JPH0674486B2 - High hardness sintered high speed steel ingot with excellent hot workability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintered high-speed steel, and more particularly to a sintered high-speed steel ingot having excellent hardness and excellent cutting performance and hot workability. .

(Prior Art) In high-speed steel, by adding a large amount of alloying elements such as W and V, fine carbides, nitrides, and the like are uniformly dispersed in the steel structure, aiming at imparting wear resistance. Although a large amount of alloying elements are added, it is extremely difficult to grind a steel ingot obtained by melting into a product.

Therefore, conventionally, a sintered high-speed steel for forming and sintering steel powder by the application of the powder metallurgy has been developed, and is frequently used for manufacturing cutting tools such as precision gear cutting tools.

(Problems to be solved by the invention) However, in recent years, in processing various materials, higher precision and lower cost have been required, and higher hardness of the work material, higher cutting speed, etc. Since the demand for cutting tools has become more severe, the development of steel grades with high hardness and excellent wear resistance has been promoted. For example,
47-42319, JP-A-50-139006, JP-A-52-65114 and the like have been proposed. However, in these proposals, a large amount of alloying elements are added in order to increase the hardness, so that inevitably the workability decreases due to the high alloying, particularly the hot workability decreases remarkably, and there is particularly high demand. It is difficult to roll and forge small diameters (eg, 20φm).

In this respect, the applicant previously proposed a high wear-resistant sintered high speed steel in Japanese Patent Publication No. 59-37740. This regulates the W and Mo contents, which are defined as the W equivalent, and the ratio of other alloying elements, C: 1.5 to 2.0%, Cr: 3.8 to 4.5%, W: 1.5 to 1
3.5%, Mo: 2.6-5.8% (however, W + 2Mo: 18-23.5%),
V: 4.2 to 5.2% and Co: 4.2 to 5.2%, the balance is adjusted to a composition consisting of Fe and unavoidable impurities, high wear resistance and excellent cutting performance, especially high sintering This is a practical application of speed steel.

However, as a result of subsequent research by the present inventor, such a sintered high-speed steel shows that when applied to a wide variety of end mill (bottom milling) tools mainly used for machining of molds among cutting tools. It turned out that there was a problem with cutting performance.

The present invention has been made to solve the problems of the sintered high-speed steel according to the applicant's proposal, and has excellent cutting performance, particularly end mill cutting performance, and excellent hot workability. It is intended to provide a high hardness sintered high speed steel ingot.

(Means for Solving Problems) In order to achieve the above object, the inventor of the present invention has a composition based on the previously proposed sintered high-speed steel as a base, and investigates the relationship between the composition and end mill cutting performance. As a result of earnest research to find improvement measures, in addition to W equivalent, W and Mo are newly added.
By controlling the relationship between the carbon equivalent Ceq and C and N defined by V and V, increasing the Co addition amount, and also controlling the process conditions and the size of primary carbide,
It has been found that a high hardness and an excellent end mill cutting performance can be realized without impairing the hot workability, and the present invention has been made here.

That is, in the present invention, C: 1.49 to 1.90%, Cr: 3 to 5%, W:
11.5 ~ 13.0%, Mo: 3 ~ 5% (however, W + 2 Mo: 19 ~ 21
%), V: 4 to 5% and Co: 7 to 12%, and C and N are Ceq + 0.10 ≦ C + 12 / 14N ≦ Ceq + 0.25 (however, Ceq = 0.19 + 0.017 (W + 2Mo) +0. 22V), the composition is such that the balance is Fe and inevitable impurities, and the average size of the primary carbides is 3 μm by the gas atomizing-hot isostatic pressing method.
The gist of the present invention is a high-hardness sintered high-speed steel ingot, which is particularly excellent in end mill cutting performance and hot workability, characterized by having m or less.

The present invention will be described in detail below based on examples.

First, the reasons for limiting the chemical components in the present invention will be described.

W, Mo: W is an alloying element that is basically important for obtaining the performance as a high speed steel, and is combined with C, N and Fe to form MC, M ₆ C type carbides, MX, M ₆ X type coals. The balance is an element that forms a nitride and dissolves into the matrix to improve wear resistance and at the same time improve tempering hardening and high temperature hardness, and contribute greatly to improvement of cutting performance. If the W content is less than 11.5%, such an effect cannot be obtained, but even if it is added in excess of 13.0%, the effect does not increase, but rather the cost is increased, which is not preferable. Therefore, the amount of W is set in the range of 11.5 to 13.0%.

Mo exhibits the same behavior and characteristics as W described above, and the addition of Mo1% has almost the same effect as the addition of W2%, but it also has the effect of lowering the quenching temperature. It is an effective element for suppressing coarsening. If the amount of Mo is less than 3%, these effects are not obtained, but if it exceeds 5%, the effect is not increased so much, so the amount of Mo is made 3 to 5%.

However, for these W and Mo, in addition to improving the normal cutting performance, in order to improve hot workability, heat treatment hardness, etc.,
It is necessary to regulate as W + 2Mo (hereinafter referred to as W equivalent). That is, as previously proposed by the present applicant, among the cutting performances, especially the continuous cutting performance and the interrupted cutting performance of the tool improve with the increase of the W equivalent, and for that purpose, 18% or more of the W equivalent is required. There, on the other hand, when it exceeds 23.5% M ₆
Carbide mainly containing C is excessively precipitated to deteriorate toughness, and tool damage due to chipping becomes dominant, resulting in deterioration of cutting performance. Therefore, in order to improve such cutting performance, the W equivalent may be set in the range of 18 to 23.5%.
However, in the case of the W equivalent in this range, if it is less than 19%, the heat treatment hardness becomes insufficient, while if it exceeds 21%, the drawing (hot workability) is deteriorated, which is not preferable. Therefore, in the present invention, the W equivalent is in the range of 19 to 21%.

Cr: Cr can improve the hardenability by being present in the substrate and carbonitride, and at the same time, can enhance the temper hardening, the high temperature hardness and the oxidation resistance during the heat treatment. For them, a Cr content of 3% or more is necessary, but even if added in excess of 5%, such effect does not increase so much. Therefore, the Cr amount is set to the range of 3 to 5%.

V: V is an element that can improve toughness, increase hardness by forming carbonitrides, and impart wear resistance. For that purpose, V amount of 4% or more is required, but 5%
The effect does not increase so much even if added over. Therefore, the amount of V is set in the range of 4 to 5%.

Co: Co is an element effective in increasing the heat resistance of the substrate and improving the high temperature hardness by adding it together with W, Mo, V, etc. mentioned above, and for this purpose 4.2% or more is required. From 5.5%, such effect tends to be saturated. However, according to the study of the present inventor, the heat treatment hardness can be increased by adding Co in a larger amount,
In particular, it has been found that the end mill cutting performance can be improved.
For that purpose, Co amount of 7% or more is necessary, while 12%
If added in excess, the hot workability will be significantly reduced. Therefore, in the present invention, the amount of Co is in the range of 7 to 12% in order to sufficiently secure the heat resistance and the high temperature hardness and further improve the end mill cutting performance.

C, N: C is an element necessary for forming a carbide or carbonitride by combining with W, Mo, Cr, etc., while being dissolved in the substrate to contribute to strengthening. The added amount depends on the amounts of carbide and carbonitride forming elements, and in the present invention, the C amount is set to a range of 1.49 to 1.90% in view of the amounts of W, Mo, Cr and the like.

On the other hand, N, which has performance similar to that of C, is an interstitial solid solution atom and facilitates the formation of stable compounds, as in the case of C described above. It is preferable to regulate the amount of N in relation to the regulation of.

However, according to the research conducted by the inventor of the present invention, at that time, the carbon equivalent Ceq Ceq = 0.19 + 0.017 (W + 2Mo) + 0.22V of the following formula, which is specially defined by the W, Mo and V amounts, is added. However, it was found that high hardness and excellent hot workability can be secured by controlling the N content together with the C content so as to satisfy Ceq + 0.10 ≦ C + 12 / 14N ≦ Ceq + 0.25.

That is, the carbon equivalent difference ΔCeq (C + 12 / 14N−Ceq) is 0.10.
%, Carbonitride formation is small and sufficient hardness cannot be obtained. Therefore, ΔCeq must be 0.10% or more, 0.25%
Up to this, excellent hot workability can be obtained. But 0.25
If it exceeds%, the hot workability deteriorates. Therefore, ΔCe
q is in the range of 0.10 to 0.25%.

The steel having the above chemical composition may be accompanied by impurities such as Si, Mn, P, S, etc., but these are allowed as long as the effects of the present invention are not impaired. For example, Si is about 0.4% or less, Mn
Is preferably controlled to about 0.4% or less, and P and S are preferably controlled to about 0.03% or less, respectively. Also,
Al combines with N to become AlN, and the effect of N is diminished. Therefore, it is desirable to control the content to 0.4% or less.

Steel having the above chemical components is a high-speed steel ingot that is sintered by powder metallurgy, and is processed into a round bar, square bar, etc. by hot working such as forging, rolling, and extrusion, and is hardened and tempered. With regard to these manufacturing processes, in the present invention, in particular, the above steel is rapidly solidified by gas atomization (eg, N ₂ gas) into a rapidly solidified steel powder, which is then subjected to hot isostatic pressing (HI
It is necessary to produce a true-density steel ingot (sintered product) by compression molding with P), and at that time, it is necessary to regulate the size of primary carbide of the steel ingot to an average size of 3 μm or less. This is because if the average size of the primary carbides exceeds 3 μm, the drawing (toughness) decreases. The surface of the water atomized powder needs to be oxidized and needs to be reduced, and since the particle shape is irregular and the packing density is low, the deformation during HIP becomes uneven and it is difficult to obtain a sound steel ingot.

Next, examples of the present invention will be described.

(Example) A sample steel having the chemical composition shown in Table 1 was melted in a high-frequency melting furnace, and the resulting molten metal was sprayed with high-pressure N ₂ gas to produce rapidly solidified steel powder.

Then, the steel powder was filled in a mild steel capsule, vacuum-deaerated and hermetically sealed, and compression-molded to a true density by HIP to obtain a sintered high-speed steel billet.

After that, using this as a test material, quenching (1200 ℃ × 3min,
OQ) and tempering (560 ° C. × 1.5 hr, AC, 3 times) were performed to examine the heat treatment hardness, and a high temperature tensile test was performed to examine the drawing and evaluate the hot workability. Further, an end mill cutting test was conducted using a test material that was quenched and tempered. These results are shown in FIGS.

The high temperature tensile test was conducted at a heating rate of 10 ° C / s
After heating to ℃ and holding for 3 minutes, it was cooled to T ℃ (test temperature, 850 ℃ ~ 1150 ℃) at a cooling rate of 5 ℃ / s and held for 2 minutes, high temperature tensile test was carried out, and the drawing was obtained. In addition, about 1200 degreeC, after hold | maintaining for 5 minutes, the high temperature tensile test was implemented.

In addition, the end mill cutting test was carried out from the test material with 2 blades and 10 mm
Create a tool with a φ shape and shape, and work material: SKD61 (HRC40) Cutting speed: 35 m / min Feed: 140 mm / min Cutting fluid: None, repeated cutting with a groove height of 1.5 mm and a thickness of 1 mm The tool life was evaluated by obtaining the cutting length until the flank wear V _B = 0.2 mm.

Maximum heat treatment hardness As is clear from Fig. 1, when ΔCeq is lower than 0.1%, sufficient heat treatment hardness cannot be obtained due to less carbonitride formation, whereas ΔCeq is 0.1 to 0.4%. High hardness is obtained in the range. On the other hand, when ΔCeq is 0.4% or more (Comparative Steel No. A6), retained austenite increases during quenching, the number of tempering increases and the hardness decreases.

Further, from FIG. 2, when W + 2Mo (%) is 19% or more (invention steel Nos. A4 and No. A8), hardness of HRC68 or more is obtained, but when W is too small as 18%, (Comparative Steel No.A
7), it is clear that HRC is 1 point lower than steel No. 4 of the present invention. If W + 2Mo (%) is 22% or more (comparative steel N
o.A9) Hardness does not increase so much.

Hot workability FIG. 6 shows the primary carbide distribution state of the high speed sintered steel of the invention steel No. A3, which has an average size of 1.5 μm and a fine carbide structure.

Regarding the hot workability of the invention steels No.A3 and No.A4 and the comparative steel No.A5, as shown in FIG. 3, ΔCeq was 0.25%.
In the following invention steels No. A3 and No. A4, the drawing shows 75% or more in the hot working temperature range (950 to 1150 ° C.), and it is understood that they have excellent hot workability. On the other hand, when ΔCeq is further increased (Comparative Steel No. A5), the reduction of the drawing as a whole and the reduction of the drawing at 1200 ° C become remarkable.

Further, from FIG. 4, even if ΔCeq is 0.25% or less, W
It can be seen that if + 2Mo (%) is 22% or more (Comparative Steel No. A9), the reduction of the drawing as a whole and the reduction of the drawing at 1200 ° C are remarkable.

End mill cutting performance As is clear from FIG. 5, even if ΔCeq and W + 2Mo (%) are within the range of the present invention, Co is too small in comparison steel No. A12.
Comparative Steel No. A11, which has poor end mill cutting performance and has a small amount of V even though the Co content is sufficient, shows only a slight improvement due to poor wear resistance. On the other hand, the steel No. A4 of the present invention shows extremely excellent cutting performance as compared with the comparative steel. This is because each alloying element was adjusted in a well-balanced manner, and it was shown that it was not achieved by simply individually controlling the Co amount or V amount, or the W + 2Mo amount or ΔCeq.

(Effects of the Invention) As described in detail above, according to the present invention, the chemical composition of the sintered high-speed steel ingot is regulated, in particular, the C and N contents in relation to the W, Mo, and V contents and Co By adjusting the amount and finely controlling the size of the primary carbides by the gas atomization-HIP method, end mill cutting performance is particularly excellent among cutting performance, hot workability is also high, and high hardness sintered high speed steel. A steel ingot can be provided. In particular, it is suitable for manufacturing tools by hot rolling, forging, extrusion and the like having a small diameter of about 20 mmφ, which has been conventionally difficult to perform hot working.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the carbon equivalent difference ΔCeq and the heat treatment hardness, FIG. 2 is a diagram showing the relationship between the W equivalent (W + 2Mo) and the heat treatment hardness, and FIGS. The figure which shows the relationship between a test temperature and a drawing, FIG. 5 is a figure which compares the cutting length of various test materials in an end mill test, and FIG. 6 is a micrograph which shows the metallographic structure of the steel ingot of this invention (x.
400).

Claims (1)

[Claims] 1. In weight% (hereinafter the same), C: 1.49 to 1.90
%, Cr: 3-5%, W: 11.5-13.0%, Mo: 3-5% (however,
W + 2Mo: 19 to 21%), V: 4 to 5% and Co: 7 to 12%, and C and N are Ceq + 0.10 ≤ C + 12/14 N ≤ Ceq + 0.25 (however, Ceq = 0.19 + 0.017). (W + 2Mo) + 0.22V), and the composition is composed of Fe and unavoidable impurities in the balance, and the average size of the primary carbides is 3 μm by the gas atomizing-hot isostatic pressing method.
A high-hardness sintered high-speed steel ingot, which is particularly excellent in end mill cutting performance and hot workability, characterized by: