The role of manganese ore reduction morphology development in setting reduction mechanisms

Please read abstract in the article.The University of Pretoriahttp://www.elsevier.com/locate/mineng2020-06-15hj2020Materials Science and Metallurgical Engineerin

Phase chemistry of submerged arc welding (SAW) fluoride based slags

Please read abstract in the article.The National Research Foundation (NRF) of South Africahttps://www.journals.elsevier.com/journal-of-materials-research-and-technologyam2021Materials Science and Metallurgical Engineerin

Non-isothermal reaction of iron ore-coal mixtures

Extensive work is reported in literature on the reduction of iron oxides with carbonaceous reductants. Most of this work considered isothermal reaction of the material mixture, although as shown in some studies, isothermal reaction conditions are not often the norm because of sample size and heating arrangement in the experiment. In industrial processes, such as the rotary hearth type processes and the IFCON® process for iron ore reduction, the norm is non-isothermal reaction. Simulation of industrial processes should take non-isothermal reaction into account if the heat transfer effects within the process are to be investigated. To avoid the complications of coal volatiles in the experimental set-up, few studies were done with coal as reductant. The primary aim of the work presented here is to quantify radiation heat transfer to the surface of an iron ore and coal mixture heated uni-directionally from the sample surface to show the importance of heat transfer in the IFCON® process. Secondary aim of this work are to show the effects of layer thickness, coal volatiles, phase chemistry and particle size in this reaction system. The experimental set-up consists of a tube furnace modified to transport the sample into and out of the experimental tube furnace heating zone under a protected atmosphere, whilst the product gas is analysed throughout the experiment by quadropole mass spectrometer. The sample surface temperature, heating zone temperatures and material bed temperatures were measured throughout the experiment. A sample cutter-splitter was developed to divide the reacted sample into three horizontal segments for chemical analyses. The sample surface temperature and the heating zone temperatures were used as inputs to a radiation network calculation to quantify radiation heat transferred to the sample surface. The radiation network calculation was calibrated against heat-mass balance calculations for pre-reduced ore and graphite samples reacted at furnace temperatures of 1300, 1400 and 1500°C. The results show that radiative and conduction heat transfer control prevails for 16 mm to 40 mm material layers heated uni-directionally from the material layer surface. It is shown that coal volatiles contribute to reduction in the stagnant material layer. Also, smaller particle sizes result in increased reaction rates because of a decrease in the diffusion limited effects which were seen in reaction of the base size of coal and ore particles.Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2009.Materials Science and Metallurgical Engineeringunrestricte

Application of unconstrained cobalt and aluminium metal powders in the alloying of carbon steel in submerged arc welding : thermodynamic analysis of gas reactions

DATA AVAILABILITY STATEMENT : The data sets presented in this study are available upon request to the corresponding author.The application of cobalt and aluminium powders in unconstrained format, not as metal powder in tubular wire nor as pre-alloyed powder, is used in this work to simplify weld metal alloying. The objective of this study is to demonstrate the application of unconstrained cobalt and aluminium powders in Submerged Arc Welding SAW to alloy the weld metal and to control the weld metal oxygen content. Aluminium powder is used to control the oxygen potential at the weld poolslag interface in order to prevent oxidation of cobalt. The results presented here show that with the addition of Aluminium powder, 70% yield of Cobalt was achieved from the cobalt powder to the weld metal. The carbon steel base-plate material and weld wire materials combination were alloyed to 5.3% Co and 4.2% Al, whilst controlling the weld metal total oxygen content to 230 ppm. Thermodynamic analysis is applied to investigate the possible chemical interaction reactions between Co and Al compounds, as well as the role of the reactions on Co yield to the weld pool. The application of unconstrained metal powders ensures productivity gains in the overall SAW process because the time consuming and expensive manufacturing of alloyed wire and alloyed powder are eliminated.The National Research Foundation of South Africa.https://www.mdpi.com/journal/applsciam2023Materials Science and Metallurgical Engineerin

Chemical interaction of Cr‐Al‐Cu metal powders in aluminum-assisted transfer of chromium in submerged arc welding of carbon steel

DATA AVAILABILITY STATEMENT : The data presented in this study are available on request from the corresponding author.In submerged arc welding (SAW) of chromium containing steels, the chromium in the weld metal is usually sourced from weld wire. Manufacturing of precise weld wire compositions for alloying of the weld metal is expensive. In addition, alloying of weld metal with high levels of copper via weld wire is hindered by work hardening of the weld wire. In the SAW process, a large quantity of oxygen is added to the weld pool. Because chromium has a high affinity for oxygen, the oxygen partial pressure at the weld pool-molten flux interface must be controlled to ensure high recovery of chromium to the weld metal. This study illustrates the application of copper as stabilizer, in conjunction with aluminum, to enhance chromium transfer to the weld pool. The stabilizer effect occurs because the Cr-Al-Cu alloy liquidus temperatures are much lower than the pure Cr liquidus temperature. The result is an increase in the total quantity of Cr, Al, and Cu powder melted into the weld pool. The application of Al powder additions to control the partial oxygen pressure at the molten flux-weld pool interface is confirmed in the presence of Cr and Cu metal powders to ensure the weld metal ppm O content is maintained at the acceptable level of 300 ppm.The National Research Foundation of South Africa.https://www.mdpi.com/journal/processesam2023Materials Science and Metallurgical Engineerin

Aluminium-assisted alloying of carbon steel in submerged arc welding with Al-Cr-Ni unconstrained metal powders : thermodynamic interpretation of gas reactions

DATA AVAILABILITY STATEMENT : The datasets presented in this study are available upon reasonable request to the corresponding author, indicated on the first page.Unconstrained metal powders of chromium and nickel, in combination with aluminium, were used in the submerged arc welding (SAW) process to simplify weld metal alloying. Unconstrained metal powders refer to non-alloyed metal powders that are not constrained in tubular wire, such as fluxed-cored and metal-cored wire. Aluminium powder is used to control the oxygen potential at the molten flux–weld pool interface. The results presented here show that the addition of aluminium powder to the weld metal enhances Cr and Ni yields to 89% for Cr and 91% for Ni, compared to lower values reported in pre-alloyed powder application. Alloying of the carbon steel in the base plate and weld wire combination was achieved at 6.0% Cr, 6.2% Ni, and 4.5% Al, with the weld metal oxygen controlled to 162 ppm O. Thermodynamic analysis was applied to investigate the likely gas reactions in the arc cavity emanating from the chemical interaction between Cr, Ni, and Al. The effects of gas-based chemical reactions on the yield of Cr and Ni to the weld pool are discussed and incorporated into our SAW reaction flow diagram. Overall SAW process productivity gains can be accomplished by using unconstrained metal powders to alloy the weld metal because expensive and time consuming steps, such as the manufacturing of alloyed wire and alloyed powder, can now be eliminated.The National Research Foundation of South Africa.https://www.mdpi.com/journal/processesam2023Materials Science and Metallurgical Engineerin

Insight into the chemical behaviour of chromium in CaF2-SiO2-Al2O3-MgO flux applied in aluminium-assisted alloying of carbon steel in submerged arc welding

DATA AVAILABILITY : The datasets presented in this study are available upon request to the corresponding author.Chromium alloying of weld metal is usually accomplished via weld wire. This is done because chromium has a high affinity for oxygen and is therefore not easily transferred across the arc. The formation chromium (VI) is one of the main concerns in welding with chromium containing consumables, especially in open arc processes, and less so in SAW (submerged arc welding). This study investigates the chemical behaviour of chromium in the application of unconstrained metal powders of Al, Cr, Cu and Ti in SAW. The application of aluminium in SAW is used to control the oxygen partial pressure in the process to prevent oxidation of elements of high oxygen affinity, such as chromium. The speciation of chromium was investigated in two-dimensional (2D) and three-dimensional (3D) post-weld slag samples. In the 2D slag samples, the chromium is contained in low concentrations in the oxy-fluoride matrix phase. The 3D samples showed dome structures in which evidence of vapour formation was identified. Chromium presents as distinct chromium spots throughout the oxy-fluoride dome walls, and it is not observed as solute in the oxy-fluoride phase. Chromium presents as chromium-rich Cr-Mn-Mg-O porous particles of less than 20 m in size, which may agglomerate into larger masses. The calculated thermochemical predominance diagrams show that the Al(l)-Al2O3(s)-AlF(g) equilibrium can maintain the partial oxygen pressure (PO2) at 1016.5 atmosphere and the partial fluorine pressure (PF2) at 1011.4 atmosphere at 2500 C. Under these gas phase conditions in the arc cavity, chromium is present as metallic chromium and may subsequently vaporise as chromium metal and combine with other vaporised elements.The National Research Foundation of South Africa.https://www.mdpi.com/journal/mineralsam2023Materials Science and Metallurgical Engineerin

Aluminium assisted nickel alloying in submerged arc welding of carbon steel : application of unconstrained metal powders

Nickel alloying of carbon steel is used to enhance steel strength and toughness. Nickel alloying of the weld metal via solid weld wire presents several difficulties as highlighted previously, such as work hardening of the solid weld wire in manufacturing and feeding through the SAW wire feeding mechanism, and expensive and time consuming manufacturing of multiple weld wire formulations. The application of nickel and aluminium powders in unconstrained format, meaning not as fluxed cored wire or as metal cored wire, is used to simplify weld metal alloying. Al powder is used to control the oxygen potential at the weld pool-molten flux interface. The results presented here show that the addition of Al powder to the weld metal enhances Ni yield to the weld metal, at 85%, compared to pre-alloyed powder Ni yields of 57–78% as applied in previous work. Carbon steel was alloyed to 6.9% Ni and 3.7% Al. Thermodynamic analysis is applied to elucidate the chemical interaction between Ni and Al, and its effects on Ni yield in the weld pool. Overall process productivity gains stem from weld metal alloying from unconstrained metal powders because the expensive and time consuming step of manufacturing alloyed wire and alloyed powder is eliminatedNational Research Foundation of South Africahttps://www.mdpi.com/journal/applsciMaterials Science and Metallurgical Engineerin

Aluminium-assisted alloying of carbon steel in submerged arc welding : application of Al-Cr-Ti-Cu unconstrained metal powders

DATA AVAILABILITY STATEMENT : The data sets presented in this study are availabable upon request to the corresponding author.Al assisted alloying of carbon steel in Submerged Arc Welding (SAW) by Al-Cr-Ti-Cu unconstrained metal powders is applied. A base case without metal powder additions is compared to two metal powder addition schedules, Al-Cu-Ti and Al-Cu-Ti-Cr. Al powder is used as a deoxidiser element to control the oxygen partial pressure at the weld pool–molten flux interface to ensure that most of the Ti and Cr metal powder is transferred into the weld pool and that the weld metal ppm O is controlled within acceptable limits of 200 to 500 ppm O. The likely sequence of alloy melt formation is deduced from the relevant alloy phase diagrams. The effect of Fe addition into the initial Al-Cu-Ti and Al-Cu-Ti-Cr alloy melt is illustrated in thermochemical calculations. Increased metal deposition productivity with metal powder addition in SAW is confirmed. The metal deposition rates increased by 19% and 40% when Al-Cu-Ti and Al-Cu-Ti-Cr powders were applied at the same weld heat input used in the absence of metal powder additions.The National Research Foundation of South Africa.https://www.mdpi.com/journal/processesam2023Materials Science and Metallurgical Engineerin

In situ modification of CaF2-SiO2-Al2 O3-MgO flux applied in the aluminium-assisted transfer of titanium in the submerged arc welding of carbon steel : process mineralogy and thermochemical analysis

DATA AVAILABILITY : The data sets presented in this study are available upon request from the corresponding author.Flux formulations are specified to target chemical and physico-chemical parameters. Chemical parameters set flux element transfer behaviours and weld metal oxygen contents. Physicochemical parameters such as slag viscosity, surface tension and melting range are targeted to ensure an acceptable weld bead profile and surface appearance. Slag detachability is an important physicochemical property required to ensure high welding productivity, smooth weld bead surface and no slag entrapment. Here, bead-on-plate welding tests were made with and without metal powder additions, including aluminium powder as a de-oxidiser. Difficult slag detachability was observed in weld runs made with metal powder additions. Mineralogy of the post-weld slags, and thermochemical calculations, show that the flux was modified due to the aluminothermic reduction of MnO and SiO2 from the slag to form alumina. Increased quantities of spinel phase were identified in the post-weld slag samples, at the weld pool–slag interface. The combined effect of increased slag viscosity, from increased spinel in the slag, and lowered weld pool solidus temperature, resulted in the formation of a rough bead surface morphology, which, in turn, caused mechanical fixation of the slag to the weld bead. Flux modification to higher CaF2 content should ensure that higher quantities of spinel phase can be tolerated in the slag.The National Research Foundation of South Africa.https://www.mdpi.com/journal/mineralsam2023Materials Science and Metallurgical Engineerin