Influence of weld undermatching strength (mis-match) on limit load and failure behavior of strain hardened austenitic stainless steel

New austenitic stainless steels strain hardened by cold rolling offer an attractive combination of elevated strength, high elongation and excellent toughness. Their exploitation, however, requires that the effects of weld mismatch are understood and taken into account in structural analysis. This paper discusses the influence of local softening on structural integrity and failure behaviour of weldedments under static load. The investigated steel grade was EN 1.4318 (AISI 301LN) in 5 mm plate thickness and cold-rolled to various delivery conditions. The experiments comprised GMAW butt welds using different filler metals. Mechanical properties of mismatching microstructural regions were determined using miniature specimen technique in conjunction with optical monitoring during the tensile test. True stress-strain curves were successfully obtained using flat-bar specimens as small as 1*2*8 mm3. Applying these data in the form of continuous strength function model, structural integrity assessment was conducted using the FITNET FFS Procedure Level 2 analysis and incorporating the Mis-Match Option. For this purpose, two different Lrmax solutions according to FITNET for undermatching welds were applied. The degree of weld undermatching and material strain hardening were evaluated against material related FADs.