Accelerated fatigue testing of powder metallurgical HIP high-speed steel for near-net shape applications

High-speed steels are commonly used for cutting tools requiring a high impact toughness and fatigue resistance. Both properties are significantly enhanced by employing the powder metallurgical (PM) production route using HIP as consolidation technique. However, the inherent oxides of the used powder may reduce the fatigue limit. Hence, subsequent forging is commonly required, which in turn precludes the possibility of near net shape production by PM. The purpose of this study is to investigate the efficiency of an isothermal holding stage that is introduced prior to the application of pressure to allow oxide size reduction during the HIP process and thereby increasing fatigue limit. The fatigue limit is assessed by accelerated fatigue testing, allowing its determination with a single specimen, which is particularly crucial for HIP processes with limited capsule volume. Good agreement is observed with results from conventional fatigue testing based on the staircase method.