Hardening Behavior Of CLAM Steel Induced By Neutron Irradiation

Reduced activation ferritic/martensitic(RAFM)steels are considered as the baseline structural material for the fusion DEMO and test reactors in future.Structural materials in a fusion reactor will undergo high displacement damage and transmutation helium/hydrogen by intense fluence of high energy neutrons(14MeV).The understanding of irradiation/helium-induced hardening and embrittlement effects in RAFM steels is one of key issues in the current fusion materials programs.So irradiation experiments on candidate fusion structural material are widely carried out to investigate the irradiation effects.In the present wok,CLAM(China low activation martensitic)steel has been selected as reduced activation martensitic steels irradiated and studied in the SINQ target irradiation program(STIP).Tensile,micro-hardness,micro structure of CLAM steels irradiated to 20.9dpa in STIP-V were investigated after irradiation to study the dose,temperature and helium effects on hardening.Firstly,the dose effect on hardening of CLAM steel was investigated.When irradiation temperature(Tirr)is below 314?,yield strength change(??y)and micro-hardness change(?HV)go higher with increasing irradiation doses(5.4-20.1dpa)and the increase becomes slow when damage doses reach?20dpa.This tendency can be explained by the Makin-Minter model.The results are in good agreement with that of other RAFM steels irradiated in STIPs.TEM evaluation of CLAM samples indicated that barrier strength of defect clusters with mean sizes 3-20nm is?0.7 and that of helium bubbles with sizes 0.5-1.5nm is?0.15.Secondly,evalution of the temperature effect on hardening of CLAM steel was carried out.Tensile,micro-hardness measurement and positron annihilation analysis were used after CLAM steel irradiated up to 5.1-20.9dpa under 56-471?.With Tirr,below?270?,dose is the dominating factor on hardening of CLAM steel.With Tirr above 314?,hardening of the CLAM samples after irradiation decreases with increasing damage dose,accompanied with a seeming increase of ductility.Because the effects of dose and temperature,there have a temperature range of hardness peak:270-320?.To investigate helium effects,annealing experiments with 1h at 600? were done to recover the irradiation defect clusters and keep the helium bubbles in samples.Micro-hardness and microstructure were investigated after annealing.TEM investigation indicated that defect clusters were disappear,and there have almost no changes on the size and density of helium bubbles.Helium bubbles are very small(0.5-1.5nm)compared with defect clusters,but it can induced significant hardening with high number density(-1024m-3),especially under high dose conditions.The dose effect,temperature effect and Helium effect on the hardening of CLAM steel were studied after irradiation in this work.The results of tensile and micro-hardness can make a contribution to the design of China ITER TBM(Test Blanket Module).Depend on the hardness data of CLAM steel and other RAFM steel with different irradiation temperature,temperature effect on hardening were discussed.The study of helium effect on hardening under higher dose range(13.0-20.8dpa)can make a contribution to the research on mechanism of helium effect.