Steel castings refer to parts made of cast steel, which have similar properties to cast iron, but better strength than cast iron. Steel castings are prone to air hole defects, inaccurate angle positioning and other shortcomings in the casting process, and the casing fracture may occur in long-term use.
1.Advantages
One of the advantages of steel castings is the flexibility of design. Designers have the greatest freedom to choose the shape and size of castings, especially for parts with complex shape and hollow section. Steel castings can be manufactured by the unique process of core assembly. Its forming and shape change are very easy. The transformation from drawing to finished product is very fast, which is conducive to rapid quotation response and shortening the delivery time. The perfect design of shape and quality, the minimum stress concentration factor and the strongest overall structure all reflect the flexibility and process advantages of steel casting design:
1) Steel castings have strong adaptability and variability in metallurgical manufacturing. Different chemical composition and microstructure control can be selected to meet the requirements of various projects; Mechanical properties and service properties can be selected in a large range through different heat treatment processes, and have good welding and processing properties.
2) The isotropy of steel casting materials and the strong overall structure of steel castings improve the engineering reliability. Coupled with the advantages of reduced weight design and short delivery time, it has competitive advantages in price and economy.
3) The weight of steel castings can vary in a wide range. Those with small weight can be investment precision castings with only tens of grams, while the weight of large steel castings can reach several tons, tens of tons or even hundreds of tons.
2.Disadvantages
(1) Uneven tissue. After the liquid metal is injected into the mold, the first layer of liquid metal in contact with the mold wall will soon solidify into finer grains because the temperature drops the fastest. With the increase of the distance from the mold wall, the influence of the mold wall decreases gradually, and the crystals grow into columnar crystals parallel to each other along the direction perpendicular to the mold wall. In the center of the casting, the heat dissipation has no significant directionality, and can grow freely in all directions until they contact each other, so the equiaxed crystal region is formed. It can be seen that the structure in the casting is uneven. Generally speaking, the grain is relatively coarse.
(2) The tissue is not dense. The crystallization of liquid metal is carried out in the way of branch growth, and the liquid metal between branches finally solidifies, but it is difficult to fill all the branches with metal liquid, resulting in the general non compactness of castings. In addition, the liquid metal injected into the mold can also form porosity or even shrinkage cavity if its volume shrinks and is not sufficiently supplemented during cooling and solidification. Graphite in iron castings often appears in flake, spherical or other shapes, which can also be regarded as a kind of non dense structure.
(3) Rough surface. Generally speaking, the surface is rough, which can not be compared with the machined surface, and the shape is also complex.