Study On Flow Behaviors, Microstructure Evolution And Properties Of 15CrMnMoVA Steel During Warm Deformtion

The aim of the present dissertation is to fabricate sub-micron ultrafine grained steel with a low carbon and low-alloyed steel of lath martensite structure by means of warm compressive deformation on a Gleeble 3500 thermo-mechanical simulation machine at temperature range of 500-700 ?C and strain rate range of 1-1-3 s-1.Microstructure morphology and microstructure evolution before and after warm deformation were observed by optical microscope (OM), transmission electron microscope (TEM) and X-ray diffractometer (XRD); At last, mechanical properties of samples deformed at different conditions were measured by microhardness tester and Gleeble 3500 thermo-mechanical simulation machine with a tensile test, and the corrosion property of deformed samples was also tested by a CHI660A type electrochemical analyzer.The results show that the peak flow stress obviously decreases with the increasing of deformation temperature and the decreasing of strain rate. The constitutive equation and Z parameter expression during warm deformation were established. Z parameter has significant effect on decreasing the peak flow stress and critical strain of dynamic recrystallization.Microstructure after deformation is composed of only ultralfined ferrite grain with mean size of 548 nm at deformed temperature of 650 ?C. It should be noted that the mean grain size does not increase apparently with the increasing of deformation temperature, and only 573 nm at deformed temperature of 700 ?C. Micro-hardness of sample deformed at 650 ?C is 431 HV, tensile strength is 1390 MPa, and total elongation is 12.5%. Microhardness and tensile strength decrease, with the deformation temperature increasing, uniform and total elongation increase. Micro-hardness of sample deformed at 700 ?C is 374 HV, tensile strength is 1174 MPa, and total elongation is 13.5%. Samples after deformation present a better corrosion property in 3.5 % (wt. %) NaCl solution. Corrosion potentials of samples defromed at 700?C and without deformed are -0.72 V and -0.98 V respectively.