JPS58493B2 - Quality improvement method in direct rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for efficiently compensating for localized temperature drops in conveyed slabs in a rolling line that continuously carries out blooming and hot rolling processes to obtain high quality. It is related to.

Originally, the steel blooming process and hot rolling process were not set up as continuous processes, but recently, as part of energy-saving measures, this process has been made continuous, and direct rolling, which directly transports the slab from the blooming process to the rolling process, has been adopted. methods are beginning to be applied.

Normally, the blooming plant and the hot-rolling plant are separated by a certain distance, so it takes 3 to 8 minutes to transport the slab after the blooming process to the hot-rolling plant. Therefore, when the slab reaches the hot rolling mill, the corner end face of the material experiences a local temperature drop over 50 to 100 mm.

When rolling a material with such local temperature differences,
For thin products of 30 mm or less, a localized reduction in rolling temperature of 50 to 80 °C occurs at about 50 mm of the edge end face (
(Refer to the curve shown by the solid line in Figure 2), as a result, the ferrite grains become coarser within about 50 mm from the edge end face of the coil, resulting in so-called grain gloss, which tends to significantly worsen the reduction of width. (See the solid curve in Figure 3).

Such products cannot be used for high-grade products such as drawn materials, and therefore the amount that can be directly rolled is limited.

In order to prevent such a drop in end face temperature, conventionally a material end heating device was installed between the finishing rolling mill and the roughing rolling mill to heat the material during rolling. Due to the influence of fluctuations and fluctuations in rolling speed, sufficient effects are not obtained despite the large equipment costs required.

Another method is to provide a process in which the slab passes through a hot-rolling heating furnace in the middle of the conveyance path from blooming to hot-rolling, thereby compensating for the decrease in the corner temperature of the slab during conveyance. However, since the entire slab is passed through a heating furnace for a long period of time in order to compensate for the local temperature, the amount of fuel consumed is large and it is extremely uneconomical.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a means for selectively performing reheating necessary for local temperature compensation during transportation, thereby eliminating the drawbacks of the conventional methods and improving the quality of the reheating process. The goal is to make it possible to obtain quality products.

A feature of the present invention is that an existing heating furnace or a new furnace that is not used during direct rolling is placed at an intermediate point of the conveyance path, and only the extraction side of this furnace is used to compensate for the temperature of the slab.

The method of the present invention will be specifically explained below with reference to FIG.

First, a new or existing hot rolling heating furnace 4 is installed at approximately the midpoint of the slab conveying path 3 connecting the blooming process 1 and the hot rough rolling mill 2.
is arranged, and the extraction side 4a of the heating furnace 4 is arranged so as to join the conveyance path.

It does not matter whether the heating furnace 4 is an existing one or a new one, but in either case, one or more unused heating furnaces that are not directly used for hot rolling work are arranged.

The present invention requires a mutual relationship between the conveyance path 3 and the heating furnace 4, so when using an existing heating furnace, the slab should be placed along the extraction side of the heating furnace. What is necessary is to provide a conveyance path 3.

On the other hand, in the present invention, when the slab leaves the blooming process and reaches the hot rolling process, the heating furnace heat retention time ΔH, which indicates the state in which each part of the slab maintains a temperature suitable for rolling, is determined by the following formula. Set the calculation in advance.

△H≧A・△T+/l−C・・・・・・・・・ (1
) where △T: T (arrival time during blooming hot rolling) - TO (standard arrival time) t: Thickness of final hot product (m) A, ni, r, C: Constants determined by experiment This invention In this method, heat is raised in the heating furnace 4 only when the heating furnace heat retention time ΔH of the slab to be transported is ΔH≧O, and the slab 5 that requires heating is heated in the heating furnace 4.
When the heating furnace reaches the position , the extractor (not shown) of the heating furnace reversely charges it into the extraction side 4a of the furnace, and heats it in the furnace for a heat retention time ΔH.

ΔH is usually about 5 to 6 minutes, and after ΔH has elapsed, the extractor extracts the material onto the conveying path again and conveys it to the hot rolling process.

When a plurality of heating furnaces are provided, it is possible to select and use any heating furnace at any time, and as shown by the dotted line charging system in FIG. Another slab 51 is placed on standby in advance, and when a discrepancy occurs between the blooming pitch and the rolling pitch, the waiting slab 51
Alternatively, the rolling pitch may be adjusted by feeding the rolled material onto a conveyance path.

In addition, in a walking beam type furnace, it is possible to reverse charge multiple slabs, which allows slabs with large ΔH (end surface temperature drop After heating a slab with a significant value of ΔH for the required time and rolling a subsequent slab with a small value of ΔH,
The ΔH large slab can be extracted and rolled.

According to the present invention, the thickness is 1.6 mm, the width is 950 mm, and the weight is 2.
When obtaining a 0 ton coil, temperature compensation was performed using a reverse charging method with △H of 6 minutes. As a result, the temperature distribution in the width direction of the coil was approximately 50°C, as shown in the dashed line curve in Figure 2. It was possible to prevent the temperature from decreasing by showing an increase in temperature, and extremely stable results were obtained for the width value and grain gloss occurrence rate as shown by the dashed-dotted curve in FIG.

When calculating △H using the above formula (1), the slab thickness is 280
m, material thickness at the entrance side of the finishing rolling mill 321B, heating temperature 12
Standard time to reach 80°C TO = 250 sec.

To give an example of the case, constant A = 1.4, constant = 720
, constant γ=1.5, and constant C=120.

In practice, the time required for charging and extraction is about 90 seconds added to the calculation time of ΔH.

According to the method of the present invention, even if an existing needle or a new furnace is used, it is possible to ensure the necessary and sufficient temperature state for each individual material, so there is no waste in fuel consumption. 20,000 Kcal/lon compared to the conventional 350,000 to 400,000 Kcal/ton, showing a significant decrease, and it has also become extremely effective in improving the quality of finished products.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the overall structure of the method of the present invention, Figure 2 is a comparison diagram of the method of the present invention and the conventional method showing the temperature distribution in the slab width direction, and Figure 3 is a diagram showing the width value and grain gloss occurrence rate. A comparison diagram between the method of the present invention and the conventional method showing trends. 1... Blooming step, 2... Hot rough rolling mill, 3... Slab conveyance path, 4... Hot rolling heating furnace, 5... ... Slab, 6... Finishing rolling mill.

Claims (1)

[Claims] 1 Calculate in advance the heating furnace heat retention time △H to compensate for the decrease in the temperature of the corner end face of the slab during the transportation process from the blooming process to the hot rolling process, and the blooming process and hot rolling process. An existing or new hot-rolling heating furnace is installed at approximately the midpoint of the conveyance path connecting the conveyance path, and the extraction side is placed in contact with the conveyance path, and when △H≧0 in the slab being conveyed, When the slab reaches the hot-rolling heating furnace, the slab is reversely charged into the furnace from the extraction side of the hot-rolling heating furnace, heating is applied to the corner part, and after △H has passed, the slab is extracted from the heating furnace. A quality improvement method in direct rolling characterized by conveying.