Development of high performance materials and processes for applications under extreme energy conditions

The austenitic stainless steel AISI 310 (25Cr-20Ni) is commonly used for loadbearing and high-temperature applications as it combines elevated strength at high temperatures along with outstanding resistance to creep deformation as well as corrosion and oxidation resistance. However, due to the continuous search for productivity enhancement and demands for sustainability, a new family of modified cast austenitic steels has been designed to enhance the creep strength of stainless steel rollers and beams. These parts convey the steel sheet blanks in the hot stamping austenizing furnace and are exposed continuously to high temperatures of 930°C (occasionally 1000°C) and significant loads and wear. 

Calphad based thermodynamic simulation tools were employed for aiding in the alloy design of three new alloys. Small additions of C, Mo, W and Nb as well as modification of Cr and Ni contents have been proposed for enhancing the creep strength. Creep tests were carried out at two test conditions, 930°C/48 MPa and 950°C/25 MPa respectively. 

Especially, one of the proposed alloys (alloy 2) showed outstanding creep properties, its creep rupture life was in both test conditions about six times larger than that of the currently used AISI 310. The creep properties of this alloy were further enhanced by using the hydrosolidification process for manufacturing test bars and component like geometries (beams) compared to the conventional gravity casting process. An advanced microstructure investigation in the field emission gun electron microscope employing energy-dispersive X-ray spectroscopy and electron backscatter diffraction was conducted on as-cast and creep test samples to observe the microstructural evolution in the different alloys and manufacturing processes.

Funding: This research has been developed with Hipermat project, funded by the European Union under grant agreement 958196.