The effect of Ce on inclusion evolution behaviour in 700 MPa class Al-killed high-strength steel was investigated through experimental observations and thermodynamic calculations. Simulated welding experiments and mechanical characterisation tests of the heat-affected zone (HAZ) were also carried out to investigate the effect of adding Ce on the welding performance. The results reveal that the typical inclusions of Ce-free steel are the CaS + Mg–Al–O + Ti(C,N) complex inclusion and isolated CaS inclusion. For Ce-containing steel, the typical inclusion is Ce–Ca–O–S + CaS + Ti(C,N). Furthermore, the number density of inclusions increases, and the average size of inclusions decreases after adding Ce. Lastly, the toughness and strength of the HAZ tested with heat inputs of 25 and 50 kJ cm–1 are evidently improved by adding Ce.
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