During the production of large-sized P92 ferrite heat-resistant seamless steel pipe by rotary piercing process

the inner surface of the steel pipe is prone to produce small cracks. Through metallographic analysis

high-temperature phase transformation calculation and high-temperature heating test

the studies show that because of the higher heating temperature and the longer heating time

which increases the surface oxidation and decarburization

during the heating process of the P92 billet with a through hole in the center make a large number of high temperature δ ferrite phases near the inner wall and then the cracks generate and propagate around the δ Ferrite phases at the subsequent process of rotary piercing. According to the mechanism of in

ternal surface cracks

through the control of the Cr＜13%

Ni

eq

＜4% for P92 pipe chemical composition

the lowering of the billet heating temperature from 1220-1250 ℃ to 1190-1220℃

and the improvement parameters of roll speed

roll distance and the piercing point

the problem of cracks on the internal surface of large-diameter P92 seamless steel pipe is effectively solved

and the yield and production efficiency of P92 seamless steel pipe are improved.