Due to lack of reliable thermal diffusivity data of sintered steels in literature, experimental investigations were conducted on samples made of different powder types (based on prealloyed, or diffusion-bonded, or admixed powders) and under different process conditions. So the influence of pressing pressure and sintering temperature on thermal diffusivity was established. Thermal diffusivity was measured using the “flash method”: a sample in the shape of a slab is irradiated with a light pulse on one of the two surfaces, and temperature of the other surface is detected by an ambient temperature pyrometer. The value of the thermal diffusivity is obtained by a least squares regression on the entire trend of the temperature vs. time using the analytical solution of the heat conduction as regression model. Results show the increase of the thermal diffusivity with increasing density. This outcome can be explained from the mutual effect of thermal conductivity and density on thermal diffusivity in porous media. The experimental results have also permitted to verify the influence of the composition of the sintered materials and carbon contents on thermal diffusivity.

Thermal Diffusivity of Sintered Steels with Flash Method at Ambient Temperature

Critical aspects of sinter-hardening of prealloyed Cr-Mo steel

Crack initiation and propagation in Chromium pre-alloyed PM-steel under cyclic loading

Effect of sinter hardening on the microstructure, density, hardness and tensile properties of Astaloy 85Mo+ 0.7% graphite was investigated. For this purpose, Astaloy 85Mo, a pre-alloyed powder, was mixed with 0.7% UF4 graphite and then pressed in single action die and sintered at 1120 °C for 30 min in N 2 -10%H 2 atmosphere. Then samples were cooled from 0. 5 to 3 °C/s sintering temperature in accordance with different cooling rates. The difference in microstructure, hardness, density and tensile properties of the samples associated with different cooling rates from sintering temperature has been investigated. The results show that the microstructure remains bainitic by changing cooling rate, but it becomes finer and then the hardness and tensile strength of the samples will increase by increasing the cooling rate from sintering temperature.

Effect of Sinter Hardening on Microstructure and Mechanical Properties of Astaloy 85Mo

Powder metallurgy ferrous precision parts are employed in numerous industrial sectors. In case of high mechanical loading, as e. g. in automotive applications, heat treatment is frequently...

Heat Treatment of Sintered Steels – what is different?*

Influence of density and surface/volume ratio on the cooling speed of sinter-hardening materials, Part two: Microstructure and microhardness distribution inside parallelepipeds

Influence of some cooling rate on microstructural and chemical properties of alloys from diffusion-bonded powders, sintered in different conditions

Industrial hot dip galvanized steels were submitted to a Cr(III)-based passivation treatment (containing phosphates) leading to Cr(VI)-free conversion layers. The characterization of the substrate and of the coatings was carried out before and after the passivation treatment by means of optical microscopy (OM) and scanning electron microscopy with energy X-ray dispersive spectrometry associated (SEM/EDS). In particular the zinc coating was preliminarily studied both superficially and in section in order to define its adequacy and its possible state of defectiveness. The corrosion behaviour was evaluated by means of electrochemical impedance spectroscopy (EIS) and salt spray test. A comparison between the protective effectiveness of the innovative Cr(III)-based passivation and the Cr(VI)-based process usually employed by manufacturers was carried out. According to the exposed preliminary results, promising outcomes were obtained with the innovative Cr(III)-based passivation by optimizing the amount of chromium in the coating.

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M. R. Pinasco

Papers

Influence of density and surface/volume ratio on the cooling speed of sinter-hardening materials, Part two: Microstructure and microhardness distribution inside parallelepipeds

Influence of some cooling rate on microstructural and chemical properties of alloys from diffusion-bonded powders, sintered in different conditions

Corrosion Resistance of Cr (III) Based Conversion Layer on Zinc Coatings in Comparison with a Traditional Cr (VI) Based Passivation Treatment

Physical and mechanical properties, microstructure and fractography of a P/M steel from diffusion-bonded powder, differently sintered or heat treated

Relazione tra tenacità e microstrutture di blocchi prebonificati di acciai per stampi di grosse dimensioni