Welding of Lean Duplex Stainless Steel grades: microstructure, corrosion resistance and mechanical properties

摘要

Recent price fluctuations of raw materials such as chromium and nickel have led to the development of stainless steel grades containing less nickel, which are known as lean duplex stainless steels. A research project has been initiated involving stainless steel manufacturers and end-users in order to study the weldability and properties of such grades. Investigations have been carried out on three lean duplex grades: UNS S32101, UNS S32202 and UNS S32304. Test pieces have been welded using several arc welding processes: Gas Tungsten Arc Welding (GTAW), Gas Metal Arc Welding (GMAW) using solid and cored wires, plasma, Submerged Arc Welding (SAW) and Shielded Metal Arc Welding (SMAW) and two plate thicknesses, 5 and 12 mm. These welded test pieces were then used for characterization work including metallographic examinations (in order to check weld quality and to measure the ferrite content), mechanical testing (hardness measurements, tensile and impact tests) and pitting corrosion on welded joints. The influence of gas shielding upon ferrite content and pitting corrosion behaviour was also studied. Pitting corrosion of welded joints has been evaluated in terms of critical pitting temperature (CPT) using a modified ASTM G150 test method. CPT and pits location, as well as mechanical testing results have been related to ferrite content and chemical analysis of both base metal and fusion zone.