Heavy wall forged pipes of grade 92: effect of heat treatment conditions on microstructure and creep resistance

The design of grade 92 steel seamless pipes has progressed significantly, but very little has been published on heavy wall forged pipes. In this work, microstructure and creep properties of 180 mm thick F92 pipes both normalised and tempered (N&T) and quenched and tempered (Q&T) are studied. Creep behaviour was assessed using both uniaxial tests and small punch creep test data analysis. Quenching treatment was able to develop cooling rates greater than 0.6 °C/s, limiting the presence of ferrite to less than 1%, while in case of normalising, the ferrite percentage was 3–4.5% (average cooling rate < 0.12 °C/s). Consequently, the Q&T steel exhibited creep strength of 20–25% higher than that of the N&T forged pipe of the same thickness. These results were exploited for the setup of a new proprietary heat treatment able to develop on heavy wall forged pipes’ creep strength levels similar to those of N&T thin seamless pipes.