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Heat Treat

Precise Cast Heat Treat

 

Post Casting Tempering or Heat Treating an alloy casting can result in significant changes from the inherent as-cast mechanical properties. Stabilization, strengthening and hardening are typical enhancements gained through adding tempering to a well cast part. Final mechanical properties are influenced greatly by a number of parameters that can be adjusted within each heat treating process. Heat treating can also negatively affect your part if done incorrectly. For example, improper quenching methods can result in excessive residual stresses in your part which will drastically reduce its fatigue life. Choosing the correct temper to optimize your part’s final properties can be a difficult task.

Typical Heat Treating Tempers are listed below. Let our experienced engineers recommend a specific Heat Treating process for your casting to ensure that your project is a success!


Temper Description/Purpose Criteria
F As Cast condition. Room temperature natural aging has insignificant changes after 48 hours. F temper castings have microstructure instability and undesirable / non-uniform residual stress. Cool to room temperature from casting temperature
O Annealed – Done to relieve stress and reduce growth. Sometimes described as “extreme over aging.” Maximizes ductility. Decreases casting hardness. Heat to 500-698F (260-370C) for 2 hrs; air cool to room temperature
T4 Solution treat and age naturally to a stable condition. Natural aging may continue slowly, particularly at elevated service temperatures, so structural stability may not be satisfactory.T4 increases machinability, hardness and strength but sacrifices ductility. Final properties largely dependent on quench.** Solution Treatment varies, but typically 6-12 hrs at 1000F. Quench at 150-212F depending on section thickness.
T5 Also known as “simplified super saturation treatment.” Cool from casting temperature and artificially age or stabilize without solution treatment. Stabilizes microstructure and increases casting hardness. Provides moderate improvement of mechanical properties from F temper. Typically 401-500F (205-260C) for 7-10hrs. Over aging will reduce casting hardness. Quenching is optional, but can improve mechanical properties if used appropriately.
T51 Provides additional stability from T5 temper by increasing aging temperature. Provides moderate improvement of mechanical properties from F temper. Caution – Over aging causes a loss of hardness and strength.
T551 Provides additional stability from T5 temper by increasing aging time. Provides moderate improvement of mechanical properties from F temper. Not recommended for machined castings. Caution – Over aging causes a loss of hardness and strength.
T6 Solution treat, quench and age artificially. T6 commonly describes the optimum strength, machinability and ductility. Mechanical properties can be greatly influenced by slight process variations within the specified ranges. Solution Treat (10-12hrs @1000F); Quench in hot water (150-212F); Natural Age at room temperature for 8+ hours; Artificial age at 310F for 3-5 hours.**
T7 Solution treat, quench and overage artificially. This temper improves ductility, thermal stability, and resistance to stress corrosion cracking. This temper provides lower mechanical properties than a typical T6 treatment. Solution Treat (12hrs @1000F); Quench in hot water (150-212F); Artificial age at 400F for 3-5 hours.**

** Although many national heat treating standards specify water quenching it is important to note that the benefits of doing so are largely geometry dependant. Many non-uniform geometries are subject to an uneven quench / cooling rate. The result of which means much higher residual stresses are established in the casting as it cools. Essentially, quenching will improve the part’s material strengths, but dramatically lower its resistance to a fatigue failure. In general, a part that is not water quenched is likely to lose 5-10% of its material strength. However, its failure resistance as a complete casting acting as a load bearing part will be increased by as much as 50%. In some cases using a glycol / water mixture or simply forced air as a quench medium can provide effective results. Though these methods are preferable, they do not guarantee uniform quenching and therefore castings are still subject to the affects of residual stresses.