Alloy 718 Ring Rolling With Pre-Strain for AGG-Free Circularity
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Solution Overview
Problem
The existing methods for producing ring-rolled materials of Fe—Ni based superalloys face challenges in achieving high circularity while preventing abnormal grain growth (AGG) during closed die forging, as it is difficult to uniformly apply effective strain and control grain refinement across the entire material.
Innovation Solution
A method involving a finishing ring rolling step with specific temperature and strain control, followed by a heating step and circularity correcting step using a ring expander, to inhibit AGG and achieve high circularity in the ring-rolled material.
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 patent applies preliminary effective strain during the ring rolling process before the circularity correction step. This preliminary deformation creates a strain state that prevents abnormal grain growth during subsequent heating, allowing the circularity correction to be performed without triggering AGG. The strain is applied in advance to establish a protective microstructural state.
Solution Approach 2:
The patent controls the effective strain rate and temperature parameters during ring rolling to satisfy specific mathematical expressions. By adjusting these parameters within defined ranges, the material achieves a strain state that inhibits abnormal grain growth while still allowing circularity correction to proceed. The parameter control transforms the material's response to subsequent heating.
2Stability of the object's composition
If effective strain satisfying Expression (1) is applied to entire region during circularity correction, then AGG is prevented, but pressing capability is insufficient to apply uniform strain
Solution Approach 1:
The patent divides the strain application into two separate stages: (1) ring rolling process where preliminary effective strain is applied, and (2) circularity correction process where additional strain is applied. This segmentation allows each process to contribute differently to the overall strain state, with the ring rolling providing the foundation strain and the circularity correction providing the final adjustment, overcoming the limitation of uniform strain application in a single step.
3Stability of the object's composition
If effective strain satisfying Expression (2) is controlled, then AGG is prevented, but strain remaining after ring rolling is not uniform making control difficult
Solution Approach 1:
The patent applies preliminary effective strain during ring rolling that creates a baseline strain state throughout the material. This preliminary strain acts as a buffer that compensates for the non-uniform strain distribution that will occur during subsequent circularity correction. By establishing this foundation strain in advance, the final strain distribution becomes sufficiently uniform to prevent AGG despite the inherent difficulties in controlling strain during circularity correction.
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 produces a ring-rolled material with high circularity and refined grain structure, enhancing the fatigue characteristics of turbine parts by preventing AGG and grain growth.
Implementation Method 1
a pair of rolling rolls including a main roll and a mandrel roll, and a pair of axial rolls
Implementation Method 2
expanding a diameter of the material for ring rolling and also pressing the material for ring rolling in an axial direction
Implementation Method 3
when the ring-shaped material for the closed die forging is prepared, if circularity correction is performed in order to obtain a high degree of circularity, there is a case in which so-called abnormal grain growth
Implementation Method 4
a fine-grained structure is created in the rotating part, for which a pinning effect of a delta phase is made use of
Data Source
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.