JPS6358220B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention complies with JIS G 4901 or JIS G 4902.
This invention relates to a treatment method for improving the stress corrosion cracking resistance of NCF 750 (commonly known as Inconel X-750) Ni-based alloy. [Prior Art] NCF 750 has conventionally been used in high-temperature, high-pressure water for internal structural materials of light water reactors, such as combustion tube support pins. Support pins in light water reactors are subjected to stress in high-temperature, high-pressure water, and due to the hassle of replacing parts in light water reactors and the serious effects of component damage,
It is required to have excellent stress corrosion cracking resistance. Therefore, the present inventor first developed a treatment method for improving the stress corrosion cracking resistance of Ni-based alloys.
We proposed a processing method in which processing is performed at a temperature of 800 to 1000°C and a processing rate of 10% or more, followed by solution treatment at 800 to 1000°C. (Unexamined Japanese Patent Publication No. 55-141553
[Problem to be solved by the invention] However, because the recrystallization temperature of Ni-based alloys is relatively high, recrystallization due to solution treatment may be incomplete depending on processing conditions, resulting in stress corrosion cracking. It was found that it causes On the other hand, in order to complete recrystallization, the solution treatment temperature was changed from 1135 to
When the temperature was increased to 1165°C, the crystal grains became coarser, resulting in a decrease in strength. Therefore, the present invention has been developed to prevent the crystal grains from becoming coarse in order to prevent a decrease in strength, and which has excellent stress cracking resistance.
The purpose of this invention is to provide a method for treating Ni-based alloys. [Means for Solving the Problems] That is, the present invention has a method of solving the problems by using Ni 70% or more, Cr 14 to 17%,
C0.08% or less, Mn1% or less, Si0.5% or less, S0.015
% or less, Co1% or less, Nb0.7~1.2%, Ti2.25~
2.75%, Al0.4~1%, Fe5~9%, Cu0.5% or less at a temperature of 1150℃ or higher and
A Ni-based product that is heat treated for 1 hour or more, processed in a temperature range of 1100 to 850°C and at a processing rate of 30% or more, and subjected to solution treatment and aging treatment. This is a treatment method for improving the stress corrosion cracking resistance of alloys. [Operation] The present invention complies with JIS G 4901 or JIS G 4902.
It is an improvement of the processing method of NCF 750 material, and the purpose of the present invention is to improve at least the high temperature strength of NCF 750 material,
It is necessary to have basic properties such as ductility and corrosion resistance. Therefore, the raw materials of the present invention meet the requirements specified in JIS.
Limited to materials within the composition range of NCF 750 materials. still,
JIS states that Co may be included as appropriate, but does not specifically specify the composition range.
Commercial INCONEL X-750 equivalent to NCF 750
(Trademark of Huntington Alloys) clearly states that the upper limit of Co content is 1%, so the raw material composition of the present invention was also set to 1% or less Co accordingly. Heat treatment before hot processing is intended to soften the raw material and increase the processing rate in the next process, but below 1150℃, this heating will be insufficient and However, if the time is less than 1 hour, it will be insufficient and the intended purpose cannot be achieved. Therefore, the heat treatment was carried out at a temperature of 1150° C. or higher and for a period of 1 hour or longer. The processing rate was set at a processing rate of 30% or higher to sufficiently refine the crystal grains in the temperature range of 1100 to 850°C so that processing cracks would not occur even at high processing rates. Solution treatment increases the ductility of the Ni-based alloy, and aging treatment aims to strengthen the precipitation, but in the present invention, it is particularly important to complete recrystallization in this step, so if necessary, solution treatment is performed. The treatment temperature is set high to promote recrystallization. According to the present invention, which is performed through the series of steps described above, heat treatment before processing prevents processing cracks during processing, increases the processing rate to refine grains, and increases the solution treatment temperature to recycle. It can make crystals perfect and prevent crystal grains from becoming coarse. By this complete recrystallization and grain refinement, stress corrosion cracking resistance and strength can be improved. The machining rate is defined as follows based on Figure 1: Machining rate (%) = a x b - a' x b' / a x b x 100 [Example] The following is an example. Therefore, the present invention will be specifically explained. Test pieces were prepared by applying the methods No. 1 to No. 4 in Table 2 to NCF 750 material having the chemical components shown in Table 1. In addition, the division by the broken line in the aging treatment column of Table 2 indicates two-stage aging, which is 816°C x 2h + 704°C x 20h. In order to investigate the stress corrosion cracking resistance of these materials, we simulated the high-temperature, high-pressure pure water environment in which the internal structural materials in light water reactors are used, and the conditions were severed to accelerate the test time. A test was conducted in which the test piece was immersed in NaOH while applying stress, and the results shown in Table 2 were obtained. From this result, the heat treatment in this example was performed at 1150°C.
No. 1 and No. 2, which were heated at ℃ for 1 hour, have better stress corrosion cracking resistance than No. 4, which has a lower heating temperature of 1050℃, and No. 3, which has a shorter heating time of 1/12 hour. It can be seen that it is excellent. Furthermore, regarding the processing conditions of the processing treatment, the higher the processing rate, the better the stress corrosion cracking resistance. for example,
No. 2 with a processing rate of 60% has better stress corrosion cracking resistance than No. 1 with a processing rate of 33%. According to the above embodiment, the heat treatment before processing is performed at a temperature of 1150°C or more and for a time of 1 hour or more, and processing is performed at a processing rate of 30% or more in a temperature range of 1100 to 850°C. This shows that it has excellent stress corrosion cracking resistance. In addition, solution treatment was performed at 1065℃ for 1 hour, and aging treatment was performed at 1065℃ for 1 hour.
The one that is heated at 719℃ for 16 hours has particularly excellent stress corrosion cracking resistance. In this case, the solution treatment temperature is high, recrystallization after processing is promoted, and mechanical toughness is also considered to be particularly excellent.

【table】

〔Effect of the invention〕

As described above, according to the method of the present invention, NCF 750
It is possible to obtain a Ni-based alloy with excellent stress corrosion cracking resistance while maintaining the mechanical properties of the material.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams for explaining the machining rate. Figure 1 shows the shape of the workpiece before processing, and Figure 2 shows the shape of the workpiece after processing. Show shape.

Claims (1)

[Claims] 1 Ni70% or more, Cr14-17%, C0.08% or less,
Mn 1% or less, Si 0.5% or less, S 0.015% or less, Co1%
Below, Nb0.7~1.2%, Ti2.25~2.75%, Al0.4~
A Ni-based alloy containing 1% Fe, 5 to 9% Fe, and 0.5% or less Cu is heat treated at a temperature of 1150°C or higher for 1 hour or more, and in a temperature range of 1100 to 850°C and 30°C. A treatment method for improving the stress corrosion cracking resistance of Ni-based alloys, which is characterized by performing processing at a processing rate of % or more, followed by solution treatment and aging treatment.