Microstructural fatigue crack growth in single-packet structures of ultra-low carbon steel lath martensite

Inhomogeneous microstructure and fatigue crack propagation of thick-section high strength steel joint welded using double-sided hybrid fiber laser-arc welding

“…The microstructure of the base metal is tempered sorbite, while that of the laser zone and arc zone are lath martensite due to the fast cooling rate of the hybrid laserarc welding process. Compared with the tempered sorbite, the lath martensite containing high density dislocation is plastic deformed in the front of the fatigue crack tip [33,34]. Therefore, the stress concentration in the front of the fatigue crack propagation is reduced to a certain extent due to the large plastic deformation in the front of the fatigue crack propagation.…”

Effect of Welding Heat Input on Microstructure and Properties of Coarse Grain Zone in Heat Affected Zone of Ultra-Low Carbon Bainitic Steel

“…At present, China's research on high strength ultra-low carbon bainitic steel has entered the mature stage, in which 400~700MPa steel has been able to meet the mass production, and applied to large structural facilities. Carbon content is extremely low, this kind of steel for low carbon bainite matrix, high strength and toughness of the alloy steel, through solid solution strengthening, grain refining strengthening 5,6 , dislocation strengthening methods such as strengthening and organization, have good welding technology and the ability of resistance to hydrogen induced cracking 7,8 , at the same time of guarantee good toughness and can guarantee high strength, steel weldability, able to meet the harsh conditions without preheating before welding and without heat treatment 9 . Jiang et al 10 analyzed that the ultra-low carbon bainitic steel has lower cold cracking sensitivity, and preheating temperature of 100°C can help completely eliminate cold cracks, generating good process weldability.The increase of preheating temperature can reduce the hardening degree of heat affected zone.…”

Hydrogen-related Fatigue Fracture under Various Test Frequencies in Low-carbon Martensitic Steel

“…Okada et al 9) conducted crystallographic analysis on fatigue crack initiation of low-carbon martensitic steel, and clearly showed that incompatibility of plastic strains between adjacent blocks was the origin for the formation of initial fatigue cracks at block boundaries. Ueki et al [10][11][12] performed crystallographic analysis on fatigue crack propagation in low-carbon martensitic steels using miniaturized compact-tension specimens. They proposed that the orientation relationship between the longitudinal directions of the martensite laths and the slip direction dominated the fatigue crack growth resistance.…”