JPH0915383A - Abrasion resistive pipe shape part - Google Patents

Abstract

PURPOSE: To improve abrasion resistivity and besides separation resistivity and corrosion resistivity by low temperature ion nitriding of the surface of a pipe shape part of austenitic stainless steel including molybdenum. CONSTITUTION: Austenitic stainless steel including molybdenum and nickel and consisting of chrome of ca. 16 to 20% and iron for the rest, for example SUS316, SUS316L, is used to execute low temperature ion nitriding at ca. 400 to 470 deg.C. As the nitride layer is mainly M4 N (M:Fe, Ni, Cr etc.), production of chrome nitride is suppressed and degradation of corrosion resistivity is prevented. Molybdenum content of 2 to 3% is desired for this. The ratio of nitrogen gas and hydrogen gas in the nitriding is set to be N2 : about 5 to 15vol%, H2 : about 95 to 85vol%. The thickness of the produced nitride layer of about 50μm is enough. By this, a pipe shape part having superior resistivity is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to wear resistant tubular members,
In particular, it relates to wear-resistant tubular members made of austenitic stainless steel such as control rods or neutron instrumentation guide tubes used in high temperature and high pressure water in a nuclear reactor.

[0002]

2. Description of the Related Art In a light water reactor type reactor, there are many structures in which a tubular member is supported along a guide for the purpose of control or instrumentation, but mutual movement is performed by vibrations accompanying the flow of cooling water or movement for the purpose of control. Contact / sliding occurs. In particular, control rods that follow load often have a large number of slides and often need to be replaced due to wear thinning. In order to prevent these abrasions, the outer surface of the contacting pipe is coated with a surface such as hard chrome plating or nickel plating, and a nitriding treatment with good abrasion resistance is also performed.

[0003]

The conventional hard chrome plating as a countermeasure against wear contains fine cracks in the plating layer, and a thin plating layer is inferior in durability. Further, in nickel plating, the nickel eluted in the cooling water is activated and the system is contaminated. In addition, the conventional ion-nitrided stainless steel has a deficiency of chromium in the treated layer matrix with the formation of chromium nitride, resulting in a marked decrease in corrosion resistance.

In view of the above-mentioned state of the art, the present invention solves the above-mentioned problems of the prior art and improves the wear resistance, and at the same time, improves the corrosion resistance and peeling resistance of the member to maintain the function of the equipment. It is an object of the present invention to provide a wear-resistant tubular member that can be used.

[0005]

The present invention comprises (1) a wear-resistant tubular member characterized in that the surface of an austenitic stainless steel tubular member containing molybdenum is subjected to low temperature ion nitriding treatment, and (2) molybdenum. The wear-resistant tubular member according to (1) above, wherein the austenitic stainless steel tubular member has a molybdenum content of 2 to 3%.
And (3) the low temperature ion nitriding treatment is 400 to 400 in a gas atmosphere of N ₂ : 5 to 15% by volume and H ₂ : 95 to 85% by volume.
At a temperature of 470 ° C. and the nitriding layer has a thickness of 10
The wear-resistant tubular member according to (1) or (2) above, wherein the wear-resistant tubular member has a thickness of 50 μm.

[0006]

In general, the ion nitriding of austenitic stainless steel is carried out at a treatment temperature of 500 to 600 ° C. by glow discharge in a dilute gas containing nitrogen gas and hydrogen gas (nitrogen gas: 10 to 80%), and N ⁺ , H ⁺ Ions are made to collide with the member and heated at a high temperature, and reduction cleaning is performed with H ⁺ ions, N ⁺ ions are generated, adsorption on the member surface and accompanying diffusion into the metal to form a nitride layer, Although it achieves an improvement in wear resistance, ion nitriding at a high temperature produces an ε phase (Fe _2-3 N), which lowers the corrosion resistance. Therefore, according to the present invention, low temperature ion nitriding that can suppress the production of ε phase is performed.

However, after low temperature ion nitriding treatment,
Also contains austenite containing Ti or Nb or nothing
In stainless steel, the main nitride layer is chromium nitride,
In such austenitic stainless steels, local cracking occurs.
The ROM is deficient, which causes deterioration of corrosion resistance.
Therefore, the present invention includes molybdenum and nickel
Containing chromium: 16 to 20%, balance: iron
-Stenitic stainless steel, eg SUS316, SU
Low temperature ion nitriding at 400-470 ° C using S316L
The processing is performed. Contains molybdenum and nickel
Austenitic stainless steel with high
When the nitriding process is performed, the nitride layer is mainly M _FourN (M: F
e, Cr, Ni, etc.) and chromium nitride
It was confirmed by X-ray diffraction that the generation was suppressed. this
Therefore, the solid solution of austenitic stainless steel as a base material
The decrease in the amount of aluminum is small, and the decrease in corrosion resistance can be suppressed. this
Such effects are less when the Mo content is less than 1%, and
If it exceeds 4%, it will adversely affect the stabilization of austenite.
You. Of these, the Mo content is preferably 2 to 3%.

It was confirmed that the ratio of nitrogen gas to hydrogen gas in the low temperature ion nitriding treatment should preferably limit the amount of nitrogen gas more than in the normal ion nitriding treatment. In the present invention, the preferable ratio is N ₂ : 5 to 15% by volume, H
₂ : 95 to 85% by volume.

The thickness of the nitrided layer formed in the present invention is 50 μm.
m is enough, 1/1 for regular pipe thickness: 0.5 mm
Equivalent to 0. Even if the tube thickness is 1.3 mm, 130 μm is not necessary. In the present invention, a hardened layer (nitriding layer) is provided to provide wear resistance, and the inside is to maintain the original characteristics of austenitic stainless steel with high toughness, and another reason is that the nitriding thickness This is because if the steel is exposed to a high temperature for a long time in order to make it thick, the ε phase is generated, and the corrosion resistance tends to be lowered.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A control rod cluster assembly as an example of the wear resistant tubular member of the present invention will be described below with reference to FIG. 1, and a low temperature ion nitriding apparatus thereof will be described with reference to FIG.

FIG. 1 shows a control rod cluster assembly of a pressurized water reactor, in which the control rod 1 has an outer tube 3 inside a neutron absorber 4.
Is inserted and pushed by the spring 2 for the purpose of fixing the position.
The control rod cluster assembly is guided by the guide plate 5, and the outer tube 3 and the inner surface of the guide plate 5 contact and slide with each other due to vertical movement of the assembly during control or horizontal vibration during holding. The outer surface of the outer tube 3 is subjected to an ion nitriding treatment in order to prevent wear and thickness reduction due to the sliding. Corrosion resistance is impaired by normal ion nitriding treatment, so it is considered that it is advantageous that the target member is used at high temperature and that the austenite stability is high.
316, the outer tube 3 has an outer diameter of 7 to 25 mm, and a wall thickness of the tube:
A thickness of about 0.4 to 1.3 mm is used, and an ion nitride layer for preventing wear is provided with a depth of 15 to 50 μm.

The ion nitriding process is performed by the apparatus having the structure shown in FIG. The sealed container 8, the exhaust device 15, the gas supply device 13, the voltage generator 14, the temperature measuring device 16, and the peep window 11 are main components, and the sealed container 8 holds the outer tube 3 to be subjected to the nitriding treatment. It is held on the metal fitting 9 via the suspension rod 6. The holding metal fitting 9 is partitioned by the sealed container 8 and the insulator 17. Caps 7 are attached to both ends of the outer tube 3 to support them at the center of the outer tube 3 and prevent nitriding of the end faces.

In the nitriding treatment, after vacuuming to about 5 Pa, glow discharge was performed to clean the surface, and then a mixed gas of nitrogen and hydrogen in the proportions shown in Table 1 was introduced, and the pressure was 130.
Nitriding was performed for 24 hours at Pa. Table 1 shows the results.
Are shown together. The test was C: 0.05%, Ni: 13.
2%, Cr: 16.4%, Mo: 2.34%, Fe: C: for comparison with an outer tube made of SUS316 consisting of the balance, C:
0.049%, Ni: 10.1%, Cr: 18.4%,
Fe: An outer tube made of SUS304 composed of the balance was used.

The corrosion resistance (corrosion area ratio) in Table 1 is represented by the area ratio of red rust (iron oxide) formed on the surface after being immersed in 60 ° C. water containing 2000 ppm of boron for 240 hours.

[0015]

[Table 1]

Test number No. in Table 1 1 to No. 8
Is a comparative example of ion nitriding of an SUS304 outer tube.
The smaller the amount of nitrogen gas in the treated gas and the lower the ion nitriding temperature, the lower the rusting area ratio. However, No. 1 which is an embodiment of the present invention. 9-No. No decrease in the rusted area ratio as observed in No. 11 is observed. In addition, No. 12
(Comparative example) contains 0.2% of CO ₂ in the processing gas, but if a small amount of CO ₂ is contained, the rusted area ratio is not reduced as much as that of the example of the present invention.

No. 1 in Table 1 7 (comparative example) and No. 10
As a result of examining the composition of the ion nitriding layer of (Example), it was found to be as shown in Table 2 below.

[0018]

[Table 2]

[0019]

According to the present invention, wear resistance can be improved by subjecting austenitic stainless steel containing molybdenum to ion nitriding under controlled temperature and atmosphere. Further, if ordinary 304 stainless steel is subjected to ion nitriding treatment by a usual method, the corrosion resistance is greatly deteriorated and the nitrided layer is eluted, so that it cannot withstand use. Therefore, it is possible to supply a tubular member which is improved as described above and can maintain excellent durability as a control rod for a nuclear reactor.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a control rod cluster assembly which is an example of a tubular member to which the present invention is applied.

FIG. 2 is a configuration diagram of an ion nitriding apparatus according to an embodiment of the present invention.

Claims (3)

[Claims] 1. A wear-resistant tubular member obtained by subjecting the surface of an austenitic stainless steel tubular member containing molybdenum to low temperature ion nitriding. 2. The wear-resistant tubular member according to claim 1, wherein the austenitic stainless steel tubular member containing molybdenum has a molybdenum content of 2 to 3%. 3. The low temperature ion nitriding treatment is performed in a gas atmosphere of N ₂ : 5 to 15% by volume and H ₂ : 95 to 85% by volume.
It is performed at a temperature of up to 470 ° C. and the nitriding layer has a thickness of 1
It is 0-50 micrometers, It is characterized by the above-mentioned.
The wear-resistant tubular member described.