NbC-TiN co-precipitation behavior and mechanical properties of X90 pipeline steels by critical-temperature rolling process

A new critical-temperature roll process (CTRP) was developed to manufacturing X90 high strength pipeline steel. The CTRP process induced high intensity NbC-TiN co-precipitation at rough rolling stage. As a result of NbC-TiN co-precipitation, ultrafine microstructure and outstanding mechanical properties of CTRP X90 steel were obtained compared with conventional TMCP X90 steel. Averaged size of pancaked austenite for CTRP steel was only 7.8 μm and less than a half of TMCP steel. High intensity co-precipitates are observed in CTRP steel, these co-precipitates have irregular shape and averaged size is about 100 nm.456