Heat Treatment for Investment casting

2022-02-15

To improve the interior quality and reach the desired mechanical properties, there are many heat treatments for Stainless steel, Carbon steel and Alloy Investment castings, such as Aging treatment Solution treatment, Normalizing, Quenching, Tempering, Hardening and Hydrogen removal.

1. Aging Treatment

Aging treatment is a heat treatment process for the investment castings after solution treatment, high temperature quenching or cold processing, placed at a higher temperature or room temperature to maintain its shape, size or properties changing with time. Through Aging treatment, hardness and strength will be increased, while internal stress will be reduced.

Aging treatment includes Natural aging, Thermal aging and Resonance aging.

- The so-called Natural aging is to place investment castings in the open air for more than half a year, so that the internal stress is reduced.

- Thermal aging, also known as Stress relief Annealing, is to heat the castings to 550~650℃, hold for 2~4hours, cool to 150~200℃ in the furnace, and then take out.

- Resonance aging is to vibrate the casting at its resonance frequency of 10-60ndn to reduce residual stress in the casting.

2. Solution treatment

Solution treatment is mainly applied to Stainless Steel investment castings, which are heated to an appropriate temperature and held in a certain time, so that the excess phase is fully dissolved, and then cooled to obtain supersaturated solid solution. The main purpose of solution treatment is to dissolve carbides or other precipitated phase in the solid solution to obtain supersaturated single-phase structure.

3. Normalizing

Normalizing is the heat treatment process of heating steel castings to above Ac temperature, holding at 30~50℃, austenizing and then cooling in the still air. Widely applied to carbon steel, some thick and complex alloy steel castings.

4. Quenching

Quenching is the heat treatment process of heating steel castings to austenization, cooling them in an appropriate way after holding time to obtain martensite or bainit