Abstract: To improve the low-temperature toughness of heat-affected zone（HAZ） of heavy plates, the inclusions of deoxidation with aluminum calcium magnesium were studied on the basis of thermodynamic calculation by Inclusions Automatic Analyzer System. The results showed that the inclusions with aluminum deoxidation were large size and low density and the main types of inclusions were Al2O3 and calcium aluminate. The main types of inclusions with calcium deoxidation were calcium aluminate parcelled MnS which size was below 3μm. The main types of inclusions with magnesium deoxidation was MgO and MgO which surfaced precipitation of TiN or MnS, and the sizes were below 1μm. After simulating welding test with heat input of 400 kJ/cm, the impact energy value at -20 ℃ on HAZ of specimen with magnesium deoxidation and calcium deoxidation reached more than 180 J.

Key words: oxide metallurgy, high heat input welding, low-temperature toughness, inclusion.