JPH08281306A - Manufacture of wide-width steel strip - Google Patents

Abstract

PURPOSE: To complete finish processing at one time by making several steel strips which are manufactured with a strip casting device into wide width by continuously welding by laser beam welding or mash seam welding and executing finish processing. CONSTITUTION: The steel strip 2 having a fixed width is manufactured with the strip casting device (SC device) 1. The steel strip 2 is fed to a welding stage in a coil shape. Two steel strips 2, 2 having the same thickness and same material are fed side by side in a butted state. The steel strips 2, 2 are made into wide width by welding the strips continuously in the longitudinal direction by laser beam welding or mash seam welding and a wide-width steel strip 3 is made. It is preferable to preliminarily cut the butt-welded place with a rotary shear. The finish processing such as pickling, cold rolling, annealing and skin pass rolling is applied to the wide-width steel strip 3. Since welding materials are not used in the laser beam welding and mash seam welding, the material of the wide-width steel strip 3 is continuous. In this way, cost merit of strip casting is achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a wide steel strip having an arbitrary width from a steel strip having a constant width produced by a strip casting apparatus.

[0002]

2. Description of the Related Art A so-called strip casting (hereinafter also referred to as SC) apparatus for directly casting a steel strip from molten steel by using twin rolls has been developed. In SC,
Since there is no need for the conventional hot rolling process of rolling a slab into a steel strip, there is an advantage that a product can be manufactured at low cost. On the other hand, since the width of the steel strip is almost equal to the length of the roll, it is always constant. Moreover, the maximum width of the steel strip by SC is limited to within about 1000 mm due to equipment cost and various technical restrictions.

In the conventional production of steel strip by a hot rolling mill, a slab having a width approximately equal to the product width is used, so that a steel strip of any width can be obtained within a range not exceeding the mill width.

By the way, the significance of producing a wide steel strip is not merely to solve the problem of productivity.

For example, large parts such as integrally molded truck chassis require wide steel strips or steel plates. In recent years, in order to meet such needs, a tailored blank (widening) technology has been developed for manufacturing a wide cold rolled steel strip by laser welding from a narrow cold rolled steel strip manufactured by a narrow mill. There is.

FIG. 6 is a schematic process diagram for explaining a method for manufacturing a wide steel strip by the above-mentioned conventional tailored blank technique and an example of obtaining a product using this steel strip as a raw material. Two separately cut plate-shaped or coil-shaped narrow-width cold-rolled steel strips 5, 5 finished cleanly are butted and laser-welded into a wide steel strip 3, for example, an integrally molded blank material 6 is manufactured.

[0007]

[Problems to be Solved by the Invention]

(1) Widening of steel strip has been applied to cold-rolled steel strip until now (for example, Application of Laser-Beam-Welded Sheet M
et al, SAE Technical Paper Series, 890853, 1989). The wide steel strip manufactured by the tailored blank technology is formed as it is welded, and the welded portion remains in the product as it is. The weld has unavoidable irregularities such as excess, undercut, and bead ripple, and the surface treatment is lost at the weld and oxide scale is attached.

Therefore, in order to obtain one wide cold-rolled steel strip having a uniform surface property by the tailored blank technique, after laser welding, pickling, cold rolling, and further surface treatment if necessary. It requires double pickling and cold rolling costs.

Even when a steel strip manufactured by SC is used, it may be possible to further widen (tailored blank) after further pickling and cold rolling. However, even in this method, two or more steel strips to be welded are separately pickled and cold-rolled, and thus work costs associated with each process are required, which is costly.

To obtain a wide steel strip by the tailored blank technology using two cold-rolled coils as raw materials, the process is (material coil production × 2 + wide steel strip production).
A total of three pickling and cold rolling steps are required.

(2) At present, the tailored blank technology is applied only to parts other than the exterior of the product, that is, parts to be used in a portion where the laser welding beat, which is a problem in appearance, cannot be seen from the outside. Therefore, it can be said that the tailored blank material cannot be used as a material for an exterior material of an automobile if it is ordinary steel, and as a material for a large product such as a bathtub that requires appearance performance if it is stainless steel.

The present invention has been made to solve the above problems (1) and (2), and the object of the present invention is to
It is an object of the present invention to provide a low-cost method for manufacturing a wide steel strip that can be applied to a component that is required to have an appearance performance, from the steel strip (hereinafter, also referred to as SC steel strip) manufactured in 1.

[0013]

The gist of the present invention resides in the following method for manufacturing a wide steel strip.

The widthwise ends of a plurality of steel strips having a constant width, the same thickness and the same material produced by the strip casting device are butted and the butted portions are made longitudinal by the laser welding or mash seam welding. A method for producing a wide steel strip, which comprises continuously welding and widening the steel to widen it, and then subjecting it to finishing treatments such as pickling and cold rolling.

The "finishing treatment such as pickling and cold rolling" referred to in the above method means pickling, cold rolling, refining in a reducing atmosphere,
And skin pass rolling (surface treatment temper rolling).

In the above method, the desirable range of steel strip temperature during welding is 200 ° C. or more and 500 ° C. or less. Further, a desirable cold rolling condition when applying laser welding is that the relationship between u and r defined by the following formula and formula satisfies r ≧ 3u.

U = [(front side UC amount + back side UC amount)] / plate thickness before rolling ... r = 1- (plate thickness after rolling / plate thickness before rolling) ...・ ・ However, UC means undercut.

[0018]

The method of the present invention for obtaining a wide steel strip from an SC steel strip will be described with reference to FIG.

FIG. 1 is a conceptual diagram illustrating an example of the method for manufacturing a wide steel strip according to the present invention. In this case, S using twin rolls
Steel strip 2 of a constant width manufactured by the C device 1 in the usual manner
Is sent to the next welding step in a coil shape without any particular cooling. In this process, two steel strips 2 and 2 having a constant width, the same thickness and the same material are fed side by side in a state of being abutted as shown in the drawing, and are continuously laser welded in the longitudinal direction of the steel strips 2 and 2. Wide welding is performed by mash seam welding to obtain a wide steel strip 3. However, it is desirable to cut the butt welding points in advance with a rotary shear (not shown).

Next, pickling (not shown), cold rolling, refining in a reducing atmosphere, skin pass rolling (surface treatment temper rolling)
A cold-rolled wide steel strip is manufactured by performing a finishing process such as.

The SC steel strip to be welded is not limited to two as shown in FIG. 1 and may be three or more. Further, the width of each SC steel strip may be different.

The reason why the welding method is limited to the laser welding or the mash seam welding is that these methods do not use a welding material, so that the material of the wide steel strip obtained is continuous and other welding is performed. This is because it is faster than the method.

Desirable methods and conditions for these weldings are as follows.

In laser welding, a laser oscillator having an output range of 3 to 25 kW is used, and laser light is emitted at a focal length range of 60 to 3.
A beam diameter range of 0.2 to 1.0 mm was narrowed down by a 00 mm lens, and the ends of two steel strips cut by a rotary shear were irradiated to the abutted portion, and the steel strip was longitudinally stretched at 3 to 25 per minute.
Weld while feeding in the speed range of m.

In the case of mash seam welding, similarly, two steel strips are overlapped at their ends by about 1 to 3 mm and the diameter is 50 mm.
Scissors with opposing rotating electrodes of ~ 500 mm, 8-5
Apply a current in the range of 0 kA and set the pressure range to 300.
~ 2000 kgf, steel strip feed speed range 3 to 3 per minute
Weld as 0 m. At this time, the weld bead becomes convex and roll scratches are likely to occur in the cold rolling process. Therefore, it is recommended to provide a bead grinder behind the rotary electrode and continuously grind the extra deposit.

In any of the above welding methods, a desirable welding temperature is 200 at one or both temperatures of the steel strip.
℃ or above.

In laser welding, the bead width is as narrow as about 1 mm, and insufficient penetration easily occurs. It is considered that when welding is performed in a state where the temperature of the steel strip immediately after being manufactured by SC is high, the bead width is widened and insufficient penetration is unlikely to occur. However, as a result of investigation by the present inventor, it was found that the bead width was significantly widened, and as a result, the steel strip temperature at which the splitting resistance of the weld line portion was improved was approximately 200 ° C. or higher. Welding was performed in a state where one or both of the temperatures were in the temperature range of 200 ° C. or higher. A desirable upper limit of the steel strip temperature is 500 ° C.

The temperature of at least one of the steel strips needs to be within the above temperature range because the bead width expansion effect can be obtained to some extent only with one of them.

Performing welding at such a high temperature is effective for improving welding efficiency, and the welding speed can be increased in both laser welding and mash seam welding.

In the method of the present invention, desirable conditions for cold rolling when laser welding and subsequent cold rolling are applied in combination are undercuts of welding beat (hereinafter, U).
The ratio between the total value of the front and back of the amount and the sheet thickness before rolling is u
Then, the reduction ratio r of the wide steel strip after welding satisfies the condition of r ≧ 3u.

By this method, it is possible to achieve a further improvement in appearance performance such that the steel strip widened by laser welding can be used as an exterior material.

FIG. 2 is an external view of a wide steel strip for explaining the cold rolling conditions. Fig. 2 (a) shows the wide steel strip 3 after laser welding, and Fig. 2 (b) shows the wide steel strip 4 after cold rolling. The above u and r are defined by the following formulas and formulas, respectively.

U = [(front side UC amount + back side UC amount)] / plate thickness before rolling ... r = 1- (plate thickness after rolling / plate thickness before rolling) ... .. In laser welding, UC occurs due to gaps that the welded part inevitably has and the irregular shape of the end surface. Even in this state, it can be used as a product of just a wide steel strip, but it is not suitable for the application requiring the above-mentioned appearance performance. Therefore, a method of eliminating UC by utilizing plastic deformation due to cold rolling was examined. As a result, it was found that if the reduction ratio r of the cold rolling was such that the condition of r ≧ 3u was satisfied, the UC portion was leveled like the base material, and the weld seam became invisible.

In the method of the present invention, at least one steel strip temperature is 200 ° C. or higher, laser welding is used, and r ≧ 3u.
When the above conditions are satisfied, the following effects can be obtained.

By setting the temperature of at least one of the steel strips to 200 ° C. or higher, it is possible to obtain an effect that the surface texture becomes relatively uniform as the bead width increases. R in cold rolling in the subsequent process
By satisfying the condition of ≧ 3u, a product having an extremely excellent appearance can be obtained by the synergistic effect of both.

In the method of welding SC steel strip as in the method of the present invention, finishing treatments such as pickling, cold rolling, refining, skin pass rolling (surface treatment temper rolling), etc. are performed in a wide process in the next step. Compared with the conventional tailored blank, that is, the method of preparing two or more steel strips finished separately into clean narrow cold-rolled steel strips, welding them, and then pickling and cold rolling again. , Low cost.

Further, from the comparison of the material narrow coil lengths,
Since the SC steel strip also has a shorter welding length than the cold-rolled steel strip, the welding cost in the method of the present invention is also advantageous.

[0038]

【Example】

(Test 1) The twin roll SC device shown in FIG.
mm, a plate width of 600 mm, and a length of 200 m were prepared from three kinds of steel strips, and these steel strips were first welded at room temperature. The material is JIS-SUS304 (18% Cr, 8
% Ni, balance Fe and impurities), SUS430 (17
% Cr, balance Fe and impurities), SPHD (0.04
% C-0.2% Mn, balance Fe and impurities).

As shown in FIG. 1, welding is carried out by two welding lines or by using FIG. 3 (a).
As described above, laser welding and mash seam welding were used for the three steel strips 2.

In laser welding, a laser oscillator with an output of 10 kW is used, and as shown in FIG. 3B, the laser beam 8 is focused by a lens 9 having a focal length of 254 mm to a beam diameter of 0.5 mm.
The ends of the two steel strips 2 cut by the rotary shear 7 are irradiated to the abutted portions as shown in FIG. 3 (a), and the steel strips 2 are fed in the longitudinal direction at a speed of 10 m / min for welding. .

In the mash seam welding, as shown in FIG. 3 (c), similarly, two steel strips 2 which are overlapped by 2 mm at the ends are sandwiched by opposing rotary electrodes 10 each having a diameter of 300 mm, and a distance of 30 k.
A current of A was applied, welding was performed at a pressing force of 1500 kgf and a steel strip feed rate of 5 m / min, a bead grinder 11 was provided behind the rotary electrode 10, and the extra scale 12 was continuously ground.

The thus widened welded steel strip is subjected to pickling, cold rolling, refining in a reducing atmosphere, skin pass rolling, and finally a cold-rolled wide steel strip having a plate thickness of 1.6 mm (two strips are used). A width of about 1200 mm and a width of about 1800 mm were produced for three pieces.

As a result, it was confirmed by the method of the present invention that a wide steel strip can be obtained by a single pickling and cold rolling, and a significant cost reduction can be achieved.

(Test 2) Two of the same three kinds of materials as above
Using the SC steel strip as a material, the temperature of each steel strip is room temperature, 10
Laser welding is performed at four levels of temperatures of 0 ° C, 200 ° C, and 300 ° C, followed by pickling, cold rolling, pure annealing, and skin pass rolling.
A cold rolled wide steel strip having a width of 1200 mm, a length of about 300 m and a plate thickness of 1.2 mm was manufactured.

The surface of the welded portion was substantially flat at a steel strip temperature of 200 ° C. or higher, but became slightly concave at 100 ° C. or lower.

Next, according to the method shown in FIGS. 4 (a) and 4 (b), a bulge test for pushing a cylinder with a steel ball having an outer diameter of 40 mmφ at 100 points at intervals of 3 m on each of these weld lines Was carried out and the occurrence of cracks in the weld line portion was investigated.

For the evaluation, a standard was adopted in which a crack at the welding line up to a depth of 15 mm was regarded as a defect. The results are shown in Table 1.

[0048]

[Table 1]

As shown in Table 1, a defect rate of 0% was achieved at a steel strip temperature of 200 ° C. or higher regardless of the steel type.

(Test 3) In the wide steel strip laser-welded under the conditions of the above-mentioned Test 1, the above-mentioned total UC amount was 0.5 mm as shown in FIG. 5 (a) (u = 0.19). . Therefore, after rolling by changing the reduction ratio r of cold rolling, the direction A-B perpendicular to the welding line was obtained by the method shown in FIGS. 5 (b) and 5 (c).
The roughness in the vicinity of the weld line between, that is, the step difference was measured on both the front and back sides of the cold-rolled wide steel strip 4.

As an evaluation criterion, when the step difference was 5 μm or less, there was no problem in appearance and the condition was good. The results are shown in Table 2. However,
The step is shown by the larger value of the front and back.

[0052]

[Table 2]

The step difference is r = which satisfies the relation of r ≧ 3u.
Under the conditions of 0.61 and r = 0.81, it was 5 μm or less, which is not a problem in appearance. On the other hand, r ≧ 3
Under the condition of r = 0.40 where the relationship of u was not satisfied, it was 11 to 12 μm, and the appearance was somewhat poor.

(Test 4) In Test 2, the temperature of the steel strip was 200 ° C.
For wide steel strip obtained by laser welding as
Cold rolling was carried out under the condition of r = 3u, and the step difference was examined as in Test 3. As a result, the level difference was significantly reduced to around 0.5 μm, and the appearance performance was greatly improved compared to the case of Test 3.

Table 3 shows the results of comparing the steps in the above-mentioned Tests 1 to 4 with the case of the wide steel strip by the conventional tailored blank technique.

[0056]

[Table 3]

As is clear from Table 3, according to the method of the present invention, it is possible to obtain a wide steel strip having excellent appearance performance of the welded portion.

[0058]

According to the conventional SC method, only steel strips having a relatively narrow constant width can be obtained. In order to obtain one wide cold-rolled steel strip by applying a tailored blank to these steel strips, a double acid strip is used. Processes such as washing and cold rolling and work costs are required.

According to the method of the present invention, by welding the SC steel strip to widen it, the work such as pickling and cold rolling can be performed only once.
Originally, the cost advantage of SC that can omit hot rolling can be utilized. Furthermore, to prevent welding defects by proper welding conditions, or by proper cold rolling conditions,
It is also possible to produce a steel strip having excellent appearance performance that can be used as a material for press-molding a large exterior material.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating an example of a method for manufacturing a wide steel strip according to the present invention.

FIG. 2 is an external view of a wide steel strip for explaining cold rolling conditions. (a) shows after laser welding and (b) shows after cold rolling.

FIG. 3 is a diagram illustrating a manufacturing method used in an example (Test 1). (a) and (b) show the case of laser welding and (c) shows the case of mash seam welding.

FIG. 4 is a diagram illustrating a bulge test method used in an example (Test 2). (a) is the measurement position and (b) is the method of pushing the steel ball.

FIG. 5 is a diagram illustrating a step difference measuring method used in Examples (Tests 3 and 4). (a) is the situation after welding, (b) and
(c) is the definition of measurement direction and step.

FIG. 6 is a diagram illustrating a conventional method (tailored blank technique).

[Explanation of symbols]

1: Strip casting (SC) device,
2: SC steel strip, 3: welded wide steel strip, 4: cold rolled wide steel strip, 5: narrow cold rolled steel strip, 6: integrally formed blank material, 7: rotary shear, 8: laser light, 9 :
Lens, 10: rotating electrode, 11: bead grinder, 12: extra scale

Claims (1)

[Claims] 1. A butt portion of a plurality of steel strips having a constant width, the same thickness and the same material manufactured by a strip casting device is abutted with each other in the width direction, and the abutted portion of the steel strip is welded by laser welding or mash seam welding. A method for producing a wide steel strip, which comprises continuously welding in the longitudinal direction to widen the steel, and then subjecting it to finishing treatments such as pickling and cold rolling.