METALLURGICAL ENGINEERING
Year:2014 | Volume:17 | Issue:55 |Papers Count:7

In order to investigate the effect of heat treatment on wear characteristics of Cr-Mo wear resistant steel, the specimens were austempered and martempered at 300oC and 200oC respectively for 2, 8, 30, and 120 minutes and the wear properties of the specimens were compared with those observed in common cycle in industry (compressed air quench). Dry sliding wear tests have been conducted using a pin-on-disk machine under different normal loads of 57.8, 81.3 and 104.8 at a constant sliding speed of 1.20 m/s. The scanning electron microscope (SEM) and X- ray diffraction (XRD) analysis of surface and wear debris of specimens shows that wear mechanism was mainly mild oxidative in all samples, however, delamination and plasticity-dominated wear mechanisms have been seen in high loads. The friction, wear rate and wear coefficient of the steels, have been explained with respect to microstructure and the wear mechanism. The comparison of wear rates shows that by using austempering and especially martempering process, wear resistance of this steel increases considerably.

The effect of cobalt ion concentration of electroplating solution on morphology, phase structure and corrosion resistance of zinc-cobalt alloy electrodeposits that were obtained from Sulfate- acid solutions by direct current on St37 steel has been studied. SEM, EDS and XRD were used to study the surface morphology, chemical composition and phase structure of coatings. Respectively corrosion behavior of Zn-Co alloy coatings were studied by Tafel polarization experiment in 3.5 wt% NaCl solution. In addition the microhardness of the Zn-Co alloy coatings was examined. The results showed that increasing of cobalt ion content of electroplating solution, increases cobalt content as well as microhardnees of the coating. The cobalt ion in the plating bath strongly affects the chemical content and phase structure, as well as corrosion stability, of Zn-Co alloys. It was also noticed that corrosion resistance of the deposits were highly influenced by the composition and morphology of the coatings. Zn-Co alloy coatings containing 1.2 wt% Co showed the highest corrosion resistance due to its single phase.

In this research, TLP bonding was used for dissimilar joints of IN-738/FSX-414 system using MBF-80 interlayer with the thickness of 50mm. TLP bonding was carried out at optimum condition (1150oC/5min) in a vaccuum furnace. Then, in order to refine the microstructure and increase the mechanical properties of the joints, homogenization treatment was carried out at 1175, 1200 and 1225oC for 1, 3 and 6 h. Optical microscope and scanning electron microscope (SEM) were used for microstructural studies and phase analysis was done using SEM/WDS analysis. Microstructural studies showed that homogenization at 1175oC/6h had no effect on removing the diffusion affected zone (DAZ) phases, but considerable reduction of these phases has occurred at 1200oC/1h. Homogenization at 1225oC for 1h caused formation of grain boundaries and secondary eutectic phases at the joint as well as coarsening of precipitates at the joint and base metal. Profile of alloying elements concentration across the joint showed that precipitation and coarsening of at the base metal and diffusion of alloying elements were the controlling factors of homogenization. Considerable reduction in the slope of alloying elements concentration profile at 1200oC was due to the rapid diffusion through the grain boundaries of the joint. Therefore, the optimum microstructural features were seen at 1225oC/1h homogenization condition.

Ecological sustainability and balance are the elements of sustainable development. In this paper, using fuzzy logic, a model is presented to monitor region wise industrial pollutants in pyrometallurgy industries. The model has been used in a case study that will determine which industry, in which region, producing which and how much pollutants, is compatible with ecology. To assess the ecological compatibility, first, the set of industries, regions, pollutants and ecological compatibility were defined, then to calculate the membership degree of the members of the ecology compatibility set, the membership function of ecological compatibility was defined. By ranking different industries in various regions, creating different pollutants, as continuous figures, the ecological compatibility of these industries was accurately compared. Given the degree of ecological compatibility in a region, the type of pollution, and the related industry, identification of the lowest degree of ecological compatibility was the first priority of this case study. Results of the conducted case study, without considering the region coefficient, show that member C241, in December 2005 with an ecological degree of compatibility equivalent to 0.0559 has the most critical condition in producing the air pollutant, carbon dioxide. However, on considering the region coefficient, member C121, in December 2005 with an ecological degree of compatibility equivalent to 0.0655 has the most critical condition in producing the air pollutant, carbon dioxide.

In this study, the effect of heat input on microstructure and mechanical properties of magnesium alloy, AZ91, were investigated. The butt welding was carried out at three different heat inputs (269, 452, and 657 J/mm), using a tungsten arc welding process under the protection of inert gas (GTAW). Microstructure observation with optical (OM) and scanning electron, microscopes (SEM) showed that with an increase of the heat input, the grains both in the fusion zone and the heat-affected zone coarsen and the width of the heat-affected zone increased. Moreover, an increase of the heat Input up to 657 J/mm resulted in a decrease of the continuous Mg17Al12 phase and an increase of the granular (particularly in weld area) and randomly dispersed. The results of tensile tests show that at high heat input the welding strength will decrease to 114 MPa, due to creation of gas voids in the welding area. This value is 21% less than that observed for lower heat input (269 J/mm).

In many manufacturing process which are based on melting and solidification, like casting, measurement of viscosity and prediction of fluidity of molten metal in variant temperatures and alloy composition could improve quality of process and decreasing losses. In this paper different methods for measurement of viscosity like capillary method, oscillating vessel viscometer, falling body or counterbalanced sphere viscometer, oscillating plate method, rotating cylinder and … have been investigated. Arrhenius equation, Andrade treatment, Hildebrand’s free volume theory, Chhabra model and … are the models which were used for estimation of viscosity of metals and alloys and their relation with temperature. Finally comparison of different procedure for viscosity measurement of molten metals is presented.