JPH0533102A - High speed tool steel excellent in grindability and having high hardness - Google Patents

Abstract

PURPOSE:To combine a hardness of >=hRC69 with high toughness by regulating the contents of W, Mo, V, C, Si, Cr, and N in a high speed tool steel to specific values, respectively. CONSTITUTION:The steel is a high speed tool steel having a composition which consists of 0.64-1.74% C, 0.02-0.33% Si, 0.1-0.5% Mn, 3-5% Cr, 3-10% Mo, <=10% W, 1-2% V, 5-15% Co, <=0.06% N, and the balance essentially Fe and where the following quantitative relations are satisfied among alloy components. (A): 14<=Weg<=24, where Weg=2[Mo%]+[W%], (B): Weg-10<=10[V%]<=Weg-4, (C): 11[DELTAC%]+4[Si%]>=-0.68, (D): 50[DELTAC%]+250]Si%]<=72.5, (E) -0.18<=DELTAC%<=+0.10, where DELTAC%=C%-Ceg, Ceg=0.06[Cr%]+0.063[Mo%]+0.033[W%]+0.2[V%], (F): F>=7.30, where F=-0.90[Mo%][C%]+0.45[W %]@{9146/28]C%]+2.4[C%]+0.84[Mo%]+0.92[W%]+2[V%-1]<1/2>+5.45[Si%]+32.7 [N%], (G): L>=20.55,where L=12.2[Mo%]-10.4[Mo%]<2>-3[W%]+7[V %]-25Si].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed tool steel, and more particularly to a high speed tool steel for producing a tool for machining a hard material which is difficult to cut, and which is easy to grind during tool manufacturing. .

[0002]

2. Description of the Related Art Among materials to be machined, HR
The number of hard-to-cut materials called difficult-to-cut materials such as high-hardness pre-hardened materials exceeding C40 and mold materials containing a large amount of carbide is increasing. Corresponding to this, in order to increase the hardness of the cutting tool and improve wear resistance, as a tool material,
SKH57 series high V-high Co high speed tool steel and AISI
-M41 to M42 grade high C-Co containing steel is used.

However, the former has a low grindability and is liable to be burnt by polishing when it is attached to a blade, and the softness caused by burning often fails to take advantage of its high hardness. Further, the latter has little problem in grindability, but lacks in toughness and is apt to cause chipping and breakage, and in order to avoid it, it is unavoidable that the hardness is lowered before use.

[0004]

The object of the present invention is to break the current state of the art of high speed tool steel as described above, to achieve a high hardness of HRC69 to 70 by proper heat treatment, and to improve the grindability. An object of the present invention is to provide a high-speed tool steel which is excellent and does not cause polishing and burning, and therefore can utilize high hardness and high toughness.

[0005]

The high hardness and high speed tool steel excellent in grindability of the present invention is basically C: 0.64.
~ 1.74%, Si: 0.02-0.33%, Mn:
0.10 to 0.50%, Cr: 3.0 to 5.0%, M
o: 3.0 to 10.0%, W: 10.0% or less, V:
1.0 to 2.0% and Co: 5.0 to 15.0% are contained, N: 0.060% or less, and the balance is substantially Fe.
A high speed tool steel having an alloy composition consisting of: A) 14 ≦ Weq ≦ 24 where Weq = 2 [Mo%] + [W%] B ) Weq-10 ≦ 10 [V%] ≦ Weq-4 C) 11 [ΔC%] + 4 [Si%] ≧ −0.68 D) 50 [ΔC%] + 250 [Si%] ≦ 72.5 E) − 0.18 ≦ ΔC% ≦ + 0.10 However, ΔC% = C% −Ceq Ceq = 0.06 [Cr%] + 0.063 [Mo%] + 0.033 [W%] + 0.2 [V%] F) F ≧ 7.30 However, F = −0.90 [Mo%] [C%] − 0.45 [W%] [C%] + 2.4 [C%] + 0.84 [Mo%] + 0.92 [ W%] +2 [V% -1 ] 1/2 +5.45 [Si%] + 32.7 [N%] G) L ≧ 20.55 proviso L = 12.2 [M %] - 10.4 [Mo%] 2 -3 [W%] + 7 [V%] -25 [Si%] after proper quenching, tempering at least 20 ° C. higher tempering temperature than the high temperature tempering temperature maximum hardness is obtained And then HRC
It is characterized by having a high hardness of 69 or more.

This tool steel may have, in addition to the basic alloy composition described above, an alloy composition containing one or both of the following optionally added groups of alloying elements: I) REM: 0.60% or less, Y: 2.0% or less, Z
1 or 2 selected from r: 2.0% and Hf: 2.0%, and II) Ni: 2.0% or less, Cu: 1.0% or less and B: 0.05% 1 type or 2 or more types.

[0007]

The high-speed tool steel of the present invention was completed with the intention of refining, focusing on the fact that vanadium carbide VC among the carbides in the steel has the greatest effect on the grindability. is there. Since VC is hard, it plays an important role in imparting wear resistance to tools, but on the other hand, primary carbides (crystallized carbides) tend to become huge, and if they become huge, grindability is impaired.

When the eutectic carbide that crystallizes upon solidification when the tool steel is melted is made into the M ₂ C type, V easily dissolves in this carbide, so that when heating during forging or rolling,
It should be possible to precipitate fine VC by the reaction of M ₂ C → M ₆ C + MC (VC). In other words,
If the primary VC does not crystallize and all VCs are VCs precipitated in the above carbide conversion reaction, it is expected that the grindability is improved. The inventors examined the crystallization limit of primary VC in order to realize such expectations. As a result, it is V amount and W equivalent Weq = 2 [Mo%]
It has been found that there is a close relationship with + [W%], and if those values satisfy the above-mentioned conditions, the primary VC does not crystallize.

That is, Weq must be 14% or more in order to secure the amount of carbide necessary to obtain sufficient cutting performance, while 24% so as not to impair hot workability.
Up to the above (condition A above). The amount of V has a lower limit of 1.0% as the minimum amount necessary for obtaining wear resistance and causing the reaction of the above formula M ₂ C → M ₆ C + MC, and the amount of VC required for wear resistance is 10 to secure
[V%] ≧ Weq-10, and then the upper limit of 2.0% as a limit for preventing primary VC from crystallizing and 10 [V%] ≦ W.
eq-4 has been defined (the condition B). This is illustrated in FIG. 1, and the Weq and the V amount must be in the shaded area in FIG.

Needless to say, the tool steel for processing difficult-to-cut materials must have high hardness.
The level reached by proper quenching and tempering is HRC6
Placed at 9-70. Appropriate quenching and tempering means that so-called overheating, such as coarsening of crystal grains and appearance of molten phase, is caused by sufficient solid solution of carbide and decomposition of retained austenite during tempering and precipitation hardening of carbide. Select a quenching temperature that does not cause an extreme decrease in toughness due to the structure, and
From the temperature (temperature A in FIG. 2) at which the maximum hardness can be obtained in the tempering hardness curve as shown in FIG.
That is, tempering is performed at a temperature higher by 0 ° C. in the shaded area in FIG. The reason for tempering at such a temperature is that when tempering in a vacuum or gas atmosphere, the operating conditions tend to fluctuate toward the lower temperature side, and the practical motivation is to avoid the resulting decrease in hardness and instability of the structure. It is based on it. However, if tempered at a temperature excessively higher than temperature A,
Since the high hardness of the corner will be diminished, the operation must be controlled to prevent such a situation.

Regarding the amount of carbon and the amount of silicon, a high amount of C is first adopted because it is necessary to increase the amount of solid solution C and the amount of carbide produced during quenching in order to secure the tempering hardness HRC69 to 70. This increase in C means the content C and C equivalent Ceq.
= 0.06 [Cr%] + 0.063 [Mo%] + 0.0
33 [W%] + 0.2 [V%] difference, ΔC% = [C
%]-To increase Ceq. Since Si in steel forms a solid solution in the carbide M ₆ C in steel, increasing Si has the same effect as increasing C. C amount and S
As a result of studying the relationship with the amount of i, in order to secure a tempering hardness of HRC69 or higher within the range of the above Weq, 11
[ΔC%] + 4 [Si%] ≧ −0.68 (condition C)
I found what I should do.

By the way, since an increase in C and an increase in Si lead to a reduction in the toughness of the tool, it is necessary to consider a measure against this point. The applicant has previously proposed that the toughness that decreases with the increase in C is supplemented with the decrease in Si, but to provide a cutting tool that can withstand the machining of difficult-to-cut materials and the unmanned cutting work, the toughness is still There is a shortage. The practical limit is to ensure 2800 MPa when the toughness is expressed by transverse rupture strength (test piece 3 × 5 × 30 mm, three-point bending test with 20 mm between fulcrums), and this toughness is HRC69 or higher. To realize, 50 [ΔC%] + 250
It is necessary to satisfy [Si%] ≦ 72.5 (the above condition D).

If the value of ΔC increases and exceeds a certain limit, the amount of retained austenite during quenching becomes excessive,
Conversely, tempering hardness begins to decrease. This limit is 0.10
%. The relationship between ΔC and the amount of Si is shown in FIG. 3, and the inside of a quadrangle surrounded by the vertical axis and three straight lines is adopted. From this figure, the upper limit value of Si of 0.33% is further derived.

Si is preferably a low amount from the viewpoint of toughness, but it is originally a deoxidizing agent, and if it is too low, the oxygen potential of the molten steel becomes high during refining and the cleanliness decreases. Therefore, 0.02% was set as the lower limit. Therefore, the Si amount is in the range of 0.02 to 0.33%. In FIG. 3 relating to ΔC and Si, a hatched region is used inside the quadrangle.
ΔC is minimum at the intersection of the two straight lines in FIG. Since this value is −0.18%, the above ΔC
A quantity range of -0.18 to + 0.10% is given.

When ΔC is given in this way, the amount of C is ΔC + Ceq. Therefore, by calculating the values of Cr, Mo, W and V which give the maximum and minimum of Ceq from the above range, C : 0.64 to 1.74%
The range of is defined.

Explaining the balance between the W content and the Mo content, it is essential to make the eutectic carbide fine by utilizing the conversion reaction of the carbide as described above. In order to realize this, the above is mentioned. It is necessary to satisfy F ≧ 7.30 (condition F). Further, in order to prevent crystallization of huge bone-like carbides during solidification, the above L ≦ 20.5 is also used.
5 (Condition G) must be met. These relationships are obtained by induction from the results shown in FIGS. 4 and 5, and even in FIG. 4 (V = 1.3%), FIG. 5 (V = 1.5%). ), Feather-like eutectic carbides precipitate only in the hatched region surrounded by the curves F and L, and the carbide conversion reaction described above is performed to generate granular M ₆ C and fine VC. Precipitate.
White circles in FIG. 4 and black circles in FIG. 5 represent typical alloy compositions.

To satisfy the condition of F ≧ 7.30, it is convenient for N to be present in a small amount, but if the content is large, it tends to coarsen VC, so 0.06
Put a limit of%.

Cr is added in an amount of 3.0% or more in order to secure hardenability. If the amount is too large, the hardness decreases and the forgeability becomes poor, so the upper limit is 8.0%.

Mn is added as a deoxidizing and desulfurizing agent and a component for improving hardenability, and is added in an amount of 0.1% or more. The upper limit of 0.5% is set because of the deterioration of hot workability.

Co is a component for improving the hardness after heat treatment, and the effect is remarkable at 5% or more, but since it gradually becomes saturated, addition is limited to within 15%.

The reasons for limiting the action and composition range of alloying components that can be added in addition to the above essential components are as follows. I) REM, Y, Zr, Hf Combines with impurities S and P in steel to improve hot workability and toughness. Further, it is also useful for miniaturization of VC by combining with N. If the amount is too large, the cleanliness of the steel will be impaired and the toughness will rather deteriorate, so the upper limit was 0.60% for REM and 2.0% for Y, Zr and Hf.

II) Ni, Cu, B Ni and Cu strengthen the matrix to enhance strength and toughness, and B enhances hardenability. Therefore, Ni is 2.0% or less, C
It is also possible to add u in the range of 1.0% or less and B in the range of 0.05% or less. Addition beyond this limit has no further effect.

[0023]

Example An alloy having the following composition (weight%, balance Fe) was melted. The comparative example is one of known molybdenum-based high speed tool steels.

Example No. 1 Example No. 2 ratio Comparative example C 1.11 1.20 1.14 Si 0.18 0.14 0.59 Mn 0.30 0.29 0.31 Cr 4.19 4.28 3.92 Mo 6.24 5. 88 8.61 W 6.00 7.04 2.09 V 1.27 1.54 1.75 Co 7.95 7.93 7.96 N 0.028 0.031 0.022 ΔC 0.013 0. 032-0.05 Weq 18.48 18.80 19.31 After hot rolling, the crystallization state of VC was examined. As a result, fine secondary crystals were observed in both Example 2 and expected carbide conversion reaction. I found out that happened. On the other hand, in the comparative example, a huge carbide was formed.

Example No. 1 and No. With respect to the test materials of 2 and Comparative Example, after quenching at 1200 ° C. or 1220 ° C., tempering was performed at various temperatures of 500 to 580 ° C., and hardness was measured. The results are shown in Fig. 6 respectively.
And shown in FIG.

Next, in the embodiment, the heat treatment condition which satisfies the condition that the hardness is HRC69 or more, that is, the quenching 120
For 0 ° C.-tempering 540, 560 or 580 ° C., the transverse rupture strength was measured as a measure of the toughness. The data is shown in FIG. 8 in relation to hardness.

Finally, the grindability was evaluated according to the following test conditions.
checked. Specimen size: 10 × 10 × 50mm Testing machine: Profile grinding machine Grindstone: WA-120 Feed: 0.02 mm / stroke Depth of cut: 0.3 mm x 5 times Grinding wheel peripheral speed: 1370 m / mm Grinding oil: None (dry type)   The grinding ratios are as follows, and the examples are target
The value of 15 was exceeded.         Example No. 1    Example No. Two    Comparative example (MH64) Hardness 69.0 69.2 68.6 Grinding ratio 16.0 15.2 13.9

[0028]

The high speed tool steel of the present invention has a hardness of HRC.
A level of 69 or higher is ensured, and high toughness is achieved at the same time. Since this tool steel has excellent grindability and does not worry about polishing and burning, it is possible to provide a tool having good wear resistance by utilizing high hardness. Therefore, this material is suitable for various applications such as end mills.

[Brief description of drawings]

FIG. 1 is a diagram shown for the purpose of explaining the reasons for limiting the composition of components in the high-speed tool steel of the present invention, in which V content and We
The graph which shows the relationship with q.

FIG. 2 is a graph of a tempering hardness curve shown for the purpose of explaining heat treatment conditions of the high speed tool steel of the present invention.

3 is a diagram for the same purpose as FIG. 1, showing ΔC
Is a graph showing the relationship between Si and the amount of Si.

FIG. 4 is a graph showing how the shape of primary-crystallized eutectic carbide differs depending on the relationship between the Mo content and the W content in the high-speed tool steel.

FIG. 5 is a graph similar to FIG.

FIG. 6 is a graph showing the hardness after quenching and tempering, which is data of Examples of the present invention.

FIG. 7 is a graph similar to FIG.

FIG. 8 is a graph showing the relationship between hardness and transverse rupture strength, which is data of Examples of the present invention.

Claims (3)

[Claims] 1. C: 0.64 to 1.74%, Si: 0.
02-0.33%, Mn: 0.10-0.50%, C
r: 3.0 to 5.0%, Mo: 3.0 to 10.0%,
W: 10.0% or less, V: 1.0 to 2.0% and C
A high-speed tool steel containing o: 5.0 to 15.0%, N: 0.060% or less, and the balance being substantially Fe. A) 14 ≦ Weq ≦ 24 where Weq = 2 [Mo%] + [W%] B) Weq-10 ≦ 10 [V%] ≦ Weq-4 C) 11 [ΔC% ] +4 [Si%] ≧ −0.68 D) 50 [ΔC%] + 250 [Si%] ≦ 72.5 E) −0.18 ≦ ΔC% ≦ + 0.10 However, ΔC% = C% −Ceq Ceq = 0.06 [Cr%] + 0.063 [Mo%] + 0.033 [W%] + 0.2 [V%] F) F ≧ 7.30 However, F = −0.90 [Mo%] [C%] -0.45 [W%] [C%] +2.4 [C%] +0.84 [Mo%] +0.92 [W%] +2 [V% -1] ^1/2 + 5.45 [Si%] + 32.7 [N%] G) L ≧ 20.55 However, L = 12.2 [Mo%]-10.4 [Mo%] ^2-3 [W%] + 7 [V% -25 [Si%] After proper quenching, tempering is performed at a tempering temperature that is at least 20 ° C higher than the high tempering temperature at which the maximum hardness is obtained, and then HRC
High hardness and high speed tool steel with excellent grindability, characterized by having a hardness of 69 or higher. 2. The alloy comprises, in addition to the above composition, REM:
High hardness and high speed according to claim 1, containing one or more selected from 0.60% or less, Y: 2.0% or less, Zr: 2.0% or less, and Hf: 2.0% or less. Tool steel. 3. The alloy comprises Ni: 2.
0% or less, Cu: 1.0% or less, and B: 0.05%
The high hardness and high speed tool steel according to claim 1 or 2, which contains one or more selected from the following.