JPH0716683B2 - Continuous warm rolling equipment for stainless steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a continuous steel for stainless steel, which is advantageous for continuous cold rolling of a metastable austenitic stainless steel strip that is particularly cold work-hardened among steel strips. Regarding warm rolling equipment.

[Conventional technology]

In general, cold rolling of stainless steel strip or the like having a large deformation resistance is usually performed reversibly by a multiple-type high-pressure rolling mill equipped with small-diameter work rolls such as a Sendzimir rolling mill. However, the reversible rolling with such a small diameter work roll has a relatively low rolling speed and low productivity.

Therefore, recently, for the purpose of improving productivity, a method of performing continuous rolling using the above high-pressure lower rolling mill as a tandem mill such as a four-stand is also partially implemented. However, with such a rolling method, the rolling speed cannot be increased so much as described above, and there are problems such as slip between the work roll and the steel strip. With a tandem rolling mill having a six-fold size and a large work roll diameter, a welding machine is further arranged on the process entrance side to continuously cold-tandem roll a stainless steel strip.

By the way, the stainless steel strip has a problem that the manufacturing cost is higher than that of the general steel strip due to its low productivity and other factors. Cold tandem rolling of the above stainless steel strip greatly contributes to this reduction in manufacturing cost, but if the material for the cold rolled steel sheet with a large thickness is used, the total cost of cold rolling can be reduced accordingly. Are known. However, if the plate thickness of this material is increased, the reduction ratio during cold rolling must be increased in order to obtain the product plate thickness, which causes a significant increase in work hardening in the latter stage of tandem rolling. Rolling will be difficult.
Also, when rolling the steel strip, it is necessary to maintain a certain level of inter-stand tension to prevent narrowing, etc.
If the work hardening of the steel strip is large, the frequency of plate breakage increases.

Among the stainless steels, metastable austenitic stainless steels such as SUS304 and SUS301, which are marked by work-hardening because some of the austenite is transformed into strain-induced martensite by cold working,
There is no example of cold rolling in a tandem rolling mill composed of heavy or six-fold rolling mills, and the profitability such as high productivity and high yield due to tandem rolling, which is common in ordinary steel strip,
Not obtained for stainless steel strip.

Therefore, in order to prevent such work hardening, a method of heating stainless steel before rolling is adopted for ordinary steel as already disclosed in JP-A-53-118259. That is, a steel strip is installed on the inlet side of the tandem rolling mill.
It is provided with a heating device which is heated to 200 ° C. or higher and is kept for a time not causing recrystallization.

[Problems to be solved by the invention]

However, in the equipment disclosed in JP-A-53-118259, since the temperature of the heated steel strip is 200 ° C. or higher, the surface of the steel strip is oxidized by oxygen in the atmosphere and tempered. Occurs. In particular, in the case of stainless steel strip, since a beautiful and bright surface is required as a product, the problem that the process load such as surface polishing increases when the temper color occurs.

Also, the smaller the distance between the heating device and the tandem rolling mill, the smaller the temperature drop of the steel sheet between them, which is convenient for processing, but it is difficult to correct the meandering of the steel strip. This meandering of the steel strip causes the steel strip to break during rolling, or the rolling shape to deteriorate.Therefore, in order to prevent this, in general, a steel strip provided with a steering device near the entrance side of the tandem rolling mill is used. The method of correcting the meandering of is adopted. The reason is,
If the heating device is sufficiently small, the steering device, the small heating device, and the tandem rolling mill can be arranged in that order, but in a high-speed line, the steel strip passing speed increases, so the heating device is large. This is because the length of the furnace becomes longer (about 50 m) and even if the meandering is corrected by the steering device before entering the heating device, the meandering occurs again before passing through the heating device and entering the rolling mill.

However, when the steering device is installed on the entrance side of the tandem rolling mill in this way, the path length of the steel strip from the heating device to the tandem rolling mill becomes large. Such conventional rolling equipment is shown in FIG. In the figure, 3 is a welding machine for connecting the steel strips 2 fed from the rewinding machine to form a continuous body, 4 is a looper for adjusting the residence time of the steel strips, 5
Is a heating device, 6 is a steering device, and 8 is a tandem rolling mill. In this equipment, the path length of the steel strip 2 between the heating device 5 and the tandem rolling mill 8 is at least 15 to 20 m.
It will be about.

Further, in the completely continuous tandem rolling mill, as shown in FIG. 7, the strip running speed of the steel strip has a pattern such as (a) acceleration, (b) high speed, (c) deceleration, and (d) low speed. It is common to perform repeated operations. This depends on the capacity of the looper 4 or the presence / absence of the capacity, but the time for suspending the equipment on the input side and the equipment on the output side may be temporarily stopped due to the welding process of the steel strip on the input side and the shearing process of the steel strip on the output side. This is because it costs. Further, when rolling the welded portion of the steel strip, it is easy to break, so it is necessary to reduce the rolling speed. Therefore, since the passage time of the stainless steel strip between the heating device 5 and the tandem rolling mill 8 changes depending on the rolling speed pattern, the temperature drop amount of the stainless steel strip during this period also changes. Therefore, there is a problem in that the plate resistance of the stainless steel strip after rolling also fluctuates because the deformation resistance during rolling also fluctuates.

The present invention has been made in view of such conventional problems, and a small heating device is provided in the vicinity of the entrance side of the rolling mill, and the stainless steel strip is connected by a laser beam. The purpose is to solve.

[Means for solving problems]

The present invention relates to a laser beam welding machine for connecting a stainless steel strip between a rewinding machine and the tandem rolling mill according to a processing order, a storage device for temporarily storing a steel strip in a strip, and a stainless steel. A heating device that heats the strip, a meandering correction device that corrects the meandering of the stainless steel strip, and a small heating device that heats the stainless steel strip that has decreased in temperature due to heat dissipation during passage of the strip to the temperature before heat dissipation are sequentially arranged. This is a continuous warm rolling facility for stainless steel strips.

[Action]

The rewound steel strips are connected by a laser beam welding machine and are continuously rolled into a continuous body. At this time, since the heat input at the joint of the steel strip is smaller than that of conventional welding, there is less grain coarsening in the vicinity of the joint, so the welding strength does not decrease so much, and therefore the fracture frequency of the weld during rolling is extremely small. Become.

The welded steel strip enters a heating device, where it is heated to a temperature within a predetermined range to reduce the martensite formation rate during rolling. Then, it goes into the meandering correction device to correct the meandering and goes into a small heating device placed immediately before the tandem rolling mill, where heat is dissipated between the heating device outlet and the small heating device inlet to lower the temperature. The steel strip is again heated to the temperature before heat dissipation and sent to the tandem rolling mill. Since the steel strip is rolled while maintaining a predetermined temperature, its deformation resistance is small, and therefore, a sufficiently high strip-passing speed can be maintained and productivity can be improved without causing fluctuations in the final strip thickness after rolling.

〔Example〕

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of the present invention. The same parts as those of the conventional example described with reference to FIG. 6 are designated by the same reference numerals, and duplicated description will be omitted.

In the figure, the hot rolled stainless steel strip 2 that has been annealed and pickled undergoes the following steps according to the processing order. That is, the stainless steel strips unwound from one or a plurality of unwinders 1a and 1b are connected to each other by the laser beam welding machine 3 to form a continuous body, and enter the looper 4. The looper 4 is equipped with a large number of winding rolls capable of expanding and contracting the passage of the stainless steel strip 2 so that the residence time of the steel strip 2 in the looper 4 can be adjusted. This time adjustment is performed, for example, in order to absorb the strip running time during welding of the steel strip 2 and the rest time for shearing the steel strip on the rolling-out side. Next, the stainless steel strip 2 enters the heating device 5 having a large furnace length from the looper 4, and is heated and maintained at a predetermined temperature (not exceeding 200 ° C.) for a period of time during which recrystallization does not occur. Reference numeral 6 is a steering device as a meandering correction device for correcting the meandering of the stainless steel strip 2 before entering the rolling mill. Reference numeral 7 denotes a small heating device provided immediately before the entrance side of the tandem rolling mill 8. The stainless steel strip 2 that has passed through the heating device 5 passes through the steering device 6, and the temperature of which heat radiation is reduced is restored to the original temperature. It is heated to a predetermined temperature to prevent the deformation resistance from increasing during the next tandem rolling. 10 is a strip that is warm-rolled by the tandem rolling mill 8 and is wound by the rewinding machines 11a and 11b, respectively, and when the wound coil diameter reaches a predetermined value, it is sheared by the running shear 9 It has become so.

Next, the operation will be described.

The rewound stainless steel strip 2 is a laser beam welding machine 3
Are connected by continuous rolling as a continuous body, the amount of off gauge can be reduced, and the yield and the like can be improved.
Here, laser beam welding is performed in MIG welding or flash butt welding because the heat input to the weld is large and coarsening of crystal grains occurs in the heat-affected zone to reduce welding strength. This is to prevent an increase in the frequency of breakage from the welded portion. Fig. 2 shows the strength of each welding method by repeated bending tests, and it can be seen that the strength of laser beam welding is remarkably strong.

In addition, the stainless steel strip 2 is placed in the heating device 5 having a large furnace length.
The increase in cold work hardening is reduced as shown in FIG. 3 by heating at a predetermined temperature not exceeding 200 ° C. for a time that does not cause recrystallization. In the figure, the horizontal axis shows the heating temperature of the stainless steel strip, and the vertical axis shows the martensite that occurs in the steel strip 2 as a volume ratio. A diagram showing the three levels of reduction ratio γ of 10, 20, 30%. Is. From this figure, it can be seen that the amount of martensite produced decreases as the plate temperature increases.
Further, when the rolling reduction is 10%, the amount of production and the amount of reduction are slight, and it shows a straight line that is almost horizontal, but when the rolling reduction is high, the remarkable martensite production is in proportion to the rolling reduction and the plate temperature is near 80 ° C. Rapidly decreases (more than half) by heating up to 80
When the temperature exceeds ℃, the decreasing tendency becomes gradual and the rolling reduction is 10%.
It is almost the same as the case of.

That is, when the stainless steel strip is heated and cold-rolled, the amount of martensite produced is reduced and the rolling load can be reduced. In addition, since it also has the effect of suppressing the increase in deformation resistance due to normal work hardening, in the case of a metastable austenitic stainless steel strip, this heating greatly contributes to reducing the rolling load or improving the rolling reduction. is there.

As described above, the cold rolling can be advantageously performed by increasing the temperature of the stainless steel strip, but if it is too high, the problem of temper color occurs. FIG. 4 shows the degree of occurrence of the temper color by a color difference meter. In the figure, the horizontal axis represents the plate temperature, and the vertical axis represents the color difference meter output (b value). It can be seen from this that when the plate temperature exceeds 200 ° C., a temper color is rapidly generated. That is, when cold rolling a stainless steel strip or a metastable austenitic stainless steel strip among them, with a tandem rolling mill, it is advantageous to heat the steel strip so that the temperature does not exceed 200 ° C. , Its temperature 80
It is desirable to keep it within the range of ~ 200 ° C.

However, even if the stainless steel strip 2 is heated by the heating device 5 as described above, the above effect cannot be obtained unless the lowering of the plate temperature due to heat radiation in the steering device 6 before entering the tandem rolling mill 8 is compensated. Now, assuming that the path length of the stainless steel strip 2 in the steering device 6 is 15 m, the temperature drop due to heat dissipation in the atmosphere is about 1 ° C./sec. Therefore, in the speed pattern shown in FIG. Then, a temperature difference of 16.2 ° C on the outlet side occurs, which changes the deformation resistance by about 10%, which causes a change in the final thickness of the stainless steel strip.

Therefore, in the present invention, the small heating device 7 is arranged on the exit side of the steering device 6 and in the immediate vicinity of the entrance side of the tandem rolling mill 8 to accurately compensate for the decrease in temperature that occurs when the steering device 6 is passed. Thus, the temperature of the steel strip on the inlet side of the rolling mill 8 is kept constant.

The heating device 5, 7 may be any device such as an induction heating device, a direct furnace, a radiant tube burner type furnace, etc., but a gas jet for blowing a combustion gas generated from a separately provided combustion device onto a steel strip. The heating device is more preferable because the device is simple and can easily cope with changes in the steel strip speed.

FIG. 5 shows another embodiment.

This is a tensioning device 12 between the large and small heating devices 5 and 7.
And a tandem rolling facility in which the steering device 6 is arranged. This tension applying device 12 is a rolling mill for stainless steel strip 8
The tension on the entry side of the steel strip is increased to improve rolling property, and the steel strip tension in the large-sized heating device 5 is reduced to prevent width shrinkage due to creep deformation of the steel strip during heating. . The operation other than the above is the same as that of the above embodiment.

〔The invention's effect〕

As described above, according to the present invention, even a steel strip of a material that is significantly work-hardened, such as a metastable austenitic stainless steel strip, is deteriorated in rollability by an ordinary tandem rolling mill, and troubles such as plate rupture are caused. The continuous cold rolling can be stably performed without causing the occurrence, and therefore, great effects such as improvement in production capacity, improvement in yield, and reduction in production cost can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an embodiment according to the present invention, FIG. 2 is a strength comparison diagram of a welded portion by each welding method of steel strips, and FIG. 3 is a relationship between heating temperature of steel strips and martensite formation amount. 4 is a diagram showing the relationship between the heating temperature of the steel strip and the occurrence of temper color, FIG. 5 is another embodiment and a schematic explanatory diagram, FIG. 6 is a schematic explanatory diagram of a conventional example, FIG. 7 is a diagram showing a pattern of steel strip speed depending on time. 1a, 1b …… Rewinder, 2,10 …… Stainless steel strip, 3 …… Laser beam welding machine, 4 …… Storing device (looper),
5 ... Heating device, 6 Meandering correction device (steering device), 7 ... Small heating device, 8 ... Tandem rolling mill.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-56-102519 (JP, A) JP-A-58-196102 (JP, A) JP-A-60-137503 (JP, A)

Claims (1)

[Claims] 1. A continuous rolling facility having a rewinding machine for rewinding a steel strip and a tandem rolling mill for rolling the rewound steel strip,
Between the rewinding machine and the tandem rolling mill, according to the processing order, a laser beam welding machine for connecting stainless steel strips, a storage device for temporarily storing the stainless steel strips in the strip, and a stainless steel strip. A heating device for heating, a meandering correction device for correcting meandering of the stainless steel strip, and a small heating device for heating the stainless steel strip whose temperature has been lowered due to heat radiation during passage of the strip are arranged in sequence. Characteristic continuous warm rolling equipment for stainless steel strip.