JPS5926370B2 - Method of heating steel billet for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating method for eliminating as much as possible the skid mark bottom temperature of a steel billet for hot rolling.

In hot rolling, slabs are continuously fed into a rolling line through a continuous heating furnace and made into plates.

Skid marks are the areas in the heating furnace where the temperature is lower than other heated areas due to contact with the skid, which serves as the supporting and conveying surface of the slab, or the shadow of the skid. This causes non-uniformity and shape defects.

Therefore, measures are being taken to suppress the occurrence of skid marks in the heating furnace as much as possible.

For example, the button on the skid may be raised to reduce shadows from below, the skid may be made to meander to avoid continuous contact with the same spot on the slab, or the top surface of the skid may be preheated to a high temperature using a high-speed burner. That's it.

However, although these methods of suppressing skid marks in heating furnaces can reduce the area of skid marks,
The reality is that the problem cannot be completely resolved, and the negative impact on rolled products remains.

The object of the present invention is to provide a heating method that can solve the above-mentioned problems and eliminate the adverse effects on rolled products caused by skid marks in an extremely simple and easy manner. After partially heating the planned skid mark portion (by induction heating), the steel billet is immediately sent to a heating furnace and heated in a conventional manner.

FIG. 1 is a plan view of the arrangement of the front and rear parts of the heating furnace in a hot rolling line. An induction heating device 4 is placed on the entry table 1 to the continuous heating furnace 2, and the hot rolling steel billet is continuously heated. When being heated in the furnace 2, induction heating is applied in advance to the portions of the steel billet where skid marks are expected to occur.

The steel piece heated at the area where the skid marks are to be marked is immediately put into a heating furnace, heated in a conventional manner, and then taken out onto a delivery table 3, where it is made into a plate by a rough mill 5 and a finishing mill 6.

FIG. 2 shows an example of the induction heating device 4.

The induction heating device consists of an iron core 7 and an electromagnetic coil 8 wound around it.
These cores and electromagnetic coils are sized and shaped to partially inductively heat the intended skid mark portion 10 of the hot rolling billet 9.

That is, when a heating current is applied to the electromagnetic coil 8, the intended skid mark portion 10 of the steel billet is placed in an alternating magnetic field and locally heated primarily due to eddy current losses.

Next, the method of the present invention will be explained in more detail based on Examples.

Induction heating is applied to a portion of the steel billet placed on the entry table immediately before it is placed in the heating furnace where skid marks are expected to be formed, and the portion is heated to approximately 700°C.

In this case, medium 1500mm, length 4000mm, thickness 2
Assuming that the planned skid mark area of a 50 mvtO steel piece has a lower surface width of 1500 mm, a length of 300 mm, and a depth of 75 mm, the preheating condition by induction heating is a frequency of 50 Hz.
Approximately 70℃ from room temperature with induction heating of 2000kW power and 1 minute
It is possible to locally heat the part to 0°C.

Subsequently, the steel slab was charged into a heating furnace, heated in a conventional manner for 3 hours, extracted from the furnace, and rolled at a finishing temperature of about 750°C.

Figure 3 shows the method of the present invention in which the skid mark area, which is scheduled to be placed in the furnace immediately before charging, is preheated for about 2 minutes by induction heating before being charged into the heating furnace, and the method in which the billet is charged into the heating furnace without preheating. This figure shows the temperature increase pattern of the steel billet compared to the conventional method of charging the billet directly into the heating furnace.The solid line A is the non-skid portion of the billet (part A in Figure 2), and the broken line B is the main billet. The dash-dotted line B indicates the temperature rise pattern curve of the skid contact area of the steel billet according to the conventional method (both are section B in FIG. 2).

That is, in the case of the above example, at the time of extraction 3 hours after charging into the furnace, the non-skid part, part A, was 1150°C in both the present method and the conventional method, and the skid contact part, part B, was 1076°C in the conventional method. ℃, whereas the temperature according to this method was 1086℃.

As the temperature deviation between the non-skid part and the skid contact part was reduced by 10°C compared to the conventional method, the plate thickness accuracy was significantly improved.
000mm, 151m thick 5S41 material plate, 2
The plate thickness deviation of the five-piece average was improved from the conventional ±0.24 mm to ±0.19 mm by implementing the above method.

The present applicant first heated the skid mark part of a hot rolling steel billet after being heated in a continuous heating furnace using an electromagnetic induction heating device installed on the rolling line, and heated the non-skid part and the skid contact part locally. However, heating the skid mark area after extracting the slab from the heating furnace reduces heat transfer efficiency due to heating in a non-magnetic temperature range. Inferiority 9: It is necessary to apply heat insulation measures to the heating device, and there is a problem that the non-heated parts are cooled, but the above problems do not occur with induction heating before charging into the furnace, as in this method. .

Furthermore, the method of the present invention can also be used in combination with conventional measures to suppress skid marks in the heating furnace, such as raising the skid button in the furnace or making the skid meander.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the arrangement side of the front and rear parts of the heating furnace when the method of the present invention is carried out in a hot rolling line, Fig. 2 is a side view of the mechanism of the induction heating device, and Fig. 3 is a plan view of the arrangement side of the inventive method and the conventional method. It is a curve diagram showing the temperature rise pattern of a steel billet in a heating furnace. 1: Entry table, 2: Continuous heating furnace, 3: Delivery table, 4: Induction heating device, 5: Rough mill, 6:
Finishing mill, 7: iron core, 8: electromagnetic coil, 9: steel billet for hot rolling, 10 varnished mark part, A: non-skid part, B varnished contact part.

Claims (1)

[Claims] 1. After partially heating the planned skid mark portion of the hot rolling billet before charging into the heating furnace by induction heating, immediately heat the billet in the heating furnace in a conventional manner. Characteristic method of heating steel billet for hot rolling.