High-temperature creep in compacted graphite iron: Tension vs. Compression

• Experiments on high-temperature creep in CGI under tension and compression. • Significant differences in creep response to tensile and compressive loading regimes. • Secondary creep rates in tension and compression are given for various stresses. • Dislocation creep is dominant in tension while diffusion creep − in compression. • Parameters for creep modelling are given for tensile and compressive creep of CGI. Cast iron is often used in high-temperature environments such as automotive cylinder heads and cylinder blocks with the temperatures ranging from 400 °C to 500 °C. The properties of cast irons start degrading at around 425 °C, with creep becoming a concern above this temperature. The asymmetric behaviour of cast irons under uniaxial tensile and compressive loading is widely reported and is even incorporated in commercial finite-element analysis packages. However, there is not much literature covering high-temperature creep in cast irons and, specifically, its compressive creep properties. In this work, extensive experimental studies are presented covering high-temperature tensile and compressive creep in compacted graphite iron (CGI) with temperatures ranging from 400 °C to 550 °C and stresses between 150 MPa to 300 MPa. This study includes comparison of secondary creep rates in tension and compression, a novel result not previously reported in the literature for CGI. The experimental results demonstrate significant differences in the high-temperature creep behaviour under tensile and compressive loading highlighting different mechanisms driving the creep response under different loading regimes. Critical parameters useful for creep modelling and simulations are reported for both tensile and compressive creep, which are expected to provide strong foundation for further work in this area.