JPS5829170B2 - Steel hot rolling equipment - Google Patents

Description

Detailed Description of the Invention The present invention 5 aims to eliminate scale defects in rolled products by effectively removing primary scale generated during heating of the steel material before hot rolling, as a steel material hot rolling equipment. related to what was done.

Generally, during hot rolling of steel materials, the steel materials are heated to a high temperature over a long period of time in a heating furnace.

The primary scale that forms in this case is descaled using high-pressure water, etc. before the rolling process, but steel types with poor descaling properties, such as zircon killed steel, aluminum guild steel, and other alloy-added In □ types such as alloy steels, this primary scale is not peeled off sufficiently and is often pushed onto the surface of the steel material during subsequent rolling, resulting in scale defects in the finished product.

As a measure to prevent such scale defects, the conventional method is to coat the surface of the steel material with Al2O3 or other oxide powder before charging it into the heating furnace to generate primary scale with excellent peelability for the rolling line. It has been adopted.

However, this method is not only insufficient as a countermeasure, but is also disadvantageous in that the work of applying such a scale remover significantly impedes the continuity of the three integrated processes in the rolling mill.

The present invention basically pursues the mechanism of peeling off the primary scale that occurs when heating steel materials before hot rolling.
The present inventors have invented an extremely simple and effective descaling method, and based on the results of comprehensive and basic research on the occurrence of scale defects and the mechanism of scale exfoliation, By clarifying the conditions under which scale is easy to peel off, maintaining the consistency of the continuous process, and creating conditions under which scale is easy to peel off, it is possible to completely remove the primary scale for descaling, and to eliminate scale flaws. The feature is that the hot rolling equipment for steel materials is equipped with a heating furnace and a high-pressure water injection descaler-1 hot rolling mill arranged in this order, and a water cooling spray for descaling the heated steel material is installed on the exit side of the heating furnace. It is at the point that I have set.

The present invention will be described in detail below based on the illustrated embodiments. Figure 1 shows a general example of the arrangement of a heating furnace, a descaler-1 rolling mill, etc. in steel hot rolling equipment for a normal plate factory. In the figure, 1,2°3 are three heating furnaces,
A roller table 5 commonly disposed on each outlet side of the four-cigarette heating furnaces 1 and 2. A descaler 56, which is a descaling unit using means such as high-pressure water jetting, is installed in the rolling mill row.
The rough rolling mill shown in FIG.

Now, click on this diagram and call the heating furnace 1 the No. 1 furnace, the heating furnace 2 the No. 2 furnace, and the heating furnace 3 the No. 3 furnace, and the slab rows for each type 1, 2, and 3 are the A row and B row, respectively. , C column, D column, E column, F
Let's call it a column.

At this time, the conveyance speed of the roller table 4 in front of the heating furnace is 1
22.52.33m/min is E'T strange, but from the viewpoint of energy saving (reducing heat loss) and productivity,
Normally, each slab is transported at the maximum speed of 122 m/min.

Therefore, each row A, B, C, D, E of each heating furnace 1.2, 3,
After extracting the slab from F, the average time for it to reach the descaler 5 (including the time for extracting the slab from the furnace by the extractor) is as shown in Table 1 below.

However, in front of the table, the time required for the slab to travel on the roller table 4 with the descaler 51 from the front of the furnace, and the time required for the slab to reach the descaler 5 from the time it is pasted to the extraction door. .

In the steel hot rolling equipment for a plate factory with such an arrangement, the present inventors conducted a total of 1,500 rolls several times.
Regarding the slabs in question, we first investigated how the slab size, heating conditions, furnace number used, time in descaler 1, and other factors were related to the state of primary scale flaking after descaling. It is.

At this time, the slab surface after descaling was photographed for all slabs, and the remaining scale was ranked into five levels based on the degree of severity and area ratio of the remaining scale, and the scale removal status was evaluated.

An example of this is shown in Reference Figure ■, and the numbers added to the right side of each slab photo in Reference Figure 1 are the examples.
The ranks are 1, 2, 3, 4, and 5 in order from the top of the reference diagram.

As is clear from this reference diagram I, U/R1 shows a good slab with 100% scale peeled off, and is ranked 2.
According to 3.4, the peeling was not good, and rank 5 was the worst peeling condition with the most remaining scale.

At this time, not all of these remaining scales become scale defects on the finished product, and most of them are peeled off during the subsequent rolling process, but the more scale remains after descaling, the higher the rank. The lower the value, the higher the probability that scale defects will appear on the product, and there is an extremely strong correlation between the rank of remaining scale and the scale defects on the product.

Regarding the above-mentioned rank, it has been found that when the residual scale rank is 3 or higher, the probability that scale defects will appear on the finished product is extremely high.

Therefore, in order to reduce scale defects, it is necessary to prevent the occurrence of residual scale of rank 3 or higher after descaling as much as possible.

Figure 2 shows S of all the slabs investigated as described above.
This shows the frequency of occurrence of each rank of each residual scale for each heating furnace 1, 2, and 3 for only i-killed slabs of the same steel type. The vertical axis shows the frequency of occurrence [shares], and the horizontal axis shows the frequency of occurrence [shares]. Ranks 1 to 5 in the reference diagram are shown.

Looking at the results of this chart, we can see that there are clear differences in the descaling status of each species.

That is, the slab in No. 3 reactor 3, which has the shortest distance to the descaler 51, is most descaled, and the farther the distance is, the worse the descaling performance is.

Therefore, for an experimental opportunity different from that shown in Fig. 2, some of the slabs from the No. 3 furnace 3 were extracted from the furnace, and after waiting for 25 seconds on the roller table 4, they were passed through the descaler 5. The descaling situation was compared with that of the slab extracted from the furnace and immediately passed through the descaler 5, and the frequency of occurrence of each rank of residual scale in the slab at this time is shown in FIG.

The solid line in the figure is the one that was air-cooled for about 25 seconds after extraction and sent to the descaler, and the dotted line is the one that was sent to the descaler immediately after extraction. It was confirmed that descaling performance was clearly deteriorated by waiting on a roller table.

Furthermore, what is shown in Figure 4 is the slab extracted from various types (
This graph shows the relationship between the scale surface temperature immediately before the descaler and the rank of the remaining scale after descaling for Si-killed steel (Si killed steel only).The horizontal axis is the scale surface temperature immediately before the descaler. , and the vertical axis shows the frequency of occurrence [strains].As is clear from the chart, when the surface temperature of the scale is low, the frequency of occurrence of ranks 3 and 4 with poor remaining scale condition is high. Prove.

This statement shows that the factor that has played a fundamentally important role among the various experimental results described in Section 1 is the scale temperature of the slab surface during descaling.

In other words, in order to maintain good descaling performance, it is necessary to keep the surface temperature of the scale as high as possible during descaling, specifically at 1000°C or higher. This is because the physical properties of scale change due to temperature. This is due to the magnitude of thermal shock during rapid cooling by the descaler.

If the heating temperature of the slab in the furnace is kept high in order to keep the temperature high during descaling, the surface of the slab will be overoxidized, which will actually deteriorate the descaling performance and reduce the Since it is not convenient from a unit standpoint, the time it is exposed to high temperatures in the furnace is as short as possible, and it is necessary to consider a means of descaling at as high a temperature as possible.

Figure 5 shows the state in which the scale surface temperature of the slab surface decreases over time using actual measurements and calculation results. In the figure, the horizontal axis indicates the air cooling time (unit: 5 ec), and the vertical axis It shows the scale surface temperature of the slab surface, and the solid curve is the calculated temperature, and the calculation conditions are as added in the same table.

The conventional hot rolling equipment used in hot rolling mills for thin sheets, rolling mills, and plate mills is basically the same as shown in the first diagram above, and these conventional equipment Now, it has already been clearly proven by the above-mentioned experiment and study results that the steel material extracted from the furnace farther from the descaler 5 has worse descaling properties. As was previously clarified, the more it is, the more it is descaled.

As a result of further advancing these research results, the present invention has found that when the scale temperature on the surface of the heated steel material extracted from the heating furnace is high, the scale can be reduced by simply cooling the surface with a water cooling device such as water spray or laminar flow. Therefore, in the present invention, the conventional hot rolling equipment as illustrated in FIG. We decided to install it, and the example of its arrangement is shown in the 6th section.
As shown in the figure.

In other words, in the same figure K $-1 mother species 1, No. 2 reactor 2.3 mother species 3,
A power-rotating heat furnace arranged like the No. 4 furnace 7, a roller table 4 commonly arranged in front of the furnace, a descaler 5 of the descaling unit, and a rough rolling mill 6 of the rolling equipment are arranged as shown in the figure. Each heating furnace 1, 2, 3 is equipped with hot rolling equipment.
．． 1 Cooling spray (water cooling) for removing scale from heated steel materials 8a, 8b, 8c, 8d, 8e on the exit side of 7, respectively
are arranged as shown in the figure.

By arranging the cooling sprays 8a to 8e in this way, the surface scales of the slabs (heated steel materials) coming out of each furnace are cooled down. The time in the past passing through the device (
The temperature is on the order of about 15 seconds, and the scale surface temperature of the slab surface at this time is about 1050°C, as shown in Figure 5.
°C or higher, and by cooling at such high temperatures, the scale easily lifts off from the steel surface.
The scale flaws are completely removed from the surface of the steel material by the high-pressure water descaling unit of the descaler 5 before the rolling installation, and therefore scale flaws in the rolled product can be eliminated.

In order to clearly understand the cooling effect of the water cooling device, the present inventors extracted the heated slab from the heating furnace, and then extracted it from the half side of the slab A in the negative width direction, as shown in the photograph substituted for the drawing in Reference Figure n. Only A1 was cooled by a cooling spray (water cooling device), the other half A2 was not cooled, and was conveyed by a roller table 4 and subjected to descaling treatment by a high-pressure water jet by a descaler 5. Yes, reference figure 1
As is clear from 1, descaling was performed well on the f outer side A1 which had been cooled in advance with a cooling spray, but descaling was not good on the untreated half side A2, and the effect of the 4 cooling treatment according to the present invention was Very clear.

The present invention is as described above, and can significantly contribute to improving the quality of products by eliminating scale defects that occur in products rolled by conventional hot rolling equipment.

Conventionally, as a descaling means for heated steel materials of this type, there are many methods that involve various changes in the water jet content and usage conditions, such as high-pressure water jet in the descaler 5 installed in front of the rolling mill, but the present invention As already mentioned, in current rolling lines, etc., there are multiple heating furnaces attached to the rolling mill, and the distance and time required to reach the rolling mill from the heating furnace are different. Moreover, the scale surface temperature differs from furnace to furnace depending on the distance and time.

Even if steel materials having different scale surface temperatures are cooled with water by being placed in a descaler at a fixed position, the descaling effect will vary.

In the present invention, from the perspective of descaling effect, the scale surface temperature is as high as possible for good descaling performance. By water-cooling the steel material coming out of the furnace, the scale surface temperature is uniformly high regardless of the difference in furnace position, so the scale can be effectively floated here, and the descaler Since the removal is of scale that has already surfaced, the scale removal effect is always stable and uniform.

In addition, since the scale surface temperature is maintained at a high temperature, there is no need to heat the heating furnace more than necessary.
There is no risk of overoxidation on the slab surface, fuel consumption can be suppressed, there is no need for the complexity of changing the heating temperature for each furnace at different distances, and ordinary water spray is sufficient for water cooling. In particular, since there is no need to use high-pressure water, the unit power consumption can be reduced, and effective descaling can be achieved with energy savings.

Moreover, according to the present invention, it is sufficient to arrange a relatively simple water cooling device in the conventional hot rolling equipment as in the embodiment, and the implementation is extremely easy, but the operation is also extremely complicated. Moreover, the continuous consistency of the hot rolling process line is not impaired in the slightest, and the effect is extremely reliable and great.

In the present invention, the description has been mainly given to a hot rolling plate mill, but this is not limited to this, and it is to be understood that the present invention can be applied to all types of heating furnaces for descaling in general hot rolling equipment. Not even a long time ago.

[Brief explanation of the drawings] Figure 1 is an explanatory diagram of an example of conventional hot rolling equipment, Figure 2 is a diagram of residual scale rank and occurrence frequency distribution of heated steel in a conventional heating furnace, and Figure 3 is a diagram of extracted steel Immediate descaler feed and descaler feed after waiting and if? Figure 4 is a diagram of the scale surface temperature and occurrence frequency distribution of each rank, Figure 5 is an explanatory diagram of the transition state of the scale surface temperature, and Figure 6 is an example of the present invention. FIG. 1.2, 3, 7...Heating furnace, 4...Roller full, 5...Descaler-6...Roughing mill, 8a-8
e...Cooling spray.

Claims (1)

[Claims] 1 A heating furnace, a high-pressure water injection descaler, and a hot rolling machine for steel materials are arranged in this order, and a water cooling device for descaling the heated steel material is provided on the outlet side of the heating furnace. Steel hot rolling equipment.