Oxygen and nitrogen are the factors, that may control ductility and toughness of the low carbon and low alloy weld metal deposits, especially at low temperatures. The oxygen and nitrogen in all weld metal of coated electrods with varied basicity index as well as all weld metal deposited in CO2 and Ar have been examined.
The influence of oxygen and nitrogen on Charpy V impact properties was analysed very carefully in the last 15 years. According to current opinion there is an optimum percentage of oxygen and nitrogen in weld metal deposits, that gives the highest impact properties. Authors of the main publications report that the optimal amount of oxygen is in the range between 200 and 400 ppm, and that optimal oxygen amount depends on many factors such as: chemical composition of the all weld metal, the welding technology and the parameters of the process. The special role of non-metalic nucleants such as spinel galaxite MnO-Al2O3, TiO, TiN on the accicular ferrite formation is underlined. Nitrogen is regarded as the negative element in low carbon and low alloy weld deposits. The lowest amount of nitrogen in all weld metal gives the best impact values of the weld metal deposit.
The reported investigations (below) are concerned with the effect of oxygen and nitrogen on properties of the SMAW all weld metal.
The effects of coating basicity and weld metal oxygen and nitrogen contents were studied on basic electodes only. The principal diameter of the electrodes was 4 mm. A typical wire was used for the electrodes (0.081%C, O.4S%Mn, 0.03%Si, 0.3Ni, 0.2Cr, 0.04%S+P). Oxygen and nitrogen contents in all wires did not exceed 120 ppm. The electrode coatings contained constant or variable proportions of the following components in powder form: (Tables are shown in the paper)
