cast steel is an iron-based alloy used to produce castings that does not undergo eutectic transformation during solidification, and is a kind of casting alloy. Cast steel is an alloy with iron and carbon as the main elements, and the carbon content is 0-2%. Cast steel is divided into three categories: cast carbon steel, cast low alloy steel and cast special steel. Due to the high amount of water glass added and the poor collapsibility, the old sand can not be recycled, and the process of carbon dioxide blowing by water glass in cast steel joints has been eliminated. Alkaline phenolic resin self-hardening sand has no phosphorus, no sulfur, good process performance and good application prospect. Ester hardening water glass self-hardening sand non-toxic, tasteless, old sand can be recycled, has been widely used in the Ministry of Railways, the Ministry of metallurgy, general machinery, the production of a few kilograms to hundreds of tons of cast steel.
Because the shrinkage of cast steel is much greater than that of cast iron, in order to prevent the shrinkage and porosity defects of castings, measures such as riser and cold iron and subsidies are mostly adopted in the casting process of cast steel to achieve sequential solidification. In addition, in order to prevent the production of shrinkage holes, porosity, porosity and cracks in the steel casting, the wall thickness should be uniform, avoid sharp and right Angle structure, add sawdust to the mold sand, add coke to the core, and use hollow core and oil sand core to improve the yield and permeability of the sand or core.
Due to the high melting point of cast steel, the corresponding pouring temperature is also high. The interaction between molten steel and casting material at high temperature can easily lead to sand sticking defects. Therefore, artificial quartz sand with high refractoriness should be used to make the mold, and the paint made of quartz powder or zirconium sand powder should be brushed on the surface of the mold. In order to reduce the gas source, improve the flow of molten steel and the strength of the cast, most steel castings are cast with dry or fast dry mold, and carbon dioxide hardened water glass sand mold can be used.
Due to the poor fluidity of liquid steel, in order to prevent cold insulation and insufficient pouring of cast steel, the wall thickness of cast steel can not be less than 8mm; The structure of the pouring system is simple, and the section size is larger than that of cast iron. In the casting process, dry casting or hot casting is used to appropriately increase the pouring temperature, and the cast steel node is generally 1520° ~ 1600 ° C, because the pouring temperature is high, the superheat of the molten steel is large, the liquid time is long, and the fluidity can be improved. But too high pouring temperature will cause coarse grain, hot cracking, porosity and sand and other defects. Therefore, generally small, thin-walled and complex castings, the pouring temperature is about the melting point temperature of steel +150℃; The pouring temperature of large, thick wall castings is about 100℃ higher than its melting point.
Advantages of steel castings
1. Greater design flexibility
This design is associated with maximum freedom of choice for the shape and size of the casting, especially for complex shapes and hollow parts, and steel castings can be manufactured from the unique process of the core casting. Easy to form and change shape and the ability to quickly produce a finished product according to the drawing can provide quick response and shorten delivery time.
2. Metallurgical manufacturing has the strongest flexibility and variability
You can choose different chemical compositions and organizational structures to meet the needs of different projects. Different heat treatment processes can select mechanical properties and can use this property in a wide range and improve weldability and serviceability.
3. Improve the overall structural strength
Due to the high reliability of the project, the cast steel node, combined with the weight reduction design and the short lead time, can improve the competitive advantage in terms of price and economy.
4. Wide range of weight variations
Small steel castings may be only 10 grams, while large steel castings can reach several tons, dozens or even hundreds of tons.
Compared to forged steel parts:
The mechanical properties of steel castings differ little in all directions and are superior to those of forged steel parts. Designers in the design of some high-tech products must consider the performance of the material in three directions, which highlights the advantages of castings. Regardless of weight, volume and one-time production, joint steel castings are easy to make complex shapes and non-stress concentrated parts.
Compared with welded structure:
In terms of shape and size, the flexibility of welded structures is stronger than that of forged steel parts, but compared with steel castings, there are still the following disadvantages:
1). It is easy to deform during welding.
2). It is difficult to form a streamlined structure.
3). High internal stress during welding.
4). Welds affect the appearance and reliability of components.
Compared with iron casting and other alloy castings:
Hongqiao steel castings can be used in a variety of working conditions, cast steel joints and mechanical properties are better than other alloy castings.
When we need high tensile strength or dynamic load parts, important pressure vessel castings and core parts that bear heavy loads at low or high temperatures, we should, in principle, give priority to steel castings.