JPS60234924A - Method and installation for continuous annealing of cold-rolled steel strip - Google Patents

Abstract

PURPOSE:To prevent the generation of heat buckling of a steel strip and to provide an increase in passing speed and an improvement in productivity in continuous annealing by adjusting the temp. at which the steel strip is led into and out of a vertical type single-pass furnace. CONSTITUTION:The steel strip S is heated to some extent by passing through a preheating zone 21 and a low-temp. heating zone 22 in a continuous annealing installation for a cold-rolled steel sheet for deep drawing, etc. and is introduced into the high-temp. heating and soaking zone 23 of the vertical single-pass furnace where the strip is subjected to the prescribed heat treatment. The steel strip is in succession cooled down to a prescribed temp. by passing through the primary cooling zone 24 and is then passed through the secondary cooling zone 25, overaging treatment zone 26 and tertiary cooling zone 27, by which prescribed material characteristics are given thereto. The temp. of the steel strip on the inlet and outlet side of the vertical type single-pass furnace is controlled at about <780 deg.C to prevent generation of the heat buckling. The generation of meandering the annealing furnace and the generation of flaws on the steel strip are thus prevented.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a continuous annealing method and continuous annealing equipment for cold-rolled steel strips, and in particular, to effectively prevent meandering and hit buckling in the continuous annealing equipment for copper strips. It is something to do.

Technical Background Generally, a vertical furnace is used as a continuous annealing furnace for cold-rolled steel strips due to the installation area and equipment cost. In such a vertical continuous annealing furnace, as shown in Figure 1,
A large number of hearth rolls 1 are arranged in rows at the top and bottom of the furnace 2 as a conveying device for the copper strip S, and the steel strip S is sequentially wound around these upper and lower hearth roll groups during roundabout threading. , a predetermined heat treatment necessary to obtain a desired material percentage is performed.

However, when the copper strip is continuously heat treated in the furnace as described above, depending on the shape of the copper strip, tension balance in the furnace, temperature conditions, etc., meandering may occur in the steel strip, making it impossible to operate smoothly. be. For this reason, in order to prevent such meandering, rolls 1' and 1'' provided with rounds as shown in FIG. 2 (al and (bl)) are generally used as hearth rolls.

This is an attempt to correct the meandering by the centering force of the crown roll, that is, by the force that moves the copper strip toward the center in the width direction of the roll.

However, if this centering force is too strong, the copper strip will buckle in its width direction, resulting in a defect called a heat buckle.

Therefore, in order to prevent both meandering and heat buckling, it is necessary to apply an appropriate amount of crown in advance to prevent both of them from occurring.There are various causes of such heat buckling, for example, The higher the heat treatment temperature, the larger the plate width, and the smaller the plate thickness,
Furthermore, the higher the sheet threading speed, the more likely heat buckling occurs, making it extremely difficult to select an appropriate round amount.

Prior art and its problems As a solution to the above-mentioned crown amount problem, for example, Japanese Utility Model Application Publication No. 55-172359 and Japanese Patent Application Publication No. 57-17
Hearth rolls with variable crowns have been proposed in Japanese Patent No. 7980 and Japanese Utility Model Application Publication No. 58-105464.

However, in order to control the amount of crown, a device for measuring crown ta for each roll and a device for controlling the amount of crown based on the measurement results are required, which requires a large amount of cost. Among these problems, there was also a problem in that the response was slow.

By the way, cold-rolled steel strips for deep drawing generally have a C content of 0.
Low carbon steel of 1% or less is used, and in particular, ultra-low carbon steel whose O content has been reduced to about 0.005% or less due to recent advances in wire melting technology is also used as a material for deep drawing steel sheets. However, these cold-rolled steel sheets for deep drawing are
It is a high-temperature annealed material that is heated to a temperature of 800°C or higher, and heat punctures are likely to occur, and this tendency becomes more pronounced as the coal becomes extremely low.

In addition, recently there has been an increasing demand for ultra-thin materials with a thickness of 0.2 or less as original plates for threading, but even in such ultra-thin materials, as the threading speed increases in response to the above requirements, heat This left a problem in that buckling was more likely to occur.

1. There was also a problem with heat buckles in the original plate for the 90mm, which was made of ultra-low carbon steel and was made of extremely soft carbon steel.

Purpose of the Invention The present invention advantageously solves the above-mentioned problems.It is an object of the present invention to advantageously solve the above-mentioned problems. The purpose of this invention is to propose a continuous annealing method for cold-sailed steel strip that can effectively prevent the occurrence of buckling, along with suitable continuous annealing equipment for its implementation.

Figure 3 shows a complete schematic diagram of a conventional continuous annealing furnace that is suitable for continuous heat treatment of tin plate blanks. In the figure, number 3 is a heating zone, 4 is a soaking zone, 5 is a slow cooling zone, and 6 is a rapid cooling zone.
The steel strip S is subjected to a predetermined heat treatment while sequentially passing through the heating zone 3, soaking zone 4, slow cooling zone 5, and rapid cooling zone 6.

Now, Fig. 4(a) and Φ) show the results of investigating the meandering of the copper strip and the frequency of occurrence of heat buckles when using the above-mentioned continuous annealing furnace, respectively, in the first half, second half, Soaking zone, slow cooling zone and rapid cooling? Figure 1 shows the relationship with the crown amount of the hearth roll.

From the figure, it can be seen that heat buckling is likely to occur in high temperature zones such as the latter half of the heating zone, the soaking zone, and the slow cooling zone, and -゛ direction meandering is difficult to occur in these high temperature zones.

Next, FIG. 5 schematically shows a continuous annealing line including a conventional continuous annealing furnace mainly intended for deep drawing copper strips. In the place shown in the figure, the steel strip S is attached to the payoff reel 7.7'
After being rewound at the inlet, the material is then subjected to pretreatment at an inlet equipment 8 such as a welder or a cleaning device, and then fed into a continuous annealing furnace 10 via an inlet louver 9. In this continuous annealing furnace IO, the steel strip S is placed in the preheating zone 11. Heating zone 12. Nabe Tropical 18
゜Primary cooling zone 14. Secondary cooling zone 15. A predetermined heat treatment is performed while sequentially passing through an overaging treatment zone 16 and a tertiary cooling zone 17', and then, after passing through an output side looper 18, a Tef & treatment is applied to an output side treatment device 19 such as a shear. Thereafter, it is wound up using a tension reel 20°20'.

FIG. 6 shows the results of investigating the rate of heat buckling when a copper strip for deep drawing was heat treated in such a continuous annealing furnace. In the figure, the horizontal axis represents the heating temperature of the copper strip, and the vertical axis represents the percentage of the number of heat buckling generating coils to the total number of coils processed.

As is clear from the figure, when the temperature of the copper strip is below 780°C, no heat buckling occurs, but when it exceeds 780"0, heat buckling begins to occur rapidly as the temperature increases. Recognize.

Figure 7 also shows the results of a survey on the occurrence of heat buckles when heat treatment was applied to tin plates (thickness: 0.2 to 0.3 mm) made of ultra-low carbon steel. shows.

As is clear from Figure 7, the occurrence of heat buckles in the ultra-low-coal Nobu9@ base plate, similar to the deep-drawn steel strip, decreased dramatically as the processing temperature decreased, and in particular, there was no heat buckling at temperatures below 700°C. .

This invention was developed in view of the occurrence of heat buckling as described above, and in the high temperature zone where heat buckling is likely to occur, the vertical furnace is moved in one pass to avoid contact with the hearth roll as much as possible, that is, the upper roll is The high-temperature zone heat treatment and primary cooling are carried out at once between the upper and lower rolls, while for the low-temperature zone, a vertical furnace with a built-in hearth roll is used. It is based on the novel finding that by appropriately controlling the temperature of the copper strip at the inlet and outlet sides, the intended purpose can be achieved very advantageously.

The structure of the invention, that is, this invention is a vertical furnace, a vertical one-pass furnace, and then connected to a vertical furnace again while sequentially forming a heating zone, a soaking zone, and a cooling zone. ! When continuously annealing a cold-rolled steel strip using a continuous annealing facility, the steel strip is introduced into and taken out of a vertical l-bath furnace at a temperature that does not cause heat buckling in the copper strip. This is a continuous annealing method for cold rolled steel strip.

The present invention also provides continuous annealing equipment equipped with a heating zone, a soaking zone, and a cooling zone, in which the heating zone and the cooling zone are each divided into a low-temperature zone and a high-temperature zone, and the low-temperature zone is a heating zone. Vertical furnace, - high-temperature heating zone which is the blade high-temperature zone,
This continuous annealing equipment for cold-rolled steel strip is characterized in that the soaking zone and the high-temperature cooling zone are connected to each other in a vertical one-pass furnace, and the subsequent low-temperature zone cooling zone is again a vertical furnace.

Note that the heat treatment Qtla in the continuous annealing equipment according to this invention
+411nMaG-4- to GWJ-1kt, L-4t
In addition to the rIC cooling zone, a preheating zone can also be placed in front of the heating zone.

This invention will be explained in detail below.

First, the continuous annealing equipment according to the present invention will be explained.
Fig. 8 shows a preferred embodiment of continuous annealing equipment for deep drawing cold steel strips, in which numeral 21 is a pre-heating zone, 22 is a low-temperature heating zone, and 28 is a high-temperature heating/soaking zone. , 24 are primary cooling zones forming high temperature zone cooling zones, and these high temperature zone heating/soaking zone 28 and primary cooling zone 24 are arranged in one bath as a vertical furnace as shown in the figure. . 25 is the second cooling zone, 26 is the overaging treatment zone, and 27 is the eighth
This is the next cooling zone.

In such continuous annealing equipment, the steel strip S is subjected to heat treatment according to a heat pattern as shown by symbol A in FIG. 9, for example, and is given a predetermined material customization. That is, the steel strip S is first passed through a preheating zone 21 and then a low-temperature heating zone 22 to raise the temperature to some extent.
The high-temperature part of the pass furnace is introduced into the soaking zone 28 where it is subjected to prescribed heat treatment, and then the temperature is lowered to a predetermined temperature while passing through the primary cooling zone 24 of the same furnace, and then transferred to the secondary cooling zone. 25,
By passing through the overaging treatment zone 26 and then the tertiary cooling zone 27, the desired material customization is imparted.

As is clear from the results shown in Figure 6 above, the copper zone temperature at the entrance and exit sides of the vertical one-bath furnace is 78.
It is necessary to control the temperature to 00 or less from the viewpoint of preventing heat buckling.

As heating means, a radiant tube burner is used in the heating/soaking zone 22.28, and direct heating by exhaust gas from the heating/soaking zone 22.28 is used in the pre-boxed pre-heating zone 21.
Alternatively, heating with air that has undergone heat exchange with exhaust gas is preferable, while gas jet cooling using atmospheric gas is preferable as the cooling means for the 1.2 and 3rd cooling zones 24 and 25° 27 to prevent over-aging. In the treatment zone 26, it is desirable to use an electric heater or radiant heating using a radiant tube.

Next, FIG. 1θ shows a preferred embodiment of continuous annealing equipment for deep drawing cold-rolled steel strips made of ultra-low carbon steel. In this example, the gist of the construction is the same as that of the equipment shown in FIG. 8 above, except that the latter low-temperature zone consists only of the secondary cooling zone 25'.

Now, in the place shown in FIG. 10, the steel strip S is sequentially passed through the preheating zone 21, the low-temperature heating zone 22, the high-temperature heating/soaking zone 23, the secondary cooling zone 24, and then the secondary cooling zone 25'. During the passage, a desired material percentage is imparted by applying a heat treatment according to a heat pattern as shown by B in FIG. 9 above, for example. Here, the temperature at the entrance and exit sides of the vertical bath furnace of the copper strip S needs to be equal to or lower than the above case.

Furthermore, FIG. 11 shows another embodiment suitable for use in annealing ultra-thin materials such as tinplate blanks made of ultra-low carbon steel and tinplate blanks with a thickness of 0.2 mm or less. The main structure of this example is the same as that shown in FIG. 10 above, but the second cooling zone 25, which is a vertical furnace in the latter half, is a rapid cooling zone.

Now, in such equipment, the steel strip S is heat-treated according to the heat pattern shown by O in FIG. 9, for example. As is clear from the results shown in FIG. 7 above, it is necessary to control the temperature of the copper strip on the exit side to 700° C. or lower, at which no heat buckling occurs.

As described above, in the method of this invention, it is necessary to introduce and remove the copper strip into the vertical one-bath furnace at a temperature that does not cause heat buckling. It cannot be determined unambiguously because it varies greatly depending on the situation. Therefore, it is important to understand in advance the temperature at which heat buckles occur for each steel type, taking into consideration the material and plate thickness.

Note that in all of the embodiments described above, the case where a preheating zone is provided has been mainly explained, but it goes without saying that there is no problem even if the preheating zone is not provided.

Next, an example of the annealing method according to the present invention will be described.

Using the continuous annealing equipment shown in Figure 8, cold-rolled deep-drawing steel strips made entirely of ultra-low carbon steel and having the sizes shown in Table 1 below are heated and heated in the high temperature section as shown in Table 1. Thirty coils were annealed under threading conditions with various changes in the introduction/induction temperature and line speed of the soaking zone and primary cooling zone.

Table 1 also shows the results of investigating the occurrence of heat buckling and meandering during the annealing process.

As is clear from the results shown in Table 1, heat knots could be prevented by heating, soaking, and primary cooling in a vertical pass furnace over a high temperature range of 780"C. Since no meandering occurred, it was possible to increase the crown amount of the upper and lower rolls of the vertical L-pass furnace and the no-roll crown of the low-temperature range vertical! furnace.

As described above, according to the present invention, the high temperature zone is
By performing high-temperature heat treatment as a bath without contacting the roll, it is possible to effectively prevent the occurrence of heat knots and meandering, and other effects are as follows.

(1) Productivity is improved because the sheet threading speed can be increased without worrying about heat buckling.

(2) Pick-up scratches, which are particularly easy to form in high-temperature ranges, that is, foreign matter on the surface of the copper strip, adhere to and accumulate on the no-throttle roll and are transferred to the copper strip, thereby greatly reducing the occurrence of scratches.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a vertical continuous annealing furnace, Fig. 2 (a) and (1)) are front views of the crown roll, respectively, and Fig. 3 is a schematic diagram of a conventional continuous annealing facility for tin plate blanks. Figure 4 (a), (1)) U shows the influence of the crown amount of the hearth roll on the meandering of the copper strip and the frequency of heat buckling, respectively, in the first half of the heating zone, the second half of the heating zone, the soaking zone, and A graph comparing the results of investigation for each slow cooling zone and rapid cooling zone. Figure 5 is a schematic diagram of a conventional continuous annealing equipment for cold rolled steel strip for deep drawing. Figure 6 is for deep drawing. Graph 81' showing the relationship between the annealing temperature and heat buckle occurrence rate of cold rolled steel strip! Figure 7 is a graph showing the relationship between annealing temperature and heat buckle occurrence rate for tinplate raw materials made of ultra-low carbon steel, and Figure 8 is a graph showing the relationship between heat buckle generation rate and heat buckle generation rate for tinplate raw materials made of ultra-low carbon steel. Fig. 9 is a schematic diagram of a continuous annealing equipment according to the invention; Fig. 9 is a diagram showing a heat pattern of a copper strip according to the method of the invention; Fig. 10 is a diagram showing a cold-rolled steel strip for deep drawing made of ultra-low carbon steel. A schematic diagram of the target continuous annealing equipment, Figure 11, is a schematic diagram of continuous annealing equipment suitable for annealing ultra-low carbon and ultra-thin base plate material for ultra-thin Nobuji.Patent applicant: Kawasaki Steel Corporation Company Figure 6 t & Temperature ('C) Figure 7 Gu10 '72θ '730 7. ! θ 751)'
71;l) Baking & Temperature ('C)

Claims (1)

[Claims] L 7Jo A tropical zone, a soaking zone, and a cooling zone are successively formed, and the continuous annealing equipment connected to the vertical furnace, the vertical 1-bath furnace, and the vertical furnace is used to perform operational annealing treatment on the cold zone. A continuous annealing method for a cold-rolled steel strip, characterized in that the steel strip is introduced into a vertical pass furnace and then removed at a temperature that does not cause heat buckling in the copper strip. Continuous annealing equipment equipped with a heating zone, a soaking zone, and a cooling zone, in which the heating zone and the cooling zone are each divided into a low temperature zone and a high temperature zone, and the low temperature zone heating zone is a vertical furnace, - The high-temperature heating zone, soaking zone, and high-temperature cooling zone, which are the blade high-temperature zones, are connected to each other in a vertical one-bath furnace, and the subsequent low-temperature zone, the cooling zone, is again a vertical furnace. Continuous annealing equipment for rolled steel strip.