Mechanism Of Microstructure And Properties Evolution With Hot Deformation In The Combined Ring Rolling For Ball Valve Parts

Ball valve as a valve to shut is widely used in the fields of water conservancy and hydropower, petrochemical and municipal construction, because of its reliable seal, compact structure, high pressure grade and easy maintenance. The ball valve core is the main components of ball valve. To optimize their production process is the key of the ball valve production. There are three traditional machining methods of ball valve core: traditional casting, hot forging + machining, molding + welding +machining. Then combined forging rolling process method was proposed, but the process to sphere is very miscellaneous and just ring rolling is not enough to complete the forming of spherical.In this paper, through the thermal simulation experiments: heating and holding experiment, sigle-pass hot compression experiment, double-pass hot compressiong experiment and sigle-pass hot compression and holding experiment, the constitutive equations of flow stress, the austenite grain size growth model and equations for predicting the volume fraction of recrystallization and grain size after recrystallizaion are established. And through secondary development, a reliable material subroutine is established on the SIMUFACT software for finite element(FE) simulation.By utilizing SIMUFACT software and material subroutine, FE models of combined ring roll for forming the ball valve core are established. And the experiments of forming ball valve core are conducted. And the reliability of the models is verified by the comparison between simulated values and measured values of diameter and grain size. By analyzing the evolution law, distribution rule of equivalent strain, temperature, the evolution law of thermal deformation is received. By analyzing the evolution law, distribution rule of grain size, dynamic recrystallization volume fraction and morphology, the microstructure evolution law is received. By analyzing the evolution law of hardness, the properties evolution law is received.Based on the analyses of thermal deformation, microstructure and properties, the coupling mechanism among deformation-temperature-grain size of combined ring rolling is revealed, and a mathematical equation for predicting the maximum and minimum of the average grain size of ball valve core under different forming conditions is established, the association of deformation-microstructure-property is concluded. Some property optimization measures of combined ring rolling processing are put forward, and the feasibility and advantage of combined rolling ring work is fully affirmed.Basing on all the conclusions in this study, the microstructure evolution performance of Q345 E steel under high temperature is supplemented; the prediction of average grain size distribution, microstructure distribution and high performance basing on deformation is realized at some degree, which has guiding significance to manufacture ball valve core by combined ring rolling.