Effective strategies for improving quenched microstructure and mechanical properties of hot-rolled seamless steel pipes

The containing Ti-Mg-Ca-O composite particles were innovatively used to achieve microstructure refinement and properties improvement of hot-rolled seamless steel pipes, and compared with conventional steel (C# steel). The results show that the C# steel mainly consisted of parallel lath martensite after on-line quenching. Under the same rolling and heat treatment conditions, dominant Ti-Mg-Ca-O composite particles in modified steel (M# steel) were effective nucleation sites of acicular ferrite, dividing the prior austenite grains and refining microstructures. The strength values of the both steels were at the same level, however, the impact energy of M# steel was significantly higher than C# steel, increasing by 28%. This study provides an effective method for further microstructure refinement of hot-rolled seamless steel tubes.