Helium effect on phase structural changes in carbon steel under post-irradiation phase recrystallization

Abstract

In the present paper a new radiation effect related to thermally irreversible structural changes during post-irradiation phase transformation in a-particle irradiated region of the sample of the U7 steel [0.77; carbon) is demonstrated. The samples of the U7 carbon steel have been irradiated at the cyclotron with a-particles with energies of 29 and 50 MeV up to dose 1.5x10 cm"^ and with protons with energy of 10 MeV up to dose 2.5x10" cm'^ at temperatures not more than 100° С The results of metallography study of as-irradiated, annealed and carburized after full decarburisation samples allow to establish two important facts. First, the irradiation of the U7 carbon steel with high-energy protons and alpha-particles which results in formation of radiation defects and hydrogen doping leaves any structural changes invariant in the process of post-irradiation annealing at temperatures 400-1100°C. Second, due to post-irradiation annealing in the range of temperatures above the а-7-transition tennperature in the helium doped sample regions of the U7 steel observes thermal irreversible structural changes (perhaps phase changes too): the formation of fine-grained ferrite-pearlite structure with an essential superiority of ferrite phase portion. It might be assumed that the main reason of the observed effect: is thermally stable complexes of helium atoms and vacancies in the form of helium bubbles rather than radiation defects.