JPS61295362A - Alloying treatment furnace - Google Patents

Abstract

PURPOSE:To improve quality as well as productivity by passing, continuously in succession, a galvanized sheet through heating-up, rapid cooling and other zones so that alloying is carried out by initial heating and the steel sheet can be cooled rapidly before the completion of the alloying up to the surface. CONSTITUTION:The hot dip galvanized steel strip 11 is introduced into the heating-up zone 28 and heated to >=about 550 deg.C to undergo alloying. The heated steel strip 11 is then introduced into the rapid cooling zone 30 and rapidly cooled before the completion of the alloying up to the surface. Subsequently, the steel strip 11 is introduced into a holding zone 32 to undergo final alloying and then cooled in a cooling zone 34 successively provided, so that excessive alloying can be inhibited.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an alloying processing furnace for hot-dip galvanized steel sheets, and more specifically, to an alloyed hot-dip galvanized steel sheet that has quality characteristics, in particular, less peeling of the coating layer during processing. (Hereinafter abbreviated as "GA steel plate")
This invention relates to an alloying processing furnace for hot-dip galvanized steel sheets for manufacturing with high productivity.

(Prior art) GA steel sheets are generally produced by hot-dip galvanized steel sheets immediately after plating.
Manufactured by continuous heat treatment. Usually, due to mutual diffusion of Fe-Zn during heat treatment, the plating layer becomes 8
．． It contains 5 to 13% Fe and is composed of a layered structure of 2.3 types of intermetallic compounds. The material obtained in this way has better paintability and weldability than ordinary galvanized steel sheets, so it is used in a wide range of applications today. During processing, powdery peeling or partial detachment of the plating layer, called powdering, is likely to occur.

As a measure to solve this drawback, what has been known so far is to lower the material temperature during alloying treatment, or to
Alternatively, it is a method of increasing Al contained in Zn, and in either case, mutual diffusion of Fe-Zn is suppressed.

As an example of various attempts to overcome the powdering phenomenon of GA steel sheets from this perspective, there are attempts to study from the aspect of the heat pattern during alloying. For example, Japanese Patent Publication No. 59-14541 proposes dividing the alloying heat treatment apparatus into a primary heating apparatus and a secondary heating apparatus, and performing the secondary heating off-line. However, although this offline method has the effect of improving powdering resistance to some extent, there is no need to mention its disadvantages again, except for the effect of boss annealing.

Furthermore, JP-A-59-173255 explains the phenomenological background for improving powdering resistance, and
It is proposed to hold the temperature below 520℃ for 6 seconds or more to alloy it after plating, but the key is to slowly alloy it over time. It states that products of good quality can be obtained.

However, since there are no regulations regarding final temperature, upper limit time, etc., such processing conditions cannot be said to be sufficient conditions, and therefore, there are many cases where the powdering resistance is poor, leading to an unnecessary increase in the furnace length. It is also possible that there are no more than .

In recent years, hot-dip galvanizing lines have been increasing their threading speeds in pursuit of high productivity, and relatively new galvanizing lines have a speed of 15
A threading speed of 0 to 200 m/win is achieved. Therefore, the above-mentioned solutions were not satisfactory from this point of view as well.

In order to manufacture a GAil plate with such high productivity, a long alloying furnace is inevitably required because the temperature of the steel plate during alloying treatment is suppressed according to the conventional concept.

However, the alloying furnace is generally arranged vertically above the plating pot, for example between the turn roll 23 and the bath surface as shown in Fig. 2, which will be described later. When the height of the building becomes very large and there is no intermediate roll, the steel strip 11 vibrates greatly between the support roll 15 and the turn roll 23.

In reality, it is possible to provide a Gll board with an intermediate roll, but this poses a major obstacle when passing a non-Gll board.

From this point of view, realistically the total length of the alloying processing furnace is 35~
Although it is often limited to 50+ m, this is the furnace length including the final cooling zone, and in reality, the length that contributes to alloying is at most 15 to 30 m. In reality, this means that in the case of 30 m, if the plate is threaded at 150 m/++in, the alloying time will be 12 seconds. In other words, in order to achieve alloying in such a short time, the temperature of the alloyed plated steel sheet must be 550°C.
For example, when the Zn coating amount is 50 g/m2 on one side, a temperature of about 100 g/m2 is required. However, since the powdering resistance generally decreases at temperatures above 530° C., if economical production is carried out using conventional methods, the powdering resistance will inevitably be poor.

(Problems to be Solved by the Invention) Thus, an object of the present invention is to provide an alloying treatment furnace that eliminates the drawbacks of these conventional methods.

Another object of the present invention is to provide an alloying furnace for producing GAtR plates in which powdering is suppressed in a relatively short alloying time.

(Means for solving the problem) As already mentioned, the temperature of the steel plate to be plated during alloying (
Powdering resistance can be improved by lowering the material temperature (hereinafter simply referred to as "material temperature"), that is, by alloying slowly to the extent that overtreatment does not occur at a low material temperature, that is, a temperature of 520 ° C or less where the ζ phase can nucleate. is said to be necessary. However, in order to achieve this, an extremely long alloying furnace is required. In this case, the purpose of the present invention is not achieved.

Therefore, the present inventors decided that alloying at temperatures of 550°C or higher significantly deteriorates powdering resistance, but the alloying conditions at 550°C or higher were used as a step in the alloying process. As a result of considering the possibility of incorporating the material into the alloying process, it was found that even if the material temperature was maintained at 550°C or higher during the initial stage of alloying heating, no deterioration of the powdering properties occurred, and the effect of shortening the alloying treatment time was observed. Then, alloying is started by initial heating to 550°C or higher, and the steel plate is rapidly cooled before alloying is completed to the surface.
A patent application was previously filed in Japanese Patent Application No. 64,162/1983 for a method comprising carrying out the final alloying treatment at 450-530°C.

The present invention has been developed as an apparatus for carrying out such a method, and by providing a quenching zone following the heating zone, heating in the heating zone can be performed without impairing powdering resistance. The temperature can be increased, which allows the length of the alloying furnace to be significantly shortened.

In other words, conventional alloying processing furnaces have a heating zone, a holding zone, and a cooling zone in succession, but with this equipment, it is possible to perform high-speed threading and obtain GA steel sheets with excellent powdering resistance. Therefore, in the present invention, a rapid cooling zone is installed between the heating zone and the holding zone, which makes it possible to heat the heating zone to a higher temperature and lower the temperature of the holding zone. The GA#lR board obtained by this heat pattern has high quality even when passed through at high speed.

In other words, the technical concept of the conventional method is that powdering resistance decreases when high temperature or high alloying speed is used, but the present invention proposes that powdering resistance is related to the alloying speed at the final stage of alloying. This is based on the technical idea that the alloying rate at the initial stage of alloying has essentially no relation to powdering properties.

Here, the final stage of alloying means that the average Fe content of the coating is 5 to 5.
It refers to the alloying region of 10% by weight, especially 8-10% by weight.

The relationship between the late-stage alloying rate and the powdering property in experiments conducted by the present inventors is shown graphically in FIGS. 1(a) and 1(middle).

Figure 1 (al is zinc plating with a coating weight of 46 g/rrr, and the average Fe content in the finished film is 10 to 1
Late alloying when 2.5% by weight, that is, average Fe content 5
Fe enrichment rate (g/
The graph shows the amount of powdering (g) against the amount of powdering (g), and as is clear from the graph, it can be seen that when the Fe enrichment rate is low, the amount of powdering generated is small.

Figure 1 (bl) is a similar graph in which the average Fe enrichment rate in the above case, that is, the average Fe enrichment rate from the start to the end of alloying, is plotted on the horizontal axis; It can be seen that no clear correlation is observed; rather, even if the average Fe enrichment rate is made considerably high, powdering does not necessarily occur significantly.

The new alloying heat treatment method based on this idea is
At the initial stage of alloying, the alloying temperature is increased as much as possible until the material temperature reaches at least 550°C. At temperatures below 500°C, the initial alloying rate is relatively low due to the strong effect of inhibiting Fe-Zn mutual diffusion of AI in Zn;
Above ℃, FeZn-Aj! Rapid alloying is achieved due to early collapse of the ternary alloy.

However, after alloying has been carried out halfway or more, it is necessary to cool the steel strip to 530° C. or lower as soon as possible in order to suppress the late stage alloying rate. However, if it is cooled to below 420°C, it will take a long time to complete the alloying, so it is desirable to maintain the temperature at 450 to 500°C.

Based on the above findings, the present inventors further investigated and invented the following alloying processing furnace of the present invention.

Therefore, the gist of the present invention is to provide an alloying processing furnace for hot-dip galvanized steel sheets in which a hot-dip galvanized steel strip is continuously alloyed. This is an alloying processing furnace in which the bands are successively arranged in this order.

The heating zone preferably performs rapid heating to 550 to 700°C, and a high frequency induction heating device may be provided as the heating means at that time, and/or its length may be as long as the above. After passing through the molten galvanizing bath, the time from rapid heating to the start of rapid cooling may be within 10 seconds, preferably within 5 seconds. A high-frequency induction heating device as a heating means is preferable for the purpose of the present invention because it can rapidly and intensely heat only the interface between the steel plate surface and the plating layer by appropriately selecting the input frequency of high-frequency induction heating.

Further, the rapid cooling zone is preferably 53 as described above.
It is used for rapid cooling to a temperature range of 0° C. or lower, and may be provided with, for example, a mist cooling and/or jet gas cooling device. Next, the holding band is used to hold the hot-dip galvanized steel sheet at that temperature after cooling, and the low-temperature alloying treatment at that time is 3 to 120 degrees.
It is preferable to do this for seconds, so that the length can be determined. More preferably, at this time, the holding band may also be provided with an appropriate heating device such as a high frequency induction heating device.

The degree of heating in the heating zone is preferably such that a liquid phase remains on the surface of the plating layer, but this means that although a Fe-Zn alloy layer is formed inside the plating layer due to interdiffusion, it is still on the surface. This refers to a state in which Fe has not yet diffused, and generally at that time the surface of the plating layer still has metallic luster. When using the device according to the present invention,
Although it depends on the plating conditions, such a state is sufficiently ensured within 10 seconds from the start of heating, as long as the temperature is about 550 to 650°C.

(Function) Next, the structure of the alloying processing furnace according to the present invention will be explained while comparing it with a conventional one.

Figure 2 shows a conventional alloyed hot-dip galvanized steel sheet manufacturing equipment 1.
0, and the steel strip 11 passes through the snout 12 and enters the molten zinc bath 1.
3 and then pulled up via a zinc roll 14 and a support roll 15. Reference numeral 16 indicates a gas wiper for adjusting the basis weight, whereby the steel strip coated with the required amount of hot-dip zinc is passed through a heating zone 18 equipped with a series of direct-fired burners 17, a holding zone 19, and also a direct-fired steel strip. The alloying treatment furnace 22 is equipped with a holding zone 21 equipped with a fire burner 20, and the alloying treatment is performed by sequentially passing through each treatment zone, and then sent to the outside of the apparatus via a turn roll 23.

On the other hand, an alloying processing furnace according to the present invention is shown in FIG. 3, and the same members are designated by the same reference numerals. After controlling the amount of coating on the hot-dip galvanized steel strip using the usual method described above,
It is introduced into the heating zone 28 as soon as possible. The heating zone has the function of heating the steel strip relatively quickly, desirably to 550° C. or higher, and desirably has a heating rate of 50° C./S or higher. For this purpose, it is desirable that the heating device for the second heating zone be of an induction heating type, but in some cases a burner with a large convection heating capacity may be used, and the heating method is not necessarily limited to a specific one.

The rapid cooling zone 30 located immediately after the heating zone 28 has the function of rapidly cooling the steel strip 11, which has been heated to at least 550.degree. C. or higher in the heating zone 28, to a temperature of 530.degree. C. or lower. In an ideal embodiment, the steel strip 11 is heated to 550° C. or higher in the heating zone 28, so it is desirable that the rapid cooling zone 30 has a cooling capacity of 20° C./S or higher. , cooling by atomizing mist using water or the like can be employed. Such a cooling means itself may be a known one,
The purpose of the holding zone 32 is to maintain the steel strip at a temperature below 530° C. in order to carry out semi-alloying and final alloying of the steel strip 11 through the heating zone 28 and the rapid cooling zone 30, To maintain this, a small capacity induction heating device (not shown) or, if the heating zone 28 is burner heated, the waste heat thereof is used.

The cooling zone 34 in the final stage is provided for the purpose of cooling the plated steel strip 11 after alloying relatively quickly and suppressing excessive alloying. Even in this case, it is preferable to use mist cooling or Use gas cooling equipment.

In the present invention, the degree of alloying is adjusted by controlling the amount of current or firing amount in the heating zone 28, as well as by controlling the amount of cooling gas or mist in the rapid cooling zone 30 and the temperature of the holding zone 32. is preferably 52
Since the temperature is below 0°C, it can be said that it is appropriate to adjust the temperature of the heating zone and the fluid flow rate of the rapid cooling zone in order to obtain a high-quality product.

Note that the concentration of M in the Zn plating layer is determined by a conventional method. It is generally contained at 0.05% or more. In the method of the present invention, since alloying can be promoted, the content is preferably 0°35-t% or less.

Hereinafter, the present invention will be explained in more detail based on Examples.

In addition, in each of the following examples, one side of 86g/r with a thickness of 0.6a+m, which was continuously manufactured by one-sided Senzima method, was used.
A galvanized steel sheet having a Zn coating amount of 1 was used as a test material. The steel plate composition at this time was C: 0.035%, St <
0.01%, Mn: 0.22%, P: 0.01%
, S: 0.009%, sol, AQ: 0.02
4%, and the effective AQ concentration in the Zn plating layer is 0.13.
It was 5%.

1 plate 300+e width, 0.51 thickness steel strip 30+ ~60m/
Hot-dip galvanizing was carried out with a coating weight of 40 g/m2 per side using the hot-dip galvanizing pilot plant shown in Fig. 3 at a sheet threading speed of 100 kW. ”/win
air jet capable of discharging gas in an amount of 120
Holding zone by induction heating furnace, maximum 5 m'/m
The sheets were passed through an alloying processing furnace equipped with a continuous cooling zone using an air jet capable of discharging gas in an amount of 1.5 in., and various alloying treatments were performed by changing the amount of air jet and the amount of current applied. The obtained steel plate was subjected to a cylindrical drawing test using a blank having a diameter of 60 ffil, and the powdering resistance was measured by forcibly peeling it off by a taping test after forming and evaluating the weight loss of the test material. The results are shown in Figure 4 (
Shown in a) and (bl).

That is, FIG. 4(a) is a graph showing the powdering resistance plotted against the sheet passing speed and the amount of current in the induction heating furnace when the air jet amount in the rapid cooling zone is 8 to 16 I+"/win. Figure 4 (BL is shown as a comparative example and is a similar graph when the air jet amount in the rapid cooling zone is set to zero. In the figure, the symbol rOJ indicates that the powdering amount is less than 0.03 g/piece. In this case, the same "・" is 0
．． 03 g/piece or more, and "x" indicates the amount of powdering in the case of no treatment (alloying to the surface layer of the plating layer is not completed and the Zn layer remains). In the present invention equipped with a belt, it has been found that high-quality GA steel sheets can be obtained during high-speed threading, as is clear from this pilot plant example.

(Effects of the Invention) As described above, the furnace according to the present invention can manufacture high-quality products with high productivity, and the apparatus according to the present invention is excellent as a high-speed, short-time heat treatment apparatus for GA steel sheets, especially It shows excellent effects on materials with a relatively large amount of adhesion or when the shark concentration in Zn is high, and productivity is improved in today's situation where alloyed hot-dip galvanizing with a high mosquito concentration is desired. The present invention is of great significance as a means to increase this.

[Brief explanation of the drawing]

Figure 1 (al and (bl) are graphs showing the relationship between the Fe enrichment rate and the average Fe enrichment rate and the amount of powdering in the late stage of alloying, respectively; Figure 2 is a schematic explanatory diagram showing a conventional device; 3 is a schematic explanatory diagram showing an apparatus according to the present invention; and FIG. 4 (al and (b) are graphs showing data of examples and comparative examples of the present invention. 28: Heating zone 30: Rapid Cooling zone 32: retention zone
34: Cooling Zone Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Akira Hirose - Tsuki ITW ((1) Book 1 Diagram <b> Liao) l (3□-'S”) Book 2 Concave Skin 3 Diagram 4 Concave (α) Funeral, 4 times (b) xh treatment i dust (m/mrn)

Claims (4)

[Claims] (1) An alloying processing furnace for hot-dip galvanized steel sheets that continuously alloys hot-dip galvanized steel strips, in which a heating zone, a rapid cooling zone, a holding zone, and a cooling zone are successively arranged in this order. Alloying processing furnace. (2) The alloying processing furnace according to claim 1, wherein the heating zone has an induction heating device. (3) The alloying processing furnace according to claim 1 or 2, wherein the rapid cooling zone is equipped with a mist cooling and/or a jet gas cooling device. (4) The alloying treatment furnace according to any one of claims 1 to 3, wherein the holding band is equipped with a heating device.