Optimization Of ZG35CrMo Valve Body On Microstructure And Casting Process

In this thesis,ZG35CrMo valve body was mainly studied. The pipeline valve body should pass hydraulic pressure test for 70MPa. However leakage inside of the casting was found in the test. There were defects in the casting, such as coarse grain, shrinkage cavity, shrinkage porosity and so on. Furthermore, the castings did not meet the request of the mechanical property, which is that the tensile strength reached 700MPa, specific elongation reached 12% and impact toughness reached 60J/cm2. The defective index of the product had reached 70% in production, which made a big waste of materials and energy sources.First, the component of 35CrMo steel was adjusted. The addition of Titanium could inhibit grain growth, improve the hardenability characteristic and strengthen the steel by deposition. By micro-alloying process, little titanium was added into 35CrMo steel to refine crystal grain and improve its mechanical property.Second, Through referening to relevant information, quenching temperature and tempering temperature was determined at 920℃and 860℃. Respectively, drawing temper was carried out at 550℃, 580℃and 610℃. The tensile strength of material reached 720MPa and the impact toughness reached 65J/cm2, which meet the request of the mechanical property, after micro-alloying and heat treatment optimization.Final, the casting technique was improved. Casting defects were forecasted by using InteCast software to simulate the temperature field of casting steel valve body. And basing on the simulation result, the casting technique was improved. Shrinkage cavity and shrinkage porosity were eliminated by adding iron chill on the valve body which make progressive solidification, together with atmospheric feeder which feed the casting.