JPS5951361B2 - Hot rolling method for steel materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for hot rolling steel materials, mainly steel plates, and in particular to a method for effectively removing surface defects such as surface scratches that occur on the surface of steel materials during hot rolling. The present invention relates to a hot rolling method that makes it possible to perform the following steps.

Conventionally, in order to remove surface defects from hot-rolled products, intermediate products (slabs, billets, etc.) are hot-rolled or cast, and then cooled and surface inspected to remove surface defects. Thereafter, the intermediate product from which defects have been removed is reheated, and the final product is produced by rough rolling and finishing rolling.

However, in this conventional method, in the intermediate product process, the heat of the steel material heated to 1,000 to 1,350°C is released, surface defects are removed, and then the intermediate product is returned to the same level as before. The heat loss is approximately 60% in one cycle of cooling and heating.
It reached 0 to 1,000 x 103 kCaI/TON, which was extremely large, and had the drawback of being a big economic waste.

Furthermore, for reheating, heavy oil, kerosene, and LNG are usually used.
Fuels mainly based on fossil fuels such as LPG and coke oven gas, or gas fuels mainly based on waste gas from blast furnaces and converters, are used, but the waste gases produced by the combustion of these fuels are large, and these waste gases are The carbon, sulfur, and nitrogen oxides (COX, SOx, NOx) contained therein are a source of pollution and have become a social problem.

One of the solutions to the problems of conventional rolling methods is to eliminate cooling at the stage of intermediate products, and therefore omit reheating of intermediate products, or to make reheating very short and to reduce the amount of heat applied. It is possible that

However, it has been thought that such a solution method is extremely difficult to apply as an actual process because it is difficult to detect and remove surface defects at the intermediate product stage.

However, in recent years, there have been calls for an energy crisis due to the depletion of petroleum energy and soaring prices, as well as the issue of pollution, which has led to the detection and removal of surface defects in the hot state of the intermediate product stage mentioned above. Technology is being developed.

A typical technique developed from this point of view is described in Japanese Patent Application Laid-Open No. 50-36350.

The key point of this technology is to remove large flaws with a hot scarf, then perform hot flaw measurement to detect flaws that could not be removed with the hot scarf, and in some cases convert the flaw position into an electrical position signal. , the flaw cleaning machine uses a control device to perform flaw care, and after completely removing flaws that may cause harmful defects in the final product among the flaws occurring in the intermediate product, rough rolling and finishing are performed. Rolling is performed in the order of rolling to produce the final product.

However, such a method has the following problems.

First, the steel surface that is inspected for defects immediately after hot scarfing has temperature unevenness and surface irregularities caused by the nozzle position of the scarfing machine. difficult to use.

Hot flaw detection methods include methods that use ultraviolet or visible light emitted from high-temperature steel materials, methods that use infrared rays, methods that project light from outside and use the reflected light, and eddy current flaw detection. However, with either method, it is difficult to perform defect inspection immediately after hot scarfing.

Furthermore, if flaws are detected after a certain period of time (more than 1 minute) has elapsed after hot scarfing to eliminate temperature unevenness, the highly heated slab surface will oxidize in the air and form scale, making it difficult to detect flaws. It's impossible.

Therefore, in this case, descaling must be carried out by incorporating descaling equipment into the line.

In this case, a technique to make inspection for defects easier by forcibly cooling the surface of the steel material with a fluid (Japanese Unexamined Patent Publication No. 49-2011) is proposed.
4488, Japanese Unexamined Patent Publication No. 49-123389, etc.), the descaling method would be a fluid injection method that can rapidly cool the surface.

On the other hand, even steel materials whose surface defects have been completely removed by cooling intermediate products using conventional methods are not without problems.

In other words, there is no means to remove surface defects that occur during reheating, and conventional measures to prevent these types of defects have been to take passive measures such as improving reheating equipment to minimize the occurrence of surface defects. was.

That is, the conventional method has the disadvantage that it is not possible to remove scratches that occur during reheating.

Furthermore, when removing defects after cooling steel materials that are to be reheated, it is not necessary to remove small defects on the surface because they become scales and disappear before rolling. The amount of scale generated in the furnace is not necessarily constant, and it is difficult to judge whether or not the defect will become a surface defect in the final product.In order to ensure the quality of the final product, surface defects in the intermediate product must be extremely small. Until the green is removed, excessive care is unavoidable.

The purpose of the present invention is to solve the above-mentioned conventional problems, and to detect surface flaws in a hot state after manufacturing an intermediate product and before finish rolling.
It is an object of the present invention to provide a method for hot rolling steel materials that can easily and accurately detect surface defects and effectively remove defects that become surface defects in the final product. It is something to do.

In hot rolling steel materials, the present invention descales an intermediate product manufactured by blooming rolling or continuous casting, and then performs hot rolling at least once. The method is characterized in that the flaws are detected in the intermediate state, the flaws are removed based on the detection results, and then the rolling is continued to produce the final hot rolled product.

Furthermore, when carrying out the method for hot rolling steel materials according to the present invention, it is preferable to automatically detect surface flaws and automatically take care of the flaws. A rolling mill that hot-rolls an intermediate product manufactured by continuous casting at least once after descaling; a surface flaw detection device that detects surface flaws in a steel material rolled by the rolling mill in a hot state; A heat-removing device that removes surface flaws based on the detection results of this detection device, and a rolling mill that continues to roll the steel material from which the surface flaws have been removed to produce the final hot-rolled product are arranged in sequence. Is it possible to use an inter-rolling device?
can.

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a flowchart showing a conventional rolling method in which a steel material is once cooled at an intermediate product stage for inspection and maintenance of surface defects.

Slag obtained by uniformly heating to a temperature suitable for blooming in a soaking furnace in a soaking process 1, for example, followed by blooming in a blooming process 2 or continuous casting in a continuous casting process 3, In the hot skirting process 4, defects are removed from the pilutte, and in the cooling process 5, the steel material is once cooled. After the defects on the surface of the cooled steel material are detected and taken care of, they are heated to a high temperature in the reheating process 8 and rolled. In step 9, it is rolled using a feed rolling mill.

In this conventional rolling method, the steel material is cooled once for surface flaw inspection and maintenance, which is not economical and has drawbacks such as the generation of pollution during reheating. There is a drawback that the defects that occur cannot be removed.

Figure 2 shows that, as shown in Figure 1, surface flaws are detected and treated in a hot state without having to be cooled down, increasing economic efficiency and reducing pollution during reheating. 2 is a flowchart showing a conventional rolling method that can prevent the above-described problems.

That is, after uniformly treating an intermediate product that has been subjected to blooming rolling or continuous casting in a hot skirting process 4, surface flaws are detected in a hot flaw detection process 9, and hot flaws are detected according to the detected flaw information. In the care step 10, the flaws are taken care of, and then the material is sent to the rolling step 8 and rolled, or if necessary, it is reheated in the reheating step 7 and then rolled.

However, in such conventional rolling methods, flaws are detected immediately after the hot scarf step 4, but in this state the steel material has uneven temperature and many surface irregularities, making it extremely difficult to accurately detect surface flaws. .

In particular, it is nearly impossible to distinguish between flaws that remain on the final product and surface flaws that disappear through heating, etc. and do not remain on the final product, so it is necessary to remove any type of flaw. There was no choice but to do excessive maintenance.

In addition, if the steel material is left for a period of time long enough for the hot scarf liquid to oxidize in order to eliminate temperature unevenness, scale will form on the surface of the steel material, making it almost impossible to inspect for defects.
It is necessary to perform descaling before use for defect inspection, and additional scaling equipment for defect inspection is required.

FIG. 3 shows a flowchart showing the sequential steps of the rolling method according to the invention, which makes it possible to eliminate the above-mentioned drawbacks.

In the present invention, slabs, billets, etc. that have been subjected to blooming and rolling in the soaking process 1 and the blooming process 2 or continuously cast in the continuous casting process 3 are treated in the hot scarf process 4, and then directly or as necessary undergo a reheating process. After reheating in step 7, rolling is performed at least once in a primary rolling step 8a.

Thereafter, in a hot flaw detection step 9, surface flaws on the steel material in a hot state are detected, and in accordance with the detected flaw information, the surface flaws are repaired in a hot state in a hot flaw care step 10.

After the treatment, rolling is continued in a secondary rolling step 8b to obtain a final product.

That is, in the present invention, the rolling operation is divided into two steps, primary rolling and secondary rolling, and hot flaw detection and hot flaw maintenance are performed between them.

According to the above-mentioned rolling method of the present invention, the drawbacks and problems of the above-mentioned conventional method are solved as follows.

First, in the present invention, the defects such as temperature unevenness and surface irregularities that occur when performing a flaw inspection immediately after hot scarfing are inspected for defects on the surface of a steel material that has been rolled at least once. The problem can be solved by this, the temperature unevenness can be almost ignored, and the surface unevenness is extremely smooth and smooth.
It is optimal for hot flaw detection.

Second, the problem of scale that occurs on the surface is solved by the present invention.
This problem is solved by performing a flaw inspection immediately after the next rolling process 8a.

That is, in general, in hot rolling, descaling is performed just before the steel material is bitten by the rolling mill rolls, because rolling with scale on the surface will result in scale defects in the final product and reduce its commercial value.

Therefore, the surface of the steel material that is rolled out of the rolling mill usually has almost no scale.

Furthermore, in hot rolling, the temperature of the rolling rolls is lower than that of the steel to be rolled, so the temperature of the rolled steel is lowered by contact with the rolls during rolling, and in particular the surface temperature of the steel may temporarily drop to 500 to 700. It is estimated that the temperature will be around ℃.

In the present invention, since the flaw inspection is performed immediately after the primary rolling, not only is there no need for a special descaling device for this flaw inspection, but the surface of the rolled steel material is There is no need for forced rapid cooling using fluid.

In the example shown in FIG. 3, after the hot scarf step 4, cooling is performed once in the cooling step 5, surface flaws are detected, and the maintenance step 6 is performed.
If the conventional method of reheating and rolling is used in the reheating step 7 or the hot scarf step 4
Surface flaws that occur during reheating when reheating after
After hot scarfing, it can be detected and treated as accurately and easily as directly pressed steel.

In addition, in such cases, there is no need to completely clean up defects after cooling, and the final product is charged into the heating furnace with small defects that disappear as scale in the reheating furnace. This means that flaws can be detected and removed after being extracted from the heating furnace for rolling, which also has the advantage of reducing the burden of maintenance after cooling.

FIG. 4 is a side view showing the configuration of an example of a rolling apparatus for carrying out the hot rolling method according to the present invention.

Slabs, billets, etc., which have been subjected to blooming rolling or continuous casting, are passed through the hot scalpers 12a and 12bi to treat the front and back surfaces, and then passed through the primary rolling mill rolls 13a and 13b. Next rolling is performed.

Immediately before this rolling roll, there is a scaling device 14a.
, and 14b are placed to remove scale on the surface of the steel material.

Immediately after the primary rolling roll, flaw inspection devices 15a and 15b are provided to detect surface flaws on the front and back surfaces of the steel material, and their detection outputs are supplied to controllers 16a and 16b.

The flaw detection devices 15a and 15b may adopt a method of detecting ultraviolet or visible light emitted from high-temperature steel materials, a method of detecting infrared rays, a method of detecting reflected light from the surface of steel materials, an eddy current flaw detection method, etc. can.

As mentioned above, the primary rolling roll 13a. Since the surface of the steel material 11 rolled by the steel material 13b has few irregularities, there is no temperature unevenness, and the scales are removed by the descaling devices 14a and 14b, detection of surface flaws becomes easy and accurate.

The controllers 16a and 16b generate a flaw cleaning signal based on the flaw inspection signal, which is sent to the hot scarfers 17a and 17b placed on the front and back sides of the primary rolled steel material.
to remove large surface defects that may remain as surface scratches in the final product.

The steel material whose surface has been treated in this way is further passed through secondary rolling rolls 18a and 18b, and rolling is continued to obtain a final product free of surface defects.

It goes without saying that the present invention is not limited to the above-mentioned examples, but can be modified in many ways.

For example, the primary rolling does not necessarily have to be performed once, but can be performed multiple times.

For this purpose, reciprocating rolling may be performed, and in this case, surface flaws can be removed even better by performing flaw inspection and maintenance each time.

In addition, in the device shown in Figure 4, the front and back surfaces of the steel material are treated, but if the final product is to remove defects only on the surface and only needs to be removed, it may not be sufficient to treat only the surface. be.

Furthermore, although the apparatus shown in FIG. 4 automatically takes care of the flaws, this can also be done manually or semi-automatically.

[Brief explanation of the drawing]

Figure 1 is a flowchart showing the sequential steps of a conventional rolling method in which surface flaw inspection and care are performed after cooling once, and Figure 2 is a flowchart showing the conventional rolling method in which surface flaw inspection and care are performed after cooling. Flowchart showing the sequential steps of the rolling method, Part 3
The figure shows the sequential steps of the rolling method of the present invention, in which primary rolling is performed immediately before hot inspection and maintenance.
FIG. 4 is a side view showing the configuration of an example of a rolling apparatus for carrying out the hot rolling method of the present invention. 1... soaking process, 2... blooming rolling process, 3... continuous casting process, 4... hot scarfing process, 8a...・・Primary rolling process, 9・・
...Hot flaw detection process, 10...Hot flaw care process, 8b...Secondary rolling process, 11...
・Steel material, 12a, 12b...Hot scarfer, 13a, 13b...Primary rolling roll, 14a
, 14b...Descaling device, 15a, 1
5b... Hot flaw inspection device, 17a, 17b...
...Hot flaw care equipment.

Claims (1)

[Claims] 1. When hot rolling steel materials, after descaling an intermediate product manufactured by blooming rolling or continuous casting, hot rolling is performed at least once, and then the surface defects of the rolled steel material are brought to a hot state. 1. A method for hot rolling steel materials, which comprises: detecting defects, removing defects based on the detection results, and then continuing rolling to produce a final hot rolled product.