JP2003268499A - High-speed tool steel quenchable at low temperature - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-speed tool steel which is quenchable at a low temperature, can be given a hardness of HRC65 or higher by either low-temperature quenching at about 1,000°C or high-temperature quenching at about 1,200°C, can reduce the heat treatment cost, and can be given stable heat treatment qualities. <P>SOLUTION: This high-speed tool steel comprises 0.6-1.3 wt.% C, 0.05-2.00 wt.% Si, 0.10-1.00 wt.% Mn, 3.50-7.00 wt.% Cr, 2.00-9.50 wt.% Mo, 1.00-16.00 wt.% W, 5-20 wt.% 2Mo+W, 0.50-2.50 wt.% V, 1.25 wt.% or lower Co, 0.01 wt.% or lower O unavoidably present, 0.002 wt.% or lower N unavoidably present, and the balance being Fe and unavoidable impurities and satisfies the following three inequalities: (1) -0.2≤ΔC=C-(0.06Cr+0.063Mo+0.033W+0.2 V)≤0.2, (2) 2Mo/(2Mo+W)≤0.9 (2), and (3) 25≤2Mo+0.3W-17V+8Cr≤36. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool and a high-speed tool steel used for various tools such as forging, forging, upsetting, and shearing in hot / warm or cold, and particularly low temperature quenching is possible. Regarding high speed tool steel.

[0002]

2. Description of the Related Art Conventionally, cutting tools, forging tools, etc. used with high hardness (HRC 65 or more) are generally referred to as high speed tool steel due to their components. JIS-SKH51 can be mentioned as a typical high speed tool steel to which Co is not added.

The characteristics of this high-speed tool steel in terms of composition are that it contains about 1% C by weight, 4% Cr, about 10% Mo and W, and 1% or more V. This high-speed tool steel is generally used after being subjected to quenching and tempering treatment to impart high hardness and high wear resistance required for cutting tools, forging tools and the like.
In the heat treatment of this high speed tool steel, high hardness (HRC65) is secured by quenching from a high temperature of about 1200 ° C and tempering at 500 to 600 ° C.

[0004]

However, the local melting start temperature of the high-speed tool steel is higher than this quenching temperature by about several tens of degrees Celsius, which causes various problems during heat treatment. That is, it is difficult to control the temperature inside the heat treatment furnace at the time of quenching, and high technology and great labor are required for temperature control during the quenching work, and the performance of the heat treatment furnace (temperature distribution in the furnace,
Depending on the heat treatment temperature control technique), the heating temperature may be exceeded and a molten structure may be locally generated.

There is also a place where the quenching temperature does not reach a sufficient quenching temperature locally due to the temperature distribution, in which case the hardness does not become sufficiently high, or the hardness varies from product to product, resulting in variations in product quality after heat treatment. There was a problem that was likely to occur. Particularly in the case of a large product, there is a problem that it is difficult to perform heat treatment stably.

Further, holding the soaking at such a high temperature places a heavy load on the heat treatment furnace, resulting in a short life of the heat treatment furnace. Furthermore, when quenching at a high temperature of about 1200 ° C., it is necessary to take measures to protect the furnace body of the heat treatment, which makes the heat treatment furnace expensive, and the quenching at such a high temperature requires high heating cost (heating energy). Then, there has been a problem that the heat treatment cost for quenching the high speed tool steel becomes high.

For example, in the case of hot or cold die steel 103
Quenching is carried out at a low temperature of about 0 ° C. In this case, the heat treatment cost for quenching is about 400 to 500 yen per kg, whereas in the case of high speed tool steel, it is 1000 per kg.
The cost was about a circle, and the heat treatment cost for quenching was twice as high.

Further, in the case of the conventional high speed tool steel, since the quenching temperature is as high as about 1200 ° C., it is not possible to perform heat treatment at the same time using the same heat treatment furnace as hot and cold die steels. Was also a factor that increases the heat treatment cost.

[0009]

The high-speed tool steel capable of low-temperature quenching according to the present invention has been devised to solve such a problem. Thus, in claim 1, the weight% is
C: 0.6 to 1.3%, Si: 0.05 to 2.00%, Mn: 0.10 to 1.00
%, Cr: 3.50 to 7.00%, Mo: 2.00 to 9.50%, W: 1.00 to 1
6.00%, 2Mo + W: 5-20%, V: 0.50-2.50%, Co: ≤ 1.
25%, inevitably present O and N are O: ≤ 0.01
%, N: ≦ 0.02%, the composition consisting of balance Fe and other unavoidable impurities, and the following equations (1), (2), (3)
It is characterized in that the hardness of HRC65 or more can be ensured under any of the quenching and holding temperatures of 1030 ° C. and 1200 ° C. -0.2 ≦ ΔC = C− (0.06Cr + 0.063Mo + 0.033W + 0.2V) ≦ 0.2 ・ ・ ・ (1) Formula 2Mo / (2Mo + W) ≦ 0.9 ・ ・ ・ (2) Formula 25 ≦ 2Mo + 0.3W-17V + 8Cr ≦ 36 ・..Formula (3)

A second aspect of the present invention is the method of the first aspect, further comprising any one or more of Nb, Ti and REM in N% by weight.
b: ≤ 1.00%, Ti: ≤ 0.5%, REM: ≤ 0.03%.

[0011]

As described above, according to the present invention, by adjusting the alloy composition in the high speed tool steel, 103
When low temperature quenching at 0 ℃ is performed, 1200 ℃
HRC in any case where high temperature quenching at
A high hardness of 65 or more is obtained.

According to the present invention, any temperature from a low temperature of about 1030 ° C., which has been conventionally used for hot or cold die steel, to a high temperature of about 1200 ° C., which is used for high speed tool steel. It is also possible to quench at.

As a result, it is possible to prevent the hardness from changing due to a temperature change of several tens of degrees Celsius during quenching in the heat treatment furnace, and to effectively prevent the occurrence of a local molten structure. Product quality can be improved.

Further, since it becomes possible to secure a high hardness by quenching at a low temperature (1000 to 1050 ° C.), which is applied to hot die steel, cold die steel, etc., it is possible to heat the heat treatment furnace at the time of quenching. In this way, it becomes possible to equip it with cold die steel, etc., increasing the chance of heat treatment. In addition, the cost for heating the furnace body protection and heating can be reduced.
With these, the heat treatment cost can be reduced. On the other hand, the same quenching temperature as before (about 1200 ° C)
Also in this case, since the hardness equivalent to that of the conventional one can be secured, it is possible to use the conventionally used heat treatment furnace.

Further, since the high hardness can be ensured under a wide range of quenching temperatures, the hardness change due to the difference in quenching temperature is small and stable hardness can be obtained, or a stable heat-treated structure can be obtained. Become. As a result, various effects such as stable heat treatment of large products can be obtained. Further, since the quenching temperature can be lowered, the burden on the heat treatment furnace can be reduced and the life of the heat treatment furnace can be improved.

Next, the reasons for limiting each chemical component in the present invention will be described in detail below. C: 0.6 to 1.3% (preferably 0.75 to 1.25%) C is an element necessary to secure the strength and wear resistance of the tool steel, and is combined with carbide forming elements such as Cr, Mo, W, V and Nb. Form carbides. Also, during quenching, it forms a solid solution in the matrix,
It is an element that ensures high hardness by forming a martensite structure having high hardness.

Therefore, 0.6% was specified as the minimum addition amount necessary to ensure the minimum hardness. Preferably, 0.75% or more is included in order to form carbide along with hardness and to easily secure wear resistance. On the other hand, when the amount of C added increases, C
A large amount of carbide is crystallized by combining with carbide forming elements such as r, Mo, W, V, Nb, and remains as a coarse carbide. To prevent this, the amount of C added must be 1.3% or less. A fine carbide structure can be stably obtained by setting the content to preferably 1.25% or less.

Si: 0.05 to 2.00% (preferably 0.1 to 2.00)
%, And more preferably 0.3 to 1.0%) Si is mainly added as a deoxidizing agent, and it forms a solid solution in both the carbide and the matrix and contributes to the increase in hardness. Therefore, add at least 0.05%. In order to stably secure high hardness, the amount of Si added is preferably increased to 0.1% or more, more preferably 0.3% or more. On the other hand, the upper limit is set to 2.00 to prevent deterioration of workability and toughness due to hot addition by adding Si.
%, And more preferably 1.0%.

Mn: 0.10 to 1.00% Mn is used as a deoxidizing element and a hardenability improving element. The upper limit is 1.00% because hot workability is deteriorated by the addition of Mn. When S is unavoidably contained, Mn is added at a lower limit of 0.10% or more to prevent deterioration of hot workability.

Cr: 3.50 to 7.00% Cr forms a carbide. The carbides are MC carbides mainly composed of V, M6C carbides mainly composed of Mo and W, M2 mainly composed of Cr.
It can be classified as 3C6 or M7C3 carbide. Here, the amount of Cr-based carbide formed is defined by the balance with the amounts of Mo, W, V, and C added. That is, the Cr addition amount is specified. It has been reported that this Cr-based carbide promotes solid solution during quenching even at low temperatures compared to Mo, W-based, and V-based carbides, but here it is necessary to consider the balance with other carbide-forming elements. There is.

In the present invention, the relationship between the amount of added Cr and the amount of added carbide forming elements such as Mo, W and V must satisfy the condition of the above formula (3). In this equation (3), the value increases with the amount of Cr added. 10 by increasing this value
It is possible to secure sufficient hardness during quenching at 30 ° C. Its lower limit is 25. In order to satisfy this value, the lower limit of Cr addition is calculated to be 3.50% after incorporating the limits of Mo, W and V.

On the other hand, in order to secure sufficient hardness by quenching at 1200 ° C. and prevent unhealthy structure such as local melting,
It is necessary that the value shown in equation (3) does not exceed 36. If the value of the formula (3) exceeds 36, the possibility of locally producing a molten structure becomes extremely high. Therefore, when the upper limit of the Cr addition amount is calculated after incorporating the limits of Mo, W, and V, it is 7.00.
%.

Mo: 2.00 to 9.50% (preferably 2.00 to 8.00%) W: 1.00 to 16.00% (preferably 5.00 to 10.00%) 2Mo + W: 5 to 20% (preferably 10 to 15%) Mo and W are M6C It forms carbides in the mold, improves wear resistance, and forms a solid solution in the matrix to contribute to increasing hardness and maintaining hardness during tempering. In order to maintain the hardness of high speed tool steel, in addition to adding the minimum carbide forming element,
It is necessary to add 2.00% or more and 1.00% or more, respectively, of Mo and W that form a solid solution in the matrix during quenching and contribute to secondary hardening during tempering. The amount required as 2Mo + W is 5%, preferably 10% or more. On the other hand, if the amount of addition of Mo and W is too large, the proportion of M6C type carbide in the carbide structure becomes high, and stable M6C carbide is formed at low temperature, making it difficult to form a solid solution of C, Mo and W in the matrix. Becomes Therefore, Mo alone must be 9.50%, W alone must be 16.00% or less, and the maximum amount of 2Mo + W must be 20%, preferably 15% or less.

V: 0.50 to 2.50% (preferably 0.65 to 1.6%) V combines with C to form a hard MC type carbide. MC carbides have less solid solution in the matrix up to high temperatures than M6C carbides and Cr-based carbides. Since MC carbide is a hard carbide, it contributes greatly to wear resistance, and at the same time it secures the minimum wear resistance as a high-speed tool steel, and at the same time remains even when quenched at a high temperature of 1200 ° C. To maintain the effect of preventing coarsening, the required amount of V is 0.50% or more. However, if a large amount is added, coarse MC carbides remain in the matrix and a uniform structure cannot be obtained. Therefore, the upper limit of the V addition amount at which coarse MC carbides do not crystallize is set to 2.50.
% And the amount of V added is less than that.

Preferably, the addition of V raises the quenching temperature to 1
The amount of V added is 0.65% so that hard MC carbide can remain in an amount that ensures wear resistance even if the temperature is increased to 200 ° C.
That is all. As a preferable upper limit, addition of V does not cause coarse carbide to crystallize, and the MC carbide amount is prevented from becoming relatively large in balance with Mo and W contents.
Determine%.

Co: ≦ 1.25% Co forms a solid solution in the matrix and increases the heat treatment hardness.
It is generally defined as an element that deteriorates hardenability, and may be inevitably mixed from scraps or the like.
Therefore, the upper limit is set to 1.25%.

O: ≤0.01% O is inevitably mixed from the atmosphere or air during melting to form a solid solution. However, if the amount of solid solution is large, it reacts with a trace amount of impurity elements such as Ca and Al and additional elements such as Si and Ti to become an oxide, which exists as inclusions in the structure. Such oxide-based inclusions serve as a starting point of fracture, leading to a decrease in strength. Therefore, in order to prevent the inclusions from lowering the strength, the O addition amount should be 0.01
It must be less than or equal to%.

N: ≦ 0.02% Like O, N inevitably mixes in from the atmosphere or the atmosphere during melting to form a solid solution. However, N combines with V to crystallize VN nitride from molten steel, and the crystallized VN serves as nuclei for VC and forms VC carbide. The structure in which non-uniform and large VC carbides are dispersed causes deterioration of toughness. Therefore, the amount of N added must be 0.02% or less to suppress the crystallization of VN nitride.

Nb: ≦ 1.00% Nb is more likely to form MC type carbides than V. Therefore, it is possible to add Nb at the same time as V. However, Nb easily forms coarse MC carbides as compared with V, so the upper limit was made 1.00%.

Ti: ≦ 0.5% Ti is an element that easily forms MC type carbides like V and Nb. Therefore, Nb and V can be added at the same time and used. However, since Ti easily combines with N to form TiN, the upper limit is
0.5%

REM: ≤0.03% REM (rare earth element) is an element applied to the morphology control of MC carbide in high V type high speed tool steel, and the same morphology control effect is expected in the high speed tool steel of the present invention. it can. Therefore, a small amount of REM may be added to control the morphology. However, REM is expensive, and excessive addition is not effective for its morphological control effect. Therefore, the upper limit effective for form control is 0.
03%

Formula (1): ΔC = C- (0.06Cr + 0.063Mo + 0.033
W + 0.2V): -0.2 to 0.2 (preferably -0.2 to 0.1) This formula (1) represents the relationship between C and the matrix forming element, and when this ΔC is 0, it is generally a carbide forming element. Are all in a state of forming carbides in the matrix. The hardness increases as ΔC increases, but the rate of increase is about 10 times the amount of change in ΔC.

Generally, high-speed steel tool steels are manufactured with ΔC in the range of −0.3 to 0, but some matrix high-speed tool steels are used in the range of ΔC of about 0.2. Therefore, in the present invention, ΔC is limited to the range of −0.2 to 0.2. Here, since the increase of ΔC causes deterioration of toughness, it is preferable that ΔC
Is -0.2 to 0.1.

Formula (2): 2Mo / (2Mo + W) ≦ 0.9 (preferably
0.3 to 0.9) 1.00% or more to improve softening resistance at high temperature
It is necessary to add W, and for that reason, it is necessary to make the component balance of the value of 2Mo / (2Mo + W) 0.9 or less. On the other hand, if the addition amount of W is large, it becomes difficult to secure the heat treatment hardness during low temperature quenching, so that the value of 2Mo / (2Mo + W) needs to be preferably 0.3 or more component balance.

Formula (3): 2Mo + 0.3W-17V + 8Cr: 25-36
(Preferably 29 to 35) This formula is a formula that mainly represents the relationship between the amount of V forming MC carbides, the amount of Mo and W forming M6C carbides, and the amount of Cr forming M23C6 carbides. Amount, M6C carbide amount, M23C6 carbide amount ratio. Here, MC carbide is other carbide (M6C, M23C
It is stable up to high temperature compared to 6). The next stable carbide is M6C, and the carbide most likely to form a solid solution is M23C6.

When the value of this equation is small, it means that a relatively large amount of V is added and a large amount of MC carbide is formed, a small amount of Cr is added and no Cr-based carbide is formed, or the amount of formation is small. In this case, quenching at a low temperature results in a shortage of Cr-based carbides that are likely to form a solid solution, and a sufficient hardness cannot be obtained. Therefore, in the present invention, the lower limit of this equation is set to 25, preferably 29. On the other hand, if this value becomes too large, the amount of Cr-based carbides formed becomes too large, and 1200
Quenching at or above ℃ causes a locally molten structure to appear, and a coarse structure of carbide causes coarse structure to prevent a normal structure from being obtained. As a result, it becomes difficult to secure the hardness by quenching at 1200 ° C. Therefore, in the present invention, the upper limit is 36, preferably 35.

[0037]

EXAMPLES Examples of the present invention will be described in detail below. <Example 1> A steel having the chemical composition shown in Table 1 was prepared as shown in FIG.
Quenching and tempering treatments were performed under the quenching conditions shown in 1, (A) -2 and the tempering conditions shown in (B). Here, quenching is performed at two temperatures of quenching holding temperatures of 1030 ° C. and 1200 ° C., and tempering is performed at 500, 520, 540, 5
Tempering was repeated twice under the conditions of 60 hr, 580 hr, and 600 ° C. for 1 hr. Then, the quenching hardness was measured under each quenching holding temperature. The results are shown in Table 2.

[0038]

[Table 1]

[Table 2]

Further, the value of the formula (3) was obtained from each chemical component, and this value was taken as the horizontal axis, and the maximum hardness after quenching and tempering was taken as the vertical axis, and their relationship is shown in FIG. As is clear from Fig. 1, when the quenching temperature is 1030 ° C, the value of equation (3) is
Above 25, it exceeds HRC65, and thereafter the increase in hardness is gradual. In the case of 1200 ° C quenching, the maximum hardness decreases as the value of the formula (3) increases. Especially when the value exceeds 36, the decrease is remarkable. From the above results, it is necessary in the present invention that the value of the expression (3) is in the range of 25 to 36.
It is preferably in the range of 29 to 35.

In Table 2, the heat treatment hardness of the commonly used high speed tool steel is HRC60 at 1030 ° C quenching.
It is in the order of or less, and it is difficult to secure high hardness by low temperature quenching. Further, in the case of commonly used hot die steel, cold die steel, etc., the cold die steel is 10
Quenching at 30 ° C is standard, and quenching from high temperatures is rarely performed. When these steel types are quenched and tempered at a high temperature of 1200 ° C., the maximum hardness hardly changes from that at 1030 ° C. In addition, since the amounts of C, Mo and W are insufficient, sufficient hardness cannot be secured at any quenching temperature.

On the other hand, in the case of the high speed tool steel of the present invention example, HR was obtained even under the low temperature quenching of 1030 ° C. and further under the high temperature quenching of 1200 ° C.
A high hardness of C65 or higher is obtained.

Example 2 Inventive steel E shown in Table 1 and cold die steel SKD11 modified 2 were melted in a 50 kg vacuum induction furnace, annealed at high temperature, and then forged (S ₀ = 10S).
(However, cross-sectional area before forging S ₀ / cross-sectional area after forging S = 10)-
Spheroidal annealing was performed, and this was used as a test material.

A 10 × 10 × 10 mm sample for heat treatment was cut out from the test material, quenched and tempered in a salt furnace under the heat treatment conditions shown in FIG. 2, and its hardness was measured on an HRC scale. Further, a cold die for CVJ (for constant velocity joint which is an undercarriage part of a car) was manufactured from these steel types and a life test was conducted. The results are shown in Table 3.

[0044]

[Table 3]

In Table 3, the invention steel E is a carbide M that is harder than the constituent carbides of the cold die steel SKD11 modified.
With a large amount of C and M6C carbides, even after quenching at 1030 ° C, the hardness after heat treatment is as high as HRC65, and it has excellent wear resistance. With a life of 35,000, the life is greatly extended.

Example 3 Invention Steel F and Hot Die Steel System S
With respect to KD61, a gear molding die was manufactured in the same manner as in Example 2, and a heat treatment sample was cut out, and the hardness after the heat treatment and the service life of the gear molding die were measured. The results are shown in Table 4.

[0047]

[Table 4]

As shown in the results of Table 4, invention steel F
In the case of, the hardness after heat treatment is H even at 1030 ° C quenching.
It has a high hardness of RC65, and its life is greatly improved to 20,000 shots compared to 4,000 shots of SKD61.

The embodiment of the present invention has been described in detail above, but this is merely an example, and the present invention can be implemented in various modified modes without departing from the spirit of the invention.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the value of expression (3) and hardness obtained in an example of the present invention.

FIG. 2 is a diagram showing a method and conditions of heat treatment performed in the same example.

Claims (2)

[Claims] 1. By weight% C: 0.6 to 1.3% Si: 0.05 to 2.00% Mn: 0.10 to 1.00% Cr: 3.50 to 7.00% Mo: 2.00 to 9.50% W: 1.00 to 16.00% 2Mo + W: 5 to 20% V: 0.50 to 2.50% Co: ≤ 1.25% Inevitably present O and N are respectively O: ≤ 0.01% N: ≤ 0.02% With the composition consisting of the balance Fe and other unavoidable impurities, the following (1) A high-speed tool steel that satisfies the formulas (2) and (3) and can be hardened at low temperature and has a hardness of HRC65 or higher at any quenching holding temperature of 1030 ° C or 1200 ° C. -0.2 ≦ ΔC = C− (0.06Cr + 0.063Mo + 0.033W + 0.2V) ≦ 0.2 ・ ・ ・ (1) Formula 2Mo / (2Mo + W) ≦ 0.9 ・ ・ ・ (2) Formula 25 ≦ 2Mo + 0.3W-17V + 8Cr ≦ 36 ・..Formula (3) 2. The method according to claim 1, further comprising any one or more of Nb, Ti and REM in a weight percentage of Nb: ≦ 1.00% Ti: ≦ 0.5% REM: ≦ 0.03%. High-speed tool steel capable of low-temperature quenching characterized by