Influence of double-sided and single-sided T-joints with full connection on welding distortion and its reduction by means of a low-transformation temperature effect in stainless steel

The formation of stresses and distortion during welding is caused by an inhomogeneous temperature distribution. Using low-heat welding processes, such as laser beam welding, can reduce distortion. However, it is not possible to prevent their formation entirely, since a temperature gradient is an inherent aspect of welding. Initiating a phase transformation from austenite to martensite at a reduced transformation temperature induces high compressive stresses. The so-called low transformation temperature (LTT) effect counteracts shrinkage and thus reduces welding distortion. This study investigates how the chemical composition, joint type (double-sided or single-sided) and seam geometry influence the formation of distortion in a 2 mm – 3 mm thick austenitic CrNi stainless steel (1.4318). The LTT effect is induced by an in situ alloying process using commercially available welding consumables, and this is confirmed by energy-dispersive X-ray spectroscopy (EDS) and hardness measurements, as well as by demonstrating its influence on welding distortion. The resulting alloys have an martensite start temperature ranging from 97 °C to 183 °C, and a hardness ranging from 395 HV1 to 264 HV1. The influence on welding distortion was investigated using in situ and ex situ distortion measurements. Depending on the alloy content and seam type, the LTT effect reduced distortion by between 23% and 83%.