JPS62205261A - Method and apparatus for manufacturing alloyed steel sheet - Google Patents

Abstract

PURPOSE:To improve the surface properties of a hot dip galvanized steel sheet by bringing rolls heated to a surface temp. above the temp. of the steel sheet into direct contact with the steel sheet to carry out alloying. CONSTITUTION:A continuously annealed steel sheet 6 is dipped in a molten zinc bath in a hot dip galvanizing pot 2 through a snout, the forward direction is changed by a sink roll and the steel sheet 6 is pulled up from the bath, and is continuously metalized. A gas is blown on the continuously hot dip galvanized steel sheet 6 from wiping nozzles 4 to remove excess molten zinc, and the steel sheet 6 is introduced into a heating zone for alloying. In the heating zone, the steel sheet 6 is heated by bringing plural heated rolls 10 into direct contact with the steel sheet 6 to carry out alloying. The heating zone is kept in a nonoxidizing atmosphere by introducing a nonoxidizing gas from an inlet 12.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method and apparatus for manufacturing an alloyed galvanized steel sheet, and particularly a method for manufacturing an alloyed steel sheet in which an alloyed steel sheet is brought into contact with a heating roll. METHODS AND APPARATUS.

(Conventional technology) Alloying treatment (heat treatment performed after hot-dip galvanizing)
Conventionally, burner heating has been the mainstream heating method in OA). In the alloying treatment using the burner heating method, as shown in FIG. It is usual to undergo a process of heating 8, then passing through a holding zone to maintain the temperature, and then cooling in a cooling zone. Figure 2 shows a typical example of the temperature pattern of the steel plate at that time.
The temperature of the steel plate at the bottom reaches a maximum temperature of approximately 550° C. in the holding zone. However, in the burner heating method, as a means to minimize oxidation of the plating surface, where the plating surface is significantly oxidized due to the contact of combustion gas with the steel plate and the high temperature atmosphere, non-oxidizing gas such as N2 gas or gauge gas is applied to the holding band after heating. There is a method of introducing a oxidizing gas to suppress the oxygen concentration in the furnace atmosphere as much as possible, but since the inside of the heating zone is constantly evacuated, a large amount of non-oxidizing gas is required.

In addition, a method has also been proposed in which the steel plate itself generates heat by induction heating and the atmosphere is kept non-oxidizing, instead of using a single gas burner. For the induction heating method, see Figure 3 fa.
LNC type and TRC shown in l and fb) respectively
There are two types of methods called types. In the case of the LNC type, as shown in FIG. 3(a), the uniformity of heating in the width direction of the steel plate 6 is good;
To heat ivi, high frequency TH of 10 kllz or more is required.
? There are problems with the equipment, such as the need for Jfa.

On the other hand, in TRC type induction heating, the same
), heat input is easy, but there is a problem that uniform heating in the width direction is difficult. In the figure, the symbol C'' indicates a high-frequency induction coil.In addition, in any of these methods, alloyed material (hereinafter referred to as rGA material) treated by induction heating is used.
) compared to GA material heated by heating,
The thickness of one layer (alloy layer) in ten layers is 17 when compared with the same degree of alloying (Fc/Fe + Zn (χ)).In other words, the alloy layer develops to be abnormally thick in the plating layer. This is thought to be caused by internal force 11 heat from the steel plate base.This too thick alloy layer causes quality problems such as peeling of the plating layer during processing.

(Problems to be Solved by the Invention) Therefore, in order to overcome the difficulties of the conventional alloying treatment described above, the present invention provides hot-dip galvanizing without using the conventionally proposed gas burner or induction heating. This is a proof that the steel plate is subjected to alloying treatment.

(Means for solving the problem) As a result of studying various heating methods for alloying treatment, the present inventors found that contact heat transfer using heating rolls eliminates contact with combustion gas, unlike burner heating. It is possible to easily make the heating process atmosphere more oxidizing.
Moreover, they discovered that heating can be performed uniformly and efficiently in the width direction, and completed the present invention.

Here, the present invention provides a method for producing an alloyed steel sheet in which heat treatment is performed immediately after hot-dip galvanizing, in which the alloying treatment is performed by bringing a heating roll having a surface temperature higher than the steel sheet temperature into direct contact with the steel sheet. This is a method for manufacturing an alloyed steel sheet, characterized by the following.

Furthermore, the present invention provides an apparatus for manufacturing an alloyed steel sheet, which comprises a heat treatment furnace divided into a heating zone and a holding zone, which receives and alloys a hot-dip galvanized steel sheet. This is an alloyed steel plate manufacturing apparatus characterized in that the atmosphere is non-oxidizing and the heating zone is provided with one or more heating rolls.

As described above, a feature of the present invention is that the heating for the alloying treatment is performed using heated rolls, and when such a configuration is adopted, unexpectedly, no deterioration of surface properties due to contact with the rolls is observed. Rather, the surface of the heating roll is alloyed with the molten zinc, and the alloyed layer does not show wettability with the molten zinc, so the plating surface properties are rather improved.

(Operation) One embodiment of the method of the present invention will be explained in more detail with reference to the accompanying drawings.

For example, as shown in FIG. 1, a steel plate 6 that has been continuously annealed in a reducing atmosphere in a continuous furnace according to a conventional method is immersed in a hot-dip galvanizing bath 2 through a snout, and then turned around by a dipping roll and removed from the galvanizing bath. It is salvaged and subjected to continuous hot-dip galvanizing. Next, after removing excess adhering zinc by blowing gas from the wiping nozzle 4 to control the basis weight, the material is introduced into a heating zone for alloying treatment.

In the present invention, as shown in an enlarged view in FIG. 4, the heating of the steel plate in the heating zone is performed by direct contact with one or more heating rolls 10.

The heating roll can be heated from inside the heating roll by, for example, an induction heating method. In this case, unlike induction heating of a thin steel plate, heating is performed by a roll, and therefore, unlike the prior art described above, a particularly high frequency power source is not required.

In the illustrated example, multiple rolls are arranged in a staggered manner, but this is to provide the required contact time between the heating roll and the steel plate, and the arrangement of the rolls can be changed as appropriate depending on the alloying treatment conditions, etc. can. The number of rolls may be appropriately selected depending on the surface temperature of the rolls and the required heating temperature.

In order to prevent oxidation of the plating layer, it is preferable to introduce a non-oxidizing gas through the inlet 12 to create a non-oxidizing gas atmosphere in the heating zone as shown in the figure.

The plated steel sheet heated to a predetermined temperature in the heating zone is then passed through a holding zone and held at that heating temperature so as to form an alloy layer between the galvanized layer and the underlying iron. This holding band can also be made of a non-oxidizing atmosphere.
Next, as shown in FIG. 1, the steel plate is passed through a cooling zone and cooled by an air jet cooler to stop the alloying reaction.

Contact heat transfer by the heating roll used in the present invention will be explained in more detail with reference to FIG. 5. As shown in FIG. 5, the contact angle θ (rad
), the length S of the circular arc that the steel plate 6 contacts is S=□×θ(m), and when the line speed is 1ρ-, the contact time δ is 2120·■.

Considering the amount of heat transfer per unit area of a steel plate, the amount of heat q required to raise the temperature of a steel plate with thickness tas from T to Tt℃ is: Q −L XIO' X r XCX (Tt −T+
) (kcal) [r-specific weight, kg/d.

C-specific heat, kcal/kg ・"C), and if the roll surface temperature is T, then the amount of heat transferred from the roll is q-α・(Ta T+ )Xδ [α-value heat transfer coefficient, kcal/rd , hr, °C).

As an example, plate thickness L-0,8-1, roll surface temperature T-7
00°C, contact angle -20°, roll diameter D = 0.3+m,
Line speed V-100 Akebono ρ-1 Steel plate temperature before heating T-
In the case of 430℃ teal, the steel plate ratio l1fftR is 7830
If the kg/d1 specific heat C is 0.15 kcal/kg, ``c'', the following calculation formula holds true.

0.8x10-”x7830xO, I5X (h 4
30) 120×100, that is, Tt-455°C.

Under such conditions, the steel plate temperature would reach approximately 550'C in the 5th roll. The range of the contact angle depends on the roll diameter, but -a is preferably about 10 to 1200.

(Effects of the Invention) As described above, the present invention is characterized by the use of a heating roll, and since the heating roll is used for heat transfer in the alloying treatment according to the present invention, the contact is made with the steel plate itself. Rather, it is contact heat transfer with molten zinc, and unlike steel plates, the true contact area is large and the heat transfer coefficient is large, so the temperature can be raised efficiently. For example, the heat transfer coefficient α between the steel plate and the roll is approximately 2000 kca.
l/rd, hr, °C, whereas α between the molten zinc and the roll is about 10000 kcal as mentioned above.
/rrr,hr.

℃ and several times larger.

■An r single-phase Fe-Zn alloy is formed on the roll surface, and Zn is difficult to wet on the r set, making it difficult for molten Zn to adhere to the roll and build-up (roll surface temperature 7
00℃ or below).

Furthermore, no Zn adheres to the roll surface at all (when the roll surface temperature is 910° C. or higher).

Therefore, it is advantageous to set the surface temperature of the heating roll to 700° C. or lower or 910° C. or higher, so that the surface properties do not deteriorate even when it comes into contact with the heating roll.

(2) Even if the heating zone is sealed with an inert gas such as gauge gas, no exhaust is required, so less gas 1 is required.

[Brief explanation of drawings]

Fig. 1 is a similar schematic diagram showing an example of a production apparatus for alloyed E plate using conventional burner heating; Fig. 2 is a heating pattern of a steel plate in the burner heating method; Fig. 3 (al and (bl and far are 1.
t! by conventional induction heating method of NG type and TRC type! A schematic diagram showing IJ temporary heating, FIG.
A partial schematic diagram showing an example and FIG. 5 are schematic explanatory diagrams for showing details of contact heat transfer by a heating roll according to the present invention.

Claims (3)

[Claims] (1) A method for manufacturing an alloyed steel sheet in which heat treatment is performed immediately after hot-dip galvanizing, which is characterized in that the alloying treatment is performed by bringing a heating roll with a surface temperature higher than the steel sheet temperature into direct contact with the steel sheet. A method for producing an alloyed steel sheet. (2) The method according to claim 1, wherein the heating roll and the steel plate are brought into contact in a non-oxidizing atmosphere. (3) An alloyed steel plate production device consisting of a heat treatment furnace divided into a heating zone and a holding zone, which receives hot-dip galvanized steel plates and alloys them, and the atmosphere in the heating zone is non-oxidizing. 1. An apparatus for manufacturing alloyed steel sheet, characterized in that the heating zone is provided with one or more heating rolls.