Evaluation of the effect of the thermal cycle on the characteristics of welded joints through the variation of the heat input of the austhenitic AISI 316L steels by the GMAW process

Abstract

Welding processes are generally used in almost every industrial segment, but there are some applications that demand special attention to the product obtained, due to the security it must offer against possible failures.

In the present study, the influence of the heat input variation on the weld bead geometry, the austenitic grain size in the HAZ, the microhardness in the HAZ (heat affect zone), and the δ ferrite volumetric fraction using the gas metal arc welding (GMAW) performed with pulsed chain spray transfer, on AISI316L steel plates. The samples had their microstructure characterized by optical microscopy, in their different regions, performing a comparative study of these regions for the different welding conditions. From the variations in the thermal contributions it was demonstrated that the choice of the ideal heat input for a given process has an important effect on the phenomena that occur during welding. The increase of the contribution caused a variation of almost 300% in the austenitic grain size, approximately 100% in the δ ferrite volumetric fraction, and about 240% in the area of the fusion zone (FZ). The temperature distributions of the plates were recorded using a thermal camera in order to monitor the maximum temperatures in each region of the welded joint, the microstructures resulting from the process were later compared with the results of the thermal cycles obtained through numerical simulations. The results showed good agreement and also contributed to the validation of the proposed numerical method, which allowed a better understanding of the thermal history during welding and, consequently, of their effects on the microstructural transformations developed in the AISI 316L steel.