Vacuum solution and aging treatment process for improving high-temperature plasticity of GH4738 rings

Abstract

A vacuum solution and aging treatment process for improving high-temperature plasticity of GH4738 rings includes: heating a GH4738 ring to 1020° C. to 1030° C. in a vacuum environment; injecting nitrogen; subjecting the GH4738 ring to aging treatment at 740° C. to 750° C.; and taking out and air-cooling the GH4738 ring. The method realizes the uniform distribution of the intragranular γ′ precipitates and the intergranular M.sub.23C.sub.6 carbides in the GH4738 ring after heat treatment. The elongation and area reduction of the alloy ring stretched at 540° C. after heat treatment are 30% and 34% respectively, which are 25% and 36% higher than those before process optimization respectively; and that at 760° C. are 49% and 70% respectively, which are 32% and 27% higher than those before process optimization respectively. The index requirements can be fully met. This process is applicable to GH4738 rings, which have a high requirement on high-temperature plasticity after heat treatment.

Claims

1. A vacuum solution and aging treatment process for improving a high-temperature plasticity of GH4738 rings of 540° C. to 760° C., comprising the following steps: step 1: putting a formed GH4738 ring into a vacuum furnace and vacuumizing the vacuum furnace to lower than 4×10.sup.−2 Pa to obtain an alloy; step 2: heating the alloy treated in the step 1 to a solution temperature of 1020° C. to 1030° C., keeping the solution temperature for 30 minutes to 60 minutes, and then injecting nitrogen to cool the alloy to a room temperature; step 3: putting the alloy treated in the step 2 into a furnace, heating the alloy to an aging temperature of 740° C. to 750° C. along with the furnace, and after the aging temperature is kept for 30 hours to 35 hours, taking out the alloy and cooling the alloy to the room temperature; wherein in the step 2, a cooling rate of the alloy is controlled in a range from 40° C/min to 80° C/min when the nitrogen is injected for cooling.

2. The vacuum solution and aging treatment process for improving the high-temperature plasticity of the GH4738 rings of 540° C. to 760° C. according to claim 1, wherein in the step 2 and the step 3, the alloy is heated to a target temperature along with the furnace at a rate of 5° C/min to 10° C/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the distribution of γ′ precipitates in the GH4738 superalloy treated by vacuum solution and aging according to Example 1.

(2) FIG. 2 is the distribution of γ′ precipitates in the GH4738 superalloy treated by vacuum solution and conventional two stage aging according to Comparative Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) The present invention will be further illustrated in detail with reference to the following specific examples, which are illustrative rather than limitative for the present invention. The alloys in the examples and the comparative examples are specifically GH4738 rings with sectional dimensions of 40*20 mm made from the same batch of materials, the components of which are shown in the following table.

(4) TABLE-US-00001 TABLE 1 Components of GH4738 Superalloy Used in Examples and Comparative Examples Component C Cr Co Mo Ti A1 Zr B Ni Content 0.05 18.90 13.55 3.80 3.20 1.55 0.05 0.007 The wt. % balance

(5) Example 1

(6) After being hot-wrought, the GH4738 ring was first machined to achieve the precise control of final size and remove the oxide layer formed in the process of hot working. The pretreated GH4738 ring was put into a vacuum furnace, and the furnace was vacuumized to lower than 4×10.sup.−2 Pa.

(7) The alloy was heated to a solution temperature of 1030° C. along with the furnace at a rate of 8° C/min, with the temperature being kept for 60 minutes, and nitrogen was then injected to cool the alloy to room temperature at a rate of 50° C/min.

(8) The alloy was heated to an aging temperature of 750° C. along with the furnace at a rate of 10° C/min, and after the temperature was kept for 35 hours, the alloy was taken out and air-cooled to room temperature.

(9) Comparative Example 1

(10) After being hot-wrought, the GH4738 ring was first machined to achieve the precise control of final size and remove the oxide layer formed in the process of hot working. The pretreated GH4738 ring was put into a vacuum furnace, and the furnace was vacuumized to lower than 2×10.sup.−2 Pa.

(11) The alloy was heated to a solution temperature of 1030° C. along with the furnace at a rate of 8° C/min, with the temperature being kept for 30 minutes, and afterwards, the alloy was first cooled to 900° C. in the furnace and then to less than 80° C. at a rate of 30° C/min.

(12) The alloy was heated to a stabilization treatment temperature of 845° C. along with the furnace at a rate of 10° C/min, and after the temperature was kept for 4 hours, the alloy was then taken out and air-cooled to room temperature; the alloy was heated to an aging treatment temperature of 760° C. along with the furnace at a rate of 10° C/min, and after the temperature was kept for 16 hours, the alloy was taken out and air-cooled to room temperature.

(13) TABLE-US-00002 TABLE 2 Test Result of Tensile Property of Alloy in Example 1 Tensile Strength Yield Strength Elongation at Reduction of MPa MPa Break % Area % 540° C. 760° C. 540° C. 760° C. 540° C. 760° C. 540° C. 760° C. Example 1 1211 850 755 689 30 49 34 70 Comparative 1202 853 748 695 24 37 25 55 example 1

(14) Example 2

(15) After being hot-wrought, the GH4738 ring was first machined to achieve the precise control of final size and remove the oxide layer formed in the process of hot working. The pretreated GH4738 ring was put into a vacuum furnace, and the furnace was vacuumized to lower than 10.sup.−3 Pa.

(16) The alloy was heated to a solution temperature of 1020° C. along with the furnace at a rate of 10° C/min, with the temperature being kept for 40 minutes, and nitrogen was then injected to cool the alloy to room temperature at a rate of 60° C/min.

(17) The alloy was heated to an aging temperature of 745° C. along with the furnace at a rate of 8° C/min, and after the temperature was kept for 30 hours, the alloy was taken out and air-cooled to room temperature.

(18) TABLE-US-00003 TABLE 3 Test Result of Tensile Property of Alloy in Example 2 Tensile Strength Yield Strength Elongation at Reduction of MPa MPa Break % Area % 540° C. 760° C. 540° C. 760° C. 540° C. 760° C. 540° C. 760° C. Example 2 1194 863 756 698 32 48 36 69 Comparative 1202 853 748 695 24 37 25 55 example 1

(19) The uniformity of the microstructure is one of the main factors affecting the plasticity of a superalloy. Adjusting the uniformity of the distribution of γ′ precipitates by optimizing the parameters of the heat treatment process is an important means to increase the plasticity of the GH4738 superalloy as a γ′ precipitation hardened alloy. According to the present invention, after vacuum solution treatment, a high cooling rate is adopted to increase the nucleation rate of the γ′ precipitates, and meanwhile, the uniformly distributed γ′ precipitates is obtained by long-time treatment at a low aging temperature of 740° C. to 750° C., so that the high-temperature plasticity of the alloy is increased. Because the carbide is hard and brittle and has an incoherent relationship with the matrix, the large-sized intergranular carbides will precede to become a crack source during hot working of superalloys, and as a result, alloy plasticity is decreased. According to the present invention, by increasing the cooling rate of the superalloy ring after solution treatment, the aggregation and growth of the large-sized M.sub.23C.sub.6 carbides are prevented.

(20) Besides the aforementioned embodiments, the present invention can also have other embodiments. All technical solutions adopting equivalent substitutions or equivalent transformation forms shall fall within the claimed protection scope of the present invention.