Influence of aluminum content on the characterization of microstructure and inclusions in high-strength steel welds

Abstract

The present study describes the methods for the characterization of the microstructure of welded joints from test welds. This comprises the analysis of the solidification microstructure (primary and secondary dendrite arm spacing) as well as the former austenite grain size and the final phase distribution. The main focus is the characterization of nonmetallic inclusions by means of SEM/EDX and light microscopy. Based on already-developed prototypes with a weld yield strength of more than 800 MPa, different kinds of inclusions and precipitates have been assessed with respect to grain refinement and the resulting impact on strength and ductility. The effect of aluminum, in the range 90 to 800 ppm, on the microstructure and the mechanical properties of high-strength steel weld metals has been studied and it has been found that at low aluminum contents good values for the tensile strength and the toughness could be obtained. The results of metallographic investigations of test welds with different alloy compositions are presented. The results indicate a significant change of the size distribution, the morphology, and the composition of the inclusions. These results are finally compared with results from literature and discussed with respect to the expected influence on the mechanical properties of the welded joint.