| With a ferritic(?)and austenite(?)two-phase structure,duplex stainless steel not only has high toughness,low brittle transition temperature,intergranular corrosion resistance and good welding performance of austenitic stainless steel,but retains the advantages of ferritic steel with high thermal conductivity and small expansion coefficient.With the worldwide shortage of nickel resources and the impact of rising nickel prices and other factors,many stainless steel enterprises turn to reduce or replace the nickel to reduce production costs which promote the development of a new nickel based stainless steel.However,due to the different structure of ferrite phase and austenite phase in duplex stainless steel,the deformation mechanism of the two phases is also different at high temperature.This paper set Mn-N economic type duplex stainless steel as the research object,using the Thermo-Calc diagram calculation software to get Mn and N elements' influences on the phase content,alloying elements,pitting equivalent and stacking fault energy;and selected one by hot compression simulation experiment on the hot deformation behavior;combining the rheological curve with the mixing rule the mechanical behavior of austenite and ferrite phase thermal deformation.The main contents are as follows:(1)While the effect of Mn element on the phase diagram of duplex stainless steel is small,N element will change the solidification mode of material,the solidification mode is divided into three types: L?L+???,L?L+???+ ?,L?L+??L+?+? ??+?,and N element has a significant influence on the precipitation phase precipitation temperature and phase temperature range.The content of N element has higher sensitivity to the ratio of two-phase content.With the increase of temperature,the content of austenite in the duplex stainless steel rises first and then decreases,and the ferrite content decreases first and then increases.With the increase of the content of N element,the PREN value of both phases will be improved.Because the Mn element has an inhibiting effect on pitting corrosion resistance of duplex stainless steel,the PREN value of both phases will decrease in different degrees.Comparedwith the Mn element,the change of the content of N element is sensitive to stacking fault energy,not only increases the temperature range of TRIP behavior to higher temperature,but also increases the temperature range of the TWIP effect.(2)The stress-strain curves under different conditions are obtained by studying the hot compression simulation.When the strain rate is low,the rheological curve is a typical dynamic recrystallization.In the initial stage of deformation,as the strain increases,the flow stress rapidly reached the peak,then the flow stress decreased slowly and gradually tends to a constant value.Through the calculation,the peak stress of the material constants of constitutive equations(?,n,Q,A)were 0.01619MPa-1,3.36,463.7 kJ/mol,7.23×1016,a peak stress constitutive model and deformation with strain compensated constitutive model based on the whole process.The best hot working range of the duplex stainless steel has two areas: a)the thermal deformation temperature range is 950~1 100?,The strain rate range is 10~30 s-1;b)the thermal deformation temperature is 1 200?.In addition,the critical deformation of the material can be increased by increasing the deformation temperature.(3)According to the stress and strain distribution law,the deformation of the material is divided into three stages: ferrite deformation,ferrite to austenite transformation strain,ferrite and austenite strain rate deformation zone.Based on the mixing rule,the rheological curves of the double phase stainless steel were predicted successfully.In addition,the mechanical behavior of the two phases under different deformation conditions was determined by JmatPro software. |
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