Creep behavior and strengthening mechanism of chemically modified heat-resistant austenitic GX40CrNiSi25-20 type steels

Three chemically modified heat-resistant austenitic casting alloys were developed to improve the creep strength of rollers and beams used in rolling beam furnaces within the hot stamping industry. The microstructural features and creep performance of the newly designed alloys were evaluated in comparison to the currently employed casting alloy GX40CrNiSi25-20. The alloy design involved small additions of carbon (C), molybdenum Mo, tungsten (W), and niobium (Nb), along with adjustments in chromium (Cr) content, aimed at enhancing creep resistance while minimizing susceptibility to σ phase formation. Creep testing was conducted under two conditions: 930 °C at 48 MPa and 950 °C at 25 MPa. Notably, one of the modified alloys demonstrated superior creep performance, exhibiting a rupture life approximately six times longer than that of the reference alloy under both testing conditions. Microstructural analysis revealed the presence of M23C6-type secondary carbides in all alloys, with variations in composition reflecting the specific alloying element additions. Ageing experiments were performed at 950 °C for durations of 1, 120, 220 and 900 h to investigate the coarsening kinetics of these secondary carbides.

Acknowledgments: This work was partially funded by the European Union’s Horizon 2020 research and innovation programme (Grant ID 958196), HIPERMAT project (“Advanced design, monitoring, development and validation of novel HIgh PERformance MATerials and components”).