Simulation Of D406A Steel Welding Component In Gradient Heat Treatment Process And Refining Grain

The finite element method was applied to simulate the evolution of thetemperature and stress fields in gradient heat treatment processes of the cylinderwelding component of steel D406A. According to the test conditions， thetemperature gradient of plank welding component of steel D406A was designed andproved. The grains were refined by cyclic heat treatment and the technics，effectand mechanism of cyclic heat treatment were analyzed in this paper.Through the established finite element model of D406A cylinder weldingcomponents in gradient heat treatment， it showed that the temperature fieldpresented gradient distribution along the axial and the temperature of weld metalzone and heat affected zone were higher than the phase-change temperature. Thestress fields also showed gradient distribution. The stress of the weld was greaterthan the base. When the temperature reached room temperature，the weld metalzone was covered by compressing axial stress，and the value was46.7MPa. Thebase metal zone was distributed with tensile axial stress，and the maximum was16.9MPa. After cooling，the radial displacement distributed symmetrically alongthe weld and the maximum amount of radial deformation was in the weld metalzone which was0.76mm. The axial deformation was elongate and the amount was0.5mm.The study of the heating area showed that：the phase transformation areaincreased with the increase of heating area，and it can restrain deformation andreduce the residual stress effectively.In view of the actual test requirements，the temperature gradient was designedby considering cycle cooling water. The calculated results was compared with theresults tested by gradient heat treatment，and they were in good agreement.By cyclic heat treatment，the grains were refined obviously after3-5timescycle phase transformation at920℃and kept for10min. The grains of the weldmetal zone changed to equiaxial form columnar crystals. And the average grain sizeof the heat affected zone reached10-26μm. On the other hand，after3timesα γ gradient cyclic transformation，it was found that the grain size could be refined to8-17μm. Compared with the results of isothermal heat treatment，thegradient one could make the difference of grain size between zones smaller andreduce the time of cycles.