Low-Cycle Fatigue Damage Mechanism and Life Prediction of High-Strength Compacted Graphite Cast Iron at Different...

Area of Science:

• Materials Science
• Mechanical Engineering
• Metallurgy

Background:

• Compacted graphite iron (CGI) is a vital engineering material.
• Understanding CGI's high-temperature mechanical behavior is crucial for its application.
• Fatigue life prediction under varying thermal conditions requires detailed investigation.

Purpose of the Study:

• To investigate the tensile and low-cycle fatigue properties of high-strength CGI (RuT450) at different temperatures (25 °C, 400 °C, 500 °C).
• To analyze the effects of temperature and strain amplitude on fatigue life and failure mechanisms.
• To develop and propose a fatigue life prediction method based on energy and damage mechanisms.

Main Methods:

• Performing tensile and low-cycle fatigue tests on RuT450 CGI at 25 °C, 400 °C, and 500 °C.
• Analyzing microstructural changes, including oxide layer formation and crack propagation.
• Comparing experimental data with existing fatigue life prediction models.

Main Results:

• Tensile strength decreases with increasing temperature, with a more rapid decline at higher temperatures.
• Fatigue life decreases significantly at elevated temperatures, especially under high strain amplitudes.
• Cyclic hardening is evident, with initial cyclic stress increasing with strain amplitude at all tested temperatures.
• Oxide layer formation around graphite and subsequent cracking observed at high temperatures, altering crack propagation dependence on ferrite.

Conclusions:

• Elevated temperatures significantly degrade the fatigue performance of high-strength CGI.
• The observed microstructural changes, particularly oxide formation, play a key role in high-temperature fatigue failure.
• A novel fatigue life prediction method integrating energy and damage mechanisms offers a promising approach for CGI materials.