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2021.12.22
The biggest difference between cast iron and cast steel lies in their chemical composition. In engineering, it is generally considered that iron is higher than 2% carbon content, and steel is lower than this value. Due to different compositions, the properties and applications are also different. Cast steel vs cast iron, which one should you choose? In this article, we going to break down the types of cast iron and types of cast steel first, and then find out their differences.
Cast iron and cast steel are popular materials used in various casting processes, such as die casting services, sand casting, investment casting, etc.
1)Gray cast iron. The carbon content is high (2.7% ~ 4.0%), the carbon mainly exists in the form of flake graphite, the fracture is gray, referred to as gray iron for short, and the melting point is low (1145 ~ 1250 ℃), small shrinkage during solidification, compressive strength and hardness close to carbon steel, good shock absorption. It is used to manufacture machine tool worktable, cylinders, and other structural parts.
2)White cast iron. Carbon and silicon content are low, carbon mainly exists in cementite form, and the fracture is silver-white. Large shrinkage during solidification, easy to produce shrinkage cavity and crack. It has high hardness, brittleness and can not withstand impact Load. It is mainly used as a blank of malleable cast iron and for making wear-resistant parts.
3) Malleable iron. Obtained from annealed white cast iron, graphite is distributed in flocculent form, which is called ductile iron for short. It has a uniform microstructure and properties, wear resistance, good plasticity, and toughness. It is used to manufacture parts with complex shapes and can bear a strong dynamic load.
4) Ductile iron. Gray cast iron is obtained by spheroidizing molten iron, and the precipitated graphite is spherical, which is called nodular iron for short. It has higher strength, better toughness, and plasticity than ordinary gray cast iron. It is used to manufacture internal combustion engines, auto parts, and agricultural machinery.
5) Compacted (Vermicular) graphite cast iron. Gray cast iron is obtained by vermicular treatment, and the precipitated graphite is vermicular. The mechanical properties are similar to that of nodular cast iron, and the casting properties are between gray cast iron and nodular cast iron. Parts used to make cars.
6) Alloy cast iron. Ordinary cast iron is obtained by adding an appropriate amount of alloy elements (such as silicon, manganese, phosphorus, nickel, chromium, molybdenum, copper, aluminum, boron, vanadium, tin, etc.). Alloy elements change the matrix structure of cast iron, so it has the corresponding characteristics of heat resistance, wear resistance, corrosion resistance, low-temperature resistance, or non magnetism. It is used to manufacture parts of mining, chemical machinery, instruments, and meters.
Cast steel is the steel used to make castings. A cast alloy. Cast steel is divided into cast carbon steel, low alloy cast steel, and special cast steel.
1)Cast carbon steel. Cast steel with carbon as the main alloying element and contains a small number of other elements. Cast low carbon steel with carbon content less than 0.2%, cast medium carbon steel with a carbon content of 0.2% ~ 0.5%, and cast high carbon steel with a carbon content greater than 0.5%. With the increase of carbon content, the strength and hardness of cast carbon steel increase. Cast carbon steel has high strength, plasticity and toughness, and low cost. It is used in heavy machinery to manufacture parts bearing a heavy load, such as rolling mill frame, hydraulic press base, etc; It is used to manufacture parts with large stress and impact on railway vehicles, such as a bolster, side frame, wheel, and coupler.
2) Low alloy cast steel. Cast steel containing manganese, chromium, copper, and other alloy elements. The total amount of alloy elements is generally less than 5%, which has great impact toughness and can obtain better mechanical properties through heat treatment. Cast low alloy steel has better service performance than carbon steel, which can reduce the quality of parts and improve the service life.
3) Special cast steel. There are many kinds of alloy cast steel refined to meet special needs. It usually contains one or more high-content alloy elements to obtain some special properties.
Although they are both iron-carbon alloys, due to the different percentages of chemical elements such as carbon, silicon, manganese, phosphorus, and sulfur, they have different metallographic structures after crystallization, showing many differences in mechanical properties and process properties.
For example, in the casting state, the elongation, reduction of area, and impact toughness of cast iron are lower than those of cast steel. The compressive strength and shock absorption of cast iron are better than that of cast steel; Gray cast iron has better liquid fluidity than cast steel, and is more suitable for casting thin-walled castings with complex structure; In the bending test, cast iron is a brittle fracture and cast steel is bending deformation. Therefore, they are suitable for casting parts with different requirements.
How to tell the difference between cast iron and cast steel in actual production and life:
1. Brightness. Cast steel is bright. Cast iron is dark and gray. The gray iron in cast iron is different from nodular iron. Nodular iron is brighter than gray iron.
2. Particles. Cast steel is very dense, and particles are generally invisible to the naked eye. Particles can be seen in both gray iron and nodular iron, and the gray iron particles are larger.
3. Sound. The sound of cast steel collision is different from the sound of iron castings.
4. Toughness. The toughness of cast steel is close to that of steel plate, the toughness of nodular cast iron is slightly inferior, the bending of thin-walled parts can reach 20-30 degrees, and the gray cast iron has no toughness.
5. Others. The surface of steel castings is rough and the area of risers and gates is large, which must be removed by gas cutting. Gas cutting of nodular cast iron can’t be eliminated.