Static bend strength of carburising steel SS 2506

Effect of austenite grain size on the static bend strength for the steel SS 2506 in a carburised condition has been studied. Bend test samples, designed to simulate the conditions in the root of a gear, were gas carburised to a nominal surface carbon content and a case depth of 0·8 wt-% and 1 mm, respectively. A Hall–Petch type relationship was found between the bend strength and the grain size. No significant differences in the carburised microstructure were observed for the various grain sizes studied. Below a critical grain size, d_crit=42 μm, the fracture mode was observed to be less intergranular at the carburised surface and this coincided with an increased hardness after fracture. Changes in the fracture mode are discussed in terms of yielding preceding fracture, and differences in the crack initiation site, as the grain size decreases.

MST/1761