Determination of the fracture toughness of carburized Pyrowear 53 steel for planetary gears by the small punch test method

Abstract

The aim of the current study was to determine the fracture toughness of different zones in carburized Pyrowear 53 steel using the small punch test (SPT) method. Firstly, Pyrowear 53 steel was quenched and tempered using different processing parameters to obtain core materials with varied microstructures and fracture toughness. The results obtained for the core material in standard fracture toughness tests were then compared with the SPT results, which allowed the determination of a formula correlating the fracture energy integral, JSPT, from the SPT with JQ integrals obtained from standardized compact tension specimens. In the next stage, Pyrowear 53 steel was carburized at 925 °C and divided into the following zones: (1) a carburized layer (up to 0.5 mm from the surface), (2) a transition layer (from 0.5 to 1.5 mm), and (3) a core zone (more than 1.5 mm). Each zone was characterized in terms of its microstructure and tensile properties using miniaturized test specimens. Finally, the fracture toughness values of the core zone (JSPT = 78–102 kJ/m2), the transition layer (JSPT = 71–80 kJ/m2), and the carburized layer (JSPT = 8.1–9.1 kJ/m2) were determined based on the obtained SPT results. It was shown that the use of such a relatively simple SPT method with the proposed energy-based approach seems to be a promising way of determining the fracture toughness of thin layers or local changes in the fracture behavior of surface-treated materials.