Key Engineering Materials Vol. 835

Abstract: This paper deals with the possibility of obtaining FeSiAl complex alloy by carbothermic reduction in a submerged arc furnace using aluminum dross, mill scale and feldspar.Bench scale experiments are carried out to clarify the effect of different variants such as reducing agent, basicity, and mill scale content of the charge on the metallic yield and chemical composition of the produced alloy.It was possible to get FeSiAl alloy containing 22% Si and 18% Al. the results reveal that to obtain such alloy less than 20% mill scale must be involved in the charge and the coke with amount 1 stoichiometric must be used.

Abstract: With the objective of partial and total replacement of nickel by nitrogen in austenitic exhausted valve steel X45CrNiW18-9, a program of work with series of experimental heats was designed. Experimental heats were carried out in 10 Kg. induction furnace under nitrogen pressure. The chemical composition of produced stainless steels was determined. The produced automotive steel grades were forged. The nitrogen contents were determined. The produced forged stainless steels were subjected to solution treatment at 1050 °C for 1 hour, followed by water cooling. Isothermal oxidation test is used to detect the behavior of new grades at different temperatures in air for solution treated stainless steels. The mass gain was measured for samples exposed to air at temperatures (500 °C, 600 °C, 700 °C, 800°C) for different time intervals, up to 1000 hrs. The oxide layer thickness for two selected steels was investigated by using optical microscope. XRD was used to detect types of oxides which are formed during oxidation process at 800 °C for 1000 hrs for represented investigated exhausted valve steels. Scanning Electron Microscope was used to make scan steels surface, after heating at 500 °C and 800 °C for l000hr. The mechanism of the oxidation of developed steels was investigated. It was found controlled by diffusion mechanism and the kinetic of oxidation process is parabolic. Oxidation rate of the investigated stainless steels for times, up to 8 h and between 200 andl000 h, at all investigated temperatures (500 °C - 800 °C), is parabolic and the oxidation is diffusion controlled. While in the time region 10 to 200 h, it obeys combined mechanisms. Partial replacement of nickel, by nitrogen, improves the oxidation resistance in air at temperature range 500°C - 800°C.

Abstract: Preparation of aluminum substrates for surface segregation enhancement of insoluble lead deposition was achieved. Sever plastic deformation 'SPD' of Al sheets was done using surface mechanical attrition treatment 'SMAT' in air. Scanning electron microscope SEM of etched Al substrates cuts showed micro-cavities both on the surface and in-depth. Orientation effects and surface inclusions of Pb inside Al surface found at 40 and 50 Hz - SMAT Al by X-Ray diffraction and energy dispersive of X-Rays EDX. Concluding that SMAT frequency limits used enhanced surface inclusions without annealing that could improve adhesion of industrial protective Pb coatings.

Abstract: Arc welding processes are widely used in the automotive industry among other welding processes. Consequently, laser welding technology is being used instead of arc welding due to the rapid heating and cooling characteristics of the laser. In this study, empirical investigations and comparative study are held out on the arc and laser beam welded joints of DP780 dual-phase steel. Accordingly, weld joint microstructures, hardness distribution, and fatigue properties cross the butt-welded joints were investigated. The results showed that laser beam welding produces narrow fusion and heat-affected zones while gas metal arc welding produced wide welds with incomplete penetration. It was observed that the microstructure of the laser joint weld metal has mainly lath martensite in the ferritic matrix, while microstructure of gas metal arc weld metal relies upon filler type. Heat-affected zone in DP780 steel exhibit hardness softening in both laser beam welding and gas metal arc welding due to martensite tempering, a wider softening region was clearly observed in heat-affected zone welded by gas metal arc welding than laser beam welding. Generally, fatigue ratio, fatigue limit and fatigue life of the welded joints were improved by using laser welding.

Abstract: Fluxing and tinning processes are usually used to improve the adhesion of the Al bearing layer on steel substrate. Commonly after grinding the surface of the steel substrate, it is briefly immersed in flux solution followed by coating steel surface with either pure Sn (in a process known as tinning process) to promote adhesion between the bearing alloys and the steel. The current work is designated to investigate the influence of tinning material for carbon steel substrate using simultaneous fluxing and tinning mixture technique. The influence of three different tinning materials on the interface structure and shear strength of cast Al-Sn bearing alloy/steel bimetal composite is evaluated for compound casting technique. Sn pure, Sn-3Cu alloy and Sn-7.5Sb-3Cu powder alloys mixed individually with flux are used as tinning materials. It was found that using of different tinning materials have a significant effect on the bonding of interface area and the shear strength of interface as well. The shear strength of the bimetal fabricated using tinning mixture contains Sn+3% Cu with flux significantly increases by 59% compared to that fabricated using tinning mixture contains pure Sn. This increment is mainly due to the improvements of the interface bond structure and lower percentage of tin oxides. Such kind of phenomena can be explained in the fact that Cu minimizes the possibility of Sn oxidation during tinning process and during preheating of tinned steel substrate before casting of Al12Sn4Si1Cu bearing alloy as well.

Abstract: The structural properties and capacitive behavior of manganese dioxide (MnO₂) films prepared by potentiostatic cathodic deposition were examined in presence and absence of pre-electrophoretically deposited reduced graphene oxide (rGO) film. The FTIR analysis reflects the formation of a MnO₂/rGO composite film structure. SEM and TEM characterization show that the MnO₂ film deposited on rGO film has finer and less compact nanostructure and grown as sparsely aggregated particles follow the open structure of underlying rGO platelets. The specific capacitance and rate capability of MnO₂/rGO film are higher than that of pristine MnO₂ film; it exhibits specific capacitance of 292 Fg^-1 at 1 mA cm^-2 and better cyclic stability at 3 mA cm^-2. The presence of 3D underlying defective rGO film creates an open structure with larger area, facilitates the electron transfer and access of the electrolyte ions through the surface of MnO₂ film and hence offering the potential of the unique capacitive behavior.

Abstract: This current work investigates the failure of high pressure (HP) scrubber lining in urea fertilizer production plant after 20 years in service. AISI 316L urea grade (UG) stainless steel scrubber lining was showed severe damage. In order to find out the root cause of failure, cracks were observed by visual inspection together with microstructure examination Chemical analysis of the base metal and corrosion products were analyzed Chemical analysis of the lining base alloy is conformed to the AISI 316L UG. Results revealed existence of chloride assisted stress corrosion cracking (SCC) initiated from pitting formed in the inner surface of the scrubber lining. Corrosion products analysis revealed existence of chloride (Cl^-). Localized pitting corrosion is attributed to Cl attack. The expected sources of chloride are water during hydrostatic testing, water vapor during passivation, chloride containing atmosphere during transportation or storage the base alloy in coastal areas and water vapor in carbamate gasses (process fluid). Pits initiated at the lining inner surface act as stress concentration sites assisted SCC initiation. Chloride SCC is caused by simultaneous action of both tensile stresses and a corrosive environment containing chloride. To overcome the scrubber failure, chloride must be eliminated and residual stresses must be controlled. Upgrading the scrubber base alloy using high-alloy duplex stainless steel (Safurex) is highly recommended.

Abstract: This work aims at optimizing the H₂ reduction time of Fe/rGO as a preparatory step for the use of the reduced catalyst in Fisher-Tropsch synthesis (FTS). The catalytic system used was Iron Nanoparticles (NPs) loaded on reduced graphene oxide (rGO) support. The as prepared sample was analyzed by TEM, FTIR and XRD spectroscopy. Samples of the produced Fe/rGO catalyst were used to optimize the reduction conditions in the FBR reactor. The three samples were reduced under 1atm H₂ gas flow of 50 sccm at 500°C for 8, 12 and 24 hrs. The samples were collected after reduction and analyzed by XRD, FTIR and TEM imaging. The best condition showing full reduction with minimal sintering was at 12hr.

Abstract: Electrical wires with melted ends showing beaded, drop-shaped, and pointed shapes are frequently encountered after fires that may provide useful information on the cause and development of the fire.Various methods have been studied for differentiating between primary arcing beads, (indicating arcing as the fire cause) and secondary arcing beads (indicating arcing as a result of the fire). There are few studies carried out on the melting globules produced due to fire heat. Also, in some major cases, primary arcing beads and secondary arcing beads are difficult to be identified by using one method. In this study, a full scheme of differentiating methods between simulated samples of melting globules, primary arcing beads and secondary arcing beads are processed with macroscopic investigation. The in-depth composition of carbon quantitative analysis and metallurgical analysis of these samples have been studied. The results of this study has proved that the real cases are compatible with simulated ones.

Abstract: Reduction in grain size of bcc based structure steel is still highly concerned in the cold rolled sheet to attain superior mechanical properties. As long as, the reduction of weight is much considered in the structure purposes, the strength/weight ratio of steel is highly demanded. In this study, an innovative technique was applied to attain ferrite grain size with hundreds of nanometer, in tandem with preserving the mechanical properties. In this approach, the micro-alloyed low carbon steel resulted from the thermomechanical process was followed by subcritical annealing regime prior to the first critical transformation temperature. To identify the effect of a micro-alloying element as vanadium, and the effect of subcritical annealing regime on the low carbon steel, two low carbon steel was subjected to studying in this research. The results refer that applying a subcritical annealing regime for the micro-alloyed low carbon steel after hot compression at intercritical annealing temperature can lead for attaining hundreds of nanometer ferrite grain size, which has a powerful effect on promoting the strength of the steel to exceed 1200 Mpa, in one hand with preserving the formability up to 20% as uniform elongation. Unexpectedly, the fine grain size obtained after the innovative technique promotes the impact toughness at room temperature, which is attributed to the fineness and the spheroid morphology of the secondary phase in conjugation with bcc ferrite structure.