WO2004046407A1

WO2004046407A1 - Special steel as hot-cool composite material and manufacturing process thereof

Info

Publication number: WO2004046407A1
Application number: PCT/KR2003/002516
Authority: WO
Inventors: Il-Kyu Lee
Original assignee: Il-Kyu Lee
Priority date: 2002-11-20
Filing date: 2003-11-20
Publication date: 2004-06-03
Also published as: KR100506328B1; AU2003284735A1; KR20040044048A

Abstract

Disclosed is special steel as hot-cool composite material, comprised of carbon of 0.45 through 0.75 weight percent, silicon of 0.5 through 1.5 weight percent, manganese of 0.4 through 1.0 weight percent, tungsten of 2.0 through 4.5 weight percent, nickel of 0 through 0.4 weight percent, chromium of 2.0 through 4.0 weight percent, molybdenum of 2.0 through 4.0 weight percent, cobalt of 0.5 through 3.0 weight percent, vanadium of 0.2 through 1.6 weight percent, and iron and inevitable impurities of residuary weight percent. The special steel of the present invention shows superior heat resistance, abrasion resistance, heat-impact resistance, corrosion resistance, impact resistance, and welding performance even under the high temperature, high pressure and high heat impact environment.

Description

SPECIAL STEEL AS HOT-COOL COMPOSITE MATERIAL AND MANUFACTURING PROCESS THEREOF

TECHNICAL FIELD The present invention relates special steel as hot-cool composite material, and a usage and a manufacturing process thereof.

Particularly, the present invention relates to special steel as hot-cool composite material, and a usage and a manufacturing process thereof, wherein the special steel has superior heat resistance, abrasion resistance, heat impact resistance, corrosion resistance, impact resistance, and welding performance when it is manufactured as an object equipped with a high-temperature part that undergoes hot metallic patterning process as well as a low-temperature part that undergoes cool metallic patterning process.

More particularly, the present invention relates to special steel as hot-cool composite material, and a usage and a manufacturing process thereof, which is employed as a roll material used on the spot that undergoes a pipe forming high-frequency welding in a welding type pipe manufacturing process, a dies metallic patterning mold for enlarging the inner diameter of a seamless pipe, a dividing shear knife of a reinforcing bar or a round bar for structural purposes, or a material for a metallic press type extruding dies, etc.

BACKGROUDN OF THE INVENTION

The hot-cool composite material of the present invention is generally used in an atmosphere of high temperature and high pressure, and also in an atmosphere of great degree of heat impact. Accordingly, a material with superior heat resistance, abrasion resistance, heat impact resistance, corrosion resistance, impact resistance, and welding performance even in such an atmosphere is required, which result in the general use of the special steel among the various metallic materials.

In general, the special steel means a kind of steel made of carbon steel alloyed with one or more than two special elements and having a special property that is proper for individual conditions. The example of the special elements used for the alloy are nickel, chromium, manganese, tungsten, cobalt, vanadium, silicon, etc., and as a proper amount of a part of or all of such elements is alloyed, the intrinsic property of the carbon steel is improved and a special property other than that of the carbon steel without such elements is achieved, and therefore, the special steel proper for a special use can be manufactured by adjusting the kind and the amount of the alloyed elements.

In other words, the property of the special steel depends on the kind and the amount of the alloyed elements, and the elements used generally for the alloy bring about such properties that nickel increases toughness, oxidation resistance, no-magnetic property, transformation point declination property, and high-temperature impact resistance, chromium increases the corrosion resistance and abrasion resistance, molybdenum prevents tempering property, tungsten increases solidity and tensile strength at high temperature, copper increases oxidation resistance in air, silicon has electromagnetic property and causes the effect to increase the heat resistance, manganese is a kind of deoxidation element and is utilizable for the effect of solid-solution strengthening, cobalt improves hot rolling property, and vanadium endows the alloy with the heat resistance and the corrosion resistance as it can endure a strong heat impact. However, the above properties become superior not when the amount of the above elements increases but when a proper amount of the above elements is alloyed.

The special steel is manufactured as needed by alloying the proper amount of such elements, and nickel-chromium steel, nickel-chromium-molybdenum steel, chromium-molybdenum steel, or manganese-chromium is used as structural steel, low- carbon steels generally used as surface hardening steel for carburizing and special steel containing nickel, chromium, molybdenum, tungsten, vanadium, etc is used as the surface hardening steel for the carburizing in case the superior performance is required, and high-carbon steel is used as tool steel.

Table 1 shows the conventional special steel known as a prior art. Table 1.

The present invention relates such special steel, and more particularly, hot-cool composite material used for the apparatus of manufacturing a pipe, reinforcing bar, round bar for structural purposes, etc.

The pipe, especially the welding type steel pipe is manufactured by welding the gap of the steel plate rolled round by a forming roll with high-frequency induced current. In such a situation, the welding spot is heated to extremely high temperature by the high- frequency induced current, and the circumferential surface of the schweib upper roll and the schweib lower roll that guide the welding spot is heated together. Therefore, it is general that the welded area is cooled by coolant in order to take a new lease of life of the roll.

As the material for the roll, SKD11 class that is a material for cold metallic patterning has been used, however, there has been a problem that the roll itself is cracked and broken even though the material has pressure resistance and abrasion resistance. Meanwhile, the roll manufactured with SKD61 class that is a material for hot metallic patterning does not has the problem of crack or breakdown, however, there is a problem that the abrasion speed is high as the processed area of the roll, i.e., the circumferential area, is softened even with the cooling process thereon as the result of heating by the high-frequency induced current even with the cooling process by coolant.

Furthermore, SKD62 class that is an expensive material for hot metallic patterning is used sometimes, however, it contributes little to the improvement of the abrasion resistance. Meanwhile, a seamless pipe is manufactured by extruding seamless pipe material, wherein the seamless pipe material heated to a temperature of 1200 ^°C is put into a container box, and a nose which is a kind of dies as an apparatus for enlarging the inner diameter is passed in an instant along a cylindrical space formed along the axis of the material. In such a situation, the nose is heated to a temperature of 700 °C to 800 ^°C that is higher than the transformation point thereof due to the high temperature of the seamless pipe material and the abrasive heat caused by the high pressure during the passage. As a result, the edge of the nose is worn away as the surface thereof is softened, by which the scratches occur at the inside of the seamless pipe. Such a phenomenon results from the abrupt declination of the hardness as the temperature of the surface of the nose becomes higher than the transformation point by the high temperature and high pressure during the extruding and accordingly the martensite organization at the room temperature is changed to the austenite organization. Furthermore, the outer diameter of the nose is expanded by the instant heating thereof during the extruding and heat is not transmitted to the inner part thereof yet to bring the case that the crack occurs on the surface of the nose.

Meanwhile, in order to prevent the adhesion of metals by the heat between the nose and the seamless pipe due to the high temperature and high pressure, it is general that a lubricant made of glass is used. After the extruding, the surface of the nose is cooled by water with a high pressure sprinkler in order to remove the lubricant and to reraise the hardness of the surface of the nose, and in such a situation, the surface of the nose is exposed to the environment of high thermal impact, which may cause the cracks. Therefore, the nose manufactured with the SKD61 class that is the conventional hot metallic patterning material can be used merely for ten times in case the seamless pipe material is a general carbon structural steel, and for one to. five times in case the seamless pipe material is a stainless steel of SUS series.

Moreover, reinforcing bar or round bar for structural purposes has been used after hot rolling, however, there is a problem that the pearlite that is a kind of inner organization of metal is so expanded that the crystal interface that is the boundary of the organization becomes great if the hot rolling material is kept in a furnace for a long period of time, which causes the lowering of the elongation and the tensile strength. Accordingly, an annealing normalizing method is employed recently that the mechanical property is improved by sprinkling the cooling water when the manufacturing of the product has been completed after the hot rolling of the material, thereby cooling the surface of the product quickly. However, in such a case, as the material that has been heated by the hot rolling to a temperature of about 850 through 900 ^°C is cooled quickly with the cooling water, even though the temperature of the surface is lowered to the temperature of about 400 through 450 ^°C , the inner temperature is still in a high temperature status of about 700 through 800 ^°C . Thus, if the SKD61 class that is the conventional hot metallic patterning material is employed as the dividing shear knife material, the abrasion speed is so high that the knife should be exchanged with a new one to lower the productivity seriously, and the SKD62 class that is also the hot metallic patterning material also hardly improves the abrasion speed problem. Furthermore, if the SKD11 class that is a cold metallic patterning material is employed, there are problems that the crack or the breakdown of the knife may cause a sudden accident and make it hard to produce the product, and for such a reason, there has been a continuous request of improvement from the steel industry.

As described above, any kind of the conventional special steels does not have the heat resistance, abrasion resistance, heat impact resistance, corrosion resistance, impact resistance and welding performance sufficient for the request under the high temperature, high pressure, and high heat-impact environment as the above-described technical field. Therefore, when the conventional special steel is employed, the manufacturing apparatus has to be exchanged with a new one because of the abrasion thereof, and the manufacturing apparatus has to be processed again, which causes the lower productivity. The present invention has been proposed to solve the above-described problems, and it is an object of the present invention to provide hot-cool composite material having a superior heat resistance, abrasion resistance, heat impact resistance, corrosion resistance, and welding performance in comparison with the conventional hot metallic patterning material or the cold metallic patterning material when it is manufactured as an object equipped with a high-temperature part that undergoes hot metallic patterning process under the high temperature, high pressure and high heat-impact environment as well as a low-temperature part that undergoes cool metallic patterning process.

More particularly, the object of the present invention is to provide special steel as hot-cool composite material, which is employed as the material for an apparatus of manufacturing the pipe, reinforcing bar, round bar- for structural purposes, etc., and maintains superior heat resistance, abrasion resistance, heat impact resistance, corrosion resistance, and welding performance even under the high temperature, high pressure, and high heat-impact environment. Another object of the present invention is to provide special steel as a roll material used on the pipe forming high-frequency welding area in especially the welding type pipe manufacturing line.

Still another object of the present invention is to provide special steel especially as a material of dies metallic patterning for enlarging the inner diameter of a seamless pipe.

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

Still another object of the present invention is to provide special steel especially as a material for a metallic press type extruding dies.

Still another object of the present invention is to provide a manufacturing method of the special steel.

Still another object of the present invention is to provide special steel manufactured by the above manufacturing method. DETAILED DESCRIPTION OF THE PRESENT INVENTION

In order to achieve the above objects, the inventor of the present invention repeated the experiments while changing the added elements and the amount thereof, and as a result, invented special steel as hot-cool composite material having ultra heat resistance, ultra corrosion resistance, ultra heat-impact resistance, ultra abrasion resistance, ultra impact resistance, and favorable welding performance.

In other words, the special steel as hot-cool composite material according to the present invention is characterized in that it comprises carbon of 0.45 through 0.75 weight percent, silicon of 0.5 through 1.5 weight percent, manganese of 0.4 through 1.0 weight percent, tungsten of 2.0 through 4.5 weight percent, nickel of 0 through 0.4 weight percent, chromium of 2.0 through 4.0 weight percent, molybdenum of 2.0 through 4.0 weight percent, cobalt of 0.5 through 3.0 weight percent, vanadium of 0.2 through 1.6 weight percent, and iron and inevitable impurities of residuary weight percent.

Among the above constituent elements, it is more preferable that the content of the carbon is 0.60 through 0.75 weight percent, the content of the tungsten is 2.0 through 4.0 weight percent, the content of the nickel is 0.1 through 0.4 weight percent, the content of the molybdenum is 2.5 through 3.5 weight percent, the content of the cobalt is 0.5 through 2.0 weight percent, and the content of the vanadium is 0.2 through 1.0 weight percent. Furthermore, the special steel as described above can be employed as a roll material used on a pipe forming high-frequency welding area in a welding type manufacturing line, as a material of dies metallic patterning for enlarging a inner diameter of a seamless pipe, as a material for dividing shear knife of a reinforcing bar or a round bar for structural purposes, or as a material for metal press type extruding dies. Meanwhile, the present invention provides a method for manufacturing special steel as hot-cool composite material, which comprises selecting and gauging a material such as iron alloy, etc., and then dissolving the material at a temperature of 1700 through 2000 ^°C ; injecting the dissolved material into a mold formed by combining molding sand; cooling the dissolved material and then performing de-sanding and sand-decay; mechanically processing after thens; and performing fine finishing after a thermal process.

According to the manufacturing method of the present invention, a master alloy containing the elements that the melting points thereof is remarkably higher than that of the other elements is preliminarily dissolved before performing a main dissolving process. Furthermore, the present invention provides special steel for use in the manufacturing apparatus for manufacturing a pipe, reinforcing bar, or round bar for structural purposes, which is manufactured by the above-described method.

The reason that the above-described composition has superior heat resistance, abrasion resistance, heat-impact resistance, corrosion resistance, impact resistance, and welding performance even under the extreme environment assumed in the present invention is as follows.

At first, among the elements of the alloy of the present invention, the carbon combines with the tungsten to form carbide of tungsten, and separately, the carbon combines with chromium and/or tungsten to form carbide of chrome and carbide of chrome-tungsten, whereby the hardness of the alloy of the present invention increases._. Moreover, such carbide has increased the abrasion resistance since it is strong against the thermal decomposition.

Furthermore, the heat resistance of chromium and molybdenum and the corrosion resistance of nickel function to prevent the oxidation of alloy of the present invention caused by the erosion or heat, which increases the preciseness of the final product to be produced remarkably.

And, the nickel and vanadium have great durability against the instant thermal impact, so such elements can endow the alloy with superior abrasion resistance even under the high temperature, high pressure, and high heat impact environment. Here, the heat impact designates the cracks on the metal mold occurring when the alloy is expanded by heat or shrink by cold during the quick heating or quick cooling, and the alloy of the present invention has superior durability against the abrupt heat impact because of the appended nickel and vanadium. Meanwhile, the reason is described hereinafter that the respective elements constituting the special steel as hot-cool composite material for use in the apparatus for manufacturing the pipe or the like of the present invention are added and the quantity or the ratio thereof is defined.

At first, the carbon is an interstitial solid element, which has great influence on the forming of the texture of the special steel. However, desired abrasion resistance cannot be achieved if the quantity thereof is lower than 0.45 weight percent, and if the quantity thereof is greater than 0.75 weight percent, the quantity of chromium and tungsten for creating carbide increases relatively, so the hardness and abrasion resistance increase whereas the strength against the impact decreases to cause the crack and damage by the abrupt heating and abrupt cooling. In particular, it is more preferable that the quantity is 0.60 through 0.75 weight percent for the abrasion resistance, impact resistance, and welding performance desired in the present invention.

The silicon among the various steels is one of the deoxidation elements with electromagnetic property, and has influence on the thermal expansion coefficient and strength. If the quantity of the silicon is lower than 0.5 weight percent, deficient deoxidation may cause malfunction on the chemical reaction, and if greater than 1.5 weight percent, excessive silicon may cause the lowering of toughness, excessive increase of thermal expansion coefficient at high temperature, and remarkable decline of all physical property. Manganese among the steels is one of the deoxidation elements, and is helpful to strengthen pearlite organization, and is added to guarantee the de-oxidation property and hot working productivity. However, a desired strength cannot be achieved if the quantity thereof is lower than 0.4 weight percent, and in such a case, a preferable deoxidation effect cannot be achieved or the hot working productivity is lowered. And, if the quantity of manganese exceeds 1.0 weight percent, the elongation decreases rapidly and surface physical property is declined even though the desired strength is secured. Tungsten among the steels generally increases the hardness and the elongation strength at high temperature, and in the present invention, forms carbide as it is carbonized alone or together with chromium by carbon as mentioned above, wherein the carbide increases the hardness of the alloy. Furthermore, the carbide of tungsten itself is not likely to be decomposed thermally, so it increases the abrasion resistance of the alloy remarkably. However, a desired ultra abrasion resistance cannot be achieved if the quantity of tungsten is lower than 2.0 weight percent, and there occur cracks by rapid heating and rapid cooling if the quantity thereof exceeds 4.5 weight percent since the segregation of the organization occurs as the melting point of tungsten is high. In particularly, 2.0 through 4.0 weight percent is preferable in order to guarantee all of the physical property required in the present invention.

Nickel among the steels generally increases elongation, durability against oxidation, non-magnetic property, lowering of the transformation point, and the resistance against the high temperature impact, and especially endows the alloy with the corrosion resistance and heat-impact resistance. However, if the quantity thereof exceeds 0.4 weight percent, there may occur the lowering of the transformation point and a required physical property cannot be secured, and especially, it is hard to achieve a desired hardness. And, the frequency of generation of cracks may increase if the quantity of nickel is lower than 0.1 weight percent under the usage of the present invention other than the usage for the dividing shear knife.

Chromium among the steels is known as the element that is added to increase the strength, corrosion resistance, and abrasion resistance, and in the present invention, it increases the hardness of the alloy as it forms carbide together with tungsten, and there provided the effect that the desired abrasion resistance can be achieved even under the high temperature as the carbide is not likely to be decomposed thermally. Furthermore, the heat resistance of chromium prevents the oxidation by the erosion of material or by the heat under the high temperature, so the preciseness of the final product is improved. However, the above-mentioned physical properties cannot be guaranteed if the quantity thereof is lower than 2.0 weight percent, and the required physical property is deteriorated remarkably if the quantity thereof exceeds 4.0 weight percent.

Molybdenum among the steels generally prevents the tempering property, and endows the alloy with strengthening effect. In the present invention, molybdenum functions to endow the alloy with the heat resistance as in the case of chromium, so as to enhance the preciseness of the product by suppressing the thermal oxidation or the erosion of the material at high temperature. However, the desired heat resistance and abrasion resistance cannot be achieved if the quantity thereof is lower than 2.0 weight percent, and to the contrary, if the quantity thereof exceeds 4.0 weight percent, the working efficiency is deteriorated and coefficient of linear expansion increases excessively. It is preferable to be 2.5 through 3.5 weight percent in order to guarantee all of the physical property desired in the present invention.

Cobalt among the steels functions to improve hot rolling property, heat resistance, corrosion resistance and impact resistance, and such an improvement of the hot rolling property is too slight if the quantity thereof is lower than 0.5 weight percent, and the costs for manufacturing the alloy increases in vain if the quantity exceeds 3.0 weight percent as the cobalt itself is too expensive. It is preferable to be 0.5 through 2.0 weight percent in order to guarantee all of the physical property desired in the present invention.

Vanadium among the steels is an element to endow heat resistance, and it prevents the cracks of the material even under the rapid heating and rapid cooling.

However, sufficient heat-impact resistance cannot be achieved with the lower quantity than 0.2 weight percent, and the effect to improve the physical property is too slight with the greater quantity than 1.6 weight percent. It is preferable to be 0.2 through 1.0 weight percent in order to guarantee all of the physical property desired in the present invention.

The special steel containing the aforementioned elements has superior heat resistance, corrosion resistance, heat-impact resistance, and especially superior abrasion resistance, impact resistance, and welding workability even under a severe environment of high temperature and high pressure, and shows excellent performance as the material of apparatus for manufacturing the pipe or the like.

In particular, the special steel as hot-cool composite material is appropriate for a material of a roll employed on a pipe forming high-frequency welding area in manufacturing a welding type pipe, a material of dies metallic mold for enlarging the inner diameter of a seamless pipe used in an extremely bad environment of high temperature, high pressure, rapid heating, and rapid cooling, a material for dividing shear knife of a reinforcing bar or a round bar for structural purposes, or a material for metal press type extruding dies, etc.

The method for manufacturing special steel as hot-cool composite material for use in the apparatus for manufacturing the pipe, the reinforcing bar, or round bar for structural purposes is comprised of following steps: selecting and gauging a material such as iron alloy, etc., and then dissolving the material at a temperature of 1700 through 2000 ^°C ; injecting the dissolved material into a mold formed by combining molding sand; cooling the dissolved material and then performing de-sanding and sand-decay; mechanically processing after thens; and performing fine finishing after a thermal process.

According to the manufacturing method of the present invention, a master alloy containing the elements that the melting points thereof is remarkably higher than that of the other elements is preliminarily dissolved before performing a main dissolving process. In general, the dissolving process during the manufacturing of the special steel generally employs a single dissolving process that the respective elements are dissolved by heating the elements to the high temperature sufficient to dissolve all of the required elements, however, the melting point of tungsten (of which melting point is 3410±20 ^°C) and that of molybdenum (of which melting point is 2622±10°C) are so high in comparison with other elements that the costs for heating become too much, and furthermore, the melting points and the scattering points of them are different from each other and the oxidative tendency is so high as to cause segregation, so it is hard to achieve desired properties.

Accordingly, the present invention can employs a double dissolving processes including a process to prepare a master alloy by preliminarily dissolving respective elements and iron, and in the case of the tungsten and molybdenum of which melting points are especially high among the required elements, it is especially efficient to employ the process for manufacturing the master alloy.

Among the manufacturing methods of the present invention, the method including the process for manufacturing the master alloy is as follows: selecting required elements and dissolving the selected elements at a temperature of 1700 through 2000 ^°C ; injecting the dissolved element into an ingot case; achieving a master alloy by cleaving the case after cooling; selecting and gauging iron alloy and the master alloy, and then dissolving the iron alloy and the master alloy at a temperature of 1700 through 2000 ^°C ; injecting the dissolved elements into a mold formed by combining molding sand; cooling it and performing de-sanding and sand-decay; mechanically processing after thens; and performing fine finishing after a thermal process.

In the manufacturing method of the present invention, the thermal process is preferably a vacuum thermal process.

According to apparatus for manufacturing the pipe, reinforcing bar, round bar for structural purposes, or the like, made of the special steel as hot-cool composite material manufactured by the above-described process, carbon, tungsten and chromium have abrasion resistance property, chromium, molybdenum and cobalt has heat resistance property so as to prevent the abrasion by softening of the hardened layer even when the abrupt heat is added under the high pressure and high temperature, so the material is appropriate for the apparatus to manufacture the pipe, reinforcing bar or round bar for structural purposes as it is strong against the abrasion and crack due to the heat impact,

1^'5 high temperature, and high pressure.

EMBODIMENT

The embodiments of the present invention are as follows. Embodiment 1.

20kg of powdered iron-tungsten (in which the quantity of tungsten is 60 weight percent), 20kg of powdered iron-molybdenum (in which the quantity of molybdenum is 60 weight percent), and 60kg of scrap iron are dissolved together at the temperature of 1800 °C , and the dissolved material is injected into an ingot case in which it is cooled, and then the case is cloven to achieve the composite master alloy of tungsten, molybdenum and iron. Embodiment 2.

The composite iron and the master alloy are selected and gauged according to the composition shown in Table 2, and then are dissolved at the temperature of 1800 °C , and then the' dissolved elements are injected into a mold formed by combining molding sand. • Then the material is cooled and undergoes the de-sanding and sand-decay, and heated to a temperature of 900 ^°C at the heating speed of 2.5 °C /min. And then such a state is maintained for about two hours (in the case that the thickness of the product is 30mm. The time maintaining such a status increases one hour for every 25mm of product thickness), and is cooled to a temperature of 650 ^°C at the cooling speed of 0.83 °C/min, and then such a temperature is maintained for about one hour and then the result is cooled in the furnace for about one and a half day to process thens. Then, the result is mechanically processed and then quenched for 100 minutes at the temperature of 850 °C and for 80 minutes at the temperature of 1030 ^°C under the vacuum environment, and then it is tempered three times at the temperature of 560 °C for the vacuum thermal process. Then, the result is cut to meet the required tolerance to achieve a final product, i.e., a roll for manufacturing welding type pipe. Embodiments 3 through 8.

The embodiment 2 is repeated, wherein the composition of the special steel in the respective embodiments is adjusted as depicted in the following table 2. Comparative Examples 1 through 10.

The embodiment 2 is repeated, wherein the composition of the special steel in the respective comparative examples is adjusted as depicted in the following table 2. SKD62 class that is the conventional hot metallic patterning material has been employed in the comparative example 10 among the comparative examples. Embodiments 9 through 15.

The embodiment 2 is repeated, wherein the composition of the special steel in the respective embodiments is adjusted as depicted in the following table 2, and the final product, the dies mold that is the nose for manufacturing the seamless pipe, is achieved while the tempering temperature is kept to 630 °C . Comparative Examples 11 through 20.

The embodiment 2 is repeated, wherein the composition of the special steel in the respective embodiments is adjusted as depicted in the following table 2, and the final product, the nose that is the dies mold for manufacturing the seamless pipe, is achieved while the tempering temperature is kept to 630 ^°C . SKD61 class that is the conventional hot metallic patterning material has been employed in the comparative example 20 among the comparative examples. Embodiments 16 through 23.

The embodiment 2 is repeated, wherein the composition of the special steel in the respective embodiments is adjusted as depicted in the following table 2, and the final product, the dividing shear knife for manufacturing the reinforcing bar or round bar for structural purposes, is achieved while the tempering temperature is kept to 630 ^°C . Comparative Examples 21 through 30.

The embodiment 2 is repeated, wherein the composition of the special steel in the respective embodiments is adjusted as depicted in the following table 2, and the final product, the dividing shear knife for manufacturing the reinforcing bar or round bar for structural purposes, is achieved while the tempering temperature is kept to 630^°C . SKD61 class that is the conventional hot metallic patterning material has been employed in the comparative example 29 among the comparative examples, and SKDl 1 class that is the conventional hot metallic patterning material has been employed in the comparative example 30 among the comparative examples. Table 2.

Table 2. (Continued.)

Experimental Example 1.

Table 3 shows the result that the welding type pipe is manufactured actually using the respective rolls of embodiments 2 through 8 and comparative examples 1 through 10. In the table 3, the amended tonnage designates the tonnage of normal product of welding type pipe (50φ ) manufactured with one set of rolls. Table 3.

Experimental Example 2.

Table 4 shows the result that the seamless pipe is manufactured actually using the respective noses of embodiments 9 through 15 and comparative examples 11 through 20. In the table 4, the respective values designate the number of normal products of seamless pipe manufactured with one nose, and the material for the^' seamless pipe is tested respectively in regard to carbon steel that is a general structural steel, and SUS series that is stainless steel. Table 4.

Experimental Example 3. Table 5 shows the result that the reinforcing bar is manufactured actually using the respective knives of embodiments 16 through 23 and comparative examples 21 through 30. In the table 5, the amended tonnage designates the tonnage of normal product of reinforcing bar (15φ ) manufactured with one knife. Table 5.

Table 5. (Continued.)

It is confirmed from the tables 3 through 5 that the special steel according to the present invention shows a superior heat resistance, abrasion resistance, heat-impact resistance, corrosion resistance, impact resistance and welding workability, in comparison with the case of SKD61 class and SKD62 class that are the conventional hot metallic patterning material and SKDl 1 class that is the conventional cold metallic patterning material.

It is because all of the physical properties of the conventional special steel are much inferior for both of the usages of hot metallic patterning portion and cold metallic patterning portion, since the conventional special steel has been intended to be used for only one of hot metallic patterning environment and cold metallic environment.

However, the inventor has invented the special steel as hot-cool composite material having the superior effect in regard to the special usage including both of the usages of hot metallic patterning portion and cold metallic patterning portion, according to the repeated experiment for a long period of time.

INDUSTRIAL APPLICABILITY

The special steel as hot-cool composite material of the present invention shows the superior heat resistance, abrasion resistance, heat-impact resistance, corrosion resistance, impact resistance, and welding workability even under the high temperature, high pressure, and high heat impact environment, by determining the kind and the quantity of the appended elements properly, and accordingly, the present invention can provide a material that is especially proper for the apparatus for manufacturing a pipe, reinforcing bar, or a round bar for structural purposes, etc.

Claims

1. A special steel as hot-cool composite material, comprising carbon of 0.45 through 0.75 weight percent, silicon of 0.5 through 1.5 weight percent, manganese of 0.4 through 1.0 weight percent, tungsten of 2.0 through 4.5 weight percent, nickel of 0 through 0.4 weight percent, chromium of 2.0 through 4.0 weight percent, molybdenum of 2.0 through 4.0 weight percent, cobalt of 0.5 through 3.0 weight percent, vanadium of 0.2 through 1.6 weight percent, and iron and inevitable impurities of residuary weight percent.

2. The special steel of claim 1, wherein content of the carbon is 0.60 through

0.75 weight percent.

3. The special steel of claim 1, wherein content of the tungsten is 2.0 through 4.0 weight percent.

4. The special steel of claim 1, wherein content of the nickel is 0.1 through 0.4 weight percent.

5. The special steel of claim 1, wherein content of the molybdenum is 2.5 through 3.5 weight percent.

6. The special steel of claim 1, wherein content of the cobalt is 0.5 through 2.0 weight percent.

7. The special steel of claim 1, wherein content of the vanadium is 0.2 through

1.0 weight percent.

8. The special steel of claim 1, wherein the special steel is employed as a material for an apparatus to manufacture a pipe, a reinforcing bar, or a round bar for structural purposes.

9. The special steel of claim 1, wherein the special steel is employed as a roll material employed on a pipe forming high-frequency welding area in a welding type manufacturing line.

10. The special steel of claim 1, wherein the special steel is employed as a material of dies metallic patterning for enlarging an inner diameter of a seamless pipe.

11. The special steel of claim 1, wherein the special steel is employed as a material for dividing shear knife of a reinforcing bar or a round bar for structural purposes.

12. The special steel of claim 1, wherein the special steel is employed as a material for metal press type extruding dies.

13. A method for manufacturing a special steel as hot-cool composite material as depicted in any one of claims 1 through 12, the method comprising the steps of: selecting and gauging a material such as iron alloy, etc., and then dissolving the material at a temperature of 1700 through 2000 ^°C ; injecting the dissolved material into a mold formed by combining molding sand; cooling the dissolved material and then performing de-sanding and sand-decay; mechanically processing after thens; and performing fine finishing after a thermal process.

14. A method for manufacturing a special steel as hot-cool composite material as depicted in any one of claims 1 through 12, the method comprising the steps of: selecting required elements and dissolving the selected elements at a temperature of 1700 through 2000 °C ; injecting the dissolved element into an ingot case; achieving a master alloy by cleaving the case after cooling; selecting and gauging iron alloy and the master alloy, and then dissolving the iron alloy and the master alloy at a temperature of 1700 through 2000 °C ; injecting the dissolved elements into a mold formed by combining molding sand; cooling it and performing de-sanding and sand-decay;' mechanically processing after thens; and performing fine finishing after a thermal process.

15. A special steel as hot-cool composite material according to any one of claims 1 through 12, the special steel manufactured by the manufacturing method as depicted in claim 13.

16. A special steel as hot-cool composite material according to any one of claims 1 through 12, the special steel manufactured by the manufacturing method as depicted in claim 14.