Computational thermodynamics study of the influence of tungsten in superduplex stainless weld metal
2012 (English)In: Welding in the World, ISSN 0043-2288, Vol. 56, no 11-12, 79-87 p.Article in journal (Refereed) Published
Tungsten is used by some duplex stainless steel producers for partial substitution of molybdenum, both elements enhancing the corrosion resistance of duplex stainless steel. The negative aspect of both molybdenum and tungsten alloying is that they increase the tendency to precipitate intermetallic phases, which may have a detrimental effect on corrosion and mechanical properties. The temperature region for intermetallic phase precipitation is about 700-1000 degrees C, depending on alloy composition, and the time for precipitation is within minutes for superduplex steels. There has been scientific discussion on the relative effects of Mo alone or Mo-W on intermetallic precipitation behaviour in superduplex steels for the past two decades. While the base material response to ageing and precipitation of intermetallic phases has been satisfactorily assessed, weld metal has proved more of a challenge. The main reason for this is that welding is a very complex process introducing many parameters to the assessment which not have to be considered in studies of base material. For example superduplex weld metal typically solidify fully ferritic but may in case excessive nitrogen is added solidify as a mixture of ferrite and austenite. The solidification mode may vary also between weld passes as a consequence of minor variations in composition. Ferritic solidification is the preferred mode, giving the well known Widmanstatten austenite, which forms in the solid state during cooling. Mixed mode solidification gives a vermicular appearance, which is known to increases the tendency to intermetallic formation. A comprehensive study using computational thermodynamics was done to investigate this matter. This study included equilibrium calculations, Scheil-Gulliver solidification simulations, and calculations of the driving force for intermetallic phase precipitation and further a study of diffusion of Mo and W in these alloy systems. The different approaches were applied on model superduplex weld metals with nominal compositions matching commercial superduplex fillers available today. The principal conclusion is that all thermodynamic calculations clearly indicates the W containing filler to show a more pronounced sensitivity to heat treatments by precipitation of intermetallic phases.
Place, publisher, year, edition, pages
2012. Vol. 56, no 11-12, 79-87 p.
Computation, Thermodynamics, Calculation, Duplex stainless steel, Weld metal
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-121332DOI: 10.1007/BF03321398ISI: 000311195500009OAI: oai:DiVA.org:kth-121332DiVA: diva2:618455
QC 201305022013-04-282013-04-282013-05-02Bibliographically approved