Influence of tension and compression dwell on the creep-fatigue properties of the austenitic cast iron Ni-resist D5S

摘要

Creep-fatigue tests with either tension or compression dwell and reference low-cycle fatigue test without dwell were conducted on the austenitic cast iron D5S in atmospheric air at 800°C to investigate the influence of dwell time on lifetime and the corresponding failure mechanisms. The addition of tension or compression dwell reduces the lifetime, by up to 50% and 80% in the tested range, respectively. Compared with tension dwell, compression dwell is found to be more detrimental and could further reduce the lifetime by up to 60%. Tension and compression dwell are seen to cause a thicker and thinner gauge length, respectively. Tension dwell causes the formation of creep pinholes at the graphite/matrix interface and subgrain boundaries, leading to the formation of internal microcracks. Compression dwell results in forming large cavities at the graphite/matrix interface. The intermetallics in an untested sample are found to contain G phase, Ni_(31)Si_(12), α-Fe, and M_7C_3. The intermetallics in an LCF-tested sample are found to contain G phase, Ni_(31)Si_(12), M_7C_3, and χ phase. Cracks inside intermetallics are found to form at the interfaces between Ni_(31)Si_(12)/χ phase, M_7C_3/χ phase, and Ni_(31)Si_(12)/M_7C_3.