PetroMat

Electrochemical investigations (polarization curves, polarization resistance measurements), together with weight loss measurements and quantitative chemical analysis of the solutions after immersion of samples were used to evaluate the corrosion behaviour of type 304L and 316L sintered austenitic stainless steels in sulphate and chloride containing solutions. The samples were sintered in nitrogen based atmosphere, at 1120 and 1190°C, and in vacuum at 1200°C and submitted to X-ray diffraction analysis and SEM observation together with EDS microanalysis before and after the corrosion tests.

Alloys with a cobalt binder content in the range from 3 to 15 wt.% were studied. The carbides grain size also range between 0.7 and 5 μm. Mechanical properties, such as transverse rupture strength and hardness, were tested. The residual porosity and the micro structure were accurately observed by optical microscopy and the carbide grain size was estimated using an optical image analyser.

The dimensional changes that occur in the steel during heat treating is one of the most difficult problems facing the heat treater. While the influence of the alloy chemical composition, of the heat treatment cycle and of the shape and dimensions of the pieces on the deformations caused by heat treatments on the wrought steels are now a days well known, the presence of the porosity in the sintered steels arouses some inconvenients which influence directly the heat treatment effects.

An X37CrMoV5.1KU hot working steel was quenched and tempered, nitrided, overcarburised, overcarburised and nitrided, and nitrocarburised for 18 and 36 h. Wear tests at 50 and 100 kg loads were performed without lubricant on the treated specimens using an A135 Amsler machine in order to determine the most effective treatment. The quenched and tempered specimens showed the worst behaviour and the nitrocarburised specimens the best.

Thermal spraying processes have many advantages that help improve the performance and extend the life of materials and components. In the present paper the properties and wear behaviour of plain carbon specimenscoated with Ni or Co based alloy powders have been studied for the coating of tools employed in hot working applications, e.g. rolls in a rod mill plant.

Graded structures obtained by coupling different WC grades, also containing cubic carbides type (Ta, Nb)C with Co as binder, were produced by vacuum sintering. Different batches of cylindrical samples were compacted by coupling two different grades and were sintered at 1450°C under vacuum. The hardness properties as well as the shrinkage due to sintering process are function of the employed grades and show gradual change between the single values of each of the coupled grades.

Sintered samples containing Mo, Ni and Mn, were plasma nitrided or nitrocarburized or sulphonitrocarburized with seven different cycles. After characterization the dry wear resistance of the treated samples was evaluated by an Amsler tribometer. The samples with the best wear resistance have a surface layer formed by martensite and retained austenite. A good wear resistance is also observed for the samples with a surface layer formed by a high amount of ε solid solution, or ε solid solution with a great carbon content.