JPS61179825A - Production of sintered co-base alloy having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To produce a sintered Co-base alloy having high strength and excellent corrosion resistance by compounding and mixing powdery Cr23C6, Cr, W, Ni, Fe, Co and C to an adequate compsn. and molding compressively the powder mixture then subjecting the molding to temporarily sintering and sintering. CONSTITUTION:The Cr23C6 powder, Cr powder, W powder, Ni powder and/or Fe powder and Co powder are so compounded as to attain the compsn. range of known stellite in terms of stellite. The C powder is further added and mixed to and with such compounded comps. at such a ratio at which C is incorporated therein at <=1% by 100wt% said compsn. After such mixture is compressively molded, the molding is sintered temporarily at temp. within a 900-1,100 deg. range in 10<-1>-10<-6> Torr vacuum, by which the oxide layer on the surface of the raw material metallic powder is reduced by C and is removed. The temporarily sintered body is in succession sintered at the temp. within a 1,210-1,280 deg.C range in the vacuum. The sintered Co-base alloy which has good dimensional accuracy, has no blowholes and directivity and has high strength and excellent corrosion resistance is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a sintered Co-based alloy that has good dimensional accuracy, no cavities or directionality, high strength, and also has improved corrosion resistance. .

[Conventional technology]

Conventionally, Co-Cr-
W-C series so-called stellite alloy (Cr: 15-334
, W: 5-22 To, one or two of Fe and N1: 1-5%, C: 0-3%, Co: remainder:
It is well known that stellite alloys with a C component of 1.8 or less have particularly high corrosion resistance;
It is also well known that the two are superior.

Casting is a common method for producing Co-based alloys having this composition, and has been widely used up to now.

[Problem that the invention seeks to solve]

However, the casting method has poor dimensional accuracy and therefore requires a high finishing load, resulting in an extremely costly manufacturing method.

Furthermore, in the method for producing a stellite alloy by Hiroaki A, the castability deteriorates as the Cr content and W content increase, and large cavities are often present during casting, making it difficult to produce a sound and strong alloy. It is difficult to obtain, and there are many problems in terms of product yield.

In addition, in the casting method, it is inevitable to crystallize coarse dendrites due to the process of melting and solidification, and these dendrites (
2, the strength of the material becomes significantly lower (especially high Cr,
In the case of high W, the strength was further reduced due to the presence of nests), and the strength was not necessarily highly reliable.

Therefore, an object of the present invention is to establish a method for producing stellite that has good dimensional accuracy, is free from cavities and directionality, has high strength, and has excellent corrosion resistance.

[Means for solving problems]

The present inventors conducted various experiments to determine whether it was possible to produce a Co-based alloy having a composition equivalent to stellite by a sintering method rather than a casting method, and as a result, the following findings were obtained.

(ω As blended raw materials, Cr, Cm l CryCs and Cr23C.

If you select cr*scs among the Cr carbides, ■C
Since the ratio of C to rl2 can be kept low, the C content can be kept low, and as a result, corrosion resistance can be kept high, and the amount of metal Cr added can be small. The amount of Cr evaporated during the sintering process in vacuum can be suppressed to a low level, and a sintered Co-based alloy with a desired composition can be easily obtained. Hardness improves because it easily reacts and forms composite metal carbide.

■ Adding a small amount of C in the form of free C to the blended composition, before main sintering (2. If pre-sintered at a specific degree of vacuum and at a specific temperature,
The free C causes reduction of the oxide layer on the surface of the raw metal powder, further promoting densification through main sintering and sufficiently improving hardness and corrosion resistance.

This invention was made as a result of further experiments based on the above findings.
It was invented by converting Cr23C powder, Cr powder, W powder, one or two of Ni powder and Fe powder, and Co powder into the composition range of known stellite. The ratio of C to 100% by weight of the blended composition is 1 to 10% (after adding and mixing 2C powder and compression molding this mixture, to
The oxide layer on the surface of the raw metal powder is oxidized by pre-sintering at a temperature within the range of 900 to 1100°C in a vacuum of
Reduced and removed by E, and then in vacuum for 12
This is a method for producing a sintered Co-based alloy with excellent corrosion resistance, characterized by sintering at a temperature within the range of 10 to 1280°C.

The present invention will be described in detail below.

■) Knowledge of the blended composition (As mentioned in the (translation) section, in this invention, Cr23C in Cr carbide is used as a blended component.
, is essential.

The composition range of stellite is Cr: 15-33t6, W
: 5 to 22, one or two of Fe and Ni = 1
~5 regrets, C: O~3 regrets, CO: remainder.

The proportion of C added is 1% by weight or less, based on 100% by weight of the blended composition of other blended components.

This means that when the above ratio exceeds 1 weight, the pre-sintering process of this invention is 8! (2, therefore, all for the reduction of oxides (;
This is because it cannot be consumed and is harmful to corrosion resistance.

n) Temporary sintering process As mentioned in the section on findings ①, the temporary sintering process is a process in which the thin oxide layer formed on the surface of the raw metal powder is eliminated by the addition of a small amount of C, and the surface of the raw metal powder is This is the process of cleaning and activating the IO-'
If it is lower than torr, the above effect is not present. On the other hand, 1
When the degree of vacuum is higher than 0"torr, the Cr component evaporates violently in the pre-sintering temperature range of this invention, making it difficult to determine the blending composition to obtain a sintered Co-based alloy with the desired composition. The degree of vacuum in the sintering process is 10-' ~
It was determined to be 10-'torr.

If the preliminary sintering temperature is less than 900°C, the reduction of oxides by C will hardly occur, and the next main sintering process will not be able to achieve sufficient strength and corrosion resistance. On the other hand, if the temperature exceeds 1100°C, the shrinkage due to heating during preliminary sintering of the green compact obtained by compression molding becomes large.

Sufficient (: Before reduction occurs, the pores no longer communicate with the outside, and as a result, reduction is interrupted, so densification is not possible in the next main sintering step. Therefore, the preliminary sintering temperature is set at 900 to 1100°C. The temperature was determined to be within the range of .

The holding time at the above temperature varies depending on the temperature etc., but is 0.5
~2.0 hours is preferred.

■) Main sintering process If the main sintering temperature is less than 1210°C, densification will be insufficient. On the other hand, if it exceeds 1280°C, it will be difficult to maintain the shape due to an increase in the amount of liquid phase, and there will be large pin holes due to gas generation. occurs, and even if the shape can be maintained, the strength will be significantly reduced. Therefore, the main sintering temperature was set at a temperature within the range of 1210 to 1280°C.

Next, the atmosphere in the main sintering step is vacuum, and the degree of vacuum is preferably 10-1 to 10'''' torr.

This is because at a vacuum level lower than 10'' torr, the reduction is insufficient, whereas at a vacuum level exceeding 10'' torr, the vapor pressure of the Cr component becomes high, so that the sintered Co base of the desired composition is This is because it becomes difficult to determine the blending composition for obtaining the alloy.

The holding time at the main sintering temperature varies depending on the composition, temperature, etc., but is preferably 0.5 to 2.0 hours.

The density of the sintered Co-based alloy obtained by the manufacturing method of the present invention explained above is 97 to 98 as a density ratio to the theoretical value of 2.
It has reached its full potential and is fully put to practical use. However, if further internal defect reduction is required, as is required in some decorative parts, the sintered body may be hot isostatically pressed to increase density.

〔Example〕

Example 1 Cr 23C powder with an average particle size of 45 μm and an average particle size of 82
A Cr powder of μm, a W powder of 3.5 μm in average particle size, a Ni powder of 63 μm in average particle size, a Co powder of 43 μm in average particle size, and a C powder of 40 μm in average particle size were prepared, and 20 layers of CruCs powder were prepared.

Cr powder: 111% by weight, W powder: 10.5% by weight, Ni powder: 1.5% by weight, and Co powder = 57% by weight (100% by weight). 2C powder was added so that the ratio of C to weight was 0.3 fi, and wet mixing was carried out in a ball mill for 48 hours. Sufficiently fine and uniform (-The mixed powder was compression-molded at 3t/d using a lubricated mold, then pre-sintered for 1 hour at 1000℃ in a 10-” torr vacuum, and then 10″″-6 Tor
Main sintering was carried out at 1260° C. for 1 hour in a vacuum of 30°C to obtain Invention Alloy 1.

Example 2 In addition to the raw material powder used in Example 1 (:, average particle size 65 μm
Prepare Fe powder of Cr ts CS powder: 200% by weight Cr powder = 1
1 weight%, W powder: 10.5% by weight, Ni powder: 1.5% by weight, 1'e powder: 1.5% by weight, Co powder: 55.5% by weight (more than 100% by weight). C powder was added so that C was 0.3% by weight based on 100% by weight of this blended composition, and the preliminary sintering temperature was set to 10500.
Example except that the main sintering temperature was 1250°C]
In the same manner as (-), the alloy 2 of the present invention was obtained.

Example 3 The raw material powder used in Examples 1 and 2 was prepared and crise
S powder: 100% by weight, near weight of Cr powder, W powder: 18.5% by weight, 1'e powder: 2.0% by weight, Co powder: 62.5% by weight (over 100% by weight). C powder was added so that C was 0.5% by weight relative to 100% by weight of this blended composition, and the preliminary sintering temperature was set at 1030°C.
Invention alloy 3 was obtained in the same manner as in Example 1 except that the single sintering temperature was 1260°C.

Comparative Example A compression molded body having the same composition as the composition for obtaining the invention alloy 1 was pre-sintered under the same manufacturing conditions as the production conditions for obtaining the invention alloy 1, except that free C was not added. , Comparative alloy 1 manufactured by main sintering; degree of vacuum in preliminary sintering step is 2
Comparative alloy 2 was manufactured under the same manufacturing conditions as those for obtaining alloy 1 of the present invention, except that the temperature was 800*°C at a temperature of 800*°C; Comparative alloy 3 manufactured under the same manufacturing conditions as those for obtaining invention alloy 1, except that the temperature was 900°C; preliminary sintering temperature 116
Comparative alloy 4 manufactured under the same manufacturing conditions as those for obtaining the invention alloy 1 except that the temperature was 0°C; conversion of the blending composition to obtain the invention alloy 1 without using Cr carbide. 100% of the above blended composition was added to a blended composition consisting of Cr powder: 29.89&, C powder: 1.21W powder: to, ss, Ni powder: 1.5%, Co powder: 571. The manufacturing conditions are the same as those for obtaining Invention Alloy 1, except that a compression molded body of a blended composition obtained by adding and mixing C powder so that the C powder is 0.3'1 is used. Comparative alloy 5 manufactured with C as Cr carbide
Cr, C, powder = 996, which is the same as the converted composition of the blending composition for obtaining the present invention alloy 1, although F and C are used.
Cr powder: 2296. W powder: 10.54, Ni powder:
1.51% Co powder: A blended composition obtained by adding and mixing C powder to a blended composition consisting of 574 so that C is 0.3% by weight per 100% by weight of the blended composition. Comparative Alloy 6 manufactured under the same conditions as those used to obtain Alloy 1 of the present invention except that a compression molded body was used; Cr and C were used as Cr carbides, but the composition was Same as converted composition 4cr, c, powder: 1
2.14. In a blended composition consisting of Cr powder: 17.7%, W powder: 10.5%, Ni powder: 1.51, and Co powder: 57%, 0.0% C was added to 100% of the blended composition by weight.
Comparative alloy 7 was also manufactured under the same manufacturing conditions as those for obtaining alloy 1 of the present invention, except that a compression molded body of a blended composition obtained by adding and mixing E C powder so that the weight ratio was 3. Manufactured. (* indicates that the manufacturing conditions of the present invention were not met.) Further, a cast alloy having the same composition as the alloy 1 of the present invention was manufactured by a precision casting method (2) to obtain a conventional alloy.

Table 1 shows the density, density ratio, transverse rupture strength, Rockwell C hardness, and corrosion rate of the alloys obtained from Examples 1 to 3 and Comparative Example 2 above.

The corrosion rate is 1-p-y as the corrosion loss after 24-hour immersion in a 24HCt aqueous solution maintained at a temperature of 20°C.

Expressed in (inch pev year).

〔Effect of the invention〕

As can be seen from Table 1, the alloy of the present invention is significantly superior to conventional alloys in terms of transverse rupture strength, Rockwell C hardness, and corrosion rate, especially in terms of transverse rupture strength and corrosion rate. Are better.

This is considered to be because the sintered CO-based alloy obtained by the manufacturing method of the present invention has almost no large cavities or directionality. In addition, dimensional accuracy and shrinkage are uniform, so
The burden of finishing work has been reduced, making it possible to lower manufacturing costs.

It can be seen that this material has excellent corrosion resistance compared to comparative alloys.

Claims (1)

[Claims] Cr_2_3C_6 powder, Cr powder, W powder, one or two of Ni powder and Fe powder, and Co powder are blended so as to have a known composition range of stellite, and this blended composition 100 C powder is added and mixed so that the ratio of C to weight% is 1% by weight or less, and after compression molding this mixture, 10^-^1 to 10^-
Preliminary sintering is performed at a temperature within the range of 900 to 1100°C in a vacuum of ^6 Torr, and the oxide layer on the surface of the raw metal powder is reduced and removed by C, followed by sintering at a temperature of 1210 to 1280°C in a vacuum. A method for producing a sintered Co-based alloy with excellent corrosion resistance, characterized by sintering at a temperature within a range.