Proton Irradiation Induced Hardening and Its Recovery During Healing Treatment of Modified 9Cr–1Mo Steel

The current paper identifies the mechanism of hardening of modified 9Cr–1Mo steel during 3 MeV proton irradiation and softening during healing treatment. The steel, when irradiated with 3 MeV protons to a dose of 0.14 dpa, showed a significant increase in hardness up to certain depth, followed by a decrease. The peak hardness appeared at a depth of 35–40 µm, which matched with the depth at which defect density was maximum as calculated using SRIM2003 code. Rietveld analysis of X-ray diffraction patterns from different depths confirmed that the defect density doubled at the subsurface after irradiation. Annealing the irradiated steel at 823 K for 30 min could partially reduce the defect density and hence, soften the steel.