Inconel 718 Forging Below D-Solvus Temperature
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Solution Overview
Problem
Current manufacturing processes for nickel superalloys like Inconel 718 often result in coarse grain zones, which degrade the mechanical properties of parts due to inadequate control over grain size during heat treatments and forging operations, particularly when forging is done above the δ-solvus temperature.
Innovation Solution
The method involves a final forging step at a temperature below the δ-solvus temperature with a local strain rate of at least 0.7 and subsequent quenching without heat treatment above 750°C, followed by tempering, to transform existing coarse grains into fine grains and prevent new coarse grain formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If forging is carried out above the δ-solvus temperature, then the alloy can be processed more easily, but coarse grain zones form which reduce mechanical properties
Solution Approach 1:
The patent applies parameter changes by precisely controlling the forging temperature to be below the δ-solvus temperature and controlling the strain rate to be at least 0.7. This parameter optimization allows the alloy to be processed while avoiding the formation of coarse grain zones, thus maintaining mechanical properties without sacrificing too much ease of manufacture
Solution Approach 2:
The patent introduces dynamic control of the deformation process by specifying a minimum strain rate of 0.7 during forging. This dynamic parameter control ensures that the alloy undergoes sufficient deformation to prevent coarse grain formation while maintaining processability, resolving the contradiction between ease of manufacture and mechanical properties
2Strength
If heat treatment is performed above 750°C after quenching, then certain mechanical properties can be improved, but new coarse grains form which degrade resilience
Solution Approach 1:
The patent applies parameter changes by limiting the heat treatment temperature to not exceed 750°C after quenching. This temperature constraint prevents the formation of new coarse grains that would degrade resilience, while still allowing sufficient heat treatment to maintain other mechanical properties
Solution Approach 2:
The patent applies preliminary action by performing quenching before heat treatment to establish a fine grain structure first, then following with controlled heat treatment at temperatures not exceeding 750°C. This sequence prevents coarse grain formation while achieving the desired mechanical properties and resilience
3Strength
If conventional heat treatments and forgings are used to achieve fine grain size, then optimal fatigue and tensile properties are obtained, but coarse grain areas still appear which reduce mechanical properties
Solution Approach 1:
The patent applies parameter changes by optimizing both temperature (below δ-solvus) and strain rate (≥0.7) parameters during the final forging stage. This dual parameter control ensures uniform fine grain size throughout the alloy without coarse grain areas, achieving optimal fatigue and tensile properties with consistent grain structure
Solution Approach 2:
The patent applies feedback control by monitoring and controlling the strain rate during forging to ensure it remains at least 0.7. This feedback mechanism ensures that the deformation is sufficient to prevent coarse grain formation while maintaining the desired fine grain size uniformity throughout the alloy
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
This approach ensures that the nickel superalloy maintains improved resilience and mechanical properties without significant reductions, achieving a grain size between 5 and 20 μm for enhanced fatigue life and yield strength.
Implementation Method 1
subsequent quenching without heat treatment above 750°C, followed by tempering, to transform existing coarse grains into fine grains and prevent new coarse grain formation
Implementation Method 2
the nickel superalloy also undergoes tempering directly after quenching following the last forging stage. The tempering operation takes place at a sufficiently low temperature to prevent the formation of coarse grains within the superalloy
Implementation Method 3
at every point M of this nickel superalloy the local strain rate D, defined by where δ i is the initial distance between point M and a point M' near M and δ f is the distance between points M and M' after forging, is at least equal to a minimum value D m equal to 0.7
Data Source
Figure 1~2
AI summary
The invention relates to a method for manufacturing Inconel 718 nickel superalloys. The last step for forging undergone by said nickel superalloy is such that said step is carried out at a temperature T less than the d-solvus temperature where, at every point M of said nickel superalloy, the local deformation rate D is at least equal to a minimum value Dm. Said method is characterized in that said nickel superalloy does not undergo heat treatment at a temperature greater than a threshold temperature Ts equal to 750° C after said quenching.