The present work investigated the influence of heat input and aging time on the microstructural characteristics and the mechanical properties of dissimilar AISI 317L austenitic stainless steel welded joints. The AWS ER2209 wire-electrode was used as filler metal, and two different heat input levels were applied (4 and 8 kJ/cm), aiming to verify the influence of this parameter on the deleterious phases precipitation. An aging heat treatment (AHT) was carried out at 700 °C for two different exposure times: 50 and 100 hours. It was observed that aging promoted a refinement of the base metal region, and all delta ferrite was transformed into the sigma phase. The microstructure of the fusion zone (without AHT) presented a significant amount of austenite that precipitated in three different morphologies: allotriomorphific of grain boundary, Widmanstätten, and intragranular. For all the thermally treated samples, it was possible to identify the presence of the σ and χ phases. Additionally, the highest concentration of the χ phase was identified in the samples submitted to 50 hours of AHT. The welding condition and AHT that presented joints with higher mechanical resistance and remarkable toughness were those welded with 4 kJ/cm heat input and with 100 hours of AHT. All welded joints showed an increase in the hardness profile after AHT. The microhardness values showed a good correlation with the microstructure and the mechanical tests so that the highest values of microhardness were observed in welded joints with heat input of 4 kJ/cm and 100 hours of AHT

O objetivo deste trabalho foi investigar a influência do metal de adição sobre as propriedades mecânicas e sobre a susceptibilidade à fissuração por corrosão sob tensão (CST) de juntas soldadas do aço inoxidável ferrítico AISI 444 em solução de MgCl2 .Dois tipos de metal de adição de aço inoxidável austenítico (E309L e E316L) foram usados, com o intuito de se produzir juntas soldadas com zonas fundidas de diferentes composições químicas. Para avaliar a susceptibilidade das juntas à CST foram realizados testes sob carga constante seguido da caracterização microestrutural dos corpos de prova testados. Os resultados de tração e dureza mostraram que a junta soldada com o metal de adição E309L apresentou limite de resistência à fratura superior ao encontrado na junta soldada com o metal de adição E316L. Testes de CST mostraram que a interface entre o metal de solda e a zona termicamente afetada (ZTA) foi a região mais susceptível à fissuração. Os resultados mostraram também que a junta do aço 444 soldada com o eletrodo E309L apresentou melhor resistência à CST. Isto pode ser atribuído a presença de uma rede de ferrite delta descontínua presente no metal de solda, a qual atuou como uma barreira à propagação de fissuras da zona fundida para a zona de ligação e ZTA do aço 444.

The aim of this study was to investigate the influence of the filler metal chemical composition on the mechanical properties and on the susceptibility to stress corrosion cracking (SSC) of ferritic stainless steel AISI 444 weldments in MgCl2. Two types of filler metal of austenitic stainless steel (E316L and E309L) were used. To evaluate the SCC susceptibility of weldments, constant load tests and metallographic examinations in tested SSC specimens were conducted. The tensile and hardness tests showed that the welded joints with the filler metal E309L presented mechanical properties superior with relation to welded joints E316L. SSC results showed that the ZTA/fusion zone interface was the most susceptible to SSC. Results also showed that the 444 weldments using E309L electrode presented the best SSC resistance. This may be attributed to the presence of a discontinuous delta-ferrite network in the matrix, which acted as a barrier to cracks propagation from the fusion zone to the interface zone and HAZ of AISI 444 steel.