Abstract: By using a self-made thermal fatigue test machine of outer-constraint mode, the influence of top-temperature of thermal cycle T t on thermal stress-strain and thermal fatigue behavior of an industrial pure iron was investigated. The T t was varied from stress/strain 773K to 1073K. The results show that, increasing of T t , the thermal stress-strain cycles can be classified into four types, they are: compressive stress cycle; compressive strain-tensile stress cycle; compressive strain-tensile stress cycle than changing to compressive tensile plastic strain cycle; and finally, compressive tensile plastic strain cycle. It is also revealed that certain relationship does exist between thermal fatigue life and characteristics of thermal stress/strain cycle. When compressive tensile plastic strain cycle were appear by increasing of T t , thermal fatigue life decreasing rapidly. The concept of thermal fatigue transition temperature, and determining method were put up in this thesis.

Key words: thermal fatigue, thermal stress-strain