In this article, we shall explore the properties, uses, composition, etc of cast steel. We have also provided a PDF for the same.
What is Steel
Before going further let us understand what is meant by Steel, It is a versatile and strong alloy consisting mainly of iron and a small amount of carbon. It is one of the most commonly used materials in our daily life. A material is tougher and more durable than plain iron when it is combined with carbon.
This material has enough strength to accommodate heavy impacts and loads making it highly suitable for applications such as vehicles, bridges, and building construction. It has gained popularity for its resilience making it a must-have material in household and industry applications
What is Cast Steel
Cast steel is the form of steel that is produced by melting and casting the molten steel into a desired shape. It is versatile and strong material widely used in several domains. Consider a common example of the car engine block which is a crucial component that acts as the housing for the cylinder and other internal parts of the car engine.
The composition of cast steel includes carbon, Sulphur, silicon, manganese, phosphorus, etc. This composition results in the greater durability and strength of cast steel as compared to regular alloy steel
Chemical Composition of cast steel
The chemical composition of cast steel is responsible for influencing its performance properties. We use these properties to designate and classify different types of steel. Carbon cast steel and Alloyed cast steel are two major types.
Carbon cast steel shares similarities with wrought steel and is classified based on its carbon content. Low-carbon cast steel (0.2% carbon) is relatively soft and not easily heat-treatable. Medium carbon cast steel (0.2-0.5% carbon) is somewhat harder and can be strengthened through heat treatment. High carbon cast steel (0.5% carbon) is employed when maximum hardness and wear resistance are desired.
Alloyed cast steel is divided into low-alloy and high-alloy categories. Low-alloy cast steel (≤ 8% alloy content) behaves similarly to regular carbon steel but exhibits enhanced hardenability. High-alloy cast steel (> 8% alloy content) is specifically designed to possess particular properties such as corrosion resistance, heat resistance, or wear resistance.
One of the common examples of alloy steel includes Hadfield’s Manganese steel which consists of about 11-15% manganese element and stainless steel which consists of less than 10.5% chromium. Stainless steel has excellent corrosion resistance thanks to the presence of chromium which forms a protective chromium oxide layer when exposed to oxygen. On the counterpart, these Hadfield’s Manganese Steel is able to withstand demanding working conditions due to the presence of manganese element that offers great resistance and strength from abrasion.
Properties of Cast Steel
The properties of cast steel can vary widely depending on factors such as chemical composition and heat treatment. These properties are carefully selected to meet the specific requirements of the intended application.
- Hardness: The ability of cast steel to resist abrasion is defined as its hardness. The ability of hardness can be controlled by varying the carbon composition in the steel alloy.
- Strength: The force required for material deformation is referred to as strength. The strength of cast steel can again be increased by increasing the composition of carbon in the composition.
- Ductility: The tendency of deformation of cast steel when it undergoes tensile stress is referred to as cast steel. This ability is controlled by lowering the carbon content so the hardness decreases and inversely ductile properties are increased.
- Toughness: The ability of the material to resist stress is referred to as toughness. This toughness property of cast steel can be controlled by adjusting the alloy composition and heat treatment process
- Wear resistance: Wear resistance refers to the ability of the material to bear friction and withstand stress. Cast steel and wrought steel have similar wear resistance abilities. To control the wear resistance property we include elements such as chromium and molybdenum to our composition.
- Corrosion resistance: The material ability to resist rust and oxidation is called its corrosion resistance. Again the resistance ability of this steel is similar to that of wrought steel. This property is dependent on the level of nickel and chromium in the composition o the alloy higher value offer higher resistance and vice versa
- Machinability: The property of the material that indicates its level of ease to perform machining processes such as drilling, grinding, and cutting. This property is controlled by varying the other properties of this steel.
- Weldability: This property refers to the ability to weld this material without any welding defects. This property is dependent on the heat treatment processes and material composition of the alloy.
- High-temperature properties: This property refers to the ability of cast steel to be employed for high-temperature applications. It also helps to find the limit at which the material’s mechanical properties start to fade away.
- Low-temperature properties: This property refers to the low toughness ability of cast steel at lower temperatures.
Cast Steel Production
Steel casting production has a history dating back to the late 1750s. However, it lagged behind the casting of other metals due to the challenges posed by steel’s high melting point and limited metal processing technology. However, advancements in furnace technology overcame these obstacles.
Modern steel foundries use two types of furnaces: electric arc and induction. In an electric arc furnace, metal batches called “heats” are melted using an electric arc generated between graphite electrodes. The charge passes between the electrodes, exposed to thermal energy from the electrical discharge.
The steel casting process in an electric arc furnace follows a tap-to-tap operating cycle. First, steel scrap and alloys are loaded into the furnace. Then, energy is supplied to the furnace interior to melt the steel, primarily through electrical energy from the electrodes and chemical energy from oxy-fuel burners and oxygen lances. Oxygen is injected to remove impurities during the melting process. Excess slag is removed before tapping out the metal. After tapping, the furnace is prepared for the next charge cycle.
In contrast, an induction furnace uses electromagnetic induction to transfer heat energy. The non-conductive charge container is surrounded by a copper coil, and alternating current through the coil induces heat within the charge. Induction furnaces can melt most metals with minimal melt loss, but they offer limited metal refining capabilities compared to electric arc furnaces.
Modern steel foundries often use recycled scrap to reduce costs and environmental impact. Scrap from obsolete cars, mechanical components, and similar items, along with internal debris generated in the casting process, is combined with alloying elements and charged into the melting furnace.
After solidification, mold removal, and cleaning, cast steel undergoes heat treatment to develop its physical properties. This includes annealing, which involves heating the castings to a specific temperature, holding them for a specific period, and then slowly cooling them. Normalizing, similar to annealing, cools the castings in the open air or with fans to achieve higher strengths. Quenching involves rapid cooling using forced air or quenching mediums like water or oil. Tempering, or stress relieving, is used to relieve internal stresses by heating the castings to a temperature below the annealing temperature, holding it, and then slowly cooling.
Cast Steel Inspection
Cast steel undergoes various inspections to ensure specific physical properties, such as dimensional accuracy, surface texture, condition, internal soundness, and chemical composition. Dimensional inspections ensure compliance with customer requirements and tolerances, sometimes requiring sample castings to be destroyed for interior measurements. Surface finish inspections assess the aesthetic appearance, detecting flaws in the surface and sub-surface. Internal soundness inspections determine acceptable defect thresholds for porosity, inclusions, and shrinkage. Chemical composition is analyzed through wet chemical or spectrochemical methods.
Steel castings are tested for mechanical properties through destructive and non-destructive testing. Destructive testing visually examines internal soundness but only provides information on the tested piece. Non-destructive testing verifies soundness without damaging the casting. Tensile properties measure a casting’s ability to withstand slow loading conditions, while bend properties assess ductility by bending a sample around a pin. Impact properties measure toughness, and hardness tests gauge wear resistance and can indicate tensile strength.
Overall, cast steel inspection and testing ensure quality control and adherence to specifications before the castings are used in their intended applications.
Uses of Cast Steel
- Automotive: Cast steel is used for engine components, suspension parts, and more.
- Construction: It is employed in structural elements for its strength and durability.
- Machinery: It is crucial for gears, valves, and machine frames.
- Energy Generation: It is used in turbine components, pressure vessels, and heat exchangers.
- Mining and Heavy Industries: Cast steel is found in mining equipment for its robustness.
- Railway and Transportation: It is used for rail components like wheels and axles.
- Oil and Gas: Cast steel plays a vital role in offshore platforms, pipelines, and drilling equipment.
Difference Between cast Steel vs cast iron
In conclusion, cast steel is a versatile and robust alloy that finds wide-ranging applications across various industries. Its properties, such as hardness, strength, ductility, toughness, and corrosion resistance, make it suitable for automotive, construction, machinery, energy generation, mining, railway, transportation, and oil and gas sectors. Through careful inspection and testing, the quality and performance of cast steel are ensured, meeting specific requirements and standards. Its uses contribute to the development of durable and reliable products in numerous domains.