KR101674091B1 - Method of manufacturing steel sheet and apparatus of manufacturing steel sheet - Google Patents

Abstract

The present invention relates to a method for producing a steel material to which copper (Cu) is added, comprising the steps of: preparing a slab to which copper (Cu) is added; firstly heating the slab by using a first heating device; A second heating process in which the surface of the slab is heated to a temperature higher than the first heating temperature by moving the slab to pass through a second heating device disposed on one side of the first heating device, Rolling the hot rolled material by moving it to a roughing mill placed on one side and moving the hot rolled material which is roughly rolled in the roughing mill to a finishing mill located at one side of the roughing mill, .
Therefore, according to the embodiment of the present invention, copper (Cu) precipitated between iron (Fe) and scale interface is re-dissolved and diffused by secondary heating at the time of primary heating for hot rolling, ) Surface cracking caused by precipitation is eliminated. Therefore, in the production of steel by hot rolling a slab to which copper (Cu) is added, it is possible to produce a steel material in which surface cracks due to copper (Cu) are not generated or reduced compared with the prior art.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a steel material,

TECHNICAL FIELD The present invention relates to a method of manufacturing a steel material and a steel material manufacturing apparatus, and more particularly, to a method of manufacturing a steel material and a steel material manufacturing apparatus capable of reducing occurrence of surface cracks in manufacturing a steel material containing copper (Cu).

Copper (Cu) -containing or copper (Cu) -containing steels are excellent in corrosion resistance and are used as materials for marine structure and the like which require excellent corrosion resistance. However, in the case of a hot-rolled steel sheet to which copper (Cu) is added, a surface crack easily occurs during hot rolling. This is because when a slab is reheated in a reheating apparatus, a concentrated liquid phase of copper (Cu) is formed at the interface between iron and scale by oxidation of iron (Fe), which causes surface cracking .

To solve this problem, there has been used a method of reducing surface cracking by increasing the solubility of copper (Cu) in austenite by adding nickel (Ni). However, Ni is an expensive element and a circulating element which is not removed by conventional oxidation scouring, and its use is restricted in terms of environment.

Korea registered patent 0573589

The present invention provides a method of manufacturing a steel material and a steel material manufacturing apparatus capable of reducing surface cracking.

The present invention provides a method of manufacturing a steel material and a steel material manufacturing apparatus capable of preventing surface cracking during hot rolling in producing a steel material containing copper (Cu).

The present invention relates to a method of manufacturing a steel material to which copper (Cu) is added, comprising the steps of: preparing a slab to which copper (Cu) is added; A first heating step of heating the slab by using a first heating device; A second heating step of moving the slab heated first through the second heating device disposed on one side of the first heating device to heat the surface of the slab to a temperature higher than the first heating temperature; Moving the secondary heated slab to a roughing mill disposed at one side of the second heating apparatus and subjecting the slab to rough rolling; And moving the hot rolled material, which is a slab rough-rolled in the roughing mill, to a finishing mill located at one side of the roughing mill, and finishing the hot rolled material.

The temperature at which the surface of the slab is secondarily heated is 1500 占 폚 to 1550 占 폚.

In the second heating of the slab, the temperature from the surface of the slab to the depth of 5 mm inward from the surface of the slab is set to 1500 to 1550 ° C.

And the moving speed at which the slab passes through the second heating device is adjusted to be 0.35 m / min to 0.65 m / min.

The secondary heating is preferably an induction heating method.

The copper (Cu) is contained in an amount of 0.2 wt% to 0.4 wt% with respect to the entire slab.

The present invention relates to a steel material producing apparatus for producing a copper (Cu) added steel by hot rolling a copper (Cu) added slab, comprising: a first heating device for first heating the slab; A second heating device located at one side of the first heating device and secondarily heating the surface of the slab heated first by the first heating device to a temperature higher than the first heating temperature; A roughing mill located at one side of the second heating apparatus for rough rolling the slab heated secondarily; And a finishing mill located at one side of the roughing mill and finishing hot rolled material as a rough-rolled slab.

The second heating device includes a coil part in a spiral shape, and the slab moves so as to pass through the inside of the coil part.

The second heating apparatus heats the surface of the slab and the inner surface to a depth of 5 mm from the surface of the slab so that the temperature is 1500 캜 to 1550 캜.

The slab preferably passes through the second heating device at a speed of 0.35 m / min to 0.65 m / min.

A steel material containing copper (Cu) is prepared by using a slab containing copper (Cu) in an amount of 0.2 wt% to 0.4 wt% with respect to the entire slab.

According to the embodiment of the present invention, the slab is heated (primary heating) to a temperature at which hot rolling is easy (primary heating), and then the slab surface is rapidly heated (secondary heating) to 1500 to 1550 占 폚. As a result, copper (Cu) precipitated between iron (Fe) and scale interface is re-dissolved and diffused by secondary heating during the first heating for hot rolling, Is removed. Therefore, in the production of steel by hot rolling a slab to which copper (Cu) is added, it is possible to produce a steel material in which surface cracks due to copper (Cu) are not generated or reduced compared with the prior art.

Also, the method of manufacturing steel according to the present invention has an advantage of preventing the occurrence of surface cracks even when expensive nickel is not applied as in the prior art.

1 is a view conceptually showing a hot rolling apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of other various forms of implementation, and that these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know completely.

The steel material to be produced by the manufacturing method according to the embodiment of the present invention is a steel material excellent in corrosion resistance due to addition of copper (Cu). A method of manufacturing a steel material according to an embodiment of the present invention is a method of manufacturing a hot rolled material by hot rolling a slab to which Cu is added to minimize or prevent surface cracking caused by copper during hot rolling And more particularly, to a method of manufacturing a steel material.

1 is a view conceptually showing a hot rolling apparatus according to an embodiment of the present invention. 2 is a view conceptually showing a heating state of the slab by the second heating apparatus of the present invention. 3 is a view conceptually showing a heating region of the slab by the second heating device.

1, a hot rolling apparatus according to an embodiment of the present invention includes a heating apparatus (hereinafter referred to as a first heating apparatus 10) for heating a slab S1 to a temperature at which rolling is easy, (Second heating device 200 (hereinafter, referred to as " second heating device 200 ") which is located at one side of the first heating device 10 and rapidly heats the surface of the slab Sl carried out from the first heating device 10 to suppress surface cracking by copper ), A roughing mill 30 for rough rolling the slab taken out of the second heating apparatus 200, a finishing mill 40 for finish rolling the roughly rolled slab (hereinafter referred to as hot rolled material S2) A cooler 50 for cooling the hot rolled steel material S2 having passed through the hot rolled steel material 40 and a winder 60 for winding and winding the cooled hot rolled steel material S2. Although not shown in the drawings, the slab is supported in the direction in which the first heating device 10, the second heating device 20, the rough rolling mill 30, the finishing mill 40 and the cooler 40 are disposed To a mobile device. The moving device may be, for example, a device including a plurality of rollers.

According to this hot rolling apparatus, the first heating apparatus 10, the second heating apparatus 200, the rough rolling mill 30, the finishing mill 40, the cooler 50, and the take-up unit 60 are sequentially arranged do. That is, the slab S1 heated in the first heating device 10 and the second heating device 200 passes through the roughing mill 30, the finishing mill 40 and the cooler 50, And then dried on the take-up roll of the take-up machine.

Since the first heating device 10, the rough rolling mill 30, the finishing mill 40, the cooler 50 and the winder 60 are the known conventional structures in the hot rolling apparatus of the same technical field, Will be omitted or briefly explained.

The first heating device 10 is a device for heating the slab S1 produced by solidifying and casting molten steel to facilitate subsequent rolling, which is commonly referred to as reheating furnace 60. [ In the first heating apparatus 10, the entire slab S1 is heated at 1100 DEG C to 1300 DEG C for about 2 hours. The first heating apparatus according to the embodiment is a heating furnace that generates hot air using an LNG and a burner and heats the slab using the hot air.

The rough rolling mill 30 is a primary rolling mill of a heated slab S1, for example, having a thickness of 200 to 250 mm, rolling the heated slab through a 5 to 7 pass rolling to a thickness of 30 to 35 mm, And fed to the finishing mill 40.

The finishing mill 40 finally rolls the rough-rolled slab S1, that is, the hot rolled material S2, to a thickness corresponding to the product characteristics.

On the other hand, when the slab to which copper (Cu) is added is heated to 1100 ° C to 1300 ° C using a first heating apparatus for hot rolling, iron (Fe) on the surface of the slab is oxidized but copper (Cu) by dissolving in pure water. The concentrated liquid copper (Cu) precipitates at the interface between the scale and iron, particularly, an oxide film produced by oxidation of iron, and penetrates between crystal grains. More specifically, it penetrates between the austenite grains. When the precipitated copper (Cu) penetrates into the austenite grains, deformation is caused to weaken the grain boundary strength, thereby causing surface cracking in the subsequent rolling process.

The above-mentioned slab surface crack is particularly generated in the hot rolling of a slab to which 0.2 weight% or more of copper (Cu) is added.

Therefore, in the embodiment of the present invention, the slab heated in the first heating device 10 is rapidly heated to 1500 ° C to 1550 ° C through the second heating device 200, thereby forming a liquid phase Copper (Cu) is re-dissolved on the surface of the slab to diffuse precipitated liquid copper (Cu), thereby suppressing surface cracking during rolling.

The second heating device 200 is positioned between the first heating device 10 and the roughing mill 30 on the movement path of the slab S1 so that the slab heated in the first heating device 10 is heated by the first heating For example, 1500 占 폚 to 1550 占 폚, compared with the heating temperature in the apparatus 10. In the second heating apparatus 200, the entire surface of the slab S1 is not heated, and the surface of the slab S1 is heated to 1500 to 1550 占 폚. More preferably, the surface of the slab S1 and the surface of the slab S1 are heated to 1500 캜 to 1550 캜 to a depth of 5 mm inward. In other words, the area heated by the second heating device 200 is up to a depth h spaced 5 mm inward from the surface of the slab S1 (see FIG. 3). This is to dissolve and dissolve precipitated copper (Cu) penetrating into the interface of iron (Fe) and scale at the surface of the slab S1 or near the surface of the slab so as to effectively prevent cracking of the slab surface.

Heating the area from the surface of the slab S1 to the depth of 5 mm from the surface of the slab S1 by the second heating device 200 to 1500 캜 to 1550 캜 effectively suppresses surface cracking of the slab Sl . This is because surface cracking of the slab S1 is mainly caused by precipitation copper (Cu) in a region within 5 mm inward from the surface of the slab S1. Further, it is not necessary to unnecessarily heat the slab S1 to a depth exceeding 5 mm from the surface of the slab S1 to 1500 deg. C to 1550 deg. C in order to suppress the surface cracking of the slab S1. When the slab S1 is moved by the moving device for a subsequent process, it is bended or attached to the moving device or stopped when the slab S1 is heated from 1500 캜 to 1550 캜 to a depth exceeding 5 mm from the surface of the slab Sl. There may be a problem of sticking.

When the heating temperature of the surface of the slab S1 in the second heating apparatus 200 is less than 1500 deg. C, it is difficult to dissolve and diffuse the precipitated copper (Cu) penetrating through the iron (Fe) Cracks may occur. On the contrary, when the surface heating temperature of the slab S1 exceeds 1,500 占 폚, it can be heated not only to the surface of the slab S1 but also to a depth of not less than 5 mm from the surface thereof, for example, In this case, when the slab S1 is moved by the mobile device for a subsequent process, there may be a problem of bending or sticking or sticking to the mobile device.

Therefore, in the present invention, it is possible to easily dissolve and diffuse the precipitated copper (Cu) and to prevent the problem from occurring when bending or moving, and to a region of 5 mm inward from the surface of the slab S1 And then heated to 1500 to 1550 占 폚.

The second heating device 200 according to the embodiment may include an induction coil part 210 formed by winding a conductor wire in a spiral shape to form a coil, and may be an induction heating device. The induction coil part 210 generates an induced electromotive force to heat the surface of the slab S1 to 1500 ° C to 1550 ° C. In the embodiment, the slab S1 is moved so as to pass through the second heating device at a speed of 0.35 to 0.65 m / min to rapidly heat the slab S1 to 1500 to 1550 占 폚. This is to ensure productivity and allow the temperature to rise from 1500 [deg.] To 1550 [deg.] C from the surface of the slab S1 to a depth of 5 mm inward.

For example, when the moving speed of the slab S 1 passing through the second heating device 200 is less than 0.35 m / min, the moving speed of the slab S 1 is slow and the productivity is lowered. On the other hand, when the moving speed of the slab S1 exceeds 0.65 m / min, it is difficult to raise the temperature from 1500 deg. C to 1550 deg. C from the slab surface to an inner depth of 5 mm.

Therefore, in the present invention, the slab heated to a temperature at which the rolling can be easily performed by the first heating device, that is, 1100 to 1300 ° C, is heated by the second heating device while the moving speed of the slab is 0.35 to 0.65 m / min . Thus, it is possible to heat the slab surface and the slab surface to an inner depth of 5 mm to 1500 ° C to 1550 ° C, thereby allowing copper (Cu) precipitated from the iron-scale interface to be re-dissolved and diffused.

Hereinafter, a method of manufacturing a steel material according to an embodiment of the present invention will be described with reference to FIGS.

The steel material produced according to the embodiment of the present invention is a copper (Cu) added steel containing copper (Cu) in an amount of 0.2 wt% to 0.4 wt% with respect to the entire steel material.

First, a slab containing copper (Cu) in an amount of not less than 0.2% by weight and not more than 0.4% by weight with respect to the entire steel is cast. The slab contains carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), aluminum (Al) and unavoidable impurities in addition to iron (Fe) and copper (Cu).

In the embodiment of the present invention, a steel material containing 0.4% by weight or less of copper (Cu) is prepared as described above. This is because even if the surface of the slab S1 is rapidly heated to 1500 占 폚 to 1550 占 폚 by using the second heating device 200 when the copper (Cu) content exceeds 0.4% by weight, cracks caused by the precipitated copper (Cu) There is a limit to inhibition. Therefore, in the method of manufacturing a steel material according to the embodiment of the present invention, a steel material containing 0.4% by weight or less of copper (Cu) is produced. More specifically, the present invention can be applied to the production of a steel material having a copper (Cu) content of 0.2 wt% or more with a high surface cracking rate.

The slab S1 is charged into the first heating device 10 and the slab S1 is heated to a temperature of 1100 to 1300 占 폚 for about 2 hours when the slab S1 containing 0.2 to 0.4% Heat it. At this time, iron (Fe) on the surface of the slab S1 is oxidized, but copper (Cu) is dissolved without being oxidized and is concentrated. Then, copper (Cu) dissolved and concentrated without being oxidized precipitates at the interface between iron (Fe) and scale, and penetrates into the austenite grains.

When the heating of the slab S1 is completed in the first heating device 10, the slab S1 is rapidly heated to 1500 to 1550 占 폚 while moving the slab toward the second heating device 200. [ That is, the slab is allowed to pass through the second heating apparatus 200 at a speed of 0.35 m / min to 0.65 m / min, so that the surface of the slab S1 and the inside of 5 mm from the surface of the slab S1 Heat rapidly.

In the present invention, the slab S1 having the copper (Cu) precipitated between the iron and scale interface heated by the first heating device 10 is directly passed through the second heating device 200, . Thus, copper (Cu) deposited between the iron (Fe) and the scale interface is redissolved and diffused. This serves to detoxify or remove surface cracking factors caused by copper (Cu) precipitation during the subsequent rolling operation.

The slabs heated by the second heating device 200 pass through the roughing mill 30, where they are rolled to a thickness of, for example, 30 to 35 mm through 5 to 7 pass rolling. The slab rolled in the roughing mill 30, that is, the hot rolled material S2, passes through the finishing mill 40 and is rolled to a thickness corresponding to the product characteristics. Thereafter, the rolled hot rolled material S2 is wound on the winder 60 in turn.

Cracks due to the copper (Cu) concentrate are not generated during rough rolling and finishing rolling. This is because even if liquid iron (Cu) precipitates at the interface between the iron (Fe) and the scale of the slab S1 by the normal reheating, that is, by the first heating device 10 as described above, As the copper (Cu) in liquid phase passes through the second heating device 200, it dissolves and diffuses into the slab surface (base material), thereby minimizing or eliminating the cause of surface cracking.

Also, the method of manufacturing steel according to the present invention has an advantage of preventing the occurrence of surface cracks even when expensive nickel is not applied as in the prior art.

Table 1 shows a comparison between the steel material produced by the method according to the embodiment of the present invention and the steel material produced by the method according to the comparative example.

The steel material according to the first to third embodiments contains 0.2 to 0.4% by weight of copper (Cu), the moving speed of the slab through the second heating device is 0.35 m / min to 0.65 m / min, And a steel material produced by heating the surface of the slab by a heating device to 1500 to 1550 占 폚. On the other hand, in the first comparative example, copper (Cu) is 0.2 to 0.4 wt%, but the rate at which the slab passes through the second heating device exceeds 0.65 and the second heating temperature of the second heating device is less than 1500 ° C It is a manufactured steel. In the second comparative example, the heating temperature by the second heating device and the second heating device passing speed of the slab satisfy the manufacturing method of the present invention, but the steel material is more than 0.4% by weight of copper (Cu).

Furtherance Heating condition characteristic C Si Mn P S Al Cu Second heating temperature
(° C) Second heating device transit time
(m / min) Surface crack
occurrence condition
First Embodiment 0.080 0.26 1.5 ? 0.01 0.0035 0.030 0.35 1530 0.42 Not occurring
Second Embodiment 0.090 0.31 1.4 ? 0.01 0.0036 0.035 0.30 1532 0.50 Not occurring
Third Embodiment 0.080 0.30 1.6 ? 0.01 0.0046 0.037 0.32 1528 0.47 Not occurring
Comparative Example 1 0.090 0.25 1.5 ? 0.01 0.0045 0.035 0.28 1430 1.00 Occur
Comparative Example 2 0.010 0.32 1.6 ? 0.01 0.0052 0.032 0.52 1540 0.53 Occur

Referring to Table 1, the copper-added steel material produced by the method according to the embodiment of the present invention did not crack on the surface. However, it was confirmed that the surface condition of the first comparative example and the first comparative steel having an addition amount of copper (Cu) of more than 0.4 wt% caused a surface crack.

In the case of the steel material according to the first to third embodiments, copper (Cu) is 0.4 wt% or less and heated to 1,500 캜 to 1,550 캜 inside the slab surface and the inside of the slab surface 5 mm by the second heating device Since the rolling was performed, surface cracks were not generated during the rolling process because the factors causing surface cracks were minimized or eliminated. That is, even when liquid copper (Cu) precipitates at the interface between iron (Fe) and scale at the time of the first heating by the first heating device, as the surface of the slab is heated to 1500 ° C to 1550 ° C, The precipitated copper between the interface between Fe and the scale is diffused.

However, in the case of the first comparative example, as the speed at which the slab passes through the second heating device exceeds 0.65, the heating rate is too fast, and the temperature from the slab surface and the surface to the depth of 5 mm is less than 1500 ° C. As a result, the precipitated copper between the interface between iron (Fe) and scale was not diffused, which caused surface cracking during rolling.

As another example, in the case of the second comparison, the temperature of the slab surface was heated to 1500 ° C to 1550 ° C at a passing speed of 0.35m / min to 0.65m / min for the second heating device. However, 0.4% by weight, it is insufficient to dissolve and diffuse all precipitated copper (Cu) even if the slab is heated to 1500 ° C to 1550 ° C using the second heating apparatus.

As described above, in the present invention, after the slab is firstly heated, the surface of the slab is heated to 1500 to 1550 占 폚 by using the second heating device to diffuse copper (Cu) precipitated between the iron and the scale. (Cu) -containing steel material in which cracks caused by precipitated copper (Cu) are removed and cracks are not generated during rolling can be produced.

10: first heating device 200: second heating device
30: rough rolling mill 40: finishing mill
50: cooler 60: winder

Claims (11)

A method of producing a steel material to which copper (Cu) is added,
Preparing a slab to which copper (Cu) is added;
A first heating step of heating the slab by using a first heating device;
A second heating step of moving the slab heated first through the second heating device disposed at one side of the first heating device to heat the surface of the slab to a temperature higher than the first heating temperature;
Moving the secondary heated slab to a roughing mill disposed at one side of the second heating apparatus and subjecting the slab to rough rolling; And
Rolling the hot rolled material, which is a slab rough-rolled in the roughing mill, to a finishing mill located at one side of the roughing mill;
/ RTI >
Wherein the copper (Cu) is contained in an amount of 0.2 wt% to 0.4 wt% with respect to the entire slab. The method according to claim 1,
And the temperature for secondary heating the surface of the slab is 1500 ° C to 1550 ° C. The method of claim 2,
Wherein a temperature from the surface of the slab to a depth of 5 mm inward from the surface of the slab is 1500 占 폚 to 1550 占 폚 in the second heating of the slab. The method of claim 3,
And the moving speed of the slab through the second heating device is adjusted to be 0.35 m / min to 0.65 m / min. The method according to any one of claims 1 to 4,
Wherein the secondary heating is an induction heating method. delete A steel material producing apparatus for producing a copper (Cu) added steel material by hot rolling a copper (Cu) added slab,
A first heating device for firstly heating the slab;
A second heating device located at one side of the first heating device and secondarily heating the surface of the slab heated first by the first heating device to a temperature higher than the first heating temperature;
A roughing mill located at one side of the second heating apparatus for rough rolling the slab heated secondarily; And
A finishing mill located at one side of the roughing mill and finishing the hot rolling material as the rough-rolled slab;
Lt; / RTI >
Wherein the slab containing copper (Cu) is contained in an amount of 0.2 wt% to 0.4 wt% with respect to the entire slab, to produce a steel material containing copper (Cu). The method of claim 7,
Said second heating device comprising a coiled portion of a helical shape,
And the slab moves so as to pass through the inside of the coil portion. The method of claim 8,
Wherein the second heating device heats the surface of the slab and the inner surface to a depth of 5 mm from the surface of the slab so that the temperature is 1500 占 폚 to 1550 占 폚. The method of claim 9,
Wherein the slab passes the second heating device at a speed of 0.35 m / min to 0.65 m / min. delete

Images