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The microstructures and mechanical properties of X80 pipeline steels produced by both novel ultra fast cooling and conventional-accelerated continuous cooling modes are investigated. Results showed that different levels of Mo addition had a remarkable effect on the microstructures and mechanical properties of the investigated pipeline steels. The proeutectoid ferrite and pearlite formation is inhibited in the high-Mo steel and acicular ferrite is obtained over a wide range of cooling rates, whereas the dominant acicular ferrite microstructure can only be obtained when the cooling rates reach up to 5 C s À1 . Very similar microstructures and mechanical properties are obtained in the low-Mo steel produced with ultra fast cooling and in the high-Mo steel produced by the conventionalaccelerated continuous cooling. It was proved by simulation and industrial trials that highstrength low-alloy steels such as pipeline steels, can be produced using the novel ultra fast cooling which also reduce alloy cost.

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