JPH10176253A - Production of unrecrystallized hot dip galvanized steel sheet in continuous type hot dip galvanizing line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow defects in plating to be hard to be generated and to prolong the service life of a roll in a bath at the time of producing a full hard material. SOLUTION: At the time of producing an unrecrystallized hot dip galvanized steel sheet in a continuous type hot dip galvanizing line in which a heating zone 1, a soaking zone 3 and a cooling zone 4 are arranged in this order, the temp. of the steel sheet to be immersed into a plating tank 9 is measured, on this measured value, the steel sheet 12 is reheated by induction heating at the rear of the cooling zone, and, while control is executed in such a manner that the temp. of the steel sheet to be immersed into the plating tank reaches the objective steel sheet temp., hot dip galvanizing is executed. By executing the control so as to regulate the temp. of the steel sheet to be immersed into the plating tank to the required objective temp. in such a manner that the fluctuation of the temp. is suppressed, the generation of defects in plating such as dross adhesion, flow marks or the like can be reduced, and furthermore, the adhesion of dross to a roll in the bath is made hard to occur, by which the service life of the roll in the bath can be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a non-recrystallized hot-dip galvanized steel sheet in a continuous hot-dip galvanizing line.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets have been widely used for various purposes as rust-preventive steel sheets which are inexpensive and have excellent corrosion resistance. Furthermore, in recent years, a hot-dip zinc-aluminum alloy-plated steel sheet in which a large amount of aluminum is added to zinc to further improve corrosion resistance has been used.

[0003] Usually, the above-mentioned steel sheet is subjected to soft annealing and cleaning of the steel sheet surface by heating a cold-rolled steel sheet which has been cold-rolled or a hot-rolled steel sheet which has been pickled and descaled to a temperature higher than a recrystallization temperature. After that, it is immersed in a plating bath filled with a molten metal having a predetermined plating composition and subjected to a predetermined hot-dip plating to be manufactured (hereinafter, referred to as a general material).

On the other hand, a non-recrystallized hot-dip galvanized steel sheet (for example, ASTM A446 grade) manufactured by subjecting a relatively thin cold-rolled steel sheet to cold-rolled steel sheet and subjecting it to a predetermined hot-dip coating without softening annealing. There is a hot-dip galvanized steel sheet of E standard (hereinafter, referred to as a full hard material), which is used for building materials that require light weight and high rigidity.

[0005] Usually, these coated steel sheets are produced in a continuous hot-dip galvanizing line in which a heating zone, a soaking zone and a cooling zone are arranged in this order.

Hereinafter, a case where a hot-dip galvanized steel sheet is manufactured in a continuous hot-dip galvanizing line of an oxidation-free furnace system will be described.

FIG. 3 is a diagram showing a heat treatment part and a main part of a plating part of a continuous hot-dip galvanizing line of an oxidation-free furnace type, wherein 1 is a non-oxidation heating furnace, 3 is a soaking zone, 4 is a cooling zone, and 8 is a cooling zone. Snout 9 is a plating tank filled with molten zinc.

Using this apparatus, a hot-dip galvanized steel sheet is manufactured as follows. In a continuous hot-dip galvanizing line of a non-oxidizing furnace system, a steel sheet usually used as an original sheet is a cold-rolled steel sheet as it is cold-rolled or a hot-rolled steel sheet pickled and descaled.

The non-oxidizing heating furnace 1 usually has a direct-fired burner, burns fuel gas at an air-fuel ratio of about 0.85 to 0.90, and makes the furnace a weakly oxidizing atmosphere. Non-oxidizing heating furnace 1
Then, after heating the material steel plate to decompose and remove oils and fats such as rolling oil adhered to the surface of the steel plate, the steel plate is led to the uniform zone 3 through the throat 2. Usually, the material steel sheet is a cold-rolled steel sheet as it is cold rolled or a hot-rolled steel sheet pickled and scaled out.

The soaking zone 3 is usually provided with a radiant tube or an electric heater as a heating source, soaks the steel sheet to a predetermined annealing temperature, flows an H ₂ -N ₂ mixed gas in countercurrent to the steel sheet, and The oxide film is reduced to activate the steel sheet surface, and at the same time, perform a predetermined annealing. When manufacturing general materials,
The steel sheet is heated to a temperature equal to or higher than the recrystallization temperature (normally, a temperature equal to or higher than 680 ° C.) to perform softening annealing.

Further, the steel sheet is guided to the cooling zone 4. Cooling zone 4
Usually, an upstream jet rapid cooling zone 5, a cooling holding zone 6, and a downstream jet rapid cooling zone 7 are provided, and a steel sheet reduced in the soaking zone 3 is cooled to a predetermined temperature in the upstream jet rapid cooling zone 5. After rapid cooling to a predetermined temperature range in the cooling holding zone 6, the material of the steel plate is homogenized. Therefore, the cooling zone has a relatively long furnace length. Next, the steel sheet is cooled in the downstream jet type rapid cooling zone 7, and the temperature of the steel sheet is set to a predetermined temperature suitable for plating.

Next, the steel sheet passes through a snout 8 and is immersed in a plating tank 9 filled with molten zinc maintained at about 460 ° C. without being exposed to the outside air.
The direction of travel is changed by 0, and the support is lifted above the plating tank 9 by a pair of support rolls 11 in the bath.

Next, the coating weight is controlled to a predetermined coating weight by a coating weight control device (not shown), and spangles are adjusted as needed to obtain a hot-dip galvanized steel sheet.

A reducing atmosphere gas usually composed of a H ₂ -N ₂ mixed gas is supplied into the furnace from the soaking zone 3 to the snout 8. The H ₂ —N ₂ mixed gas is supplied into the furnace from the snout 8, the cooling zone 4, and the soaking zone 3 by the H ₂ —N ₂ mixed gas supply device 20, and flows countercurrently to the running steel sheet. It flows out of the throat 2 to the non-oxidizing heating furnace 1 and burns in the non-oxidizing heating furnace 1 together with the fuel gas.

In the case of producing a full-hard material in a continuous hot-dip galvanizing line of an oxidation-free furnace system, usually, a cold-rolled cold-rolled steel sheet made of low-carbon steel whose production cost is low is used. It is necessary to prevent the softening of the steel sheet by remarkably lowering the heat treatment temperature as compared with a general material annealed at a high temperature of 680 ° C. or higher. Normally, after heating to a temperature of about 500 ° C or lower, which is lower than the recrystallization temperature, to remove the rolling oil adhering to the steel sheet, reduce and activate the steel sheet surface, it is maintained at about 460 ° C through a cooling zone. It is immersed in the plating tank 9 filled with the molten zinc and hot-dip plated.

[0016]

In the case of producing a hot-dip galvanized full-hard material in the above-mentioned plating line, plating defects such as dross draw and hot water wrinkles are likely to occur on the surface of the steel plate after plating, and the rolls in the bath may be damaged. There is a problem that the dross adheres and the life of the roll in the bath is significantly shortened. Also,
Since the heat treatment is performed at a low temperature of about 500 ° C., the surface of the steel sheet is not always sufficiently cleaned, so that there is a problem that poor plating adhesion is likely to occur.

When the heat treatment temperature is increased, the above problem is somewhat improved, but the steel sheet is softened and the desired material cannot be stably secured.

As a hot-dip zinc-aluminum alloy plated steel sheet obtained by adding a large amount of aluminum to zinc which has recently been used, a Zn-Al based steel containing a small amount of misch metal in addition to 3 to 10 wt% of Al Alloy plating, for example 4 ~
A so-called Zn-5% Al-based zinc-aluminum alloy plated steel sheet typified by a Zn-Al-based alloy plating containing 5 wt% Al or a Zn-Al-based alloy plating containing 25-75 wt% Al, for example, 55 wt% Al-1 Z containing 0.6 wt% Si
So-called Zn-55% A represented by n-Al alloy plating
There is an l-based zinc-aluminum alloy plated steel sheet.

When a Zn-5% Al-based zinc-aluminum alloy plated steel sheet is manufactured, the plating bath temperature is almost the same as that of hot-dip galvanizing, but the generation of plating defects and the shortening of the life of the roll in the bath are performed. There is a problem that the problem becomes more remarkable than in the case of hot-dip galvanizing.

The plating bath temperature is set to a higher temperature of 600 ° C.
In the case of a Zn-55% Al-based zinc-aluminum alloy-plated steel sheet of a certain degree, the above problem is more remarkable, and it is a fact that stable production cannot be performed from an economical viewpoint.

The present invention has been made in view of the above circumstances, and in a continuous hot-dip galvanizing line, when producing a full-hard material, plating defects hardly occur, and the life of a roll in a bath can be extended. An object of the present invention is to provide a method for manufacturing a full hard material.

[0022]

As described above, in the case of producing a hot-dip galvanized full-hard material, the temperature of a steel sheet in a non-oxidizing heating furnace or a soaking zone is about 500 ° C. or less, which is lower than the recrystallization temperature. The temperature is low and the surface of the steel sheet cannot be sufficiently cleaned.

In the cooling zone of the continuous hot-dip galvanizing line of the non-oxidizing furnace type, a heating device such as a cooling device and an electric heater is provided in order to adjust the temperature of the steel sheet to a predetermined temperature. However, conventionally, since the production volume of general materials is large, the production equipment of the plating line has equipment specifications suitable for production of general materials. Therefore, in the cooling zone, mainly the purpose of the non-oxidizing heating furnace, the purpose of cooling the steel plate heated to a predetermined annealing temperature of high temperature in the soaking zone and keeping it in a predetermined temperature range, Heating capacity is small. Therefore, when producing a full hard material, the steel sheet that has left the solitary zone is supercooled in the cooling zone, and the temperature of the steel sheet entering the plating tank is lower than that of a general material.

The inventors of the present invention have reported that plating defects such as dross pulling and hot water wrinkling occurring in full-hard materials are caused by insufficient cleaning of the steel sheet surface due to the heat treatment at a low temperature or overcooling of the steel sheet in a cooling zone. Thought to be involved. Considering that there is little room for raising the heat treatment temperature of the non-oxidizing heating furnace or soaking zone due to material restrictions, by examining heat treatment conditions after the cooling zone, plating conditions, etc. investigated.

As a result, the occurrence of hot water wrinkles is related to the temperature of the steel sheet entering the plating tank. The steel sheet before entering the plating tank is reheated, and the temperature of the steel sheet entering the plating tank is defined as the plating bath temperature. If the temperature is increased to the same level, the generation of hot water wrinkles can be reduced.Dross pulling is affected by the temperature of the steel sheet entering the plating tank and its fluctuation, and the temperature of the steel sheet entering the plating tank is reduced to the same level as the plating bath temperature. It has been found that it can be reduced by increasing the value and reducing the variation. Further, when the reheating is performed by induction heating, the effect of preventing dross pulling and hot water wrinkles is greater, and dross adhesion to the roll in the bath is prevented, and the life of the roll in the bath can be extended. We have found that plating adhesion can also be improved.

The present invention is based on this finding,
The characteristic configuration is as follows. (1) When manufacturing a non-recrystallized hot-dip galvanized steel sheet in a continuous hot-dip galvanizing line in which a heating zone, a soaking zone and a cooling zone are arranged in this order, the temperature of the steel sheet entering the galvanizing tank is measured. Continuous hot-dip galvanizing, in which the steel sheet is reheated by induction heating at the rear of the cooling zone based on this measurement value and hot-dip galvanizing is performed while controlling the steel sheet temperature entering the plating tank to the target steel sheet temperature This is a method for producing a non-recrystallized hot-dip galvanized steel sheet in a line. (2) The method for producing a non-recrystallized hot-dip galvanized steel sheet in a continuous hot-dip galvanizing line in which the hot-dip galvanizing is hot-dip galvanizing in the method of the above (1).

The temperature of the steel sheet entering the plating tank is measured by controlling the temperature of the steel sheet entering the plating tank based on the measured value by induction heating having excellent controllability at the rear of the cooling zone. The temperature can be controlled with high accuracy by suppressing temperature fluctuation. Therefore, occurrence of plating defects such as dross pulling and hot water wrinkles can be reduced. In addition, dross is less likely to adhere to the roll in the bath, and the life of the roll in the bath can be extended. Further, the steel sheet is not softened, and the plating adhesion is improved.

By the above-mentioned method, plating defects such as dross pulling and hot water wrinkles are reduced and plating adhesion is improved. The reason for induction heating is that it has a heating effect on the surface layer of the steel sheet. As a result, we believe that the effect of strengthening the reduction and activation of the steel sheet surface may be significant.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The same parts as those shown in the already described figures are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, reference numeral 13 denotes an induction heating device installed at the rear of the cooling zone.
, An induction heating coil 14 is connected to a high frequency power supply 15.
Reference numeral 16 denotes a steel sheet temperature measuring device that enters the plating tank 9,
17 is based on the deviation between the measured steel sheet temperature and the target temperature,
This is a control device that controls the output of the high-frequency power supply 15 of the induction heating device 13.

Using this apparatus, a full hard material is manufactured as follows. In a conventional manner, the steel sheet 12 is heated in the non-oxidizing heating furnace 1 and the soaking furnace 3 within a temperature range not exceeding the recrystallization temperature.
Is heated to remove rolling oil adhering to the surface of the steel sheet, reduce and activate the surface of the steel sheet, and then pass the sheet through the cooling zone 4.
Based on the deviation between the measured value of the steel plate temperature measured by the steel plate temperature measuring device 16 and the target steel plate temperature, the steel plate is reheated by the induction heating device 13 at the rear of the cooling zone, and the steel plate temperature entering the plating tank 9 becomes the target temperature. And the steel sheet 12 is guided to the plating tank 9.

Since the steel sheet temperature can be controlled quickly and accurately, the steel sheet entering the plating tank 9 is controlled to a predetermined target steel sheet temperature without being supercooled or overheated. Accordingly, dross pulling, plating defects such as hot water wrinkles, etc. are less likely to occur on the steel sheet surface after plating, dross is less likely to adhere to the roll in the bath, and the life of the roll in the bath can be extended. Further, the steel sheet is not softened, and the plating adhesion is improved.

When manufacturing a hot-dip galvanized steel sheet or a Zn-5% Al-based hot-dip zinc-aluminum alloy coated steel sheet, the steel sheet temperature at the outlet of the non-oxidizing heating furnace, the steel sheet temperature at the soaking zone outlet, and the plating bath temperature must be in accordance with ordinary methods. Can be. For example, it is preferable that the temperature of the steel sheet at the outlet of the non-oxidizing heating furnace is about 450 ° C., the temperature of the steel sheet at the outlet of the soaking zone is about 480 ° C., and the temperature of the plating bath is about 460 ° C.

Further, it is preferable that the target steel sheet temperature of the steel sheet entering the plating tank is not lower than the plating bath temperature −10 ° C. and not higher than the recrystallization temperature of the steel sheet. FIG. 2 shows the relationship between the temperature of a steel sheet entering a plating bath and the state of occurrence of plating defects when a hot-dip galvanized full-hard material is manufactured using the apparatus of FIG. 1 at a plating bath temperature of 460 ° C. FIG. If the temperature of the steel sheet is equal to or higher than the plating bath temperature −10 ° C., dross pulling and generation of hot water wrinkles are not recognized, and the effect of preventing generation of plating defects is large.

When producing a Zn-55% Al-based hot-dip zinc-aluminum alloy coated steel sheet, plating defects can be reduced by setting the temperature of the steel sheet entering the plating tank as described above. In the case of a Zn-55% Al-based hot-dip zinc-aluminum alloy-plated steel sheet, the plating bath temperature is as high as about 600 ° C., but if the heating is carried out for a short time, the steel sheet hardly softens as described above. However, when the running speed of the steel sheet is low, the softening of the steel sheet may be large, so in this case, even if the steel sheet is heated at a lower temperature than the steel sheet does not soften, the reduction of plating defects,
This has the effect of extending the life of the roll in the bath.

Although the embodiment of the present invention has been described for the case of a continuous hot-dip galvanizing line of a non-oxidizing furnace type, the present invention is not limited to the above-mentioned line. The present invention can be widely applied to a continuous hot-dip galvanizing line such as a direct-fired heating furnace system or a total radiation tube heating system in which cooling zones are arranged in this order.

[0037]

EXAMPLE A low-carbon ordinary steel sheet of various sizes cold-rolled by a conventional method was used as an original sheet, and the apparatus shown in FIG.
z, using a high-frequency induction heating device with an output of 1200 kw,
Plating is performed in a galvanizing bath containing 0.18 wt% of Al and 0.15 wt% of Pb to produce a hot-dip galvanized full-hard material according to the method of the present invention. The occurrence of plating defects, plating adhesion, materials, and the life of the roll in the bath were investigated.

With respect to hot water wrinkles, discontinuous defects were counted with a defect length of 2 m per chip, and continuous defects were counted with the actual length as the defect length, and the ratio of the total defect length to the total coil length was determined. Regarding the dross pulling, the degree of the defect generation area was visually observed.

The plating adhesion was 1 when the inner bending interval was 0 t.
After bending by 80 °, the plated layer outside the bent portion was subjected to a cellophane tape adhesion peel test, and the presence or absence of peeling and cracking of the plated layer was visually observed to determine the following.

：: No peeling or crack is observed. Δ: Crack is observed. X: Partial peeling is observed. Defective and expressed as a percentage of defective.

The life of the roll in the bath was evaluated by the number of days of continuous production of the full hard material without changing the roll.

Table 1 shows the production conditions of typical sizes of the method of the present invention and the results of the examination of the above items.

[0043]

[Table 1]

For comparison, a galvanized full-hard material was manufactured by a conventional method using the apparatus shown in FIG. 3, and the same investigation as in the method of the present invention was conducted on the obtained coated steel sheet. Was. Table 2 shows the results of the survey.

[0045]

[Table 2]

In the conventional method, since the temperature of the steel sheet penetrating the plating bath is lower than the target steel sheet temperature, many plating defects occur, the plating adhesion is poor, and the material is unstable.
In particular, when the thickness is 0.27 mm, the above-mentioned problem is more remarkable because the temperature of the steel sheet entering the plating tank is much lower than the target steel sheet temperature. In addition, the roll life is short.

On the other hand, in the method of the present invention, the temperature of the steel sheet entering the plating bath is controlled to the same temperature as the plating bath temperature by induction heating, so that the occurrence of plating defects is greatly improved as compared with the conventional method. Excellent plating adhesion and no occurrence of defective materials. Further, the life of the roll in the bath is extended more than three times as compared with the conventional method.

The present embodiment is an example in which a full-hard material of hot-dip galvanization is manufactured, but a Zn-5% Al-based hot-dip zinc-aluminum alloy plated steel sheet or a Zn-55% Al-based hot-dip zinc-aluminum alloy Similar results can be obtained in the case of manufacturing a full-hard material of a plated steel sheet.

[0049]

According to the present invention, the temperature of a steel sheet entering a plating tank can be quickly and accurately controlled to a target temperature in the production of a full-hard material, so that a dross is drawn on a steel sheet surface after plating, hot water wrinkles, etc. Plating defects are less likely to occur, and dross is less likely to adhere to the rolls in the bath, thereby extending the life of the rolls in the bath. In addition, plating adhesion is improved, and occurrence of defective materials can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing a main part of a hot-dip galvanizing line for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the temperature of a steel sheet entering a plating tank and the state of occurrence of plating defects.

FIG. 3 is a diagram showing a main part of a hot-dip galvanizing line for explaining a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating zone (non-oxidizing heating furnace) 2 Throat 3 Soaking zone 4 Cooling zone 8 Snout 9 Plating tank 10 Sink roll 11 Support roll 12 Steel plate 13 Induction heating device 14 Induction heating coil 15 High frequency power supply 16 Steel plate temperature measuring device 17 Control device

Claims (2)

[Claims] When a non-recrystallized hot-dip galvanized steel sheet is manufactured in a continuous hot-dip galvanizing line in which a heating zone, a soaking zone, and a cooling zone are arranged in this order, the temperature of a steel sheet entering a galvanizing tank is measured. Then, based on this measured value, the steel sheet is reheated by induction heating at the rear of the cooling zone, and hot dip galvanizing is performed while controlling the temperature of the steel sheet entering the plating tank to the target steel sheet temperature. A method for producing a non-recrystallized hot-dip galvanized steel sheet in a continuous hot-dip galvanizing line. 2. The method for producing a non-recrystallized hot-dip galvanized steel sheet in a continuous hot-dip galvanizing line according to claim 1, wherein the hot-dip galvanizing is galvanizing.