JP3224289B2 - Hot joining method of steel plate or steel coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hot-joining steel plates or steel coils and forming a welded portion which does not break even after being worked by rolling or the like.

[0002]

2. Description of the Related Art In a steel manufacturing process, continuous rolling by joining the end faces of a steel plate or a steel coil has been put to practical use in the cold rolling which is a lower step. That is, a looper is provided in the middle of the cold rolling process to secure a sufficient welding time, and as a highly reliable welding means, for example, laser, resistance seam welding, flash butt welding, or the like is employed, and the end face of the steel sheet or the steel coil is used. They are joined together.

However, in the hot rolling, which is the upper process,
There are various restrictions such as high temperature, thick plate thickness, and the inability to provide a looper.The method of joining steel sheets and steel coils for efficient continuous rolling is naturally limited, and the joining time is long. It is not possible at present. In hot joining of steel sheets and steel coils, the surface to be joined is exposed to the air, so scale growth starts immediately after crop shearing, and if this scale remains on the joining surface, there is a major problem that solid phase joining becomes difficult. .

One of the methods for joining steel sheets and steel coils at a high temperature is hot solid phase welding.
And Japanese Patent Application Laid-Open No. 60-240304 disclose the method. In this method, in order to suppress the generation of oxide scale on the surface to be joined, for example, a method of covering the joining surface with an antioxidant has been proposed. Hot solid-phase bonding is possible by rolling if the generation of oxide scale is prevented, but it is quite difficult to cover the entire bonding surface with an antioxidant on an actual line.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method capable of reliably joining hot steel end faces of steel plates or steel coils even when such scales are generated. . That is, even if the scale is present, it is sufficient to completely remove the scale so that there is no problem at the bonding interface. One method is a mechanical removal method, but it is difficult to confirm whether or not the removal was successful at a high temperature, which is not practical.
Another way is to completely dissolve and let it surface or make it harmless. The present invention has been made based on the latter idea.

[0006]

According to the present invention, there is provided a method for hot joining two end faces of a steel plate or a steel coil , wherein the temperature of the steel plate or the steel coil is 800 to 1000 ° C.
Alternatively, the joints where the ends of the steel coils are joined to each other are welded by a butt arc welding method with a penetration depth of 90% or more of the plate thickness, and the ends of the steel plates or steel coils are upset within 15 seconds from the start of welding. A hot joining method for a steel plate or a steel coil, characterized in that oxides caused by scale are removed from the joints by the method.

[0007]

The operation of the present invention will be described in detail. When hot joining steel plates or steel coils, in order to detoxify the oxide scale on the surface to be joined, a method is to melt this scale together with the steel and float it as an oxide in the molten metal. Most sure. Although there are several possible melting methods, arc welding is a method that can be performed at low cost in terms of equipment.

[0008] That is, the method of joining the end surfaces of a steel plate or a steel coil to each other and integrating the oxide scale with the molten metal by arc welding is the lowest cost and reliable method. I could n’t surface,
The scale generated at high temperatures will remain in the weld metal, but the scale generated at high temperatures will be a cause of breakage from the welded part during the subsequent process of rolling if it remains in the weld metal. desirable.

Further, when the workpiece is at a high temperature of 800 ° C. or more,
It takes time to solidify and cool the weld metal, and if rolling is performed before the temperature becomes the same as that of the base metal, uneven rolling will occur due to the temperature difference. In order to solve these problems, it is necessary to melt the steel sheet once, and then immediately remove the steel sheet or the steel coil by an upset that presses and presses the end faces of the steel coil. Therefore, in the present invention, a method of upsetting after welding is adopted. In order for this method to be effective,
As shown in FIG.
A penetration depth P of the weld metal 2 of 90% or more is required, and the thickness t of the steel plate (or steel coil) 1 as shown in FIG.
When the partial penetration depth ratio P of the weld metal 2 is less than 90%, the unmelted portion of the base material is disturbed, and upset cannot be performed well.

[0010] Even if the penetration is complete, the coagulation proceeds sufficiently if the timing of the upset is delayed, so that the upset becomes difficult as a result. Therefore, the upset must be performed within 15 seconds after the start of welding. Within this time range, the welded portion remains unsolidified and can be upset. Also steel plate or steel coil to be welded
Must be 800-1000 ° C. The temperature is 8
If the temperature is lower than 00 ° C, the heat removal rate of the weld metal increases, and
Solidification is likely to occur and upset becomes insufficient. I
If the temperature is lower than 800 ° C, only high temperature welds
Is rolled, while the temperature of the base metal is low.
There is a problem that the load is large. The temperature is 1000 ℃
Above, the scale generated will be thicker and
Cause of breakage from the welded part during rolling in the subsequent process
Becomes As a matter of course, when welding is performed with complete penetration, a backing for preventing burn-through is required. In addition, in order to upset within 15 seconds after the start of welding, the length that can be welded is limited. However, if a plurality of welding torches are used, there is no particular problem with a wide steel plate or steel coil. Upsets can also be expected to be effective in preventing blood vessels such as weld cracks.

[0011]

An embodiment of the present invention will be described. The steel plate of rolled steel material SM490 for welding structure having a width of 200 mm, a length of 300 mm, and a thickness of 12 mm shown in FIG. 3 was heated in a heating furnace, and butt MIG welding was performed at a high temperature. Table 1 shows the welding conditions.
The penetration depth ratio was changed by changing the welding current among the welding conditions. Also, the time conditions for upsetting after the start of welding were changed. Immediately after the end of the upset, the test piece was continuously rolled by a small rolling mill of 7 stands, and the condition of the joint after rolling was observed.

[0012]

[Table 1]

The penetration ratio was measured by separately preparing a non-rolled test piece. Table 2 shows the rolling results after welding. In Examples A1 to A5 of the present invention, the upset exerted a sufficient effect, and a joined portion having no problem was obtained even after rolling, whereas the comparative example had problems.

[0014]

[Table 2]

That is, in the case of B-1, the penetration depth ratio is only 60% and the root base metal remains, so that upset cannot be performed sufficiently, and the oxide in the weld metal in the remaining root is extremely large. It broke before rolling to the end. Since the base material temperature in B-2 is 750 ° C. and lower, heat extraction rate of the weld metal is also increased, partly in spite of upset within 15 seconds after the start of the weld solidification is completed, somewhat insufficient upset Became. Therefore, there is a problem that only the high-temperature weld is elongated, and conversely, the base material has a low temperature, so that the load on the rolling mill is large.

In B-3, the upset was performed 20 seconds after the start of welding, so that non-uniform elongation occurred as in B-2. B-4 and B-5 showed the same tendency as B-1 because the penetration depth ratio was as low as 80%. B-6 is an example in which upset was not performed, but a large amount of oxides remained in the weld metal, or cracks presumed to be caused by welding defects occurred, and the rolling elongation of the weld was large. There's a problem.

[0017]

As described above, according to the present invention, it is possible to stably join a steel plate and a steel coil, which had been a problem in the past, in a hot state, and to obtain a welded portion which can sufficiently withstand continuous hot rolling. Therefore, it is possible to significantly reduce costs in the steel manufacturing process.

[Brief description of the drawings]

FIG. 1 is a side view showing a penetration depth ratio of the present invention.

FIG. 2 is a side view showing an insufficient penetration depth ratio of a comparative example.

FIG. 3 is a perspective view showing a test piece used for hot bonding of an example of the present invention and a comparative example.

[Explanation of symbols]

 1 steel plate or steel coil 2 weld metal P penetration depth t plate thickness

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B21B 15/00 B21B 1/26 B23K 9/025

Claims (1)

(57) [Claims] 1. A method for hot joining the end faces of a steel sheet or a steel coil, wherein the temperature of the steel sheet or the steel coil is
800 ~ 1000 ℃, the end of the steel plate or steel coil butted joints are welded by butt arc welding method with a penetration depth of 90% or more of the plate thickness, within 15 seconds from the start of this welding A hot joining method for a steel plate or a steel coil, wherein an oxide caused by scale is removed from the joined portion by upsetting end faces of the steel coil.