Incoloy 909 superalloy was treated at 950°C to form coatings of different chemical composition by thermochemical diffusion. Packing of the samples in reactive powders lead to the formation of iron borides (Fe 2 B and FeB) together with nickel boride, NiB, and nickel silicide, Ni 2 Si, on the surface of the alloy depending on the exposure time. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses suggest that growth of the coatings is controlled by diffusion of reactive species into the metal structure. Microabrasion wear resistance of the coated specimens was studied at 1 N load for a fixed sliding speed of 0.11 m s −1 and it was compared against uncoated samples of the alloy. It was found that coating the alloy for 12 and 20 h increased the hardness of the alloy and therefore its wear resistance.

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ABSTRACT:The phase transformations of high carbon steel during quenching and equalizing were modelled using commercial computer packages based on the finite element method and the kinetic transformation of steel. The model was used to predict the temperature and microstructural changes taking place within balls of two different sizes that are used for grinding mineral ores. A good correlation between the temperatures measured by inserted thermocouples and those predicted by the model was obtained after modifying the thermal conductivity of the steel within the temperature domain at which mixed phases are present. The phase transformations predicted were confirmed by metallographic analyses. RESUMEN:Simulación del temple en bolas de desgaste de acero. Las transformaciones de fase en aceros de alto carbono durante su temple y un posterior periodo de estabilización fueron modelizadas por medio del uso de paquetes computacionales basados en el método del elemento finito y de la transformación cinética de los aceros. El modelo se usó para predecir los cambios de temperatura y microestructura que se presentan en bolas de dos diferentes tamaños empleadas en estaciones de molienda de minerales. Se encontró una buena correlación entre las temperaturas medidas mediante la inserción de termopares y aquellas predichas por el modelo una vez que se modificó la conductividad térmica del acero en el intervalo mixto de fases. La predicción de las transformaciones de fase se confirmó a través del análisis metalográfico.

A simulation model has been used to calculate temperature distribution and internal stresses of steel ingots. The aim of this study is to optimize the heating cycles without compromising the mechanical integrity of the ingots, which ideally will result in a reduction in energy consumption and an increase in furnace productivity. The heating cycles of three ingots of different materials (ASTM A105, AISI 4330, and AISI 8630) and sizes (1.60, 1.75 and 1.32 m) are optimized. The optimization procedure of the heating cycle is based on a time reduction at each step of the set point. The phase transformation temperature at the ingot center was taken as a reference because this is where the higher stresses are developed. A sample of a 1 m ∅ AISI 8630 ingot was characterized with a Scanning Electron Microscope, Energy-dispersive X-ray Spectroscopy, X-Ray Diffraction, and Differential Scanning Calorimetry. Results show precipitates in the as-cast condition, which will eventually be dissolved after a complete heating cycle.

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