Differences between valves made from cast and forged materials

Every proper valve expert knows that valves are made from cast and forged materials. But do you know, what is the difference between them and why are they called like that? We will now try to answer those questions.

Casting

Casting is a method of producing various object by pouring liquid (molted) metal (steel), or another liquid or suspension capable of solidifying, into the mold of the required shape. The casting method is chosen primarily for products of complicated shapes, which cannot be produced by a different method or are made in complicated or expensive way (e.g., by machining or welding).

After pouring the steel into the mold, the liquid steel is in immediate contact with a cold wall, which cause decreasing the temperature of the steel and its crystallization. The casting temperature, for example of carbon steel, is around 1 450 °C.

Properties of casting steel

Cast steels have a chemical composition like forge steels but compared to forge steels they have worse mechanical properties which can be improved by their heat treatment. For cast steels the beneficial effect of forging (compaction of the material) is not possible. The advantage is the possibility of casting complicated shapes, which cannot be produced by forging and the material savings due to this.

Forging

Forging is a nondestructive technological process of material processing, in which the shape and mechanical properties of this material change. While forging metals, it is necessary to exceed the elasticity limit but not to exceed the strength limit. Therefore, ductile materials are suitable for forging, i.e., materials that have those two limits sufficiently far apart. Forging methods includes rolling (sheet metal), forging, drawing, extrusion.

During the forging, the grains are stretched and subsequently softened, giving the steel a homogeneous structure and better mechanical properties. From the above mentioned is clear that the forge materials have better mechanical properties and inner structure than cast materials. Forging is divided into cold and hot forging, which is carried out at temperature up to 1 200 °C.