Experimental Study On Crack Growth Rate Of Welding-joint For ADB610 Steel

Because of the good mechanical and welding properties, ADB610, a new kind of crack free low-carbon bainitic steel without hardening and tempering, is widely used in many areas. But the research works on it are limited to simple mechanical property, welding property and impact toughness. However, the research works on fracture toughness and crack growth rate, the important criterions of break-designing and life-estimating, are rarely reported.First, an experimental study work on fracture toughness of ADB610 welding-joints is finished; then, both experimental and numerical study on crack growth rate under constant amplitude loading are conducted; at last, the evaluating life work is done according to the crack propagation model obtained from the experimental and numerical study. In the completely experimental study on crack growth rate process, four normal methods, based on (a,N), (da/dN,△K), introducing a random function and Monte Carlo method, are used. The numerical study is based on the fatigue model, simplifies from the classical fatigue theory, and associated with finite element method (calculating the elastic-plastic results), the damage rate is used on the prediction of crack growth rate.According to the study, following results are obtained. The fracture toughness is larger than 70 MPa√m. The P-da/dN-△K curves of the ADB610 welding-joint at different confidence level are obtained with weld heat input is 25kJ/cm. The method based on (da/dN,△K) is the most appropriate one in four methods. The evaluating-life obtained from the numerical method is closely to the life obtained from experimental method at confidence level 99.9%, and therefore the simplify fatigue model is available. Furthermore, after a simple cooperation of experimental life and estimating-life in three zones:heating-zone, welding-zone and base metal, it is clear that the statical rule, the estimating-life in heating-zone and welding-zone are a little less than base metal's, is right. On the other hand, welding-joint of ADB610 is good in fracture and fatigue.