Study On Recrystallization Behavior Under Hot Deformation And Grain Size Prediction Of 55 Steel

To evaluate metal hot forgings quality,there are two major indicators: forming dimensions and microstructure properties.Forming dimensions meet assembly requirements to ensure that products can be used normally.And whether microstructure property is good or not,it directly affects service life of products,in terms of a certain aspect,microstructure property has more important significance.Grain size is an important parameter to evaluate the microstructure of hot forgings,according to classic Hall-Petch relationship,small grain size microstructure can significantly increase the comprehensive mechanical property of metallic material.Therefore,through reasonable method to predict grain size evolution of material hot forming,this can provide theoretical basic for quality control of the actual hot forgings.In this paper,using microstructural simulation method combined with finite element numerical analysis and physics experiment,the grain size evolution regulation of 55 steel hot compression and a special-shaped forging hot forming studied systematically,at the same time,in order to realize effective grain size prediction results at Deform-3D software reprocessing window.It should be firstly on model-3800 thermal/mechanical simulator by single,double pass experiment combined with metallographic experiment data to establish thermal forming microstructure evolution including dynamic and static recrystallization Yada phenomenological model of 55 steel.The concrete research work are as follows:(1)Dynamic recrystallization behavior regulation of 55 steel thermal deformation was studied by using single pass experiment,mainly including: dynamic recrystallization deformation activation energy and thermoplastic deformation constitutive relation of 55 steel were established;using strain hardening rate (?)model Poliak and Jonas purposed,dynamic recrystallization critical stress and strain ratio in the critical condition was obtained;the peak strain model related to initial austenite grain size and the kinetics equation of dynamic recrystallization was established.(2)Static recrystallization behavior of 55 steel thermal deformation was studied by using double pass experiment,it was concluded that the effect of different parameters on static recrystallization behavior can be summarized as: when compression temperature increases,or strain rate increases,or the first pass deformation degree increases,or initial austenite grain size smaller,the volume percent of static recrystallization is higher according to formula calculated.And through experimental data regression,we established the kinetic equation of static recrystallization.(3)Through bringing the established relevant parameters into Deform-3D software to establish grain size prediction finite element simulation system of this material hot compression deformation,from intuitive level to predict and analysis microstructural evolution of hot compression experiment including dynamic,static recrystallization and growth of grain size.(4)Combined with thermoplastic deformation macro and micro multi-scale finite element coupling system,the macro-micro simulation of hot forming was carried out for an example of a special-shaped forging production.Finally,By comparison with the actual cooling microstructure of A,B position,we found that the grain size of A position is smaller,which is consistent with result of grain size prediction,and phenomenological model used for grain size prediction is verified.Research results show that: Based on the established Yada phenomenological model,the grain size prediction result of 55 steel hot forming is effective,which provides an important tool for achieving macro forming dimension and microstructure properties two-way control of hot forgings simultaneously.