Metalurgical Evaluation of Austenitic Stainless Surfacing Welding Over SAE 4130 Steel

The objective of this study was to make a metallurgical evaluation of the austenitic stainless surfacing welding on the sealing area of the riser tubes made of SAE 4130 steel. The study was divided into two steps. The first step aims to determine the dilution rate and deposition rate for the minimum and maximum levels of heat input according to the WPS for TIG and SMAW processes, followed by analysis and study on the Schaeffler diagram in order to identify the welding consumable best suited to attend the stablished quality criteria. This study identified the electrode 312 as the filler material for the first layer, and the electrodes 309 and 308 for the second layer. Both using the maximum heat input of the WPS and the SMAW process, with benefits to productivity. The second step has as objective the validation of the empirical results found in the 1st step, with the execution of surfacing welds with two layers each, and the metallurgical characterization of the welded joints by mechanical testing and microstructural analysis by optical and electronic microscopy. The results of mechanical testing and microstructure were considered satisfactory, filling the adopted quality criteria. An austenitic-ferritic microstructure with delta ferrite content between 10 and 15 % was observed for both layers of the surfacing. The electrode 312 assumed a prominent position in the application of the 1st layer of the surfacing weld over the SAE 4130 steel, according to its higher content of delta ferrite and chromium, avoiding hot cracks formation. For the second layer, both the 309 and 308 may be used. All welds were made with high heat input, ensuring increased productivity, without significant change in the physical and mechanical characteristics.