Ferritic steels that are generally used in pressure vessels and various reactor support structures in light water reactors exhibit dynamic strain aging (DSA) resulting in increased work-hardening accompanied by ductility loss. DSA is due mainly to interstitial impurity atoms (IIAs) such as C and N that diffuse to the gliding dislocations and lock them resulting in load fluctuations. While there is a possibility of adding this embrittlement known as blue brittleness to the well-known radiation embrittlement, it has been amply demonstrated that radiation exposure leads to decreased concentrations of IIAs in solution. Thus the critical temperature for DSA increases with increased neutron fluence very similar to the increase observed in dry hydrogen treated mild steel samples with decreased concentration of nitrogen in solution with increased treatment time. We summarize here the mechanical and fracture studies made on three different materials: a mild steel and two ferritic steels (A533B and A516 Grade70). Tensile, 3-point bend and compact tension (CT) specimens were used in characterizing mechanical and fracture behaviors of these materials. Superimposed radiation effects are considered on subsize 3-point bend specimens of A533B and A516 steels. Thin wire samples were used to investigate tensile properties of mild steel at various test temperatures before and after irradiation with special attention to DSA. In addition, effects of interstitial nitrogen are evaluated by heat treating to different times in dry hydrogen atmosphere.
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