JPS61159285A - Joining method of billet in hot rolling - Google Patents

Abstract

PURPOSE:To finish and roll a preceding billet and succeeding billet to an endless billet with high efficiency by butting the rear end of the preceding billet and the front end of the succeeding billet which are cut just before two pairs of rolls between two pairs of rolls and heating electrically the butt part via said rolls and press-welding the butt part. CONSTITUTION:The rear end of the preceding billet 2' and the front end of the succeeding billet 2 are cut by a crop shear and thereafter said ends move to the space between the rolls 13 and 14. The front end of the succeeding billet 2 is first butted to the rear end of the preceding billet 2' under the bite to the rear rolls 14, 14' and in this state electricity is conducted to the billet 2 and the billet 2' via the rolls 13, 14 and the contact surfaces of both billets 2 and 2' are heated and press-welded. The scale existing on the surfaces to be joined of the billets is discharged together with the molten layer on the surfaces of the billets or melted into the molten layer in the stage of butting the billets, by which the billets are joined efficiently. The front rolls 13 are operated at the prescribed push quantity. Guide plates 15 prevent the shifting of the joint surfaces of the billets.

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 (1) poor biting of the tip of the steel billet, and (2) defective thickness between the tip and rear end of the billet.

■For example, when the leading and trailing ends of the strip pass through the finishing mill row, the work rolls are likely to be damaged, reducing rolling efficiency due to an increase in the number of roll changes, and causing problems such as the upper back of the roll unit. invite

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. 53-75419
The publication discloses a method using a flash welding machine, but this method requires the flash welding machine to run together with the sheet bar, or requires a looper in the post process of the welding machine. If the surface to be welded is large, such as the end of a sheet bar, the weight of the flashco welding machine is extremely large (it is expected to weigh more than 100 m1. Running a welding machine has the problem of making the line long, which is also undesirable from a maintenance standpoint.Furthermore, when the hot sheet bar is lifted with a looper, the austenite crystal grains become coarse, which is a material problem. In addition, there are problems with 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 bevel processing at 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 new joining method is developed on the R11 flight that does not require running joining equipment and does not require looper equipment. It is an object of this invention to develop.

Furthermore, joining of steel billets needs to be carried out in a short time without reducing the passing speed of the steel billet, as in the case where the temperature of the steel billet decreases 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 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 butted part is passed through the rolls. This is a method for joining steel pieces in hot rolling, which is characterized in that the steel pieces are welded by electrical heating and pressure welding.

Note that the above-mentioned steel billet is a general term for slabs, sheet bars, pulleys, 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 1.
Then, this sheet bar 2 is wound up in a coil box 6, and the temperature is kept uniform over the entire length by the recuperation of the sheet bar 2. Subsequently, the sheet bar 2 is extracted from the coil box 6, and the preceding sheets 1 to 1 are connected to the sheet bar joining device 8.
It is joined to the rear end of the bar by butt welding. Next, it is rolled to a predetermined thickness in the finishing rolling mill group 9 to form slips, cooled on a runout table 10, and rolled into a running shear 1.
After cutting it to a predetermined length in step 1, it is wound up in down coiler 12.

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

FIG. 2 shows a leading seat bar 2' and a trailing seat bar 2'.
In addition, a specific example of a bonding device will be shown. The joining device is composed of a front roll 13, 13', a rear roll 14° 14-1 guide plate 15, and a power source 16. It should be noted that among the latter rolls, rolls 13 and 14 are energized rolls connected to a power source 16, and current can be passed to 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 roll 14, 14-, and then Electricity is applied to the row sheet bar 2 and the preceding sheet bar 2' from the rolls 13.degree. 14 to the sheet bars 2 and 2' so that their contact surfaces are brought into pressure contact under heating, thereby joining the sheet bars 2 and 2-.

In this process, the scale existing on one end surface of the sheet bar (the surface to be joined) is discharged or dissolved into the molten layer on the surface layer of the end surface when the sheet bars are butted together.
Seat bars can be joined efficiently.

Further, the guide plate 15 is a metal material to prevent the seat bar joint from shifting when the trailing seat bar 2 is butted together, and since it is in a high temperature environment, it is preferable to use heat-resistant steel, heat-resistant alloy, ceramic, etc. , it is necessary to be an insulator.

Furthermore, the rolls 13, 14 serve as electrodes and clamps, and in particular the front roll 13 also serves to push the sheet bar into the preceding sheet 1. That is, by increasing the circumferential speed of the front roll 13 compared to the circumferential speed of the rear roll 14, the relative speeds of the trailing sheet bar 2 and the leading sheet bar 2 are changed to push the sheet bars against each other.

The push-up (upset) at this time is 10 to 100
A range of mm is desirable; if it is less than 10 mm, sufficient bonding strength will not be obtained if scale is present, and if it is more than 100 man, deformation in the thickness direction of the joint will become large, which is undesirable for the next rolling process. Further, since the rear roll 14 is located before the sea bar is fed into the finishing rolling mill group, it also serves to lightly roll down the excess buildup at the joint (joint part).

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. No breakage occurs under the following bonding conditions.

The joining conditions can mainly include the temperature of the steel billet during upsetting and ablation.

First, if we assume that the scale is less than about 40 μm thick, which is formed between the time the steel billet is cut by the crop shear and the time it enters the joining equipment, if the billet temperature is 1000°C or higher,
When finish rolling is performed using seven stands with a rolling reduction of 10 to 60%, the upset may be 15 mm or more. Furthermore, in this invention, an energizing roll is used between the steel pieces to heat the joint by applying electricity, so the temperature of the steel pieces is 900~900℃.
Joints can be reliably created even at 1000°C.

(Function) Since a hot steel piece (900 to 1200°C) is softened, it is in a state where it easily undergoes plastic deformation with relatively low stress. Therefore, by applying stress or impact force that causes the pieces of steel to butt against each other and come into close contact, the area of the butt 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 when the newly formed surfaces are brought into contact by butting each other, a low stress is applied for a short period of time to form a metallic bond.In this way, hot joining of steel pieces is achieved by butt pressure welding. Are better.

(Example) Steel type: 5S41 Dimensions: Thickness 52m1. Width 450mm, length 4000m
Cutting method for the end faces to be welded: Crop shear. Using two pieces of steel, heat them to 1000℃, descale them, and charge them into the welding device shown in Figure 2 as leading and trailing pieces, respectively. did. The circumferential speeds of the front roll and the rear roll at this time were 60 m 2 /min and 40 m 2 /min.

Two pieces of steel are collided between the front and rear rolls, and current is applied at that moment (current density: 1600A/c/),
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 give a plate thickness of 2.3 ml and a length of 90 marks. 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.

Moreover, 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 drawings]

Figure 1 is a diagram showing the hot rolling process; 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 in front of the two pairs of rolls arranged along the rolling direction, and then the trailing steel piece is cut. Cut the tip of the following steel piece, and butt the tip of the trailing steel piece against the rear end of the preceding steel piece located between the two pairs of rolls, and heat the abutted part through the rolls to press them together. A method for joining steel pieces in hot rolling, characterized by: