Numerical Simulation On Quenching Process Of Large Diameter And Thick Wall Gas Cylinder

Large diameter and thick wall gas cylinder endure high pressure and work in fatigueconditions of unloading and loading for a long time. One of the reasons which gascylinders explode is the high residual stress level after heat treatment. On account of itscharacteristics of big size and high-mass, the large diameter and thick wall gas cylinder’sheat treatment is often very complicated. Quenching is an important part in heat treatmentprocess and plays a key role in the final quality of work. The numerical simulationtechnology can simulate the quenching process accurately, and forecast quenching quality,provides a way of effective study method for the cylinder quenching process formulationand implementation.First of all, through the experiment, this paper measured the high temperaturemechanical properties of30CrMo steel and the normal temperature density and specificheat of different microstructures in30CrMo steel at different temperatures by drainagemethod and the differential scanning calorimetry and the TTT, CCT curves. The accuratedates obtained in the experiments provide reliable reference parameters and inputparameters.Secondly, the mathematical model of cylinder quenching process was establishedbased on the consideration of the relationship of temperature-microstructure-stress and thenonlinear of thermal physical properties and the latent heat of phase change and thetransformation plasticity in the heat treatment process. The geometry model and finiteelement model were built by using software of CAD and CAE. Afterwards, two kinds ofquenching process in Groove were simulated through making use of element softwareDEFORM and combing actual production, and analyzed the temperature field,microstructure field and stress field of the special nodes in cylinder.Then, for the issues of big temperature gradient in cylinder body and high residualstress and low amount of martensitic appearing in the simulated results proposed the rackquenching way, namely “the internal are intermittent radial sprayed and the outside of thecylinders are sprayed water continuously”. According to the changes of microstructure and temperature in the quenching process arranging the intermittent spray time of internalsurface can regulate the temperature gradient and the pressure in the bottle, reduce thequenching stress and ensure the quantity of martensitic transformation. Meanwhile radialspraying makes microstructure of internal surface transformation simultaneously andensure the hardness of the cylinder’s inside and outside to be more uniform.In the final, by the microstructure comparison of simulation and test proved that themathematical model is exact veracious.