Microstructure and Mechanical Properties of Advanced High-Silicon Austempered Steel

This paper has attempted to investigate microstructure evolution as a function of silicon content using Thermo-Calc software as a computational prediction technique. This research work aims to evaluate the mechanical properties of investigated steel and outline their relationship with the microstructure.Thermo-Calc was used for calculating phase volume fractions of a set of silicon-containing steel alloys. The mechanical properties of investigated steels such as tensile properties, hardness, and impact toughness) were evaluated from a microstructure point of view. The fracture surface of tensile samples was studied utilizing a scanning electron microscope equipped with energy-dispersive x-ray (point micro-analysis). The experimental results revealed that microstructure evaluations were close to the predicted computational by Thermo-Calc software. Also, the results showed that the microstructure of the high silicon steel (≥ 1.5 wt.%) is more dense, well homogenous and contains a volume fraction of 93% Bcc-ferrite at approximately, and 1.5% Fcc-austenite, as well as 5.5% different types of carbides. Also, The experimental results showed that the mechanical properties of the steel containing silicon (1.59 wt.%) have a remarkable enhancement of toughness in combination with high hardness and tensile strength compared to low silicon steel. The yield strength (1088 MPa) and elongation (16.4%) were obtained for austempered steel containing 1.59 wt.% silicon. The fracture surface mode of the investigated steel transition from brittle to ductile fracture according to the silicon content related to obtained microstructure.