American scholars studied the influence of the sampling direction of Q235NH steel on its periodic fatigue, deformation and fracture behavior. Compared with other high-strength alloy q235nh weather-resistant steel with similar chemical composition and processing technology, Q235NH weather-resistant steel has significantly higher strength, plasticity and toughness. In this study, after the alloy steel bars provided were sampled from the transverse and longitudinal directions, they were refined and processed in accordance with the metallographic standard requirements for tensile testing and stress control cycle fatigue testing.
The study reached the following main conclusions:
First, the structure of the Q235NH weathering steel is mainly ferrite islands distributed on martensite and uniformly dispersed fine alloy carbides. The composition of Q235NH alloy steel determines that there is a considerable amount of martensite in the structure, which is mainly a needle-like, extremely thin tube martensite.
Second, the elastic modulus of the steel in the transverse direction is 10% lower than that in the longitudinal direction, and the yield strength is the same.
Third, the stress fatigue life of longitudinally sampled samples is lower than that of horizontally sampled samples.
Fourth, there is a local stress concentration at the interface between the ferrite phase and the martensite phase, which has a great harm to the fatigue resistance of the steel.
Fifth, fatigue fracture shows the characteristics of local ductile-brittle failure mechanism.
Sixth, the fatigue zone of Q235NH alloy steel is mainly composed of short crack origin, early micro-crack growth zone and short and obvious crack stable growth zone.
