Contrary to other keyhole welding applications on duplex stainless steels, a proper cooling time and a dilution were achieved during hybrid plasma gas metal arc welding that provided sufficient reconstructive transformation of austenite without sacrificing its high efficiency and productivity. Simultaneous utilization of keyhole and metal deposition in the hybrid welding procedure enabled us to get an as-welded 11 mm-thick standard duplex stainless steel plate in a single pass. Me examination on hybrid plasma-gas metal arc weldments revealed only primary austenite in ferrite matrix, whereas in addition to reconstructive transformation of primary austenite during solidification, secondary austenite was also transformed in a displacive manner due to successive thermal cycles during multi-pass gas metal arc welding. On the one hand, secondary austenite provided barriers and retarded the crack propagation during the tests in laboratory air. On the other hand, chromium and molybdenum depletion in the neighborhood of secondary austenite precipitates yielded relatively high crack propagation rates in multi-pass weldments under chloride attack.