CN111621728B

CN111621728B - Method for uniformly refining mixed crystal structure of solid solution GH4169 alloy forging

Info

Publication number: CN111621728B
Application number: CN202010622921.7A
Authority: CN
Inventors: 陈明松; 王冠强; 蔺永诚; 马艳永
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2020-07-01
Filing date: 2020-07-01
Publication date: 2021-07-20
Anticipated expiration: 2040-07-01
Also published as: CN111621728A

Abstract

The invention discloses a method for uniformly refining a solid solution state GH4169 alloy forging mixed crystal structure. The method comprises the following steps: (1) carrying out aging treatment on the solid solution GH4169 alloy forging with the mixed crystal structure, wherein the aging temperature is controlled to be 890-910 ℃, and the aging time is controlled to be 9-24 hours; (2) and (3) carrying out continuous cooling annealing treatment on the forged piece after the aging treatment, wherein the initial annealing temperature is controlled to be 1000-1040 ℃, the annealing time is controlled to be 10-30 minutes, and the final annealing temperature is controlled to be 950-990 ℃. The method provided by the invention can economically and efficiently refine the mixed crystal structure of the GH4169 alloy forging in a solid solution state to be above ASTM10 level.

Description

Method for uniformly refining mixed crystal structure of solid solution GH4169 alloy forging

Technical Field

The invention belongs to the technical field of heat treatment of nickel-based superalloy materials, and relates to a method for uniformly refining mixed crystal structure of a solid solution GH4169 alloy forging.

Background

The nickel-based high-temperature alloy is one of the most widely applied alloy materials in the field of aviation at present, wherein the GH4169 alloy is widely applied to manufacturing key parts such as turbine disk casings, compressor disks, blades and the like of aeroengines due to higher strength and plasticity, good corrosion resistance and oxidation resistance and good fatigue performance.

The relation between the performance of the material and the microstructure is inseparable, the mechanical properties such as strength, fatigue performance and the like of the material can be improved to a great extent by refining the microstructure, and the structure is uniformly distributed, so that the whole forge piece can show uniform material properties. Therefore, in order to obtain a high-quality GH4169 alloy material, the microstructure evolution needs to be regulated and controlled. At present, in the thermal deformation process of a forging, the dynamic recrystallization degrees of different strain regions are inconsistent due to the uneven deformation of a blank in the thermoplastic deformation, so that the tissues of all parts of the forging are uneven, and the inside of the forging shows different and different material properties in different regions. Moreover, the uneven deformation in the forging process is difficult to solve by adjusting technological parameters. The existing process for improving the mixed crystal condition of the forging structure is to perform pre-aging before forging deformation to precipitate a delta phase, and regulate and control the recrystallization behavior of the structure through the particle-excited nucleation and pinning effects of the recrystallization behavior of the delta phase relative structure, but still cannot eliminate the uneven structure of mixed crystal. Therefore, the method is a new idea for controlling the static and sub-dynamic recrystallization behaviors of the structure by carrying out heat treatment on the forging so as to achieve the purpose of refining and homogenizing the grain structure. However, no mature process exists at present on how to realize the homogenization and refinement of the uneven structure of the solid solution forging by heat treatment after forging. Therefore, an economical and efficient new method is urgently needed to be invented, and the method can effectively improve the fine grain degree of the forged structure of the solid solution GH4169 alloy and can obviously improve the integral nonuniformity of the structure.

Disclosure of Invention

The invention aims to provide a method for uniformly refining a solid solution GH4169 alloy forging mixed crystal structure, which is characterized in that the method controls the recrystallization behavior of the structure by regulating and controlling heat treatment process parameters in the process of an efficient heat treatment process path, so that the uniformity and the refining degree of the solid solution GH4169 alloy forging mixed crystal structure are remarkably improved, and the problems that the process path economy and the grain refining efficiency are not comprehensively considered in the prior art are solved.

The scheme for solving the problems is as follows:

step 1: carrying out aging treatment on the solid solution GH4169 alloy forging with the mixed crystal structure, wherein the aging temperature is controlled to be 890-910 ℃, and the aging time is controlled to be 9-24 hours;

step 2: carrying out continuous cooling annealing treatment on the forged piece after the aging treatment, wherein the initial annealing temperature is controlled to be 1000-1040 ℃, the annealing time is controlled to be 10-30 minutes, and the final annealing temperature is controlled to be 950-990 ℃;

the solid solution state GH4169 alloy forging in the step 1 means that a forging blank of the alloy forging is subjected to solid solution treatment to eliminate a delta phase, and the process conditions of the solid solution treatment are as follows: the solid solution temperature is 1020-1050 ℃, and the solid solution time is 40-60 minutes;

the thermoplastic forming process of the solid solution GH4169 alloy forging with the mixed crystal structure in the step 1 needs to meet the following conditions: the deformation temperature is controlled between 950 ℃ and 1010 ℃, and the minimum value of the equivalent strain rate needs to be more than 0.0018s^-1The minimum equivalent strain value is greater than 0.2.

The invention has the beneficial effects that: the method fully utilizes the temperature, time, dislocation energy and delta relative action mechanism of static and sub-dynamic recrystallization in the forged structure, realizes the homogenization and refinement of the uneven grain structure of the GH4169 alloy forging under an efficient heat treatment process path, and provides a new method for the jump of the overall structure quality of the GH4169 alloy forging.

The principle is as follows: and a large amount of second phases are separated out through the first low-temperature aging annealing treatment. In the second high-temperature recrystallization annealing process, a large amount of second phases provide nucleation sites for recrystallization, and the densely distributed morphological characteristics of the second phases can also effectively prevent the growth of dynamic recrystallization grains generated in the forging deformation process. In addition, high temperatures can effectively promote recrystallization nucleation, recrystallization growth, and delta phase dissolution by promoting thermal diffusion of atoms. Therefore, the nucleation rate of the grain structure is increased under the high-temperature annealing treatment, the excessive growth of the grains becomes more obvious, and the growth rate is difficult to control, so that the uniform and fine grain structure is difficult to obtain. In view of the fact that the recrystallization rate can be effectively slowed down by reducing the temperature and the growth behavior of the crystal grain structure can be controlled by separating out a small amount of delta phase, the heat preservation process is designed to be a continuous cooling process, the temperature and the influence of the recrystallization behavior of the delta phase relative to the structure can be effectively and cooperatively controlled, and the whole crystal grain structure becomes thin, small and uniform. Finally, the aims of refining the crystal grains of the nickel-based alloy forging and improving the uniformity of the structure are fulfilled.

Drawings

FIG. 1 is a preparation process curve of a GH4169 alloy forging;

FIG. 2 is an initial structure of a GH4169 alloy forging stock after forging;

FIG. 3 temperature vs. time curves for dual annealing aging of GH4169 alloy after forging in example 1;

FIG. 4 the grain structure of GH4169 alloy after two-stage annealing aging treatment in example 1;

FIG. 5 temperature vs. time curve for two-stage annealing aging after forging of GH4169 alloy in example 2;

FIG. 6 the grain structure of GH4169 alloy after two-stage annealing aging treatment in example 2;

Detailed Description

The invention is described in detail below with reference to the drawings and the specific embodiments.

The invention relates to a method for economically and efficiently refining the structure of a GH4169 alloy forging, which takes a typical industrial GH4169 alloy forging blank as an object in all the following embodiments.

Example 1

Step 1: carrying out solution treatment on a GH4169 alloy forging stock at the solution temperature of 1040 +/-5 ℃ for 45 minutes, and then quenching the GH4169 alloy forging stock, wherein the quenching medium is room-temperature water;

step 2: heating the solution treated GH4169 alloy to 950 ℃, preserving heat until the temperature of the forging stock is uniform, and then preserving heat for 0.1s^-1The strain rate of the alloy applies deformation, the deformation is stopped when the deformation reaches 50 percent, the equivalent strain range of the core area is 0.77 to 0.90, and the equivalent strain range of the edge area is 0.22 to 0.34; the structures of the GH4169 alloy forging stock after the solid solution forging process and the forging of the steps 1 and 2 are respectively shown in the figures 1 and 2;

and step 3: carrying out aging treatment on the forged piece obtained in the step 2, wherein the aging temperature is 900 +/-5 ℃, the aging time is 12 hours, and then quenching, wherein a quenching medium is room temperature water;

and 4, step 4: annealing the aged GH4169 forged piece at 990 +/-5 ℃ for 60 minutes, and then quenching the forged piece, wherein a quenching medium is room-temperature water; the process route for implementing the steps 3-4 is shown in FIG. 3, and the structure after heat treatment is shown in FIG. 4;

the results of EBSD observation of the GH4169 alloy before and after the heat treatment process are shown in fig. 2 and 4. FIG. 2 shows the core structure of the forged original forging, the structure morphology is represented by coarse flat-long grains along the deformation elongation direction, a small amount of dynamic recrystallization grains are distributed around the original large grain boundary, the structure is mainly the original large grains, and the average grain size of the deformed mixed crystal structure is statistically 34.84 μm. In FIG. 4, the structure is completely recrystallized, so that the deformed mixed crystal structure of the forging is eliminated, and crystal grains are fine and uniformly distributed under the influence of the delta phase pinning effect. The grain structure of the alloy reaches the grade of ASTM9, and the grain size of the alloy is calculated to be 16.67 μm. The experimental scheme shows that grains can be uniformly refined by carrying out two-stage annealing treatment of firstly carrying out aging precipitation on delta phase and then carrying out recrystallization annealing on the deformed forge piece. The principle is to refine the grains by utilizing the synergistic effect between the recrystallization during annealing and the pinning of the second phase. Compared with other methods for improving the structural uniformity of the forged piece by forging the alloy blank for multiple times at high temperature, the method has the advantages of simplicity and convenience in operation, high efficiency, low cost, easiness in implementation, capability of greatly reducing the requirement on the forging process and the like.

Example 2

step 2: heating the solution treated GH4169 alloy to 950 ℃, preserving heat until the temperature of the forging stock is uniform, and then preserving heat for 0.1s^-1The strain rate of the alloy applies deformation, the deformation is stopped when the deformation reaches 50 percent, the equivalent strain range of the core area is 0.77 to 0.90, and the equivalent strain range of the edge area is 0.22 to 0.34;

and 4, step 4: carrying out continuous cooling annealing treatment on the GH4169 forged piece subjected to aging treatment, wherein the annealing starting temperature is 1020 +/-5 ℃, the total annealing time is 20 minutes, the annealing finishing temperature is 970 +/-5 ℃, and then quenching is carried out, wherein a quenching medium is room-temperature water; the process route for implementing steps 3-4 is shown in FIG. 5, and the structure after heat treatment is shown in FIG. 6;

the results of EBSD observation of the GH4169 alloy before and after the heat treatment process are shown in fig. 2 and 6. The structure in the figure 6 treated by the process in the figure 5 has complete recrystallization behavior, the deformed mixed crystal structure of the forging is eliminated, and crystal grains are fine and uniformly distributed under the influence of the delta phase pinning effect. The grain structure of the material reaches the grade of ASTM11, and the average grain size is counted to be 9.00 mu m. Comparing fig. 2, fig. 4 and fig. 6, it can be seen that the method of the present invention can eliminate the original mixed crystal by complete recrystallization behavior with less incubation time, and the obtained grain structure is finer and more uniform. The method fully utilizes the synergistic effect of promoting recrystallization nucleation at high temperature, slowing the growth rate of recrystallization and the relative recrystallization behavior of delta at low temperature to uniformly refine grains. Compared with the uniform refining method of the two-stage heat preservation and heat treatment in the embodiment 1, the method has the advantages of low cost, high efficiency, good uniform refining effect of crystal grains and the like. Comparative example 1 and example 2 demonstrate the significant advantage of the proposed process.

While the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments, which are exemplary, not restrictive, and any invention that does not exceed the scope of the claims is intended to be protected.

Claims

1. A method for uniformly refining mixed crystal structure of a solid solution state GH4169 alloy forging is characterized in that the method can uniformly refine the mixed crystal structure of the solid solution state GH4169 alloy forging to be above ASTM10 level through a combined process of delta aging and cooling annealing treatment, and the method comprises the following steps: