JPH0718365A - Corrosion resistant and wear resistant chromium base alloy - Google Patents

Abstract

PURPOSE:To develop a Cr base alloy excellent in wear resistance and corrosion resistance in high temp. water by adding and incorporating specified amounts of C, Si and W into a Cr-Ni base alloy having a specified compsn. CONSTITUTION:As a metallic material for a valve seat used for the primary cooling material system of an atomic power plate or like, a corrosion resistant Cr alloy or the like contg., by weight, 34 to 43% Ni is added and incorporated with 0.3 to 2.0% C, 0.9 to 3% Si and 2 to 5% W. Hard carbides are formed in an austenitic matrix or a two phase matrix of austenite and ferrite, the wear resistance, castability and cladding by welding of the alloy are improved by the addition of Si, and hard WC is formed by the addition of W, by which the Cr-Ni base alloy excellent in wear resistance and corrosion resistance in high temp. water in an atomic power plant can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion-resistant and wear-resistant chromium-based alloy, and more particularly to the alloy applied to a primary coolant system such as a nuclear power plant.

[0002]

2. Description of the Prior Art Stellite, which is a cobalt-based alloy (or cobalt-containing alloy) having excellent wear resistance, is used for the valve seats and in-core equipment sliding members used in the primary coolant system in conventional nuclear power plants. It is used in filling materials and casting materials. Although these cobalt-based alloys (or cobalt-containing alloys) have excellent wear resistance and corrosion resistance,
Cobalt as an alloy component is taken into the reactor primary coolant due to wear and corrosion during use. Cobalt in the coolant is converted to radioisotope cobalt-60 when it is irradiated with neutrons while circulating in the core. The cobalt 60 is deposited on the surface of the primary coolant system equipment, which is one of the causes of an increase in radiation exposure of workers during regular plant inspections. On the other hand, in the commercially available wear-resistant nickel-based alloys shown in Table 1 below,
As shown in FIGS. 1 and 2, the corrosion resistance and wear resistance of Stellite No. 6 (TIG ・ ・ ・ Tungsten Inert Gas ar
Inferior to c).

[0003]

[Table 1]

[0004]

As described above, conventionally, the valve seat and the sliding member for the equipment in the furnace are made of Stellite which is a cobalt-based alloy (or cobalt-containing alloy) having excellent wear resistance. However, it is one of the causes of the increased radiation exposure of workers in regular inspection work. Therefore, from the related fields including the electric power industry, a measure for reducing the radiation exposure dose in a nuclear power plant is desired. Therefore, in order to reduce the radiation exposure caused by the valve seat and the sliding members in the reactor equipment, a low-cobalt alloy or a non-cobalt alloy with excellent wear resistance, which replaces the cobalt-based alloy (or alloy containing cobalt), such as stellite, is used. It is necessary to apply the alloy to valve seats and in-core equipment sliding members.

According to the above-mentioned state of the art and the above-mentioned demands, the present invention aims to provide a low-cobalt alloy or a non-cobalt alloy which is superior in corrosion resistance and wear resistance in high temperature water to commercially available nickel-base alloys.

[0006]

The low cobalt alloy or the non-cobalt alloy excellent in corrosion resistance and wear resistance in high temperature water of the present invention is a Cr-based Ni-Ni-based alloy from the viewpoints described below.
This is due to the fact that it is made of a W-Si-C type alloy. To improve the corrosion resistance, increase the chromium content in the matrix or alloy. To improve wear resistance, a large amount of eutectic carbide such as chromium carbide is precipitated in the matrix. That is, the alloy contains a large amount of chromium and contains carbon. To improve wear resistance, it contains tungsten that strengthens the matrix of the alloy. Include silicon in the alloy to improve wear resistance and casting / buildup properties.

From the above, the chromium-based alloy of the present invention has a carbon (C) content of 0.3-2% and a silicon (Si) content of 0.9-3.
%, Tungsten (W) 2 to 5%, nickel (Ni) 3
4 to 43% and unavoidable impurities, and the balance consisting essentially of chromium (Cr), which is basically characterized in that eutectic carbides are precipitated in the austenite matrix or in the austenite and ferrite two-phase matrix. Is.

[0008]

As described above, the chromium-based alloy of the present invention has carbon (C) of 0.3 to 2%, silicon (Si) of 0.9 to 3%, tungsten (W) of 2 to 5%, nickel (Ni). ) 34-4
3% and unavoidable impurities are contained, and the balance is substantially composed of chromium (Cr), and the basic feature is that eutectic carbide is precipitated in the austenite matrix or in the austenite and ferrite two-phase matrix. The reasons for limitation are given for each of the components specified in the present invention. Carbon (C) is effective in solid-solution hardening an austenite matrix and precipitating a hard eutectic alloy carbide, improving the hardness of the alloy and improving wear resistance. However, if the carbon (C) is less than 0.3, the hardness is low and the wear resistance is lowered, which is preferable, and if it is added in excess of 2%, it becomes brittle and cracks may occur during buildup, which is not preferable.
Silicon (Si) is effective for improving the wear resistance of the alloy and for improving the castability and build-up property. However, silicon (S
When i) is less than 0.9, the effect of improving wear resistance is small,
Addition in excess of 3% is not preferable because it tends to form a high hardness and brittle phase. Tungsten (W) is effective in solid solution hardening an alloy and improving wear resistance.
However, if the content of tungsten (W) is less than 2%, the hardness becomes low and the wear resistance decreases, and if it exceeds 5%, the toughness decreases, which is not preferable. Nickel (Ni) is effective in improving the toughness of the chromium-based alloy and also in improving the corrosion resistance, and in consideration of the balance with other components such as chromium (Cr), it is 34 to 43.
%. Chromium (Cr) improves the corrosion resistance of the alloy and combines with carbon (C) to form hard chromium carbide (C
r ₇ C ₃ , Cr ₂₃ C _3, etc.) to improve wear resistance.

[0009]

EXAMPLES Hereinafter, examples carried out in relation to the present invention will be described. The developed alloys of the present invention shown in Table 2 are each 50 k
g was vacuum melted and pulverized by the gas atomizing method. Since the powder is used as overlay welding by the PTA (Plasma Transferrd Arc) method, 70 to 3 is obtained by sieving.
A 50 mesh powder was selected. The commercially available alloys shown in Table 1 and the developed alloys shown in Table 2 were powdered by the PTA method and Stellite No. 6 TIG (Tungste
n Inert Gas arc) method, 304 stainless steel (2
Overlay welding (thickness: about 5 to 7 mm) was performed on 50 liters × 150 W × 40 tmm). Next, test pieces were taken from these built-up metal parts, and a sliding wear test and a general corrosion test described later were carried out.

[0010]

[Table 2]

[Test Method] 〇Sliding wear test A sliding wear test was conducted in high temperature water to evaluate the wear resistance. The sliding wear test was carried out using a moving piece and a fixed piece taken from the same alloy. Table 3 shows the test conditions at this time.
The wear resistance was evaluated by the specific wear amount. ○ General corrosion test A general corrosion test was performed in high temperature water to evaluate the general corrosion resistance. Table 4 shows the corrosion test environment at this time. The general corrosion resistance was evaluated by the corrosion rate.

[0012]

[Table 3]

[0013]

[Table 4]

Of the above tests, the sliding wear test results are shown in FIG.
The general corrosion test results are shown in FIG. As shown in FIGS. 1 and 2, it is understood that the wear resistance and general corrosion resistance of the alloy of the present invention in high temperature water are superior to those of the commercially available nickel-base alloy.

[0015]

Industrial Applicability According to the present invention, a valve seat used in a primary cooling system of a nuclear power plant or a sliding member for in-core equipment, which has a wear resistance in high temperature water and a lower cobalt than a commercially available nickel-based alloy, A product having excellent corrosion resistance was obtained.
Therefore, if the alloy of the present invention is applied to the valve sheet of the primary coolant system or the sliding member of the in-core device in place of stellite, the radiation exposure dose of the worker during the regular inspection of the nuclear power plant can be reduced.

[Brief description of drawings]

FIG. 1 is a chart showing the results of sliding wear test of trial alloys and comparative alloys of Examples of the present invention.

FIG. 2 is a chart showing the results of a general corrosion test of a trial alloy and a comparative alloy of Examples of the present invention.

Claims (1)

[Claims] 1. A weight ratio of carbon (C): 0.3 to 2%,
Silicon (Si): 0.9-3%, Tungsten (W):
2 to 5%, nickel (Ni): 34 to 43%, and unavoidable impurities, and the balance being substantially chromium (Cr).