Frontiers

This study explores the microstructural characterization of pearlite phase transformation in high-strength low-alloy API X60 steel, which is used in pipelines. Understanding the formation, phase percentages, and morphology of the pearlitic phase is crucial since it affects the mechanical properties of the considered steel. In this research, a phase-field model, particularly the Cahn–Hilliard approach, was used in order to simulate the formation and morphology of the pearlite phase in response to different heat treatments. Both double- and triple-well potentials were considered for comprehensively studying pearlite’s morphology in the simulations. The simulation results were then compared with experimental outcomes obtained by metallography and field-emission scanning electron microscopy analyses. Considering the double-well potential can help simulate only two phases, ferrite and cementite, which is less compatible with the experiment results than the triple-well potential, which gives the possibility of simulating a three-phase microstructure, ferrite, cementite, and austenite, and a better match with experimental data. The study revealed that as the cooling rate increases, the interlamellar spacing and layer thickness decrease. Additionally, the difference between experimental and simulation results using triple-well potential was approximately ∼10%. Therefore, triple-well potential formulation predictions have better agreements with experimental results for the development circumstance of pearlitic structures.

The increasing demand for oil and natural gas has compelled companies to seek out these resources in challenging environments, such as humid or extremely cold weather. Pipeline steels not only need to possess high strength and toughness to withstand these harsh conditions but also provide an economical and safe means for transporting oil and natural gas over long distances (Dong et al., 2010). Consequently, the production, installation, and commissioning of large-diameter pipes, which are used over extensive lengths and under high-pressure conditions, have become critical in terms of economy and safety (Shin et al., 2006; Olivares et al., 2008). For acquiring the required properties, steels should be subjected to various processes, including the austenite–pearlite transformation in low-carbon steels and fine-tuning the microstructure to control steel properties (Dong, 2012). High-strength low-alloy (HSLA) steels are a class of low-carbon steels that are enriched with small amounts of alloying elements like molybdenum, niobium, titanium, and vanadium to increase the strength of steels (DeArdo et al., 2009; Morrison, 2009). Pipeline steels are a group of microalloyed steels that typically have low carbon content (