Effect of Cooling Process on Microstructure and Mechanical Properties of X100 Pipeline Steel

The effect of cooling rate and finish cooling temperature after rolling on microstructure and mechanical properties of X100 pipeline steel has been investigated by thermomechanical simulation experiment and hot rolling experiment. Also, microstructure and fracture morphology of X100 pipeline steel have been observed by optical microscopy, transmission electron microscopy, and scanning electron microscopy. The results reveal that finish cooling temperature and cooling rate can strongly affect the microstructure and mechanical properties of experimental steel. To obtain excellent mechanical properties of X100 pipeline steel successfully, the cooling process parameters should be carefully designed. For present instance, the optimal cooling processing schedule has been acquired: the cooling rate after rolling should be adopted in the range of 27–33 °C s−1 and the finish cooling temperature should be controlled within the temperature range 535–560 °C. High strength of X100 pipeline steel is from a mixture of bainitic ferrite laths with a mean width of 0.55 µm containing high-density dislocations, dispersed fine M/A islands, and dispersed nano-precipitates. Moreover, dispersed fine M/A islands and fine inclusions can effectively hinder crack propagation and improve the low-temperature toughness of X100 pipeline steel.