Numerical Simulation And Experiment On Heat Treatment Process Of Large Diameter And Thick Wall Gas Cylinder

Large diameter and thick wall gas cylinder endure high pressure and work in fatigue conditions of unloading and loading for a long time. One of the reasons which gas cylinders explode is the high residual stress level after heat treatment. On account of its characteristics of big size and high-mass, the large diameter and thick wall gas cylinder’s heat treatment is often very complicated. Quenching and tempering is an important part in heat treatment process and plays a key role in the final quality of work. The numerical simulation technology can simulate the quenching and tempering process accurately, and forecast heat treatment quality, provides a way of effective study method for the cylinder quenching process formulation and implementation.First of all, Through the method of consulting documents, this paper obtained the high temperature mechanical properties of 30 Cr Mo steel and the normal temperature density and specific heat of different microstructures in 30 Cr Mo steel at different temperatures by drainage method and the differential scanning calorimetry and the TTT, CCT curves. The accurate dates obtained in the experiments provide reliable reference parameters and input parameters.Secondly, the mathematical model of cylinder quenching process was established based on the consideration of the relationship of temperature-microstructure-stress and the nonlinear of thermal physical properties and the latent heat of phase change and the transformation plasticity in the heat treatment process. The geometry model and finite element model were built by using software of CAD and CAE. Afterwards, two kinds of traditional quenching and tempering process were simulated through making use of element software DEFORM 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 Sufficient strength but lack of toughnessin in the cylinders in useproposed the new Heat Treatment Process, namely “Q-P” and “Q-P-T”.The new Heat Treatment Process “Q-P” and “Q-P-T”can regulate the temperature gradient and the pressure in the bottle, reduce the quenching stress and ensure the quantity of martensitic transformation. After the heat treatment,Cylinder obtaineda lower degree ofresidual stress.In the final, by tensile test SEM hardness testand XRD proved that the mathematical model is exact veracious, and analysised the advantage of every crafts.