Alloy 718 Ring Expansion for Circularity Without Grain Coarsening
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Solution Overview
Problem
The challenge lies in preventing abnormal grain growth (AGG) during the closed die forging of ring-shaped materials for aircraft engine turbine parts, which is difficult to control due to non-uniform strain distribution and high pressing capability requirements, leading to impaired fatigue properties.
Innovation Solution
A method involving ring rolling with specific temperature and strain control steps, including a finishing ring rolling step at 900-980°C, an intermediate ring rolling step at 980-1010°C, and a circularity correcting step using a ring expander to achieve a high circularity and inhibit AGG, ensuring sufficient strain storage and recrystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If circularity correction is performed to obtain high degree of circularity, then circularity is improved, but abnormal grain growth occurs during subsequent heating
Solution Approach 1:
The invention applies preliminary effective strain during the circularity correction step to prepare the material for subsequent heating. By introducing controlled strain before heating, the material is pre-conditioned to resist abnormal grain growth that would otherwise occur during the heating process to closed die forging temperature.
Solution Approach 2:
The invention changes the parameters of the circularity correction process by specifying an effective strain range (0.005 to 0.05) and effective strain rate range (0.001 to 0.1 s^-1). These parameter changes ensure that the correction produces the desired circularity while simultaneously preventing abnormal grain growth during subsequent heating.
2Stability of the object's composition
If effective strain satisfying Expression (1) is applied in circularity correction step, then abnormal grain growth is prevented, but pressing capability requirements cannot be met
Solution Approach 1:
The invention segments the ring rolling process into multiple steps: a first ring rolling step to achieve basic shape, followed by a circularity correction step with controlled strain parameters. This segmentation allows each step to be optimized independently - the first step for shape formation and the correction step for grain size control while meeting pressing capability requirements.
Solution Approach 2:
The invention applies partial strain during the circularity correction step, using only the amount necessary to prevent abnormal grain growth (effective strain of 0.005 to 0.05) rather than applying excessive strain that would compromise pressing capability. This partial action achieves the minimum necessary protection against grain growth while preserving manufacturing flexibility.
3Stability of the object's composition
If effective strain satisfying Expression (2) is applied in ring rolling step, then abnormal grain growth is prevented, but strain distribution becomes non-uniform and difficult to control
Solution Approach 1:
The invention applies preliminary effective strain during the ring rolling step to establish a baseline strain distribution in the material. This preliminary strain serves as a foundation that prevents abnormal grain growth during subsequent heating, while the strain is distributed in a controlled manner that does not create the non-uniformity problems associated with applying Expression (2) throughout the entire ring rolling process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces a ring-rolled material with high circularity and inhibited grain growth, enhancing the fatigue characteristics of turbine parts by maintaining a fine-grained structure and preventing AGG, thus improving the reliability of aircraft engine components.
Implementation Method 1
heating a material for ring rolling in a temperature range of 900 to 980°C, and expanding a diameter of the material for ring rolling and also pressing the material for ring rolling in an axial direction
Implementation Method 2
a heating step of heating a ring-rolled material that has been rolled by the finishing ring rolling step, in a temperature range of 980 to 1010°C
Implementation Method 3
a circularity correcting step of improving a circularity of the ring-rolled material that has been heated by the heating step, while expanding a diameter of the ring-rolled material by using a ring expander including a pipe-expanding cone and a pipe-expanding die, wherein, in the circularity correcting step, a diameter expansion rate for an outer diameter of the ring of the ring-rolled material is up to 0.8%
Data Source
Figure 1~2
AI summary
The present invention provides a method for producing a ring-rolled material of an Fe-Ni based superalloy which inhibits AGG, has a fine-grained structure having an ASTM grain size number of at least 8, and has high circularity. A method for producing a ring-rolled material of an Fe-Ni based superalloy having a composition of an Alloy 718 comprises: heating a ring-shaped material for ring rolling having the composition, in a temperature range of 900°C to 980°C, and performing finishing ring rolling, as a finishing ring rolling step; heating the ring-rolled material that has been subjected to the finishing ring rolling, in a temperature range of 980 to 1010°C; and correcting ellipticalness while expanding a diameter of the ring-rolled material by using a ring expander.