Casting vs Forging: Steel Process Comparison

Quick Reference

Casting: steel melted and poured into molds for complex shapes (gears, valve bodies, machinery). Forging: heated solid steel shaped under pressure for superior strength (shafts, fasteners, forged fittings). Forged products have finer grain structure, better tensile strength, and higher fatigue resistance. Castings offer design flexibility for intricate geometries.

Steel items can be produced through either casting or forging processes. In steel casting, the metal is melted until it becomes liquid and is then poured into a mold to form the desired shape. Conversely, steel forging involves applying mechanical pressure to heated solid steel blocks (like ingots or billets), and permanently molding them into the required products.

Steel Forging vs. Casting

Basic Definitions

Steel casting and forging are two fundamental manufacturing processes used to form steel into desired products, each with distinct characteristics, advantages, and applications. Understanding the differences between these methods is crucial for choosing the most suitable approach for specific industrial needs.

Steel Casting

Steel casting involves melting steel into a liquid state and pouring it into a mold, where it solidifies into a specific shape. This process is advantageous for creating complex shapes and components that would be challenging to manufacture through other methods. Cast steel products can range from simple parts like gears and valves to intricate designs such as components for heavy machinery and automotive assemblies.

Steel casting finds applications in industries where complex shapes or specialized materials are required, including automotive, mining, aerospace, and construction.

Steel Forging

Forging involves heating solid steel blocks (ingots or billets) and then deforming them under high pressure or impact to achieve the desired shape. This process can be performed at various temperatures, leading to classifications such as cold forging, warm forging, and hot forging.

Steel forging is widely used in industries requiring high-strength components, such as automotive and aerospace for parts like gears, shafts, levers, and critical fasteners (including valves).

Both manufacturing processes require the application of high temperatures to steel raw materials (to liquefy or make it malleable) and the execution of CNC machining work at the end of the process to obtain the final product.

Final products may also undergo surface finish treatment, such as painting, powder coating, polishing, various types of coating (for example zinc plating) and wear protection/hardening (application of tungsten carbide overlay).

Last but not least, cast and forged parts may be assembled, welded, brazed, and hard-faced before being shipped as final products.

The products resulting from casting and forging processes have different properties in terms of surface porosity (generally better for forged vs. cast products), grain structure (finer for forged products), tensile strength (generally superior for forged products), and fatigue resistance.

These alternative manufacturing processes are therefore used (and suited for) different circumstances and applications.

Choosing Between Cast & Forged Products

Decision Factor	Casting	Forging
Design complexity	Complex shapes, internal cavities	Simpler shapes (complex = expensive)
Size	Virtually unlimited	Limited by press capacity
Material properties	Wide alloy selection	Superior strength/toughness
Production volume	Better for small-medium batches	Better for large runs
Initial cost	High mold cost, lower unit cost at volume	High tooling cost, efficient at scale
Integrity	May have porosity	No voids, consistent properties

When to choose CASTING:

• Parts too complex or expensive to forge (e.g., large valve bodies)
• Parts with internal cavities
• Very large parts with no practical size limit
• Special alloys difficult to forge (high Ni/Mo content)
• Small lot production where forging dies aren’t justified

When to choose FORGING:

• Maximum strength, toughness, and fatigue resistance required
• Parts subject to high impact and mechanical stress
• Zero tolerance for porosity, voids, or gas pockets
• High wear resistance needed
• High-end applications where quality and integrity outweigh cost/time
• Critical pressure-containing components

The evolution of casting technologies has reduced the gap between the physical properties of cast vs. forged products making modern cast products very competitive in terms of quality, strength, and wear resistance: however, in many fields, steel forging remains, still, the preferred manufacturing option (example: small sized valves, i.e. forged valves, or high-pressure valves).

Pro Tip

When the spec says “forged” but you’re quoted cast products at a lower price, don’t assume they’re equivalent. Forged components are specified for a reason - usually fatigue resistance or pressure integrity in critical service. Substituting cast for forged without engineering review can lead to field failures, especially in cyclic pressure or high-vibration applications.

Read about forging steel on Wikipedia.

Fields of Application

Steel casting and forging are used to produce products and parts for a multitude of sectors, including but not limited to:

• petrochemical plants (for example forged valves, forged fittings, flanges, etc)
• power generation and waste processing
• mining and mineral processing
• agriculture and livestock handling
• water treatment
• aeronautics
• automobile industry (pulleys and gear wheels)
• materials handling
• brickworks
• asphalt plants
• stormwater parts
• rendering plants
• railways

Steel Casting

Definition

Steel casting is a manufacturing process that involves melting steel until it becomes liquid, then pouring the molten steel into a mold where it solidifies into the desired shape. This method allows for the production of parts with complex geometries and detailed features that might be challenging to achieve through other manufacturing processes.

cast valve body

The molds used can be made from a variety of materials, including sand, metal, or ceramics, depending on the precision, surface finish, and reuse requirements of the casting. Steel castings are utilized across a broad range of industries, including automotive, aerospace, construction, and energy, due to their versatility in shape and size, and the ability to tailor the material properties through the selection of specific steel alloys and post-casting treatments such as heat treatment.

This process is particularly valuable for producing components that require high strength, durability, and resistance to wear and corrosion.

Steel Casting Process

The steel casting manufacturing process involves several key steps that transform steel into precisely shaped components. This process is known for its ability to produce complex shapes and sizes, offering flexibility in design and material properties.

Here’s an overview of the main stages in the steel casting manufacturing process:

Casting Process: Pattern Making → Mold Making → Melting & Pouring → Solidification → Mold Removal → Cleaning & Finishing → Inspection & QC

1. Pattern Making. A pattern representing the final shape is created from wood, plastic, or metal-slightly larger than the final part to account for shrinkage.

2. Mold Making. Molding material (sand with binders) is packed around the pattern. When removed, it leaves a cavity matching the part shape. Complex parts use two-half molds (cope and drag) with cores for internal cavities.

3. Melting and Pouring. Steel is melted at >1600°C (2900°F) with controlled alloy composition, then poured into the mold carefully to fill completely and avoid defects.

4. Solidification and Cooling. Steel cools and solidifies in the mold. Cooling rates affect microstructure; directional solidification minimizes stresses and defects.

5. Mold Removal. Sand molds are broken away; metal molds are opened and reused.

6. Cleaning and Finishing. Residual mold material is removed, gates/runners cut off. Parts undergo grinding, machining, and heat treatment for final properties.

7. Inspection and Quality Control. Final inspection ensures dimensional accuracy and material properties. NDT methods (X-ray, ultrasonic) detect internal defects.

Advantages/disadvantages Of Cast Steel

Advantages

Cast steel offers a unique set of advantages that make it a preferred choice for a wide range of applications across various industries. These benefits stem from the versatility of the casting process as well as the intrinsic properties of steel. Here are some of the key advantages of cast steel:

1. Design Flexibility

Cast steel allows for the production of complex shapes and intricate designs that are difficult or impossible to achieve with other manufacturing processes. This flexibility enables designers and engineers to create components with optimized geometries for specific applications, incorporating features like internal cavities, contours, and complex external shapes without the need for assembly or welding of multiple parts.

2. Material Properties

Steel casting can utilize a wide range of steel alloys, offering the ability to tailor the material properties to specific application requirements. This includes adjusting the alloy composition to enhance strength, ductility, wear resistance, impact resistance, and corrosion resistance. Additionally, post-casting heat treatments can further modify the mechanical properties, providing additional customization options to meet the demands of the application.

3. Large Component Production

The steel casting process is well-suited for producing large components that would be challenging or cost-prohibitive to manufacture through forging or machining from a solid block of steel. This capability is particularly valuable in industries such as mining, construction, maritime, and energy, where large, durable components are essential.

4. Cost-Effectiveness

For small to medium production volumes, casting can be more cost-effective than other manufacturing methods, especially for complex shapes that would require extensive machining or assembly of multiple parts. The ability to produce near-net-shape components reduces the need for additional processing and material waste, further contributing to cost savings.

5. Surface Finish and Detail

Cast steel can achieve a good surface finish and a high level of detail directly from the mold, reducing the need for additional finishing processes. This is beneficial for parts that require precise dimensions or aesthetic considerations.

6. Reliability

Steel castings undergo stringent quality control and testing procedures to ensure they meet the required specifications and standards. Non-destructive testing (NDT) techniques, such as x-ray, ultrasonic, and magnetic particle inspection, help detect any internal or surface defects, ensuring the reliability and performance of the cast component in its intended application.

7. Speed to Market

The casting process can be relatively quick from design to production, especially for prototypes or limited production runs. This speed can significantly reduce the time to market for new products or components, providing a competitive advantage.

In conclusion, the combination of design flexibility, customizable material properties, and cost-effectiveness makes cast steel a versatile and valuable option for a wide range of industrial applications. From heavy machinery and automotive components to artistic and architectural elements, the advantages of cast steel enable engineers and designers to meet complex challenges and deliver innovative solutions.

Disadvantages

The manufacturing and utilization of cast steel components offer distinct advantages but also come with certain disadvantages. Understanding these can help in making informed decisions about when and how to use cast steel in various applications:

1. Cost

• Initial Costs: The production of cast steel components can involve high initial costs due to the need for specialized molds, which can be expensive to manufacture, especially for intricate designs or low production volumes. This can make cast steel less economical for small batches.

• Material Costs: Steel, especially alloyed varieties used in casting for enhanced properties, can be more expensive than other metals, adding to the overall cost of the casting process.

2. Surface Finish and Tolerances

• Surface Finish: Cast steel might have a rougher surface finish compared to other manufacturing processes like forging or machining. This can necessitate additional finishing processes, increasing production time and costs.

• Dimensional Tolerances: Achieving tight dimensional tolerances can be more challenging with cast steel, especially for complex shapes or large components. This might require further machining or processing to meet precise specifications.

3. Porosity and Defects

• Porosity: The casting process can introduce porosity (tiny holes or voids) in the steel, which can affect the mechanical strength and integrity of the part. Porosity is particularly concerning in applications where pressure integrity or structural strength is critical.

• Defects: Castings are susceptible to various defects such as shrinkage cavities, cold shuts, and inclusions. These defects not only compromise the structural integrity and mechanical properties of the part but also require rigorous inspection and quality control measures to detect and mitigate.

Common Mistake

Accepting cast valve bodies based on visual inspection alone. Surface appearance tells you nothing about internal porosity or shrinkage voids - always require radiographic (RT) or ultrasonic (UT) examination for pressure-containing castings. The cost of NDT is negligible compared to the cost of a field failure.

4. Material Limitations

• Alloy Restrictions: While casting allows for the use of a wide range of alloys, some compositions might not be suitable for casting due to their melting characteristics or reactions with mold materials. This can limit the choice of materials for specific applications.

• Size and Weight Limitations: There are practical limits to the size and weight of cast steel components, dictated by the capacity of foundry equipment and the challenges of managing heat dissipation and material properties uniformly across large castings.

5. Environmental Considerations

• Energy Consumption: The melting and casting of steel require significant amounts of energy, contributing to the environmental footprint of cast steel products.

• Waste Production: The process can generate waste, including used molds and cores, excess metal from gates and risers, and defective castings, which need to be managed and recycled when possible.

Types of Steel Casting Processes

Summary of casting methods:

Process	Best For	Size/Volume
Sand Casting	Large parts, versatile shapes	Large, small-medium runs
Investment (Lost Wax)	Complex details, tight tolerances	Up to 100kg, 1.5m max
Centrifugal	Cylindrical parts (pipes, rings)	Any cylindrical shape
Continuous	Basic shapes for further processing	Billets, blooms, slabs
Shell Molding	Better finish than sand	Medium-high volume
Vacuum	High-integrity, defect-free	Aerospace, power generation
Die Casting	High-volume small parts	Primarily non-ferrous metals

Sand Casting

Sand casting is the oldest casting method and consists of pouring liquid metal into binders that resist the molten metal (such as clay bonded/green sand hard bonded/resin, thermosetting resin sand, and shell).

This is the most common and versatile method, using sand molds to create steel parts. The sand can be shaped into complex forms, making it suitable for a wide range of components including automotive frames, heavy machinery components, and decorative pieces.

Investment Casting (Lost Wax Casting)

This term refers to precision molding executed by injecting the liquid metal into a metal die and a ceramic coating. The mold material can be hard wax, lost wax, lost foam, and similar. Investment casting is the preferred method for manufacturing parts with a high number of details, and small parts that cannot afford the costs of traditional sand casting.

A wax model is coated with refractory material to create a mold. After the wax is melted out, molten steel is poured into the cavity. This method provides excellent surface finish and dimensional accuracy, ideal for small, complex components with tight tolerances, such as turbine blades, medical equipment, and firearm components.

Centrifugal Casting

Molten steel is poured into a rotating mold, creating parts with cylindrical shapes. The centrifugal force pushes the molten steel against the mold walls, producing a dense and uniform casting. Used for components requiring high material integrity, such as pipes, cylinders, and rings.

Continuous Casting

A highly efficient process where molten steel is solidified in a continuous strand through a mold. The solidified steel is then cut into desired lengths. This method significantly reduces the need for further processing. Primarily used for producing basic shapes like billets, blooms, and slabs, which are further processed into various steel products.

Shell Molding

Similar to sand casting, but uses a resin-coated sand that bonds to form a shell around the pattern. This method offers a better surface finish and more precise dimensions than traditional sand casting. Suitable for medium to high-volume production of small to medium-sized parts, such as valve components and gear housings.

Vacuum Casting

A process where molten steel is poured into a mold under a vacuum. This reduces the occurrence of defects and improves the quality of the casting by minimizing turbulence and gas entrapment. Used for components that require high integrity and are free of pores and voids, such as in the aerospace and power generation industries.

Die Casting

While die casting is predominantly used with non-ferrous metals due to the high melting point of steel, there are specialized high-pressure die-casting processes capable of handling steel alloys. Suitable for high-volume production of small, precise components that require a good surface finish.

Steel Forging

Definition

Steel forging is a manufacturing process involving the shaping of metal using localized compressive forces. In steel forging, steel is heated to a high temperature, making it pliable, and then it is hammered, pressed, or rolled into a desired shape.

This process can be performed at various temperatures, leading to different classifications such as hot forging, warm forging, and cold forging, each offering distinct advantages in terms of the material’s ductility and finished properties.

Steel forging appeared in China in the ancient ages to produce various types of metal products.

While the methods and equipment for creating forged components have evolved since those old days-from traditional anvils, hammers, and manual labor to modern automated machinery like hydraulic presses-the fundamental process of steel forging remains consistent. It involves heating solid steel blocks and then shaping them into finished products through the application of mechanical forces, such as hammering.

Forging Process

The steel forging process transforms steel into strong, durable components through force and heat:

Forging Process: Material Selection → Heating → Forging → Shaping → Trimming → Heat Treatment → Finishing → Inspection & Testing

1. Material Selection. Steel grade is chosen based on required properties (strength, ductility, wear/corrosion resistance). Common grades: carbon steel, alloy steel, stainless steel, tool steel.

2. Heating. Steel is heated to 950-1250°C (1742-2282°F) to become pliable. Temperature varies by steel type and forging method (hot, warm, or cold).

3. Forging. Steel is shaped using one of these techniques:

• Hammer Forging (Drop Forging): Repeated hammer strikes on anvil for precise shapes
• Press Forging: Hydraulic/mechanical press applies gradual pressure-better control, suited for large production
• Rolled Forging: Steel passes through rolls to decrease thickness/increase length-for cylindrical shapes

4. Shaping. Internal grain structure deforms to conform to the part shape, enhancing strength and toughness.

5. Trimming. Excess material (flash) is removed while hot or after cooling.

6. Heat Treatment. Annealing, normalizing, quenching, or tempering adjusts hardness, ductility, and relieves internal stresses.

7. Finishing. Machining, grinding, and polishing achieve final surface finish and dimensions.

8. Inspection and Testing. Dimensional checks, visual inspection, and NDT methods (ultrasonic, magnetic particle) ensure quality.

Upon completion of the process, the resulting products possess remarkable strength, impact toughness, and resistance to wear. This is attributed to the metallurgical changes, specifically recrystallization and grain refinement, that occur due to the thermal and mechanical treatments applied during the process.

Field Note

For critical applications like high-pressure valve bodies or turbine components, request grain flow documentation from the forge. The forging die design should orient grain flow parallel to the primary stress direction - a poorly designed forging with grain flow perpendicular to stress behaves little better than a casting in fatigue service.

The video below shows how steel forging works:

Advantages/disadvantages Of Forged Steel

Forged steel, known for its strength and reliability, is a preferred material for many industrial applications. However, like any manufacturing process, steel forging has its set of advantages and disadvantages. Understanding these can help in making informed decisions about its use in specific applications.

Advantages of Forged Steel

1. Superior Strength and Toughness

Forging refines the grain structure of the steel, aligning it with the shape of the product. This enhances the mechanical properties of the steel, making forged parts stronger and more resistant to impact and fatigue compared to cast or machined parts.

2. Improved Reliability

The forging process produces parts with consistent material properties and without internal voids, cracks, or other defects that could weaken the part. This uniformity ensures high reliability and performance, especially in critical applications.

3. Reduced Material Waste

Modern forging techniques are highly efficient, often resulting in less material waste compared to other manufacturing processes like casting or machining. This efficiency can lead to cost savings, especially in high-volume production.

4. Versatility in Materials

Steel forging can be performed with a wide range of alloys, allowing for the production of parts with specific properties tailored to the application, including high-temperature resistance, corrosion resistance, and wear resistance.

5. Cost-Effective for Large Production Runs

Although the initial setup and tooling costs can be high, forging can be more cost-effective than other processes for large production runs due to its material efficiency and the reduced need for secondary processing.

Disadvantages of Forged Steel

1. Higher Initial Costs

The initial costs for setup and tooling in forging can be significant, especially for complex shapes. This can make forging less economical for small production runs compared to other manufacturing processes.

2. Limitations on Shape Complexity

While forging can produce a wide range of shapes, extremely complex or intricate designs may be challenging to achieve through forging alone and might require additional machining or processing.

3. Size Limitations

The size of forgings is generally limited by the capacity of the forging equipment. Very large components might be difficult or impractical to forge and may require alternative manufacturing methods.

4. Need for Secondary Processing

Depending on the application’s requirements, forged parts may require secondary processes such as machining, heat treatment, or surface finishing to achieve the desired dimensions, properties, or surface quality.

5. Energy Intensive

The forging process, particularly hot forging, requires significant amounts of energy to heat the metal, which can impact the overall environmental footprint of the manufacturing process

Types of Steel Forging Processes

Steel forging processes vary in technique and application, each suited to different manufacturing requirements. These processes are categorized by temperature (cold, warm, or hot forging) and method of applying force (hammer or press forging).

By Temperature:

Type	Temperature	Advantages	Best For
Hot Forging	950-1250°C (1742-2282°F)	Easy shaping, less force needed, no strain hardening	Complex shapes, high strength parts (automotive, construction)
Warm Forging	650-950°C (1202-1742°F)	Balance of formability and precision	Medium-complexity parts, cost-effective
Cold Forging	Room temperature	Excellent surface finish, work hardening strengthens part	Small precision parts (fasteners, bolts, screws)

Hot forging allows steel to be shaped easily as the high temperature increases plasticity and reduces resistance to deformation. Enables forging of complex shapes with less force and energy, and reduces strain hardening during the process.

Cold forging is carried out at or near room temperature, offering a cleaner finish and stronger products due to strain hardening. Produces parts with excellent surface finish and dimensional accuracy; the strength of the steel increases through work hardening.

Warm forging serves as a middle ground between hot and cold forging, balancing the benefits of both. Allows for reduced force compared to cold forging while achieving better dimensional accuracy than hot forging.

4. Open-Die Forging

• Description: In open-die forging, the steel is worked between two flat or simply contoured dies that do not enclose the workpiece, allowing the material to flow outward as it is forged.
• Advantages: Highly versatile, capable of producing very large parts, and allows for the adjustment of the workpiece during forging.
• Applications: Ideal for large, simple shapes such as shafts, bars, beams, and plates.

Open die forging involves shaping metal by pressing or hammering it between two dies that don’t entirely enclose the material. The piece of metal is worked upon through successive movements of the dies, which apply force to mold the metal into the desired shape. This technique is demonstrated in the action showcased in the video below:

5. Closed-Die Forging (Impression-Die Forging)

• Description: Steel is compressed between two or more dies that contain a precut profile of the desired part, resulting in a more precise and complex shape.
• Advantages: Produces parts with close tolerances and minimal waste; suitable for high-volume production.
• Applications: Widely used for automotive, aerospace, and industrial components that require detailed features and high strength.

Closed-die forging is a process where the dies close in on the workpiece, either completely enclosing it or partially. The process begins by placing a piece of heated raw material, roughly shaped or sized to match the final product, into the lower die. This process is demonstrated in the following video:

6. Seamless Rolled Ring Forging

• Description: This process involves piercing a hole in a thick, round piece of metal to create a donut shape, which is then rolled and stretched to produce a seamless ring.
• Advantages: Efficiently produces rings with excellent structural integrity and homogeneous characteristics.
• Applications: Commonly used for bearings, flanges, gear rings, and wind turbine components.

Difference between Open-Die & Closed-Die Forging

Feature	Open-Die Forging	Closed-Die Forging
Die configuration	Flat dies, workpiece not enclosed	Dies contain precut profile, enclose workpiece
Size capability	Very large parts possible	Limited by die size and press capacity
Precision	Lower - requires machining	High - close tolerances, minimal machining
Complexity	Simple shapes only	Complex geometries with details
Production volume	Low volume, one-offs	High volume, mass production
Material waste	Higher (less precise shape)	Lower (near-net shape)
Setup cost	Lower	Higher (complex dies)
Unit cost	Higher at volume	Lower at volume
Applications	Shafts, beams, large industrial parts	Gears, levers, fasteners, automotive/aerospace

Related Steel Products

Structural Steel Sections

• Steel Plates - Hot-rolled plates for construction and manufacturing
• IPE/IPN Steel Beams - European I-beam profiles for structural applications
• HSS Hollow Sections - Square and rectangular tubular sections
• RSA Steel Angles - Equal and unequal angle sections
• UPN/UPE Channels - U-shaped channel sections

Material Properties

• Density of Metals - Reference table for metal densities
• CE Marking for Steel Products - European conformity requirements for construction products