Research On Properties Of 316LN Stainless Steel Prepared By Powder Metallurgy

Powder metallurgy stainless steels span a variety of industries,including aerospace,automotive,chemical processing,medical,and recreational,for the well-known economic value in terms of net shape processing and more efficient material utilization.However,it has relatively poor corrosion and mechanical properties due to the residual porosity compared to the conventional cast and wrought stainless steels.Researchers have improved its properties by using novel sintering techniques or by addition of second phases.In this paper,we researched the effect of sintering temperature and Sn content on the mechanical properties,pitting corrosion resistance and the microstructure of sintered 316LN SS.The sintered density was measured by the Archimedes method.The mechanical properties were measured by hardness and tensile tests.The pitting behavior was investigated by electrochemical tests and FeC13 immersion test.Microstructure was analyzed by optical microscope,scanning electron microscope(SEM)with energy dispersive spectrometer(EDS)analysis.The properties and microstructure of 316LN SS were investigated as a function of sintering temperature.The results indicated that,sintered density increased linearly with an increase of sintering temperature.The mechanical properties of 316LN SS was significantly improved with supersolidus(1375 ?)state sintering,which could be attributed to the decrease of the size and number of residual pores and the more regular shape.The fracture forms of all 316LN SS were ductile fracture at the sintering temperature from 1300? to 1400?.However,the pore size increased and grains coarsen at 1400?C,so the dimple size increased with irregular shape,and strength and elongation of 316LN SS decreased.Electrochemcial tests and FeCl3 immersion tests showed that the pitting corrosion resistance of 316LN SS improved with an increase in sintering temperature,due to the decrease of real active areas exposed in test solution.The pitting potential Epit of 316LN SS sintered at 1375 ? was 326.93mv and its charge transfer resistance R2 was always high after 80 days.The lager pit size after constant potential polarization and the higher corrosion rate in FeCl3 solution showed that the larger pores and grain coarsening of 316LN SS sintered at 1400? promote the sensitivity for corrosion tendency.The properties and microstruture of 316LN SS were also investigated as a function of Sn content.The results indicated that,the number of residual pores was eliminated continuously with increasing Sn content.However,pore size increased obviously as Sn content exceed lwt.%.The 316LN SS containing lwt.%Sn had the small pores with spherical shape.The mechanical properties of 316LN SS deteriorated and dimple size increased with irregular shape when Sn content from 3wt.%to 4wt.%was added.Because the significant coarsening of pores and grains and the inclusion particles at the grain boundaries.Electrochemcial tests and FeCl3 immersion tests showed pitting corrosion resistance was improved significantly for sintered 316LN SS containing lwt.%Sn compared to straight sintered samples.However,the large amount of Sn decreased Epit and reduced the corrosion resistance,although the sintered density increased.The corrosion behaviors of the sintered 316LN containing Sn were not just correlated with the residual porosity.