| Duplex Stainless Steel(DSS)is the fastest-growing and most cost-effective stainless steel in the modern times.High alloy content 2507 and resource-saving 2101 are the two most representative types of duplex stainless steel.Although the alloy content and various performance indexes of the two are very different,due to the common structural characteristics of austenite and ferrite coexisting,they will have inconsistent two-phase deformation resistance and poor thermoplasticity during the hot deformation process.Quality problems such as surface cracking and uneven tissue deformation have a serious impact on the product quality of the duplex stainless-steel sheet and the deep processing of the subsequent materials.Therefore,to carry out basic theoretical research and experimental analysis on the problems of thermoplasticity and microstructure evolution under the temperature-stress-strain multi-field coupling conditions of the two typical steel grades of duplex stainless steel,and to establish relevant prediction models and processing drawings during high temperature deformation.It provides theoretical basis for alloy composition design and hot working process optimization,and has important academic research significance and practical value.The research samples in this paper were taken from industrially produced 2507 and 2101 duplex stainless steel continuous casting billets,and the heat deformation temperature was obtained from Gleeble-3 800 thermal simulation testing machine at 950～1200℃(2507 test steel)and 1000～1150℃(2101 Test steel)/strain rate of 0.01～10 s-1 under the conditions of hot compression of the two test steels under real stress-true strain curve,study their work hardening effect and dynamic softening behavior,and establish the corresponding constitutive equation;Observation and analysis of the microstructure evolution in different deformation processes by optical electron microscope,grasping the influence of different deformation parameters on the dynamic softening of the two test steels,and comparing the fracture morphology at different deformation temperatures by scanning electron microscope analysis to clarify the two test steels High-temperature tensile fracture mechanism;based on the dynamic material model,two hot-work diagrams of two-phase stainless steel were constructed.Through analysis of the characteristics of the two-phase structure in the safe area and the unstable area,it is recommended to determine the best heat of the two steel types Processing technology range.The main results obtained are as follows:1.When the strain rate is constant,the flow stress is inversely proportional to the deformation temperature;when the deformation temperature is constant,the flow stress is proportional to the strain rate;the two duplex stainless steels are at a high strain rate(10 s-1),Rheological curves all appear as "yield-like platform",that is,secondary hardening occurs.2.For 2507 duplex stainless steel,with the increase of strain rate at 10500C,the dynamic recrystallization of austenite decreases,and the grain size gradually increases;under the condition of low strain rate(0.01 s-1),both are dynamic The softening mechanism of crystallization is more uniform around 1100℃,too high temperature is not conducive to the occurrence of dynamic recrystallization.For 2101 stainless steel,with the increase of strain rate at 1000℃,the dynamic recovery of ferrite and austenite decreases,and the grain size gradually decreases;under low strain rate conditions(0.01 s-1),only the deformation temperature When it is 1050℃,the softening mechanism is dynamic recrystallization type,and the rest are all dynamic recovery type;combined with the metallographic structure,it can be seen that the austenite ratio of 2101 is significantly reduced under the condition of high temperature and low strain rate(1150℃,0.01 s-1),The dynamic recovery of ferrite is more adequate.3.The high-temperature tensile strength of both duplex stainless steels decreases with increasing deformation temperature,and the thermoplasticity increases.The hightemperature tensile strength of 2507 duplex stainless steel is significantly higher than that of 2101 duplex stainless steel;the scanning results of tensile fractures show that 2507 test steel has better thermoplasticity in the range of 1050～1100℃;The test steel has a better thermoplasticity in the range of 1000～1100℃.When the temperature is higher than 1150℃,the fracture of both steels is partially melted.4.Arrhenius constitutive model is used to establish the peak stress constitutive equations of two duplex stainless steels:2507:ε=3.69 × 1015[sinh(0.0101σ)]4.18 exp(-41457/RT)2101:ε=4.94 × 1017[sinh(0.0121Oa)]4.95 exp(-60195/RT)5.Based on the dynamic material model,the hot working diagrams of two duplex stainless steels were constructed.By analyzing the microstructure of different regions under different deformation conditions,the optimal thermal processing area with power dissipation value η greater than 30%and uniform deformation of the structure,was determined as follows:The optimized process range of duplex stainless steel 2507 is 1060～1120℃,and the strain rate is 0.01-0.1 s-1;The optimized process range of duplex stainless steel 2101 is 1000～1050℃,and the strain rate is 0.1 s-1. |
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