Evaluation of microstructural effects on mechanical properties of CT80 grade coiled tubing Steel

The microstructure formation and mechanical properties of coiled tube CT80 grade steel was investigated with different heat treatments. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to evaluate the microstructure. Acicular ferrite, polygonal and quasi-polygonal ferrite, granular bainite, martensite, pearlite, and small Martensite-Austenite (MA) islands with the banding structure were revealed in original and heat treated samples. In order to assess the effect of grain size and microstructure, mechanical properties were evaluated by hardness, charpy impact, tensile, and fatigue life tests. The best mechanical properties by tensile and fatigue test is obtained from the normalized specimen with the grain size of ASTM 13.