KR101311771B1 - Method for reheating steel materials - Google Patents

Abstract

The heating method of the material of the present invention comprises the steps of charging a carbon steel material containing silicon in a heating furnace; Preheating the material; A first heating step of raising the temperature of the material; A second heating step of reducing the temperature of the furnace to reduce the temperature deviation between the surface and the inside of the material; A third heating step of raising the temperature of the material; And it comprises a cracking step to reduce the temperature deviation of the surface and the inside of the material, characterized in that the temperature of the material in the heating furnace is maintained below the melting point of the Payalite.
According to the present invention it is possible to significantly improve the surface quality of the material through the heating process control. In particular, it is possible to essentially remove the red scale of the material comprising 0.15% to 1.20% by weight of carbon and 0.10% or more by weight of silicon.

Description

Method for reheating steel materials

The present invention relates to a method of heating a material, and more particularly to a method of heating a material that can significantly improve the surface quality of the material.

In the case of the exterior plate material for automobiles, the plate material for home appliances, surface quality becomes a very important control factor, and scalability defects are pointed out as a big problem of such hot rolled steel sheet. Recently, automobile finished car makers and companies handling various electronic products are demanding the demand for the surface quality of the hot rolled steel sheet.

In order to improve the surface quality, the descaler is installed during hot rolling to remove the scale of the surface of the hot rolled steel sheet, but there are scale defects that are not removed even by the descaler.

The technical structure described above is a background technique for assisting the understanding of the present invention, and does not mean the prior art widely known in the technical field to which the present invention belongs.

An object of the present invention is to provide a method of heating a material that can significantly improve the surface quality of the material.

Another object of the present invention is to provide a method for heating a material which can fundamentally remove red scale.

Still another object of the present invention is to provide a method for heating a material which can improve the surface quality of a material including 0.15 wt% to 1.20 wt% carbon and 0.10 wt% or more silicon.

Method for heating a material according to an aspect of the present invention comprises the steps of charging a carbon steel material containing silicon in a heating furnace; Preheating the material; A first heating step of raising the temperature of the material; A second heating step of reducing the temperature of the heating furnace to reduce the temperature deviation between the surface and the inside of the material; A third heating step of raising the temperature of the material; And a cracking step for reducing the temperature deviation between the surface and the inside of the material, wherein the temperature of the material in the heating furnace is maintained below the melting point of the Payalite.

The material may comprise 0.15 wt% to 1.2 wt% carbon and at least 0.1 wt% silicon.

The first the first temperature (T _1), the temperature (T _2), the third heating step of the second gayeoldae of the heating furnace for performing the second heating step of gayeoldae of the heating furnace for performing the heating step The temperature T ₃ of the third heating zone of the heating furnace performed and the temperature T ₄ of the cracking zone of the heating furnace performing the cracking step may be T ₂ <T ₄ <T ₃ <T ₁ .

Specifically, the T ₁ may be 1,190 ℃ to 1,210 ℃.

Specifically, T ₂ may be 1,130 ° C. to 1,160 ° C.

Specifically, T ₃ may be 1,170 ° C. to 1,190 ° C.

Specifically, the T ₄ may be 1,160 ℃ to 1,180 ℃.

More specifically, T ₁ may be 1,200 ° C., T ₂ may be 1,150 ° C., T ₃ may be 1,180 ° C., and T ₄ may be 1,170 ° C.

The ashing time of the material may be 160 minutes to 230 minutes.

Temperature difference between the material surface after finishing the first heating step (ΔT ₁ ), Temperature difference between the material surface after the second heating step (ΔT ₂ ), and the material surface and inside after the third heating step between the temperature difference (ΔT _3), after the cracking step the material surface and the temperature difference within the (ΔT ₄₎ ΔT ₄ <ΔT ₂ , ΔT ₃ < The relationship of ΔT ₁ can be satisfied.

According to the present invention it is possible to significantly improve the surface quality of the material through the heating process control. In particular, it is possible to fundamentally eliminate the enemy scale of a material comprising from 0.15% to 1.2% by weight of carbon and at least 0.1% by weight of silicon.

1 is a view showing a temperature profile and a furnace temperature of a material according to an embodiment of the present invention.
2 is a partial cross-sectional view of a heating furnace according to an embodiment of the present invention.
3 is a perspective view of a rolling apparatus according to an embodiment of the present invention.
4 is a cross-sectional view showing the interface structure of the material according to an embodiment of the present invention.

Hereinafter, an embodiment of a heating method of a material according to the present invention will be described with reference to the accompanying drawings. In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or an operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

1 is a view showing a temperature profile and a furnace temperature of a material according to an embodiment of the present invention, Figure 2 is a partial cross-sectional view of the heating furnace according to an embodiment of the present invention, Figure 3 is an embodiment of the present invention 4 is a sectional view showing an interface structure of a raw material according to an embodiment of the present invention.

The present invention relates to a method for heating a carbon steel material containing silicon, and more particularly, to a method for heating a material containing 0.15 wt% to 1.20 wt% carbon (C) and 0.10 wt% or more silicon (Si). will be.

In the present invention, the object to be heated in the furnace and the object subjected to hot rolling are referred to collectively as 'material'. That is, the material may refer to slabs, blooms, billets, and the like, manufactured through a playing process. In addition, the slab or bloom is supplied to a heating furnace and heated, followed by rough rolling, finishing rolling, and the like. The material refers to a bar after rough rolling, a strip after finishing rolling, and the like. May be used.

Silicon is a ferrite stabilizing element and an element that improves the activity of carbon. During heat treatment, it helps to move carbon in Cementite of Perlite structure and decreases carbon content in the structure, thereby improving toughness and ductility. In addition, silicon is added as a deoxidizer to remove oxygen in the steel during the steelmaking process, and is dissolved in ferrite to increase strength.

However, when silicon is added to the steel, a red scale occurs in the hot rolling process, and the red scale is hardly peeled off by a descaler, thereby deteriorating the surface quality of the hot rolled steel sheet. In particular, in the case of high carbon steel containing 0.15 wt% to 1.20 wt% carbon, the silicon content is higher than that of general steels in order to improve heat treatment. That is, the silicon content is often higher than 0.10% by weight, in particular 0.30% by weight or more. In this case, many red scales occur during hot rolling of the material.

Red scales are known to be produced by Payallite (Fe ₂ SiO ₄ ) formed on the material surface. The present invention can maintain the temperature of the material below the melting point (about 1,173 ℃) of the Payalite while the material is passed through the heating furnace to suppress the production of Payalite. In addition, by controlling the heating conditions in the furnace to reduce the temperature deviation between the surface and the inside of the material to prevent the generation of scalability defects, including red scale, and to reduce the heating temperature of the material to facilitate the subsequent rolling process can do.

1 and 2, the heating method of the material according to an embodiment of the present invention is a pre-heating step (not shown), the first heating step, the second heating step, the third heating step and cracks to preheat the material Steps. In the drawing shown in FIG. 1, the solid line represents the temperature change of the inside (center) of the material temperature-time graph, and the dashed-dotted line represents the temperature change of the material surface.

The preheating stage is the preheating stage F ₀ of the heating furnace 100, the first heating stage S ₁ is the first heating stage F ₁ of the heating furnace 100, and the second heating stage S ₂ is the heating furnace. The second heating table F ₂ , the third heating step (S ₃ ) of the third heating table (F ₃ ) of the heating furnace 100, the cracking step (S ₄ ) corresponds to the cracking zone (F ₄ ) of the heating furnace. do.

The preheating step (not shown) is a step of preheating the material S charged in the heating furnace 100. The preheating step is the heat (hot air) from the heating apparatus (112, 116, 120, 124) of the heating furnace installed for the subsequent heating step (F ₁ , F ₂ , F ₃ ) and the cracking step (F ₄ ) ) To preheat the material. That is, in the preheating zone F ₀ of the heating furnace 100, a heating device may not exist on the upper and lower portions of the raw material S. Of course, according to the configuration of the heating furnace 100 may be provided with a heating device in the preheating zone (F ₀ ).

The first heating step (S ₁ ) is a section for increasing the temperature of the material that passed the preheating step is a section for heating to a constant temperature to roll the material. In the first heating step S ₁ , the temperature of the heating furnace 100 is set to T ₁ . Since the material S is heated from the surface, the temperature of the surface of the material S is maintained higher and the heat is transferred to the inside, so that the temperature of the material S increases gradually. After finishing the first heating step (S ₁ ) the temperature difference between the surface and the inside of the material (S) is ΔT ₁ .

In the present invention, the temperature inside the material (S) means the temperature of the point located in the center of the thickness of the material (S), the center of the length, and the width of the material (S), more specifically the temperature at the center of gravity of the material (S) it means.

The second heating step (S ₂ ) is a section for reducing the temperature deviation of the surface and the inside of the material (S) by lowering the temperature of the heating furnace. To this end, the temperature of the heating furnace 100 during the second heating step S ₂ is set to T ₂ (T ₂ <T ₁ ) lower than the first heating step S ₁ . Since the surface is gradually cooled from the surface of the material S, the temperature deviation between the surface of the material and the interior is reduced after a certain time. That is, after the second heating step S ₂ , the temperature difference ΔT ₂ between the surface of the material S and the inside becomes smaller than ΔT ₁ .

The third heating step S ₃ is a section for increasing the temperature of the material S again. It is desirable to keep the temperature of the material S (i.e., the surface of the material and the inside of it) below the melting point (T _m ) of the payalite to prevent the formation of red scale, but to reduce the rolling load as much as possible It is preferable to keep the high. Therefore, the third heating step (S ₃ ) is a section that allows the rolling to be made smoothly by raising the temperature of the material surface and the inside as high as possible while maintaining the temperature of the material below the melting point (T _m ) of the payalite. For this purpose, the temperature T ₃ of the furnace is preferably set higher than T ₂ and lower than T ₁ .

The temperature difference ΔT ₃ between the surface and the inside of the material S after passing through the third heating step S ₃ may be smaller than or larger than ΔT ₂ , but preferably smaller than ΔT ₁ . That is, the heating time (process time) of the second heating step (S ₂ ), the temperature of the heating furnace, the heating time of the third heating step (S ₃ ), the temperature of the heating furnace, and the shape, physical properties, etc. of the material (S) It may vary.

The cracking step (S ₄ ) is a section that finally reduces the temperature difference between the material (S) surface and the interior. In the cracking step S ₄ , it is preferable to keep the temperature of the surface of the material S and the temperature below the melting point T _m of the Payalite and to reduce the temperature difference between the material surface and the material as much as possible. In this way, suppression of scale generation including red scale, reduction of rolling load, prevention of rolling failure due to temperature variation between the material surface and the inside, and the like are possible. That is, it is preferred that the cracking step (S ₄₎ the material surface and the temperature difference within the ΔT ₄ after finishing is minimized. Specifically, ΔT ₄ <ΔT ₂ , ΔT ₃ < It is preferable to make it ΔT ₁ . Ideally, ΔT ₄ would be 0 ° C., but a slight temperature deviation may occur due to the limitations of the production process.

The total process time during the preheating step, the first heating step (S ₁ ), the second heating step (S ₂ ), the third heating step (S ₃ ), and the cracking step (S ₄ ), that is, the rework time is 160 Minutes to 230 minutes are preferred. If it is less than 160 minutes, it is difficult to reduce the temperature deviation between the surface and the inside of the material while heating the material (S) below the melting point (T _m ) of the Payalite, and if it exceeds 230 minutes, it is not preferable in terms of productivity. Therefore, the resetting time may be effective to set to 160 minutes to 230 minutes, preferably 180 minutes to 200 minutes.

Specifically, within the idle time range, the preheating step is 50 minutes ± 10 minutes, the first heating step (S ₁ ) 30 minutes ± 10 minutes, the second heating step (S ₂ ) 25 minutes ± 10 minutes, The three heating stages (S ₃ ) may be valid for 35 minutes ± 10 minutes and the cracking stage (S ₄ ) for 40 minutes ± 10 minutes, but there is no limit to the rework time of each heating and cracking step.

The material S must be kept below the melting point of the Payalite while passing through the furnace 100. To this end, a temperature T ₁ of the first heating zone, a temperature T ₂ of the second heating zone, a temperature T ₃ of the third heating zone, and a temperature T _{4 of the} cracking zone are set to satisfy T ₂ <T ₄ <T ₃ <T ₁ . It is preferable in view of scale suppression such as red scale, reduction of temperature difference between the material surface and the inside, and rolling efficiency.

The temperature relationship is only one embodiment, and if the material (S) is maintained below the melting point (T _m ) of the Payalite is not limited to the method of setting the temperature of the heating furnace.

For example, the temperature of the first heating zone F ₁ for performing the first heating step S ₁ for heating the material S may be set to 1,190 ° C. to 1,210 ° C., preferably 1,200 ° C. It is preferable to heat 30 minutes ± 10 minutes in the above temperature range. A second temperature of the second gayeoldae (F ₂₎ to perform the heating step (S ₂₎ may be set to 1,130 to 1,160 ℃ ℃, preferably from 1,140 to 1,150 ℃ ℃, preferably 1,150 ℃ more. It is preferable to heat 25 minutes ± 10 minutes in the above temperature range. The temperature of the third heating zone (F ₃ ) performing the third heating step (S ₃ ) may be set to 1,170 ℃ to 1,190 ℃, preferably 1,180 ℃. It is preferable to heat 35 minutes ± 10 minutes in the above temperature range. The temperature of the crack zone F ₄ for performing the cracking step S ₄ may be set to 1,160 ° C. to 1,180 ° C., preferably 1,170 ° C. It is preferable to crack for 40 minutes ± 10 minutes in the above temperature range.

2, the heating furnace 100 according to an embodiment of the present invention is a preheating table (F ₀ ), the first heating table (F ₁ ), the second heating table (F ₂ ), the third heating table (F ₃ ). And cracks F ₄ .

The raw material S is charged through the charging unit 102 and is extracted from the heating furnace through the extraction unit 104. The charging unit 102 may be opened and closed by the charging door 106, and the extraction unit 104 may be configured to be opened and closed by the extraction door 108.

The heating furnace 100 may further include a skid beam 110 which is continuously arranged from the charging unit 102 to the extraction unit 104 and on which the material S to be heated is mounted. The skid beam 110 may be composed of a fixed beam for supporting the material S and a walking beam for advancing the material S, and the working beam while the material S is heated in the heating furnace 100. By raising, advancing, lowering and reversing the silver raw material S, the raw material S can be gradually transferred from the charging unit 102 toward the extraction unit 104.

The first heating table F ₁ may be provided with a first heating device 112 and a first temperature measuring device 114 for measuring the temperature of the first heating table F ₁ . The second heating device 116, the second temperature measuring device 118, the third heating device 120, and the second heating device F ₂ , the third heating table F ₃ , and the cracking table F ₄ , respectively. The third temperature measuring device 122, the fourth heating device 124 and the fourth temperature measuring device 126 may be provided. The preheating zone F ₀ may or may not have a heating device and a temperature measuring device. There may be no heating device but a temperature measuring device may be present. The position of the temperature measuring device 114, 118, 122, 124 is not limited, it may be installed on the cover portion of the upper portion of the heating furnace (100).

The first heating device 112, the second heating device 116, the third heating device 120 and the fourth heating device 124 is a gas such as heavy oil, natural gas, coke oven gas (COG) The burner may be a burner that increases the temperature in the furnace 100 by hot air by burning the gas, or may be an infrared heater, but a burner is preferable in view of cost. A plurality of burners may be installed and may be installed at both the upper and lower portions of the material S, or may be installed at only one of the upper and lower portions.

The first temperature measuring device 114, the second temperature measuring device 118, the third temperature measuring device 122, and the fourth temperature measuring device 126 may be used without limitation as long as the device can measure temperature. Thermocouples are preferred.

Preheating zone (F ₀ ), first heating zone (F ₁ ), second heating zone (F ₂ ), third heating zone (F ₃ ) and crack zone according to the initial temperature of the raw material (S), the final temperature required for extraction, etc. The target temperature, the temperature increase rate, the residence time and the like in (F ₄ ) are respectively controlled.

The temperature of the material (S) must be kept to less than a page to know light melting point and the temperature of the first gayeoldae (F ₁₎ To this end (T _1), the temperature of the second gayeoldae _{(F 2) (T 2)} , third temperature gayeoldae _{(F 3) (T 3)} , cracks for (F ₄₎ the temperature (T _{4) to, T 2 <T 4 <T} 3 scale inhibition, such as would ever scale to set so as to satisfy the <T ₁ between the It is preferable in terms of reducing the temperature difference between the surface of the material and the inside and rolling efficiency.

Referring to Figure 3, the rolling apparatus according to an embodiment of the present invention is a heating furnace 100, sizing press 200, rough rolling mill 210, edge heater 220, descaler 230, finishing mill ( 240, a runout table 250, a cooling unit 260, and a winding machine 270 may be included.

Heating furnace 100 is a reheating furnace (Reheating furnace) for hot rolling the material (S), since the configuration and processing conditions of the heating furnace 100 has been described above, a detailed description thereof will be omitted.

Slab sizing press (200) is a width rolling mill to reduce the width variation in the longitudinal direction of the material (S) and to roll to a certain width in accordance with the requirements of the end user. Rough mill (210, Roughing Mill) is rolled to the appropriate thickness and width required in finishing rolling. The movement of the raw material S from the entry side to the exit side of the rough rolling mill 210 or the movement of the raw material S from the exit side to the entrance side is called a pass, and such a pass may be performed a plurality of times. By using the recuperation phenomenon, it is possible to set a waiting time for reducing the temperature gradient of the material (S).

The edge heater 220 may be installed to prevent a temperature drop of the edge portion of the material S, and the descaler 230 may remove the scale of the surface of the material S with high pressure water.

The finishing mill 240 is a device for manufacturing a steel sheet into a final shape such as a thickness or a width required by a customer or a cold rolling process. The material S passing through the finishing mill 240 may be cooled to a target temperature by laminar flow cooling water from the cooling unit 260 while passing through the runout table 250, and then the winder 270 can be wound up. It may be air cooled instead of cooling by the cooling water.

The rolling device described above is just one embodiment and some of the devices constituting the rolling device may be omitted, and other additional devices may be further included. For example, a descaler may be added before, after or inside the roughing mill. As another example, a descaler may be added before and after the sizing press 200. As another example, it may further include an edger (Edger Mill) for equalizing the width deviation caused by the sizing press. In addition, it is attached for convenience of the name of the above-mentioned apparatus, and other names may be used.

Referring to Figure 4, the steel (material) is sequentially on the surface of the base iron (Base steel, A) Wheatite (B, Wustite, FeO), magnetite (C, Magnetite, Fe ₃ O ₄ ), hematite (D, Hematite, Fe ₂ O ₃ ) scale may be created and present. The method of heating a material according to an embodiment of the present invention reduces the temperature of the material below the melting point of the Payalite, even if the Payalite is not produced or produced between the base iron (A) and the Wheatite (B). There is an advantage that can greatly weaken.

Payalite is produced by the reaction of silicon oxide (SiO ₂ ) derived from silicon present in the Wheatite (B) and the base iron (A), and is not removed by the descaler because of its high adhesion to the base iron (A). This will cause red scale after finishing the rolling process. In particular, the payallite is dissolved and cooled, and the adhesion with the base iron (A) is greatly increased, and thus, it is not removed by the descaler.

According to the present invention, by keeping the temperature of the material in the heating furnace at or below the melting point of the payalite, it is possible to suppress the generation of the payalite or to significantly weaken the adhesion of the generated payalite to easily remove the scale by the descaler. The surface quality of the raw material after the rolling process can be greatly improved.

In addition, even after the rolling process is completed, even if the scale is not removed or regenerated, the pickling process may be easily removed.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. will be. In addition, the illustrated rolling device is merely exemplary, and the technical spirit of the present invention may be applied to other rolling devices. Accordingly, the true scope of the present invention should be determined by the following claims.

100: heating furnace 102: charging unit
104: extraction unit 106: charging door
108: extraction door 110: skid beam
112: first heating device 114: first temperature measuring device
116: second heating device 118: second temperature measuring device
120: third heating device 122: third temperature measuring device
124: fourth heating device 126: fourth temperature measuring device
200: sizing press 210: roughing mill
220: edge heater 230: descaler
240: finishing mill 250: runout table
260: cooling unit 270: winder

Claims (10)

Charging a carbon steel material containing silicon into a furnace;
Preheating the material;
A first heating step of raising the temperature of the material;
A second heating step of reducing the temperature of the heating furnace to reduce the temperature deviation between the surface and the inside of the material;
A third heating step of raising the temperature of the material; And
It includes a cracking step to reduce the temperature deviation of the surface and the inside of the material,
The temperature of the material in the heating furnace is kept below the melting point of the payalite,
The first the first temperature (T _1), the temperature (T _2), the third heating step of the second gayeoldae of the heating furnace for performing the second heating step of gayeoldae of the heating furnace for performing the heating step The temperature T ₃ of the third heating zone of the heating furnace performed and the temperature T ₄ of the cracking zone of the heating furnace performing the cracking step are T ₂ <T ₄ <T ₃ <T ₁ Heating method of the material.
delete delete The method of claim 1,
The T ₁ is a heating method of the material, characterized in that 1,190 ℃ to 1,210 ℃.
The method of claim 1,
The T ₂ is a heating method of the material, characterized in that 1,130 ℃ to 1,160 ℃.
The method of claim 1,
The T ₃ is a heating method of the material, characterized in that 1,170 ℃ to 1,190 ℃.
The method of claim 1,
The T ₄ is a heating method of the material, characterized in that 1,160 ℃ to 1,180 ℃.
The method of claim 1,
Wherein T ₁ is 1,200 ℃, T ₂ is 1,150 ℃, T ₃ is 1,180 ℃, T ₄ is a heating method of the material, characterized in that 1,170 ℃.
The method of claim 1,
The material's heating time is 160 minutes to 230 minutes.
The method of claim 1,
Temperature difference between the material surface after finishing the first heating step (ΔT ₁ ), Temperature difference between the material surface after the second heating step (ΔT ₂ ), and the material surface and inside after the third heating step between the temperature difference (ΔT _3), after the cracking step the material surface and the temperature difference within the (ΔT ₄₎ ΔT ₄ <ΔT ₂ , ΔT ₃ < A method of heating a material, which satisfies the relationship of ΔT ₁ .

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