JPS6014825B2 - Ni-based heat-resistant alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Ni-based heat-resistant alloy, and more particularly to a Ni-based heat-resistant alloy that has excellent creep strength, thermal fatigue strength, and high-temperature sulfide corrosion resistance, and does not contain any expensive elements. Regarding basic heat-resistant alloys.

GASTER PISO blades have creep rupture strength that is sufficient to withstand the centrifugal force generated due to high-temperature and high-speed rotation, as well as sulfide corrosion caused by sulfur contained in combustion gas, and are suitable for starting, stopping, and air-cooling of gas turbine blades. It is also required to have sufficient resistance against thermal fatigue caused by

Among the conventional heat-resistant alloys, excellent alloys having the above-mentioned properties include IN-7 (manufactured by Inco Corporation, composition listed below) and Tokusekki Publication No. 49-13024 (composition listed below).

However, this alloy contains expensive elements such as Ta, Nb, and Mo, and has the problem that its creep rupture strength, thermal fatigue strength, and sulfide corrosion resistance are insufficient. By solving this problem, it does not contain the expensive elements mentioned above, and has a high creep strength and thermal fatigue strength of m-7.
It has better properties than 3-hada C alloy, and also
The object of the present invention is to provide an Nj-based heat-resistant alloy that has better sulfide corrosion resistance than the alloy described in Publication No. 13024.

As a result of research to achieve the above object, the present inventors believe that the sulfide corrosion resistance of Ni-based heat-resistant alloys is generally determined by the Cr content, and that the higher the Cr content, the better the sulfide corrosion resistance. However, as a result of testing a large number of alloys, it was confirmed that Cr improves sulfide corrosion resistance, and it was also determined that Mo is extremely harmful to sulfide corrosion resistance.

Based on this knowledge, the present invention was completed by examining the thermal fatigue strength by high-temperature pull test and high-temperature low-cycle fatigue test without incorporating Mo. The constituent elements and composition of the alloy of the present invention are Co5-18%, Cr14-16%, W9-11%.
, AI2-3%, Ti4-5%, CO. 05-0.2%
, B.O. 001-0.05%, Zro. 001~0.2
%, and the remainder is a Ni-based heat-resistant alloy consisting essentially of Ni. The effects of each constituent element and the reasons for limiting the composition range are as follows.

Co dissolves in the y phase and the y' phase represented by Ni3AI, strengthens these phases as a solid solution, and also strengthens the y phase of the y phase.
'Increase the number of phase precipitation chambers and promote precipitation strengthening.

In order to obtain the above effects in the alloy of the present invention, 5% or more of Co is required, but if it exceeds 18%. Harmful precipitates such as phases are formed, resulting in insufficient creep rupture strength. Therefore, Co is 5
It was limited to ~18%. Cr not only improves sulfide corrosion resistance, but also serves to strengthen the y-phase by forming a large amount of solid solution therein. In order to obtain these effects in the alloy of the present invention, 14% or more of Cr is required, but if it exceeds 16%. The creep rupture strength, high-temperature tensile strength, and high-temperature fatigue strength are all reduced due to the formation of harmful phases such as phase. Therefore, the Cr content is 14 to 16
%. W precipitates into the y-phase and y'-phase and significantly solid-solution strengthens these phases.

In order to obtain this effect, the alloy of the present invention needs to contain W in an amount of 9% or more, but if it exceeds 11%, the sulfide corrosion resistance deteriorates. Harmful precipitates such as phases also occur and reduce high temperature fatigue strength. Therefore, W was limited to 9 to 11%. A
I is an element necessary to form the y' phase, and must be contained in an amount of 2% or more in order to sufficiently strengthen the alloy of the present invention by precipitation. However, if it is contained in an amount of 3% or more, the ductility of the alloy of the present invention decreases, and therefore the high temperature fatigue strength decreases. Therefore, the AI content was limited to 2-3%. Most of Tj solidifies into the y' phase, resulting in significant solid solution strengthening, and increases the amount of the y' phase, contributing to precipitation strengthening.

In order to obtain these effects in the present invention, 4% or less of Ti is required, but if it exceeds 5%, a phase is formed and the creep rupture strength is reduced. Therefore, the amount of Ti was limited to 4 to 5%. C forms three types of carbides: MC type, M Momme C6 type, and Hato C type, and mainly strengthens grain boundaries.

In order to fully obtain this effect with the alloy of the present invention, C must be 0.05%.
The above is necessary, but if it exceeds 0.2%, a large amount of coarse MC type or 3C6 type carbides will crystallize, resulting in a decrease in creep rupture strength. Therefore, the C content should be increased from 0.05% to
It was limited to 0.2%. B segregates at grain boundaries, improves grain boundary strength at high temperatures, and increases creep rupture life and fracture elongation. It also increases high temperature tensile strength. In order to obtain this effect in the alloy of the present invention, 0.001% or more of B is required. However, if the B content exceeds 0.05%, eutectic with a low melting point is generated at the grain boundaries, making it easy to cause melt damage. Therefore, the B content of the alloy of the present invention is 0.001 to 0.05%.
limited to. Like B, Zr is also a grain boundary strengthening element, and 0.
0.001% or more is required, but if it exceeds 0.2%, intermetallic compounds are formed at grain boundaries, resulting in a decrease in creep rupture strength and high temperature tensile strength.

Therefore, the Zr content was limited to 0.001 to 0.2%. Examples Table 1 shows the compositions of Examples of the alloys of the present invention and Comparative Examples of conventional alloys.

For these alloys, a creep rupture test (JIS, Z-2272), a high temperature tensile test (JIS, G-0567), and a high temperature fatigue test were conducted on the coin bank material and the AI coated material.

The results are shown in Table 2 below. Table 1 Table 2 * After coating with AI, it was heat treated at 1120° C. for 2 hours and cooled in air.

*The high temperature fatigue test was conducted on row cattle with 0.25% soil strain and 30 cycles per hour. As this result shows, '1
}In the coin banashi material, the alloy of the present invention and the subordinate alloy are:
Although the creep rupture elongation is almost the same, the rupture life of the alloy of the present invention is very superior. ■As is clear from the results for AI-coated materials, the alloy of the present invention has the following properties: fracture life and fracture elongation in creep rupture tests, fracture strength in high temperature tensile tests, 0.2% yield strength, fracture elongation, and high temperature Compared to conventional alloys, the number of cycles required to break during fatigue testing is greatly improved in all respects.

The alloy described in Tokukan Sho 49-13024 containing Mo contains 75% Na2S04 and 25% as shown in Table 5 of the publication.
Corrosion was carried out for 2 hours in a composition salt of 90% NaCI, resulting in a corrosion loss rate of 9 to 11%.

On the other hand, even if the IM sound is corroded for two hours under the same conditions, the amount of corrosion is extremely small, being on the order of 0.2%.

This is because the protective film of C203 is easily formed. Because it does not contain expensive elements, it can be manufactured at low cost, and it is superior to conventional alloys in all aspects of creep rupture strength, high temperature fatigue strength, and high temperature tensile strength.
It also has excellent sulfide corrosion resistance.

Therefore, we believe that this will contribute to increasing the efficiency of gas turbines in terms of both price and performance.

Claims (1)

[Claims] 1% by weight: Co5-18%, Cr14-16%, W9
~11%, Al2~3%, Ti4~5%, C0.05~
0.2%, B0.001-0.05%, Zr0.001
~0.2%, with the remainder consisting essentially of Ni
Base heat-resistant alloy.