KR101758523B1

KR101758523B1 - Method for manufacturing wire rod with excellent mechanical descalability

Info

Publication number: KR101758523B1
Application number: KR1020150184900A
Authority: KR
Inventors: 허혜진; 양요셉
Original assignee: 주식회사 포스코
Priority date: 2015-12-23
Filing date: 2015-12-23
Publication date: 2017-07-17
Also published as: KR20170075860A

Abstract

A step of hot rolling a billet to obtain a wire rod; a step of cooling the wire rod after water-cooling; and a step of air-cooling the wound wire rod, wherein the tonnage of the roll in the final rolling stand ) Of not more than 200 tons (excluding 0 tons) is disclosed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a wire cord for a tire cord having excellent mechanical peelability,

The present invention relates to a method for producing a wire rod material for tire cords excellent in mechanical peelability.

Generally, the wire rod is manufactured by rolling a billet, and an example of such a wire rod manufacturing process is shown in FIG. First, a billet which has been continuously cast is heated to a predetermined temperature in a heating furnace 1, then hot-rolled in a wire rod mill 2, and rapidly cooled to a coiling temperature by a water- Thereafter, it falls from the winder 4 to the wire coil on the ring and is transported from the cooling conveyor 5, and the air blowing speed is appropriately controlled by the lower blower 6, so that it is manufactured into a wire product meeting the customer's application characteristics.

Since the wire rods manufactured through such a manufacturing process generate a large scale on the surface thereof during the cooling process, the scaling process is necessarily performed before the secondary processing (drawing process).

Examples of the scale peeling method include a chemical peeling method in which pickling is performed using hydrochloric acid or sulfuric acid, a mechanical peeling method such as a bobbing method, a shot blast method, and an air blasting method. Generally, in the case of mild steel wire, the scale has been removed by a chemical stripping method. However, in recent years, there has been a tendency to switch to a mechanical stripping method for the purpose of environmental problems and cost reduction due to pickling treatment.

However, in the case of producing a wire cord for tire cord by a conventional method, in the process after winding, a scale drop occurs in the core, and a secondary scale is generated at this dropout region. Such a secondary scale has poor mechanical separation properties There is a problem that disconnection is caused in the secondary processing (drawing process) or plating failure is caused in the subsequent plating process.

Accordingly, there is a need for a technique for manufacturing wire rods for tire cords which is easy to remove scale by mechanical stripping at the time of secondary machining (drawing machining) by preventing scale from peeling during the wire rod manufacturing process.

One of the objects of the present invention is to provide a method for producing a wire cord for tire cords excellent in mechanical peelability.

According to one aspect of the present invention, there is provided a method of manufacturing a wire rolling mill, comprising the steps of: hot rolling a billet to obtain a wire rod; cooling the wire rod after water cooling; and air cooling the wound wire rod; Wherein the tonnage of the roll of the tire is less than 200 tons (excluding 0 ton).

According to the present invention, it is advantageous that scaling off of the scale during the wire rod manufacturing process is effectively suppressed, and scale removal by the mechanical stripping method during secondary processing is easy.

1 is a schematic view showing a conventional wire rod manufacturing process.
Fig. 2 (a) is a photograph of the surface of a wire rod produced under the condition that the tonnage of the roll in the final rolling stand is 467 tons, Fig. 2 (b) This is a photograph of the surface of a wire manufactured under the condition of a tonnage of 200 tons.
Fig. 3 (a) is a photograph of a section of a wire rod produced under the condition of a coiling temperature of 830 캜 under a scanning electron microscope (FE-SEM, Field Emission Scanning Electron Microscope) (FE-SEM, Field Emission Scanning Electron Microscope) of a wire rod produced under the condition of a temperature of 30 ° C.
Fig. 4 (a) is a graph showing the results of a comparison between the wire rods manufactured by primary co-cooling the wound wire rod to 700 캜 under the condition of an average cooling rate of 35 캜 / sec and secondary co- Fig. 4 (b) is a photograph showing the surface of the wound wire rod. Fig. 4 (b) shows the results of the primary coiling of the wound wire rod to 700 캜 under the condition of an average cooling rate of 28 캜 / sec. 2 is a photograph of the surface of a wire rod produced by air cooling.
Fig. 5 (a) is a graph showing the results of the wire drawing process, in which the wound wire rod is firstly air-cooled to 700 캜 under the condition of an average cooling rate of 35 캜 / sec and then subjected to secondary air- Fig. 5 (b) is a photograph of the wire roughed up to 700 deg. C at an average cooling rate of 28 deg. C / sec. And then subjected to a secondary scaling test at a cooling rate of 14 DEG C / sec at an average cooling rate of up to 600 DEG C under a condition of mechanical annealing under the condition of a scale of peeled off from the wire, It is a photograph observing the surface.

Hereinafter, a method for manufacturing a wire cord for a tire cord, which is one aspect of the present invention, will be described in detail.

The present invention relates to a method for manufacturing a wire cord for a tire cord, comprising the steps of obtaining a wire rod by hot rolling the billet, water cooling the wire rod, winding the wire rod, and air cooling the wound wire rod. The present invention can be applied to the alloy composition and the composition range without limitation. However, one example suitable for the application of the present invention is that the wire comprises, by weight, 0.75 to 0.88% of C, 0.15 to 0.3% of Si, 0.4 to 0.8% of Mn, 0.2% or less of Cr %), P: not more than 0.03%, S: not more than 0.025%, and the balance Fe and unavoidable impurities may be more satisfactory to the present invention than the present invention.

According to the present invention, the tonnage of the roll in the final rolling stand is controlled in hot rolling, thereby securing the adhesion of the scale formed on the surface of the wire.

Normally rolling is carried out without specifically controlling the tonnage of the roll during the rolling of the wire cord for tire cord. However, as a result of the inventors' study, the volume tonnage of the roll, in particular, the tonnage of the roll in the final rolling stand, has a great influence on the adhesion of the scale.

FIG. 2 (a) is a photograph of the surface of a wire rod manufactured under the condition that the tonnage of the roll in the final rolling stand is 467 tons, and it can be seen that much scale peeling occurred. 2 (a) was subjected to a descaling test by mechanical peeling. As a result, the scale was mostly in the form of powder, and a large amount of scale remained on the surface of the wire after descaling .

FIG. 2 (b) is a photograph of the surface of a wire rod manufactured under the condition that the tonnage of the roll in the final rolling stand is 200 tons, and it can be seen that scale peeling did not occur. Further, a descaling test was conducted on the wire material according to Fig. 2 (b) by mechanical peeling. As a result, most of the scales were flaky, and residual scale was not found on the surface of the wire after de- I did.

As shown in FIG. 2 (b), the tonnage of the roll in the final rolling stand for producing the wire cord for tire cord in which scale separation does not occur is less than 200 tons (excluding 0 tons). If the tonnage is more than 200 tons, the surface roughness becomes worse, and the possibility of occurrence of cracks in the scale is increased. As a result, there is a possibility that the initial peeling occurs and the possibility of causing secondary scale may increase.

As described above, it is possible to manufacture a wire cord for tire cord excellent in mechanical peelability by controlling the tonnage of the roll in the final rolling stand to 200 ton or less (excluding 0 ton) at the time of hot rolling.

However, in order to further improve the mechanical peelability of the wire cord for tire cord, the coiling temperature and / or the air cooling rate can be controlled under the following conditions.

Coiling Control of temperature

The coiling temperature is the initial temperature of the cooling process which determines the physical properties of the wire, which may have a great influence on the mechanical peelability of the wire. Generally, in the case of wire rods for tire cords, the winding temperature is controlled to be as low as 850 DEG C or less for controlling the shape of the winding coils. In contrast, in the present invention, the coiling temperature is controlled to be 860 DEG C or higher, more preferably 870 DEG C or higher.

This upward reeling temperature has two technical implications.

First, when the water content existing on the surface of the wire rod during the air-cooling of the wire rod is excessive, a stress difference occurs around the pores in the scale, causing the scale to peel off, thereby deteriorating the mechanical peelability of the wire rod. In the present invention, the amount of cooling water in the water jacket is reduced due to the upward winding temperature, so that the moisture content present on the surface of the wire at the time of air cooling is reduced, thereby effectively preventing deterioration of the mechanical peelability of the wire rod.

Second, the upward direction of the coiling temperature aids in the growth of the scale formed on the surface of the wire rod, thereby increasing the thickness of the surface scale layer and consequently improving the mechanical peelability of the wire rod.

Fig. 3 (a) is a photograph of a section of a wire rod produced under the condition of a coiling temperature of 830 캜 under a scanning electron microscope (FE-SEM, Field Emission Scanning Electron Microscope) (FE-SEM, Field Emission Scanning Electron Microscope) of a wire rod produced under the condition of a temperature of 30 ° C.

Referring to FIG. 3, it can be seen that when the coiling temperature is 880 ° C., the thickness is improved by about 50% (about 8 μm → about 12 μm) as compared with the case where the coiling temperature is 830 ° C.

On the other hand, the higher the coiling temperature, the more favorable the improvement in the mechanical peelability of the wire, but when it is too high, it is difficult to control the shape of the winding coil. The upper limit is preferably controlled at 900 캜, Do.

Air cooling Control of speed

The air cooling rate is a factor that determines the composition of the scale included in the surface scale layer, which may also have a great influence on the mechanical peelability of the wire rod. As described above, the air cooling is performed in the stelmor conveyor, and the cooling rate in the air cooling is determined by the moving speed of the cooling conveyor 5 and the blowing amount of the lower blower 6.

On the other hand, the scale included in the surface scale layer includes FeO, Fe ₂ O ₃ , and Fe ₃ O _{4. As a} result of research conducted by the inventors of the present invention, the higher the FeO fraction and the lower the Fe ₃ O ₄ fraction, It helps to improve the sex. Therefore, in the temperature range in which FeO is actively formed, the cooling rate is maximized to maximize the staying time in the temperature range, and the cooling rate is maximized in the temperature range where Fe ₃ O ₄ is actively formed, thereby minimizing the time spent in this temperature range There is a need.

In order to achieve such a purpose, the wound wire rod is subjected to primary air-cooling at an average cooling rate of 30 DEG C / sec or less to a temperature of 700 DEG C on the basis of the surface temperature of the wire rod, It is preferable to perform secondary air cooling at an average cooling rate of not less than < RTI ID = 0.0 > C / sec.

Fig. 4 (a) is a graph showing the results of a comparison between the wire rods manufactured by primary co-cooling the wound wire rod to 700 캜 under the condition of an average cooling rate of 35 캜 / sec and secondary co- Fig. 4 (b) is a photograph showing the surface of the wound wire rod. Fig. 4 (b) shows the results of the primary coiling of the wound wire rod to 700 캜 under the condition of an average cooling rate of 28 캜 / sec. 2 is a photograph of the surface of a wire rod produced by air cooling.

Fig. 5 (a) is a graph showing the results of the wire drawing process, in which the wound wire rod is firstly air-cooled to 700 캜 under the condition of an average cooling rate of 35 캜 / sec and then subjected to secondary air- Fig. 5 (b) is a photograph of the wire roughed up to 700 deg. C at an average cooling rate of 28 deg. C / sec. And then subjected to a secondary scaling test at a cooling rate of 14 DEG C / sec at an average cooling rate of up to 600 DEG C under a condition of mechanical annealing under the condition of a scale of peeled off from the wire, It is a photograph observing the surface.

4 and 5, when the air cooling rate satisfies the conditions proposed in the present invention, it is confirmed that the scale peeling form (powder form → play key form) is excellent and the scale is effectively removed by mechanical peeling.

Claims

Hot rolling the billet to obtain a wire rod; Water-cooling the wire rod, and winding the wire rod; And air cooling the wound wire rod,
Wherein the rolling tonnage of the roll in the final rolling stand is 200 tons or less (excluding 0 tons) at the time of rolling the wire rod.

The method according to claim 1,
Wherein the coiling temperature is 860 to 900 占 폚 at the time of winding.

The method according to claim 1,
The air-cooled primary wire is subjected to primary air-cooling at an average cooling rate of 30 DEG C / sec or less to a temperature of 700 DEG C on the basis of the surface temperature of the wire, and the primary air- Or more at an average cooling rate that is higher than the average cooling rate.

The method according to claim 1,
The billet includes, by weight%, 0.75 to 0.88% of C, 0.15 to 0.3% of Si, 0.4 to 0.8% of Mn, 0.2% or less of Cr (exclusive of 0%), 0.03% or less of P, , The balance Fe, and unavoidable impurities.