Welding compatibility: The alloy can be welded using common fusion welding methods, such as gas tungsten arc welding (GTAW/TIG), gas metal arc welding (GMAW/MIG), and shielded metal arc welding (SMAW). Among these, GTAW is the most recommended, as it provides precise heat input control and minimizes the risk of weld metal contamination.
Pre-welding precautions:
Cleaning: The base metal surface within 25–50 mm of the weld joint must be thoroughly cleaned to remove oil, grease, oxide scales, and other contaminants. Any residual sulfur or chloride impurities can cause weld cracking or embrittlement.
Preheating: Unlike carbon steels, Incoloy 925 generally does not require preheating for thin-walled components (≤ 12 mm). For thick-walled parts (> 12 mm), a low-temperature preheat of 100–150°C (212–302°F) is recommended to reduce weld zone temperature gradients and prevent cold cracking.
Post-welding treatment:
Stress relief annealing: After welding, stress relief annealing at 620–650°C (1148–1202°F) for 2–4 hours is essential. This step relieves residual welding stresses and avoids intergranular cracking caused by stress concentration.
Aging treatment: If the welded component requires high strength, a subsequent aging treatment at 700–720°C (1292–1328°F) for 8 hours (followed by air cooling) can restore the precipitation strengthening effect of the alloy, as welding heat input may dissolve the γ' phase in the heat-affected zone (HAZ).
Key limitations: Welding should be avoided when the alloy is in the fully aged state, as the coarse strengthening phases in this state will increase the risk of HAZ embrittlement and cracking. It is preferable to weld the alloy in the solution-annealed state and perform aging treatment after welding.
Hot workability
Incoloy 925 has excellent hot workability within the optimal temperature range, which is the primary processing method for shaping the alloy into forgings, plates, and pipes.
Optimal temperature range: The recommended hot working temperature is 950–1150°C (1742–2102°F). Below 900°C (1652°F), the alloy's strength increases significantly, leading to high deformation resistance and difficulty in processing; above 1200°C (2192°F), grain coarsening will occur, which impairs the alloy's mechanical performance.
Processing requirements: Hot working should be performed with sufficient deformation per pass (≥ 20%) to break coarse grains and refine the microstructure. After hot working, the alloy must be rapidly cooled (air cooling or water quenching) to suppress the precipitation of brittle phases and prepare for subsequent aging treatment.
Cold workability
Incoloy 925 has moderate cold workability, which is suitable for forming processes such as bending, drawing, and stamping.
Pretreatment: Cold working should be based on the solution-annealed state of the alloy, as this state has the lowest hardness and the best ductility.
Intermediate annealing: When the cold deformation amount exceeds 15–20%, intermediate annealing at 900–950°C (1652–1742°F) for 1–2 hours is required to eliminate work hardening, restore ductility, and avoid cracking during subsequent processing.
Precautions: Avoid excessive cold deformation, as this will cause severe work hardening and reduce the alloy's toughness. After cold working, a full solution annealing + aging treatment is needed to restore the alloy's target mechanical properties.
2.What processing requirements should be noted during production?
Contamination control: During all processing steps, avoid contact with sulfur, lead, and low-melting-point metals, as these elements can cause embrittlement of Incoloy 925.
Heat treatment atmosphere: Solution annealing and aging should be carried out in a clean, dry atmosphere (e.g., purified argon or vacuum) to prevent oxidation and carburization of the alloy surface.
Tool selection: Use high-hardness, wear-resistant tools (e.g., cemented carbide tools) for machining, and adopt low cutting speed and sufficient coolant to avoid overheating of the workpiece.
Inspection after processing: Conduct non-destructive testing (NDT) such as ultrasonic testing (UT) and dye penetrant testing (PT) on key components to detect internal defects or surface cracks caused by improper processing.
