KR100506328B1 - Special steel as hot-cool composite material and manufacturing process thereof - Google Patents

Abstract

The present invention relates to a steel sheet comprising 0.45 wt% to 0.75 wt% of carbon (C), 0.5 to 1.5 wt% of silicon (Si), 0.4 to 1.0 wt% of manganese (Mn), 2.0 to 4.5 wt% of tungsten (W) (Cr), 2.0 to 4.0 wt% of molybdenum (Mo), 2.0 to 4.0 wt% of cobalt (Co), 0.2 to 1.6 wt% of vanadium (V) Which is inevitable impurities, and a method of manufacturing the same.

The special steel of the present invention exhibits excellent heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability even under high temperature, high pressure and high temperature impact environment.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a special cold-

TECHNICAL FIELD [0001] The present invention relates to a special steel as a cold / heat composite material, a use thereof, and a manufacturing method thereof.

More specifically, the present invention relates to a special cold-hard composite material having excellent heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance, and weldability for a subject having both a high temperature portion corresponding to a hot metal mold treatment and a low temperature portion corresponding to a cold- , Its use and manufacturing method.

More particularly, the present invention relates to a roll material used for pipe-forming high-frequency welding in a welded pipe manufacturing process, a dies mold for expanding the inner diameter of the steel pipe, a split shearing knife (for example, a dividing shear knife, or a metal press extrusion die, a use thereof, and a manufacturing method thereof.

The cold composite material of the present invention is generally used in an environment of a high temperature and a high pressure, and also in a heat shocked environment. Therefore, a material having excellent heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability is required in the above environment. As a result, special steel is generally used among metal materials.

Typically, special steel means a steel having specific physical properties suitable for each case by alloying carbon steel with one or more special elements. These special elements for alloying include nickel (Ni), chromium (Cr), manganese (Mn), tungsten (W), cobalt (Co), vanadium (V) and silicon (Si) The specific properties thereof are improved and the special properties different from those of the un-added carbon steel are exhibited. Therefore, it is possible to produce special steel suitable for special use by controlling the additive element and the content of the additive.

In particular, special steels vary in their properties depending on the alloy being alloyed. Looking at the characteristics of alloying elements in general, nickel increases toughness, increases oxidation resistance, non-magnetic, low transformation point high temperature impact resistance and chrome increases corrosion resistance and abrasion resistance. Molybdenum prevents toughness property, tungsten increases hardness and tensile strength at high temperature, copper increases oxidation resistance in air, silicon has electromagnetic property, improves heat resistance, Manganese is one of the deoxidizing elements effective for solubility strengthening effect, cobalt enhances hot rolling property, and vanadium can withstand strong thermal shock, thereby giving heat resistance and corrosion resistance to the alloy. However, by increasing the amount of the alloy of the above-mentioned elements, the above-mentioned properties do not become better, and they exhibit better properties than when an appropriate amount is alloyed.

Nickel-chromium steel, nickel-chromium-molybdenum steel, chromium-molybdenum steel, and manganese-chrome steel are used for the structural steel. As the surface hardened steel for carburizing, Low carbon steels are used. However, special steels containing nickel, chromium, molybdenum, tungsten, vanadium and the like are used when superior performance is required, and high carbon steels are used as tool steels.

Conventional special steels are known from Table 1 below.

division Standard symbol C Si Mn Cr Mo W V Usage alloy Tool steel SKS11 1.2 to 1.3 0.35 or less 0.5 or less 0.2 to 0.5 - 3.0 to 4.0 0.1 to 0.3 Byte (bite). Cold drawing die. SKS21 1.0 to 1.1 0.35 or less 0.5 or less 0.2 to 0.5 - 0.5 to 1.0 0.1 to 0.25 Tap. Drill. A cutter. Trimming die. SKS42 0.75-0.85 0.35 or less 0.5 or less 0.25 to 0.5 - 1.5 to 2.5 0.15 to 0.3 chisel. punch. Knife. SKS7 1.1 to 1.2 0.35 or less 0.5 or less 0.2 to 0.5 - 2.0 to 2.5 - buzz. SKD2 1.8 ~ 2.2 0.4 or less 0.6 or less 12 to 15 - 2.5 to 3.5 - Fresh die. Trimming die. SKD4 0.25-0.35 0.4 or less 0.6 or less 2 to 3 - 5 to 6 0.3 to 0.9 Press die. Die casting die. Extrusion dice. SKD11 1.4 to 1.6 0.4 or less 0.6 or less 11-13 0.8 to 1.2 - 0.2 to 0.5 gauge. Twisting die. Screw casting die SKD62 0.32-0.42 0.8 to 1.2 0.5 or less 4.5 to 5.5 1.0 to 1.5 1.0 to 1.5 0.2 to 0.6 Press type extrusion die. SKD61 0.32-0.42 0.8 to 1.2 0.5 or less 4.5 to 5.5 1.0 to 1.5 - 0.8 to 1.2 Die casting die. Extrusion dice. ① SKS11, SKS21, SKS7: alloy tool steel, cutting tool steel ② SKS42: alloy tool steel, impact resistant tool steel ③ SKD2, SKD11: alloy tool steel for cold forming ④ SKD4, SKD62, SKD61: alloy tool steel being.

The present invention particularly relates to a cold / heat composite material for a pipe making machine, a reinforcing bar or a structural round bar.

[0002] Pipes, especially welded steel pipes, are manufactured by welding a gap of a rolled steel plate with a high frequency induction current by means of a forming roll. At this time, the welding portion is heated to an extremely high temperature by the high-frequency induction current, which heats the circumferential surfaces of the schweib upper roll and the scrabb lower roll together to induce the welding portion. Therefore, it is common to cool the welded area to extend the service life of the roll.

Although SKD11 paper, which is a conventional cold metal material, is used as the material of the roll, there is a problem that the roll itself cracks or breaks despite the pressure resistance and abrasion resistance of the material.

On the other hand, the roll manufactured using SKD61, which is a hot metal material, has no crack or breakage problem as in the case of SKD11. However, even if cooling water treatment is performed as a result of heating by high frequency induction current, the working portion of the roll, It has a high speed problem.

And some of SKD62 paper which is an expensive hot-mold material is used, but the degree of improvement of abrasion resistance is not so high.

On the other hand, the seamless steel pipe is made of a steel pipe material heated to 1200 ° C. in a container box and dies as an inner diameter expanding device in a cylindrical space extending along the axis of the material. (Nose), which is a kind of a non-gaseous (steel) pipe, by passing the material instantly.

In this case, the nose is heated to 700 to 800 ° C, which is higher than the transformation point due to the high heat of the steel-free (steel) pipe material and the frictional heat due to the high pressure when passing through. As a result, the surface is softened, and the edges of the nose are worn out, causing scratches in the steel pipe.

This is because the temperature of the nose surface rises above the transformation point due to high temperature and high pressure at the time of extrusion, resulting in a drastic decrease in hardness as martensite structure at normal temperature changes into austenite structure.

In addition, due to the instantaneous heating of the nose during extrusion, the outer diameter is thermally expanded, and the inner surface is not yet subjected to heat conduction, thereby causing cracks on the surface of the nose.

On the other hand, it is common to use a glass material lubricant to prevent the material of the steel pipe and the nose from sticking out due to high temperature and high pressure during extrusion. However, after extrusion, the nose surface is water cooled by the high-pressure spraying device to remove the lubricant and raise the nose surface hardness. In this case, the nose surface may be exposed to a high thermal shock environment and cracks may occur.

Therefore, the nose made of SKD61, which is a conventional hot-mold material, has about 10 times in the case of a carbon steel pipe having no carbon steel structure and about 1 to 5 times in the case of a steel pipe made of stainless steel I could not use it.

However, when the rolled material is kept in the heating furnace for a long time, the pearlite, which is one of the internal structures of the metal, expands and the grain boundaries, which are the boundary lines of the structure, become larger. There was a problem that the strength was lowered. In recent years, the annealing normalizing method has been employed in which the surface of the product is quenched by hot-rolling the material and then spraying the cooling water in the product finishing step to improve the mechanical properties.

In this case, if the material heated to about 850 to 900 ° C by hot rolling is quenched by cooling water, the surface temperature is lowered to about 400 to 450 ° C, but the internal temperature is still high at about 700 to 800 ° C. Therefore, if SKD61, which is a conventional hot-forming metal material, is used as a split shear knife material which is continuously cut to a predetermined length, the productivity due to the knife replacement is drastically lowered, and the same hot mold material, SKD62, The degree of improvement is small. In addition, when SKD11, a cold metal material, is used, there is a risk of safety accidents due to cracks and breakage of the knife, and production can not be done.

As described above, in the high-temperature, high-pressure and high-temperature impact environments as in the above-mentioned fields, any conventional special steel does not have the required level of heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability. Therefore, when conventional special steel is used, the wear of the manufacturing equipment is severe, and it is necessary to replace the steel from time to time, which necessitates reprocessing, resulting in a decrease in production efficiency.

The object of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide a hot metal mold having a high temperature part corresponding to a hot metal mold process and a low temperature part corresponding to a cold mold process under a high temperature, high pressure, The present invention has been made to provide a cold and heat-resistant composite material having excellent heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability as compared with a cold metal material.

Specifically, the object of the present invention is to provide a cold-heat composite material which is used as a material for manufacturing a pipe, a reinforcing bar or a structural round bar, and which has excellent heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability in a high temperature, high pressure, It is in the provision of special steel as material.

Another object of the present invention is to provide a special steel as a roll material used in a pipe-forming high-frequency welding portion, in particular, in the process of manufacturing a welded pipe.

It is still another object of the present invention to provide a special steel as a die metal mold material for expanding the inner diameter of a steelless steel pipe.

Still another object of the present invention is to provide a special steel as a split shear knife material of a reinforcing bar or a structural round bar.

It is still another object of the present invention to provide a special steel as a metal press extrusion die material.

It is still another object of the present invention to provide a method of manufacturing such a special steel.

It is still another object of the present invention to provide a special steel produced by the above production method.

In order to achieve the above object, the inventor of the present invention has found that, as a result of repeatedly controlling the additive element and its content, the inventors of the present invention have found that the superalloy And invented special steel as a cold / heat composite material.

That is, the special steel as a cold / heat composite material for a pipe or the like manufacturing machine of the present invention comprises 0.45 to 0.75 wt% of carbon (C), 0.5 to 1.5 wt% of silicon (Si), 0.4 to 1.0 wt% of manganese (Mn) 2.0 to 4.5 wt% of nickel, 0 to 0.4 wt% of nickel, 2.0 to 4.0 wt% of chromium, 2.0 to 4.0 wt% of molybdenum, 0.5 to 3.0 wt% of cobalt, 0.2 to 1.6% by weight, and the balance of iron (Fe) and other unavoidable impurities.

The content of carbon is more preferably 0.60 to 0.75 wt.%, The content of tungsten is more preferably 2.0 to 4.0 wt.%, The content of nickel is more preferably 0.1 to 0.4 wt.%, The content of molybdenum is more preferably 2.5 to 3.5% by weight, the content of cobalt is more preferably 0.5 to 2.0% by weight, and the content of vanadium is more preferably 0.2 to 1.0% by weight.

In addition, the special steel may be used as a roll material used on a pipe-forming high-frequency welding portion in a welded pipe manufacturing process or as a dies mold material for expanding the inner diameter of a steel pipe, It may be used as a shearing knife material, or may be used as other metal press extrusion dies.

The present invention also provides a method for producing a special steel as the cold /

Alloying iron and the like are selected and calibrated and dissolved at a temperature of 1700 to 2000 占 폚;

Injecting the melt into a mold formed after the molding sand has been blended;

Cooling and decanting and decaying;

Subjecting it to softening annealing and then machining;

Finishing is performed after heat treatment.

The production method of the present invention can preliminarily prepare the parent alloy containing the elements whose melting points are significantly higher than those of the other elements before the dissolution process.

The present invention also provides a special steel for a pipe making machine, a reinforcing bar or a structural round bar manufactured by the above manufacturing method.

First, the reason why the above-described constituent elements have excellent heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability in an extreme environment intended by the present invention will be described.

First, carbon and tungsten are combined with each other to form a carbide of tungsten, and carbon and chromium and / or tungsten are combined with each other to form a carbide of chromium and a carbide of chromium-tungsten, thereby increasing the hardness of the alloy . Furthermore, such carbides are not readily pyrolyzed, resulting in increased wear resistance.

In addition, the heat resistance of chromium and molybdenum and the corrosion resistance of nickel significantly prevent the corrosion of the alloy or the oxidation due to heat at high temperatures, thereby significantly increasing the precision of the final product to be produced.

Since nickel and vanadium are resistant to instantaneous thermal shock, the above elements can impart excellent wear resistance to the alloy in a high temperature, high pressure, thermal shock, and strong environment. Here, heat shock refers to cracking of a mold caused by thermal expansion or cooling shrinkage of the alloy during rapid heating or rapid cooling, and the alloy of the present invention has excellent resistance to instantaneous thermal shock due to the addition of nickel and vanadium.

On the other hand, the reasons for adding the respective constituent elements constituting the special steel as the cold / thermal composite material for manufacturing pipes of the present invention and the reasons for limiting the numerical values will be described in detail as follows.

First, carbon is an invasive element of employment, which has a great influence on the texture formation of special steels. However, when the content is less than 0.45% by weight, the desired abrasion resistance can not be obtained. When the content is more than 0.75% by weight, the content of chromium and tungsten for carbide formation is relatively increased to increase hardness and abrasion resistance. It is liable to be cracked and broken by rapid heating and quenching. More preferably from 0.60 to 0.75% by weight for the abrasion resistance, impact resistance and weldability of the present invention.

Silicon in steel is one of the deoxidizing elements with electromagnetic properties and affects the thermal expansion coefficient and strength. When the content of silicon is less than 0.5% by weight, deoxidation is insufficient and there is a problem in the chemical reaction of the ternary elements. When the content of silicon exceeds 1.5% by weight, the toughness is lowered due to the excess of silicon component and the thermal expansion coefficient at high temperature is excessively increased The physical properties are remarkably lowered.

Manganese in the steel is one of the deoxidizing elements and is useful for strengthening pearlite structure and added for ensuring deacidification and hot workability. However, when the content is less than 0.4% by weight, not only the desired strength can not be secured but also a predetermined deoxidizing effect can not be obtained or the hot workability is also lowered. When the content of manganese exceeds 1.0 wt%, the desired strength is secured, but the elongation rate is rapidly decreased and the surface properties are deteriorated.

Tungsten in steel generally increases hardness and tensile strength at high temperatures. In the present invention, as mentioned above, carbide is formed by carbon alone or together with chromium to increase the hardness of the alloy by the carbide . Further, since the carbide itself of tungsten is not easily decomposed, the abrasion resistance of the alloy is remarkably increased. However, when the content of tungsten is less than 2.0% by weight, the intended superabrasion resistance can not be ensured. When the content exceeds 4.5% by weight, the melting point of tungsten is high and a segregation phenomenon of the structure occurs. Cracks occur. Particularly, 2.0 to 4.0% by weight is more preferable for securing physical properties of the present invention.

Nickel in steel generally increases toughness, oxidation resistance, non-magnetic, low transformation point high temperature impact resistance, and especially imparts corrosion resistance and thermal shock resistance to alloys. However, when the content exceeds 0.4% by weight, the transformation point is lowered and necessary physical properties can not be secured, and it is difficult to achieve the desired hardness. If the content of nickel is less than 0.1% by weight, the crack occurrence frequency may increase.

In the present invention, chromium in steel is generally added to increase the strength of the alloy, corrosion resistance and abrasion resistance. In the present invention, carbide is formed together with tungsten, thereby increasing the hardness of the alloy. Since the carbide is not easily decomposed, The desired abrasion resistance can be maintained. Furthermore, the heat resistance of chromium improves the precision of the final product to be produced because it prevents oxidation or erosion of the material at high temperatures. However, when the content is less than 2.0% by weight, the above-mentioned physical properties can not be secured, and when 4.0% by weight or more, required properties of the alloy are significantly reduced.

Molybdenum in the steel generally prevents tempering and gives the alloy a strengthening effect. In the present invention, as in the case of chromium, heat resistance is imparted to an alloy to suppress erosion or thermal oxidation of the material at high temperatures, thereby improving the accuracy of a product. However, when the content is less than 2.0% by weight, desired heat resistance and abrasion resistance can not be secured. On the other hand, when the content exceeds 4.0% by weight, workability is deteriorated and the linear expansion coefficient is excessively increased. In order to secure the physical properties of the present invention, 2.5 to 3.5% by weight is particularly preferable.

Cobalt in the steel improves the hot rolling property and improves the heat resistance, corrosion resistance and impact resistance. When the content is less than 0.5% by weight, the effect of improving the rolling property is insignificant and the cost of cobalt itself is very high If the amount is more than 3.0% by weight, the production cost of the alloy is increased excessively. In order to secure the physical properties of the present invention, 0.5 to 2.0 wt% is more preferable.

Vanadium in the steel is an element added to the alloy for imparting thermal shock resistance, and prevents cracking of the material even in rapid heating and rapid cooling. However, when the amount is less than 0.2% by weight, sufficient heat shock resistance can not be ensured. When the amount exceeds 1.6% by weight, the effect of improving the physical properties is insignificant. In order to secure the physical properties of the present invention, it is more preferable to contain 0.2 to 1.0% by weight.

The special steel of the present invention containing the above-mentioned elements has excellent heat resistance, corrosion resistance and thermal shock resistance even in a severe environment of high temperature and high pressure, and is excellent in abrasion resistance, impact resistance and weldability, do.

Particularly, the special steel as the cold / thermal composite material according to the present invention is used as a cold rolled composite pipe in the production of a welded pipe, a roll used on a pipe forming high frequency welding portion, a die mold for expanding the inner diameter of a steel pipe used in the worst conditions of high temperature, high pressure, , Split shear knife of reinforcing bar or structural round bar, or other metal press extrusion dies.

A method for manufacturing a special steel as a cold / thermal composite material for a manufacturing machine such as a pipe, a reinforcing bar or a structural round bar comprises the following steps:

Alloying iron and the like are selected and calibrated and dissolved at a temperature of 1700 to 2000 占 폚;

Injecting the melt into a mold formed after the molding sand has been blended;

Cooling and decanting and decaying;

Subjecting it to softening annealing and then machining;

Finishing is performed after heat treatment.

The production method of the present invention can preliminarily prepare the parent alloy containing the elements whose melting points are significantly higher than those of the other elements before the dissolution process.

(Melting point: 3410 ± 20 ° C) and molybdenum (melting point: 2622 ± 10 ° C) were used in the melting process for producing special steels. However, ° C) is remarkably higher than that of the other elements, so that it is difficult to obtain the desired properties of the final product such that the heating cost rises more than necessary and the melting point and the scattering point are different and the oxidation property is increased and segregation occurs.

Therefore, the present invention can adopt a double melting process including a step of preliminary melting each of the necessary elements and iron to prepare a parent alloy. In the case of tungsten and molybdenum having a high melting point, among the necessary elements, It is efficient.

Among the manufacturing methods of the present invention, the manufacturing method including the mother alloy manufacturing process is as follows:

Selecting necessary elements and dissolving at a temperature of 1700 to 2000 占 폚;

Injecting the melt into an ingot case;

Cooling it and then cladding the case to obtain a parent alloy;

Alloy iron and parent alloy are selected and calibrated and melted at a temperature of 1700 to 2000 占 폚;

Injecting the melt into a mold formed after the molding sand has been blended;

Cooling and decanting and decaying;

Subjecting it to softening annealing and then machining;

Finishing is performed after heat treatment.

The heat treatment in the production method of the present invention is preferably a vacuum heat treatment.

In the manufacturing apparatuses of pipes, reinforcing bars, structural rods and the like made of special steel as a cold / heat composite material manufactured by the above steps, since carbon, tungsten and chromium have wear resistance and chromium, molybdenum and cobalt are heat resistant, It is resistant to abrasion and cracking due to thermal shock, high temperature and high pressure, and is suitable as a material for manufacturing pipes such as pipes, reinforcing bars or structural rods.

An embodiment of the present invention is as follows.

Example 1

20 kg of powdered iron-tungsten (tungsten content: 60 wt%), 20 kg of powdered iron-molybdenum (molybdenum content: 60 wt%) and 60 kg of scrap iron were dissolved at 1800 캜, Shell to produce tungsten and a mixed parent alloy of molybdenum and iron.

Example 2

The alloys and parent alloys were selected and calibrated with the composition shown in the following Table 2, and then melted at a temperature of 1800 ° C, and these were injected separately into a molded mold after mixing with molding sand. After cooling, it is decalcified and decayed, heated to 900 ° C. at a heating rate of 2.5 ° C./minute and maintained at that temperature for 2 hours (based on a product thickness of 30 mm. When the product thickness is increased by 25 mm, And then cooled to 650 DEG C at a cooling rate of 0.83 DEG C / min. Thereafter, the resultant was held at the same temperature for 1 hour and then subjected to softening annealing in a heat treatment furnace for 1.5 days. After machining, it was quenched at 850 ° C for 100 minutes and at 1030 ° C for 80 minutes under vacuum, tempered three times at 560 ° C, and vacuum heat-treated. The finished product was subjected to finishing to meet the tolerance requirement to obtain a roll for manufacturing a welded pipe as a final product.

Examples 3 to 8

Example 2 was repeated except that the composition of the special steels in each example was adjusted as described in Table 2 below.

Comparative Examples 1 to 10

Example 2 was repeated except that the compositions of the special steels of each comparative example were adjusted as described in Table 2 below. In Comparative Example 10 of this Comparative Example, SKD62, which is a conventional hot metal mold material, was used.

Examples 9 to 15

Example 2 was repeated except that the composition of the special steel of each example was adjusted as shown in Table 2 below and the tempering temperature was set at 630 캜 to obtain a die metal mold (nose) for producing seamless steel pipes.

Comparative Examples 11 to 20

Example 2 was repeated except that the composition of the special steel of each comparative example was adjusted as shown in Table 2 below and the tempering temperature was 630 캜 to obtain a die metal mold (nose) for producing seamless steel pipes. In Comparative Example 20 of this comparative example, SKD61, which is a conventional hot metal material, was used.

Examples 16 to 23

Example 2 was repeated except that the composition of the special steels in each example was adjusted as shown in Table 2 below and the tempering temperature was 630 캜 to obtain a split shear knife for making reinforcing bar or structural round bar, which was the final product.

Comparative Examples 21 to 30

Example 2 was repeated except that the composition of the special steels of each comparative example was adjusted as set forth in Table 2 below and the tempering temperature was 630 캜 to obtain a split shear knife for making reinforcing bar or structural round bar, Comparative Example 29 of this Comparative Example used SKD61, which is a conventional hot metal material, and Comparative Example 30, SKD11, which is a conventional cold metal material.

No. C Si Mn W Ni Cr Mo Co V Examples 2, 9, 16 0.70 1.2 0.8 3.0 0.3 3.0 3.3 1.0 0.8 Examples 3, 10, 17 0.50 1.2 0.8 3.0 0.3 3.0 3.3 1.0 0.8 Examples 4, 11, 18 0.70 1.2 0.8 4.5 0.3 3.0 3.3 1.0 0.8 Examples 5, 12 and 20 0.70 1.2 0.8 3.0 0.3 3.0 2.0 1.0 0.8 Examples 6, 13 and 21 0.70 1.2 0.8 3.0 0.3 3.0 4.0 1.0 0.8 Examples 7, 14, 22 0.70 1.2 0.8 3.0 0.3 3.0 3.3 3.0 0.8 Examples 8, 15, 23 0.70 1.2 0.8 3.0 0.3 3.0 3.3 1.0 1.6 Example 19 0.70 1.2 0.8 3.0 0 3.0 3.3 1.0 0.8 Comparative Examples 1, 11, 21 0.40 1.2 0.8 3.0 0.3 3.0 3.3 1.0 0.8 Comparative Examples 2, 12, 22 0.70 0.2 0.8 3.0 0.3 3.0 3.3 1.0 0.8 Comparative Examples 3, 13, 23 0.70 1.2 0.1 3.0 0.3 3.0 3.3 1.0 0.8 Comparative Examples 4, 14, 24 0.70 1.2 0.8 1.0 0.3 3.0 3.3 1.0 0.8 Comparative Examples 5 and 15 0.70 1.2 0.8 3.0 0 3.0 3.3 1.0 0.8 Comparative Examples 6, 16, 25 0.70 1.2 0.8 3.0 0.3 1.0 3.3 1.0 0.8 Comparative Examples 7, 17, 26 0.70 1.2 0.8 3.0 0.3 3.0 1.0 1.0 0.8 Comparative Examples 8, 18, 27 0.70 1.2 0.8 3.0 0.3 3.0 3.3 0.2 0.8 Comparative Examples 9, 19 and 28 0.70 1.2 0.8 3.0 0.3 3.0 3.3 1.0 0.1 Comparative Example 10 0.32-0.42 0.8 to 1.2 0.5 or less 1.0 to 1.5 - 4.5 to 5.5 1.0 to 1.5 - 0.2 to 0.6 Comparative Examples 20 and 29 0.32-0.42 0.8 to 1.2 0.5 or less - - 4.5 to 5.5 1.0 to 1.5 - 0.8 to 1.2 Comparative Example 30 1.4 to 1.6 0.4 or less 0.6 or less - - 11-13 0.8 to 1.2 - 0.2 to 0.5

Test Example 1

The results of the actual welded pipe production using the rolls of Examples 2 to 8 and Comparative Examples 1 to 10 are shown in Table 3 below. The corrected tonnage in Table 3 indicates the number of welded pipes 50 ) Indicates the tonnage of the normal product.

No. Calibrated tonnage Example 2 1450 Example 3 1020 Example 4 1100 Example 5 1050 Example 6 1230 Example 7 1150 Example 8 1180 Comparative Example 1 220 Comparative Example 2 450 Comparative Example 3 430 Comparative Example 4 480 Comparative Example 5 310 Comparative Example 6 570 Comparative Example 7 260 Comparative Example 8 490 Comparative Example 9 230 Comparative Example 10 200

Test Example 2

The results are shown in Table 4 below, using the noses of Examples 9 to 15 and Comparative Examples 11 to 20, respectively. Each value in Table 4 indicates the number of normal steel pipe products manufactured using Nose One, and the non-steel pipe material was tested for SUS, which is a carbon steel for general structure and stainless steel, respectively.

No. Carbon steel SUS Example 9 73 38 Example 10 51 30 Example 11 57 34 Example 12 52 31 Example 13 59 35 Example 14 53 31 Example 15 57 33 Comparative Example 11 12 3 Comparative Example 12 23 5 Comparative Example 13 22 5 Comparative Example 14 24 5 Comparative Example 15 16 4 Comparative Example 16 23 6 Comparative Example 17 13 4 Comparative Example 18 20 6 Comparative Example 19 11 3 Comparative Example 20 10 3

Test Example 3

The actual reinforcing bars were produced using the knives of Examples 16 to 23 and Comparative Examples 21 to 30, and the results are shown in Table 5 below. In Table 5, the tonnage corrected is the rebar produced using one knife (15 ) Indicates the tonnage of the normal product.

No. Calibrated tonnage Example 16 1220 Example 17 930 Example 18 980 Example 19 1060 Example 20 930 Example 21 1010 Example 22 950 Example 23 970 Comparative Example 21 310 Comparative Example 22 580 Comparative Example 23 510 Comparative Example 24 540 Comparative Example 25 580 Comparative Example 26 320 Comparative Example 27 570 Comparative Example 28 320 Comparative Example 29 300 Comparative Example 30 45 (crack generation)

From the above Tables 3 to 5, it can be seen that the special steel of the present invention exhibits remarkable heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability compared to SKD61 and SKD62, which are conventional hot metal materials, and SKD11, which is a cold- have.

This is because the purpose of the conventional special steel is to be used only for a hot mold environment or a cold mold environment, and therefore, the properties of the hot metal mold and the cold mold mold are remarkably deteriorated.

In contrast, the present inventor has been able to provide a special steel as a cold / heat composite material having excellent effects for a specific application including both a hot metal mold part and a cold metal mold part as a result of a long repeated experiment.

As described above, the special steel as the cold and thermal composite material of the present invention can exhibit high heat resistance, abrasion resistance, thermal shock resistance, corrosion resistance, impact resistance and weldability even under high temperature, high pressure, Therefore, the present invention can provide a material particularly suitable for a pipe making machine, a reinforcing bar or a structural round bar.

Claims (16)

(Ni), 0.1 to 0.4 wt% of nickel (Ni), 0.5 to 1.5 wt% of silicon (Si), 0.4 to 1.0 wt% of manganese (Mn), 2.0 to 4.5 wt% of tungsten (Fe), and other unavoidable impurities, such as chromium (Cr) 2.0 to 4.0 wt%, molybdenum (Mo) 2.0 to 4.0 wt%, cobalt (Co) 0.5 to 3.0 wt%, vanadium A special steel as a cold / heat composite material for pipes, rebars or structural rods. delete delete delete delete delete delete delete The special steel as a cold and heat resistant composite material for a pipe, a reinforcing bar or a structural round bar according to claim 1, wherein the special steel is used as a roll material used on a pipe-shaped high-frequency welded part in a welded pipe manufacturing process. The special steel as a cold and heat resistant composite material according to claim 1, wherein the special steel is used as a die material for expanding the inner diameter of the steel pipe. delete The special steel as a cold and heat resistant composite material according to claim 1, wherein the special steel is used as a metal press extrusion die material. delete delete delete delete