Effect of controlled rolling/controlled cooling parameters on microstructure and mechanical properties of the novel pipeline steel

Abstract

The study of controlled rolling/controlled cooling process parameters which affect the microstructure and mechanical properties of a novel pipeline steel have been optimized by the orthogonal experiment with four factors and three levels in this paper. However, the parameters of thermo-mechanical control process (TMCP) optimized by the Gleeble-3500 hot simulator could not satisfy performance requirements of the X100 pipeline steel. In order to improve the performance of this steel, the influence of finish cooling temperature (FCT) on the microstructure and property is studied in detail. It is found that, as this steel is thermo-mechanically treated by this set of parameters (the start heating temperature, finish rolling temperature (FRT), FCT and cooling rate of 1,180 °C, 810 °C, 350 °C and 35 °C/s, respectively), the microstructures are mainly composed of granular bainite (GB) and acicular ferrite (AF). The effective grain sizes are below 20 µm; the steel reached the optimal balance between the strength and the toughness; the yield strength is 695 MPa; the tensile strength is 768 MPa; the elongation is 16.6 %; the impact energy is 262 J at room temperature. All indexes could meet the requirements of X100 pipeline steel.

Keywords

Controlled rolling/controlled cooling / Finish cooling temperature (FCT) / Microstructure / Mechanical properties / X100 pipeline steel

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