Research On High-temperature Creep Behavior Of Continuous Casting Slabs During Solidification

Based on the project of National Natural Science Foundation of China,“the creep behavior analysis of steel in solid-liquid phases during solidification(No.51671124)”,this high-temperature creep behavior of continuous casting slabs during solidification were investigated in this paper to explore the high-temperature creep behavior of steel in the process of continuous casting and its stress-strain law,and then to interpret the quantized characteristics of high-temperature creep behavior.On the basis of investigation and analysis,the viscous-elastic-plastic characteristics of high-temperature creep behavior of continuous casting slab were defined in this paper;a database of high-temperature physical parameters of 2101 duplex stainless steel,involving the whole temperature range of continuous casting,were established;a thermo-mechanical coupling finite-element model was developed for describing the high-temperature creep behavior of continuous casting slab;the creep limit of 2101 duplex stainless steel caused by a vertical continuous caster of BAOSTEEL were calculated;the in-situ stress-strain value of micro-alloyed steel during solidification were measured;a quantized criterion for formation of cracks caused by high-temperature creep was proposed.The main conclusions are as follows:(1)During solidification,there are three phases for continuous casting slab: liquid phase,solid-liquid phase,and solid phase.The deformation behaviors of steel showed elastic,plastic,and viscous.Viscous-elastic deformation occurs before the yield point,while viscous-plastic deformation occurs once passing the yield point,which belongs to the high-temperature creep behavior of steel in liquid-solid phase.(2)Based on the viscous-elastic-plastic deformation of materials in different ranges of temperature,a thermo-mechanical coupling finite-element model for describing the high-temperature creep behaviors of continuous casting slabs was established by introducing the work hardening correction factor.The numerical analysis of the high-temperature creep limit of 2101 duplex stainless steel was carried out on the caster above-mentioned.The results show that the maximum values of thermal stress in the corner,narrow surface center,and billet center were 40.4,20.8,and 4.9 MPa,respectively.With raising the superheat of liquid steel and casting speed,the temperature of continuous casting slab increased.When the superheat increased by 10 ?,the temperature of wide surface center of slab at the exit of caster raised by 3 ?,and the thermal stress increased accordingly.With the casting speed increased by 0.2 m/min,the temperature of wide surface center of slab at the exit of caster raised by 78 ?,but the thermal stress decreased accordingly.At the distance of 7.4 m from the meniscus,the slab has completely solidified.(3)The in-situ stress-strain measurements of micro-alloyed steel during solidification were carried out by a stress-strain simultaneous measurement instrument.The results show that the strain of J55 steel sample was 1.16% and its maximum stress was 33.3 MPa during cooling from 1526 ? to 226 ?.J55 steel shows good hightemperature plasticity and high-temperature strength.At the cooling rate of 0.5 ?/s,the transformation products of J55 are ferrite and pearlite.The thermal stress value lowered its high-temperature strength,thereby not resulting in occurrence of cracks.However,when a material suffers from a greater external force in the high-temperature embrittlement zone(1226-1515 ?),cracks will occur.