JPH04361A - Build-up powder for atomic power plant equipment - Google Patents

Abstract

PURPOSE:To obtain an Ni-based alloy coating layer excellent in resistance to wear and corrosion by using an alloy powder contg. specified amts. of C, Si, Mn, Cr, Mo, Ti, Nb, Fe, Al and the balance Ni and inevitable impurities and specifying the amt. of Co as the impurity. CONSTITUTION:The build-up alloy powder for an atomic power plant device contains, by weight, 0.05-0.15% C, <=0.15% Si, 0.1-1% Mn, 20-30% Cr, <=10% Mo, <=3.5% Ti, 3.5-7% Nb, <=15% Fe, <=2% Al, <=0.3% N and the balance Ni and inevitable inpurities, and the amt. of Co as the impurity is controlled to <=0.02%. One or more kinds among the nitride, carbide and oxide of metallic elements are mixed into the alloy powder by <=70wt.%. Consequently, the sliding parts such as the valve and valve seat in an atomic power plant are padded with the powder, and the resistance to wear and corrosion is improved.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention provides a hardfacing layer for sliding parts such as valves and valve seats used in nuclear power plants to improve their wear resistance and corrosion resistance. It relates to a powder material used to form.

(Prior Art) Many mechanical parts used in sliding parts are required to have both wear resistance and corrosion resistance.

One such example is the valves and valve seats used in the piping of nuclear power plants, such as light water reactors, and these require excellent wear resistance as well as corrosion resistance (particularly stress corrosion cracking resistance). Rather than constructing the entire part from a material with excellent wear and corrosion resistance, it is better to apply a coating layer (overlay) with excellent wear and corrosion resistance to the sliding parts using methods such as thermal spraying or overlay welding. It is preferable to form N) from the viewpoint of reducing material costs. Overlay technology can also be used to repair worn or corroded parts.

Conventionally, Co-Cr-W alloys have been known as corrosion-resistant and wear-resistant alloys, and they are also used as build-up materials for light water reactor parts, such as Stellite 6 (trade name), which contains approximately 28% Cr and C. An alloy consisting of: about 1%, Fe: about 3%, W: about 4%, and the balance Co is used. (In this specification, all percentages related to alloy components mean percentage by weight.) However, since the above-mentioned stellite alloy contains a large amount of Co, when it is used for filling up the valves and valve seats of the piping system of a light water reactor, it is difficult to Contamination by induced radioactivity becomes a problem during periodic inspections.

(Problems to be Solved by the Invention) An object of the present invention is to provide a powder material for forming a hardened build-up layer with excellent wear resistance and corrosion resistance, which can be applied to light water reactor piping valves, etc. The objective is to provide materials that are free from the problem of radioactive contamination.

(Means for solving problems) The gist of the present invention is in (1) and (2) below.

(1) In weight%, C: 0.05-0.15%, Si:
0.15% or less, Mn: 0.1-1%, Cr: 20-3
0%, Mo: 10% or less, Ti: 3.5% or less, N
b: 3.5-7%, Fe: 15% or less, Al:
2% or less, N: 0.3% or less, the remainder consisting of Ni and unavoidable impurities, and CO as an impurity being 0.02% or less.

(2) Add 70% by weight of one or more powders of nitrides, carbides, and oxides of metal elements to the alloy powder described in (1) above.
Composite powder for overlay mixed as below.

The alloy powder in (1) above is preferably a substantially spherical powder obtained by gas atomizing a molten metal having the above composition. In particular, according to the atomization method using nitrogen gas as an atomizing medium, fine nitrides can be dispersed and generated in the alloy powder.

In (2) above, the nitride is, for example, TiN.

5iJn, NbN, CBN, TaN, and carbides include, for example, TiC, SiC, WC, ZrC, MOZC.
and the oxide is, for example, Al goz, T
i(h, ZrO2.

These powders preferably have a particle size of 1 to 20 micron steel.

When using powder materials with these hard particles added,
In order to improve wear resistance, it is essential that hard particles are uniformly dispersed in the built-up layer formed by a method such as thermal spraying. However, when manufacturing powder materials, simply mixing the alloy powder and hard particles that make up the base causes the hard particles to aggregate and float when this composite powder is thermally sprayed or welded to form a metal coating phase. This phenomenon may occur and the target fine dispersion may not be achieved.

In order to avoid this, it is preferable to use a mechanical alloying method to create a structure in which the hard phase is dispersed within the matrix composition of each particle.

The main features of the present invention are that, in order to eliminate the above-mentioned problem of induced radioactivity, the content of Co has been reduced to a level where induced radioactivity does not have a substantial adverse effect;
The composition of the powder material was selected so that a hardened build-up layer with excellent corrosion resistance and wear resistance could be formed without substantially containing any.

Conventional Co-free materials have poor corrosion resistance and wear resistance in the build-up portion even when used as build-up material due to inappropriate chemical component content and lack of hard dispersed phase. In order to improve this point, the composition of the powder material of the present invention is specified as described above.

(Function) Hereinafter, the function of each component of the alloy powder for overlay of the present invention and the reason for limiting the content will be explained.

C: C combines with Cr to form M. Cr carbide called C6 is formed at the grain boundaries and serves to strengthen the grain boundary bonding force of the crystal grains. Further, C combines with Ti and Nb to generate TiC and NbC to form a dispersed hard phase and increase wear resistance. Due to such effects, 0.05% or more is required to provide a predetermined wear resistance to the built-up layer.

However, when C exceeds 0.15%, Nb and Ti become Ni.
T′ phase (NisTi) and γ“ phase (NisTi) formed by combining with
iJb), not only does the strength and hardness of the build-up layer decrease, but also stress corrosion cracking occurs, causing the build-up layer to easily break and fall off. Therefore, the C content is 0.05
~0.15%.

Si:Si has the effect of removing oxygen as an impurity in the alloy, but on the other hand, if it exceeds 0.15%, it impedes the semi-continuous precipitation of M23C6 at grain boundaries and reduces stress corrosion cracking resistance. Therefore, the Si content should be 0.15% or less.

Mn: Mn is M at the grain boundary. It is an element that promotes semi-continuous precipitation of C4, and must be contained in an amount of 0.1% or more, but if the content exceeds 1%, it promotes the precipitation of a brittle phase that impairs ductility. Therefore, the appropriate content of Mn is 0.1 to 1
%.

Cr: Cr is M! The IC & type carbide die carving is an important element that not only contributes to improving the wear resistance as described above, but also improves the stress corrosion cracking resistance of the built-up layer. In order to ensure these effects, it is necessary to contain 20% or more. However, if the content exceeds 30%, when a metal coating phase is formed by a build-up method such as thermal spraying or PTA welding, a brittle phase will be generated and the mechanical properties will be extremely deteriorated. Therefore, the appropriate content of Cr is 20 to 30%.

Mo: Mo improves pitting corrosion resistance and crevice corrosion resistance, but
If the content exceeds 10%, it is M. Suppresses grain boundary precipitation of C4 and deteriorates stress corrosion cracking resistance. Therefore, Mo is 1
The content is preferably up to 0%.

Ti: Ti combines with Ni to precipitate the above-mentioned γ' phase and increase the strength. If the content exceeds 3.5%, ductility deteriorates, η phase precipitates, and stress corrosion cracking resistance decreases. Therefore, the Ti content was set to 3.5% or less.

Nb: Nb combines with Ni to form the above-mentioned T" phase or δ
Precipitate phases to increase strength. In addition, Nb combines with C and precipitates in the crystal grains in the form of NbC, suppressing excessive precipitation of carbides at grain boundaries and improving stress corrosion cracking resistance. To ensure these effects, 3.5%
It is necessary to contain the above amount. However, if the content exceeds 7%, stress corrosion cracking resistance decreases. Therefore, the appropriate range of Nb content is 3.5 to 7%.

N: N disperses hard particles in the built-up layer as TiN or NbN to improve wear resistance. However, N is 0.3%
If it exceeds this, the amount of the γ' phase and γ' phase produced is reduced, and the hardening caused by these is reduced, resulting in a decrease in the hardness of the matrix and deterioration in toughness. In the present invention, N is actively added, but for the above reasons, the upper limit of its content is 0.3
%.

Fe: Fe is an element that improves the stability of the structure during plastic working, but if the content exceeds 15%, it impairs ductility. Therefore, the Fe content is limited to 15% or less.

82: ^2 combines with Ni to precipitate a γ' phase called N1JN to increase strength. However, if it exceeds 2%, stress corrosion cracking resistance decreases.

Co: Co is an impurity that should be minimized in the overlay alloy powder of the present invention. Set the allowable upper limit to 0,
The reason for setting it at 0.2% is to suppress exposure to radiation due to induced radiation below a level that poses no practical problem.

One of the overlay powder materials of the present invention consists of the above-mentioned components, with the remainder being Ni and inevitable impurities.

If overlay is done using such material, TiN will be added to the base.
, NbN, TiC, NbC, or the like is formed, and this layer has excellent corrosion resistance and wear resistance.

However, in order to further improve the wear resistance of the sliding parts of valves and valve seats, hard particles of nitrides, carbides, and oxides are mixed in advance with the above alloy powder, and these hard particles are incorporated into the metal structure. The appropriate amount of such hard particles to be added is 70% or less. If it exceeds 70%, thermal spraying becomes difficult.

As mentioned above, hard particles such as nitrides are preferably produced by mechanical alloying. In other words, by using a ball mill, Viberobot, Attritor (trade name), etc., alloy powder is mixed with NbN, TiN, TiC, NbC. The powder is pulverized and mixed uniformly in a predetermined ratio to form a composite, which is then thermally sprayed or P
This is to prevent separation from occurring when contacting TAfiI.

The powder material of the present invention produced as described above can be obtained by plasma spraying, PTA (Plasma Transfer
A hardened layer with excellent wear resistance and corrosion resistance is formed by overlaying at a predetermined location of the part by edArc)i welding or the like.

Hereinafter, the effects of the present invention will be specifically explained using Examples.

(Example) ■ Wear resistance evaluation test In order to evaluate the sliding wear of valves and valve seats in a light water reactor environment, the Bowden wear test shown in Figure 1 was conducted under the environment and test conditions shown in Table 1. The coefficient of friction was measured using a steel ball manufactured by JIS S [IJ2] as a mating material.

■ Stress corrosion cracking test In order to evaluate the stress corrosion cracking resistance under the light water reactor environment, the U-bend test piece shown in Figure 2 was immersed in the environment shown in Table 2, which simulates the secondary water of a pressurized water reactor. A stress corrosion cracking test was then carried out on each specimen under high stress to investigate the presence or absence of cracks.

■ Table 3 shows the powder manufacturing conditions and properties of the sample materials used in the sample material tests.
The chemical composition is shown in Tables 4-1 to 4-4, and the impurities include P and S at a maximum of 0.01% each.
Cu is contained at a maximum of about 0.07%.

■Metal coating layer formation method Using JIS SUS 304 stainless steel having the composition shown in Table 5 as a base material, a metal coating layer was formed by plasma spraying and PTA welding. The conditions are shown in Tables 6 and 7.
Each is shown in the table.

(Hereafter, margin) Table 1 Measuring method and conditions for friction coefficient Table 5 Base material composition (weight%, Fe: bal,) Table 2 Corrosion resistance test conditions Table 6 Table 3 Conditions for forming metal coating layer by plasma spraying Powder manufacturing conditions and powder properties Table 7 death·.

Conditions for forming a metal coating layer by PTA welding (hereinafter referred to as blank space) ■ Test results The results are shown in FIGS. 3 to 10.

Figure 3 shows data on friction coefficients due to differences in C content of alloy powders. In the C content range of the present invention, the friction coefficients are much lower than those of comparative examples (alloys 1 and 2), and the wear resistance is It can be seen that the quality is good.

Figure 4 shows that the powder of Alloy 3 in Table 4-1 has an average particle size of 5 μm.
NbN was mixed in a ball mill with different amounts of added NbN.
This is the result of investigating the relationship between content and friction coefficient. As shown in the figure, the friction coefficient is further reduced by adding and compositing NbN particles, and it can be seen that this is highly effective in suppressing sliding wear.

Figure 5 shows the relationship between the particle size and friction coefficient of added NbN particles (addition amount: 20% by weight). When hard particles with a minimum diameter of 1 μm or more, preferably 5 μm or more are used, It can be seen that the friction coefficient is further reduced and there is a greater effect in suppressing sliding wear than in the case of adding hard particles containing particles smaller than 5 μm, the results of which are shown in FIG. 4.

Figure 6 shows Tic as an example of adding hard particles other than NbN.
This shows the relationship between TiC content and friction coefficient when composited with TiC particles.
The following fine particles were removed. It can be seen that addition of Tic and compounding further reduce the friction coefficient and are highly effective in suppressing sliding wear. Furthermore, in addition to NbN and TiC, even if particles of a nitrogen compound powder of a metal element, a carbide powder of a metal element, or an oxide powder of a metal element, which generally have a Vickers hardness of 1500 or more, are mixed and dispersed,
The coefficient of friction was reduced, which was effective in suppressing sliding wear.

Figure 7 shows that NbN is added to the powder of alloy 3 of the present invention in Table 4-1.
This table shows the results of measuring the mixing time when the powder (21% by weight) was mixed using a ball mill and the friction coefficient of the part where the powder mixed with the ball mill was welded overlay by the PTA method under the conditions shown in Table 1. be.

From Figure 7, it is effective to reduce sliding wear by reducing the friction coefficient of the weld buildup by uniformly mixing the alloy of the present invention and hard particles using a mechanical alloying method when producing a composite powder. It turns out that there is.

FIG. 8 shows the stress corrosion cracking test results for the sample materials shown in Table 4-2. Cracks occur when the contents of C and Nb are out of the range defined by the present invention.

FIG. 9 shows the stress corrosion cracking test results for the sample materials shown in Table 4-3. It can be seen here that cracks occur when the contents of C and Cr are out of the range defined by the present invention.

FIG. 10 shows the stress corrosion cracking test results for the sample materials in Table 4-4. This figure shows that stress corrosion cracking occurs when the C and Ti contents are out of the range defined by the present invention.

(Effects of the Invention) By using the overlay material of the present invention, a Ni-based alloy coating layer having excellent wear resistance and corrosion resistance can be obtained.

This overlay material can be used for manufacturing and repairing all kinds of mechanical parts, but since it does not substantially contain Co and there is no concern about induced radioactivity, it is used for in-core piping in nuclear power plants such as light water reactors and new converter reactors. It is suitable for building up sliding parts such as valves and valve seats to improve their wear resistance and corrosion resistance.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing an outline of the method for measuring the coefficient of friction, Figure 2 is an explanatory diagram of a test piece for a corrosion test, and Figure 3 is an illustration of the C content of alloy powder and build-up using the powder. Figure 4 shows the relationship between the NbN content of the powder material and the friction coefficient of the built-up layer using that powder. Figure 5 shows the relationship between the NbN content of the powder material and the friction coefficient of the built-up layer using that powder. Figure 6 shows the relationship between the particle size of NbN particles and the friction coefficient of the built-up layer using the powder. FIG. 7 is a diagram showing the relationship between the mixing time when NbN1 powder is mixed with the alloy powder of the present invention using a ball mill and the friction coefficient of a built-up layer using the powder. FIG. 8, FIG. 9, and FIG. 10 are diagrams showing the results of stress corrosion cracking tests.

Claims (2)

[Claims] (1) In weight%, C: 0.05-0.15%, Si: 0
．． 15% or less, Mn: 0.1-1%, Cr: 20-30
%, Mo: 10% or less, Ti: 3.5% or less, Nb: 3
．． 5-7%, Fe: 15% or less, Al: 2% or less, N:
0.3% or less, the remainder consisting of Ni and unavoidable impurities,
An alloy powder for overlaying nuclear power plant equipment containing 0.02% or less of Co as an impurity. (2) A composite powder for overlaying nuclear power plant equipment, which is obtained by mixing the alloy powder according to claim (1) with powder of one or more types of nitrides, carbides, and oxides of metal elements in an amount of 70% by weight or less.