Mechanical Properties of Fusion Reactor First Wall Candidate Material JLF1

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Mechanical property changes of JLF1 low activation ferritic/martensitic steel (Fe-9Cr-2W-0.2V-Ta) after heavy neutron irradiation were widely investigated using small size specimens (l.5 mm CVN, l/3 CVN, SSJ-tensile, W-tensile). One of the most important problems in irradiated ferritic/martensitic steel is increase of the ductile-to-brittle transition temperature (DBTT). DBTT increase in JLF1 after neutron irradiation up to 6Odpa was estimated to be still below room temperature, and the highest DBTT was measured to be 255K following irradiation of about 25dpa. There was no clear specimen size dependence in DBTT.Results of tensile tests using SSJ and/or W specimens showed that 0.2% proof stress of JLF1 once increased with irradiation up to 15-20dpa followed by the decrease with further irradiation. This results indicated that there was a maximum of 0.2% proof stress around 15-20dpa, and that dose dependence of DBTT was closely related to that of 0.2% proof stress. This means that the change of DBTT in JLF1 is considered to be mainly caused by hardening mechanism due to irradiation.