In analogy to the classification of metal weld deposits and arc welding processes of low-carbon and low-alloy steel in terms of the amount of hydrogen in metal weld deposits, a similar classification was given in terms of the amount of nitrogen. Different methods of arc welding processes were chosen, such as welding with coated electrodes (basic, rutile, acid, oxidic electrodes), shielded arc welding process MIG/MAG, submerged arc welding process (various wires, fluxes, shielded gases). The amount of nitrogen, the percentage of acicular ferrite and the impact toughness of metal weld deposits were mainly analysed. On the bases of these studies together with amounts of O, Mn, Mo, Ni there were given some mathematical relations of impact toughness of metal weld deposit in terms of the amount of all mentioned elements and acicular ferrite. Metallographical structures and fractography tests of metal weld deposit with varied amount of acicular ferrite were presented by putting attention to non-metallic inclusions and their morphology presented in metal weld deposit. The studies were also made on the classification of metal weld deposits and arc welding processes of low carbon and low alloy steel in terms of the amount of nitrogen in metal weld deposits on the following processes: low-nitrogen processes, medium-nitrogen processes, high-nitrogen processes.
The influence of nitrogen contents in weld metal deposit on impact properties was well analyzed [1–16] in the last 20 years. It was suggested that nitrogen has similar role as carbon in the ferrite. Every 100 ppm of nitrogen in the ferrite a may prove hardness of welds above 10 HV. Nitrogen could be regarded as an alloy element in steel and welds. The amount of nitrogen in low-carbon and low-alloy steel is limited.
