Effects of Heating and Cooling Speed and Hold Time on Thermal Fatigue

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Effects of heating and cooling speed, and hold time at maximum cycle temperature on thermal fatigue life subjected to mechanical strain cycling independently were experimentally investigated. Heating and cooling time apparently did not affect the number of cycles to fracture, but there was marked difference between the photomicrograph of the specimen fractured at 5 seconds of heating and cooling time, and that at 18 seconds. Increasing the hold time at 700°C in high mechanical strain region increased the number of cycles to fracture, whereas the same increase in low mechanical strain region decreased the number of cycles to fracture. The time of exposure at 500°C did not affect the number of cycles to fracture in high mechanical strain region, and increasing the hold time at the same temperature in low mechanical strain region decreased the number of cycles to fracture.