JP2844688B2 - Method for producing Co-based alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is required for a cutting tool because it can be obtained at a low cost due to a small amount of expensive additional elements and a simple heat treatment. The present invention relates to a method for producing a Co-based alloy having both hardness and toughness.

[Conventional technology and problems of the invention]

Co-based alloys generally called stellite are not used in cutting tools except for some types because of their low hardness.

In other words, stellite is used as a cutting tool.
No.100 (trade name), whose composition is Cr: 26% by weight,
W: 15%, C: 2.5%, Co is limited to high tungsten and high carbon alloys such as Co.

To obtain the appropriateness as a cutting tool material,
As shown in Japanese Patent No. 171, Nb, Ta, V, Zr, etc. are added to components corresponding to stellite No. 100 to improve properties such as toughness, but in any case, these alloys However, since it is extremely difficult to work, it is necessary to use the cast material as it is, and it is difficult to cope with various types of tools.

Therefore, instead of increasing the content ratio of W and C in the stellite-based alloy, it has been attempted to increase the hardness by aging treatment or the like. For example, Japanese Patent Publication Nos. 63-4904-4906 and 63-5546
The publication discloses that the hardness is increased by applying an aging treatment at 700 to 1000 ° C. while applying a stress or after applying a deformation (permanent strain).

However, in these methods, since the content of Fe and Ni is increased to make the component system easily deformable, the Vickers hardness increases from Hv250 to about 300 even after the aging treatment, and cutting tools are required. Hardness has not been obtained.

It has also been reported that aging treatment is performed by adding an additional element (Japanese Patent Publication No. 49-21919, Japanese Patent Publication No. 55-43062).
The alloy disclosed in the former publication has a hardness slightly higher than Hv300 and cannot be used for cutting tools. According to the method disclosed in the latter publication, the hardness is sufficiently increased,
Because the toughness decreases, the application range as a cutting tool is narrow,
Cost is high.

As described above, Co-based alloys that can be used as cutting tools are limited to Stellite No. 100 or its improved products. It is inferior to the system improvement material. For example, compared to stellite, high-speed steel has the same hardness and excellent toughness, and cemented carbide has excellent hardness and toughness, so the demand for Co-based alloys as cutting tool materials is increasing. It tends to be sluggish.

Therefore, for a Co-based alloy, it is desired to improve hardness and toughness or to improve one property while maintaining one property in order to give a superior difference to other alloy-based materials. However, since the hardness and the toughness are contradictory properties, the actual situation has not been satisfied with the demand.

An object of the present invention is to provide a method for producing a Co-based alloy, which is effective as a solution to such a problem.

[Means for solving the problem]

The alloy produced by the method of the present invention has a weight ratio of Cr: 26.0
~ 33.0%, W: 3.0 ~ 13.0%, C: 0.9 ~ 2.0%, Fe + Ni: 5%
It contains the following, with the balance being substantially the composition of Co.

When this alloy is made by a conventional method, it has an incomplete hardness and cannot be cold worked.

For this reason, according to the present invention, cold working is firstly enabled through a specific processing step, and the properties usable as a cutting tool are imparted by the cold working, solution treatment and aging treatment. The steps for that are as follows.

(1) The particle size of precipitated carbide in the material alloy is controlled to 5 μm or less by a method such as rapid solidification.

(2) Next, the material alloy is solutionized at a temperature of 1000 ° C. or more and a melting point or less.

(3) After that, cold working with a reduction rate of 10% or more is performed.

(4) After that, it is kept in a heating atmosphere at 550 to 650 ° C. for 30 minutes or more and 2 hours or less to effect aging.

When a cutting tool is made from the alloy obtained through the above steps, it is desirable to perform rough grinding and cutting between the steps (3) and (4) to obtain the target tool shape.

[Action]

Work hardening and age hardening are phenomena commonly found in metals. According to the present invention, the cold working for work hardening, which could not be expected with a composition having a small amount of Fe + Ni, is performed in the above (1),
This is made possible by the process (2), and since the accumulated strain at the surface portion is larger than that at the center portion in the cold working, the surface portion hardness is higher than the center portion hardness. Further, when this is subjected to aging treatment, the hardness of the surface portion is further increased, and the required characteristics of the cutting tool such as high hardness in the surface portion serving as the cutting portion, low hardness in the center portion and high toughness are satisfied.

In order to achieve the purpose of high hardness, after cold working,
It is important to perform aging treatment at a lower temperature than before, and this process is reversed, or the aging temperature is
° C), the desired hardness cannot be obtained.

Hereinafter, the reasons for limiting the component content, the processing conditions, and the like will be summarized and described.

(A) Ingredients: Cr, W: form carbides or dissolve in the matrix to increase hardness. Cr <26%, W <3 in weight ratio (the same applies hereinafter)
%, The effect is insufficient, and if Cr> 33%, W> 12%, it becomes too hard and cold working is difficult.

C: Form carbides of Cr and W and increase hardness. When the content of C is 0.9% or less, the effect of addition is small, and when it exceeds 2%, the alloy hardness becomes excessive and cold working is hindered.

Fe + Ni: included as an impurity. Although it is an unnecessary element, the production cost increases when the content is forcibly reduced. On the other hand, when these amounts are 5% or more, the hardness is not sufficiently increased.

Co: Matrix, excellent in high-temperature strength.

(B) Controlling the carbide particle size to 5 μm or less As a method for this, the following methods are available, and any of them may be used.

1) Hot isostatic pressing of quenched powder (HIP method).

2) Hot extrusion of quenched powder.

3) Casting into a mold with a large cooling capacity such as a copper mold.

4) A drop casting method in which the molten metal is sprayed with a gas, and the spray particles are continuously adhered to a receiving pan while solidifying and solidified on the receiving pan.

This carbide is very hard compared to the matrix Co,
Since the alloy is difficult to deform when deformed, if the particle size is large, separation and cracking occur at the interface with the matrix.

However, if the particle size is 5 μm or less, the matrix is easily deformed and absorbs the entire amount of deformation, so that no crack occurs.

(C) When the solution temperature is 1000 ° C or less, sufficient solution does not proceed, and cold drawing of 10% or more cannot be performed.

(D) Amount of cold work If the surface reduction rate is 10% or less, the hardness of the cutting tool will not reach the required hardness after any aging treatment.

(E) Aging treatment When the temperature is 550 ° C or lower and 650 ° C or higher, the hardness is not sufficiently increased. The same applies when the processing time is 30 minutes or less and 2 hours or more.

For example, when a normal processing temperature of 800 ° C. is used, the hardness is lower than that after cold working.

The reason that it is desirable to perform rough grinding and cutting before aging treatment when turning into a tool is that it is easy to work before it is not sufficiently hard before aging, and it is necessary to process some finishing allowance in the final process. This is due to the fact that large deformation at the time of aging treatment is prevented by pre-roughing.

〔Example〕

Test materials having the compositions shown in Table 1 were prepared, and the following experiments 1 to 5 were performed.

(Experiment 1) Powder HIP method (temperature 1150 ° C, molding pressure 1000kg / cm ² ), powder extrusion method (heating temperature 1200 ° C, extrusion ratio 12), droplet casting, using the materials of the components in Table 1 Method (bath temperature 14
An ingot of about 3 kg was made at 70 ° C. and a gas pressure of 15 kg / cm ² ).

Then, each ingot is hot rolled to 7m
When processed to a round bar of m, the material became too hard and could not be processed.

In each of the components, the HIP material, the extruded material, and the cast material had a substantially uniform size of precipitated carbide of 5 μm or less. Therefore, in the subsequent experiments, only the HIP material was used. Before cold working, solution treatment was performed at 1150 ° C.

As a result, any material alloy that did not solution,
Cracks were generated at the area reduction rate of less than 10% at the time of cold working in the next step, but no trouble was found in the case of solution.

(Experiment 2) 600% of the HIP that had been cold worked 20% in Experiment 1
It was subjected to a heat treatment at 30 ° C. for 30 minutes. Table 2 shows the properties of the alloy thus obtained. In the table, is a normal molten cast material.

As can be seen from the table, the material that satisfies the composition of the present invention has a high surface hardness and also has excellent other properties, and can be used as a cutting tool.

(Experiment 3) Annealed material, work hardened material after solution heat treatment (processing amount 5%, 10%
%, 20% and 40%) were examined for aging characteristics. The results are shown in FIG.

From now on, processing amount 10% or more, aging treatment temperature 550 ~ 650 ℃
It can be seen that the surface of the alloy shows high hardness.

(Experiment 4) A 20% cold-worked material was aged at 600 ° C., and the change in surface hardness with time was examined. FIG. 2 shows the result. From this result, it can be seen that the surface portion of the alloy becomes sufficiently hard between 30 minutes and 2 hours.

(Experiment 5) After the solution treatment, the material was cold-worked from 8 mm to 7 mm in diameter (23.4% reduction in area), and then subjected to rough groove processing for forming an end mill. Then, after aging treatment at 600 ° C. for 40 minutes, finishing was performed to obtain a solid end mill.

When comparing the performance of this prototype end mill with the conventional Co-based alloy end mill by cutting the same work material, the prototype end mill made of the alloy of the present invention can perform very good cutting, cutting performance, durability Both were superior to conventional end mills.

Furthermore, in comparison with the high-speed steel SKH51 end mill,
1.5 times cutting speed was possible.

〔effect〕

As described above, the present invention measures the hardness of the surface by work hardening, which was not previously expected with alloys of the same composition, by controlling the grain size of precipitated carbides in the material alloy and by solution treatment, and thereafter, Since the aging treatment was performed at a temperature that was not considered to be hardened, the surface hardness was further increased,
An alloy having ideal properties as a cutting tool, that is, a Co-based alloy having high hardness on the surface and high toughness on the inside can be manufactured and provided at low cost.

Further, according to this method, by performing rough processing before aging treatment, processing restrictions due to hardness can be relaxed, and thus, the obtained alloy can be used for various types of cutting tools.

The alloy obtained by the method of the present invention is most suitable for a cutting tool, but can also be used for a mechanical element or a structural material requiring similar characteristics. For example, it is effective as a material for a rotating shaft, a sliding shaft, and the like that require reliability of wear resistance and breakage resistance.

[Brief description of the drawings]

FIG. 1 is a graph showing the aging characteristics (the relationship between the pre-processed amount and the aging temperature and the hardness) of one of the test materials used in the effect confirmation experiment, and FIG. Aging characteristics (600
4 is a graph showing the relationship between aging time and hardness at ° C.).

────────────────────────────────────────────────── ⁶ Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C22F 1/00 691 C22F 1/00 691B 691C 694 694A (56) References JP-A-62-202066 (JP, A) 63-4905 (JP, B2) JP 55-4828 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22F 1/10 C22C 19/07

Claims (2)

(57) [Claims] (1) Cr: 26.0-33.0%, W: 3.0-13.0 by weight ratio
%, C: 0.9-2.0%, Fe + Ni: 5% or less, with the balance being the following: 1)
To 4 μm or less by any one of the methods described in (1) to (4), the material alloy is solution-treated at a temperature of 1000 ° C. or higher and a melting point or lower, and then subjected to cold working at a surface reduction rate of 10% or higher. Aging treatment for 30 minutes or more and 2 hours or less in a heating atmosphere. 1) Hot isostatic pressing of quenched powder (HIP method). 2) Hot extrusion of quenched powder. 3) Casting into a mold with a large cooling capacity such as a copper mold. 4) A drop casting method in which the molten metal is sprayed with a gas, and the spray particles are continuously adhered to a receiving pan while solidifying and solidified on the receiving pan. 2. The method for producing a Co-based alloy according to claim 1, wherein after the cold working and before the aging treatment, a rough working for forming a target tool is performed.