Relationship between microstructure and hydrogen induced cracking behavior in a low alloy pipeline steel

Hydrogen induced cracking (HIC) behaviors of a high strength pipeline steel with three different microstructures, granular bainite & lath bainite (GB + LB), granular bainite & acicular ferrite (GB + AF), and quasi-polygonal ferrite (QF), were studied by using corrosion experiment based on standard NACE TM 0284. The HIC experiment was conducted in hydrogen sulfide (H2S)-saturated solution. The experimental results show that the steel with GB + AF and QF microstructure present excellent corrosion resistance to HIC, whereas the phases of bainite lath and martensite/austenite in LB + GB microstructure are responsible for poor corrosion resistance. Compared with ferrite phase, the bainite microstructure exhibits higher strength and crack susceptibility of HIC. The AF + GB microstructure is believed to have the best combination of mechanical properties and resistance to HIC among the designed steels.