JPS5855843B2 - Hot joint 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).

The heating process, 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 one by one 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.

As a result of detailed studies on scale control and bonding, the present inventors discovered a method for controlling scale using powders such as chlorides, sulfates, nitrates, carbonates, phosphates, etc., and made continuous rolling possible.

In other words, the present invention provides a method for overlapping and joining the rear end of the preceding steel material and the leading end of the succeeding steel material between the hot rough rolling process and the hot finishing rolling process of the steel material. A powder consisting of one or more of Na chlorides, sulfates, nitrates, carbonates, and phosphates having a melting point below that temperature is applied to the surface of the steel material, and if necessary, the powder is applied to the steel material to be rolled. The gist of this article is a hot joining method for steel materials, which is characterized by driving a nail-shaped material having a strength greater than the strength of the material into the overlapping portion, temporarily fixing it, and press-welding it.

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 mm.

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.

As described above, by controlling the scale according to the present invention, joining of steel materials becomes easy and continuous rolling becomes possible.

Furthermore, if a plurality of nail-like 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 fixed, the joining can be stably performed and 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/mwi''.

These intermediate rolled materials are overlapped at the tail end of the leading □ band and the tip end of the trailing steel strip, and in this state, for example, a nail-like material having the same alloy composition as the steel strip is driven into the overlapped part. Stop it.

Since the nail-shaped material is driven into the overlapping part of the copper strips at room temperature, its strength (yield stress) is approximately 25 kg/mwj.
It is sufficiently strong.

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 copper strip, and rolling proceeds without applying any impact load to the rolls.

For this reason, the nail-like material to be driven into the overlapping portion of the copper strips should be made of the same material as the steel strip, or a material with physical properties similar to those of the steel strip.

According to the present invention, whether the welding is performed immediately before hot finishing rolling or the coating agent is supplied at any point after rough rolling, the welding is not only effective. The same effect can be obtained by coating the joint surface of any of the subsequent steel materials, which is extremely advantageous in practice.

The method of the present invention can be applied to steel sheets, long steel products, etc., as well as Al, CuZn, etc.
Of course, it is also effective when applied to continuous hot rolling of non-ferrous metals such as alloys thereof 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 m is roughly rolled to 30 mm on a normal hot rolling line.
After reducing the area to mm1Fl, a 2.5-mm hot-rolled plate was finished rolled. In this case, the scale shown in Table 1 was applied to the rear end surface of the preceding material at any point between rough rolling and finish rolling. After applying the regulating agent and overlapping the tips of the trailing materials, two types of finish rolling were performed: one without tacking with rivets, and the other with tacking with rivets using a gunpowder rivet machine.

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.

The first pass of the finishing mill was reduced by 30 degrees, 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 problem.

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)

[Scope of Claims] 1. When joining the trailing end of the preceding steel material and the leading end of the following steel material by overlapping them between the hot rough rolling process and the hot finishing rolling process of the steel material, Powder consisting of one or more types of Na chlorides, sulfates, nitrates, carbonates, and phosphates having a melting point below the surface temperature of the steel material is applied to the surface of the steel material, and then the powder is overlapped and pressure welded. A hot joint method for steel materials characterized by: 2. When joining the rear end of the preceding steel material and the leading end of the succeeding steel material by overlapping them between the hot rough rolling process and the hot finishing rolling process of the steel material, the surface temperature of the steel material at the joint location must be lower than the surface temperature of the steel material at the joint location. After applying a powder consisting of one or more types of Na chloride, sulfate, nitrate, carbonate, and phosphate having a melting point to the surface of the steel material, the strength of the pressure-welded steel material at that time is A hot joining method for steel materials, which is characterized by driving a nail-like material with great strength into the overlapping parts, temporarily fixing it, and pressure-welding it.