Improvement of HAZ Toughness of Steel Plate for High Heat Input Welding by Inclusion Control with Mg Deoxidation

The effect of Mg content on the evolution behavior of inclusions in the steel plates with Mg deoxidation was investigated based on the experimental studies and thermodynamic calculations. Simulating welding process and Charpy impact test were also carried out to evaluate the Heat Affected Zone (HAZ) toughness of steel plates. The typical inclusions found in the steels were the complex inclusions comprising central oxide and peripheral MnS. With the increase of Mg content in the steel samples from 0 to 27, 38 and 99 ppm, the phase of central oxide inclusions changed sequentially from Al2O3 to (Mg-Ti-O), and MgO, which is consistent with the thermodynamic calculation results. Furthermore, the size of inclusions decreases and the number density of inclusions increases with the increase of Mg content. The HAZ toughness of steel plates after welding with heat input of 400 kJ cm(-1) has been greatly improved by inclusion control with Mg deoxidation.