The solidification mode of the pump valve casting mainly refers to the structure of the structure when the liquid solid is coexisting during the solidification period of the casting. Substantially this depends on the crystal morphology of the solid phase (equal crystal, columnar crystal, etc.) and the structural form of the grain population or grain aggregate (eg, eutectic grains of cast iron, ie, eutectic, etc.). The form of the solid phase structure is certain, and the coexisting liquid phase distribution is also determined, which in turn determines the solidification mode of the casting. At the same time, as the temperature decreases, the liquid phase continuously changes to a solid phase.
Annealing is one of the heat treatment methods for pump valve castings
Annealing is one of the heat treatment methods for pump valve castings. Annealing is divided into graphitization annealing and stress relief annealing.
1. Graphitization annealing: The graphitization annealing of the pump valve castings is to reduce the hardness, improve the processing performance, and improve the plasticity and toughness of the cast iron.
If there is no eutectic cementite in the casting or its quantity is small, low temperature graphitization annealing can be performed; when the number of eutectic cementite in the casting is large, high temperature graphitization annealing is required.
2. Stress relief annealing: In order to eliminate the residual stress of the casting, stabilize its geometry, reduce or eliminate the distortion generated after the cutting process, the casting needs to be subjected to stress relief annealing.
The determination of the stress relief annealing temperature must take into account the chemical composition of the cast iron. Ordinary pump valve castings When the temperature rises above 550 ° C, partial cementite graphitization and granulation may occur, resulting in lower strength and hardness. When an alloying element is contained, the temperature at which cementite begins to decompose can be increased to about 650 °C.www.dmgcastings.com