To Investigate the Effect of Heat Treatment on API X70 Pipeline Steel

Abstract

API pipeline steels are designed in such a way that they can survive in high temperatures and high pressure in different environments. The API X70 pipeline steel has a very fine-grained microstructure so it has high strength and ductility. In present work, the heat treatment of API X70 steel was performed at different tempering temperature and microstructural analysis was studied. Mechanical and microstructural behavior of base metal and heat-treated API X70 steel was studied. The distinct phases such as ferrite, pearlite and some carbides that form during the heat treatment are visible in the microstructure of the heat-treated samples, XRD as well as SEM analysis of base and heat-treated specimens were performed. Major peaks of iron were observed for both base and heat-treated samples during XRD analysis. XRD analysis of API X70 steel in which maximum peak intensity was present at an angle 2Ɵ = 40.18 and 44.6. SEM analysis of base as well as heat treated API X70 steel exhibit different phases such as Acicular, ferrite-pearlite and small inclusions of carbides. Various phases such as ferrite as well as pearlite were observed for the specimen tempered at 650 °C for 3 Hours. Base metal typically exhibits acicular ferrite microstructure. The microhardness of base metal (28.25 HRC) is higher as compared to the heat-treated steel (6.87 HRC).