In the present study the authors have used X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to assess how surface oxides limit the gas nitriding depth of gas atomised M4 high speed steel powder and compacts. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been used for phase identification. In model experiments XPS and AES analyses of vacuum annealed powder were performed in an interconnected furnace, limiting reoxidation. Sintering cycles with and without vacuum annealing treatment were also evaluated. Generally, the authors found that an increased vacuum annealing treatment time decreased the amount of residual oxygen, which improved densification. AES and XPS analyses of the model experiments showed that the vacuum annealing time increased the absorption of nitrogen. In the sintered compacts, SEM, AES and XRD analysis as well as Thermo-Calc simulations showed that similar amounts of nitrogen were tied to vanadium carbonitrides. An AES comparison between the model and sintering experiments showed that the nitrogen absorption had the Sieverts' law dependence once the surface oxide had been removed.

The casting processes are characterized by complex relationships between predictors and responses. It is the fundamental understanding of these complex relationships that often involves hundreds of factors, which improves quality without losing productivity and raising cost. In this work, cast solid solution strengthened ferritic spheroidal graphite irons GJS-500-14 and GJS-600-10 (EN 1563:2012) have been evaluated. These materials offer stronger components with good machinability owing to their even hardness properties. In this case the predictors are chemical composition, gating layout, foundry set-up, testing procedure and equipment etc. and the responses are the tensile properties (Rp0.2, Rm, A5). Here 200 tensile specimens compiled from industrial foundry melts from over 30 years of research have created a state-of-the-art platform for statistical engineering in order to perform Exploratory Data Analysis (EDA) and data visualization. This statistical platform has provided new insight on how foundries should treat complex relationships between predictors and responses in order to identify sources of variation and interaction effects.

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The grey iron microstructure Fe-2C-2Si powder based compact is tailored by different kinds of in situ and post sintering processing. This has been achieved by combining thermodynamic and kinetics modelling of microstructure development with sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa. Applying optimised sintering conditions led to a grey iron like microstructure with 95% relative sintered density. Sinter hardening the compacts led to 500 MPa in yield strength and 600 MPa in ultimate tensile strength in combination with ductile fracture. Quenched and tempered condition showed the same strength values, but combined with brittle fracture due to martensitic structure. Pore rounding and partial pore filling by graphite were obtained by austenising isothermal hold during the cooling of the sintering cycle.