| Nuclear grade316LN stainless steel is a kind of ultra-low carbon austeniticstainless steel,it has excellent welding, hot and cold processability and good corrosionresistance.The C content which be controlled in low level that will improve thecorrosion resistence of the materials,adding nitrogen element will not only ensure highstrength,but also increase the microstructure stability and the corrosion resistence of316LN austenitic stainless steel,the suitable nitrogen content is the key to ensure steelstructure and properties of steel.The article through studying the influence of nitrogen content on structure,mechanical property and corrosion resistance of316LN steel under solution treatment atdifferent temperature,determining the optimal nitrogen content and solution treatmenttemperature,by exploring the thermoplastic deformation behavior of316LN steel afteralloy optimized,to provide the reference data and theoretical support of the developmentresearch and industrial production of nuclear power pipe steel using ultra-lowtemperature environment.After nitrogen alloy optimize of316LN steel found that the nitrogen element of316LN steel has a significant role in refine grain size.The316LN steel strength andhardness increased linearly with the increase of nitrogen content,and the strength of316LN at-196℃greater than the room temperature.The elongation under roomtemperature decreased,and the elongation changed increase before decrease trend under-196℃temperature.The316LN steel impact energy present increase before decreasetrend at room temperature with the increase of nitrogen content,when nitrogen contentwas0.14%,the316LN steel had maximum impact energy under solution treatment atdifferent temperatures,and the-196℃cryogenic impact energy presented gradually decreasing trendency.The results of FeCl3chemical immersion method,anodicpolarization method and EPR method showed that the pitting corrosion resistance of316LN steel increased,the intergranular corrosion resistance presented increase beforedecrease tendencyencyency with the increasing of nitrogen content.When nitrogencontent was0.14%,the intergranular corrosion resistance was the best performance.The316LN steel intergranular corrosion resistance improved with the increase of solutiontreatment temperature.The microstructure observation showed that the nitrogen elementstrongly inhibited ferritic phase appears,sigma, χ phase formed and grown of316LNsteel,and intensively steadied austenitic microstructure,it significantly reduced theaustenitic structure by the plastic deformation under-196℃temperature of martensitephase transformation.Based on the comprehensive evaluation results of mechanical property andcorrosion resistance showed that316LN steel was0.14%nitrogen content undersolution treatment at1100℃,the grain size was up to level6,and the comprehensiveproperties was excellent.By Gleeble thermal simulation method to study the hot deformation behavior of316LN steel after composition optimization.it determined that the best thermoplastictemperature was1175~1250℃by hot tensile test,the reduction of area was more than69%,the deformation resistance was less than60MPa,and there was different levels ofdynamic recrystallization in hot deformation process.Discovered by hot compressiontest that lower the deformation temperature and raise the deformation rate were notbeneficial to occur of dynamic recrystallization.The deformation temperature and thedeformation rate had a great impact on the peak stress,the steady state rheologicalstress,and its corresponding strain of316LN steel.The deformation activation energywas computed as496.079KJ/mol,the Z parameter equation and the flow stress equationbe determined.By the hot processing map of316LN steel showed that the hot processinginstability area shifted with the increasing of strain measure, and the optimum hotprocessing area gradually moved from high temperature area to low.The energydissipation efficiency generally showed a increase trendency with the increasing oftemperature and strain rate lower,it facilitated the hot plastic deformation processes. |
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