What are the commonly used foundry metals?
Common cast metals include gray iron, ductile iron, malleable iron, and cast steel. Commonly cast non-ferrous metals include brass, tin bronze, tin-free bronze, aluminum alloy and more.
How many types of casting materials are there?
Eight types of casting materials are commonly used, including gray iron, malleable iron, ductile iron, vermicular iron, cast steel, cast aluminum alloy, cast bronze and cast brass, among others. Here are descriptions of its features and applications:
1. gray cast iron
Gray iron is known for its good fluidity and minimal shrinkage during cooling. It has low resistance, but presents plasticity and tenacity.
The elastic modulus of gray iron varies from 80,000 to 140,000 MPa, depending on the microstructure. Its compressive strength is three to four times greater than its tensile strength.
In addition to these properties, gray iron also has good wear resistance and vibration absorption, as well as not being sensitive to notches. It is also easy to machine. However, its welding performance is poor.
Gray iron has a maximum temperature limit of 300 to 400°C, beyond which it cannot withstand prolonged exposure. Despite this limitation, it continues to be the most used type of cast iron, representing 85% to 90% of all cast iron production.
2. Malleable iron
Malleable iron has properties inferior to gray iron, but superior to cast steel. It is mainly used to produce small, thin-walled castings that require a certain level of strength and toughness.
Furthermore, malleable iron has good corrosion resistance and machinability. Furthermore, its impact resistance is three to four times greater than that of gray iron.
3. Ductile iron
Although gray iron castings are often considered to be of superior quality, ductile iron castings are still widely used and offer several advantages. For example, ductile iron is known for its excellent machinability and can exhibit significant changes in properties through heat treatment.
Ductile iron also has a higher tensile strength than gray iron and cast steel, as well as a higher yield to tensile strength ratio than malleable iron and steel.
Furthermore, it has the best plasticity among cast irons, although its impact resistance is between that of cast steel and gray iron.
Ductile iron also excels in other areas, such as its excellent low-temperature properties and high fatigue resistance, which are comparable to #45 steel, but with lower sensitivity to stress concentration than steel.
Furthermore, it offers good resistance to wear, heat and corrosion.
Another advantage of ductile iron is its vibration damping ratio, which is 1:1.8:4.3 when compared to steel and gray cast iron.
Given these characteristics, ductile iron is increasingly used as an important material for a variety of applications, despite its historical reputation for being prone to defects.
4. Vermicular graphite iron
The mechanical properties of vermicular graphite cast iron are between those of gray cast iron and ductile iron, making it a material with good solidity, heat resistance and wear resistance.
Compared to nodular cast iron, its casting quality is better and comparable to that of gray cast iron.
Its strength is comparable to nodular iron and it has anti-vibration properties, thermal conductivity and casting performance similar to gray iron. However, it has better plasticity and fatigue resistance than gray iron.
Vermicular graphite cast iron inevitably contains a certain amount of spheroidal graphite, which increases its strength and rigidity, but may compromise the castability of the cast iron. This can also decrease the processability and thermal conductivity of castings.
5. Cast steel
The casting performance of cast steel is often considered poor due to its low fluidity and high shrinkage.
However, it has comprehensive mechanical properties, including excellent strength, toughness and plasticity. In fact, the tensile strength of cast steel is almost equal to its compressive strength.
In addition to these properties, special cast steels have unique characteristics such as heat resistance and corrosion resistance.
6. Cast aluminum alloy
The density of aluminum alloys is only one-third that of iron, making them an ideal choice for manufacturing lightweight structures.
Some aluminum alloys can be further strengthened through heat treatment, improving their overall properties.
7. Cast bronze
Bronze is classified into two types: tin bronze and tin-free bronze. Tin bronze has excellent wear and corrosion resistance, high strength and hardness.
However, it has poor casting performance and is susceptible to segregation and shrinkage porosity. Tempering does not improve its resistance.
Tin-free bronze is typically made from aluminum bronze or lead bronze, which has inferior casting performance. Aluminum bronze has high strength and presents significant resistance to wear and corrosion.
On the other hand, lead bronze has high fatigue resistance, good thermal conductivity and excellent acid resistance.
8. Cast Brass
Large shrinkage, high overall strength, good plasticity, good corrosion resistance and wear resistance.
Good cutting performance.
Comparison of Common Cast Iron Materials
| gray cast iron | malleable iron | Ductile iron | Vermicular graphite cast iron | |
| Graphite morphology | Scaly | Flocculent | Globular | Vermicular |
| Summary | Cast iron obtained by fully executing the first stage graphitization process | White cast iron is a type of high strength and toughness cast iron obtained by graphitization annealing | Spheroidal graphite was obtained by spheroidization and inoculation | Vermicular graphite was obtained by vermiculation and inoculation |
| Castability | good | Worse than gray cast iron | Worse than gray cast iron | good |
| Cutting performance | good | good | good | very good |
| Wear resistance | good | good | good | good |
| Strength/hardness | Ferrite: low Perlite: high |
Superior to gray cast iron | Very high | Superior to gray cast iron |
| Plasticity/toughness | Very low | Close to the molten steel | Very high | Superior to gray cast iron |
| Application | Cylinder, flywheel, piston, brake wheel, pressure valve, etc. | Small and medium-sized parts with complex shape and bearing impact, such as wrenches, agricultural tools and gears | Parts that require high strength and toughness, such as internal combustion engine crankshaft and valve | Parts that can operate permanently under thermal shock, such as diesel engine heads |
| Comments | Low-level sensitivity | Forging and pressing is not allowed | High heat resistance, corrosion resistance and fatigue resistance (2 times gray cast iron) | Thermal conductivity, thermal fatigue resistance, growth resistance and oxidation resistance |
