What is the state of banded structure of steel pipe

The cooling rate of the steel pipe is less than the critical cooling rate of eliminating banded structure after it is kept in the furnace from normalizing temperature. When it is cooled slowly, the ferrite is first precipitated in the austenite carbon poor zone of the steel (the carbon poor zone is related to the parent phase of banded structure). With the slow cooling and the decrease of temperature, the amount of proeutectoid ferrite increases gradually until the austenite is cooled. At room temperature, the banded structure of ferrite and pearlite appears in the microstructure of steel pipe.

In the metallographic examination of hot rolled seamless steel pipe or hot expanded seamless steel pipe, banded structure defects are often found in low carbon deformed steels of 20, 20G, A106B and A106C, which can reach 4 to 5 in severe cases.