JPH0330473B2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The technical content described in this specification regarding hot rolling is to propose a joining method for steel billets useful for endless rolling in which finish rolling is performed continuously. .

Conventionally, in hot rolling of steel, strip coils have been manufactured by heating slabs to a predetermined temperature in a heating furnace and rolling them one by one in a rough rolling mill group and a finishing rolling mill group.

This method of rolling slabs one by one causes the following problems, particularly in the finishing mill. That is, there are large variations in product dimensions, such as poor biting of the tip of the steel billet and poor thickness between the tip and rear end of the billet.

For example, when the leading and trailing ends of the strip pass through a row of finishing mills, work rolls are likely to be flawed, leading to a decrease in rolling efficiency due to an increase in the number of roll changes, and an increase in roll consumption.

By the way, as a method for solving these problems, there is a method of joining steel pieces before and during finish rolling.

(Prior art) Regarding this method of joining steel pieces, Japanese Patent Application Laid-Open No. 53-7559
The publication discloses a method using a flash welding machine, but this method requires the flash welding machine to be run together with the sheet bar, or a looper is required in the post process of the welding machine. If the surface to be joined is large, such as the end of a sheet bar,
The weight of flash welding machines has become extremely large.
It is expected to be over 100 tons. Running a welding machine, which is such a large and heavy object, poses a problem in that the line becomes long, which is also undesirable from the viewpoint of maintenance. Furthermore, when a hot sheet bar is lifted with a looper, there is a material problem in that the austenite crystal grains become coarse, and there is also a problem in maintenance equipment for the looper roll, making industrialization extremely difficult.

Furthermore, Japanese Patent Application Laid-Open No. 53-138960 discloses a method using butt pressure welding, but this method requires beveling of the butt portion, and in the process where the sheet bar is threaded continuously at high speed. The efficiency of beveling work is extremely low, making it difficult to industrialize.

(Problems to be solved by the invention) In order to achieve a continuous rolling method for steel billets with a high product yield and good production efficiency, a simple and new joining method that does not require running joining equipment and looper equipment is developed. It is an object of this invention to develop.

Furthermore, the joining of the steel billets needs to be carried out in a short time without reducing the passing speed of the steel billet so that the temperature of the steel billet does not drop and reheating is required before finish rolling.

Furthermore, when joining steel pieces, it is necessary to remove scale from the steel surface.

(Means for Solving the Problems) This invention involves cutting the rear end of a preceding steel piece before two pairs of rolls arranged along the rolling direction during hot finishing rolling, and pulling the leading steel piece. Next, the leading end of the trailing steel piece is cut, and the leading end of the trailing steel piece is butted against the rear end of the leading steel piece located between the two pairs of rolls, and the abutted part is energized through the rolls. This is a method for joining steel pieces in hot rolling, which is characterized by heating and pressure welding.

Note that the above-mentioned steel billet is a general term for slabs, sheet bars, blooms, billets, and rolled materials in these rolling processes.

Now, FIG. 1 schematically shows the equipment layout of an endless rolling line for manufacturing strips from sheet bars by rolling slabs. First, a slab 1 heated to a predetermined temperature in a heating furnace 4 is descaled and then rolled in multiple passes to a desired dimension by a rough rolling mill group 5 to form a sheet bar 2. It is wound up into a coil box 6 and kept at a uniform temperature over the entire length by heat recovery from the sheet bar 2. Subsequently, the seat bar 2 is taken out from the coil box 6, and is joined to the rear end of the preceding seat bar by butt pressure welding in the seat bar joining device 8. The strip is then rolled to a predetermined thickness using the finish rolling mill group 9, and the strip is rolled onto the runout table 1.
0, cut to a predetermined length by a running shear 11, and then wound up by a down coiler 12.

Here, the method of joining the seat bars will be explained.

FIG. 2 shows a specific example of the joining device together with the leading seat bar 2' and the trailing seat bar 2. The joining device is composed of front rolls 13, 13', rear rolls 14, 14', a guide plate 15, and a power source 16. You, roll 13 of the latter rolls.
and 14 are current-carrying rolls connected to a power source 16, allowing current to flow through the sheet bar located between the rolls 13 and 14.

To join the sheet bars, first, the tip of the trailing sheet bar 2 from the coil box or rough rolling mill group is butted against the rear end of the leading sheet bar 2' that is biting into the trailing rolls 14, 14'. The sheet bars 2 and 2' are energized from the rolls 13 and 14 to the row sheet bar 2 and the preceding sheet bar 2', and their contact surfaces are pressed together under heating.
and 2' are joined.

In this process, the scale present on the sheet bar end surfaces (surfaces to be joined) is discharged or melted into the molten layer on the surface layer of the end surfaces when the sheet bars are butted together, and the sheet bars can be efficiently joined.

Further, the guide plate 15 is a jig for preventing the seat bar joint from shifting when the trailing seat bar 2 is butted together, and is used in a high-temperature environment or with heat-resistant steel.
It is desirable to use a heat-resistant alloy or ceramic, and it is necessary to use an insulating material.

Further, the rolls 13 and 14 serve as electrodes and clamps, especially the front roll 13.
also serves to push the seat bar into the preceding seat bar. That is, by increasing the circumferential speed of the front roll 13 compared to the circumferential speed of the rear roll 14, the relative speed between the trailing sheet bar 2 and the leading sheet bar 2' is changed to push the sheet bars against each other. . The pushing amount (upset distance) at this time is preferably in the range of 10 to 100 mm. If it is less than 10 mm, sufficient joint strength will not be obtained if scale is present, and if it is more than 100 mm, the deformation in the thickness direction of the joint will be large. Therefore, this is not preferable in terms of rolling in the next step. Further, since the rear roll 14 is located before the sheet bar is fed into the finishing rolling mill group, it also serves to lightly roll down the excess buildup at the joint (joint).

By the way, when joining steel pieces, scale remains locally at the interface of the joint, and the joint strength is lower than the strength of the base metal, and there is a risk that the joint will be crimped and break during the subsequent finish rolling. However, no breakage occurs under the following bonding conditions.

The joining conditions include mainly the upset distance and the temperature of the steel billet during upsetting.
First, if we assume that the scale is less than approximately 40 μm thick, which is generated between the time the steel piece is cut by the crop shear and the time it enters the joining equipment, the temperature of the steel piece is 1000 μm or less.
When finish rolling is carried out in 7 stands with a rolling reduction of 10 to 60% per stand at a temperature of 15 mm or more, the upset margin may be 15 mm or more. Furthermore, in this invention, since the joint is heated by applying electricity using an energizing roll between the steel pieces, a joint can be reliably created even when the temperature of the steel pieces is 900 to 1000°C.

(Function) Since the steel piece is softened in the hot state (900 to 1200°C), it is in a state where it easily undergoes plastic deformation with relatively low stress. Therefore, by applying stress or impact force that brings the pieces of steel into close contact with each other, the area of the abutting surfaces increases. In the process of increasing this area, the scale existing in the surface layer of the surface to be joined is destroyed and dispersed, and a new surface is exposed. These newly formed surfaces are in an activated state, and if the newly formed surfaces are butted against each other and come into contact, a metallic bond will be formed by applying low stress for a short period of time. As described above, butt pressure welding is excellent for hot joining of steel pieces.

(Example) Steel type: SS41 Dimensions: Thickness 52mm, Width 450mm, Length 4000mm Cutting method for the cross section to be joined: Crop shear, using two steel pieces, heated to 1000℃ and then descaled. They were charged into the welding apparatus shown in FIG. 2 as leading and trailing billets, respectively. The circumferential speeds of the front roll and rear roll at this time are 60 m/min and 40 m/min.
And so.

Two pieces of steel are collided between the front and rear rolls, and a current is applied at that moment (current density: 1600A/cm ² ).
The temperature of the joint was raised to 1,300 to 1,400°C, and the current was cut off by pressing with a front roll until the pressing amount reached 30 mm.

Subsequently, it was subjected to a commonly used finishing rolling mill (6 stands) to obtain a plate having a thickness of 2.3 mm and a length of 90 cm. At this time, there was no breakage at the joint of the steel billet, and finish rolling could be performed.

(Effects of the Invention) As explained above, according to the present invention, endless finish rolling of steel slabs can be achieved, the product yield of hot rolled sheets is high, and a work process with high production efficiency can be obtained.

Furthermore, it becomes possible to apply a uniform high tension over the entire length of the strip, which has been impossible with conventional rolling techniques, and it is possible to easily realize thin rolling of high-strength materials.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a hot rolling process, and FIG. 2 is an explanatory diagram showing a joining device for steel pieces.

Claims (1)

[Claims] 1. During hot finish rolling, the rear end of the leading steel piece is cut before two pairs of rolls arranged along the rolling direction, and then the trailing steel piece is cut. The leading end is cut off, and the leading end of the trailing steel piece is butted against the rear end of the leading steel piece located between the two pairs of rolls, and the abutted part is heated with electricity through the rolls to be pressure-welded. Features of joining method of steel pieces in hot rolling.