Study Of Transformation Plasticity And Numerical Simulation Of Heat Treatment Of A508-3 Steel Used For Large Nuclear Power Forgings

With the exhaustion of the traditional resources, the development and utilization of nuclear energy becomes more important. The study on A508-3 steel used in nuclear pressure vessels has important research significance for nuclear safety.Material's mechanical properties are very critical for using. In this paper, true stress strain curves of bainite and austenite were obtained through the experimental measurement. Elastic modulus, yield strength and plastic modulus were calculated from the curves.Phase transformation plasticity parameter K of A508-3 is an important parameter for numerical simulation of heat treatment process. With the aid of Gleeble 3500 thermal simulator, dilatometric curves of bainite and austenite were gained. The phase transformation plasticity parameter K based on Greenwood-Johnson model was computed from the curves tested. The expressions between the parameter K and stress were K=4.17×105+2.53×10-6σandK=2.26×10-4.Stresses have no obvious effects on the austenitic transformation temperature at low heating rate, but at a higher heating rate, the austenitic transformation temperature Acl decreases and Ac3 increases dramatically with the increasing stress. During the bainitic transformation process, stress accelerated the process in the first, then impeded the phase transformation process.Numerical simulation of heat treatment process has great significance for predicting the heat treatment structure and deformation. Simulation was carried out by using an asymmetrical cylinder specimen. The results were shown as follows:(1) during air cooling, the mainly structure of specimen was bainite; under oil and water cooling condition, the cooling rate was rapid. During oil cooling, the structure of outer surface was martensite and the center was a mixture structure consisting of martensite and bainite. When using water quenching, the thickness of martensite surface became much thicker and martensite had a majority in the center of specimen; (2) there was an obvious difference between the deformation of specimen with phase transformation plasticity and the deformation without considering phase transformation plasticity under air cooling condition. Consideration of phase transformation plasticity could improve the simulation precision.