JPS6017816B2 - Method for improving stress corrosion cracking resistance of high nickel alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a stress corrosion cracking resistant high nickel alloy, and in particular to a method for improving the stress corrosion cracking resistance of a high nickel alloy. This paper relates to a method for improving the stress corrosion cracking resistance of high nickel alloys by reducing their susceptibility to stress corrosion cracking.

Currently, high Ni alloys such as Inconel 900 (Inco Fertilizer 1600) and Ni-Cr are used in steam generators at nuclear power plants.
-Fe alloy Incoloy 800
) and other high-quality materials are used.

These materials have superior resistance to stress corrosion cracking caused by chlorides compared to general austenitic stainless steel, and their superiority has been proven by their use in numerous steam generators. ing. However, there are still many unknowns about the behavior of these alloys in high-temperature, high-pressure water, especially their stress corrosion cracking properties, and there are still problems that need to be improved in this kind of environment, and so far there have been no efforts to elucidate this phenomenon or to take countermeasures. Not established. The present inventors conducted research on the causes of cracking in high nickel alloys with the aim of completely preventing cracking accidents in the steam generators of nuclear power plants, where accidents are not permitted. discovered that the behavior of sulfur is
Further research revealed that the cracking susceptibility of high-Ni alloys can be significantly reduced by adding elements that easily form compounds with sulfur to the alloy, fixing sulfur to that element, and lowering the activity of sulfur. The present invention was completed based on this finding.

That is, the present invention includes aluminum, which is added unavoidably or actively to improve mechanical properties and corrosion resistance, C: 0.15% or less, Si: 0.50% or less, Mn:
1.00% or less, Ni: 72% or more, Cr: 14-17
%, Fe: 6 to 10%, Cu: 0.50% or less, relative to the amount of sulfur element in the alloy component containing unavoidable impurities, one or more of molybdenum and palladium elements and aluminum element in the component. The total amount is at least 1M in atomic percentage
Molybdenum, palladium element 1 to make it more than the sound
Add seeds or more and cast, then 3 with a total of 0 to 80,000
This relates to a method for improving the stress corrosion cracking resistance of high nickel alloys, which is characterized by heating and holding for 0 minutes or more and then air cooling. Materials for heat exchanger tubes in steam generators,
It is an excellent stress corrosion resistant alloy material. A rectangular test piece with a diameter of 1 inch, a length of 8 ribs, and a thickness of 1 inch was prepared from an alloy having the composition shown in Table 1 below, and this was made into a double U* pent test piece and heated in high-temperature, high-pressure water for about 10 minutes. A stress corrosion cracking test for 1,000 hours was conducted to investigate the effects of added elements and heat treatment. The amount of dissolved oxygen in the high-temperature, high-pressure water was 5 to 1 pb. The results are shown in Table 2 below. Table 2 shows the results of 1,000, 5,000, and 10,000 hour tests of the materials listed in Table 1 that have been subjected to various heat treatments. showed the influence of Table 1' Test material ■ is commercially available Inconel 600, ■ is commercially available Inconel 600 with Mo added, and ■ is commercially available Inconel 6.
00 with Pd added.

Table 2 The reason why all the sample materials in Table 2 are heat treated at i130qo for 30 minutes and cooled with water is to erase the thermal history of the manufacturing process of each sample material and eliminate the effects associated with it.

From the results in Table 2, we can see that those added with elements that easily form compounds with sulfur, such as Mo and Pd, are superior in stress corrosion cracking resistance to conventional high nickel alloys containing N. It will be seen that those heat-treated to produce stable sulfides of these elements have even better stress corrosion cracking resistance. As a result, it will be appreciated that stress corrosion cracking resistance is improved by reducing freely behaving sulfur. At this time, the amount of Mo and Pd elements to be added may be at least an amount sufficient to convert the sulfur element contained in the high nickel alloy (that is, the high nickel alloy below Inconel 600 or simply referred to as an alloy) into a stable sulfide.

Note that high nickel alloys originally contain AI, which acts to generate sulfides and fix free sulfur.
Since Al alone contained in general high nickel alloys is insufficient, Mo and Pd elements are added.
Therefore, the amount of Mo and Pd elements added varies depending on the amount of AI originally contained in the high nickel alloy, and generally, the amount of Mo and Pd added varies depending on the amount of Al originally contained in the high nickel alloy.
(Mo and/or Pd)] element is set so that the amount of the element is at least 1 Pt in terms of atomic percentage. In addition, 10
If it is less than twice that, it takes too much time to fix the sulfur element, which is a practical problem. Also, if more Mo and Pd are added, the price of the alloy will increase, but the purpose of the present invention can be achieved.
No particular upper limit is set. The conditions for the treatment to produce stable sulfides of these elements include heat treatment at 650 to 800 qo for about 30 minutes or more, followed by air cooling.
Sulfides of Mo and Pd are easily generated by holding in this temperature range, and the holding time may be 30 minutes or more, but exceeding 2 hours is not particularly advantageous for the formation of sulfides of these elements. Generally, it is best to hold the powder in this temperature range for 3 to 2 hours. So far Mo
Alternatively, an example in which Pd was added was given and explained to prove its effect, but it will be explained below that a similar effect is obtained when both Mo and Pd are added. The amount of Mo in sample village ■ in Table 1 was set to 0.3%, and Pd
A material to which 0.2% of was added was designated as sample material (2). Using this sample material, the same test pieces as described above were made, and the same tests as described above were conducted. Table 3 shows the results.

Claims (1)

[Claims] 1 Contains aluminum that is added unavoidably or actively to improve mechanical properties and corrosion resistance, C: 0.15
% or less, Si: 0.50% or less, Mn: 1.00% or less, Ni: 72% or more, Cr: 14-17%, Fe: 6-
10%, Cu: 0.50% or less, the total amount of one or more of molybdenum and palladium elements and the aluminum element in the component is an atomic percentage with respect to the amount of sulfur element in the alloy component containing unavoidable impurities. A high nickel alloy, characterized in that it is cast by adding one or more of the elements molybdenum and palladium so that the temperature is at least 10 times or more, and then heated and held at 680 to 800°C for 30 minutes or more, and then air cooled. A method for improving stress corrosion cracking resistance.