Hwan Gyo Jung

Effect of Microstructure on Hydrogen-Induced Cracking of Linepipe Steels

Abstract Hydrogen-induced cracking (HIC) has been studied phenomenologically. The effect of microstructure on HIC is discussed for steels having two different levels of nonmetallic inclusions. Steels with different microstructures were produced by a thermomechanically controlled process (TMCP) from two different heats, which had different levels of nonmetallic inclusions. Ferrite/pearlite (F/P), ferrite/acicular ferrite (F/AF), and ferrite/bainite (F/B) were three representative microstructures of the tested steels. For the steels with higher inclusion levels, the minimum permissible inclusion level for HIC not to develop varied according to the steel microstructure. On the other hand, HIC occurred in the martensite/austenite (M/A) constituents regardless of steel microstructure above a certain concentration. It was shown that M/A constituents were easily embrittled by hydrogen atoms. Steels having a F/AF were resistant to HIC in the tested service condition; they exhibited a wide range of diffusible hydr...

Numerical study on hydrogen permeation of ferritic steel evaluated under constant load

Hydrogen permeation of two kinds of ferritic steel with different level of 2nd phase particles are compared utilising electrochemical permeation technique evaluated under various loads. This study indicates that tensile stress in plastic domain induces expansion of the interface between the 2nd phase particles and steel matrix, and formation of blister crack. Such microstructural-discontinuity provides additional hydrogen traps, resulting in slower diffusion and lower steady-state permeation flux. These phenomena appear predominantly in steel containing coarse-sized inclusion and precipitate having sharp extremities. The numerical analysis also supports that the steel containing coarse-sized 2nd phase particles with sharp extremities exhibits higher parameters of hydrogen capture rate per irreversible traps and blister crack formation rate than the steel containing fine-sized ones with spherical shape.