Interaction of Interstitial Impurities with Radiation-Induced Defects Leading to Improved Elevated Temperature Mechanical Properties of Mild Steel

Improvements in both the yield strength and ductility were noted in mild steel at elevated temperatures (≳315 K) following neutron irradiation to 2 × 10²² n/m², in contrast to hitherto observed radiation hardening and embrittlement. This beneficial effect was shown to be due to the interaction of interstitial impurities with radiation-produced defects resulting in reduced concentration of interstitial carbon and nitrogen in solution, and thus blue brittleness is suppressed following radiation exposure. Consequently, the energy absorbed by the irradiated material (a measure of toughness) improved at these temperatures. In the temperature range examined, namely from 300 to 550 K, Lüders strain increased following neutron irradiation. While the Lüders strain of unirradiated material exhibited a peak at ∼460 K due to dynamic strain aging, it decreased continuously with test temperature following neutron irradiation. Radiation exposure resulted in decreased rates of work hardening at all of the test temperatures. Peaks in the temperature dependence of the work-hardening parameter are noted for the unirradiated material in the serrated flow regime. Thermal recovery of radiation damage resulted in increased rates of work hardening at elevated temperatures.