The effect of tempering temperature on the combined strength and toughness of a low carbon Mn-Si-Cr steel with the microstructure of martensite or carbide free bainite-martensite (CFB/M) has experimentally been investigated. The study reveals that the presence of CFB in a mixed microstructure retards the softening of the steel during tempering and also retards the tempered martensite embrittlement (TME) onset temperature. The air-cooled CFB/M possesses a better combination of strength and toughness compared with water quenched full martensite after tempering within some intermediate temperature range. Filmy rather than blocky retained austenite was found in the air-cooled CFB/M microstructure. The filmy retained austenite in CFB/M has a good stability. Carbon enriched filmy retained austenite in CFB might improve the toughness of the steel after tempering at intermediate temperature range.