Duplex Stainless Steels (DSS) and Superduplex Stainless Steels (SDSS) have a strong appeal in the petrochemical industry. These steels have excellent properties, such as corrosion resistance and good toughness besides good weldability. Welding techniques take into account the loss of alloying elements during the process, so this loss is usually compensated by the addition of a filler metal rich in alloying elements. A possible problem would be during the welding of these materials in adverse conditions in service, where the operator could have difficulties in welding with the filler metal. Therefore, in this work, two DSS and one SDSS were welded, by autogenous Tungsten Inert Gas (TIG), i.e., without addition of a filler metal, by three different heat inputs. After welding, microstructural, mechanical, and electrochemical analysis was performed. The microstructures were characterized for each welding condition, with the aid of optical microscopy (OM). Vickers hardness, Charpy-V, and cyclic polarization tests were also performed. After the electrochemical tests, the samples were analyzed by scanning electron microscopy (SEM). The SDSS welded with high heat input kept the balance of the austenite and ferrite, and toughness above the limit value. The hardness values remain constant in the weld regions and SDSS is the most resistant to corrosion.

This paper presents the numerical simulation of the technology of gaseous fuel utilisation for iron ore sintering. The proposed methodology is to partially replace the solid fuel by steelworks gases. A multiphase mathematical model based on transport equations of momentum, energy and chemical species coupled with chemical reaction and phase transformations was proposed to analyse temperature distributions of the process. A base case of actual industrial operation of a large sintering machine was monitored with thermocouples inserted into the sinter bed to validate the model. The model was used to predict four cases of fuel gas utilisation: feeding from N01 to N15 wind boxes with blast furnace gas (BFG); natural gas (NG); coke oven gas (COG); and a 50–50 mixture of BFG and COG. The model predictions indicated that for all cases the sintering zone is enlarged and the solid fuel consumption could be decreased.

Recently, the synthetic natural gas (SNG) has been available for large consumers in the Brazilian domestic market. The SNG is a suitable fuel with potential use to several processes and facilities of the steel industry. This paper investigates the injection of SNG into charcoal blast furnaces as a substitute for granular charcoal charged from the top and pulverized charcoal injections with potential increase of productivity and decrease of specific CO₂ emissions. In order to study the effect of replacement of granular charcoal and injection of pulverized charcoal the well known Blast Furnace Five Fluid Model (BF-FFM) is applied to describe detailed phenomena within the process. This model treats the blast furnace as a five-phase reactor, accounting for gas, lump solids (raw iron ore, sinter, pellets and granular charcoal), hot metal, pulverized charcoal, and molten slag. The model is based on conservation equations for mass, momentum, energy and chemical species numerically solved based on the finite volume method (FVM). The SNG has high amount of H₂ and strongly affects the inner conditions of the reactor and only a comprehensive model with detailed chemical reaction rates can properly predict the inner parameters of the process and hence furnish useful information to design smooth operational conditions. The simulation results obtained in this study indicated that smooth operations using SNG up to 25 N m³/t of pig iron could be achieved simultaneously by increasing the productivity up to 58% and with a decrease of 40 kg/thm on the granular charcoal charged.

A numerical simulation procedure is proposed for analyzing the partial replacement of pulverized coal injection by hydrogen, oxygen, and blast furnace gas (BFG) injections mixed with pulverized coal (PCI) within the tuyeres of large blast furnaces. The massive use of hydrogen-rich gas is extremely interesting for ironmaking blast furnaces in the context of net-zero carbon hot metal production. Likewise, this new approach allows for increasing productivity and for reducing the specific emissions of carbon dioxide toward a net-zero carbon ironmaking technology. Nevertheless, the mixture of pulverized coal injection and gas injection is a complex technology. In addition to the impact on chemical reactions and energy exchange, the internal temperature and gas flow patterns can also change drastically. With a view to assessing the state of the furnace in this complex operation, a comprehensive mathematical model utilizing multiphase theory was developed. The model simultaneously handles bulk solids (sinter, pellets, small coke, granular coke, and also iron ore), gas, liquid metal and slag, and coal powder phases. The associated conservation equations take into account momentum, mass, chemical species, and energy while being discretized and solved using finite volume techniques. The numerical model was validated against the reference operating conditions using 220 kg per ton of pig iron (kg/t_HM) of pulverized coal. Therefore, the combined injection of different concentrations of fuel hydrogen, blast furnace gas, and oxygen was simulated for replacing 40, 60, and 80 kg/t_HM of coal injection. Theoretical analysis showed that the best scenario with stable operation conditions could be achieved with a productivity increase of 20% corresponding to a CO₂ reduction of 15% and 60 kg/t_HM of PCI replacement.