Microstructure Evolution of the Semi-Macro Segregation Induced Banded Structure in High Strength Oil Tubes During Quenching and Tempering Treatments.

C110 oil well casing tubes should have high strength and corrosion resistance which is commonly used for deep wells operation containing corrosive media. In this paper, the microstructure evolution of a kind of semi-macro segregation originated banded structure in casing tubes is studied under different heat treatments. It is shown that the characteristics of the banded structure will change significantly in subsequent hot working and heat treatment processes. For the hot-rolled ones, the banded structure is composed of pearlite plus bainite. After quenching, it evolves into martensite band with high concentration solute elements. Finally, the banded structure will change into a carbide banding under the following tempering process. The temperature and cooling rate of the tempering practice show an obvious effect on the final band structure. To improve anti-SSC (sulfide stress corrosion cracking) performance, the favorable QT (quenching and tempering) practice for C110 steel should be a higher tempering temperature and a quicker cooling rate, from which the banded structure defects can be decreased together with an obvious improvement of the tube wall hardness uniformity.