Heat Treatment of Pressure Cast Steel for UK Standard Room Temperature and High Temperature Applications and Its Room Temperature Mechanical Properties
Introduction
Pressure cast steel is a common material used in engineering structures in the UK. It has excellent corrosion resistance, high strength and high modulus of elasticity, making it suitable for most applications. Its strength is further enhanced by heat-treating it to produce a more homogeneous microstructure that is more resistant to deformation and cracking.
In order to provide the most efficient and effective use of this material, there is a need to understand the various heat treatment processes and the way they influence the properties of the material. This paper explores the heat treatment processes that can be applied to UK standard pressure-cast steel. It will discuss the room temperature characteristics of the steel and its associated mechanical properties. Combining this information with a consideration of the temperature ranges of other British standards, it will analyse how these different temperatures affect both the mechanical and physical properties of this material.
Room Temperature Characteristics of Pressure Cast Steel
UK cast pressure steel typically consists of iron, nickel and chromium. These metals are alloys used in a variety of combinations to achieve desired properties. The microstructure of the metal consists of ferrite and martensite, the proportion between them determining the strength and toughness of the material.
At room temperature, cast steel is usually in its austenitic (FCC) state. There are two different phases of this structure, ferrite and martensite, with different amounts and sizes of grain boundaries. Ferrite is the softer of the two and has a high plasticity and ductility. This can be beneficial for forming and fabrication processes, and allows for good drawability. Martensite is harder and more brittle, with lower plasticity and ductility. It is more resistant to crack propagation, but can be prone to embrittlement.
Mechanical Properties of Pressure Cast Steel at Room Temperature
As mentioned above, the mechanical properties of pressure cast steel vary greatly depending on the alloy ratio and the heat treatment applied to the material. However, some general trends are seen when heat-treating cast steel.
As the temperature increases, the yield strength, ultimate tensile strength and Young’s modulus all decrease. This is due to the averageness of grain size, which increases as the temperature increases, leading to a decrease in the strength of the material overall. Conversely, the elongation and plasticity increase with temperature.
High Temperature Treatments of Pressure Cast Steel
Due to their corrosion resistance, pressure cast steel is often used in high temperature applications. Under these conditions, the microstructure of the steel can be altered to adjust the properties for the task. The most common treatments include annealing, quenching and tempering.
Annealing is the process of heating the steel to a temperature above its transformation range, then slowly cooling it back down. This process allows for a more homogenous and grain-aligned structure. The higher the temperature, the more homogenous the microstructure and the lower the strength.
Quenching involves rapidly cooling the steel to temperature below the transformation range. This causes the martensite to form rapidly, which increases the hardness of the steel. However, this can lead to embrittlement of the steel and therefore should be used in moderation.
Finally, tempering is a process of heating the steel to a temperature below the transformation range, then allowing it to cool slowly. This allows for the excess martensite to convert back to ferrite, resulting in greater toughness and strength. Different hardness is achieved by varying the tempering temperature, with higher temperatures resulting in greater hardness.
Conclusion
This paper has explored the heat treatments applied to UK standard pressure cast steel and the room temperature mechanical properties associated with them. It has highlighted the changes in mechanical and physical properties when working with different temperatures, and has detailed the processes of annealing, quenching and tempering in order to alter the properties of the steel for specific applications. For optimal performance and safety, it is important to understand the different heat treatments and associated properties in order to apply the most suitable method for a given application.
