The effects of cooling rate and finish rolling temperature on the microstructure refinement and martensite /austenite(M/A) islands in X70 pipeline steel were studied with a Gleeble thermal-mechanical simulation machine. When the cooling rate increasing,the grain size of ferrite decreases,the volume fraction of M/A islands increases first and then decreases,but the dimensional change of M/A islands is opposite to the volume fraction.With the finish rolling temperature rising,ferrite in the steel slightly gro...