Elastoplastic deformation behavior of grains during tension of Q355B slab at high temperature
Taking the continuously cast Q355B slab in a domestic steel plant as the research object,the tensile tests were carried out at the temperatures of 1 300,1 340 and 1 380℃and the strain rate of 0.001 1/s on a Gleeble-3800 thermo-mechanical simulation tester.Based on the obtained grain morphology,representative volumetric elements of grains near the fracture were selected,and a finite element model(RVE-FEM)was established with the Ramberg-Osgood constitutive equation.Then,the deformation mechanism of the grain structure and the distribution patterns of the stress and strain during tension processes at high temperature were revealed.The results show that the closer to the fracture,the larger the average grain size is,and the smaller the stress it can bear.Because of the uneven distribution of grains and grain boundaries,the irregular distribution of stress appears in grains and at the grain boundary,and the high stress is mainly concentrated at the grain boundary.At the temperature of 1 380℃,the average stresses are 7.01 and 9.91 MPa in grains and at the grain boundary as the sample is at 70 mm below the slab surface.With the increase of the tensile temperature,the average size of grains enhances,the area of the grain boundaries reduces.It causes that the hindrance to deformation is weakened,and the yield and tensile strengths decline.At 60 mm below the slab surface,the yield strength and maximum tensile strength decrease from 9.87 to 4.36 MPa and from 12.51 to 4.49 MPa,respectively,as the temperature increases from 1 300 to 1 380℃.At the temperature of 1 380℃,the yield strength and maximum tensile strength decrease from 9.44 to 7.42 MPa and from 10.75 to 9.10 MPa,respectively,as the sample moves from 10 to 40 mm below the slab surface.The stress-strain curves calculated by RVE-FEM agree with the measured results at different temperatures and sampling locations.The grain size is a decisive factor for the tensile property,and it depends on the size of the initial solidification struc-ture and the tensile temperature.From the slab surface to the center,the secondary dendrite arm spacing increases.It causes that the grain size increases at the same tensile temperature.Particularly,from 10 to 40 mm below the sur-face,the length of the grain's long axis is the key factor.For the same sampling position,the lengths of the grain's long and short axes increase significantly with the increase of tensile temperature.
Q355B slabtensile test at high temperaturegrain morphologystress distributionfinite element simulation
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