Journal of Advanced Processes in Materials Engineering
Year:2009 | Volume:3 | Issue:1 (8)|Papers Count:8

Microstructures of the Incoloy 800 in the solutionised, aged and (aged + solution annealed) conditions and the as-cast HP heat resistant steel were characterised. The weldability of two alloys in different condition was investigated. It was found that dissimilar welding between aged alloy 800 and HP steel was not successful due to liquation cracking in the HAZ of the aged Incoloy 800. The effect of solution annealing on the microstructure of the aged Incoloy 800 and weldability of two alloys were investigated. It was found that during solution annealing, the precipitates that already formed in the aging stage can be decomposed leading to the formation of titanium carbide (TiC). In addition, solution annealing was improved the weldability of two alloys. The hot cracking susceptibility was evaluated by the Varestraint test.

Nowadays cobalt is mostly produced through electrowinning process of sulfate solution. Regarding competitive cobalt precipitation and hydrogen evolution in the cathode during reduction in a sulfate bath, investigation on the mechanism of metal precipitation is of great importance. In the present work, study on the kinetics of cobalt electrowinning and the mechanism of involved reactions have been carried out. The obtained results, represent that the cobalt precipitation by depletion of hydroxides. The effects of temperature and scan rate parameters were studied on electrowinning of cobalt by cyclic voltammetry technique. The diffusion coefficient and rate constant of the reaction were measured and calculated by performed experiments.

In this research, the copper extraction from the activated copper concentrate of Miduk mine was studied by leaching in the diluts sulfuric acid solution. The effect of mechanical activation on the roasting was studied and the combined effect of activation and roasting on the leaching processes was investigated. Samples of sulfide concentrate mixed with lime were activated under air atmosphere and oxygen for different times. minimum temperature and required time for roasting were obtained using thermal analysis (TG-DSC). The activated samples were roasted in argon and air atmosphere in 750oC for 20minutes. The samples roasted under air atmosphere and a sample of inactivated concentrate was leached for different times. The results of XRD phase analysis indicated that activated samples under the air atmosphere a significant amount of sulfur in concentrate is converted into CaS and CaSO4 as a result of roasting. The result of atomic absorption analysis showed that about 70% of copper recovery reached in the first 30 minutes of leaching process and increase of time until 4 hours had littel impact on copper recovery. Due to insolubility of CaS and CaSO4 in acid, the sulfur remains in solid waste of leaching. This waste contains CaS, CaSO4, Fe2O3 and insoluble silicates.

Particulate TiC - reinforced ferrous matrix composites have been in interest in recent years, due to their dominant properties. In this research, the effect of graphite formation through heat treatment on wear properties of these composites at as-cast and heat-treated conditions were investigated. Some specimens were centrifugally casted in a zirconia mould and followed by heat treatment at 980oC to decomposition of cementite and formation of graphite. The microstructure and wear properties were studied by optical microscope and wear test machine respectively. The results showed that formation of graphite reduced the friction coefficient and weight loss of samples. This confirm self-lubricant role of graphite phase in microstructure.

Hot tearing is a common defect which occurs during solidification of cast alloys with large mushy zones. In the present research a new hot tearing criterion, namely NNC, is proposed which takes into account both mechanical and metallurgical aspects of solidification. NNC was validated by examining the effects of copper content on the hot tearing of A206 aluminum alloy. NNC was able to satisfactory predict the decreasing trend of hot tearing by increasing the copper content as shown by other researchers. NNC is capable of providing reasonable prediction of hot tearing tendency of cast alloys provided the required thermal and mechanical parameters are correctly determined from a hot tearing test previously developed by the authors.

Magnesia-carbon refractory brick has attracted attention in steelmaking industry due to special properties of heat resistance and non wettability with steel melt. Hot corrosion of slag line and the need to repair and replace with the new brick is a problem. In this research the effect of different slag additions on corrosion of magnesia-carbon refractories in ladle furnace is studied. Results show that the addition of dolomite powder, magnesite carbon used bricks (waste), sintered magnesium oxide and talc in proportions of 15% and 30% to be replaced with the amount of slag is beneficial. The most effective additive in corrosion resistance increase is dolomite.

Two steps aging is a novel heat treatment for 7000 series a Aluminum which improves the stress corrosion cracking (SCC) resistance of these alloys without any considerable influence on their strength. The heat treatment included a post-quenching pre-strain of 5%, a high-temperature aging at 200oC for several minutes and a subsequent low-temperature aging at 120oC for24 h as conventional T6 treatment. This research concentrates on improvement of this heat treatment for Al-7075 alloy. One stage rolling prior to high temperature aging and also one stage before the second step of aging resulted in simultaneous increasing the strength and SCC resistance of the alloy similar to those obtained by T6 and T73 treatments respectively. Strain induced at the first step of rolling caused more forming h phase particles and the second rolling led to breaking the grain boundary precipitates and increasing the anodic surfaces which subsequently reduced the dissolution of the particles.

Effect of vanadium on austenite transformation kinetic in microalloy mild-steel has been investigated. The evolution of hardness and microstructure has been studied in two carbon steels with vanadium and without vanadium after austenitization and quenching in water. Austenite transformation kinetic has been investigated by Avrami equation which has been resulted from hardness and microstructure. The results indicated the rate of austenite transformation decrease in microalloy steel while temperature of austenitization is lower than 950oC. Austenite transformation kinetic is increased when vanadium precipitation is dissolved.