JPS5823465B2 - It's hard to believe that you'll be able to do so. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous hot-dip galvanizing method for silicon guild steel sheets and an apparatus therefor.

Conventionally, rimmed steel sheets and capped steel sheets, which have excellent galvanizing properties, have been mainly used for hot-dip galvanizing base sheets, but with the spread of continuous casting, guild steel sheets can be obtained at low cost, and killed steel sheets using silicon have become available. Killed steel plates can also be obtained at low cost by rolling processed steel ingots or slabs, so there is a growing demand for inexpensive galvanized steel plates using guild steel plates as the plated base plates to be supplied to the market. There is.

However, when silicon guild steel sheets are plated using the conventional hot-dip galvanizing method, the adhesion of the zinc coating is poorer than when rimmed steel sheets are plated, so the plated zinc easily peels off. The temperature of the hot-dip galvanizing method that has been commonly used to remove
Within this range, attempts have been made to improve plating adhesion by changing the Al concentration of the bath, but none of them succeeded. There was a strong demand for legal development.

The purpose of the present invention is to provide a continuous hot-dip galvanizing method and an apparatus for improving the poor zinc plating adhesion of silicon-killed steel sheets. During continuous hot-dip galvanizing, the temperature of the plating bath at least in the vicinity of the plating bath into which the original plate is introduced is maintained within a predetermined temperature range, and the Al concentration of the plating bath and the temperature of the plating bath are adjusted to the original plate to be plated. The present invention was completed by newly discovering that plating with good adhesion can be achieved by adjusting the Si content of the metal, and by devising an apparatus for carrying out this process.

The present invention will be explained in detail below.

In the present invention, the plating bath temperature ("C) t and the plating bath Al concentration [(01
) is adjusted according to the Si content of the original plate, and the correlation between these will be explained based on experimental data.

The experimental plating furnace used in the research of the present invention simulates a continuous hot-dip galvanizing line, and the steel plate is, for example, 0.05% C and 0.34% Mn.

Based on a Si killed steel having a composition of SiO, 11%, Po, 013%, 80.012%, and the remainder substantially Fe, experiments were conducted by varying the Si% up and down.

A steel plate cold-rolled at a rolling reduction of 70 parts is placed in a plating furnace, and the plate temperature is brought to 700°C in a nitrogen atmosphere containing 15 parts by volume of hydrogen.
The surface of the steel plate was cleaned by heating for 3 minutes, and then the plate temperature was cooled to 460°C in a heat insulating zone in the furnace, and then the steel plate was heated in a hot-dip galvanizing bath kept at a predetermined temperature in the same furnace for 5 minutes. The plated metal is immersed for a second, and when pulled up, the plated amount is controlled and cooled using an N2 gas wiper, and the plated metal is 17 to 20 μm per side on both sides of the steel plate.
A plated steel sheet was obtained.

As a plating bath, the molten metal mainly consists of Zn, containing 22% PbO, 1% CaO, and trace amounts of other elements.

Those to which Al was added in varying amounts were used.

FIG. 1 shows the relationship between the Si content in the original plate and the plating adhesion when the original plate was plated with the Al content in the bath at 0.16% and the bath temperature maintained at 465°C.

In the same figure, the value indicating plating adhesion is 18
When bent at 0° close bending, the visual condition of the plating on the bent portion is determined based on the following criteria.

Adhesion 1: The plating on the bent part is largely peeled off.

Adhesion 2: The plating on the bent part is partially peeled off.

Adhesion 3: Cracks have occurred in the plating at the bent part.

Adhesion 4: Cracks that occur in the plating at the bent portion are minute and can be almost ignored.

Adhesion 5: No cracks in the plating at the bent part.

According to the above criteria, adhesion of 4 or higher is practically acceptable.

From Figure 1, it can be seen that the higher the Si% of the original plate, the worse the plating adhesion, that is, the lower the adhesion value.
% or more, the adhesion is 4 or less.

In the next experiment, a steel plate with 0.11% Si was used, and the kl of the bath was
When the concentration was 0.16% and the bath temperature was varied,
Figure 2 shows the results of examining changes in plating adhesion.

From the same figure, it can be seen that the adhesion of the plating is good when the bath temperature exceeds 470°C and is in the range of 540°C, and the adhesion value can be set to 4 or more.

In the next experiment, a steel plate with 0.11% Si was used, the bath temperature was set to 480°C, and the AA concentration in the bath was varied.
Figure 3 shows the results of examining changes in plating adhesion.

From the same figure, as A[ increases above 0.12%, the plating adhesion gradually improves, and the adhesion remains almost constant above 0.30%.

In accordance with the experiment 1 described above, the inventors conducted numerous experiments by varying various factors thought to affect plating adhesion over various ranges, and found that each factor had an effect on plating adhesion. When we investigated the effects on gender and their correlations, we obtained the following results.

Multiple regression analysis results of each factor affecting plating adhesion 1 Characteristic value ¥1 - Plating adhesion evaluation 1.0 to 4.5 2 factors X1 = Si content in steel plate (coefficient) 0 to 0.15 coefficient X2 -
Zinc bath temperature (℃) 459-479℃X3=A
X gas flow rate (Nm”/h) 15-5ONm'/h N4-line speed (m, pom) 65-75m, p, m
Coupling X6 = Air cooling 5 zone temperature ('C) 398-510
°CX7 - Heating 6-8 zone temperature (℃) 875-905
About 70 cases of °C3 data.

However, the plate thickness is 0.60 to 0.63mm, and the amount of plating is 31H.
g/rrt 4 Average value average variance Y13.1 2.7 X10.0749 5.24 X2468.6 32803 X, 39.47 2763. OX,
67.23 4706.0 average
Dispersion X, 0.1807 12.65 X6 424.6 29723. OX7889
．． 2 62241.05 Multiple correlation 6 Multiple correlation Y, -11,9721-5,8310X"+0.05
99X7-0.0042X3-0.0232X, +11
．． 7801 formula % formula % (1) Next, the above (1) obtained by the multiple regression analysis as described above.
) When examining the significance of each factor X1 to X7 in the equation, X3. X4. X6 and X7 have low significance;
It has been found that even if each is replaced with a constant, there is almost no effect on the plating adhesion evaluation (¥1) of the solution of equation (1) above.

The level of significance was determined by comparing the case where each of the factors X1 to X7 was deleted, that is, when they were not considered as a factor, with the formula (1) above, and the factors with high significance were determined. When deleted, the correlation coefficient r decreased significantly, whereas for those with low significance, there was almost no decrease.

Therefore, factor X3. X4. By substituting and rearranging their average values for X6 and X7, equation (1) becomes Yl--2
6,:3-5.83X1+0.06X2+11.78X
.

By substituting the condition Y1≧4, which indicates good plating adhesion, into this equation, the conditions for good plating treatment are: Si content in the steel sheet [Si%], zinc bath temperature t, and As a relational expression for the A7 concentration in the bath (Ckl ratio), the following equation (2) is used: 0.06 t+11.78 Ckl ratio: ] -5,83
CS i) -26,3≧4...(2) It is expressed as follows.

However, if the Si content in the steel sheet is more than 0.20%, the hardness of the original sheet becomes too high and the plating adhesion deteriorates, so the Si content needs to be 0.20% or less.

Furthermore, if the l concentration in the bath is less than 0.12%, the plating adhesion will deteriorate, and such deterioration will not be improved even if the plating bath temperature is increased, while if it is more than 0.30%, the plating adhesion will deteriorate. It does not particularly improve adhesion, but on the contrary, the viscosity of the bath increases, and the A1 yield decreases due to the generation of dross. Therefore, the hole l concentration in the bath is 0.12 to 0.30'.
% range.

Furthermore, if the plating bath temperature is below 470°C, the plating adhesion will be poor and cannot be put to practical use.On the other hand, if the temperature is higher than 540°C, the Fe-Ze alloy layer will develop significantly and the plating adhesion will deteriorate extremely. The bath temperature was limited to a range of over 470°C to 540°C.

Next, a plating apparatus suitable for use in carrying out the present invention will be described.

In carrying out the method of the present invention, it is necessary to maintain the temperature of the zinc bath higher than that conventionally employed in the hot-dip galvanizing method and within an appropriately narrow temperature range.
It has been found that the conventional apparatus suffers from the following drawbacks.

In other words, in order to maintain the temperature of the molten zinc bath in the chute above 470°C and below 540°C without installing a sub-tank, the temperature of the original plate entering the chute can be increased, but controlling it to such a high level is not possible in continuous operation. Moreover, it has the disadvantage that its control is difficult.

In addition, the overall bath temperature in a galvanized bathtub can be raised, but ordinary zinc bathtubs are made of steel plates that are resistant to corrosion at normal zinc bath temperatures, and as the bath temperature rises, the rate of erosion increases. However, there is a disadvantage that the life of the tank is shortened, and even if the life can be extended by changing the steel type of the steel plate used for the tank, maintaining the overall bath bath temperature at a high temperature is disadvantageous in terms of thermoeconomics. .

It is also possible to provide a heating device in the chute to locally heat the zinc bath in that area.

However, this method has the drawback that the bath temperature within the narrow chute tends to be uneven, and the bath surface becomes excessively high temperature, generating zinc fume, which is deposited on the original plate and poses a problem in actual operation.

Since the implementation of the method of the present invention using conventionally known devices has the various drawbacks mentioned above, the present inventor aimed to provide an apparatus free from these drawbacks, and in order to achieve this goal, a zinc bath was prepared in advance. Molten zinc whose temperature and Al concentration are precisely controlled is supplied into the chute from a sub-tank where the temperature and Al concentration in the bath can be precisely controlled, and the molten zinc is pumped to size by a weir installed at the bottom of the chute. The purpose of the present invention is to provide a plating apparatus capable of making the temperature and Al concentration of molten zinc inside a chute more uniform by holding the molten zinc inside the chute.

Next, the apparatus of the present invention will be explained with reference to FIG. 4 showing an example of its embodiment.

The apparatus of the present invention is provided with a hot-dip galvanizing bath 1 and a sub-tank 2, a chute 3 for introducing a plated original plate treated in a reduction annealing process is inserted into the diagonal opening of the galvanizing bath 1, and a zinc roll 4 is provided inside the plating bathtub 1.

A weir 5 is provided at the lower end of the chute 3 to prevent the flow of the plating bath between the chute 3 and the plating bath 1, while the sub-tank 2 is provided with a weir 5 for freely discharging the zinc alloy for plating charged therein. A heating device 6 for heating and melting is provided.

The sub-tank 2 and chute 3 are connected by a pipe r for supplying molten zinc into the chute 3, in which a pump 8 and a valve 9 are inserted in series, and a valve 11 and a pump 12 are inserted in series to supply molten zinc into the chute 3. The plating bath 1 and the sub-tank 2 are connected by a pipe 10 for discharging zinc from the plating bath 1.

Next, the operation of the apparatus of the present invention will be described. The plated original plate 13 that has been previously treated in a reduction process is introduced into the chute 3, immersed in a zinc bath,
Go in the direction of the arrow and leave the bathtub 1.

Molten zinc with a predetermined temperature and a predetermined Al concentration is supplied from a sub-tank above the weir 5 in the chute 3, and the weir 5 temporarily stagnates the flow of the molten zinc into the bathtub 1, so that the molten zinc in the chute The turbulent flow promotes uniformity of the temperature and Al concentration of the molten zinc in the chute.

The temperature of the molten zinc flowing into the bathtub 1 through the weir 5 decreases somewhat in the bathtub 1, so it is returned to the sub-tank 2 via a pipe 10 via a valve 11 and a pump 12, and is again brought to a predetermined temperature and a predetermined Al concentration. It is regulated and supplied into the chute 3 via a pump 8 and a valve 9 through a pipe γ.

Therefore, molten zinc is constantly circulated between the subtank 2, the chute 3, and the bathtub 10.

According to the apparatus of the present invention, it is possible to easily control the temperature of the plating bath at least in the vicinity where the plating original plate is introduced into the plating bath, that is, in the chute, to a predetermined temperature accurately, and it is not necessary to control the entire plating bath 1 to a predetermined temperature. Since there is no need to maintain the temperature, it is very advantageous in terms of thermoeconomics, and by temporarily retaining the flow of molten zinc from the chute 3 to the bath 1 by the weir 5, the bath temperature and bath composition can be made uniform. It is a key feature of the device of the present invention that is greatly facilitated.

Next, the present invention will be explained with reference to examples.

Example I C0.04%, Si0.11%, Mn0.31%.

Po, 0110! ,, 80.014 steel plate (plate thickness 0.
60mm, width 914mm) bathtub size length 2920m
The line speed was 65 m/min using a continuous hot-dip galvanizing apparatus in which the apparatus of the present invention was attached to a hot-dip galvanizing bath having a width of 2320 mm, a width of 2320 mm, a depth of 3000 mm, and a bath capacity of 80 tons.
Nominal zinc adhesion amount at 2.5m immersion length and 2 seconds immersion time
Plating was performed at 1g/rtX.

For comparison, plating was performed using the conventional method under the same conditions as described above.

The results are shown in Table 1. In this case, the nominal adhesion amount is 38
Actual adhesion amount for 197m is 305 g/rrl'
The plating thickness on both sides was 21.5 μm.

As can be seen from the table, the only difference in the conditions between the method of the present invention and the conventional method is the AA concentration in the bath, but the method of the present invention had much better plating adhesion.

Note) Bath temperature: average molten zinc temperature of the entire bath (B)
...Temperature of molten zinc in direct contact with the steel plate surrounded by the chute Example 2 C0.03%, Sio, 14%, Mn0.28%,
PO, 010%, 80.011% steel plate (plate thickness 0.60
mm, width 914 mm) using the apparatus described in Example 1.
Plating was carried out under the same conditions as in Example 1 except for the bath temperature.

For comparison, plating was also performed using the conventional method.

In addition, in the conventional method, the temperature of molten zinc in the chute is 47
The temperature was set at 5°C, which is 20°C lower than that temperature in the method of the present invention.

The results are shown in Table 2. As can be seen from the table, the method of the present invention has much better plating adhesion.

As explained above, according to the method and apparatus of the present invention, even if a silicon-killed steel sheet is used as the plated plate, it is possible to produce a galvanized steel plate having the same excellent toughness adhesion as when a rimmed steel plate is used as the plated plate. can.

The apparatus of the present invention can be used not only to carry out the method of the present invention, but also to carry out the conventional method of hot-dip galvanizing a rimmed steel plate, and in this case, the pumps 8 and 12 are It is sufficient to stop the bath, close the valves 9 and 11, and heat the bathtub 1 from the outside to 470°C or less as in the conventional method.In this case, since the bath temperature is 470°C or less,
The melting of the tank walls of the bathtub 1 was the same as in the conventional method.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between plating adhesion and Si content of the original plate, Figure 2 is a diagram showing the relationship between plating adhesion and bath temperature,
FIG. 3 is a diagram showing the relationship between plating adhesion and Al content in the bath, and FIG. 4 is a system diagram showing an example of the apparatus of the present invention. 1... Hot-dip galvanized bathtub, 2... Sub-tank, 3... Chute, 4... Zinc roll, 5... Weir, 6...・・・・・・Heating device,
r, 10... Pipe, 8, 12... Pump, 9, 11... Valve, 13...
Original plate.

Claims (1)

[Claims] When continuously hot-dip galvanizing a silicon-killed steel sheet containing 0.20% or less of I-Si, 0.12% of Si is added to the coating bath.
In addition to adding Al in the range of ~0.30%, the temperature of the plating bath at least near the introduction part of the silicon guild steel sheet is increased to 4.
After maintaining the temperature within the range of over 70°C and up to 540°C,
Moreover, the Si content in the steel plate [Si%] and the kl concentration in the bath [A1
%) and a plating bath temperature t in the vicinity of the steel sheet introduction part satisfy the following formula (%). 2. A plating bath containing a plating solution, a chute for introducing the plating stock plate into the plating bath under a protective atmosphere, and a continuous tank equipped with a zinc roll installed in the tank and controlling the heat dipping and rounding of the plating stock plate. In the hot-dip galvanizing apparatus, a sub-tank separate from the plating bath is connected to the tank wall and the chute immersion part to control the circulation flow of the plating solution, and is capable of freely adjusting the plating solution temperature and the concentration of people in the bath. 1. An apparatus for continuous hot-dip galvanizing silicon guild steel sheets, characterized in that a weir is provided at the lower end of the chute for immersion.