Cast Steel Grades for High Temperature Service
Cast steel is a ferrous alloy that is used in many applications where temperatures reach up to 800 °C. It has excellent mechanical properties and wear resistance and is generally more cost-effective than other types of steel alloys. The various grades of cast steel are primarily defined by their carbon levels, alloy additions and microstructures.
Low carbon grades are used primarily for parts requiring improved machinability and have a carbon content of less than 0.30%. These grades are often used in machined components such as valve parts and gear housings. Medium carbon grades are mainly used for applications requiring a combination of good strength and wear resistance. With their carbon content ranging from 0.30% to 0.60%, these grades find use in a variety of components that operate in high-temperature environments. High carbon grades are used in most applications under high temperatures and have a carbon content of 0.60- ~ 2.00%.
When selecting a suitable grade for high-temperature applications, the following criteria should be considered:
Creep strength: At elevated temperatures, creep strength is the primary factor for selecting a steel grade for a particular application. Low alloy steel castings have the best creep strength and have better weldability. They are used primarily for elevated temperature applications.
Fatigue strength: The fatigue strength of cast steel should be considered for applications that might experience high stress, vibration or shock. Cast steel grades with higher carbon content and a fine grain structure generally have improved fatigue strength.
Elevated temperature strength: The tensile strength of cast steel is reduced as the temperature is increased. Low carbon grades usually maintain their strength up to temperatures of 350–400 °C and are suitable for parts used at elevated temperatures. Medium carbon steel loses its strength after heating to temperatures of 400–550 °C, while higher carbon grades can withstand temperatures of up to 600–800 °C and are suitable for parts exposed to high temperatures.
Heat treatment: The mechanical properties of cast steel can be modified by appropriate heat treatments. Quenching and tempering give the steel higher strength and toughness, making it suitable for parts that experience high stress or shock.
Corrosion and wear resistance: Cast steel is rarely used in corrosive environments due to its lack of corrosion resistance. However, some grades have a good combination of wear and corrosion resistance, making them suitable for parts exposed to both.
Cost: The cost of cast steel varies depending on the grade, size and complexity of the part. Low carbon grades are usually the least expensive, while high carbon grades are more expensive due to their superior properties.
By taking the above considerations into account when selecting a grade of cast steel for high temperature service, engineers can ensure that the part will perform effectively and reliably in the application.
