JPH06100976A - Shank material for high speed steel tools with excellent fatigue life - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a shank material with excellent strength, formability, and fatigue resistance after heat treatment. [Composition] A shank material for high speed steel tools characterized by the following composition (1), (2) or (3). (1) C: 0.3-0.6%, Si: 0.05% to less than 0.40%,
Mn: 0.05 to 1.5%, P: 0.020% or less, S: 0.010% or less, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%,
Ni: 0.1-1.0%, V: 0.03-0.5%, sol.
A composition containing Al: 0.01 to 0.10% and N: 0.003 to 0.010%, with the balance being Fe and an unavoidable alloying component. (2) In addition to the components of (1) above, Nb: 0.01 to 0.5%, N
b: Composition containing 0.01 to 0.5% and Ti: 0.005 to 0.010%. (3) In addition to the above (1) or (2) components, Ca: 0.001
Composition containing ~ 0.01%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material having excellent fatigue life which is used as a base metal (shank material) for a cutting tool using high speed steel such as end mills and band saws.

[0002]

2. Description of the Related Art In cutting tools such as band saws and end mills, high speed steel has been used for the purpose of improving the wear resistance of the blade. However, making the entire tool from high speed steel is very expensive. Therefore, for the purpose of cost reduction, carbon steel, low alloy steel, etc. are used for the shank portion, and this shank portion is joined to the blade material of high speed steel by flash butt welding, friction welding, or electron beam welding, and thereafter, It is common to give high strength by heat treatment such as quenching and tempering.

The shank material of the cutting tool manufactured as described above is required to have the following characteristics in consideration of being subjected to welding and heat treatment. That is, the weldability is good, the movement of C (carbon) in the weld is small, the carburization of the blade part and the decarburization of the shank part are suppressed, and the heat treatment is performed at the same time in the state of being joined with the high speed steel Can secure sufficient strength and toughness, can secure hardness close to the blade part in the tempered state, and suppresses the growth of austenite grains during quenching and heating to improve fatigue resistance, and also suppresses non-metallic inclusions in steel. And so on. Further, from the viewpoint of formability, punching, while satisfying the above-mentioned weldability and heat treatment property,
It is also necessary to have good formability that can reduce tool wear during forming such as cutting.

The followings are already known as inventions relating to the shank material.

(1) Invention of Japanese Examined Patent Publication No. 61-12022 The steel according to the present invention is a Si deoxidized steel, and it is difficult to suppress the growth of austenite grains during high temperature heating, and the above requirements cannot be satisfied.

(2) Japanese Patent Laid-Open No. 4-59942 and 4-
Inventions of No. 59943 The steels of these inventions have a high Si content, and the solid solution hardening thereof causes poor formability and cannot satisfy the above requirements.

[0007]

DISCLOSURE OF THE INVENTION The present invention eliminates the drawbacks of the shank materials proposed hitherto, has all the characteristics described above, and provides a shank material which is particularly excellent in terms of fatigue life. It was made for the purpose of doing.

[0008]

Means for Solving the Problems The present invention includes the following (1)
The gist is the shank material of (4). Hereinafter, all% related to the content of alloy components mean% by weight.

(1) C: 0.3 to 0.6%, Si: 0.05% to 0.
Less than 40%, Mn: 0.05-1.5%, P: 0.020% or less,
S: 0.010% or less, Cr: 0.5 to 2.0%, Mo:
0.5 to 2.0%, Ni: 0.1 to 1.0%, V: 0.0
3 to 0.5%, sol.Al: 0.01 to 0.10%, N: 0.003 to 0.010
%, The balance being Fe and inevitable impurities, and a shank material for high speed steel tools.

(2) In addition to the components of (1) above, Nb: 0.01
A shank material for high-speed steel tools, characterized in that it contains ~ 0.5% and the balance is Fe and inevitable impurities.

(3) In addition to the components of (1) above, Nb: 0.01
A shank material for high-speed steel tools, characterized in that it contains ~ 0.5% and Ti: 0.005 to 0.010% and the balance is Fe and inevitable impurities.

The shank material of the above (1) to (3) can further contain Ca: 0.001 to 0.01% in addition to the above components.

[0013]

The function and the reason for limiting the content of the individual alloy components constituting the shank material of the present invention will be explained later.
First, the knowledge on which the present invention is based will be described.

(A) Regarding weldability, in order to prevent damage at the weld portion between the blade portion and the shank material, the C content of the conventional shank material is JIS G 3311 SK5 to SK7, which is generally used as tool steel.
Alternatively, the C content of SKS2 to 7 is used as a guide. However, in the high carbon steels for these tools, martensite having low toughness is formed in friction welding, flash butt welding or electron beam welding, which causes a problem of breakage during use. In the present invention, the amount of C is lowered for the purpose of forming a quenched structure (martensite) having excellent toughness. further,
Based on the finding that the addition of alloying elements such as Cr and Mo is effective in order to suppress the diffusion movement of C between the shank portion and the blade portion in the welded portion, it was decided to add these appropriate amounts. .

Specifically, in order to prevent damage due to brittle fracture at the weld between the blade and the shank material, the C content of the shank material is
It is appropriate to keep it below 0.6%. Further, it is effective to contain Cr in the range of 0.5 to 2.0% and Mo in the range of 0.5 to 2.0% for the purpose of suppressing diffusion movement of C between the shank portion and the blade portion in the welded portion.

(B) Regarding heat treatability, in order to secure sufficient strength and toughness even if heat treatment is simultaneously performed in a state of being joined with high speed steel, the amount of C must be 0.3% or more,
At the same time, it is effective to add alloy elements such as Cr, Mo, Ni and V in order to secure hardenability. In order to secure the hardness close to that of the blade portion in the tempered state, it is effective to add alloy components such as Cr, Mo, Ni and V which increase the temper softening resistance.

Specifically, in consideration of the above-mentioned weldability and heat treatment property, the C content is set in the range of 0.3 to 0.6%, and then Cr:
0.5 to 2.0%, Mo: 0.5 to 2.0%, Ni: 0.1 to 1.0%,
V: 0.03 to 0.5% It was decided to contain in the range.

(C) Regarding the fatigue resistance after heat treatment, in the quenching treatment for high-speed steel, 1100-12, which is higher than the quenching temperature (800-900 ° C) generally used for high-carbon steel.
A heating temperature of 00 ° C is adopted. When heated at such a high temperature, the austenite grains are usually coarsened and the fatigue strength during use is significantly reduced. As a countermeasure against this, it is necessary to use a precipitate capable of suppressing austenite grain growth even at high temperatures. In a Si deoxidized steel such as the steel disclosed in Japanese Patent Publication No. 61-2022, it is difficult to suppress austenite grain growth and the tool life is shortened. So in the present invention
It was decided to reduce the amount of Si added and perform deoxidation with Al.

If the steel is deoxidized from Al and contains a considerable amount of sol.Al, coarsening of austenite grains is suppressed to some extent. However, even with Al deoxidized steel, a considerable amount of Al is added to prevent coarsening, or carbonitrides are further formed,
An alloy component other than Al that can maintain this at a high temperature is required. In the present invention, sol.Al and N, or N in addition to these
It was decided to utilize precipitation of Nb (CN), TiNb (CN), or the like by adding b or Ti and Nb in combination.

In order to improve the fatigue resistance after the heat treatment, the grain size of the austenite grains needs to be in the range of No. 8-10. For that purpose, sol.Al: 0.01 to 0.10% and N: 0.003 to 0.
010% is essential, and it is desirable to further contain Nb: 0.01 to 0.5%, or Nb and Ti: 0.005 to 0.1% in combination.

In addition to controlling the austenite grain size, it is also effective to add Ca as necessary in order to control MnS precipitated in the steel. The content range is 0.001〜
0.01% is suitable.

(D) Formability With respect to formability, in order to manufacture a shank material at low cost, formability capable of reducing tool wear during forming such as punching and cutting should be maintained while satisfying the above weldability and heat treatability. There must be. If it is only to improve the formability, the content of each alloying element may be reduced, but as described above, it is necessary to carefully control the alloying element in order to secure the strength and fatigue life after heat treatment. . The present inventor has found that reduction of Si, which is largely affected by solid solution hardening and has little effect on strength after heat treatment, makes moldability and strength compatible with each other and improves overall properties. Therefore, in the present invention, the Si content range is 0.05 to 0.40.
%.

The effect of each component and the reason for limiting the content will be described below.

C: The strength of the shank material after quenching / tempering mainly depends on the amount of C, and a certain amount or more of C is required to increase the strength after tempering. In the shank material of the present invention, in order to set the hardness after quenching / tempering to the same level as that of the blade material of high speed steel, a hardness of HRC 48 or higher is targeted. Therefore, C is required to be at least 0.3% in consideration of the tempering temperature and the contents of other alloying elements. on the other hand,
The upper limit of C was set to 0.6% for the purpose of improving the toughness after quenching and tempering and ensuring the formability in punching or cutting before heat treatment.

Si: In addition to being added to the steel as a deoxidizing agent in the steel making stage, it is also an effective component for increasing the temper softening resistance in the quenching and tempering stages. To get this effect
0.05% or more is required. However, Si forms a solid solution in ferrite to increase its hardness, and as described above, deteriorates formability. Therefore, in the present invention, the Si content is limited to less than 0.40%.

Mn: Mn is an element effective for increasing the hardenability and the temper softening resistance in the quenching / tempering stage. Further, S in the steel is fixed as MnS to increase the toughness after quenching and tempering. If the purpose is only to secure the toughness, it may be 0.05% or more, but in order to increase the temper softening resistance, 0.8% or more is desirable. But,
The excessive addition of Mn deteriorates the toughness after quenching and tempering, so the upper limit of its content is 1.5%.

P: P is an element that deteriorates the toughness after quenching and tempering, so its content should be as small as possible. In particular, when the material of the present invention is used with high strength, 0.02% is added to improve impact resistance and fatigue resistance.
It is necessary to keep below. However, lowering P in high-carbon, high-alloy steel leads to higher manufacturing costs, so the lower limit of actual production is about 0.005%.

S: S, like P, is an element that deteriorates the toughness after quenching and tempering, and the smaller the content, the better. As described above, in order to secure the impact resistance and fatigue resistance of the shank material used with high strength, 0.01% was made the upper limit. However, even in the case of S, lowering S in the high-carbon and high-alloy region involves cost increase, so the lower limit of actual production is about 0.002%.

Cr: Cr, like Mn, is an element effective for increasing the hardenability and the temper softening resistance in the quenching / tempering stage. Since the tempering temperature of the Cr-containing steel can be set higher, the toughness can be improved. To obtain these effects, the Cr content in steel must be 0.5% or more.
However, when it exceeds 2.0%, this effect is saturated, which only leads to an increase in cost, and further, it may form a solid solution in cementite and inhibit the decomposition of cementite during heating during quenching treatment. Therefore, in the present invention, the upper limit of the Cr amount is set
It was set at 2.0%.

Mo: Mo has a function of remarkably increasing the temper softening resistance in the quenching / tempering stage, like Cr. Therefore, even in the Mo-containing steel, the tempering temperature can be set to be high and the toughness can be improved. Mo also has an effect of suppressing deterioration of toughness due to elements such as S. To obtain these effects, the amount of Mo in steel must be 0.5% or more.

However, if it exceeds 2.0%, these effects do not increase and the manufacturing cost only increases. Further, like Cr, it may form a solid solution in cementite and inhibit the decomposition of cementite during heating during the quenching treatment.
Therefore, the upper limit of the Mo content is 2.0%.

Ni: Ni has the effect of increasing the matrix strength during the quenching and tempering steps, and also has the effect of suppressing the growth of austenite grains during heating during quenching and improving fatigue resistance. In order to obtain this effect, the content of 0.1% or more is required, but excessive addition causes cost increase and the strength may decrease due to solid solution softening of Ni, so the upper limit of Ni content is 1.0%. And

V: Usually, the shank material is welded and joined to the blade material, quenched, and then tempered at a temperature of 400 to 600 ° C. To increase the softening resistance at this temperature,
It is effective to add V to precipitate fine carbides. To obtain this effect, the content of 0.03% or more is required, but V itself is an expensive element, and its content is limited to 0.5% to avoid cost increase due to excessive addition.

Sol.Al: Al is added as a deoxidizing material in the steelmaking stage. In addition, by forming a nitride, grain growth of austenite during heating during quenching is suppressed.
Further, it is effective in suppressing bubbles generated at the weld interface between the shank portion and the blade portion. To obtain these effects, sol.Al
It is necessary to contain 0.01% or more. For high-strength shank material, the heating temperature during quenching is 1000 ° C or higher (normally 11
Since it is as high as 00 to 1200 ° C., it is desirable that sol.Al is present in an amount of 0.05% or more in order to ensure the grain growth suppressing effect. However, excessive addition of Al increases non-metallic inclusions such as oxides and deteriorates toughness and fatigue resistance, so sol.
The upper limit of Al content should be 0.10%.

N: To improve the fatigue resistance, it is necessary to contain 0.003% or more of N in order to precipitate Al, or a nitride of Al and Nb or Al, Nb and Ti.
However, excessive addition of N causes a decrease in toughness, so the upper limit was made 0.010%.

In addition to the above components, Nb or Nb
Ti can be added. Further, Ca can be further added to both the steel to which these are not added and the steel to which they are added.

Nb: The shank material is required to have high strength and long life. However, the heating at the time of quenching after welding with the blade material is as high as 1100 to 1200 ° C as described above, and if the alloy components are not particularly taken into consideration, the austenite grains grow coarsely and therefore the resistance is high. Fatigue characteristics deteriorate. To compensate for this, Al and N are used.
A single precipitate such as AlN alone has a weak effect of suppressing grain growth at high temperature. Therefore, it is desirable to form a precipitate that can suppress austenite grain growth at high temperature.

Since Nb is an element that combines with N to form a nitride, its addition has the effect of supplementing the grain growth suppressing effect. To obtain this effect, 0.01% or more is required, but the upper limit is 0.5% to prevent cost increase.

Ti: A composite precipitate of Ti and Nb, ie, Ti, for the purpose of further supplementing the grain growth suppressing effect of the above-mentioned Nb-based precipitate.
It is also desirable to add Ti to form TiNb (CN). To form this composite precipitate, 0.005% or more
Although Ti is necessary, if added excessively, precipitates such as TiN will be formed, resulting in deterioration of toughness and cost increase, so the upper limit was made 0.1%.

Ca: In a material used with high strength such as the shank material of the present invention, minute inclusions also cause fatigue fracture during use. Ca has a function of reducing sulfide (MnS) -based inclusions, that is, A-based inclusions and improving fatigue resistance. This effect is expected to be 0.001% or more
This is the case when Ca is contained. However, excessive addition of Ca causes cost increase, so the upper limit is made 0.01%.

[0041]

Example 1 Steels A to C having the compositions shown in Table 1 were hot-rolled, further cold-rolled at a rolling reduction of 50% to a plate thickness of 1.2 mm, and then annealed by soaking at 690 ° C. for 24 hours. Then, the mechanical properties after annealing were measured.

Next, assuming the quenching and tempering conditions after welding with the blade portion, after heating in an electric furnace at 1200 ° C. for 60 seconds, quenching in oil at 90 ° C. Tempering (twice) was performed by heating at 40 ° C. for 40 minutes, and then the mechanical properties and the amount of A-type (sulfide) inclusions were measured. Note that tempering does not sufficiently soften once, so in this example, 2
However, if the holding time is extended, it may be tempered once.

Table 2 shows the above measurement results. The A-type inclusions in the steel were measured according to JIS G0555, and the crystal grain size was measured according to JIS G0551. In the bending test, a test piece having a width of 5 mm and a length of 30 mm was cut out from a steel plate having a thickness of 1.2 mm, and a test was performed with a span length of 10 mm and a central one-point load method. For the fatigue test, use a leaf spring fatigue tester and check if the stress is 931 N / mm ² .
It was performed with an amplitude of 15 mm.

Steel B corresponds to the shank material proposed in Japanese Patent Publication No. 61-2022. This is sol.
Since it contains little Al and does not contain any of Nb, Ti and Ca, the austenite grains become coarse after quenching and quenching, and the fatigue life is short.

The steel rod is the shank material of the present invention.
The fatigue life of these materials is extended by increasing sol.Al and adding Nb and Ti. sol.Al as well as Nb or Nb
The steel with Ti added is more excellent, and the steel with Ca added has significantly reduced sulfide inclusions and has a much longer fatigue life.

Although the weldability was not directly evaluated, it can be said that there is no problem in the welded portion with respect to the steel roach because the fatigue life deteriorates when the strength of the welded portion is insufficient.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

Example 2 Steels (No. 1) having the compositions shown in (1) and (2) of Table 3
.About.30), test pieces were prepared in the same manner as in Example 1, and various tests were performed under the same conditions. The results are shown in Table 4 (1) and
Shown in (2).

Steel Nos. 1 to 25 are shank materials of the present invention,
No. 26 is steel equivalent to SNCM220 shown in JIS G3311.
Nos. 27 to 30 are comparative materials in which any of the components is out of the range defined by the present invention.

As is clear from Table 1 (1) and (2), the steel of No. 26 (SNCM220) given as a comparative material has a low C and Mo content and does not contain V, so the strength is low, and Nb, Ti, Ca
Fatigue life is remarkably short because of no addition of. Steel No.
Since No. 27 has a high Si content, its strength in an annealed state is extremely high, and there is a problem in formability. In addition, due to the decrease in toughness due to high Si, the transverse rupture strength after quenching and tempering is small.

Steel No. 28 has an excessively low V, has a relatively small strength after quenching and tempering, and has a short fatigue life. In addition, steel No.
In the case of No. 29, it is difficult to suppress grain growth during quenching and heating due to the low N content, and austenite is coarsened to shorten the fatigue life. On the other hand, Steel No. 30 has an excessive amount of N, which deteriorates the toughness and decreases the transverse rupture strength.

In contrast to the above-mentioned comparative materials, the materials of the present invention of Nos. 1 to 25 have high strength of a level capable of retaining good moldability and good fatigue resistance.

[0054]

[Table 3 (1)]

[0055]

[Table 3 (2)]

[0056]

[Table 4 (1)]

[0057]

[Table 4 (2)]

[0058]

INDUSTRIAL APPLICABILITY The present invention provides a material having excellent overall characteristics as a shank material by properly combining various kinds and contents of alloy components. This shank material has a good balance of strength and formability and is excellent in fatigue resistance after being heat-treated by quenching and tempering after welding with a blade portion, and thus is extremely practical.

Claims (4)

[Claims] 1. By weight%, C: 0.3 to 0.6%, Si: 0.05% to less than 0.40%, Mn: 0.05 to 1.5%, P: 0.020% or less,
S: 0.010% or less, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, N
i: 0.1-1.0%, V: 0.03-0.5%, sol.Al:0.01-0.1
A shank material for high speed steel tools, which contains 0% and N: 0.003 to 0.010%, and the balance is Fe and inevitable impurities. 2. In addition to the component according to claim 1, Nb:
A shank material for high speed steel tools, characterized by containing 0.01 to 0.5% by weight and the balance being Fe and inevitable impurities. 3. In addition to the component according to claim 1, Nb:
A shank material for high speed steel tools, characterized by containing 0.01 to 0.5% by weight and Ti: 0.005 to 0.010% by weight and the balance being Fe and inevitable impurities. 4. In addition to the components according to claim 1, 2 or 3, Ca: 0.001 to 0.01% by weight is further contained, and the balance is Fe and inevitable impurities. A shank material for high speed steel tools according to any of 1.