New generation ferritic and duplex stainless steels: Preliminary study on mechanical and in-service properties of base materials and welded joints

This pre-screening study covers two novel ferritic and one duplex stainless steel: the 17% Cr - double Nb+Ti stabilised EN 1.4509 and EN 1.4521, the latter with additional 2% Mo alloying, and the so-called "lean duplex" grade EN 1.4162 with 21.5% Cr - 5% Mn - 1.5% Ni - N. In addition, a third ferritic stainless steel: , the 12% Cr grade EN 1.4003, was included solely for the toughness investigation. The materials were used as sheets of 2 and 3 mm thickness. The three ferritic base materials were characterised by using Charpy-V impact and fracture toughness testing, whereas reference impact and fracture toughness data for EN 1.4162 was acquired from literature. Welded joints were fabricated using gas metal arc (GMAW) and laser welding (LBW). The joints were subjected to tensile testing, as well as microstructural analysis. It can be concluded from the results that, based on the impact and fracture toughness, some of the test materials are well suited to low temperature structural applications, too. Clear differences, however, were observed in the toughness behaviour between the ferritic grades that should be taken into account in materials selection and structural design. Possibilities to reliably predict the fracture toughness T0 reference temperature on the basis of the Charpy T27J/28J data were evaluated. The weld microhardness tests did not reveal any significant softening effect due to welding operations. Microstructural characterisation revealed that retaining the desired ferrite-austenite balance in duplex laser beam welds still remains a challenge.