Revista de Metalurgia

Acid pickling of carbon steel

Arkaiz Anderez — 2022-11-08

This study reviews the possibilities of recovering the pickling waters from carbon and galvanised steel. Acid pickling with hydrochloric acid (HCl) is the most widely used chemical process to remove iron oxides from the metal surface without any significant attack on the steel itself. The acid pickling bath contains mainly ferrous chloride (FeCl₂) produced by the reaction between the steel and free hydrochloric acid. However, zinc chloride (ZnCl₂) is also found in the pickling of carbon steel parts prior to galvanisation, as the hooks and tools used to hang the carbon steel parts are also galvanised and reuse again polluting with Zn the pickling waters. Pickling water recovery or recycling technologies primarily seek the reuse of HCl in two ways. Partially by recovering the unreacted HCl or fully by breaking the FeCl₂ bond through Pyrolysis technologies such as fluidised bed and spray roasting which in turn produces another iron oxide by-product. However, the most common by-product produced by pickling water recovery and recycling technologies is ferric chloride (FeCl₃), as it is a coagulant widely used in wastewater treatment. However, if the pickling water contains ZnCl₂ or other metals, the production of FeCl₃ becomes unattractive and the pickling water is neutralised and deposited in landfill sites. This study also discusses a wide range of technologies capable of recovering all or part of the pickling water, including galvanic pickling water, that are usually excluded from circular economy strategies.

Effect of boron treatment on the microstructure and toughness of Ti-containing steel weld metals

Zhan-Hang Cui — 2022-10-19

Ti-containing steel weld metals with boron addition contents of 0-85 ppm were prepared, and their microstructural characteristics as well as the impact toughness were investigated. The results show that in these microstructures, compared to the weld metal without boron, the addition of 22-39 ppm boron results in a remarkable increase in the amount of acicular ferrite at the expense of grain boundary ferrite, idiomorphic ferrite and side-plate ferrite. However, with a further increase in the boron content up to 61-85 ppm, the bainitic ferrite is formed, accompanied with a drop in the amount of acicular ferrite. In the acicular ferrite, the size of martensite-austenite (M/A) islands is much smaller, and the amount is much lower than those found in the bainitic ferrite. In the case of the weld metals primarily composed of acicular ferrite, during the fracture of the impact specimens, the crack propagation path is more bent in comparison with the weld metals with large amounts of grain boundary ferrite, idiomorphic ferrite, side-plate ferrite or bainitic ferrite, which that the presence of acicular ferrite improves the toughness of the weld metals. The coarse martensite-austenite islands readily induce micro-cracks at the interface between martensite-austenite islands and ferrite matrix, deteriorating the toughness. The weld metals with B contents of 22-39 ppm exhibit outstanding impact toughness because of high amount of acicular ferrite, accompanied with fine martensite-austenite islands.

Weldability of ductile cast iron using AISI-316L stainless steel ER rod

Javier Cárcel Carrasco — 2022-10-19

This paper analyzes the corrosion resistance and the mechanical and microstructural properties of a welded joint of ductile cast iron using AISI316L stainless steel as filler material and three different heat treatments: preheating at 250 and 450 ºC and a post-weld annealing treatment. The results show the presence of ledeburite at the interface between the weld bead and the heat affected zone and at the root pass, along with a loss of strength and ductility when the welding coupons are preheated. An annealing does not eliminate the presence of ledeburite and leads to a massive precipitation of chromium carbides at the areas of the weld bead where dilution is higher. Corrosion rate was lower for the annealed coupon, but in that case, the corrosion of the weld bead increases due to the precipitation of chromium carbides.

Mechanical properties optimization and microstructures of diffusion bonded AA2014/AA7075 al alloys

Antony Sagai Francis Britto — 2022-11-08

Diffusion bonding has been successfully used to join dissimilar high-strength aluminium alloys. In bonding AA2014 with AA7075 aluminium alloy, the main diffusion bonding process parameters were optimized to achieve optimum shear and ram tensile strengths. For the strategical planning of experiments, the design of experiment concept was used, as well as the response surface methodology to create statistical models for optimizing the process parameters. The bond strength improved as the interface thickness increased, but above 6 µm (at about 375 °C), the bond strength began to deteriorate. Similarly, the stiffness of the joint interface increased as the process temperature increased due to the development of interfacial phases. The empirical findings were evaluated, and the optimal bonding range was determined in order to maximize the bond’s shear and ram tensile strength.

The removal of toxic metals from liquid effluents by ion exchange resins. Part XVIII: Vanadium(V)/H+/Amberlite 958

Francisco José Alguacil — 2022-12-27

The ion exchange resin Amberlite 958 was used to investigate its behaviour on the removal of hazardous vanadium(V) from aqueous media. This investigation was carried out under various hydrodynamic conditions and chemical conditions, such as variation of the stirring speed, variation of the pH of the aqueous solution, resin dosage, initial vanadium(V) in the aqueous solution, and temperature. Vanadium(V) uptake onto the resin was highly dependent on the pH of the solution, and thus, to the vanadium(V) speciation in this phase; the ion exchange process had an endothermic character. The experimental data, under different experimental conditions, were fitted to various models: kinetics (stirring speed), rate law (vanadium concentration) and model isotherms (resin dosage). Multiwalled carbon nanotubes were also investigated on vanadium(V) removal from the solution. Vanadium(V) loaded onto the resin can be eluted under acidic conditions.