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The fractography and mechanical behaviour of fatigue crack propagation in the heat-affected zone (HAZ) of AISI 4140 steel welded using the shielded metal arc process was analysed. Different austenitic grain size was obtained by normalizing performed at 1200 °C for 5 and 10 hours after welding. Three point bending fatigue tests on pre-cracked specimens along the HAZ revealed that coarse grains promoted an increase in fatigue crack growth rate, hence causing a reduction in both fracture toughness and critical crack length, and a transgranular brittle final fracture with an area fraction of dimple zones connecting cleavage facets. A fractographic analysis proved that as the normalizing time increased the crack length decreased. The increase in the river patterns on the fatigue crack propagation in zone II was also evidenced and final brittle fracture because of transgranular quasicleavage was observed. Larger grains induced a deterioration of the fatigue resistance of the HAZ.

Efecto del mantequillado en las propiedades mecánicas de uniones soldadas disímiles en barras de refuerzo para estructuras de concreto RESUMENEn este trabajo se ha investigado la influencia de utilizar Inconel 182 como material de “mantequillado” en las propiedades mecánicas de uniones disimiles acero al carbono-inoxidable manufacturadas por soldadura con electrodo recubierto. Para ello se han empleado las siguientes técnicas: análisis microestructural, ensayos de microdureza Vickers y ensayos mecánicos de tensión. Se ha empleado el proceso de soldadura con electrodo recubierto por que es el más común en la soldadura de campo para la construcción. Los resultados demuestran que aun cuando las uniones disimiles sin “mantequillado” presentan defectos, sus propiedades mecánicas son superiores a las de las uniones soldadas con “mantequillado”. Esta metodología es propuesta para la rehabilitación de estructuras de concreto para ambiente marino con barras de acero como refuerzos.Palabras clave: mantequillado; uniones soldadas con materiales disimiles; propiedades mecánicas; microestructura; defectos. Effect of buttering in mechanical properties of dissimilar metal weld joints for reinforcement bars in concrete structures ABSTRACTIn this work, the influence of Inconel 182 as buttering material in the mechanical properties of dissimilar metal welds between plain carbon steel and stainless steel bars welded using SMAW has been investigated using microstructural analysis, Vickers microhardness testing, and tensile tests. Welding with SMAW process is commonly applied in field welding of concrete structures; therefore this process was selected for this work. The results indicated that even if the joints contain defects generated by the welder, the mechanical properties of dissimilar welded joint without buttering are higher than the properties of joints with buttering. This methodology is proposed for the rehabilitation of concrete structures with steel bars as reinforcements, which are located in marine enviroments.  Keywords: buttering, dissimilar metal weld joints; mechanical properties; microstructure; defects. Efeito da introdução de um terceiro material sobre as propriedades mecânicas das juntas soldadas entre aço carbono e aço inox, em barras de aço para estruturas de concreto RESUMOEste artigo investiga a influência da utilização de Inconel 182 como um terceiro material, nas propriedades mecânicas de diferentes aços inoxidáveis soldados a aços carbono com uso de eletrodo revestido. Para tanto foram usados os seguintes métodos: análise microestrutural, ensaios de microdureza Vickers e ensaios mecânicos de tensão. Tem sido empregado o processo de solda com eletrodo revestido, porque é o mais comum no campo de solda para a construção. Os resultados mostram que quando as uniões são realizadas sem esse terceiro material, as propriedades mecânicas são superiores às das juntas soldadas com auxílio do Inconel 182. Esta metodologia, ora criticada, tem sido proposta para a reabilitação de estruturas de concreto em ambiente marinho, com uso de barras de aço inox como reforços.Palavras-chave: juntas soldadas com materiais diferentes; propriedades mecânicas; microestrutura; defeitos.

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The main objective of this work is to study the electrochemical behavior of galvanic coupling between carbon steel, CS, and stainless steel, SS, in an alkaline environment simulating the conditions prevailing in a repaired structure in which stainless steel rebar’s will be an option. Previously research conducted in different parts of the world on this subject reach agreement with the fact that AISI 304 SS and 316 SS embedded in concrete offers high corrosion resistance in aggressive environments but only for the case of new structures, and no further explanation has been given on the behavior of SS when in contact with CS. Galvanic coupling between these two metals should increase the corrosion process of the more anodic, CS in this case, but this phenomenon does not occur in practice. Galvanic coupling was investigated by means of the electrochemical coulostatic technique. Tests performed allow determining the Tafel slopes of anodic and cathodic processes. The Tafel slope values obtained show that the process is being controlled by the reduction of oxygen, O2 in the environment where the samples were placed. On the basis of these kinetic parameters, a mechanism for the corrosion process is proposed in which the rate determining step would be O2 mass transfer process. The diffusion of O2 would take place through a formed oxide film, passivating in nature. Due to the formation of this oxide film, the cathodic oxygen reduction reaction, ORR, on stainless steel surface would be very slow. The high polarization of ORR rate would be the factor controlling the whole process, then minimizing the risk of damage by galvanic corrosion, demonstrating the feasibility of using stainless steel in the repairing of concrete structures.