Evaluation The Effect Of The Grain Size On Intergranular Corrosion Of Austenitic Stainless Steel Using EPR

As an advanced materials joining technology, diffusion bonding has been widelyused in aerospace and nuclear power industries recently. Diffusion bonding hanattracted extensive attention in package in Micro-chemical Mechanical Systems.Austenitic stainless steels are preferably selected for manufacturing micro heatexchangers and micro-reactors due to its excellent corrosion resistance and goodmechanical properties. Because of corrosion medium in Micro-chemical mechanicalsystem and effect of vacuum diffusion bonding process on corrosion properties ofaustenitic stainless steels, it is therefore essential to investigate corrosion behavior ofthe diffiong bonded joints of austenitic stainless steels for both optimization ofbonding parameters and reliable package of engineering structures.Electrochemical Potentiokinetic Reactivation(EPR)is generally used toevaluating of intergranular corrosion austenitic stainless steels. It is non-destructive,rapid and quatitetive behavior and can be used for industrial on-site inspection ofmaterial sensitivity to intergranular corrosion.The main contents of the article are as follows:(1) Different times of solution treatments on1100℃has been conducted on316Laustenitic stainless steel crude materials. The experimental results show that:with the time longer, the grain sizes of austenistic steel bigger after solutiontreatments on1100℃,the process of solution treatments from half an hour to threehours, the sizes of grains changed evidently; compared to the pure material, theaverage grain diameters increased from46μm to55μm only across half an hour.The significant growth of grains can be observated by the metallographic electronmicroscope on200X, applicating the grain rating software of metallographic electronmicroscope for assessing the average grain sizes are as followed:55μm(1100℃/0.5h)、77μm(1100℃/1.0h)、89μm(1100℃/1.5h)、110μm(1100℃/2.0h)、145μm(1100℃/2.5h)，173μm(1100℃/3.0h).（2）The sensitization tests are conducted on316LSS diffusion bongding jointsand pure materials after solid treatment under the same condition. The experimentalresults show that:under the same sensitization treatment time,as the holding time, theprecipitates on solided materials sample became clear with the time longer. Whenthe sensitization time was extended to100hours,observed of the grain boundaryscattered prepicitates; Compared to the pure materials which was already sensitizedafer100holding time with the same condition, but diffusion bonding joints sampleshaven’t observed any carbide precipitates.(3) Double loop electrochemical potentiokinetic reactivation (EPR) testing method is employed to assess intergranular corrosion for316L diffusion bonded jointsand solided materials in H2SO4+Na2S4O6solution, determined the influence of grainsize on sensitivity of316L diffusion bonded joints and solided materials intergranularcorrosion. The experimental results show that: diffusion bonding joints specimenswith larger grain size, the activation rate is significantly less than the smaller grainsize of the solution base metal remobilization rate value, indicating that the diffusionbonding joints resistance to intergranular corrosion than solid solided materials.