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Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., △ quantity. Both carbon and manganese show negative △ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative △ C and △ Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. △ Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal.

Various fluorides, CaF 2 , Na 3 AlF 6 , K 2 SiF 6 , MnF 3 , and MgF 2 , were added to rutile-type flux cored wires at concentrations of 1.8-2.3% and their effects on hydrogen reduction in weld metals were studied. All the fluorides reduced the hydrogen content but there were differences in the levels of reduction among the wires; CaF 2 showed the greatest reduction and MnF 3 showed the least. The hydrogen content in the weld metals was not influenced by the fluorine formed in the arc but by the slag basicity due to the small amount of fluorides added. The weld metal with higher slag basicities had a lower hydrogen content. The effects of fluorides on the arc stability, weld metal hardness, and microstructure were also examined. Because of the higher ionization potential of Mn, the wire containing MnF3 had the most unstable arc during welding. The wire containing MnF3 also produced a lower weld metal hardness than the other wires owing to its lower weld metal hardenability due to the greater oxidation loss of the C, Si, and Mn elements during welding.

The variation of simulated heat affected zone (HAZ) toughness with nitrogen content in titanium containing thermomechanically controlled rolled steel was investigated and interpreted in terms of its microstructure and the amount of free nitrogen present. Measurement of the amounts of titanium and aluminium in precipitates extracted from the HAZ showed that 13 ± 45%TiN and 72 ± 79%AlN were dissolved at 1400°C peak temperature. The measured amount of titanium was in good agreement with the amount calculated by means of thermodynamic analysis, indicating that such analysis can be used to estimate the amounts of TiN and free nitrogen in the HAZ at a given peak temperature. Simulated HAZ toughness was in¯uenced not only by the microstructure, in turn in¯uenced by the amount of undissolved TiN at the peak temperature, but also by the amount of free nitrogen present after the formation of BN during the cooling cycle. Multiple regression analysis of the simulated HAZ toughness showed that the detrimental effect of free nitrogen was much greater than the bene® cial effect of TiN in this experimental condition.MST/5042

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