Effect Of Work Hardening On Driving Force Of Environmentally Assisted Cracking Of 316L SS

Environmental assisted cracking(EAC)can be regarded as a slow process of oxide film cracking and regeneration under interaction of mechanics,materials and corrosive environment in crack tip of micro-environment.It’s an important failure form of key structural materials of nuclear power in service.Cold bending in the manufacturing process of nuclear power structure materials,bending caused by assembly errors,and tensile deformation of materials in the heat-affected zone caused by cooling shrinkage of the weld seam will cause different degrees of plastic deformation of the material,resulting in work hardening.Work hardening affects the EAC crack growth rate,and EAC crack growth rate is affected by crack growth driving force.In order to study effect of work hardening on crack growth rate of EAC,influence of work hardening on driving force of crack growth of 316L SS was analyzed by means of theory,experiment and finite element simulation.The main research contents are described as follows:(1)The mechanical parameters of work hardening of 316L SS were experimental obtained and Vickers hardness of materials with different work hardening degrees was measured,and relationship between hardness and mechanical parameters was established.The corresponding relationship between Vickers hardness and stress-strain of material during continuous stretching is obtained through experiments,and the empirical relationship between the Vickers hardness and stress-strain of 316L SS is established.The Vickers hardness distribution of the notch is obtained by experiment,and established relationship is applied to notched specimen to obtain the distribution of mechanical parameters under uneven hardening of the notch.By combining empirical formula with finite element simulation,the distribution law of Vickers hardness of notch is obtained,and comparing with experimental results,and feasibility of the empirical formula is verified.(2)Combined with stress-strain distribution law of crack tip plastic zone,uneven notch hardening characteristics and notch hardening acquisition method are extended to crack tip to obtain distribution of Vickers hardness and mechanical parameters of crack tip under sudden load(earthquake and maintain)conditions law.The oxide film morphology at EAC crack tip was obtained by a slow strain rate tensile simulation experiment in nuclear power-water circuit environment,and the influence of oxide film morphology on EAC crack tip hardening rule was analyzed.Combined with hardening distribution law of EAC crack tip,a calculation model of EAC crack tip with uneven hardening was established.(3)On the basis of EAC finite element calculation model,distribution of stress and strain field of EAC crack tip was compared and analyzed under condition of without hardening at crack tip and with hardening at crack tip.Influence of mechanical parameters of 316L SS on stress-strain field of EAC crack tip without hardening and with hardening is studied.Effect of work hardening of 316L stainless steel on stress-strain field of EAC crack tip is obtained.(4)Based on distribution of tensile stress which is most easily leads to cracking of EAC crack tip,distribution of driving force for EAC crack growth is compared and analyzed when there is no hardening at crack tip and hardening at crack tip;Influence of 316L SS mechanical parameters on driving force of EAC crack growth and the sensitivity of crack driving force to material mechanical parameters are analyzed,and effect of material mechanical parameters on EAC crack growth rate is further obtained.The effect of work hardening on EAC crack growth driving force and crack growth rate of 316L stainless steel was studied,and the distribution of EAC crack growth driving force and crack growth rate were obtained.(5)Experimental analysis of hardness of 316L SS in the heat-affected zone of nuclear power safety end welded joint.Based on this,the effect of work hardening degree of 316L SS in heat affected zone on stress-strain field of EAC crack tip on fusion line and heat affected zone is analyzed.Effect of the work hardening degree of 316L SS in heat affected zone on driving force and crack growth rate of EAC crack growth was studied.Distribution of driving force and crack growth rate of EAC on fusion line and heat affected zone are obtained.