KR100305697B1 - Hot rolling method for preventing surface defects during rough rolling of stainless steel - Google Patents

Abstract

PURPOSE: A method is provided which manufactures a hot rolled stainless steel sheet having superior surface quality by installing steam sprayers at the outlet side of widthwise rolling rolls and the outlet side of No. 1 rough rolling stand during the hot rolling process, thereby effectively preventing "M" shaped defects. CONSTITUTION: In a hot rolling process producing stainless, the hot rolling method for preventing surface defects during rough rolling of stainless steel comprises the step of installing steam sprayers(14) at points each of which are 2500 mm distanced from the outlet side of widthwise rolling rolls(17) and the outlet side of No. 1 rough rolling stand(18) during the hot rolling process so as to prevent "M" shaped defects generated at the No. 1 rough rolling stand(18) and the No. 2 rough rolling stand(19), thereby spraying stream onto the slab surface of up to 200 mm points of both edge parts of a stainless steel slab in a pressure of 15 to 25 kgf/cm¬2 and hurriedly building a rough structured scale layer on the rolled material before rolling a stainless steel rolled material with No. 1 rolls and No. 2 rolls of the rough rolling stands so that the stainless steel rolled material is smoothly rolled using the scale layer as a lubricating agent.

Description

Hot rolling method for preventing rough surface defects of stainless steel

The present invention relates to a hot rolling method for preventing surface defects during rough rolling of stainless steel, and more particularly, M generated in the first rough rolling stand and the second rough rolling stand during stainless steel hot rolling. In order to prevent mold defects, water vapor injection devices are installed on the exit of the width rolling roll and the exit of the first rough rolling stand during the hot rolling process to artificially create scale on the surface of the stainless slab to effectively prevent M-type defects. A method for producing this excellent stainless hot rolled steel sheet.

In general, in the rough rolling shear portions 18 and 19 during the process of hot rolling stainless steel, friction occurs between the surface layer of the rolled material and the rolls, and the width of the stainless slab 11 is caused by friction between the surface layer of the rolled material and the rolls. Cracks are generated in the direction, which causes the surface quality of the product to degrade.

Conventionally, during the hot rolling process for producing stainless steel, oil or solid lubricant is sprayed on the work roll surface immediately before rolling in the rough rolling shear to form an oil film between the roll and the rolled material so that rolling between the roll and the rolled material occurs smoothly. To prevent cracks occurring in the width direction of the stainless slab 11.

Figure 1 schematically shows a hot rolling method of a conventional stainless steel to prevent the M-type defect by the hydraulic rolling as described above.

In this conventional method, oil and water are sprayed together on the surfaces of the rough rolling rolls 18 and 19 when rolling the stainless slab 11 evicted from a heating furnace (not shown). Oil and water are sprayed with 10 nozzles / cm ² of hydraulic pressure on the working rolls of the F1, F2, and F3 stands with 6 nozzles 16 per hour.

When oil and water are sprayed, an oil film is formed between the roll and the rolled material to exert a lubricating effect, thereby suppressing friction between the rolled material and the roll.

When the above method is used, the friction between the rolled material and the roll is suppressed to prevent defects occurring on the surface of the steel sheet. However, oil and solid lubricants are used to contaminate the atmosphere of the hot rolling mill and contaminate the cooling water. Environmental problems occur.

In addition, due to the lubrication action of the oil and the solid lubricant deteriorates the flowability of the rough rolling process, the workability is lowered, there is a problem that the productivity is lowered.

In addition, in order to suppress the surface defects of stainless steel, a roll material having a small coefficient of friction may be selected and used (p264 of firing and processing 28 (1987), p35 of steel research No. 335 (1989)).

However, it is not effective to reduce surface defects of stainless steel by selecting roll material with small friction coefficient and to reduce the defect rate.

The present invention for solving the above problems is to roll out the rolled roll during hot rolling process to prevent M-type defects occurring in the first rough rolling stand and the second rough rolling stand of the hot rolling process for producing stainless steel It is an object of the present invention to provide a method for manufacturing a stainless steel hot rolled steel sheet having excellent surface quality by effectively preventing the M-type defect by installing a steam spraying device on the exit side of the first rough rolling stand.

In order to achieve the above object, the present invention provides a rolled rolled side and a first rolled roll during hot rolling to prevent M-type defects occurring in the first rough rolling stand and the second rough rolling stand of the hot rolling process for producing stainless steel. By installing a water vapor injection device at 2500mm on the exit side of the cold rolling stand and spraying water vapor at a pressure of 15-25kg / cm ^{2 on} the surface of the slab up to 200mm on both edges of the stainless slab, It is a method of effectively preventing M-type defects by urging a scale layer of a rough structure on the surface of a rolling material before rolling by the first roll and the second roll, so that lubrication rolling by the scale layer is performed during rolling.

1 is a schematic view of a conventional stainless steel hot rolling method,

2 is a schematic view of a stainless steel hot rolling method of the present invention;

3 is a schematic view showing the water vapor injection value of the present invention.

<Description of Major Symbols in Drawing>

11: Stainless steel slab 12: High pressure descaling device

13: Oil jet device 14: Steam jet device

15: Head 16: nozzle

17: Edge roll 18: R1 roll

19: R2 roll

Figure 2 schematically shows the M-type defect prevention hot rolling method of the present invention.

As shown in FIG. 2, the present invention provides a lateral rolling to prevent M-type defects occurring in the first rough rolling stand 18 and the second rough rolling stand 19 of the hot rolling process for producing stainless steel. The steam jetting device 14 is mounted at a position of 2500 mm without equipment interference on the exit side of the roll 17 and the exit side of the first rough rolling stand 18.

The water vapor spraying device 14 impregnates the scale layer of the rough structure on the surface of the rolling material by spraying water vapor onto the rolling material before the stainless rolling material is rolled by each rough rolling roll.

Since the scale layer formed on the surface of the rolled material is lubricated at the time of rolling, lubrication rolling at the time of rolling prevents M-type defects.

The occurrence of M-type defects is highly dependent on the high temperature oxidation amount of the stainless rolling material. As the scale layer on the surface of the rolled material becomes thicker, friction between the roll and the rolled material decreases during rolling due to lubrication by the scale layer. Therefore, by forming a sufficiently thick scale layer on the surface of the rolled material before rolling, this M-type defect can be prevented.

3 is a schematic view of a steam injection device 14 of the M-type defect prevention hot rolling method of the present invention.

During hot rolling of stainless steel, the edge of the slab is subjected to mechanical plastic deformation due to the width rolling, and the peeling form of the slab surface has a dog bone shape. However, the scale layer of the surface layer portion does not keep up with this plastic strain and is completely peeled off and is directly exposed to the surface of stainless steel.

At the center where plastic deformation cannot be achieved due to the rolling, the bonding force between the stainless metal and the scale layer is strong, and the residual scale layer remains because only the ability of the high-pressure water sprayed from the descaling device is not completely peeled off.

M-type defects occur mainly in the 0-200mm area on both edges where the scale is completely peeled off and exposed directly to the surface of stainless steel.

Therefore, when steam injection device 14 is installed in this part and water vapor is sprayed at a pressure of 15-25 kg / cm ² , the scale layer of the rough structure on the surface of the rolled material is suddenly rolled before being rolled by the rough rolling roll. Lubrication rolling is performed by the layer to prevent M-type defects.

Hereinafter, the present invention will be described in detail through examples.

(Example)

Table 1 shows the scale generation amount according to the pressure of the steam injection device.

Water vapor pressure (kg / cm ² ) 5 10 15 20 25 30 Scale production amount (㎛) 0.5 1.5 3.2 3.8 3.5 3.0

According to Table 1, the scale generation amount is 2.0 μm or less at 5-10 kg / cm ² water vapor pressure, but the scale generation amount is 3.0 μm or more at 15 kg / cm ² or more, and the scale generation amount is more than 30 kg / cm ² or more. It can be seen that the decrease.

As the thickness of the scale layer increases, the lubrication effect is excellent during hot rolling, so the appropriate steam pressure is 15-25 kg / cm ² .

Table 2 shows the incidence of M-type defects when hot rolling by the conventional method and the method according to the present invention.

Conventional rolling method Rolling method of the present invention M-type defect rate 5-10% 0-5% Pollution atmosphere O × cooling water O × Production cost rise Cost increase by using oil Use existing steam line

In case of rolling by the conventional method, the incidence of M-type defects of stainless steel is 5-10%, so that defects are relatively low, and the conventional method is also a good method for preventing defects.

However, environmental and cooling water pollution problems exist all the time, and oil is required, and cost increases due to the introduction of equipment.

The method according to the present invention has a very low M-type defect rate of 0-5%, and there is no environmental and cooling water pollution problem, and there is no cause of cost increase since the existing steam injection line is used as it is. Prevention method.

The present invention as described above can produce a stainless hot rolled steel sheet excellent in surface quality by effectively preventing the M-type defects by artificially creating a scale on the surface of the stainless bar by installing a water vapor spraying device on the width of the rolled roll exit and the rough-rolled stand exit. It has an effect.

Claims (1)

In the hot rolling process for producing stainless steel, the rolled roll 17 exits during the hot rolling process to prevent M-type defects occurring in the first rough rolling stand 18 and the second rough rolling stand 19. Water vapor injection device 14 was installed at 2500mm from the No. 1 crude rolling stand 18, and water vapor was applied to the surface of the slab up to 200mm at both edges of the stainless slab 11 at a pressure of 15-25 kg in / cm ² . After spraying and before the stainless rolling material is rolled by the first roll and the second roll of the rough rolling stand, the scale layer of the rough structure on the surface of the rolling material is urged to perform lubrication rolling by the scale layer during rolling. Hot rolling method for preventing rough rolling surface defects of stainless steel.

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