1. Core Mechanical Property Indicators (Room Temperature, After Standard Heat Treatment)
Solution annealing: Heat to 927–982 °C, hold for 30–60 minutes, then water-quench to room temperature.
Aging treatment: Reheat to 482–510 °C, hold for 4–8 hours, then air-cool.
Yield Strength (0.2% Offset): ≥ 793 MPa (115,000 psi)
This value represents the stress at which the alloy undergoes permanent plastic deformation of 0.2%. It is a critical index for evaluating the alloy's resistance to deformation under load, which is far higher than that of the non-heat-treatable Monel 400 (yield strength only 240 MPa, 35,000 psi).
Elongation (in 50 mm gauge length): ≥ 20%
Elongation reflects the plastic deformation capacity of the alloy before fracture. Monel K500 maintains good ductility while having ultra-high strength, which avoids brittle fracture during processing (e.g., cold heading, threading) or service.
2. Effect of Heat Treatment Variations on Indicators
Incomplete aging (low temperature or short time): The precipitation of Ni₃(Al,Ti) strengthening phases is insufficient. At this time, the yield strength decreases to 620–700 MPa, while the elongation increases to 25–30%.
Over-aging (high temperature or long time): The strengthening phases coarsen and aggregate, leading to a decrease in yield strength to 690–760 MPa, and the elongation slightly rises to 22–26%.
Omitted aging (only solution annealing): The alloy is in a softened state, with a yield strength of only about 276 MPa and an elongation of up to 40%, which loses the core advantage of high strength.
3. Effect of Temperature on Yield Strength and Elongation
Yield strength trend: As temperature rises, the yield strength of Monel K500 gradually decreases. When the temperature exceeds 427 °C, the decrease rate accelerates, because the strengthening phases begin to dissolve and lose their dispersion strengthening effect.
Elongation trend: With the increase of temperature, the ductility of the alloy improves, and the elongation increases accordingly, which means the alloy is less prone to brittle fracture in high-temperature environments.
4. Key Notes
Specimen Form: For forged or cold-worked Monel K500 fasteners, the yield strength may be 5–10% higher than the standard value, while the elongation may decrease by 2–3% due to work hardening.
Standard Compliance: Different application fields have different requirements for indicators. For example, aerospace-grade Monel K500 requires a yield strength of ≥ 827 MPa, while industrial-grade products can be slightly lower.
