Effect of welding processes on fatigue crack growth behaviour of AISI 409M ferritic stainless steel joints fabricated using duplex stainless steel fillers

The present investigation aims to study the effect of welding processes such as shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) on fatigue crack growth behaviour of the ferritic stainless steel (FSS) conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material and AISI 2209 grade duplex stainless steel (DSS) was used as filler metal, for preparing single pass butt welded joints. Centre cracked tensile (CCT) specimens were used to evaluate the fatigue crack growth behaviour. From this investigation, it is found that the GTAW joints showed superior fatigue crack growth resistance compared with SMAW and GMAW joints. The reasons for the superior performance were discussed in detail.     

Gamma (γ) phase transformation in pulsed GTAW weld metal of duplex stainless steel

The cooling rate and large undercooling significantly affect the fusion zone microstructure in pulsed GTAW weldment under the same heat input condition. The weld pool solidified at fast cooling rate about 139 °C/s superimposed a relative amount of undercooling has a desired higher γ content of about 37 vol.% without tradition nitrogen addition or post-weld heat treatment. The final structure of the pulsed weld metal at 7 °C plate consists of a great amount of desirable intra-granular austenite γ^′₂ (IGA) inside the grain matrix, besides Widmannstätten austenite γ^′₂ (W) and grain boundary austenite γ₂ (GBA). It results in the weldment with an uniform microhardness distribution and a homogeneous mechanical property.