Effect Of Nitrogen Content On Mechanical Behaviors During Hot Deformation For Nuclear Grade316LN Steels

Due to its less carbon and more nitrogen,316LN steel has better mechanical properties and intergranular stress corrosion resistance than316steel, so it is widely used in the energy field, especially in fast neutron reactors. N content has many effects on the microstructure and properties of316LN steel. In the actual production,316LN steel is often thermal processed (rolling, forging, welding and heat treatment, etc.). Different N contents inevitably lead to different thermal processing characteristics of316LN steel. Although there have been many reports about the effects of N content on the deformation characteristics of CrMn austenitic stainless steel with more than0.5wt%N content, the rules of the effects of N content on the deformation characteristics of CrNi austenitic stainless steel with far less than0.5wt%N content is not very clear.In this dissertation, mechanical behaviors of316LN steel with two different N nitrogen content (0.08wt%and0.17wt%) under the deformation conditions of800～1200℃and0.001～10s-1were studied, in order to reveal the rules of the effects of N content on the deformation characteristics of CrNi austenitic stainless steel and provide experimental basis for the composition optimization of316LN steel. The main results obtained are as follows:When deformed at800～1200℃and0.001～10s-1, for316LN steel with0.08wt%and0.17wt%N, the hot deformation equations are ε=1.63×1019[sinh(0.00556σ)]6.76exp(-487000/RT) and ε=6.41×1021[sinh(0.00521σ)]7.06exp(-549000/RT) respectively; the relationships between dynamic recrystallization critical strain εc and the parameter Z are εc=0.1361n(Z/A)+0.266and εc=0.1211n(Z/A)+0.229, respectively. The flow stress of316LN steel decreases with deformation temperature increasing and strain rate reducing.The flow stress of316LN steel increases with nitrogen content increasing. When deformed at low temperature (800～1000℃), the effect of nitrogen content on the flow stress is more obvious than that deformed at high temperature (1100~1200℃).When nitrogen content increases from0.08wt%to0.17wt%, the hot deformationactivation energy of316LN steel increases from487kJ/mole to549kJ/mol, and workhardening exponent increases from6.76to7.06, which means that the increase in nitrogencontent increases the hot deformation difficulty and promotes the occurrence of hardening.Under the same deformation conditions, the critical strain for dynamicrecrystallization starting reduces with N content increasing.The increase in the nitrogen content leads to an increase in the power dissipationduring the hot deformation and range of flow instability region.