Authors investigated, as part of a study on super alloys for springs, the spring properties at the room temperature or elevated temperature of Refractaloy 26 type alloy, which was treated with various combinations of solution temperature, aging temperature, aging time and cold reduction before or after aging.
Characteristics at the room temperature were determined by tensile, hardness, grain size or bending tests to confirm the spring properties.
Characteristics at the elevated temperature were investigated using coil springs treated with an optimum heat treatment and cold working (to develop the superior room temperature properties). For this object, compression coil springs were manufactured and heated from room temperature, with the temperature and deflection registered.To confirm the stability of deflection under load and heating, coil springs were heated and cooled cyclically.Also the micro-structure and the process of precipitation were observed in representative treatments with the help of electron-microscope.
Results obtained were as follows:
1) Without cold working, a combination of 982°C (solution treatment) and 732°C (aging treatment) develops more favorable mechanical properties in the alloy than other combinations.
2) The cold working (up to 50% reduction) before aging improves the low temperature characteristics, but somehow deteriorates the quality of spring at the elevated temperatures. The higher the cold reduction, and the higher the aging temperature, the shorter is the optimum aging time.
3) The rigidity is influenced by the aging temperature, while the aging time or cold reduction does not affect it noticeably.
4) The proportional limit of twisting is influenced by the temperature and time of aging and also by the cold reduction.
5) Several or more cycles are required to estimate the deflectional stability under repeated heating condition, which is mainly affectedby the load, temperature of heat cycle or treatments given to the spring.
6) Permissible temperature for this alloy is up to about 600°C for one strengthened only by heat treatment, and up to about 500°C for one strengthened by heat treatment and cold working.