Abstract: Samples were taken from different locations of non-quenched and tempered steel billets,andinclusionsofthesesampleswere analyzedbySEM-EDSandAspex.Precipitation ofinclusion had been calculated usingFactsagesoftware. The results showed that,the average sizeofinclusions increasedgraduallyandinclusiondensity decreasedgradually from edge to center ofthe billet. Besides,oxides didn't change much in size and sulfide size increased gradually. The inclusions types were main sulfide and oxide. The precipitation temperature of oxide was 1400-1600 ℃, and composition of the oxide were in solid area of the ternary phase diagram at steel making temperature,so they were not easy to aggregate. The quantity of MnS was increasing at the temperature of 1450 ℃,and a substantial precipitation of MnS begins at 1350 ℃.Duringthe solidification process,MnSwasprecipitatedonoxide as the core.

Key words: non-quenched and tempered steel, inclusion, continuous casting billet, sulfide