JP3049567B2 - Manufacturing method of Ni-base heat-resistant alloy material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a Ni-base heat-resistant alloy material, and more particularly, to a metal structure even when a Ni-base heat-resistant alloy material has a large shape. The present invention relates to a method for manufacturing a Ni-base heat-resistant alloy material for miniaturization.

(Prior Art) Ni-base heat-resistant alloy is a material that maintains excellent mechanical properties even at a high temperature of 650 ° C. or higher, and is used in the field of gas turbines and the like.

In general, this material is prepared by melting a Ni-base heat-resistant alloy having a desired structure by vacuum induction melting or vacuum arc melting, and subjecting the ingot to multiple ingot forging or rolling at a desired forging ratio, usually in multiple rounds. The billet is subjected to finishing such as stamping and forging, and then subjected to a heat treatment.

(Problems to be Solved by the Invention) By the way, Ni-based alloys are generally difficult to process because of their high recrystallization temperatures. For this reason, it is customary to process the ingot while taking the forging ratio into small increments.

As a result, there arises a problem that the forged structure near the surface layer is broken, but the structure is harder to be broken toward the center.

In the case of a billet recrystallized in such a forged state, the surface layer has a fine-grained structure, but the central portion has a coarse-grained structure. Even if this billet is subjected to finish forging, it is very difficult to make the coarse particles in the center part fine.

In particular, when the size of the ingot is large, the above-mentioned tendency becomes noticeable, and sometimes a large coarse particle is generated at the center of the billet.

Such giant grains hardly disappear when they are in a dead zone during stamping and forging, and remain as they are, causing deterioration of mechanical properties such as fatigue and creep strength of the material.

The present invention solves such a problem, and a method for producing a Ni-based heat-resistant alloy material having a microstructure having a uniform microstructure up to the center without the presence of giant grains even in the case of a large-sized material. For the purpose of providing.

(Means / Functions for Solving the Problems) In order to solve the above problems, in the present invention,
C: 0.2% by weight or less, Si: 1% by weight or less, Mn: 2% by weight or less, Cr: 1
3 to 25% by weight, Ti: 5% by weight or less, Al: 5% by weight or less, balance: Ni
Ni-base heat-resistant alloy ingots composed of unavoidable impurities
A step of obtaining a billet by performing hot working at a temperature of 1200 ° C. or more at a working ratio of 30% or more (hereinafter, referred to as a first step); applying heat treatment to the obtained billet to reduce the grain structure of the billet to JIS0551. A step of forming a structure having a uniform grain size, which comprises recrystallized grains having a prescribed grain size number of 1 or more (hereinafter referred to as a second step); and treating the treated product with 1100 to 11
A method for producing a Ni-based heat-resistant alloy material, characterized by comprising a step of heating to 60 ° C. and performing a finish processing at a processing rate of 30% or more (hereinafter, referred to as a third step); .

First, the first step is for destroying the forged structure of the ingot, and at the same time, in the second step which is performed after this step, as described later, although the coarse grains are present, the grain sizes are uniform. The purpose is to grow the tissue in the center of the billet.

In the first step, first, a Ni-based alloy having the above-described structure is melted by an ordinary method, and then an ingot is manufactured.

In the alloy, C is a component that contributes to the improvement of ductility at high temperatures, but if it is contained in an excessively large amount, the hot workability is impaired, so the upper limit is set to 0.2% by weight.

Si is a component that contributes to deoxidation in smelting, but if contained in a large amount, ductility is impaired, so the upper limit is set to 1% by weight.

Mn is a component that contributes to deoxidation during alloy smelting and enhances hot workability.However, if contained in a large amount, there is a problem that hot workability and metallographic stability are impaired. Therefore, its upper limit is set to 2% by weight.

Cr is a component for improving the oxidation resistance and heat resistance of the alloy. If the content is less than 13% by weight, oxidation resistance and heat resistance are impaired, and if it exceeds 25% by weight, hot workability and organizational stability are impaired.
25% by weight.

Both Ti and Al are components that contribute to the precipitation strengthening of the alloy by forming a metal compound Ni ₃ (Ti, Al) with the base Ni, but if they are contained in a large amount, they become hot Since the processability is impaired, the upper limit of the content is 5
% By weight.

The alloy used in the present invention further comprises Nb: 5% by weight or less, W: 10
One or more of the following by weight: Mo: 20% by weight, Co: 30% by weight or less. When these components are contained, the strength at high temperatures can be improved.

Further, B, Zr, Hf, Mg, Y, a rare earth element, and the like may be contained in several percent or less.

Hot working of ingot, temperature 1200 ℃ or more, working rate 30
%.

When hot working that does not satisfy the above conditions is performed, in the second step, it is impossible to grow a structure in which the grain size of recrystallized grains is uniform by recrystallization up to the center of the billet. In addition, it is difficult to form a fine-grained microstructure up to the center even when the finish processing is performed.

The second step is performed for the purpose of subjecting the billet obtained in the first step to a heat treatment to form a structure in which the central portion is coarse but has a uniform particle size.

In addition, the structure in which the grain size of the recrystallized grains is uniform is JISG05
It refers to a structure composed of crystal grains whose crystal grain number specified by 51 is 1 or more.

When the central part has such a structure, when the finishing process is performed in the next third step, each coarse particle is finely broken,
The central portion can have a microstructure in which fine grains are aggregated.

In order to obtain this coarse-grained structure, the billet obtained in the first step is re-heated in a heating furnace, and the center thereof is
Heat treatment is performed at a temperature of 00 ° C. for 30 minutes or more. If the heat treatment is performed such that the temperature of the central portion is lower than 1200 ° C., recrystallization does not sufficiently proceed, and huge coarse particles remain in the central portion.

By performing such a treatment, the recrystallized grains on the surface layer side of the billet also become slightly coarser as the temperature rises, but the larger coarse grains in the center part become finer than that. As a result, the billet has a relatively uniform texture as a whole.

The third step is to subject the treated product obtained in the second step to finish forging or rolling to destroy a structure in which the recrystallized grains have a uniform grain size to obtain a fine grain structure. Done.

The processing temperature at this time is controlled in the range of 1100 ° C to 1600 ° C, and the processing rate is 30% or more.

When the processing temperature is higher than 1160 ° C, even if the fracture of the structure in which the grain size of the recrystallized grains is adjusted by the processing progresses, the process in which the obtained fine grains grow into coarse grains again occurs at the same time. There is no meaning in finishing work for the purpose of destroying a structure in which crystal grains have a uniform grain size. Also,
If the processing temperature is lower than 1100 ° C., inconveniences such as cracks and chips will begin to occur during the finishing process.

Further, when the working ratio is smaller than 30%, the structure in which the grain size of the recrystallized grains is uniform is not sufficiently destroyed, and a good microstructure cannot be obtained.

(Example of the invention) C: 0.02% by weight, Si: 0.02% by weight, Mn: 0.01% by weight, P: 0.003%
% By weight, S: 0.0004% by weight, Cu: 0.01% by weight, Cr: 19.52% by weight, Mo: 4.17% by weight, Co: 13.15% by weight, Ti: 3.12% by weight, Al:
1.47 wt%, Fe: 0.33 wt%, B: 0.003 wt%, Zr: 0.046 wt%, Ni-based alloy consisting of Ni: bal is melted and the ingot (420mm in diameter) is processed at 1200 ° C temperature. A 30% hot forging was performed, and the obtained forged product was kept in a 1200 ° C. soaking furnace for 15 hours.

When the forged product after the heat treatment was cut into slices and the recrystallized structure at the center was observed, the grain size number was 1-2. By the way, when the forged product was soaked at 1160 ° C. for 1 hour and the structure at the center was observed, huge coarse grains having a grain size number of about −1 to −4 were observed, and this was observed in the longitudinal direction. Existed.

After that, the heat-treated billet is processed at a temperature of 1160 ° C.
A 40% finish forging was performed, and the structure at the center was observed.
No giant coarse grains were observed at all, and the grain size number at the center was in the range of 3-5.

(Effect of the Invention) As is clear from the above description, according to the method of the present invention,
A large-sized Ni-based heat-resistant alloy material having no microparticles at the center and having a uniform microstructure having a crystal grain size number of 3 or more can be produced. Therefore, the method of the present invention has great industrial value, for example, as a method for producing a disk material for a large industrial gas turbine.

Claims (3)

(57) [Claims] C: 0.2% by weight or less, Si: 1% by weight or less, Mn: 2% by weight or less, Cr: 13 to 25% by weight, Ti: 5% by weight or less, Al: 5% by weight
The remainder: the process of obtaining a billet by subjecting an ingot of Ni-base heat-resistant alloy consisting of Ni and unavoidable impurities to hot working at a temperature of 1200 ° C or more at a working ratio of 30% or more; heat treatment of the obtained billet , The grain structure of the billet, JISG0551
A process of forming a structure having a uniform grain size, consisting of recrystallized grains having a grain size number of 1 or more specified in the above; and heating the processed product to 1100 to 1160 ° C. and finishing to a working rate of 30% or more. A method for producing a Ni-base heat-resistant alloy material, comprising the steps of: 2. The Ni-base heat-resistant alloy further comprises Nb: 5% by weight.
The Ni-base heat-resistant alloy material according to claim 1, wherein one or more of W: 10% by weight or less, Mo: 2% by weight or less, and Co: 30% by weight or less are contained. Production method. 3. The Ni-base heat-resistant alloy material according to claim 1, wherein said Ni-base heat-resistant alloy contains B, Zr, Hf, Mg, Y, and a rare earth element. Production method.