JPS6348925B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a molten metal plated steel plate in which a steel plate is coated with a metal or alloy having a relatively low melting point such as Zn or Al. [Prior Art] In general, molten metal plated steel sheets are produced by heat-treating the steel plate to be used as the original plate in an oxidizing atmosphere gas to burn off fats and oils adhering to the surface, and then applying a high-concentration hydrogen atmosphere gas (75% Hz) or the non-oxidizing furnace method, which burns and removes fats and oils attached to the surface in a heating furnace in an atmospheric gas with a low hydrogen concentration (10 to 20% Hz), and then cools. It is manufactured by lowering the temperature in a furnace to a temperature suitable for plating, then introducing it into a molten plating metal bath and immersing it. This manufacturing method is commonly used because of the operational advantage that continuous plating can be performed without cutting the steel plate into coils. [Problems to be solved by the invention] However, in this production method, the hydrogen in the reducing gas used as the atmosphere gas in the heating furnace is
Although it is extremely effective for activating the surface of steel sheets, it is absorbed into the steel at high temperatures, becomes molecular hydrogen between the plating layer and the steel substrate (base iron), and expands, causing the plating layer to swell. There is a problem that causes plating defects called blisters. In addition, hydrogen in the reducing gas generates reaction products on the aluminizing bath surface in the snout during aluminizing, which becomes floating scum and adheres to the steel plate, causing the problem of unplated areas. Ta. For these reasons, it is not possible to obtain a molten metal plated steel sheet with excellent plating adhesion, and for this reason, the C in the steel
A method of creating fine irregularities on the surface of a steel plate with a reduced content (Japanese Patent Publication No. 52-36962), which actively generates an oxide film during oxidation treatment and reduces it.
Method for making a porous steel plate surface (Special Publication 1973-
Various solutions have been developed and put into practical use, such as (No. 44141). Recently, a molten metal plating method (Japanese Unexamined Patent Publication No. 56-33463) has been developed in which a steel plate is pre-plated with Cu, Ni, etc., and passed through a Sendzimer line maintained in an atmosphere with a hydrogen concentration below the explosive limit. ing. However, although both methods can produce molten metal-plated steel sheets with fewer unplated areas and better plating adhesion than the previous methods described above, the quality varies widely and there is still room for improvement. It was left behind. [Means for solving the problems] The present invention solves these problems, and
The present invention provides a method for producing a molten metal plated steel sheet with extremely few unplated areas and excellent plating adhesion. The gist is that a coating layer of Ni or Ni-based alloy is applied to a surface-cleaned steel plate with a coating weight of 0.002 to 1.5 g/m ² per side, and then dried at a temperature of 150°C or less.
Next, inert gas or hydrogen with a dew point of -35℃ or less
This is a production method in which the material is heated in an indirect heating furnace kept in an atmosphere of inert gas containing 10% or less, and then passed through a molten metal plating bath without exposing it to the atmosphere. [Function] The present invention will be explained in detail below. Molten steel is melted into a desired steel composition in a melting furnace such as a converter or electric furnace, and then becomes a slab through continuous casting or ingot making/slaking. A plated original sheet (steel sheet) that has been cleaned by applying normal pretreatment such as mechanical or chemical methods to the surface of a hot-rolled sheet, cold-rolled sheet, or annealed sheet manufactured through the manufacturing process of thin steel sheets.
Ni ^or
Apply a coating layer of Ni-based alloy. The Ni or Ni-based alloy coating layer improves the hot-dip plating properties of the steel sheet, eliminates the occurrence of unplated areas, and acts as an intermediary to increase the adhesion between the steel sheet and the upper layer plating. Alternatively, it may be applied by applying a solution containing Ni ions. In this case, the basis weight per one side of the coating layer is
If it is less than 0.002 g/m ² , the above-mentioned effect of improving melt plating property cannot be obtained, and if it exceeds 1.5 g/m ² , the effect reaches saturation and the amount of hydrogen absorption increases, causing peeling of the coating layer and causing the product to deteriorate. The adhesion of the plating will be significantly deteriorated. This is followed by drying at a temperature below 150°C. Drying is
This dehydration work is performed to prevent the formation of blisters due to moisture mixed into the coating layer when plating steel plates or applying solution. However, drying at temperatures exceeding 150°C must be avoided because the rapid rate of temperature increase will cause cracks in the coating layer and deteriorate plating adhesion. The Ni or Ni-based alloy coated steel sheet that has been dried in this manner is heat treated in an indirect heating furnace. Heat treatment involves heating the coated steel sheet to annealing or raising the temperature to the temperature at which it is introduced into a molten metal plating bath. The process is then carried out in an inert gas furnace atmosphere with a dew point of −35° C. or lower and an extremely low moisture content such as N ₂ or Ar, or an inert gas containing 10% or less hydrogen. In particular, inert gas containing more than 10% hydrogen generates reaction products on the aluminized bath surface, forming scum and causing unplated areas. In addition, the impurity gas oxygen contained in the furnace atmosphere gas must be suppressed to 10 PPM or less.
Preferred for the purposes of the present invention. In this way, the coated steel sheet heated to high temperature in a non-oxidizing state maintains an activated surface without being exposed to the atmosphere, and melts single metals or composite metals such as Zn and Al. The metal plating bath is passed through the plating bath while being cooled to the introduction temperature, and the upper layer is plated with a predetermined basis weight of Zn, Al, etc. [Examples] Examples of the present invention will be described below. Example 1 A 0.8 mm x 100 mm aluminium-killed steel plated plate (cold-rolled plate) was used, and a steel plate cleaning device, an electric plating device, a dryer, a heating-cooling furnace, and a molten metal plating device were arranged in the running direction of the plated plate. On a continuous plating line, plating was performed using an electroplating method with a Ni plating amount in the range of 0 to 2 g/m ² (per side), dried at a temperature of 100°C, and then dried at a dew point of -50°C at N _z 100%. The plate temperature is maintained in a heating furnace maintained at a gas atmosphere of
After heating to 800℃, galvanizing was performed.
As a result, by applying Ni plating in advance, the melt plating properties were significantly improved, and the appropriate amount of Ni deposited was 0.002
In the range of ~1.5 g/m ² , no plating occurred and the plating adhesion was good. Furthermore, the performance of the plated product was better than that of the conventional method, and particularly in aluminum plating, a remarkable effect was seen in preventing non-metals.

[Table] Example 2 Ni was removed on a continuous plating line using a hot rolling pickling solution (aluminum killed steel) with a plate thickness of 2.3 mm and a plate width of 100 mm.
After plating 0.1 g/m ² (one side), drying at a temperature of 60℃, and changing the Hz concentration in the furnace atmosphere (dew point -40℃) to a range of 0 to 30%, the results of galvanizing are shown below. It is shown in Table 2. The hydrogen concentration in the atmosphere inside the heating furnace is 10
% or less has a remarkable effect on preventing blistering. Furthermore, when plating hot-rolled materials, conventionally it was necessary to heat the material to around 800°C to activate the surface, but with the present invention, good plating can be achieved by heating at a low temperature.

[Table] Example 3 Using an aluminium-killed steel plating original plate with a thickness of 0.8 mm and a width of 100 mm, the amount of nickel plating (drying temperature -
110℃), aluminum-10 by changing the atmospheric conditions in the heating furnace.
Aluminization was performed in a %Si plating bath. As shown in Table 3, the amount of nickel plating was 0.002.
g/m ² (one side) or more and the moisture content in the heating furnace atmosphere is below the dew point of -40°C, good plating adhesion is obtained, and moreover, the plating performance is superior to that of the conventional method.

[Table] Example 4 A cold-rolled steel plate (aluminum killed steel) with a thickness of 0.8 mm and a width of 100 mm was plated with Ni alloy (1 g/m ² ) on a continuous plating line, and then dried at a temperature of 50°C. After heating the plate to a temperature of 800°C in a heating furnace with a dew point of −50°C and a heating furnace atmosphere of 100% N _z , aluminizing was performed. As a result, as shown in Table 4, Ni
-Fe (1-40%), Ni-Co (1-30%), Ni-Cu
(1-40%), Ni-P (1-20%), Ni-Mo (1-40%), Ni-P (1-20%), Ni-Mo (1-40%),
30%) etc. had a remarkable effect on improving plating performance.

【table】

〔Effect of the invention〕

As described above, since the present invention is not a plating method that oxidizes a steel sheet like the conventional continuous plating, it is possible to produce a molten metal plated steel sheet with extremely few unplated areas and excellent plating adhesion. Further, the present invention provides a conveyor roll (hearth roll) provided in a heating furnace in a continuous plating line.
Since no build-up occurs in the plated steel plate, there are no indentation defects in the plated steel plate due to roll transfer, and it is possible to produce a molten metal plated steel plate with excellent appearance.

[Brief explanation of drawings]

The figure shows the test results of Example 5.

Claims (1)

[Claims] 1 0.002~ per side on a steel plate whose surface has been cleaned
A coating layer of Ni or Ni-based alloy with a weight of 1.5 g/m ² is applied and dried at a temperature below 150°C, followed by dew point -
It is characterized by being heat-treated in an indirect heating furnace maintained in an atmosphere of inert gas at 35°C or less or inert gas containing 10% or less hydrogen, and then passing through a molten metal plating bath without exposing it to the atmosphere. A method for manufacturing a molten metal plated steel sheet with few unplated areas and excellent plating adhesion.