KR100376495B1 - A method of manufacturing Co-free having superior wear resistance high speed steels - Google Patents

Abstract

PURPOSE: An improved tool steel manufacturing method in which non-cobalt contained high speed tool steel has uniformed carbide structure obtained by spray forming simpler than prior manufacturing process and particularly has superior abrasion resistance is provided. CONSTITUTION: In a method for manufacturing high speed tool steel by spray forming, the method for manufacturing non-cobalt contained high speed tool steel having superior abrasion resistance comprises the processes of melting the alloy so that the basic composition contains a of 4.2 to 5.6 wt.%, b of 4.0 to 6.0 wt.%, c of 1.3 to 1.7 wt.%, x of 6.0 to 12.0 wt.%, y of 6.0 to 18.0 wt.% and z of 59 to 78.5 wt.% after preparing alloy having CraVbCcMoxWyFez as a basic composition; maintaining temperature of melt in the range of liquidus line temperature of the melt±(70-170) deg.C; obtaining bulk material by ejecting gas onto the melt maintained to the range of liquidus line temperature of the melt±(70-170) deg.C; and hot working the bulk material to a temperature of 1,000 to 1,150 deg.C, wherein the hot working is hot forging in which forging ratio is maintained to 6 or more, wherein the hot working is performed by hot rolling in which reduction ratio is maintained to 80% or more, and wherein the hot working is hot extrusion in which extruding ratio is maintained to 10:1 or more.

Description

A method of manufacturing Co-free having superior wear resistance high speed steels}

The present invention relates to a method for manufacturing a high-speed coated oral cavity, and more particularly, to a method for manufacturing a high-speed coated oral cavity having high wear resistance without containing cobalt (Co) which secures high cutting speed and high speed.

High-speed coated steel is high carbon alloy steel with a large amount of carbide forming elements, and its mechanical properties depend on the shape, size, and distribution of carbides in the alloy. It can be called tool steel.

Conventional high-speed coated oral contains Co, which secures high temperature wear resistance, thereby further improving cutting speed. However, Co increases the manufacturing cost of high-speed coated steel because the price of the raw material is high. Therefore, the high speed coated oral which has abrasion resistance even if Co is excluded for the general purpose of the high speed coated oral is known.

Until now, the main manufacturing method of high speed coating oral which does not contain cobalt (Co) has been the method by casting. However, the billet for tool steel manufactured by casting has a disadvantage in that carbides are coarsened in the alloy at the time of casting, and the coarse carbides are unevenly distributed in the billet, and thus have poor wear resistance, workability, low toughness and low impact characteristics. In addition, the casting method has a disadvantage in that the type and content of alloying elements that can be added are limited due to the formation of coarse carbides and severe segregation of microstructures.

On the other hand, in recent years, a method of manufacturing a tool steel by spray forming has been proposed, which is simple in manufacturing and has many advantages in manufacturing (Korean Patent Application No. 94-38977). However, until now, the spray forming method has been applied only to a specific composition due to the degree of segregation of carbides, but has not yet reached the commercialization stage.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The present invention provides an improved tool steel which has a uniform carbide structure, in particular, excellent abrasion resistance, by a simple spray molding method for manufacturing a high-speed coated steel containing no Co. To provide a manufacturing method, the object is.

1 is a photograph showing the microstructure of a specimen hot worked according to the present invention.

The manufacturing method of the present invention for achieving the above object, in the method for producing a high-speed coated oral by spray forming, Cr _a V _b C _c Mo _x W _y Fe _z as a basic composition, the content 4.2% ≤a≤5.6%, 4.0% ≤b≤6.0%, 1.3% ≤c≤1.7%, 6.0% ≤x≤12.0%, 6.0% ≤y≤18.0%, 59% ≤z And dissolving the alloy to have a composition of ≦ 78.5%, and then obtaining the bulk material by gas spraying the melt, and hot working the base material.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, the cold working tool steel of the present invention is a tool steel made of Cr-VC-Mo-W-Fe-based alloy and basically forms Cr _a -V _b, -C _c -Mo _x -W _y -Fe _z , Each component composition is controlled here to prevent segregation and to distribute the carbide evenly within the matrix. To this end, each component composition is 4.2% ≤a≤5.6%, 4.0% ≤b≤6.0%, 1.3% ≤c≤1.7%, 6.0% ≤x≤12.0%, 6.0% ≤y≤18.0%, 59% ≦ z ≦ 78.5%.

Specifically, Cr is an alloying element required for improving the hardenability of tool steel, and if its composition is maintained in the range of 4.2 to 5.6%, there is no difference in hardness and wear resistance.

When the content of V is insufficient, cementite (Fe ₃ C) carbide may be formed, and when the content is excessive, process MC carbide may be formed, so the content of V needs to be adjusted in the range of 4.0 to 6.0%. Do.

When C is contained in the range of 1.3 to 1.7% as an essential element for forming carbide and improving hardenability, no difference in structure occurs in the carbide structure.

Mo is a typical carbide forming element of tool steels, and its composition should be maintained in the range of 6.0 to 12.0%, because if the Mo content is less than 6.0%, coarse herring-bone due to excessive tungsten or carbon This is because acicular process M ₂ C carbide is formed when the process form M ₆ C carbide is formed and exceeds 12.0%.

W is a representative carbide element of tool steel and should be contained in the range of 6.0-18.0%, because when W is less than 6.0%, coarse process M ₂ C carbide is formed, and when 18.0% is exceeded, process M ₆ C carbide is formed. Because it is formed.

After dissolving the alloy to have the composition as described above, the melt is obtained by gas spraying, and the casting method uses spray molding.

Spray forming sprays molten metal in a tundish with a gas jet and impinges on a substrate, thereby maintaining a liquid state of about 50 to 70%, and having a uniform material such as a billet. It is a method of manufacturing.

Here, it is important to prepare a base material having a spherical MC + M ₆ C carbide structure by maintaining the temperature of the melt just before gas injection in the range of the liquidus temperature + (70 ~ 170 ℃) in order to obtain a base material having MC carbide . If the melt temperature is lower than liquidus temperature + 70 ℃, the nozzle is clogged during operation and manufacturing of the base metal is impossible.If the liquidus temperature exceeds + 170 ℃, coarse eutectic carbides are formed due to temperature rise due to excessive caloric inflow. Can be formed.

Here, the liquidus temperature according to the alloy composition can be obtained by the following equation (1).

[Equation 1]

Liquidus temperature (° C) = 1536- {0.1 + 83.9 [% C] +10 [% C] ² +1.5 [% Cr] +3.3 [% Mo] +2 [% V]}

(Wherein all elements are weight percent by weight)

Spraying is performed after adjusting the melt temperature as described above, in which case the spraying conditions may be ordinary spraying conditions. For example, the preferred spray molding condition is that the melt flow diameter of the tundish is about 3-9 mm, and the flying distance of the droplets is about 400-700 mm, and the primary and secondary gas pressures of the gas nozzle are 1.5-4 bar and 5-10 bar, respectively. And the scanning frequency of each nozzle is in the range of about 12-18 cycles / sec.

The base material manufactured by spray molding as described above is hot working, the hot working may be any of hot forging, hot rolling and hot extrusion. However, since the microstructure of the base material exhibits a nonuniform carbide structure composed of MC and M ₆ C carbides distributed along grain boundaries and MC carbide finely precipitated in grains, the hot working temperature should be appropriately set during hot working.

According to the present invention, the hot working temperature is preferably 1000-1150 ° C. The reason is that if the hot working temperature is less than 1000 ℃, the hot working temperature is low, so severe cracks occur along the grain boundaries during hot processing, so that the hot working is not possible smoothly.If the hot working temperature is over 1150 ℃, M ₆ C carbide and grain size This is because the increase in adversely affects the physical properties.

When hot forging is used as the hot working method of the heated base material as described above, the forging ratio needs to be 6 or more. This is because the forging ratio should be 6 or more in order to uniformly distribute the microstructure of the base material having the non-uniform carbide structure.

In this case, in the case of hot rolling, the reduction ratio is 80% or more, and in the case of extrusion, the extrusion ratio is 10: 1 or more, and the effect is similar.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

The alloy system prepared as shown in Table 1 below was dissolved in an air induction furnace, and then prepared into a billet using a spray molding apparatus.

Each alloy thus prepared was hot forged at a forging ratio of 8 at 1100 ° C., and finally hardened to measure mechanical properties, and the results are shown in Table 1 below.

In the curing treatment, all alloys were austenized at 1176 ° C. for 10 minutes, and then cooled in oil, followed by 3 times of treatment at 560 ° C. for 3 hours.

Mechanical properties of the hardened alloy as described above were evaluated by the hardness and wear resistance. First, the hardness was measured by a rockwall hardness tester by processing a hardness specimen of 20 × 20 × 20 (mm) standard, wear resistance evaluation was processed a wear specimen of 30 × 30 × 5 (mm) standard, and the SKD61 alloy steel relative material The load was carried out at a load of 100 kgf.

In the following Table 1, the comparative materials (1, 2) are manufactured by a method of ordinary casting and are known as M2 and M42. All of them were subjected to the same hot working and curing treatment as in the present invention, and mechanical properties were compared in the same manner.

Alloy composition (% by weight) Melting temperature (℃) Hardness (HRc) Abrasion Resistance (Load Reduction) (mg / km) Cr V C Mo W Fe Inventive Example 1 4.2 5 1.43 6.1 17.8 bal. 1430 69.0 46 Inventive Example 2 4.2 5 1.51 8.8 12.3 bal. 67.1 51 Inventive Example 3 4.2 5 1.53 11.9 6.5 bal. 68.3 62 Comparative Example 1 (M2) 4.2 2 0.8 5.0 6.2 bal. Alloy manufactured by ordinary casting method 62.1 103 Comparative Example 2 (M42) 3.9 1.2 1.1 9.5 1.5 bal. 63.3 121

As shown in Table 1, in the case of the present invention (1-3) compared with the comparative examples (1,2) cast in a conventional manner, the hardness was increased to about 110 to 120%, wear resistance is about 2- Increased more than threefold.

For reference, Figure 1 shows a microstructure after hot processing the billet prepared according to the present invention showed a uniform MC carbide structure.

In view of the above results, the present invention exhibited significantly improved physical properties while exhibiting an equivalent level in manufacturing unit cost compared to M2 alloys and M42 alloys currently widely used.

As described above, according to the present invention, it is possible to inexpensively manufacture high toughness and high wear resistance high-speed coated steel having a uniform distribution of fine carbides, thereby replacing M2 alloy and M42 alloy which are widely used at the same time, and at the same time, high quality high speed This has a useful effect in expanding the application of tool steel materials.

Claims (4)

In the method of manufacturing a high-speed coated oral by spray forming, Cr _a V _b C _c Mo _x W _y Fe _z as a basic composition, the content is 4.2% ≤a≤5.6%, 4.0% ≤b≤6.0%, 1.3% ≤c≤1.7%, After dissolving the alloy so as to have a composition of 6.0% ≤x≤12.0%, 6.0% ≤y≤18.0%, 59% ≤z≤78.5%, the temperature of the melt is in the range of liquidus temperature of the melt + (70-170) ° C. A method of producing a high-speed coated oral having excellent abrasion resistance without cobalt, characterized in that it comprises a bulk material obtained by gas spraying and hot working at 1000 to 1150 ° C. The method of manufacturing a high-speed coated oral with excellent abrasion resistance without cobalt according to claim 1, wherein the hot working is hot forging in which the forging ratio is 6 or more. The method for producing a high speed coated oral coating having excellent abrasion resistance without cobalt according to claim 1, wherein the hot working is performed by hot rolling with a reduction ratio of 80% or more. The method of manufacturing a high-speed coated oral having excellent abrasion resistance without cobalt according to claim 1, wherein the hot working is hot extrusion with an extrusion ratio of 10: 1 or more.

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