Research On Hot Deformation Characteristics And Recrystallization Of Coiled Tubing Steel

The Coiled Tubing Steel has been deformed by Gleeble-3500thermal simulation machine in the range of temperature850-1000℃at0.001～5s-1strain rate. The plastic deformation behaviors have been investigated and a constitutive model is developed. How strain, deformation temperature and strain rate influence DRX and microstructure, which are analyzed by OM and TEM. Meanwhile, DRX dynamic equation and recrystallized grain size model are set up. Optimal deformation parameters and instability regions are determined according to the processing map theory and microstructure, and TMCP process is determined. The following conclusions have been drawn from this investigation:(1) The effect of deformation conditions on the flow stress of CT80steel has been studied. At the same deformation temperature and different strain rates, when the strain rate is higher and the stress is stronger, and it isn’t easier to start dynamic recrystallization; At the same strain rate and different deformation temperature, when the deformation temperature is higher and the stress is lower, dynamic recrystallization is easier to occur.(2) The model of constitutive relation of CT80steel at the strain rate of0.001-5s-1and the temperature of850-1100℃has been established using Origin software, and it has higher fitting precision.(3) The dynamic recrystallization behavior of CT80steel has been studied using single-pass hot compression experiments. The Parameter Z and hot deformation activation energy Q of CT80steel in condition of hot compression have been obtained. Also, the flow stress equation, critical strain expression and kinetic equations for dynamic recrystallization of CT80steel have been established.(4) According to the theory of processing map, the processing map of CT80steel has been established on dynamic material model. In the processing map, the optimal deformation parameters (strain, strain rate and deformation temperature) for multi-stand tandem hot rolling are given and the instable regions not suitable for hot rolling could also be seen.(5) According to the analysis to properties of CT80steel rolled in the laboratory,optimal processing parameters are acquired in the following that Rough Rolling temperature is1100℃, finish rolling temperature is950℃, starting cooling temperature is850℃-860℃, cooling speed is15-20℃/s, the final cooling temperature is about580℃-600℃. Mechanical properties of the sample acquired meet all the requirements of CT80steel that yield strength is not less than572MPa, tensile strength is not less than621MPa, yield ratio is not more than85%, elongation is not less than28%, hardness is not more than22HRC.