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In this work, the effect of heat input and aging treatment on the microstructural characteristics and mechanical properties of similar AISI 317L austenitic stainless steel weldments used in the petroleum industry was investigated. The filler metal used was the AWS ER317L electrode at two different heat input levels (4 and 8 kJ/cm) in order to verify the influence of this parameter on the precipitation of deleterious phases. The specimens were aged at 700 °C for 50 and 100 h. Quantification and microchemical mapping of precipitated phases after welding and aging thermal treatment (ATT) were performed. Vickers hardness and tensile tests were used to evaluate the mechanical properties. It was observed that aging promoted a refinement of the base metal region, and all delta ferrite was transformed into sigma phase. The delta ferrite present in the fusion zone was completely transformed into sigma and chi phases. In the aged specimens for 100 h a lower occurrence of the secondary austenite phase (γ2) was identified, which indicates that with the increase of ATT time the dissolution of γ2 occurred in the already precipitated sigma phase. All welding conditions showed an increase in tensile strength, yield limit and hardness with the ATT.

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe-Cr-Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with M s temperature below 200uC and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.