Is neutron radiation exposure always detrimental to metals (steels)?
It is well established that irradiated metals and alloys exhibit increased mechanical strength accompanied by reduced ductility, commonly referred to as irradiation strengthening and embrittlement. We talk about radiation damage and environmental degradation of metals following radiation exposure. Indeed, there have been numerous conferences and symposia held and planned on this subject, which include research work and discussions with the central theme being the damage created in materials by neutron radiation exposure. Radiation embrittlement in metals is believed to be due mainly to (1) changes in flow properties because of the interaction of dislocations with irradiation-produced defects1, and (2) precipitation of transmutation-produced gases and irradiation-induced segregation at grain boundaries which are potential fracture sites2. Contrary to the previously observed radiation embrittlement in metals, I report here that neutron irradiation of mild steel improved both the mechanical strength and ductility at 373 K even at relatively high (∼1018 neutrons cm−2), fast (>1 MeV) neutron doses. To my knowledge, such improvement has never been observed before.
Strain-aging behavior of irradiated and denitrided mild steel
Abstract Influences of neutron irradiation and dry hydrogen treatment on yield point phenomena in mild steel were examined. Static strain-aging studies were performed on vacuum-annealed, dry-hydrogen-treated and neutron-irradiated samples. Hardening due to neutron radiation damage exhibited a cube root dependence of the fluence. In addition to an increase in the lower yield stress, the Luder strain increased with dose up to 1018 neutrons cm−2, and at higher doses an apparently rounded yield was observed because of fracture during the Luder straining. The increase in the Luder strain followed a (Φt) 1 3 law, similar to that for radiation hardening. Static strain-aging studies revealed a complex time dependence of the strain-aging index f and seem to illustrate a two-stage process: initially, atmosphere locking and, for long aging times, locking due to precipitation. The effect of neutron irradiation was very similar to the effect of dry hydrogen treatment; the rate of aging decreased and, at high fluences (or longer exposures to dry hydrogen), essentially non-aging steel was obtained. However, the kinetics and/or mechanism of strain aging are not affected by neutron radiation (or dry hydrogen treatment).
Precipitation Process of Carbon in Alpha-Iron
The precipitation process of carbon in alpha-iron was studied by measuring the internal friction, and by observing the precipitates by electron microscope. The experimental results are expressed fairly well by the formula which expresses the sum of the two processes, one being the absorption of carbon atoms by the precipitates by way of dislocations and the other being the absorption of carbon atoms through the surfaces of the precipitates by the diffusion-limited process. The observation of the precipitates supports this explanation of the precipitation process.