at 910°C using the method shown in Figure 1:
Zinc containing 10% 90f/rr on one side? Plated one by one. The temperature rise of the steel plate was within 110°C x 5 seconds. Despite having a high Si content, the plating adhesion was good and the strength properties were unchanged from before plating, resulting in a Pu-erh face type thick-grained iron and zinc alloy plated steel sheet.

That is, Table 1 shows the composition of the copper strip, Table 2 shows the manufacturing conditions, and Table 3 shows the material properties of the steel strip before plating and after plating.

〔Effect of the invention〕

By implementing the method of the present invention, pre-plating treatment (heat treatment) can be omitted in hot-dip plating, deterioration of the steel strip material can be prevented, and the desired steel strip material and plating material can be reliably obtained. Industrially excellent effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a roll coater one-type hot-dip plating apparatus. 1...Payoff reel 2...Copper band 3...Bath
4...Roll 5...Gas spray nozzle 6
...Tension reel 7... Steel strip coil 8.
...Heater 9...Cooling gas jet nozzle.

Claims (1)

[Scope of Claims] 1. Prior to hot-dipping a steel plate, the steel plate is coated with a metal layer having a lower melting point than the hot-dip plated metal, and the temperature of the steel plate is maintained after coating with the metal layer until the end of hot-dip plating. A hot-dip plating method characterized by plating while suppressing the temperature to below the melting point of the hot-dip plating metal. 2. The hot-dip plating method according to claim 1, wherein the melting point of the metal to be coated in advance is 300° C. or lower. 3 A metal layer is coated on the surface of a steel plate, and the plated metal is melted at a temperature higher than the melting point of the metal layer, and the temperature of the steel plate is increased to 300℃.
3. The hot-dip plating method according to claim 1 or 2, characterized in that plating is carried out while controlling the temperature to below .degree.