JPS5855844B2 - Continuous hot rolling method for steel materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining rolled material for continuous rolling in the finish rolling stage of a steel strip.

Most mass-produced metal products are made into products through ingot formation, hot processing (rolling), and cold processing (rolling).

Heating, which is a pre-process of hot working, is performed as a slab or billet, and therefore, in the hot working process, each slab or billet is processed intermittently.

The period from the end of rolling of one material to the next rolling is a major factor in determining loss time on a rolling line.

If continuous rolling becomes possible by combining the materials before rolling instead of interrupted rolling, the benefits will be: ■ Dramatic improvement in productivity, ■ Significant reduction in heat intensity and power consumption, and ■ Increased yield. ,■It will become extremely large due to labor saving, etc.

However, a major problem with joining materials for continuous rolling is the scale that exists on the steel surface.

Continuous rolling becomes possible depending on how this scale is controlled.

Furthermore, in order to stabilize the pressure welding, it is effective to temporarily attach the joint portions before the pressure welding.

As a result of detailed studies on scale control and bonding, the present inventor discovered a scale control method and tacking method using oxide or composite oxide powder, which made continuous rolling possible.

That is, the present invention is a method of overlapping and joining the tail end of a preceding steel material and the head end of a succeeding steel material between a hot rough rolling process and a hot finishing rolling process, the method comprising: ,
N having a melting point below the surface temperature of the steel material in the joint part
After applying the powder containing the oxides of either or both of A and B as an essential component, they are overlapped and temporarily fixed by driving a nail-shaped material having a strength greater than the strength of the steel material to be welded at that time. The gist of this paper is a continuous hot rolling method for steel materials, which is characterized by pressure welding.

The present invention will be explained in more detail.

Continuous rolling requires joining two steel materials, and the joint strength must be strong enough to withstand tensile stress and not break during the next hot finish rolling process.

There is a scale of 20μ or more on the surface of the material before hot finish rolling, and when two materials are overlapped and joined, if there is scale on the joint surface, it may be inhibited by it and it may be impossible to join.
Bonding strength that can withstand breakage cannot be obtained.

On the other hand, if there is no scale on the bonding surface, bonding can be easily achieved with a relatively small pressure.

By applying a low melting point substance, a molten film is formed, which suppresses oxidation on the steel surface, and the scale that is present before application reacts with the coating agent, becoming a low melting point solid solution and escaping from the joint surface during pressure welding. Then, a metal contact is made and the bonding conditions are realized.

In this way, about 30 m after rough rolling where the scale is removed from the overlapping part, which is usually 300 mm long.
The tail end of the leading steel strip and the leading end of the trailing steel strip, both of which have a thickness of m, are twice the thickness of the copper strip after rough rolling. The steel strip is installed and thereby reduced to a thickness at or near the steady portion, thus joining the tail end of the leading steel strip and the leading end of the trailing steel strip.

In the above explanation, the overlapping parts are crimped by a rotor press to reduce the thickness, but the thickness can be reduced by crimping in one stand or several stands of the first stage of the finishing mill row without providing a rotor press. It may be decreased.

The length of the overlapping portion is preferably 100 to 500 m5.

If it is less than 100 mm, the strength of the joint is insufficient, and if the
If it is more than mm, the amount of the cut-off portion becomes large and the yield decreases.

By controlling the scale of the present invention in this way, joining of steel materials becomes easy and continuous rolling becomes possible.

Furthermore, if a plurality of nail-shaped materials having a strength greater than the strength of the materials to be welded are driven into the overlapped portion before pressure welding and temporarily fastened, it is possible to stably join and be more effective.

To further explain this point, the temperature of the intermediate rolled material just before being rolled in the finishing mill is usually 950 to 1050.
It is ℃.

In this temperature range, the strength (yield stress) of the intermediate rolled material (copper strip) is 7 to 8 kg/crlt.

These intermediate rolled materials are overlapped at the tail end of the leading steel strip and the tip end of the trailing steel strip, and in this state, for example, a nail-shaped material having the same alloy composition as the steel strip is driven into the overlapping portion. Temporarily fasten.

Since the nail-shaped material is driven into the overlapping portion of the steel strips at room temperature, its strength (yield stress) is approximately 25 kg/-, which is sufficient strength.

Although the temperature of the nail-shaped material driven into the overlapping portion of the steel strip increases due to heat transfer from the steel strip, it has sufficient strength until the rolling of the overlapping portion progresses several passes.

After the overlapping portion has been sufficiently rolled, the nail-like material reaches the same temperature as the steel strip, and rolling proceeds without applying any impact load to the rolls.

For this reason, it is preferable that the nail-shaped material driven into the overlapping portion of the steel strip be made of the same material as the copper strip, or a material with physical properties similar to those of the copper strip.

According to the present invention, even if the welding is carried out immediately before cracking finish rolling or if the coating agent is supplied at the successor portion of the rough rolling, it is not only effective for the welding, but also one-sided coating (previous steel material or subsequent steel material). Coating on the joint surfaces of any of the steel materials is similarly effective and is extremely advantageous in practice.

The method of the present invention can be applied to steel plates, long steel products, etc., as well as Al and Cu.

Of course, it is also effective when applied to continuous hot rolling of Zn and its alloys and other non-ferrous metals.

Next, examples of the present invention will be given.

A low carbon steel slab with a thickness of 250 mm, a width of 1200 mm, and a length of 10' is roughly rolled on a normal hot rolling line.
After reducing the area to 0 plate thickness, a hot-rolled plate of 2.5 mπ was finished rolled. In this case, the surface of the rear end of the preceding material was coated at any point between rough rolling and finish rolling as shown in Table 1. After applying a scale control agent and overlapping the leading ends of the trailing materials, tacking was done with rivets and finish rolling was performed.

Table 1 shows the composition of the scale regulator, the rolling temperature, the presence or absence of tacking with rivets, and the joining conditions and joining results.

*B203 (45.6%) -5i02 (17.5%)
-Na20 (25,0%) -A1203 (4,5%
') -Cab (5,0%) MgO (2nd, 4th section) The first pass of the finishing mill was rolled by 30%, but subsequent rolling was performed with the same reduction distribution as in the conventional method.

As a result, finish rolling could be carried out without any problems.

As shown in the examples, according to the present invention, a bonding force that can withstand the tensile stress during the hot finish rolling process can be obtained without any problem, and continuous rolling is possible, so productivity is significantly improved, and
Yield is further improved, and significant benefits are brought about in terms of energy and labor savings.

Claims (1)

[Claims] 1. A method of overlapping and joining the tail end of the preceding steel material and the head end of the succeeding steel material between the hot rough rolling process and the hot finish rolling process of the steel material, wherein the joining surface is Na and B having a melting point below the surface temperature of the steel material in the part
After applying a powder containing one or both of the oxides as an essential component, they are overlapped and a nail-like material having a strength greater than the strength of the steel material to be welded at that time is driven in to temporarily secure and pressure weld. A continuous hot rolling method for steel materials characterized by: