Analysis of Abnormality of L80-9Cr Continuous Casting Billet

The 9Cr steel pipe is manufactured by means of the process of CC billet+hot-extrusion. However obvious abnormalities like cutting difficulty are found with the L80-9Cr CC billet during the cutting operation. Relevant analysis is conducted with sample as taken from the abnormal section of the said CC billet,which reveals that in the abnormal area,there exist in the microstructure contents not only ferrite+carbide,but also certain content of the martensite structure,and that the hardness of the abnormal area is remarkably higher than that of the normal area,but the contents are not obviously other than those of the ferrite and pearlite areas. It is regarded via the analysis that during the annealing process,part of the marstenite has not completely transformed into ferrite+pearlite,and thus much more residual marstenite leads to local high hardness of the CC billet,which in turn causes cutting difficulties like frequent oblique cutting,and uneven color of the sawed pipe end face. Accordingly the time for the follow-up annealing of the billet is extended,and then no more abnormalities as above mentioned are found.