KR101763483B1

KR101763483B1 - Method of manufacturing high speed tool steel having superior strength casting

Info

Publication number: KR101763483B1
Application number: KR1020150161148A
Authority: KR
Inventors: 백응률; 이은혜; 고현곤
Original assignee: 영남대학교 산학협력단
Priority date: 2015-11-17
Filing date: 2015-11-17
Publication date: 2017-08-02
Also published as: KR20170057906A

Abstract

The present invention relates to a method of manufacturing a high-strength casting high-speed tool steel, which provides a new method for improving physical properties such as strength and hardness of a high-speed tool steel. It is possible to manufacture high-strength casting and high-speed tool steels improved in physical properties by reducing the size of MC carbide by adding a small amount of titanium to a high-speed tool steel using alloy steel containing carbon, chromium, molybdenum, tungsten and vanadium, High-strength casting high-speed tool steel is a very useful technology that can be expected to be applied to rolling rolls, blade materials, and cutting tools for wire rod and special steel bar.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a high-

The present invention relates to a method of manufacturing high-strength casting high-speed tool steel, and more particularly, to a method of manufacturing high-strength casting high-speed tool steel in which physical properties such as hardness and bending strength are improved by adding a small amount of titanium (Ti).

High-speed tool steels are high-carbon and high alloy steels containing alloying elements such as chromium (Cr), vanadium (V), tungsten (W), and molybdenum (Mo) It has excellent abrasion resistance, thermal fatigue and high temperature properties by element addition.

These steels have been widely used since the second half of 1990 in the rolling of steel or hot rolled steel sheet, and have achieved wear resistance three to five times higher than conventional ADM rolls and DCI rolls, . However, hot rolled work rolls are subjected to heat shock due to rapid contact with the rolled material during heating and cooling by cooling water during use, and the surface of the rolled roll becomes rough due to thermal fatigue caused thereby. In severe cases, In addition, the introduction of high-speed tool steel rolls has been tried and investigated several times in the rolling of wire rods and special steel rods, but the wear characteristics of high speed tool steel rolls occurring during rolling have been problematic, It is not applied to highly demanded rolling.

High-speed tool steels are widely used for cutting tools, cold forging tools, warm machining tools, blades, woodworking tools, and the like. The use of mold materials is increasing. Due to the advancement of industrial technology, there have been various researches for extending the life of materials in industrial fields, as they prefer materials that can withstand the extreme environments of precision processing, heat resistance, abrasion resistance and fatigue resistance rather than simple molds. Research is underway to improve the physical properties of high speed tool steel through the control of alloying elements, but there is a high need for technology development to solve this problem.

Japanese Laid-Open Patent Publication No. 2014-208870

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The present inventors have conducted intensive research and various experiments and have found that the addition of a small amount of titanium to a high-speed tool steel using alloy steels containing carbon, chromium, molybdenum, tungsten, and vanadium makes it possible to improve hardness and bending strength The present invention also provides a method of manufacturing a high-strength casting high-speed tool steel having improved physical properties.

The present invention relates to a method of manufacturing a high-speed tool steel using alloy steels containing carbon, chromium, molybdenum, tungsten, and vanadium, wherein the alloy steel contains 0.06 to 0.1% by weight of titanium (Ti) ; Austenitizing the melt at 950 to 1150 占 폚; Cooling the austenitized melt; And tempering the cooled molten metal at 450 to 650 DEG C for 2 to 4 times.

According to the present invention, by adding a small amount of titanium (Ti) to a high-speed tool steel using an alloy steel containing carbon, chromium, molybdenum, tungsten and vanadium, physical properties such as hardness and bending strength are improved, High-strength casting high-speed tool steel applicable to blade materials, cutting tools, and the like can be manufactured.

1 is a view showing a base structure of a high-speed tool steel roll shown in Table 1. Fig.
Figure 2 shows the microstructure of a high speed tool steel roll having the alloy composition of Table 2;
Fig. 3 is a graph showing the fraction of the process carbide and the cell size of the high-speed tool steel roll having the alloy composition of Table 3. Fig.
FIG. 4 is a diagram showing the Fe-5Cr-5W-5Mo-5V-C phase diagram.
5 is an optical microscope view of a high-speed tool steel roll.
6 is a diagram schematically showing a heat treatment condition.
7 is a graph showing a cooling curve graph of the test piece.
8 is a scanning electron microscope (SEM) photograph of the test piece.
9 is a diagram showing the result of qualitative analysis with EDX at a high magnification.
10 is a graph showing volume fraction and size of each test section of each test section.
11 is a graph showing volume fraction and size of each test section of each test section.
12 is a graph showing volume fraction and size of each test section of each test section.
13 is a view showing a liquid phase surface diagram of a Fe-5Cr-5W-5Mo-VC alloy system.
FIG. 14 is a graph showing the influence of the addition of titanium on the volume fraction of MC, M ₂ C, and M ₆ C carbides.
Fig. 15 is a graph showing the influence of titanium on the volume fraction of total carbide.
16 is a view showing an SEM image of the base structure in the cast state.
17 is a view showing an SEM image of the base structure of the high-speed tool steel roll after the heat treatment.
18 is a view showing an SEM image of the base structure after the heat treatment.
19 is a graph showing the influence of titanium on the volume fraction of M ₂₃ C ₆ carbide.
FIG. 20 is a view showing the known hardness value according to the content of titanium after casting and heat treatment. FIG.
21 is a graph showing the total hardness value according to the content of titanium after casting and heat treatment.
22 is a diagram schematically showing a 3 point bend test for measuring the bending strength.
FIG. 23 is a graph showing the influence of bending strength upon titanium addition and the relationship between the dimple size and the bending strength with respect to the primary γ size. FIG.
24 is a graph showing the influence on the fracture surface after the heat treatment in the addition of titanium.

Hereinafter, the present invention will be described in more detail.

The present invention will be described with reference to the drawings according to the embodiments of the present invention, however, it is to be understood that the scope of the present invention is not limited thereto.

The inventors of the present invention have confirmed that physical properties, particularly hardness and bending strength, are improved as compared with conventional high-speed tool steels by further containing titanium (Ti) in alloy steel while researching and developing a manufacturing method of high-strength casting high- It came to the following.

The high strength casting high-speed tool steel may have a volume fraction (V) of total carbide of 0 < V < / = 16%.

The high strength casting high speed tool steel may have a Rockwell hardness (Rockwell) of 55 to 70. [

The high strength cast high speed tool steel may have a bending strength of 150 to 200 kgf / mm < ² >.

Wherein the high strength casting high speed tool steel comprises at least one carbide selected from the group consisting of MC carbide, M ₂ C carbide, M ₆ C carbide and M ₂₃ C ₆ carbide, wherein M is selected from chromium, molybdenum, tungsten, vanadium and titanium Metal.

The MC carbide may have an average diameter of 6.0 to 12 [mu] m.

The present invention also provides a method for producing a ferritic stainless steel which comprises 0.5 to 2.5% by weight of carbon (C), 3.0 to 5.5% by weight of chromium (Cr), 4.0 to 5.0% by weight of molybdenum (Mo), 4.5 to 5.5% (Si): 0.5 to 1.0 wt%, Mn: 0.5 to 1.0 wt%, Ni (Ni): 0.3 to 0.6 wt%, and titanium (Ti): 0.06 By weight to 0.1% by weight, and the remainder consisting of iron (Fe) and unavoidable impurities.

Each alloy element will be described below.

Carbon (C)

The carbon content in the high-speed tool steel ranges from 0.5 to 2.5% by weight, and is an element capable of improving abrasion resistance by precipitating carbides by bonding with V, W, Mo, and Cr which are mainly carbide forming elements.

The amount of carbon necessary for forming the carbide can be calculated through a stoichiometric carbon equivalent, and can be represented by the following formula (1).

[Chemical Formula 1]

After the carbide is formed, the remaining carbon is dissolved in the matrix. When the carbon content is less than 0.4%, lath-type martensite can be formed. When the carbon content is more than 0.4%, plate-type martensite can be formed And the shape of the martensite affects the overall hardness value of the high-speed tool steel roll, so that the carbon content in the matrix is very important.

The content of carbon in the matrix can be calculated through the following formula (3), and the base can be strengthened by precipitating fine carbides in the matrix.

(2)

(3)

Matrix hardness would be controlled by

Referring to Table 1, the following Table 1 shows the carbide fraction, the carbon content in the matrix, the known hardness value, and the total hardness value. When the total hardness values according to the carbide fractions are compared, It can be seen that the carbide fraction is the highest at 17.8%, but the total hardness value is the lowest. Therefore, it can not be confirmed that the higher the carbide content, the higher the total hardness value. On the other hand,

The higher the value, the higher the total hardness value. The higher the hardness value, the higher the value.

Carbide volume fraction (pct) role MC M ₇ C ₃ gun CE ** SCE ** CE-SCE Base hardness (HV) Overall hardness (HV) A 8.2 3.8 12.0 1.92 1.712 0.208 647 675 B 12.4 5.4 17.8 1.98 1.854 0.126 637 656 C 8.5 7.5 15.9 1.89 1.893 0 632 658 D 9.7 6.3 16.0 2.28 1.861 0.419 715 751 E 4.3 9.2 13.5 2.01 1.423 0.587 726 756

Referring to FIG. 1, there is shown a photograph of a base structure of a high-speed tool steel roll shown in Table 1, and may have a tempered martensite mixed with a lass type and a plate type in a base structure of all rolls. The formation rate of martensite can vary depending on the high-speed tool steel roll, and the plate-like tempered martensite can be observed more frequently on the high-speed tool steel rolls D and E.

Therefore, in the case of the high-speed tool steel roll, it can be seen that the value of the known hardness affects the value of the overall hardness rather than the fraction of the carbide,

Since the forming ratio of the lath type and the plate type tempered martensite is different depending on the value,

By controlling the value, the shape of the base structure can be controlled to increase the hardness value of the high speed tool steel roll.

Vanadium (V)

The vanadium content in the high-speed tool steel roll may range from 4.0 to 5.0 wt%. The vanadium is an element that forms a VC carbide by bonding with carbon. It can improve abrasion resistance by forming a large amount of VC carbide in the outer layer portion of a high-speed tool steel roll. Further, the specific gravity of VC carbide is much smaller than the specific gravity of molten metal Therefore, segregation may occur inside. Vanadium is a ferrite stabilizing element and has little influence on the temperatures of the solidus and liquidus lines.

Chromium (Cr)

The content of chromium in the high-speed tool steel roll may range from 3.0 to 5.5 wt%. The chromium may be dissolved in the matrix to increase the hardness of the matrix by depositing fine carbides, and some chromium may combine with carbon to form Cr ₇ C ₃ carbide. Since Cr ₇ C ₃ is softer than VC carbide, its abrasion resistance is reduced, and it is adversely affected by fracture toughness because it is formed at the triple point where the boundaries or cells of the solidification cell are in contact with each other.

Molybdenum (Mo)

The molybdenum content in the high-speed tool steel roll may range from 4.0 to 5.0 wt%. The molybdenum is an element which forms carbides of Mo ₂ C and M ₆ C in combination with carbon and has a smaller atomic weight (about 1/2 times) than that of tungsten, so that when molybdenum is the same wt% as tungsten, And therefore 1% Mo can be replaced with 1.6% to 2.0% tungsten.

The molybdenum is a ferrite stabilizing element, and the addition of molybdenum serves to lower the temperature of the liquid phase,

Wow

Lt; RTI ID = 0.0 > temperature. &Lt; / RTI >

Tungsten (W)

The content of tungsten in the high-speed tool steel roll may range from 4.5 to 5.5 wt%. The tungsten is an element that bonds with carbon, such as molybdenum, and does not affect the temperature of the liquidus. In particular, tungsten is a major element of M ₆ C, which acts to raise the temperature at which process reactions occur

Wow

It is possible to reduce the temperature difference at which the reaction takes place, thereby reducing the time margin for precipitating the MC carbide.

Titanium (Ti)

The content of titanium in the high-speed tool steel roll may range from 0.06 to 0.1 wt%. The titanium is a strong carbide forming element by having a high carbon affinity. That is, the titanium added in the molten metal reacts with the carbon in the liquid to preferentially produce TiC, so the wt% of the carbon in the liquid phase is reduced and the carbon wt% of the state is shifted to the left

Can be induced to undergo transformation, and therefore,

And the amount of total carbide can be reduced as the carbide due to the process reaction is formed in the liquid phase, which is further reduced by the expansion of the austenite structure. Also, since TiC has a lattice constant similar to that of VC, TiC serves as a crystal nucleus, which can prevent the VC from becoming larger in size.

Referring to FIG. 2, there is shown a microstructure photograph of a high-speed tool steel roll having an alloy composition of Table 2, wherein a dark portion is a martensite structure and a bright phase is a process carbide. The microstructure of Ti ₃ added with titanium can be finely crystallized as compared with the microstructure of M ₇ without Ti. This is because TiC, which is primarily crystallized, serves as an inoculant, and the process carbide can be finely crystallized.

C Si Mn Cr Mo Ti V W Fe M7 1.01 0.40 0.33 3.90 8.30 ... 2.00 1.60 Honey. Ti3 1.00 0.33 0.29 4.10 8.20 0.71 1.00 1.50 Honey.

Referring to FIG. 3, graphs showing the fraction of the process carbide and the cell size of the high-speed roll having the alloy composition shown in Table 3 are shown. As titanium is added, both the fraction of the process carbide and the cell size can be reduced.

C Si Mn Cr Mo Ti V W Fe M7 1.01 0.40 0.33 3.90 8.30 ... 2.00 1.60 Honey. Ti1 1.02 0.32 0.31 4.00 8.00 0.13 1.70 1.50 Honey. Ti2 1.06 0.41 0.33 4.00 8.00 0.33 1.60 1.40 Honey. Ti3 1.00 0.33 0.29 4.10 8.20 0.71 1.00 1.50 Honey. Ti4 1.09 0.37 0.41 4.20 8.10 1.40 0.60 1.60 Honey. Ti5 1.03 0.34 0.29 4.00 8.20 0.08 1.90 1.20 Honey. Ti6 1.00 0.43 0.32 4.00 8.40 0.20 1.90 0.80 Honey. Ti7 1.01 0.40 0.24 4.00 8.60 0.23 2.10 0.50 Honey. Ti8 1.04 0.35 0.30 4.00 8.30 0.31 1.90 ... Honey.

Referring to FIG. 4, when titanium is added, TiC is preferentially produced due to high carbon affinity of titanium, so that carbon wt% in the liquid phase is decreased to move C wt% of the state to the left.

The austenite phase is increased and the process reaction occurs in a reduced liquid phase, so that the process carbide can be reduced.

In the case of the high-speed tool steel roll, during the heat treatment, a part of the process carbide, M ₆ C, may be decomposed in the austenizing step and solidified in the matrix. The constituent elements dissolved in the matrix may cure the martensite in the heat treatment step and may precipitate into fine secondary carbides in the matrix, and as the secondary carbide precipitation increases, the matrix may be further cured and the strength may also increase .

The overall percentage of eutectic carbide when the titanium addition is reduced can be increased than when the amount of M ₆ C carbide is decomposed during heat treatment has not been added to the titanium, therefore, in the case of high-speed tool steel rolls by the addition of titanium M ₆ of the heat treatment The amount of decomposition of the C-step carbide can be increased, and the amount of the secondary carbides formed in the base increases, so that the tendency of the hardening of the base structure can be increased. Due to such a change, it may happen that the appropriate tempering temperature having the maximum hardness is adjusted downward when titanium is not added when the titanium is added.

Referring to FIG. 5, as the annealing temperature is increased, the hardness is increased by increasing the secondary carbide. When the temperature is higher than the predetermined temperature, the adjacent carbides of the precipitated secondary carbides are superimposed on each other, In this state, the hardness decreases as the temperature increases.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

(Example 1)

1. Specimen Preparation

Fe-60% Mo, Fe-60% Cr, and Fe-76% W were measured using a high frequency induction furnace with a capacity of 2 kg. After the Fe-80% V, Fe- 72% Ti master alloy and gatan the contents dissolved in to match the target composition was produced in the test piece by injection molding in a scanning CO ₂ at 1550 ℃.

At this time, the carbon concentration required for forming the carbide was calculated using the following formula (1). In order to obtain a high-hardness martensite structure, the carbon content in the matrix was controlled using the following formulas (2) and (3).

[Chemical Formula 1]

(2)

(3)

Matrix hardness would be controlled by

In the case of carbide forming elements, the contents of Mo and W were increased to make more MC carbides having a higher hardness value, and a specimen with solidification along the cross-section of Fe-5Cr-5W-5Mo-VC system was prepared Respectively. Further, in order to obtain a high fracture toughness value, the content of V is fixed to 5% or more to crystallize the MC carbide in the cell,

By lengthening the section,

The reaction was attempted to reduce the amount of M ₂ C, M ₇ C ₃ carbide.

For accurate analysis of the specimens, the prepared specimens were cut and quantitated by SPECTRO-METER. The chemical compositions of the test specimens prepared in this study are shown in Table 4 below.

Alloy type Chemical composition (wt%) Sample C Si Mn Ni Cr Mo W V Ti CE-C _SEC T-0 1.95 0.8 0.6 0.4 5.0 4.5 5.0 4.5 0 0.5 T-3 1.95 0.8 0.6 0.4 5.0 4.5 5.0 4.5 0.03 0.5 T-6 1.95 0.8 0.6 0.4 5.0 4.5 5.0 4.5 0.06 0.5 T-10 1.95 0.8 0.6 0.4 5.0 4.5 5.0 4.5 0.1 0.5 T-20 1.95 0.8 0.6 0.4 5.0 4.5 5.0 4.5 0.2 0.5

2. Heat treatment conditions

Referring to FIG. 6, the apparatus for heat treatment was austenitized at 1050 ° C. using an electric box furnace, and then cooled to room temperature. Three stages of tempering at 550 ° C. were performed to remove residual austenite and residual stress. At this time, the heat treatment holding time of the test piece was maintained at 1 hour (1.0 h / in) per inch of the test piece thickness.

(Experimental Example 1)

1. Microstructure Observation

The prepared test specimens were cut and sanded to # 100 ~ # 2000 with a sand paper, and then subjected to quenching using a diamond suspension of 1 탆. Then, to analyze the carbides in the test specimen in detail, Murakami _{(Murakami, 10 g K 3 Fe} (CN) 6 + 10 g NaOH + 100 ㎖ distilled water) to the etching with the etching solution was observed with an optical microscope (OM), base organizations Murakami _{(Murakami, 10 g K 3 Fe} (CN ) ₆ + 10 g NaOH + 100 ml distilled water) and etching with Picric hydrochloric (5 ml HCl + 4 g C ₆ H ₃ O ₇ N ₃ + 100 ml CH ₃ OH) and observed with a scanning electron microscope Respectively. In addition, the amount of alloying elements in the matrix and carbide was quantitatively analyzed by energy spectroscopy (EDS) method. In addition, the fracture surface according to the banding test was observed with a scanning electron microscope (SEM).

Referring to FIG. 7, a cooling curve graph of the test piece is shown. T-0 and T-3 test specimens are classified into Primary (austenite), Next

,

The reaction takes place in the order of T-6, T-10. T-20 specimens are the first

After the reaction, Primary (austenite),

,

The reaction was observed in the order of. Also, at this time, when the content of Ti was 0.6% or more, it was confirmed that the section where the TiC was crystallized was clearly revealed in the cooling curve.

Referring to FIG. 8, a scanning electron microscope photograph of the test piece is shown. In FIG. 8 (a), the black carbide is the VC carbide precipitated when the process solidification proceeds, and the gray lamellar carbide is M ₂ C carbide mainly composed of Mo and W, and the M ₆ carbide is M ₆ C carbide.

8 (b) in which titanium was added in 0.03%, MC carbide was spherical and finely crystallized as compared with FIG. 8 (a), but the effect thereof was insufficient. 8 (a) and 8 (b), it can be seen that the VC carbide is crystallized in a continuous form, whereas in FIGS. 8 (c) and 8 8 (d) and 8 (e), it can be seen that the VC carbide is spherically dispersed and black small points can be observed inside the VC carbide.

Referring to FIG. 9, the result of qualitative analysis by EDX at a high magnification is shown. As a result of analyzing the black part in the MC carbide, titanium was identified and identified as TiC, and gray part was identified as VC. The lattice constants of Ti carbide and VC carbide were 4.327 Å and 4.165 Å, respectively, which is similar to that of Ti carbide and VC carbide. .

Referring to Table 5, the number and size of TiC carbide are shown in Table 5 below. When TiC carbide is 0.03%, the amount of TiC carbide is extremely small and does not greatly affect the size and shape of MC carbide. However, The size of MC carbide was remarkably reduced and the morphology was confirmed to be spherical. As a result, it was confirmed that the effect of titanium influences the size and shape of MC carbide when the content of titanium is 0.06% or more.

Number of TiC Carbide MC Carbide size (㎛) T-0 0 20.4 T-3 5 18 T-6 38 11.4 T-10 81 8.3 T-20 85 8.1

2. Calculation of carbide volume fraction and size

The volume fraction of various carbides produced from microstructure and the size of MC carbide were measured by optical microscope (OM) and quantitatively measured by using an image analyzer.

10, 11, and 12, FIGS. 10, 11, and 12 are graphs showing the volume fraction and size of each test section of each test section.

Primary

(austenite) volume and size. As the content of titanium increases,

the amount of austenite was increased, and the size was reduced. This is because the TiC is preferentially crystallized as described above and the weight% of carbon in the liquid phase is reduced. Therefore, in the state diagram of FIG. 13,

Point in

(To the left). therefore,

The reaction period of Ti is longer than Ti

the proportion of austenite is increased, and by the pinning effect of TiC,

it was confirmed that the size of the austenite was reduced.

11

As the reaction interval

As the content of titanium increases,

The amount was reduced, and the size was also reduced. first,

The solidification process up to the start of the reaction is shown in the state diagram of FIG. 13

,

Primary

austenite is formed and reaches point a 'and point b', where the concentration of the residual liquid phase is high carbon, high vanadium,

During the solidification of the process, the formation of VC carbide actively proceeded due to the initial high vanadium concentration. As the titanium is added in the state diagram of FIG. 13

Although the reaction period is long,

And the volume fraction of the microcapsules was reduced. This is Primary

As the fraction of austenite increases,

Since the process solidification proceeds,

And the TiC carbide serves as the nucleus of the VC carbide as described above

It is confirmed that the size of the paper is reduced.

12 is a cross-

As the reaction interval

As the content of titanium increases,

The amount was reduced, and the size was also reduced. This is because, as described above, the process solidification proceeds in the reduced liquid phase

Of the total population.

Referring to FIGS. 14 and 15, it can be seen that the carbides of M ₂ C and M ₆ C are significantly reduced as compared with the MC carbide, as a graph showing the volume fraction of each carbide and the volume fraction of the total carbide. This means that the MC, M ₂ C, and M ₆ C carbides are reduced because the process solidification proceeds in the reduced liquid phase,

While the response period of the

It was confirmed that the fraction of M ₂ C and M ₆ C carbide was significantly reduced as compared with the MC carbide fraction because there was no change in the reaction period.

3. Mechanical experiments

(1) Hardness test

Hardness experiments were performed using a Rockwell hardness tester.

The surface of the specimen was polished to # 1000 with sandpaper to measure the hardness change of the high-speed tool steel roll by titanium, and after 10 measurements with a Rockwell "C" scale (load 150 kg) And the average value of the remaining 8 times was shown. Further, in order to measure the microhardness of the base structure, sand polishing was carried out with a sandpaper to a # 100 to # 2000 atmosphere, followed by quenching using a 1 탆 diamond suspension, followed by 20 times of Vickers hardness (load: 1000 g) After the measurement, the average value of the remaining 18 values except for the highest value and the lowest value was shown.

Referring to FIG. 16, there is shown a photograph of a base structure in a cast state observed with a scanning electron microscope. All of the test pieces showed a martensitic structure mixed with a lass type and a plate type. As titanium was added, a plate type martensite And it was confirmed that it was observed a lot. As the amount of titanium was decreased, the total amount of carbide was decreased, so that the amount of carbon employed in the matrix was increased and more plate - like martensite was observed.

Referring to FIG. 17, tempered martensite structure was observed in all the test specimens after the heat treatment, and fine white spherical carbides were observed more in comparison with the casted structure. It can be seen that the elements of the component dissolved in the matrix were precipitated as fine secondary carbides in the matrix during the heat treatment. As a result of EDX analysis, it was confirmed that the content of chromium was high and it was finely crystallized in the matrix, This can be confirmed from FIG.

Further, referring to FIG. 19, as the content of titanium increases, the fraction of MC, M ₂ C, and M ₆ C carbides, which are process carbides, decreases, and the amount of carbon employed in the matrix increases. Thus, M ₂₃ C ₆ carbide Of the total amount.

20 is a graph showing the known hardness values according to the content of titanium after the casting and the heat treatment, wherein the values of the known hardness values after the heat treatment were higher than those in the casting state, It is known that the hardness of the base increases as the site is cured and fine secondary carbides are precipitated in the matrix. As the amount of titanium increases, the fraction of M ₂₃ C ₆ carbide, which is a secondary carbide, The hardness value was also increased.

Referring to FIG. 21, as shown in FIG. 15, when the titanium content is increased, the hardness value is measured to be high even though the fraction of the carbide is decreased as the titanium content is increased. . Since the fraction of carbide in the high-speed tool steel roll is about 15%, it is known that the hardness value greatly affects the overall hardness value. Accordingly, it has been confirmed that the overall hardness value increases with the increase of the known hardness value.

(2) Bending strength

Referring to FIG. 22, the bending strength was measured by a 3 point bend test. The size of specimen was 4 × 3 × 40 ㎜, and the loading condition was 0.5 ㎜ / min. The bending strength is determined by the following formula (4).

[Chemical Formula 4]

Where P _f is the maximum load at failure and σ _f is the bending strength calculated by the breaking stress. By measuring the bending strength, the toughness of a weak material can be measured.

Since the toughness can be measured by measuring the flexural strength of a material such as the high-speed tool steel roll, a 3 point banding test was performed to measure the toughness. 23, it was confirmed that the bending strength value was higher as the titanium was added. Referring to Figure 24, 3 point banding test of wave observation of a cross section, as the flexural strength of the test piece fracture surface shape was added to titanium was seen with small cleaved, as a result of analyzing the black part crack took place the first M ₂ C, And M ₆ C carbide. It was confirmed that the particles of the process carbide first served as the nucleation sites of the cracks before the base cracks occurred. Therefore, referring to FIG. 24, as the titanium is added, the fraction of M ₂ C and M ₆ C carbide is reduced as well as being finely crystallized. Therefore, it is confirmed that the initial point of crack is late and the bending strength value is high I could. Also, the dimension of the fracture was 63 ㎛,

The size of austenite was 57.6 ㎛. As a result, the cracks start from M ₂ C and M ₆ C carbides, and the base structure Primary

(austenite) and was destroyed. Also, as the titanium is added,

it was confirmed that the size of the austenite became small, and the propagation of the crack became difficult, thereby increasing the bending strength value.

The alloy composition of C, Cr, Mo, W, and V was fixed so that the content of titanium was 0 wt%, 0.03 wt%, 0.06 wt%, 0.1 wt%, and 0.2 wt% And microstructure observation and mechanical tests were carried out.

As the titanium is added, the reaction period of the primary γ and L → γ + MC becomes longer. This is because TiC is preferentially produced in the liquid phase due to high carbon affinity of titanium, and the wt% carbon of the liquid phase state is shifted to the left. Therefore, it was found that MC, M ₂ C and M ₆ C carbide were decreased by increasing the fraction of the initial γ. In addition, the L → γ + MC reaction interval is longer, whereas the L → γ + M ₂ C + M ₆ C reaction period remains almost unchanged, so that the carbide fraction of M ₂ C and M ₆ C is significantly reduced compared to the MC carbide fraction .

When the titanium content was 0 wt% or 0.03 wt%, the size of the MC carbide was 20.4 μm or 18 μm, but the size of MC carbide was reduced to 11.4 μm at 0.06 wt%. In addition, at 0.1 wt% and 0.2 wt%, the MC carbide size was 8.3 ㎛ and 8.1 ㎛, respectively, but the Ti content was 0.06 wt%. However, at more than 0.1 wt% .

The values of the known hardness and the total hardness after the heat treatment were increased compared to the known hardness and the total hardness of the casting state. It was confirmed that the hardness value after tempering was increased due to the precipitation of secondary carbides such as M ₂₃ C ₆ during tempering. Also, as the addition of titanium increased, the values of hardness and total hardness increased. It was confirmed that the content of carbon in the matrix increased and the hardness value of the specimen to which titanium was added increased due to the plate - like martensite.

Since the initial cracks occur mainly in M ₂ C and M ₆ C carbides, as the content of titanium increases, the carbides of M ₂ C and M ₆ C decrease,

the size of the austenite was reduced, and the propagation of the cracks was increased, so that the bending strength value was increased.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims

A method for manufacturing a high-speed tool steel using alloy steels containing carbon, chromium, molybdenum, tungsten, vanadium, silicon, manganese, and nickel and the remainder comprising iron and unavoidable impurities,
From 0.5 to 2.5% by weight of carbon, from 3.0 to 5.5% by weight of chromium, from 4.0 to 5.0% by weight of molybdenum, from 4.5 to 5.5% by weight of tungsten, from 4.0 to 5.0% by weight of vanadium, (Ti) is contained in an amount of 0.06 to 0.1% by weight based on 100% by weight of the total alloy steel containing 1.0% by weight of manganese and 0.3 to 0.6% by weight of nickel and the balance of iron and unavoidable impurities. step;
Austenitizing the melt at 950 to 1150 占 폚;
Cooling the austenitized alloy steel; And
And tempering the cooled alloy steel at 450 to 650 DEG C two to four times.

The high strength casting high speed tool steel according to claim 1, wherein the high strength casting high speed tool steel comprises at least one carbide selected from the group consisting of MC carbide, M ₂ C carbide, M ₆ C carbide and M ₂₃ C ₆ carbide, wherein M is at least one selected from the group consisting of chromium, molybdenum, tungsten, Vanadium, and titanium. &Lt; Desc / Clms Page number 24 >

3. The method of claim 2, wherein the MC carbide is an average diameter of 6.0 to 12 [mu] m.