THE EFFECT OF COOLING RATE ON THE MECHANICAL AND CORROSION PROPERTIES OF SAF 2205 (UNS 31803) DUPLEX STAINLESS STEEL WELDS J.D. Kordatos 1 , G. Fourlaris 2 and G. Papadimitriou 1 1 Laboratory of Physical Metallurgy, National Technical University of Athens, Heroon Polytechniou, 9 Athens, Greece 2 Department of Materials Engineering, University of Wales Swansea, Swansea, SA2 8PP, UK (Received July 3, 2000) (Accepted in revised form September 6, 2000) Keywords: Duplex stainless steels; Microstructure; Pitting; Intergranular corrosion; Impact testing Introduction The weldability of duplex stainless steels is related to the possibility of forming or maintaining a microstructure with a ratio of ferrite to austenite phase of about 50:50. Approximately at least 40% of austenite is required to produce a nitride free weld microstructure in the heat affected zone and this is obtained by welding a material of balanced composition with a heat input that allows the austenite to form by nitrogen redistribution during cooling. Research work has also been carried out on the composition of the filler metals in order to obtain the desired ratio of ferrite to austenite in the weld metal [1]. During welding and subsequently, several transformations take place in the heat-affected zone and in the weld metal. The metallurgical aspects of these transformations have been successfully explained by many researchers [2], [3], [4]. However, the effect of the cooling rate on the microstructure of the welded joints and as a consequence on the strength and corrosion resistance of DSS weldments, is a matter of continuous interest. In this paper an attempt is made to correlate the impact strength and corrosion resistance of DSS weldments to the cooling rate and to explain their interdependence through microstructural observa- tions. Experimental Procedure The DSS used was the SAF 2205 (UNS S31803) grade in the form of 4 mm plate, manufactured by AVESTA, Sweden. The chemical analysis of the material and the welding conditions (GTAW welds) [5] are summarized in Table 1. Eight weldments with a length of 40 cm were prepared. Half of them were left to cool slowly in air down to the ambient temperature (22°C) and the other half were submerged in cold water (set to 10°C) directly after welding. Metallographic specimens were cut transverse to the welding direction. They were examined using scanning electron microscopy. Quantitative image analysis was performed in order to determine the volume fraction of austenite and ferrite in the weld zones. Vickers hardness measurements transverse to the weld were performed using a load of 20Kg. In addition, microhardness measurements on the two phases (austenite and ferrite) were recorded, using a load of 200g. Scripta mater. 44 (2001) 401– 408 www.elsevier.com/locate/scriptamat 1359-6462/01/$–see front matter. © 2001 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S1359-6462(00)00613-8