Influence of Filler Metals on Microstructure and Mechanical Properties of Gas Metal Arc Welded High Strength Steel

Nowadays, the automotive industry shows an ever-growing need for the application of high strength materials. The high strength steels are one of the most important materials used at present; these steels have excellent properties such as high yield strength and low weight. These properties are insured by their versatile and complex microstructures. The use of these steels is advantageous from the standpoint of economic application and fuel consumption. Furthermore, the weight loss of vehicles results in the reduction of pollutants and greenhouse gases emissions. Besides that, the application of high strength steels also causes an improvement in strength, stiffness, and other performance characteristic. In spite of the aforementioned advantages, there are still difficulties with their wider use due to their limited formability and weldability. The welding of high strength steels can be a great challenge because of cold cracking sensitivity, reduction of strength and toughness of heat affected zone and filler metal selection. To take advantage of the outstanding mechanical properties of high strength steels, it is very important to select the appropriate welding method with the exact welding parameters. In the present research work the effect of the filler metals on microstructure and mechanical properties of a high strength structural steel (Alform 1100M x-treme) having 15 mm thickness welded by gas metal arc welding was investigated. The chosen filler metals were the Bohler Union X96 (undermatching condition) and Bohler alform 1100 L-MC (matching condition). During the welding experiments, the t(8/5) cooling time was regulated. Based on our former investigations (physical simulations on the examined material) and recommendations in the literature, the chosen t(8/5) cooling time was 5 s. The welding parameters were determined based on the cooling time. After welding, different destructive and non-destructive investigations (optical microscope, hardness tests) were performed to compare the microstructure and mechanical properties of the joints made by different filler metals.