Alloy 718 Ring Rolling for Circularity Without Abnormal Grain Growth
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Solution Overview
Problem
The challenge in producing ring-rolled materials for aircraft engine turbine parts is the occurrence of abnormal grain growth (AGG) during closed die forging, which impairs fatigue properties due to non-uniform strain distribution and high circularity requirements, making it difficult to prevent coarse grain formation using existing strain conditions.
Innovation Solution
A method involving ring rolling with specific temperature ranges and axial pressing using a ring rolling mill, followed by a circularity correcting step without reheating, to optimize strain storage and prevent AGG, ensuring a high-circularity, fine-grained structure.
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 ring rolling process before circularity correction to prevent abnormal grain growth during subsequent heating. By storing strain energy in advance, the material resists grain growth when heated for closed die forging, even after circularity correction is performed.
Solution Approach 2:
The invention changes the parameters of effective strain and effective strain rate during ring rolling to satisfy specific mathematical expressions. By controlling these parameters within defined ranges, the material achieves both high circularity after correction and resistance to abnormal grain growth during heating.
2Stability of the object's composition
If effective strain satisfying Expression (1) is applied only by circularity correction step, then AGG is prevented, but pressing capability is insufficient to apply strain to entire region
Solution Approach 1:
The invention divides the strain application process into two segments: ring rolling step and circularity correction step. The ring rolling step applies the majority of effective strain to the entire material region, while the circularity correction step provides additional strain and achieves shape refinement. This segmentation allows both sufficient strain application and high circularity to be achieved.
3Shape
If ring rolling is performed to achieve high circularity, then circularity is improved, but non-uniform strain distribution remains making AGG prevention difficult
Solution Approach 1:
The invention maintains continuous strain application through the combined ring rolling and circularity correction process. By ensuring that effective strain is accumulated continuously and uniformly throughout the material during both steps, the strain distribution becomes more uniform, preventing localized regions that would be prone to abnormal grain growth.
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 effectively inhibits AGG and grain growth, enhancing the fatigue characteristics of turbine parts by maintaining strain and preventing recrystallization, thus improving the reliability of aircraft engine components.
Implementation Method 1
expanding a diameter of the material for ring rolling and also pressing the material for ring rolling in an axial direction
Implementation Method 2
heating the material for ring rolling to a temperature range of higher than 980°C and up to 1010°C
Implementation Method 3
a pinning effect of a delta phase is made use of
Data Source
Figure 1~2
AI summary
A method for producing a ring-rolled material of an Fe-Ni based superalloy, which has a high circularity, can inhibit AGG, and can inhibit grain growth. A method for producing a ring-rolled material of an Fe-Ni based superalloy having a composition of an Alloy 718comprises: a finishing ring rolling step of 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; and a circularity correcting step of correcting an ellipticalness of the ring-rolled material that has been rolled in the finishing ring rolling 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 the ring-rolled material that has been rolled in the finishing ring rolling step is subjected to circularity correction without being reheated or after having been heated to up to 960°C.