| Summary: | Low cycle fatigue (LCF) behaviour of a tool steel YXMI under quenching and tempered conditions is reported, the alloy was quenching at 1220°C for 18min and then tempering at 540°C for lh, three tempering cycles, which resulted in tempered martensite, precipitate carbide and untempered martensite structure, total axial strain controlled LCF tests were conducted at strain rate varies from 0.008 to 0.0144 s"1 at total strain amplitude ranges from 1% to 2%, in the room temperature. The cycles stress response behaviour, The material shows evidence of very high cyclic softening, varying between 30 MPa and 200 MPa depending on strain amplitude, this softening can reach up to 30% of the first cycle amplitude. Such behaviour is commonly explained as follows: the initial high dislocation density that results from the quenching, decreases during cycling and generates dislocation cell structures and the tool steel shows cyclic softenting.
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