Abstract This study analysed the integrity of welded joints of a UNS S32205 duplex stainless steel, using different welding energies: 0.5 kJ.mm-1, 1.0 kJ.mm-1, and 3.5 kJ.mm-1. Microstructural characterisation, tensile testing, intergranular attack susceptibility testing (ASTM A262 practice A) and pitting/crevice corrosion resistance tests (critical pitting temperature test, ASTM G48 practice C) were performed in these welded joints. The results showed that the tensile properties of the welded joints did not vary significantly with the welding energy. The microstructure's ferrite content in the molten zone (MZ) was proportional to the welding energy: the ferrite concentration in the 0.5 kJ.mm-1 weldings was approximately 75%. When the welding energy increased to 3.5 kJ.mm-1, the amount of ferrite dropped to 54%. The 3.5 kJ.mm-1 welded joint featured a comparatively higher proportion of coarser austenite grains. The HAZ of the 3.5 kJ.mm-1 welded joint was comparatively more susceptible to the intergranular attack along the α/γ interfaces, while in the base metal and the other two welded joints, the intergranular attack along the α/γ interfaces was not prominent. Additionally, the pitting corrosion took place preferentially in the ferrite phase of the HAZ for all welding conditions.

Carmakers must achieve the worldwide targets for lightweight materials, safety and reducing the fuel consumption. The use of press-hardened steel (PHS), in vehicle structures has been contributing with these requirements. This type of steel is widely used for the hot-stamping which consists in heating the steel blank to total austenitization temperature and then transferring it from the furnace into the die tool where the steel is formed and quenched at the same time. PHS is usually protect with metallic coatings in order to avoid both steel oxidation and decarburization. Hot-dip Al-Si coating is currently the main used in this application. However, alternative coatings, like zinc-based, are under investigation. This work aims at evaluating the corrosion resistance of the 22MnB5 grade PHS, electroplated with Zn-Ni, before and after hot stamping, using the scanning vibrating electrode technique (SVET). Results from SVET showed that samples prior to hot stamping, the corrosion mechanism was uniform over the exposed surface, and was mainly related to selective dissolution of zinc from the coating. On the other hand, hot stamped samples showed localized corrosion mechanism with decrease in current with time of immersion due to the formation of corrosion products on the exposed surface.

Abstract Stress corrosion cracking (SCC) of UNS S31603 austenitic stainless steel (ASS), UNS S32205 duplex stainless steel (DSS) and UNS S32750 super duplex stainless steel (SDSS) was investigated. SCC tests were carried out at 110 ºC for 500 h under drops of synthetic seawater (DET, drop evaporation test). Two loading conditions were investigated: 50 % and 100 % of the experimental yield strength of each steel. DSS and SDSS specimens showed no susceptibility to SCC under loading of 50 % of their yield strength, contrary to ASS, but all steels fractured at the highest load. SCC nucleated under the salt deposit formed on the surface of all specimens. SCC propagation was mainly transgranular, but SCC propagation of DSS also featured crack ramification in the austenite phase. In addition, SDSS also presented crack propagation along the ferrite/austenite interfaces. Transgranular cleavage fracture was also observed in all fractured specimens, but DSS also presented ferrite/austenite interfacial brittle fracture, while SDSS also featured intergranular brittle fracture.

A porosidade de camadas de fosfato de zinco sobre aço baixo carbono, processadas em diferentes tempos de imersão (30 s, 45 s e 85 s), foi avaliada por meio das seguintes técnicas eletroquímicas: polarização anódica (P A), polarização linear catódica (P LC), cronoamperometria (C A), voltametria cíclica (VC), espectroscopia de impedância eletroquímica (EIE); e também por microscopia eletrônica de varredura (MEV). As técnicas de P A, VC e EIE foram exploradas qualitativamente, enquanto que as de P LC e C A quantitativamente. As análises qualitativas (P A, VC, EIE) indicaram que a porosidade das camadas fosfatizadas aumentou com a diminuição do tempo de imersão. Os valores porcentuais de porosidade (P LC, C A) e as imagens de MEV confirmaram estes resultados.

The porosity of zinc phosphate layers on low carbon steel processed in different immersion times (30 s, 45 s and 85 s) was evaluated through the following electrochemistry techniques: anodic polarization (P A), cathodic linear polarization (P CL/P LC), cronoamperometry (C A), cyclic voltammetric (CV/VC), spectroscopy impedance electrochemistry (EIS/EIE); and also scanning electron microscopy (SEM/MEV). The techniques P A, CV and EIS were qualitatively explored, while the P CL and C A quantitatively. The qualitative analyses (P A, CV, EIS) indicated that the phosphated layers porosity increased with the decrease of the immersion time. The porosity percents values (P CL, C A) and MEV images confirmed these results.