Austenitic stainless steel and nickel-base alloys welds are widely used in nuclear reactor components, plants of energy generation, chemical, and petrochemical industries, due to their high corrosion resistance. The post weld heat treatments (PWHT) are generally applied to welding in order to relieve the welding residual stress. The aim of this work was to evaluate the influence of different PWHT on corrosion behavior of a dissimilar weld joint of two AISI 316L austenitic stainless steel plates with a nickel-base alloy as filler material in saline environments. The material was submitted to heat treatments for three hours at 600, 700 and 800 °C. The weld joint was examined by optical microscopy to determine the effects of PWHT in the microstructure. The corrosion behavior of the samples before and after heat treatment was evaluated using cyclic potentiodynamic polarization (CPP) in sodium chloride solutions (19% v/v) and pH 4.0 at room temperature. Metallographic analyses showed that delta ferrite dissolute as PWHT temperature increased. CPP curves demonstrated an increase of pitting corrosion resistance as the PWHT temperature rises, although the pit size has been increased. The heat treated weld joint at 600 °C showed a similar corrosion resistance compared to as-welded material.

Corrosion testing was performed in white liquor from a Brazilian Kraft mill. Specimens of duplex stainless steel (DSS) and lean duplex (LDSS) were exposed at 170 °C for 30 days to simulate conditions of the digester. Corrosion rates were determined from weight loss measurements. After this exposure, the corrosion products formed on the steel surface was characterized by using scanning electron microscope (SEM) equipped with EDS, X-Ray Diffraction (XRD), and X-ray photoelectron spectrometer (XPS). EBSD can be used to quantify of basis balance phases in DSS and LDSS. General corrosion rates for UNS S32304 LDSS were higher than the UNS 31803 DSS in industrial white liquor at 170 °C for 30 days. XPS and XRD analyses indicated that the film formed after the immersion test may be consisted by Fe and Cr oxides and sulphides.

The results of the corrosion tests, in chloride environment, of lean duplex stainless steel UNS S32304 welded by submerged arc welding (SAW) process variant with cold wire, indicated that the sample with higher heat input heat input (HI) (2.7 kJ/mm) had higher corrosion resistance, which can be explained by higher amount of austenite and lower amount of precipitates. Therefore, the results indicate that the use of HI above the limit recommended by literature (2.5 kJ/mm) may produce welds with adequate corrosion resistance with SAW with cold wire addition, because this technique has the potential to deliver higher productivity still controlling the process HI.

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