Study On The Effect Of He~+ Irradiation On Microstructure And Properties Of Stainless Steel Weld By TIG Weldings

Stainless steel materials are widely used in the nuclear power industry because of their good mechanical properties.However,the environment of nuclear reactors is quite special.The radiation damages and the effects of material properties caused by neutron radiation are hot issues,which domestic and foreign scholars have begun to study in recent years.Scholars at home and abroad have done a lot of research on the radiation effect of nuclear power materials,but relatively little research has been done on the radiation effect of welds.In this paper,304 austenitic stainless steel,430ferritic stainless steel and T91 martensitic stainless steel were manually TIG welded,and the welds were irradiated with He⁺.The SRIM software was used to simulate the irradiation damage of three types of stainless steel welds.The crystal structure and surface micro-morphology of the three stainless steel welds after irradiation were characterized through XRD,SEM and other tests.The influence of different irradiation doses on the micro-morphology of the three kinds of non steel weld was studied;Nano-indentation was used to characterize the surface hardness of welds before and after irradiation.Combined with TEM test and the theory of irradiation hardening,the effects of irradiation dose on hardening of weld irradiation and the hardening resistance of three stainless steel joints were studied;Finally,combined with the engineering application environment,the effects of three stainless steel welds on the corrosion resistance of stainless steel welds were investigated.SRIM simulation showed that after the same dose of He⁺ions irradiate the three materials,there was no significant difference in the damage amount of the three stainless steel welds,the peak corresponding to the He⁺ion concentration and the maximum depth of He⁺irradiation.When the radiation dose increases,the damage amount of the three types of stainless steel welds and the maximum depth of He⁺radiation increase,and the proportion of incident ions that produce secondary cascade collisions also increases.After irradiation,the diffraction peak angle of the（111）crystal plane of the 304 weld seam first shifted to a high angle and then to a low angle with the increase of the irradiation dose,indicating that the irradiation produced compressive stress,which resulted in a decrease in the crystal plane spacing.When the dose was increased,the interstitial atom clusters migrated and aggregated to the stress field area during the irradiation process,so that the residual tensile stress was relaxed;The diffraction angles of the（111）crystal planes of the welds of 430 and T91all shifted to a small angle with the increase of the irradiation dose,indicating that the influence of vacancy defects was greater than that of interstitial atoms,and the interplanar spacing was increased.After irradiation,the intensity of the XRD diffraction peaks of the three types of stainless steel welds changed,and the crystal grain orientation of the material changed;Dislocation loops with small size of20～40nm were used to segment the grain,which cause the diffraction peaks to widen to varying degrees.Dislocations,dislocation loops and helium bubbles formed in the stainless steel weld after irradiation lead to the change of surface morphology and irradiation hardening.Small holes and bumps appeared on the surface of the welds after irradiation,and the higher the irradiation dose,the more obvious the surface morphology changed.Irradiation at different doses caused the roughness of the three stainless steel welds to increase first and then decrease.When the irradiation dose was2.1×10¹⁶ n/cm²,the increase in roughness was attributed to the sputtering effect caused by He⁺irradiation,which has an etching effect on the surface.When the radiation dose was increased to 2.1×10¹⁷ n/cm²,the roughness decreased,which was due to the bridging effect of the ion radiation deposition effect on the damaged area.As the irradiation dose increased,the thermal effect of irradiation increased,the size and distribution density of irradiation defectsincreased,the density of dislocation channels increased,the increase in irradiation hardening increased.When the radiation dose was the same,the radiation hardening rate of 430 and T91 stainless steel welds was close,and the radiation hardening rate of 304 austenitic stainless steel welds was the highest,indicating that the radiation hardening resistance of 304austenitic stainless steel welds was poor.The introduction of tensile stress had the greatest impact on the irradiation defects on the surface of 304 stainless steel welds.Under the action of external tensile stress,the defect spacing of 304 stainless steel welds had the largest change,which was reduced by 61.5%.The increase in the size of irradiation defects was also the most obvious increase in 304 stainless steel welds,an increase of 59.2%.When a tensile stress is applied,new dislocations are introduced.These dislocations will directly lead to the hardening of the material.At the same time,they cooperate with the irradiation effect to attract and grow up the defects caused by the irradiation,which further leads to the hardening of the material.The relative hardness of T91,304,and 430 stainless steel welds under tensile stress increased by 6.2%,9.3%,and 15%.Comprehensive comparison of these three materials in terms of the radiation hardening resistance under the action of applied tensile stress,the radiation hardening resistance of the T91 martensitic stainless steel weld was relatively excellent.After irradiation,the corrosion resistance of the three stainless steel welds decreases.The higher the irradiation dose,the worse the corrosion resistance.Irradiation has a great effect on the corrosion resistance of 304 and 430 stainless steel welds,but little effect on the corrosion resistance of T91 stainless steel welds.