JPH06145856A - Corrosion and wear resistant cobalt-based alloy - Google Patents

Abstract

PURPOSE:To obtain a Co-based alloy having excellent resistance to impact wear by imparting a compsn. consisting of a specified % each of Cr, Mo, B, Si, C, Fe and Ni and the balance Co. CONSTITUTION:A compsn. consisting of 21-29% Cr, 15-24% Mo, 0.5-2% B, >=0.1% Si and the balance essentially Co is imparted to a Co alloy. The resulting objective alloy has high corrosion resistance useful for the constituent members of a kneader and molding machine for plastics. Thus corrosion and wear are suppressed and the damage of such members such as cracking or chipping can be inhibited or prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cobalt (Co) -based alloy having excellent corrosion resistance, wear resistance and the like, which is useful as a material constituting a plastic kneader or a molding machine.

[0002]

2. Description of the Related Art Conventionally, a nitride steel cylinder has been used as a constituent member of a plastic molding machine or a kneading machine for raw material pellets used for plastic molding, for example, a cylindrical cylinder. In recent years, in response to demands for flame retardancy and high strength of plastic molded products, flame retardants such as halogen compounds and hard fibers such as ceramics as reinforcing fibers have been kneaded in a resin. For this reason, the kneading machine for raw material pellets, cylinders, screws, nozzles, etc., which compose molding machines such as injection molding and extrusion molding, are subject to the weight effect of corrosion due to the flame retardant and wear due to the hard fibers, and are thus worn out compared to conventional ones. Severely, the service life tends to be shortened.
As a countermeasure for this, a so-called centrifugal coating method or powder metallurgy method is applied with an alloy having corrosion resistance and wear resistance as a lining material to coat and protect the inner surface of the cylinder with a corrosion- and wear-resistant alloy. As the alloy, for example, Cr: 25 to 32%, W: 4 to 25%,
C: 1 to 3.5%, alloy consisting of balance Co and impurities, or Cr: 6 to 12%, Mo: 25 to 30%, Si: 2
An alloy consisting of ~ 3.5% and the balance Co and impurities is used.

[0003]

Conventional lining alloys have good corrosion resistance to various acids and excellent toughness, but have low hardness and insufficient wear resistance. In particular, there is a problem that cracks and defects are likely to occur during impact wear due to contact between metal members such as a cylinder and a screw in a plastic molding machine. The present invention is
In view of the above, improved corrosion resistance and corrosion resistance effective for improving and stabilizing the durability of cylinders, screws, nozzles, and other related members (such as molds) that constitute a plastic kneader or molding machine. It is intended to provide a Co-based alloy having excellent wear resistance and the like, and particularly excellent in impact wear resistance between metal members.

[0004]

The Co-based alloy of the present invention comprises:
Cr: 21-29%, Mo: 15-24%, B: 0.5
~ 2%, Si: 0.1% or more, less than 0.5%, C: 1%
Hereinafter, it has a chemical composition of Fe: 2% or less, Ni: 2% or less, and the balance being substantially Co.

[0005]

The Co-based alloy of the present invention having the above composition is
It has a complex structure in which molybdenum boride and chromium carbide are relatively finely dispersed in a quaternary alloy phase of Co, Cr, Mo, Si, and has high corrosion resistance, wear resistance, impact wear resistance, high temperature strength, etc. I have it. The solid solution of Cr, Mo, etc. in the matrix provides high corrosion resistance, and the self-lubricating property of the boride dispersed in the matrix enhances the corrosion resistance / impact wear resistance. It is considered that high temperature strength is imparted. Further, the alloy of the present invention has good fluidity in a molten state, can be both spray-milled of molten metal, and cast, and when applied to a constituent member such as a plastic molding machine, the powder is a raw material. Can be freely selected according to the shape of the member and other conveniences.

The reasons for limiting the components of the alloy of the present invention are as follows. Cr: 21-29% Cr forms the alloy phase together with Co, Mo, B, Si and the like. Hardness and corrosion resistance are enhanced by the addition of Cr. The amount of addition is 21% or more because if it is less than that, corrosion resistance becomes insufficient and the effect of improving hardness and toughness becomes insufficient. The effect increases with the addition amount, but
On the other hand, since it lowers the toughness, 29% was made the upper limit.

Mo: 15-24% Mo forms the alloy phase together with Co, Cr, B, Si and the like. The addition of Mo improves hardness and corrosion resistance.
The lower limit of the amount added is set to 15%, because if it is less than that, the effect of improving corrosion resistance is insufficient, and the effect can be enhanced by increasing the amount, but up to 24% is sufficient, Limits the economic efficiency, so the upper limit is set.

B: 0.5-2% B combines with Mo to form a molybdenum boride having self-lubricating properties. The uniform dispersion of molybdenum boride in the matrix enhances its wear resistance and impact wear resistance as a self-lubricating effect. In order to make this effect sufficient, the lower limit of the amount added was set to 0.5%. The effect is increased by increasing the amount added, but if it is too large, the corrosion resistance to oxidizing acids is impaired, so 2% was made the upper limit.

Si: 0.1% or more and less than 0.5% Si lowers the melting point of the alloy and enhances the fluidity of the molten metal, thereby improving its spraying / powdering properties and castability. Improves powder sinterability. To obtain this effect, 0.1% or more is required. However, the addition amount was 0.
Up to 5% is sufficient, and if it is added more than Co-Mo-
This causes embrittlement of the alloy and deterioration of corrosion resistance due to generation and increase of Si phase. Therefore, it is necessary to limit it to less than 0.5%.

C: 1% or less C forms chromium carbides, and as a fine dispersion effect thereof, enhances hardness and wear resistance of the alloy and contributes to improvement of high temperature strength. However, as the amount of C increases, the amount of carbides of Cr and Mo becomes excessive, which causes embrittlement of the alloy, and the corrosion resistance becomes insufficient as the effective amount of Cr and Mo in the matrix decreases. Therefore, the upper limit is 1%. Preferably,
It is 0.04 to 1%.

Co: Balance component Co is a basic element for forming the alloy of the present invention having high corrosion resistance and wear resistance and high toughness in addition to the above elements.

Fe: 2% or less, Ni: 2% or less Fe and Ni are impurity elements, and their mixing causes reduction in corrosion resistance. Therefore, the smaller the mixing amount, the better.
Within the range of up to 2%, the gist of the present invention is not impaired. Therefore, a mixture of 2% or less is allowed.

Cylinders, screens, nozzles and other parts which are constituent members of a plastic kneader / molding machine formed by applying the alloy of the present invention do not necessarily have to have the entire thickness of the alloy of the present invention. A metal block made of structural steel or the like having a required shape corresponding to a target member may be used as a base material, and the alloy of the present invention may be applied as a lining material on the surface of a region where corrosion resistance, wear resistance and the like are required. The alloy of the present invention may be powdered by, for example, a centrifugal atomization method, and a powder obtained by classifying to an appropriate particle size may be used as a sintering raw material to form a sintered alloy layer covering the surface of the base material. Is a uniaxial cylinder or the like, the centrifugal coating method is applied, while the cylindrical base material is rotated about the horizontal axis, the molten alloy of the present invention is injected into the hollow hole, and centrifugal force is applied. Under the action of, an alloy layer may be formed on the inner peripheral surface of the base material cylindrical body. The thickness of the coating alloy layer is, for example, 1 to 10
It may be about mm.

[0014]

【Example】

(I) Manufacture of test material Powdering The molten alloy melted in a high-frequency melting furnace (Ar atmosphere) is pulverized by a centrifugal spraying granulator and classified to obtain a sintering raw material powder. Particle size: 44-250 μm. A can made of sintered steel (internal size: φ60 × 60, mm) is used as a canning material, the above powder is put into it, and the powder is placed in a vacuum and sealed by welding, and then hot isostatic pressing is performed. Attached to. Treatment temperature: 1100 ° C ± 10 ° C, Pressure: 1100kgf
/ Cm ² , time: ² Hr. After the treatment was completed, the canning material was removed by machining, and a disc-shaped sintered alloy block was collected.

Table 1 shows the chemical composition of the test sintered alloys. N
o. Nos. 1 to 3 are invention examples. Nos. 11 to 19 are comparative examples. 11 and No. No. 12 is an example of a conventional material, No. 12 13 to 19 have compositions similar to those of the inventive examples, but the contents of any element (underlined in the table) deviate from the definition of the present invention. Table 2 shows the results of the following tests obtained for each test material.

(II) Material characteristics (i) Hardness Five points on the board surface of the sintered alloy block were measured with a Rockwell C scale. The numerical value in the "hardness" column in the table indicates the average value of 5 points.

(Ii) Abrasion resistance A specific amount of abrasion (mm ² / mm ² / Rikken-Okoshi type rapid abrasion tester
kgf) is measured. The principle of this wear test is to press a rotating disk against a flat test piece and evaluate the wear resistance from the depth, width, etc. of wear marks produced on the surface of the test piece. Test conditions Counterpart material: SUJ-2 (HRc 60) Wear distance: 400 mm Final load: 6.2 kgf Wear speed: 1.05 m / sec

(Iii) Impact wear resistance tester (see FIG. 1) A lathe 1 and a test piece mounting base 2 are provided, and a test piece A is installed on the test piece mounting base 2 via a load cell 3, A metal ring B is eccentrically attached to the first member as a mating member. Lathe 1
The ring (counterpart material) B mounted on the test piece A is rotatably driven, and impact wear is repeatedly applied to the surface of the test piece A under constant torque and load. The pressing load applied to the test piece A by the ring B is detected by the load cell 3 and adjusted to a constant value. After repeatedly subjecting the surface of the test piece to impact wear for a predetermined time, the presence or absence of cracks in the wear mark on the surface of the test piece is determined by a color check. This test method reproduces the phenomenon of cracks and defects caused by contact (impact wear) between metal members such as cylinders and screws in the actual machine operation of plastic kneading and molding, and the test results show the impact wear in the actual machine operation. It enables reliable evaluation of resistance. Test condition Counterpart material ring: Alloy tool steel SKD11 (HRc 60)
(Material equivalent to plastic of plastic molding machine) Load: 150kgf, 200kgf, 260kgf 3
Level Rotational speed: 0.46 m / sec Test time: 200 sec, 3 cycles (After applying impact wear due to the ring on the surface of the test piece for 200 seconds, stop it once and let the test piece fall to room temperature as one cycle Repeated 3 times) A color check was performed on the wear mark after each cycle of impact wear on the surface of the test piece. In Table 2, "I", "II" and "III" in the "Impact Wear Characteristics" column are the color check judgment results after the impact wear of 1, 2 and 3 cycles, respectively, and "○" indicates no crack. , "X" means that a crack has occurred (the cycle after the occurrence of a crack is omitted).

(Iv) Corrosion resistance 24% hydrochloric acid aqueous solution as a non-oxidizing acid, 2 as an oxidizing acid
A 0% sulfuric acid aqueous solution (both of which has a liquid temperature of 50 ° C.) was used as a test solution, and a columnar test piece (10 × 10 × 10, mm) was suspended and immersed in the test solution, and corrosion loss after 24 hours (mg) Was measured.

(V) Microstructure observation Specimen No. The test piece of No. 2 was mirror-finished by rough polishing (using diamond fine particles) and buffing, and then the deposition state of the deposit was observed by a component image of a scanning electron microscope. FIG. 2 shows the component image. In the figure, the white precipitate in the matrix is molybdenum boride, and the black precipitate is chromium carbide. (Molybdenum boride: particle size about 0.3 to 3 μm, area ratio about 25%, chromium carbide: particle size about 0.3 to 1.5 μm, area ratio about 20%). It is observed that the molybdenum boride and chromium carbide have a uniformly finely dispersed structure.

[0021]

[Table 1]

[0022]

[Table 2]

As shown in Table 2, Invention Example No. 1-3
Is a conventional material. 11 and No. Compared with No. 12, the conventional material No. No. 11 has low hardness and abrasion resistance, and poor corrosion resistance to non-oxidizing acid. Also,
Regarding impact and wear characteristics, cracks also occur at a load of 200 kgf or more. No. No. 12 has excellent hardness and wear resistance, and also has good corrosion resistance to non-oxidizing acids, but has low corrosion resistance to oxidizing acids, and cracks have already occurred in the impact wear test under a load of 150 kgf. is doing. On the other hand, Invention Examples 1 to 3 have a high degree of corrosion resistance with respect to both non-oxidizing acids and oxidizing acids, and have high hardness and wear resistance, and despite their high hardness, In the impact wear test, a load of 26
No cracking occurs even under a severe condition of 0 kgf, toughness is excellent, and excellent impact wear resistance is provided.

Further, in Comparative Example No. Nos. 13 to 19 have compositions similar to those of the invention examples, but lack some of corrosion resistance, wear resistance, and impact wear characteristics because some of the constituent elements are excessive or deficient, and do not reach the invention examples. . That is, No. Thirteen
(Excess amount of C) has a composition extremely similar to that of the invention example,
It has high hardness and high wear resistance, and has excellent corrosion resistance to non-oxidizing acids and oxidizing acids, but C
Since the amount is excessive, the impact wear resistance is not sufficient and the load is 20
Cracks are generated under the impact wear condition of 0 kgf. This is because the over-precipitation of carbide caused a decrease in toughness. No. 14 (Si excess) is extremely hard
Although it has high wear resistance, it is poor in corrosion resistance, and its impact wear resistance does not reach that of the invention examples. This is S
This is because a large amount of Co-Mo-Si phase was generated because the amount of i was excessive. No. 15 (Cr shortage, S
i) is insufficient, the impact wear characteristics are relatively good,
The hardness and wear resistance are not sufficient, and the corrosion resistance is also poor. No. No. 16 (excess Cr content, excess Si content) has high hardness and high wear resistance and sufficient corrosion resistance, but has poor toughness and poor impact wear characteristics. No. 17 (M
Insufficient amount of o and excess amount of Si) has excellent hardness and wear resistance, but poor corrosion resistance to non-oxidizing acid. No. 1
No. 8 (excess B amount, excess Si amount) has excellent hardness and wear resistance, but has low corrosion resistance to oxidizing acids and poor impact wear resistance. No. No. 19 (insufficient amount of B, excessive amount of Si) has sufficient hardness and wear resistance, but has low corrosion resistance and insufficient toughness, and the impact wear property remains at a low level. From these facts, it is understood that it is necessary to satisfy the component constitution of the present invention in order to obtain a sufficient improvement effect on various properties such as corrosion resistance, hardness / wear resistance, and impact wear characteristics.

[0025]

Industrial Applicability The cobalt-based alloy of the present invention has a high degree of corrosion resistance and wear resistance useful as a material for the components of a plastic kneader / molding machine. Further, it has high hardness and good toughness, and has outstanding resistance to impact wear caused by contact between metal members, for example, a cylinder and a screw. Therefore, by applying the alloy of the present invention to these members, corrosion and wear are reduced, and damage to the members such as cracks and chips is prevented and prevented, and the effects of improving the service life and reducing maintenance are obtained. To be The alloy of the present invention is not limited to the above-mentioned applications, and is also useful as a material for constituting parts of various apparatuses and devices that require corrosion resistance, wear resistance, toughness and the like.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an impact wear tester.

FIG. 2 is a drawing-substituting micrograph showing a metal structure.

[Explanation of symbols]

1: Lathe, 2: Test piece mount, 3: Load detector, A: Test piece, B: Counterpart material (ring).

Front Page Continuation (72) Inventor Hiroaki Okano 1-1-1 Hama, Amagasaki City, Hyogo Prefecture Kubota Technology Development Laboratory Co., Ltd.

Claims (1)

[Claims] 1. Cr: 21-29%, Mo: 15-24
%, B: 0.5 to 2%, Si: 0.1% or more, 0.5%
Less than, C: 1% or less, Fe: 2% or less, Ni: 2% or less, the balance is a corrosion- and wear-resistant cobalt alloy consisting essentially of Co.