KR100331962B1 - Method for manufacturing high cleanliness tool steel with improved macro/micro-solidification structure - Google Patents

Abstract

PURPOSE: A method for manufacturing high cleanliness alloy tool steel (hot and cold working tool steel) and high cleanliness high speed tool steel to which light rare earth metal (REM) such as Ce, La, Nd, Pr and Y, and REM+Ca are added based on vacuum induction furnace melting and electric furnace melting is provided. CONSTITUTION: The method for manufacturing high cleanliness hot working tool steel comprises a step of preparing molten steel of ordinary hot working tool steel comprising 0.1 to 1.0 wt.% of C, 0.2 to 0.8 wt.% of Si, 0.3 to 4.0 wt.% of Mn, 0.001 to 4.0 wt.% of Ni, 1.5 to 6.0 wt.% of Cr, 0.3 to 4.0 wt.% of Mo, 0.1 to 3.5 wt.% of V, 0.005 to 0.2 wt.% of W, 0.005 to 0.1 wt.% of Al, and a balance of Fe and trace impurities contained during electric furnace steelmaking; a step of deoxidizing and desulfurizing the prepared molten steel under the degree of vacuum of 1x10¬-1 torr or less so that the deoxidized and desulfurized molten steel contains 15 ppm or less of oxygen and 100 ppm or less of sulfur respectively; a step of adding light rare earth metal or misch metal (Ce, Nd, La, Pr and Fe), calcium (Ca) or a mixture of the misch metal and calcium to the pre-deoxidized and desulfurized molten steel within the rare earth metal range of 0.0002 to 0.25 wt.%, and the calcium range of 0.001 to 0.1 wt.%; a step of manufacturing steel ingot by cooling molten steel in the temperature range of 1600±50 deg.C; and a step of hot rolling or forging the manufactured steel ingot in the temperature range of 1200±50 deg.C.

Description

Manufacturing method of high clean tool steel with improved macro and micro solidification structure

[Field of Invention]

The present invention is a light rare earth element (Ce, La, Nd, Pr, Y, etc .: based on REM) based on vacuum induction furnace melting and electric melting, and high-purity alloy steel oral steel (REM + Ca added) Cold work oral cavity) and a high-cleaning high speed oral cavity.

[Prior art]

Recently, as the acceptance of high-grade steel increases, the rate of vacuum treatment after the tapping of the electric melting furnace is increasing, and its importance is further emphasized. The purpose of vacuum treatment of molten steel is to produce ultra-low carbon steel by reducing the components such as hydrogen and nitrogen by refluxing molten steel after tapping in an electric melting furnace under low pressure, or by inducing decarburization and deoxidation by CO gas generation. In addition, to obtain clean steel by separating the non-metallic inclusions in the molten steel by molten steel stirring or reflux.

In general, excessive non-metallic inclusions and impurities such as alumina (Al ₂ O ₃ ) and manganese sulfide (MnS) present in existing tool steels impair the cleanliness of the steel, and at the same time, various properties such as impact, machinability, thermal fatigue characteristics, etc. In addition, high hardness oxides such as Al ₂ O ₃ impair workability during hot rolling and hot forging, and MnS is stretched in the processing direction and mechanical properties in the direction perpendicular to the processing direction. To make a remarkable difference.

Therefore, researches for improving cleanliness and shape control of steel materials have been repeated depending on ladle refining or vacuum refining for a long time, but the limits have been reached.

The present invention has been made to solve the above problems, and after controlling the content of sulfur (S), the content of aluminum (Al) during ladle refining after melting molten steel in a specific component range and pre-deoxidation and Perform preliminary desulfurization, adjust the addition time and method of adding REM and REM + Ca to the molten steel to reduce impurities such as O, S, P, N, etc. At the same time, a small amount of spherical rare earth (RE) composite inclusions and Ca-containing RE composite inclusions remain in the molten steel to coagulate macro and micro coagulation using heterogeneous nucleation of the RE composite composites during solidification. It is an object of the present invention to provide a method for producing high-clean tool steel that improves the structure.

Figure 1 is a tissue photograph showing the shape of the non-metallic inclusions in the tool steel material prepared according to the present invention and conventional embodiments.

2 is a tissue photograph showing a microcoagulation structure as a mark in a tool steel material manufactured according to the present invention and a conventional embodiment.

In order to achieve the object of the present invention as described above, the manufacturing method of the high-clean hot-hole oral cavity of the present invention by weight% C: 0.1% to 1.0%, Si: 0.2% to 0.8%, Mn: 0.3% to 4.0%, Ni: 0.001% to 4.0%, Cr: 1.5% to 6.0%, Mo: 0.3% to 4.0%, V: 0.1% to 3.5%, W: 0.005% to 0.2%, Al: 0.005% to 0.1% Solving the remaining amount of the molten steel of the general hot-air oral cavity consisting of Fe and trace impurities that may be contained during steelmaking; Deoxidizing and desulfurizing the molten steel so that the oxygen content and the sulfur content are 15 ppm or less and 100 ppm or less, respectively, at a vacuum degree of 1 × 10 ⁻¹ torr or less; To the pre-deoxidation and desulfurized molten steel, rare earth elements 0.0002% to 0.25% and Ca: 0.001 to 0.1% can be added alone or in combination with calcium and lightly added with misc metal (Ce, Nd, La, Pr, Fe). Rare earth elements (Ce, La, Nd, Pr, Y) and calcium can be added alone or in combination of two to three or more components, and the addition time is immediately after vacuum refining or just before injection of molten steel during steel ingot manufacture. It is injected into the lower injection pipe, or it is injected into the mold during molten steel injection, and the method of addition is 100% injection completion at the time of addition, select a certain time and a certain amount from the initial injection to completion, or 40% injection at the beginning of molten steel injection. The remaining 60% is divided into three minutes before the completion of injection; Cooling the molten steel at 1600 ° C. ± 50 ° C. to produce a steel ingot; And hot rolling or forging the steel ingot at 1200 ° C. ± 50 ° C., and retains the spherical light rare earth-based composite inclusions or the light rare earth-calcium-based composite inclusions of 5 μm or less, and the final rare earth element content and calcium. The amount satisfies REM% / S% = 2 to 90, [REM%] [5%] = 3 × 10 ^{-5 to} 100 × 10 ^-5 , and Ca% / S% = 1 or less compared to the sulfur element amount. It features.

In order to achieve the above object, the manufacturing method of the high clean cold oral cavity of the present invention is C: 1.0% to 1.7%, Si: 0.2% to 0.6%, Mn: 0.2% to 0.7%, Ni: 0.001% to 4.0%, Cr: 3.5% to 15.0%, Mo: 0.1% to 2.0%, V: 0.1% to 3.0%, W: 0.005% to 0.2%, Al: 0.005% to 0.1%. Dissolving a molten steel of a general cold oral cavity composed of trace impurities that may be contained during steelmaking with electricity; Deoxidation and desulfurization treatment of the molten steel such that the oxygen content and the sulfur content are 15 ppm or less and 100 ppm or less, respectively, at a vacuum degree of 1 × 10 ⁻¹ torr or less; To the pre-deoxidation and desulfurized molten steel, rare earth elements: 0.0002% to 0.25%, and Ca: 0.001 to 0.1%, respectively, are added alone or added to the mismetals (Ce, Nd, La, Pr, Y) and calcium. Compound to three or more components can be added in combination, and the addition time is added into the lower injection pipe immediately after vacuum refining or just before injection of molten steel during the manufacture of ingot, or into the mold during injection of molten steel, and the addition method is 100% input completion, or a predetermined time and a predetermined amount from the initial injection to completion, or 40% in the initial molten steel injection and the remaining 60% divided into three minutes before completion of the injection; Hot rolling or forging at 1600 ° C. ± 50 ° C., and residual spherical light rare earth composite inclusions or light rare earth-calcium composite inclusions of 5 μm or less and less than 0.06%, and the final rare earth element content and calcium amount are sulfur It satisfies REM% / S% = 2 to 90, [REM%] [S%] = 3 × 10 ^{-5 to} 100 × 10 ^-5 , and Ca% / S% = 1 or less relative to the element amount do.

In order to achieve the above object, the manufacturing method of the high-cleaning high speed oral cavity of the present invention is weight% C: 0.1% to 1.0%, Si: 0.2% to 0.8%, Mn: 0.3% to 4.0%, V: 0.1% to Solving the molten steel of the general high-clean high-speed coating steel containing 3.5%, W: 0.005% to 0.2%, Al: 0.005% to 0.1%, the remaining amount is composed of Fe and trace impurities that can be contained during steelmaking; Deoxidation and desulfurization treatment of the molten steel such that the oxygen content and the sulfur content are 15 ppm or less and 50 ppm or less, respectively, at a vacuum degree of 1 × 10 ⁻¹ torr or less; To the pre-deoxidation and desulfurized molten steel, rare earth elements: 0.0002% to 0.25%, and Ca: 0.001 to 0.1% are added in addition to the misch metals (Ce, Nd, La, Pr, Fe) alone or separately for calcium. They may be added in two to three components or more, and the addition time is immediately after vacuum refining or immediately before injection of molten steel during the manufacture of steel ingots, or into the mold during injection of molten steel. Adding 100% at the time of addition, or selecting a certain amount of time from the beginning of the injection to completion, or 40% at the beginning of the molten steel injection and dividing the remaining 60% until 3 minutes before the completion of injection; Cooling the molten steel at 1600 ° C. ± 50 ° C. to produce a steel ingot; And hot rolling or forging the steel ingot at 1200 ° C. ± 50 ° C., and retains the spherical light rare earth-based composite inclusion or the light rare earth-calcium-based composite inclusion below 5 μm, and the final rare earth element content and calcium. The amount satisfies REM% / S% = 2 to 90, [REM%] [S%] = 3 × 10 ^-5 to 100 × 10 ^-5 , and Ca% / S% = 1 or less compared to elemental sulfur. It is characterized by.

EMBODIMENT OF THE INVENTION Hereinafter, the manufacturing method of the high clean mouth hole of this invention is demonstrated in detail.

In order to maximize the effect of addition of REM and at the same time to add Al with added REM and at the same time the limited range is 0.005 to 0.1%, while utilizing the properties of Al-kilted steel and controlling the sole generation of RE-Oxide after REM addition, Al was added before REM addition for the purpose of sufficient pre-oxidation, and the limited range was made into 0.005 to 0.1%, and the vacuum degree before REM addition was made into 1x10 <^-1> rr or less. If the vacuum degree is less than 1 × 10 ^-1 torr or Al is less than 0.005%, there is no sufficient pre-oxidation effect. If Al is more than 0.1%, a large amount of A1 ₂ O ₃ is produced and the deoxidation and desulfurization effects of REM are inhibited. So let's put that limit.

In order to obtain the high cleanliness and solidification structure improvement effect of the tool steel required by the present invention, the amount of S in the molten steel should be controlled to less than 15 ppm and the amount of S to 100 ppm and 50 ppm or less through deoxidation and desulfurization treatment before REM addition. If dissolved oxygen is more than 15ppm before adding REM, the formation of RE-Oxide, which is a high hardness oxide in molten steel, is free. If the amount of S is more than 100ppm, a large amount of RE-based composite inclusions are generated, which adversely affects the material.

The form of single addition of REM in molten steel or complex addition of REM + Ca is based on the following. Firstly added in the form of mischmetal (Ce, La, Nd, Pr, Fe), secondly added to each of the rare earth elements Ce, La, Nd, Pr, Y, etc., thirdly added mischmetal + Ca, fourth Ce, La, Nd, Pr, Y, and Ca are added two to three components or more.

In addition, the timing of the addition of REM and REM + Ca in molten steel is generally added after vacuum refining in the steelmaking process, immediately before injection of molten steel in the manufacture of ingots, and added into the injecting tube before injection of molten steel, and added into the mold during molten steel injection into the mold. It is not added in the melting furnace or before vacuum refining to minimize the formation of bi-sulfur reaction and Re-Oxide due to the time delay from the addition of REM to the ingot as shown in the following equation.

2RES (S) + 2O = RE ₂ O ₂ S (S) + S

RE ₂ O ₂ S (S) + O = RE ₂ O ₃ (S) + S

The more REM and REM + Ca in molten steel, the more harmful non-metallic inclusions and impurities such as Al ₂ O ₃ and MnS can be significantly reduced. But some remain in the molten steel and remain in the steel after molten steel solidification. That is, when excessively added, there is a large deoxidation and desulfurization effect, but rather adverse effects on the characteristics. In order to achieve both the purpose of sufficient deoxidation, desulfurization effect and small amount of RE-based composite inclusions in the steel, the appropriate amount of REM and Ca is required. Therefore, the final REM amount is limited to 0.0002% to 0.25%. However, it is based on satisfying REM% / S% = 2 to 90 and [REM%] [S%] = 3 × 10 ^{−5 to} 100 × 10 ⁻⁵ as compared with the final amount of S. When 0.0002% or less, REM% / S% = 2 or less, and [REM%] [S%] = 3 × 10 ^-5 or less, the shape control of nonmetallic inclusions is not sufficient, 0.25% or more, REM% / S% = 90 or more When [REM%] [S%] = 100 × 10 ^{-5 or} more, the deoxidation and desulfurization effect as large as the added amount is not seen, and it is not economical and adversely affects the characteristics. Deoxidation and desulfurization reaction by adding REM and Ca in molten steel is as follows.

2RE + 2O = RE ₂ O ₂ S

xRE + yS = RE _x S _y

Ca + (x + 1/3) Al ₂ O ₃ = CaO _x Al ₂ O ₃ + 2 / 3Al

CaO + 2 / 3Al + S = CaS + 1 / 3Al ₂ O ₃

The method of adding REM and REM + Ca in molten steel is based on two methods of adding all the appropriate amounts of REM at a predetermined time or adding the appropriate amount of REM at a predetermined time interval.

There are two ways to add the REM amount at regular time intervals, but the most effective method for the addition time in the mold or in the injection pipe is to add 40% at the beginning of the injection time and the remaining REM amount is constant. Divide at intervals and add 100% until 3 minutes before injection. The final Ca amount is limited to the range of 0.001% to 0.1%. However, compared with the final S amount, Ca% / S% = 1 or less. When Ca is less than 0.001%, sufficient pre-deoxidation effect and shape control effect of nonmetallic inclusions are not seen, and when it is 0.1% or more and Ca% / S% = 1 or more, the effect of REM addition is inhibited.

EXAMPLE

Hereinafter, the present invention will be described in more detail with reference to Examples.

<Example 1>

First, in order to manufacture hot tool steel, a 60 ton electric furnace was used, and the conventional steelmaking method was applied, and the composition range of the general hot hole steel, that is, in weight%, C: 0.1% to 1.0%, Si: 0.2% to 0.8%, and Mn: 0.3% to 4.0%, Ni: 0.001% to 4.0%, Cr: 1.5% to 6.0%, Mo: 0.3% to 4.0%, V: 0.1% to 3.5%, W: 0.005% to 0.2%, Al: 0.005% It contains ˜0.1%, and the remaining amount is dissolved in molten steel composed of Fe and trace impurities that can be contained in steel making. Two 6-ton ingots are made, one is ingot and the other is scrap in the middle of the ingot. After remelting using a 50kg vacuum induction furnace, 18kg class steel ingots were prepared for specimens R and C, which were applied to the existing steelmaking method, and specimens A and C. Residual water in a 60 ton electric furnace was fabricated from specimens B, D, E, and F in 6 ton ingots according to the invention method shown in Table 1.

Next, the cold oral and high speed oral systems also melted the molten steel by applying the existing steelmaking method, and then adopted the method of manufacturing the test mass in the hot oral cavity to produce 6 ton ingots and 18 kg ingots.

Cold work steels have a composition range of general cold work steels, that is, by weight%, C: 1.0% to 1.7%, Si: 0.2% to 0.6%, Mn: 0.2% to 0.7%, Ni: 0.001% to 4.0%, Cr: 3.5% -15.0% Mo: 0.1%-2.0%, V: 0.1%-3.0%, W: 0.005%-0.2%, Al: 0.005%-0.1%, the remaining amount can be contained during steelmaking with Fe and electricity After melting molten steel composed of trace impurities, two 6-ton ingots were made, similar to the case of hot working steel, one ingot was made of V, and the other was scrapped from the middle of the ingot, using a 50 kg vacuum induction furnace. After re-melting, specimen S, which applied the existing steelmaking method, and specimens H and J, which were applied to the invention method, were fabricated as 18kg steel ingot. Residual water in a 60 ton electric furnace was prepared in 6 ton ingots after solvent with specimens G, I, K and L according to the invention method shown in Table 1.

The high speed coating oral is composed of the general high speed coating oral composition, that is, in weight%, C: 0.5% to 1.5%, Si: 0.2% to 0.6%, Mn: 0.25 to 0.5%, Ni: 0.08% or less, Cr: 4.0% to 6.0% , Mo: 3.5% to 9.0%, V: 1.0% to 5.0%, W: 4.0% to 13.0%, Al: 0.005% to 0.1%, and the remaining amount is trace impurities that may be contained during steelmaking with Fe and electricity. After melting molten steel consisting of two, 6 ton steel ingots were made, one ingot was made into W, the other was scrapped from the middle of the ingot, and remelted using a 50kg vacuum induction furnace. The applied specimen T and the specimens M and N to which the invention method was applied were made of 18 kg ingot. Residual water in a 60 ton electric furnace was prepared in 6 ton ingots after solvent with specimens O, P, and Q according to the invention method shown in Table 1.

Reclassifying the ingot specimens shown in Table 1, A to Q are the methods of the present invention, where A and C are 18 kg ingots for hot oral cavity, and B, D, E and F are 6 ton ingots for hot oral cavity. , H, J are 18kg ingots for cold oral steel, G, I, K, L are 6ton ingots for cold oral steel, M, N are 18kg ingots for high speed steel, O, P, Q are for high speed steel It is a 6ton ingot.

In the specimens, the 6-ton ingot was forged to 320 ψ at 1200 ° C., and the 18 kg ingot was forged to 33 ψ at 1200 ° C.

<Table 1>

In order to examine whether the prepared specimens are suitable for hot work, cold work, and high speed work, the amount of O, S, P, N, total Al, and Soluble Al remaining in the steel ingot manufactured by the existing steelmaking and invention methods The analytical value measured at the 1/2 position of the ingot and the total nonmetallic inclusions remaining in the forged material are shown in Table 2.

<Table 2>

As can be seen from Table 2, the amount of O and S in the material manufactured according to the invention method was significantly reduced than the material manufactured according to the existing steelmaking method and the comparative method, and the amount of P and N was somewhat lower than that of the conventional steelmaking method and the comparative method. Reduced. Compared with the total Al content and the Al content of the soluble Al was about 50% or less in the conventional steelmaking method and the comparative method, while the material using the invention method was more than 80%.

Total non-metallic inclusions were measured in accordance with KS D 0204 at 1 / 2R positions of materials forged with 320ψ and 33ψ, and the results are shown in Table 2. The total nonmetallic inclusions in the material manufactured according to the present invention are based on RE system. After the composite inclusions and Ca-containing RE inclusions were formed, some of them were removed by the flotation separation effect, resulting in a reduction of up to 76.1% and at least 29.5%, compared to materials manufactured by conventional steelmaking and comparative methods.

1 shows the observation of the shape of the nonmetallic inclusions with an optical microscope at a position where the total amount of nonmetallic inclusions of the material prepared according to Comparative Method R and Inventive Methods C, H and P was measured. In the R material prepared by the comparative method, MnS was elongated in the forging direction, and high hardness oxides such as Al ₂ O ₃ were broken during the forging and elongated in the processing direction, and the formation position was the initial austenite grain boundary, but the invention method C RE-based composite inclusions and Ca-containing composite inclusions formed from H, P-based materials were elongated in the processing direction and maintained the fine spherical shape. The formation position was not only in the initial austenite grain boundary but also in the mouth. As it was, it was evenly distributed throughout the material.

2 is a result of observing the microcoagulation structure of the cross section of the steel ingots produced by Comparative Method R and Inventive Methods A and C. FIG. From the macromicrograph on the left side of FIG. 2, the solidification structure of the steel ingots prepared by Inventive Methods A and C was dense and the central segregation represented by the central Porosity and P segregation was significantly reduced compared to the material prepared by Comparative Method R. It can be seen that.

In addition, although not shown, the cold working steel and the high speed tool steel to which the present invention was applied also exhibited a dense solidified structure and significantly reduced central segregation.

From the microcoagulation structure located on the right side of FIG. 2, in the case of the materials A and C to which the present invention was applied, the unsolubilized solute accumulation region (black region) was significantly reduced and the size of the MC and M ₂ C carbides became considerably finer.

As described above, the manufacturing method of the high-cleaning steel ball of the present invention is as shown in Table 3, the amount of O in the molten steel before the addition of REM less than 15ppm, S content 100ppm and 50ppm REM% / S% = 2 ~ 82, [REM%] [S%] = 5 × 10 ^-5 ~ 92 × 10 ^-5 , Ca% / By setting S% = 0.33 or less, highly purified materials can be obtained.

<Table 3>

In addition, the macro- and microcoagulation structure was also remarkably improved as a small amount of RE-based composite inclusions and RE-based composite inclusions containing Ca were left without attempting to completely remove non-metallic inclusions.

Although specific embodiments of the present invention have been described and illustrated herein, modifications and variations can be made by those skilled in the art. Accordingly, the following claims are to be understood as including all modifications and variations as long as they fall within the true spirit and scope of the present invention.

As described above, the present method for manufacturing high-clean tool steel improves cleanliness by adding light rare earth elements and Ca to reduce impurities and total non-metallic inclusions, and improves heterogeneous nucleation performance of RE-based composite inclusions during solidification. The macromicro coagulation structure was improved to obtain a high clean tool steel.

Claims (6)

By weight% C: 0.1%-1.0%, Si: 0.2%-0.8%, Mn: 0.3%-4.0%, Ni: 0.001%-4.0%, Cr: 1.5%-6.0%, Mo: 0.3%-4.0% , V: 0.1% to 3.5%, W: 0.005% to 0.2%, Al: 0.005% to 0.1%, and the remaining amount is the molten steel of general hot-hole oral steel composed of Fe and trace impurities that may be contained during steelmaking. Solvent step; Deoxidation and desulfurization treatment of the molten steel such that the oxygen content and the sulfur content are 15 ppm or less and 100 ppm or less, respectively, at a vacuum degree of 1 × 10 ⁻¹ torr or less; Pre-deoxidation and desulfurization molten steel can be added alone or in combination with calcium in the rare earth elements 0.0002% to 0.25%, Ca: 0.001 to 0.1%. Rare earth elements (Ce, La, Nd, Pr, Y) and calcium can be added alone or in combination of two to three or more components, and the addition time is immediately after vacuum refining or just before injection of molten steel during steel ingot manufacture. Inject into the lower injection, or into the mold during molten steel injection, the method of addition is 100% complete at the time of addition, select a certain time and a certain amount from the beginning to the end of the injection, or 40% at the beginning of molten steel injection The remaining 60% is divided into three minutes before the completion of injection; Cooling the molten steel at 1600 ° C. ± 50 ° C. to produce a steel ingot; And hot rolling or forging the steel ingot at 1200 ° C. ± 50 ° C., and retains the spherical light rare earth-based composite inclusion or the light rare earth-calcium-based composite inclusion below 5 μm and the final rare earth element content and calcium. The amount satisfies REM% / S% = 2 to 90, [REM%] [5%] = 3 × 10 ^{-5 to} 100 × 10 ^-5 , and Ca% / S% = 1 or less compared to the elemental sulfur content. A method of manufacturing a high clean hot oral cavity, characterized in that. The method of claim 1, wherein when calcium is added together with the light rare earth element, its content is in the range of 0.0002% to 0.25% for light rare earth elements or mismetal, and 0.001% to 0.1% for Ca: Method of manufacturing tool steel. By weight% C: 1.0%-1.7%, Si: 0.2%-0.6%, Mn: 0.2%-0.7%, Ni: 0.001%-4.0%, Cr: 3.5%,-15.0%, Mo: 0.1%-2.0 %, V: 0.1% to 3.0%, W: 0.005% to 0.2%, Al: 0.005% to 0.1%, and the remaining amount is molten steel of general cold oral steel which is composed of Fe and trace impurities that may be contained during steelmaking. Solving step; Deoxidation and desulfurization treatment of the molten steel such that the oxygen content and the sulfur content are 15 ppm or less and 100 ppm or less, respectively, at a vacuum degree of 1 × 10 ¹ torr or less; Pre-deoxidation and desulfurized molten steel are added alone or added to the mismetals (Ce, Nd, La, Pr, Y) and calcium so as to exist in the range of rare earth elements: 0.0002% to 0.25% and Ca: 0.001 to 0.1%. Compound to three or more components can be added in combination, and the addition time is added into the lower injection pipe immediately after vacuum refining or just before injection of molten steel during the manufacture of ingot, or into the mold during injection of molten steel, and the addition method is Completion of 100%, or select a certain time and a certain amount from the beginning to completion of the injection, or 40% in the initial molten steel injection and the remaining 60% divided into three minutes before completion of the injection; Hot rolling or forging at 1600 ° C ± 50 ° C, and remaining 5 μm or less spherical light rare earth-based composite inclusions or light rare earth-calcium-based composite inclusions below 0.06%, and the final rare earth element content and calcium amount are sulfur It satisfies REM% / S% = 2 to 90, [REM%] [S%] = 3 × 10 ^{-5 to} 100 × 10 ^-5 , and Ca% / S% = 1 or less relative to the element amount A method of manufacturing a high clean cold work oral. The method of claim 3, wherein when calcium is added together with the light rare earth element, its content is in the range of 0.0002% to 0.25% for light rare earth elements or mismetal, and 0.001% to 0.1% for Ca. Method of manufacturing tool steel. By weight% C: 0.5%-1.5%, Si: 0.2%-0.6%, Mn: 0.25%-0.50%, Ni: 0.08% or less, Cr: 4.0%-6.0%, Mo: 3.5%-9.0%, V : 1.0% to 5.0%, W: 4.0% to 13.0%, Al: 0.005% to 0.1%, and the remaining amount is dissolved in the molten steel of general high-speed coating oral steel composed of Fe and trace impurities that may be contained in steelmaking. step; Deoxidation and desulfurization treatment of the molten steel such that the oxygen content and the sulfur content are 15 ppm or less and 50 ppm or less, respectively, at a vacuum degree of 1 × 10 ⁻¹ torr or less; To the pre-deoxidation and desulfurized molten steel, rare earth elements: 0.0002% to 0.25%, and Ca: 0.001 to 0.1% are added in addition to the misch metals (Ce, Nd, La, Pr, Fe) alone or separately for calcium. They may be added in two to three components or more, and the addition time is immediately after vacuum refining or immediately before injection of molten steel during the manufacture of steel ingots, or into the mold during injection of molten steel. Adding 100% at the time of addition, or selecting a certain amount of time from the beginning of the injection to completion, or 40% at the beginning of the molten steel injection and dividing the remaining 60% until 3 minutes before the completion of injection; Cooling the molten steel at 1600 ° C. ± 50 ° C. to produce a steel ingot; And hot rolling or forging the steel ingot at 1200 ° C. ± 50 ° C., and retains the spherical light rare earth-based composite inclusions or the light rare earth-calcium-based composite inclusions of 5 μm or less, and the final rare earth element content and calcium. The amount satisfies REM% / S% = 2 to 90, [REM%] [S%] = 3 × 10 ^{-5 to} 100 × 10 ^-5 , and Ca% / S% = 1 or less relative to the elemental sulfur content. A method of manufacturing a high clean high speed oral cavity, characterized in that. The method of claim 5, wherein when calcium is added together with the light rare earth element, its content is in the range of 0.0002% to 0.25% of light rare earth element or mismetal, and 0.001% to 0.1% of Ca: Method of manufacturing tool steel.