JPH0857501A - Joining method of continuous hot-rolled billets - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an on-line joining method of steel billets for performing hot rolling of steel billets with a completely continuous material. [Structure] When hot rolling a steel slab having a thickness of 10 to 100 mm, a plurality of steel slabs heated to 800 to 1400 ° C.
The end portion of the preceding steel piece and the beginning portion of the following steel piece are butted, the plate-shaped consumable electrode is made parallel to the butted portion, and gas shield arc welding is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining steel slabs used when continuously hot rolling steel slabs.

[0002]

2. Description of the Related Art Steel products are manufactured through refining, casting and hot rolling processes. Depending on the product, cold rolling is then performed. Most of casting is performed by continuous casting, and cold rolling is often performed continuously. However, in the current state of hot rolling, the surface of the slab or bloom is once repaired and then rolled intermittently. If this hot rolling can be made continuous, stable quality and a significant improvement in manufacturing efficiency are expected. This requires a simple joining method for slabs and blooms.

However, the economical rolling time for one slab is about 10 to 20 seconds, and the joining by hot rolling needs to be performed in a shorter time than this. For example, JP-A-6-71
As disclosed in Japanese Patent No. 307, a method has also been proposed in which the ends of the steel pieces to be joined are shaped into an easy shape for joining and the force of hot rolling is used for joining. However, in this case as well, it is difficult to perform reliable joining because it is difficult to control the temperature of the billet or an oxide is formed on the joining surface. For this reason, welding that is usually performed for joining steels is preferable because of high reliability of joining.

[0004]

However, the thickness of the hot-rolled steel strip is usually about 50 mm, and it is difficult to join it by ordinary covered arc welding, submerged arc welding, gas shielded arc welding or the like. For example, covered arc welding and submerged arc welding cannot be applied because slag is produced. Further, in gas shielded arc welding, in order to weld a long welding line in an extremely short time, the electrodes must be moved at high current and at high speed. This requires a driving device with excessive power, and also has a high arc force, which causes a problem that the molten pool retreats abnormally for a long time. On the other hand, for example, joining of high energy beams such as laser welding as disclosed in Japanese Patent Laid-Open No. 5-200410 can be considered. However, high-energy beam welding is also very difficult because there is a restriction that the opening of the groove is usually about 0.5 mm or less. An object of the present invention is to provide a joining means that can withstand the tensile force of hot rolling for an extremely short time, which is necessary for continuously hot rolling a steel slab.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is that when hot rolling a steel slab having a thickness of 10 to 100 mm, a plurality of steel slabs heated to 800 to 1400 ° C. A joining method for continuous hot-rolled steel slabs, characterized in that a terminal end and a starting end of a subsequent steel slab are butted, a plate-shaped consumable electrode is made parallel to the abutment, and gas shield arc welding is performed.

[0006]

1 is a perspective view showing the welding method of the present invention.
FIG. 3 is a conceptual diagram of a continuous hot rolling line to which the present invention is applied. In FIG. 2, 1A, 1B, 1C, 1D, and 1E are steel billets, and 5A and 5B are rolling rolls, showing two stands. Reference numeral 2 is a welding apparatus for carrying out the joining method of the present invention, and FIG. 1 is an enlarged view of the welding apparatus. Again 4
Is a shear for cutting the end of the steel piece, and 3 is a heating device. In FIG. 2, the heating device 3 is on the extension of the pass line of the rolling mill, but when multiple heating devices are used, they are installed aside and the steel pieces are alternately extracted from the multiple heating devices onto the roller table. How to do it.

In FIG. 2, 6 is a plate-shaped consumable electrode, and 7 is a feed roll. A welding torch 8 is provided with a gas shield nozzle for ejecting a shield gas from the lower portion, and contacts the consumable electrode 6 to supply electric power. In the figure, 9 is a shield gas supply pipe, 11 is a power supply line, and 10 is a cooling water pipe (water supply / drainage 2 for cooling the torch with water).
Only one of the books is shown).

In the present invention, the steel plate has a plate thickness of 10 to 100.
mm. If it is less than 10 mm, the advantage of the present invention is small, so that it is 10 mm or more, and if the sheet thickness exceeds 100 mm, it is usually unsuitable for continuous rolling because it is rolled a plurality of times by the same rolling mill. The heating temperature of the billet is 800 to 14
Set to 00 ° C. The higher the billet temperature, the softer the billet and the deeper the weld penetration. Since the joint strength required for the first rolling is obtained at 800 ° C or higher and the hardness is such that hot rolling is possible, the temperature is set to 800 ° C or higher, and if it is heated to too high temperature, the oxidation is large, and the solidification after welding is slow. Therefore, the temperature was set to 1400 ° C or lower.

In welding, a plate-shaped consumable electrode 6 is used in gas shielded arc welding and is attached parallel to the welding line. The plate thickness of the plate-shaped consumable electrode is preferably 0.2 to 2 mm, and if it is too thin or too thick, there are problems such as unstable feeding of the electrode. The plate width of the consumable electrode is 2
0 to 300 mm is preferable, and if it is less than 20 mm, the effect of widening the plate width is small. Further, if the diameter exceeds 300 mm, there is a problem that the shield or the torch for power feeding becomes very large, or stable welding is difficult.

If a plate-shaped consumable electrode is used, a long welding line can be welded even if an arc is generated for a very short time of 3 to 5 seconds.
Therefore, even if the electrode does not move in the welding line direction, a welding length corresponding to the electrode width can be obtained, it is not necessary to move the electrode in the welding line direction at high speed, and the molten pool does not retreat for a long time. Further, if the electrode is moved along the welding line, the welding length becomes longer accordingly. Since the movement of the electrodes in the welding line direction is complicated, it is preferable to adjust the electrode width or adjust the electrodes by a plurality of electrodes. The electrode width and the number of electrodes are selected according to the width and plate thickness of the steel piece. Since the steel pieces are joined while being rolled, the welded portion naturally moves in the rolling direction. For this reason,
The consumable electrode also needs to move in the rolling direction at the same speed as the billet as the billet moves.

It is most preferable that the steel pieces are joined uniformly on the entire line, but it is not always necessary to join them uniformly on the whole line as long as they are joined in an amount that can withstand the tensile force of the rolling mill. Usually, 15% or more of the steel slab cross-sectional area should be joined. For this reason, when the width of the steel slab is wide, even if the steel pieces are intermittently joined at a plurality of points, the total of the joint cross-sectional areas may be 15% or more of the steel slab cross-sectional area. At this time, it is preferable that both ends of the butted portion are joined.

The material of the plate-shaped consumable electrode may be the same as that for ordinary welding. When steel is joined, iron is the main component,
C, Si, as a deoxidizing material and a strength adjusting material,
Components such as Mn, Cu, Ni, Cr, Mo, Nb, Ti, and Al are added within the range of about 3% if necessary. When applied to stainless steel, heat resistant steel, etc., it contains 3 to 60% of Ni, Cr, Mo and the like.

The welding shield gas is a mixture of carbon dioxide gas, argon and helium alone or in combination,
What added hydrogen, oxygen, nitrogen, etc. to these may be sufficient. It is preferable to use a double shield because the electrode area becomes large. The current and voltage may be selected in the range of 600 to 3000 A and 22 to 55 V according to the cross-sectional area of the plate-shaped consumable electrode.

Further, when the start ends and the end ends of the steel pieces are not aligned and the positions to be joined are not within the interval range where they can be joined due to a gap of 5 mm or more, the steel pieces are shaped by cutting or the like.
Cutting includes shear cutting, gas cutting, laser cutting, and mechanical cutting such as sawing. At this time, if the welding surplus is much higher than the surface of the steel sheet, it will hinder the rolling process, and
It is preferable to cut into a V, Y or X-shaped groove. The unneeded portion such as the center of the steel slab is 5 m
Even if there is an interval of m or more, there is no problem because the interval may be filled by the subsequent hot rolling. Further, it is also preferable to protect the cut surface with nitrogen, argon or the like in order to prevent oxidation of the cut surface.

[0015]

Example 1 is an example of the present invention, in which 1350 two pieces of ordinary steel having a plate thickness of 100 mm and a width of 500 mm are rolled.
After heating to 0 ° C., the ends were gas-cut into a Y-shaped groove and butted. The maximum distance between the roots of the butting was within 2 mm. Fe with a thickness of 0.3 mm and a width of 150 mm:
97%, C: 0.1%, Si: 0.8%, Mn: 1.2
%, And a consumable electrode composed of other unavoidable components was used, carbon dioxide was used as the shield gas, and an arc was generated for 3 seconds at a current of 1200 A, and the two ends of the butted portion were joined together. This was immediately hot rolled. Rolling was possible without breaking the joint.

Example 2 is also an example of the present invention, in which two pieces of ordinary steel having a plate thickness of a rolled steel plate of 10 mm and a plate width of 500 mm are 800.
After heating to 0 ° C., the ends were shear cut and butted. Due to shear cutting, a maximum gap of 4.5 mm was formed at the butted portion, and this was used as a groove for welding. The consumable electrode has a thickness of 0.3 mm, a width of 80 mm, Fe: 97%, and C:
It consists of 0.1%, Si: 0.8%, Mn: 1.2%, and other unavoidable components. At both ends and the center of the steel slab, a carbon dioxide gas shield is used, and an arc is generated for 3 seconds at a current of 800A. Joined. This was immediately hot rolled. Rolling was possible without breaking the joint.

Example 3 is a comparative example, in which two plain steel sheets having a thickness of 50 mm and a width of 500 mm are rolled at 700 ° C.
After heating, the ends were shear cut and butted. Fe: 97% with a diameter of 4.8 mm, C: 0.08
%, Si: 0.8%, Mn: 1.4%, and other inevitable consumable electrodes are used, and carbon dioxide gas shields are used at two locations on both ends of the steel sheet, with a current of 1000 A and an electrode moving speed of 3.5 m / min. Welded for 3 seconds and immediately hot rolled. However, in the welding, the molten steel was largely ejected to the back, and sufficient joining could not be achieved. Even during hot rolling, the steel that had popped out and solidified was bitten in, and stable rolling could not be performed.

[0018]

By using the joining method of the present invention, continuous hot rolling of thick steel slabs becomes possible. The continuous rolling improves the operating rate of the equipment. In addition, there are no defective rolling points at the leading and trailing ends, the yield is improved, and rolling is possible with a constant pressing force, and the quality such as flatness is also improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a welding method of the present invention.

FIG. 2 is a conceptual diagram of a continuous hot rolling line to which the present invention is applied.

[Explanation of symbols]

 1A, 1B, 1C, 1D, 1E Steel piece 2 Welding device 3 Heating device 4 Shear 5A, 5B Rolling roll 6 Consumable electrode 7 Feeding roll 8 Welding torch 9 Shield gas supply pipe 10 Cooling water pipe 11 Power supply line

Claims (1)

[Claims] 1. When hot rolling a steel slab having a thickness of 10 to 100 mm, a plurality of steel slabs heated to 800 to 1400 ° C. are butt-joined with an end portion of a preceding steel slab and a starting end portion of a subsequent steel slab, A method for joining continuous hot-rolled steel slabs, characterized in that a plate-shaped consumable electrode is parallel to a butt portion and gas shielded arc welding is performed.