Effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel

The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated. The steel was tempered at 600 degrees C for 1-3 h. Detailed characterization was carried out to characterize the microstructure, especially the dislocation density and grain size. The hydrogen permeation test and thermal desorption spectroscopy test were also implemented. The dislocation density decreases, the amount of carbide increases, and carbides (M23C6 and MX) coarsen with the tempering time increasing. After tempered at 600 degrees C for 3 h, the diffusible hydrogen trapped by lattice and dislocation decreases while the non-diffusible hydrogen trapped by carbides increases, leading to the best hydrogen embrittlement resistance, although hydrogen diffuses rapidly due to the reduction of dislocation density. And the fracture mode changes from a combination of brittle cleavage and ductile dimpled fracture to fully ductile dimple fracture under hydrogen charging condition. Moreover, a phenomenon that hydrogen accelerates the dislocations movement of the steel during deformation was observed, which is related to the fact that hydrogen enhanced localized plasticity mechanism.

Automated summary

The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel was investigated. The study found that with increasing tempering time, the dislocation density decreases and the amount of carbide increases. After tempering for 3 hours, the reduction in dislocation density leads to rapid hydrogen diffusion, but the carbide can trap more hydrogen, resulting in the best hydrogen embrittlement resistance. Under hydrogen charging condition, the fracture mode also changes.