Influence of process parameters and alloying type on properties of laser quenched PM-steels

Different alloyed PM steels have been laser quenched in industrial equipment laser diodes (4 kW, controlled by material surface temperature). The aim of this work is to investigate their responses to different process condition and different alloying metals, i.e. Cu, Ni, Mo, Cr and C. Furthermore the microstructure of hardened layer, heat affected zone (HAZ) and bulk zone Pre-alloyed, diffusion bonded and hybrid raw materials have been used. Design of Experiments has been the approach for evaluating the effect of treatment parameters (i.e temperature, spot size and speed) and to develop predictive models, correlating such parameters to hardening depth and scratch hardness number. Results demonstrated which valuable properties could be achieved, even through relatively low alloying. The promising results are encouraging since they allow to forecast a possible positive combination of high local hardness and wear resistance of high precision PM part

El tabaquismo en los pacientes de hemodiálisis. Prevalencia de consumo y actitudes

El objetivo del estudio es conocer la prevalencia y las características del hábito tabáquico en los pacientes incluidos en hemodiálisis en nuestra provincia y estudiar así mismo, algunas actitudes y conocimientos relacionadas con este hábito que nos orienten en la creación de un Plan Sanitario para la disminución del consumo de tabaco en los pacientes de diálisis

Electroless Ni coatings for the improvement of wear resistance of bearings for lightweight rotary gear pumps

The possibility of improving the performances of current aluminiumalloys in the bearings region of lightweight external gear pumps has beeninvestigated. Two different electroless Ni-based coatings, one containing highpercentages of P (10–14%) and the other modified with the addition of 25 wt%PTFE micrometric spheres, deposited on 2011 Al alloy, were characterisedby scratch test and ball-on-disc tests. Comparison with an antifrictionSn-containing Al-alloy was performed. The PTFE-containing coating presentsthe lowest wear rate and friction against steel. However, the presence of PTFEspheres and the hardness mismatch with the substrate tends to favour tensilecracking of the coating

Corrosion resistance improvement of nitrocarburised and post-oxidised steels by oil impregnation

Nitrocarburising is a well known process developed to improve superficial hardness and wear resistance of steels; a subsequent post-oxidation step is often useful to enhance the corrosion resistance. In this work, an additional step was evaluated: nitrocarburised and post-oxidised parts were impregnated in lubricant oil in order to improve their wear and corrosion resistance. The effectiveness of this new treatment, in terms of corrosion resistance, was assessed for two steels, 20MnCr5 and 42CrMo4, using two different oils. The results obtained from corrosion tests show that the impregnation treatment increases the corrosion resistance, in both acidic and chlorurated media

A Novel Methods for Fracture Toughness Evaluation of Tool Steels with Post-Tempering Cryogenic Treatment

Cryogenic treatments are usually carried out immediately after quenching, but their use can be extended to post tempering in order to improve their fracture toughness. This research paper focuses on the influence of post-tempering cryogenic treatment on the microstructure and mechanical properties of tempered AISI M2, AISI D2, and X105CrCoMo18 steels. The aforementioned steels have been analysed after tempering and tempering + cryogenic treatment with scanning electron microscopy, X-ray diffraction for residual stress measurements, and micro- and nano-indentation to determine Young’s modulus and plasticity factor measurement. Besides the improvement of toughness, a further aim of the present work is the investigation of the pertinence of a novel technique for characterizing the fracture toughness via scratch experiments on cryogenically-treated steels. Results show that the application of post-tempering cryogenic treatment on AISI M2, AISI D2, and X105CrCoMo18 steels induce precipitation of fine and homogeneously dispersed sub-micrometric carbides which do not alter hardness and Young’s modulus values, but reduce residual stresses and increase fracture toughness. Finally, scratch test proved to be an alternative simple technique to determine the fracture toughness of cryogenically treated steels

Effects of Surface Morphology on the Wear and Corrosion Resistance of Post-Treated Nitrided and Nitrocarburized 42CrMo4 Steel

The surface of alloyed carbon steel was subjected to thermochemical modification by nitrocarburizing and nitriding with or without postoxidation in order to improve its mechanical properties, corrosion, and wear resistance. Treated samples were characterized by testing their basic properties (compound layer thickness, nitriding, nitrocarburizing depth, and surface hardness) according to standards. Detailed estimation of the modified metal surface was performed by additional testing: X-ray diffraction, microstructure, surface roughness and topography, and wear and corrosion resistance. The surface layer obtained after nitrocarburizing treatment consists mainly of ε-Fe2-3(N,C) and γ'-Fe4(N,C); similarly, the nitrided surface is formed by ε-Fe2-3N and γ'-Fe4N iron nitrides. The surface layer after postoxidation contains additionally Fe3O4. The results obtained show that nitrocarburization, nitridation, and postoxidation result in better mechanical, wear, and corrosion resistance of 42CrMo4 steel, and postoxidized sample properties are influenced by surface morphology

Improvement of wear and corrosion resistance of ferrous alloys by post-nitrocarburizing treatments

Gas nitrocarburizing and post-oxidation treatments were performed on 42CrMo4 and 20MnCr5 steels, G30 and GS600 cast irons, to improve wear and corrosion resistance. In both materials the thickness of the compounds layer, mainly composed by epsilon- and gamma’- phase, resulted about 15-20 micron and the measured diffusion layer was about 150 micron thick. A subsequent oxidizing step, followed by impregnation with a two different lubricating oils was performed in order to further enhance corrosion resistance. Wear resistance against alumina was measured using a ball-on-disk tribometer and the corrosion characteristics of the samples were studied using salt spray test in accordance with ASTM B117. Experimental results show that the nitrocarburizing treatment improves significantly the wear resistance of the steels but not the wear resistance of the studied cast irons. The steels present almost the same tribological behaviour, ascribable to the formation of similar compounds, while cast irons present different wear resistance due to their chemical composition and the graphite morphology. The application of nitrocarburizing alone does not significantly improve corrosion resistance and it may even promote localized corrosion. The subsequent post-oxidation step leads to a slight decrease of the corrosion rate, because it partially seals the porous nitrocarburized layer. The final oil impregnation step resulted much more effective in further decreasing the corrosion rate and this final treatment in some cases improves also the wear resistance

Effect of quenching method on the wear and corrosion resistance of stainless steel AISI 420 (TYPE 30Kh13)

The effect of different kinds of quenching, i.e., laser, vacuum, and induction ones, on the mechanical properties and wear and corrosion resistances of stainless steel AISI 420 is studied. It is shown that all the three kinds of heat treatment raise considerably the wear resistance of the steel due to growth in the hardness. Laser and vacuum quenching also increases the corrosion resistance. After induction quenching the resistance to corrosion is lower than in untreated steel

Comparison - By nanoindentation - Among PM steels obtained from diffusion-bonded powders (nominally equivalent)

In principle, powdered raw materials, produced by a given process and having equal chemical com-position, are supposed to be equivalent. In previous research works, the differences among response to sintering behaviour have been investigated on P/M steels based on four diffusionbonded powders (Fe + Ni + Cu + Mo), with atomized iron base, at the same alloy contents. Two levels of carbon (0.3 and 0.6 wt%) and two sintering conditions have been investigated, in industrial manufacturing conditions. However the comparison of dimensional changes, carbon content, and hardness reveals only modest differences. The comparison of microhardness distribution, fractal analysis, pore features, microstructure patterns show some clear differences, sometimes not univocal. The previously achieved results show that the claimed equivalence is not adequately and completely confirmed by closer and more complete comparative evaluation of experimental data. Only accurate analyses of microhardness and microstructure distributions seem powerful tools to rate, with modest sensitivity, the real similarity of the so claimed equivalent ironbase powders. Clearer differences have been shown by dilatometric analysis. To verify these observed differences, nanoindentation tests have been carried out. Each material has been characterized by nanoindentation measurement, for any process condition. The measured values, plotted on normal distribution graphs, only partially confirm the differences revealed by dilatometry. Some different ranking of diffusion level results from nanoindentation. This recently developed method, suitable to characterize very small volumes of material, appears suitable to find even minor differences among materials that could appear equivalent if evaluated by simpler and easier test methods

Microwave ignited combustion synthesis of metal and intermetallic matrix composites

Aim of this work is to present the results concerning the application of microwave assisted combustion synthesis (MACS) approach in the production of different kind of cermets and intermetallic matrix composite (IMC). Combustion synthesis allows taking advantages from the heat generated from exothermic reactions, which can derive from the synthesis of the intermetallic matrix, of the reinforcement, or both. Microwaves were used to ignite such combustion reactions exploiting their heating selectivity. The use of a single mode applicator allowed also investigating any "specific" microwave effects ascribable to separate electric and magnetic fields