JPH06240427A - Production of precipitation hardening superalloy - Google Patents

Abstract

PURPOSE:To produce a large-size, thick-walled, precipitation hardening superalloy used, e.g., for gas turbine disk for power generation use without causing deterioration in strength at the time of heat treatment. CONSTITUTION:After solid solution heat treatment, the alloy is cooled down to the prescribed temp. at a cooling velocity equal to or lower than air cooling velocity. Intermediate aging is done in the course of the above cooling or is done by holding at the above temp. for prescribed time. Then rapid cooling is performed, followed by aging treatment. By this method, the occurrence of deterioration in strength can be prevented at the time of heat treatment for a large-size, thick-walled member, and a large-size, thick-walled precipitation hardening superalloy having uniform and sufficient strength 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 method for producing a precipitation-hardening superheat-resistant alloy used for gas turbine disks for power generation, etc. This is a suitable manufacturing method.

[0002]

Various conditions have been set for heat treatment of precipitation hardening type super heat resistant alloys such as Fe-Ni based alloys, but basically, a combination of solution treatment and aging treatment is used. Is done by. In these heat treatments, the precipitation phase generated in the manufacturing process up to the previous stage is once solid-solved by the solution treatment, and then the hardening precipitation phase is uniformly dispersed and precipitated in the matrix by the aging treatment for strengthening. Is. On the other hand, an intermediate aging treatment may be performed between the solution treatment and the aging treatment, and the heat treatment may be performed in three stages.
This intermediate aging treatment is intended to precipitate a stable phase different from the hardened precipitation phase to be precipitated by the aging treatment and effectively utilize it to improve the characteristics.

In such a three-stage heat treatment, cooling after the solution treatment is performed by air cooling or a cooling method having a faster cooling rate (accelerated cooling such as oil cooling or water cooling), and after the intermediate aging treatment and Cooling after the aging treatment is performed by air cooling. The reason is that if the cooling after the solution treatment is delayed, phase precipitation may occur during cooling, which may adversely affect the phase precipitation behavior in the subsequent intermediate aging treatment and aging treatment. Is air cooling, large size
The thick material is subjected to accelerated cooling such as oil cooling or water cooling.

[0004]

However, when the precipitation-hardening superheat-resistant alloy is subjected to the above-described three-step heat treatment, the decrease in strength poses a problem especially in thick-walled members. This is because when a thick member is accelerated and cooled after solution treatment, strain occurs due to rapid cooling, and during the subsequent intermediate aging treatment, a coarse stable phase different from the hardened precipitation phase precipitates in the grains, leading to a decrease in strength. This is because. On the other hand, it is conceivable to suppress the occurrence of strain by air-cooling after the solid solution treatment of the thick member, but the hardening precipitation phase grows and coarsens during the cooling, and especially in the case of a thick member. This leads to a decrease in strength. As described above, the reduction in strength of the thick member is unavoidable even if the cooling rate is selected in the above heat treatment. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a manufacturing method for preventing the reduction in strength and the occurrence of strain in the thick member described above.

[0005]

In other words, in order to solve the above-mentioned problems, a method for producing a precipitation hardening type super heat resistant alloy according to the present invention is such that after solution treatment, it is air cooled or cooled to a predetermined temperature at a slower cooling rate. At the same time, the temperature is maintained for a predetermined time to perform an intermediate aging treatment, followed by quenching and further aging treatment. Further, the second invention is characterized in that after the solution treatment, it is cooled by air or at a slower cooling rate than that, followed by rapid cooling and further aging treatment.

The conditions of the solution treatment, the intermediate aging treatment and the aging treatment in the above method are appropriately selected according to the composition of the super heat resistant alloy except for the cooling rate after the solution treatment and the intermediate aging treatment. If this is shown as an example of Inconel 706 alloy (trademark) which is a Fe-Ni based super heat resistant alloy, it is 925 ° C.
Solution treatment at ˜980 ° C., intermediate aging treatment at a temperature of 800 ° C. to 850 ° C. for 5 hours or less (the temperature and time are selected according to the components and the cooling rate after the solution treatment). In addition, 72
The aging treatment is performed at 0 ° C. for 8 hours and at 620 ° C. for 8 hours. Further, as in the second aspect of the invention, depending on the alloy species and the cooling rate after the solution treatment, the intermediate aging progresses during the cooling, and it is not necessary to maintain at a predetermined temperature.

The cooling after the solution treatment is carried out by air cooling or slow cooling whose cooling rate is slower than that described above. Air cooling includes air cooling as well as blast cooling, and slow cooling is also performed by a method such as furnace cooling.
The cooling after the intermediate aging treatment is performed by blast cooling, accelerated cooling such as water cooling or oil cooling. The present invention is intended for precipitation hardening type super heat resistant alloys, but naturally other than the above Fe-Ni base super heat resistant alloys, for example, Ni base, Fe bases, Co base super heat resistant alloys and the like can also be targeted. The invention of the present application is particularly suitable for large-sized / thick-walled members, but the object of the present invention is not limited to this, and can be applied to thin-walled members, similar to large-sized thick-walled members. The effect of can be obtained.

[0008]

The coarse stable phase precipitated by the accelerated cooling after the solution treatment causes the strength reduction due to the following mechanism. That is, when a relatively thick member is subjected to solution treatment and then accelerated cooling, thermal stress occurs and intragranular slip occurs in the high stress portion. When the intermediate aging treatment is applied in such a state, the stable phase preferentially precipitates and coarsens on the slip surface. Generally, the stable phase that precipitates during the intermediate aging treatment also contains the element that forms the hardening precipitation phase (hereinafter referred to as the hardening element). As a result, the amount of the hardened precipitation phase that precipitates in the final aging treatment is significantly reduced, which causes the strength to decrease.

Therefore, in order not to cause such a decrease in strength, cooling after the solution treatment is performed by air cooling or slow cooling according to the constitution of the present invention so as to prevent intragranular slip before the intermediate aging treatment. It is effective to prevent the generation of thermal stress. However, it has been conventionally considered that when cooling after the solution treatment is performed by air cooling or slow cooling, precipitation / growth coarsening of the hardening precipitation phase occurs during the cooling, which causes other strength reduction. Even though the above method can prevent the strength reduction due to one of the causes, there is a concern that the strength reduction due to the other cause may be caused.

Here, as a result of detailed investigation of the behavior of the hardening precipitation phase, the inventors of the present invention have found that the hardening precipitation phase precipitated during cooling after the solution treatment re-dissolves during the intermediate aging treatment. It was found that the cooling rate after the intermediate aging treatment mainly controls the state of the hardening precipitation phase before the treatment. This is a phenomenon caused by the fact that the intermediate aging temperature is generally higher than the precipitation temperature of the hardening precipitation phase (that is, the aging temperature). Therefore, as one method, it is possible to prevent the decrease in strength due to the coarsening of the hardening precipitation phase by performing cooling after the intermediate aging treatment by accelerating the cooling after the solution treatment by air cooling or slow cooling. It is considered to be.

However, in a member having a very thick wall, precipitation and coarsening of the hardening precipitation phase proceed during air cooling or slow cooling after the solution treatment, and the solid solution does not form a sufficient solid solution even in the intermediate aging treatment, and the strength of the member is increased. It may cause a decrease. Therefore, the present invention further advances the above idea and stops the air cooling after the solution treatment at the intermediate aging treatment temperature and keeps this temperature or gradually cools this temperature range to precipitate a stable phase at the grain boundary. By accelerating and then cooling, even a very thick member is devised so that precipitation and hardening of the hardening precipitation phase do not proceed during cooling. As a result, it is possible to reliably prevent a decrease in strength due to the coarsening of the hardening precipitation phase.

[0012]

EXAMPLE As an example of the present invention, an example applied to Inconel 706 alloy (trademark, the same applies hereinafter), which is a Fe-Ni based precipitation hardening type super heat resistant alloy, is shown below. Inconel 706 alloy is 845 ° C x 3 when creep strength is required.
The standard (AMS standard) stipulates that an intermediate aging treatment (also referred to as stabilization treatment) of heating for a period of time and then air cooling should be performed between the solution treatment and the aging treatment. Therefore, using Inconel 706 alloy having the composition shown in Table 1, 300 mm × 500 mm × 500 m as a thick member
m block is prepared, solution treatment (980 ° C. × 3 hours), intermediate aging treatment (845 ° C. × 3 hours) and aging treatment (720 ° C. × 8 hours heating, cooling at a cooling rate of 50 ° C./hour, 620 ° C. After heating for 8 hours, air-cooling was performed in three steps. Further, as another example, Example 2 in which cooling after the solution treatment is performed at a slower cooling rate to perform intermediate aging during cooling, and the aging treatment is performed by cooling without holding at a predetermined temperature is performed. It was

Among them, in Examples 1 and 2, the cooling after the solution treatment was performed by furnace cooling and the cooling after the intermediate aging treatment was performed by water cooling as shown in the heat pattern of FIG. On the other hand, in Comparative Example, as shown in FIG. 2, cooling after solution treatment is performed by water cooling or air cooling (cooling), and after cooling to room temperature, cooling after intermediate aging treatment is also water cooling or air cooling (cooling). I went there.
The mechanical properties of the surface layer portion and the thickness center portion of each of the obtained test materials were measured at room temperature, and the results are shown in Table 2. Further, 600, 650 for the thickness center of each test material,
A creep rupture test was performed at 700 ° C., and the results are shown in Table 3.

As is clear from Table 2, the test materials 1 and 2 of the examples have excellent strength, whereas the test materials 3 and 4 of the comparative example show a marked decrease in strength. This is due to intragranular precipitation of the above-mentioned coarse stable phase (η phase in Inconel 706 alloy). On the other hand, the test material 6 which has been air-cooled in both the solution treatment and the intermediate aging treatment does not show a significant decrease in strength as compared with the water-cooled material, but has a low strength. This is because precipitation and growth coarsening of the γ'phase, which is a hardening precipitation phase, occurred. The test material 5 in which the cooling after the intermediate aging treatment was water cooling has the highest strength among the comparative examples, but it is lower than the examples, and the effect of air cooling after the solution treatment remains. Further, as is clear from Table 3, the test materials of the examples have a very long creep rupture time and excellent creep characteristics as compared with the test materials of the comparative examples.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

As described above, according to the method for producing a precipitation hardening type super heat resistant alloy of the present invention, after solution treatment, it is cooled to a predetermined temperature by air cooling or a cooling rate slower than that, and in the meantime. Aging is performed, or this temperature is maintained for a predetermined time for intermediate aging treatment, followed by rapid cooling and then aging treatment, so the strength reduction during heat treatment, which was a problem with large thick parts, is reduced. It is possible to prevent and produce a precipitation-hardening superheat-resistant alloy that is uniform and has sufficient strength. Further, the same effect can be obtained with a small and thin member.

[Brief description of drawings]

FIG. 1 is a heat treatment heat pattern diagram of an example of the present invention.

FIG. 2 is a heat treatment heat pattern diagram of a comparative example.

Claims (2)

[Claims] 1. In a method for producing a precipitation hardening type super heat-resistant alloy, after solution treatment, cooling is performed to a predetermined temperature by air cooling or a cooling rate slower than that, and the intermediate aging treatment is performed by maintaining this temperature for a predetermined time. Then, the method for producing a precipitation-hardening superheat-resistant alloy is characterized by performing quenching and then aging treatment. 2. A method for producing a precipitation-hardening superheat-resistant alloy, characterized in that after solution treatment, it is cooled to a predetermined temperature by air cooling or a cooling rate slower than that, then rapidly cooled, and then an aging treatment is performed. For producing precipitation hardening type super heat resistant alloy