1.Hot Working Temperature Range of Inconel 625
The hot working of Inconel 625 is typically performed within a temperature range of 1170°C to 925°C (2140°F to 1700°F).
• The initial forging or hot deformation temperature is usually close to 1170°C (2140°F), as this is where the alloy exhibits good ductility and relatively low flow stress.
• The minimum finishing temperature should be above 925°C (1700°F) to avoid the formation of undesirable microstructures, such as strain-induced precipitation of intermetallic phases, which can cause embrittlement.
• After hot working, the material is typically air-cooled to room temperature. No special cooling rate is required to maintain its properties, but rapid cooling may help minimize grain growth.
• It is important to avoid heating above 1200°C (2190°F) because excessive grain growth and potential incipient melting can occur.
2.Deep Drawing and Formability of Inconel 625
Inconel 625 does not possess good deep drawability compared to low-carbon steels or some stainless steels. Its formability characteristics are as follows:• High strength at room temperature: Inconel 625 has a high yield strength (typically 550–700 MPa in the annealed condition), which requires significantly higher forming forces
.• Low ductility and limited strain hardening capacity: These factors restrict its ability to undergo large plastic deformation during deep drawing.
• Susceptibility to work hardening: The alloy work hardens rapidly, making it prone to cracking during deep drawing unless intermediate annealing is performed.
• Springback is significant: Due to its high strength and elastic modulus, springback after forming is substantial, complicating dimensional control.
3.Suitability for Complex Shapes
While Inconel 625 is not ideal for deep drawing complex shapes, it can still be formed into moderately complex components using the following approaches:
• Warm or hot forming: Forming at temperatures between 200°C and 600°C (390°F and 1110°F) improves ductility and reduces forming forces.
• Intermediate annealing: Annealing at 980°C to 1010°C (1800°F to 1850°F) for 30–60 minutes, followed by air cooling, can restore ductility during multi-stage forming.
• Superplastic forming (SPF): At temperatures around 900°C to 980°C (1650°F to 1800°F), Inconel 625 can exhibit superplastic behavior, allowing the production of very complex, thin-walled components with large surface areas.
• Incremental forming processes: Techniques such as spin forming or incremental sheet forming can be used for low-volume, complex parts.
Summary
• Hot working range: 1170°C down to 925°C.• Deep drawability: Poor at room temperature due to high strength and limited ductility.
• Complex shapes: Feasible using warm/hot forming, intermediate annealing, or superplastic forming, but not recommended for conventional deep drawing.
