JPH0336286A - Descaling method and production of plated steel plate using the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Applications) The present invention is a phase adjustment method for removing scale generated on the surface of steel materials such as cast slabs, steel slabs, steel wires, @sawn materials, and hot rolled steel materials. This paper relates to a descaling method and a galvanized steel plate manufacturing method using the same.

(Prior Art) For example, scale, which is an oxide film of iron, is formed on the surface of a hot rolled steel sheet manufactured by hot rolling. This scale must be completely removed when cold-rolling a hot-rolled steel sheet.The descaling methods applied to hot-rolled steel sheets include the pickling method and the mechanical method, as is well known. There is a descaling method, and a descaling method that combines both is also used in some cases.
No. 8 also discloses a descaling method in which the surface of a steel material is locally heated with flame and then pickled or mechanically descaled.

(Problems to be Solved by the Invention) Among these descaling methods, the pickling method requires a long pickling tank and large-scale waste acid treatment equipment, requiring a large amount of space and increasing equipment costs. Furthermore, since a large amount of acid is used, it is not economical and has the disadvantage of creating a poor working environment. Furthermore, this strength has poor descaling properties when the plate is passed through an acid solution. Therefore, in some cases, attempts have been made to crack the scale layer through pretreatment such as skin bath, scale blotting, and coil quenching, or to perform descaling with a brush during pickling.

However, even with these improvements, problems such as the space occupied by the device still remain unsolved.

On the other hand, the mechanical descaling method has woody defects that prevent uniform descaling like the pickling method. Therefore, at present, it is used only as a pre-treatment for pickling, or as an auxiliary means during pickling, such as the second brush.

On the other hand, similar to the above-mentioned skin pass method, local heating using flame is basically intended to make it easier to remove scale from the surface of the steel material, and it is assumed that it is used in combination with the pickling method or mechanical descaling method. However, the present invention has not yet been able to solve the above problems.The present invention aims to solve the above problems by utilizing the direct flame reduction effect of a burner. The purpose is to provide law.

Another object of the present invention is to provide an economical method for manufacturing galvanized steel sheets using the above descaling method.

(Means for solving the problem) The direct flame reduction effect of the burner itself is already well known.
Direct-fire non-oxidation furnaces used in continuous annealing equipment for cold-rolled steel sheets, continuous annealing equipment in molten zinc coating lines, etc. utilize this effect. The direct fire reduction action in the direct fire non-oxidation furnace of the molten galvanizing line is as follows.

In hot-dip galvanizing lines, cold-rolled steel sheets are mainly used as the material to be plated. This A plate is manufactured by descaling a hot rolled steel plate by pickling and cold rolling it. In a non-oxidizing furnace preheating line with a non-oxidizing furnace,
The cold-rolled steel sheet is first cleaned as a pre-treatment, then subjected to direct fire heating with a burner in a non-oxidizing furnace, indirect heating with a radian tube in a heating zone, and then passed through a cooling zone and passed through a zinc pot. Boarded.

In the non-oxidizing furnace, the steel plate is heated without oxidation by direct fire burners on both sides, and the rolled citron adhering to the surface is removed by combustion. A feature of direct flame heating is that the heating rate of the wA plate is significantly faster than indirect heat using radiant tubes or the like. In a non-oxidizing furnace, combustion in the burner is performed at an air-to-air ratio of around 0.9, the atmosphere is kept non-oxidizing or weakly oxidizing, and the steel plate is heated to 500 to 600'C while preventing excessive oxidation.

In the next heating zone, the steel plate is heated indirectly by radiant tubes 11 from both the front and back surfaces, and heated to the annealing temperature by a force U. In the heating zone, the inside of the furnace is maintained with reducing atmospheric gas sent from the snout and cooling zone, so the thin oxide film of hundreds of sizes on the surface of the steel sheet that is generated in the non-oxidation furnace is reduced. The atmosphere in the heating zone contains 10 to 75% N7 and the rest is N.
It is a mixed gas of 2. The steel plate that has passed through the heating zone is simultaneously reduced and cooled by reducing atmospheric gas in the cooling zone (enters the zinc bath).

Heat treatment and plating work are performed on the cold rolled steel sheet through the processes described above, and direct flame reduction heating is performed using a burner in the non-oxidation furnace. However, steel plates are usually heated at temperatures of 500 to 600℃.
Since the steel is transported from the non-oxidizing furnace to the heating zone in a state of Further, the reducing atmospheric gas in the heating zone and the cooling zone only reduces a thin oxide film of several hundred sizes.

As described above, in the past, a very thin oxide film of 01 μm or less was reduced by a combination of direct flame reduction action and N2 + H2 mixed gas atmosphere to prevent subsequent oxidation, but hot-rolled steel sheets, Direct flame reduction has not been applied to thick scales of 5 to 10 μm that form on the surfaces of slabs, copper pieces, steel wires, forged materials, etc., and even if it is applied, sufficient descaling effects cannot be obtained. It was said that it would not be possible.

By the way, the direct heating method for steel plates involves controlling the combustion system of the heating furnace to ensure that the combustion gas that hits the steel plates is in a reduced state, and heating the steel plates with great force and thermal speed without oxidizing the steel plates. A direct heating n thermal power method for steel plates has been proposed in JP-A-60-1.21230. However, in this method, a steel plate with an oxide film thickness of approximately 600 Å is heated and reduction is only performed until the oxide film thickness becomes 20λ at a plate temperature of 700°C. Therefore, it is impossible to completely reduce materials such as hot-rolled steel sheets with a scale thickness of 5 to μm.

The present inventors have been continuing their research on the effect of direct flame reduction on the scale that forms on the surface of hot-rolled S+ sheets under these circumstances, and in the process, they The temperature of the steel material when performing direct flame heating in the reduction area is 600.
It has been found that even thick scales of 5 to 10 μm can be removed by adjusting the reducing power to 0.degree. It was also discovered that even if residual scale forms during direct heating, it is possible to remove the residual scale during cooling by strengthening the reducing power of the cooling atmosphere.

The present invention was made based on this knowledge, and involves holding or passing a steel material on which scale has formed on the surface within the flame reduction zone of a burner at a temperature of 600°C or higher, and then
Summary of a method for descaling steel materials, which is characterized in that the steel material is cooled in an atmosphere whose reducing power is adjusted according to ○, N, and the temperature G of the steel material in the atmosphere so that no scale ultimately remains. shall be.

In addition, the method for manufacturing galvanized steel sheets of the present invention is an extremely low-cost plating method in which hot-rolled copper sheets are directly used as the plated material by utilizing the above-mentioned descaling method, and hot-dip galvanized steel plates are produced without pickling. This is a steel sheet manufacturing method, and its characteristics are that hot-rolled steel sheets with scales are heated under direct heating power of 11
The hot-rolled steel sheet is passed through a heating furnace in which the hot-rolled steel sheet is passed through the flame reduction zone of the burner at a temperature of 600° C. or higher, and then the hot-rolled steel sheet is passed through the flame reduction zone of the burner until finally no scale remains. The hot rolled steel sheet is passed through a coating bath after being cooled in an atmosphere L[i] in which the reducing power is adjusted according to the amount of 02 in the atmosphere and the temperature of the copper phase so that the hot rolled steel sheet is not heated.

An important point in the present invention is that the steel plate on which the steel plate is formed is held or passed within the reduction zone of the burner flame at a temperature of 600'C or higher. FIG. 3 is a graph showing the relationship between the burner combustion gas temperature and the steel material temperature. Looking at the relationship between the combustion gas flow rate and steel material temperature currently being processed in actual operation, the combustion gas temperature is 1200 to 1
At 300'C, the steel is placed in the reducing region when the steel temperature is 500-600C. In continuous hot-dip plating equipment, as mentioned above, cold-rolled steel sheets are heated to
'lIndirect heating by radiant tubes in the tropics. The heat treatment temperature in this power 11 tropical region is 700 to 800°C, and from this point of view, the direct heating power II heat temperature in the previous stage is 500°C.
A temperature of ~600°C was considered sufficient. However, the reducing power of 1-12 etc. becomes stronger as the steel temperature increases. The present invention increases the temperature of the steel material during direct heating, and exerts sufficient reducing power on the steel material even after cooling after direct heating. That is, by increasing the temperature of the steel material during direct flame heating, the steel plate is strongly descaled by both the direct flame reducing power of the burner and the atmospheric reducing power during cooling.

As a burner for direct flame heating, one that exhibits sufficient reducing power even in a region where the steel material temperature is high is preferable, and an example of such a burner is the one proposed in Utility Model Application No. 168,668/1983. .

As will be discussed later, the reduction range of this burner extends to a copper material temperature of 950°C, as shown in Figure 3, and the reduction range is sufficient even at a steel material temperature of 750°C or higher, which was outside the reduction range in conventional burners. Reduction power can be obtained.

(Function) Next, processing conditions in the descaling method and the galvanized steel plate manufacturing method of the present invention will be explained.

In the method of the present invention, the steel material to be treated is heated by direct flame reduction at 600° C. or higher. For this purpose, the steel material is usually preheated to 600°C or higher. The temperature when heating steel materials over direct fire is 600'C.
If it is less than 100%, descaling due to the direct flame reduction effect of the burner will not be promoted. In order to enhance this direct fire reduction effect, it is desirable that the temperature of the steel material when heated under direct fire is 800°C or higher. The upper limit of temperature when heating steel materials over direct fire is 950℃.
is desirable. If the steel material is heated to a temperature exceeding this temperature, the concentration of unburned CO and H2 in the twisting gas, as well as the concentration of active reducing ions, will decrease, and the reducing effect will begin to decrease.

The direct flame heating time for the steel material is adjusted appropriately based on the temperature and scale thickness of the steel material, etc., and in the case of hot rolled steel plate, it is
0 seconds is appropriate. That is, the steel material is held in the flame reduction zone for 10 seconds or passed through the flame reduction zone in 10 seconds. During the process of direct heating with a burner, scale is removed by the reductive action of unburned CO and H4 in the combustion gas and active reducing ions. As a combustion gas,
It is possible to use coal furnace gas, converter gas, blast furnace gas, etc.

As for the burner, it is desirable to have a swirling vane interposed between the burning air jet pipe and the fuel jet pipe to mix the combustion air with the fuel flow as a swirling flow (Utility Application No. 62-16).
866f3). Approximately 10μm per second by using this burner
Thick scale can be removed.

After direct heating, the steel material is cooled. During this cooling (1), it is important not to oxidize the steel surface.The conditions are divided into two depending on the amount of O2 in the atmosphere.If the O2N in the atmosphere is less than 1100pp,
Alternatively, oxidation of the steel surface can be prevented by cooling in an inert gas (100%) such as Ar. 02N is 1100
If the amount is more than pp, cooling is performed while preventing oxidation of the steel surface in a mixed gas of the above gas and a reducing gas such as I2, and the greater the amount of O2, the higher the mixing ratio of the reducing gas.

In addition, secondary scale may occur in steel materials that have been heated by direct fire, depending on the direct fire power (1) heat temperature.

In that case, the secondary scale is removed by increasing the combination ratio of the reducing gas in the cold JJI atmosphere.

The lower the direct heating temperature, the higher the reducing gas mixing ratio. Figure 4 shows the relationship between the temperature and the mixing ratio of reducing gas when heating steel materials over an open flame. The good reduction region is asymptotic to both straight cottons at I (2 concentration 1%, open fire) J11 thermal temperature 600°C.

(Example] The present invention will be explained in detail below.

FIG. 1 shows an apparatus suitable for carrying out the descaling of the present invention.

The apparatus includes a furnace body 10 having a structure in which a preheating zone 11, a direct flame reduction zone 12, and a cooling zone 13 are connected in order. For example, a hot rolled steel plate 20, which is a steel material to be treated, is placed in a preheating zone 1 in a furnace body 10.
1, direct fire reduction zone 12, cooling zone 13. The preheating zone 11 is equipped with heat exchange equipment to preheat the hot-rolled plate 20 to 600°C or higher, and the direct-fire reduction zone 12 is equipped with a plurality of heat-exchanging equipment so that both sides of the hot-rolled steel plate 20 can be exposed to flame reduction zones. A burner 30 is provided. In addition, in the cooling zone 13, 02
The atmospheric gas composition is determined depending on the amount and preheating temperature.

The results of descaling a hot rolled steel plate using the above device are as follows.

The hot-rolled steel plate was made of low carbon steel and had a thickness of 1.6 mm, and had scales of 5 to 8 μm on the surface before descaling. The total length of the furnace body is 60 m, and the advancing speed of the hot rolled steel plate is 120 m/mi.
n, the band passage time of the hot rolled steel plate is j, and the preheating zone is 8.
seconds, 10 seconds in the open flame reduction zone, and 12 seconds in the cooling zone. The preheating temperature of the hot rolled steel plate was varied between 550 and 900 degrees,
The atmosphere in the cooling zone is N.

(100%), N, -) 11° (5%), N2+82 (
10%) and N2+Hz (20%). The combustion gas is coke oven gas, ○ in the atmosphere,
The amount is 0.5%. The descaling results are shown in Table 1.

The descaling status is the state where no scale layer remains on the surface.
, A state in which a scale layer of approximately 045 to 1.0 μm remains is represented by Δ, and a state in which a scale layer of 1.0 μm or more remains is represented by ×.

As shown in Table 1, when the preheating temperature, that is, the temperature during direct flame heating of the steel material, is less than 600'C, descaling performance is poor regardless of the cooling gas composition. Also, the cooling gas IJ1 command is N2
(100%), circle the cooling zone.

(500 ppm), descaling properties are poor regardless of the preheating temperature. On the other hand, the preheating temperature is 600
At 1650℃, the cooling gas composition is N2+142 (20
%), slightly better descaling properties are obtained. 700
'C or higher, the descaling property becomes very good in the case of N7+1-12 (20%), and N2-I-1-12 (1
Very good descaling was obtained even at 800℃ (0%).
In the above, good descaling properties were obtained for all gases except for N and (1,00%). By the way, if you try to obtain the same level of descaling performance by pickling, you will need a tank length of about 100 m.

Next, a method for manufacturing a hot-dip galvanized steel sheet according to the present invention will be explained.

The manufacturing equipment for continuous hot-dip galvanized steel sheets includes oxidation furnace method,
Typical examples include the non-oxidizing preheating furnace method, the U and S steel methods, the 6 Cirrus method, and the Wheeling method.

Of these, the oxidation furnace method, non-oxidation preheating furnace method, and US Steel method have annealing equipment inside the line, and the Cirrus method has two types, annealing inside and outside the line. The wheeling method is an out-of-line annealing type.

Production equipment suitable for the production method of the present invention is an oxidation furnace type and a non-oxidation preheating furnace type that do not have a pickling tank but have a direct-fired reduction burner, and the latter type of non-oxidation preheating furnace type equipment is particularly suitable. be. Figure 2 shows the equipment structure and heat pattern for the non-oxidation preheating method. The steel plate is placed in a non-oxidizing furnace 41 and a heating zone 4.
2, gradual cooling zone 43, No. 1, jet cooler 44, adjustment cooling zone 45, No. 2, passing through the dienoto cooler 46 in order, and enters into the zinc bottom 48 through the snout 47.

Conventionally, cold-rolled steel plates were mainly used as steel plates, and the fil plates were heated to 500 to 600°C in an open flame furnace in a non-oxidizing furnace 41, as shown by the solid line in the graph of Figure 2. After being further heated to about 700 degrees Celsius at Tropical 42,
It is cooled in a cooling zone 43 and a cooler 44.

In contrast to such conventional methods, the manufacturing method of the present invention uses a hot-rolled steel sheet with scale still attached as one steel sheet.

Then, this copper plate is heated, for example, in a non-oxidation furnace 41 to a higher temperature than conventionally, for example, 800 to 900°C. Thereby, the steel plate is subjected to direct flame reduction at a temperature of 600'C or more.

Then, the atmosphere of the next heating zone 42 and cooling zone 43 is as described above.
Maintain the atmosphere in which the reducing power is adjusted according to the temperature during I heat, and pass the above @ board through it. Using this tool 22, the scale on the surface of the steel sheet is removed, and the scale-free hot rolled copper sheet is galvanized.

[Effects of the Invention] Since the descaling method of the present invention does not use acid, there is no need to treat waste acid, and the equipment can be simplified. Furthermore, it does not cause corrosion of equipment or problems in the working environment, and the processing space can be saved compared to pickling. The main advantage is that it can also suppress uneven descaling, which is a problem with mechanical descaling, and it does not require use in conjunction with other descaling methods.

The galvanized steel sheet production method of the present invention uses a hot-rolled steel plate with 41 scales still attached as the plated plate, removes the scale in the heat treatment process, and supplies it to the plating bath, so compared to the conventional production method. The pickling process and cold rolling process of the hot-rolled II plate are omitted, making it possible to significantly reduce the cost of the Mesoco l-hoe plate.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an apparatus suitable for carrying out the descaling method of the present invention, and FIG.
lit! Fig. 3 is a graph showing the relationship between the combustion gas temperature of the burner and the direct heating temperature of the copper material, and Fig. d is a graph showing the good reduction region. In the figure, 10: Furnace body, 11: Pre-heating zone, 11 Direct fire reduction, 11
C, 13: Cooling zone, 20: Steel +4.30; Burner, 41
・Non-oxidation furnace, 42. Heating 4j), 43, Cooling 411.4
8: (IE?, i X1mi ・) l-. one

Claims (2)

[Claims] (1) A steel material with scale formed on its surface is held or passed through the flame reduction zone of a burner at a temperature of 600°C or higher, and then the steel material is finally exposed to O_2 in the atmosphere so that no scale remains. A descaling method characterized by cooling in an atmosphere whose reducing power is adjusted depending on the amount and the temperature of the steel material. (2) Pass the hot-rolled steel sheet with scales through a direct-fired heating furnace, pass the hot-rolled steel sheet into the flame reduction zone of a burner at a temperature of 600°C or higher in the direct-fired heating furnace, and then is cooled in an atmosphere in which the reducing power is adjusted according to the amount of O_2 in the atmosphere and the temperature of the steel material so that no scale ultimately remains, and then the hot-rolled steel sheet is passed through a plating bath. A method for producing plated steel sheets.