Alloy Steel Casting: Common Grades, Properties and Applications

Alloy steel casting refers to the metal casting process of forming objects by pouring molten alloy steel into molds to achieve specific shapes and sizes. Alloy steel castings are among the most widely used metal components and are integral to many aspects of our lives—including cars, planes, machinery components, trains, and even small art products. In this article, we will explore what alloy steel casting is, the common grades of alloy steel castings, their properties, and their applications. By reading this article, you will gain a better understanding of alloy steel casting.

What is Alloy Steel Casting?

Alloy steel castings are parts and components made using metal casting processes such as investment casting, sand casting, shell mold casting, and lost foam casting. Most casting processes involve melting the alloy steel and pouring it into a mold, where it solidifies into the desired shape. Once the steel cools and solidifies, it is removed from the mold and may undergo further processing such as machining, surface treatment, and heat treatment to achieve the final specifications.

Alloy steel itself is steel that has been alloyed with other elements in addition to carbon to enhance its mechanical properties and to provide greater resistance to corrosion and heat. The additional elements typically include chromium, nickel, manganese, molybdenum, vanadium, silicon, and boron, each contributing specific properties to the steel. Alloy steel castings are used in various applications where parts need to withstand high stress, pressure, or harsh environments. We will cover these specific applications later on in the article for your reference to understand what alloy steel castings are used on.

What are the common grades of alloy steel?

Alloy steel grades are categorized based on the specific alloying elements added to the steel. These elements enhance various properties of the steel such as strength, hardness, wear resistance, and corrosion resistance. Below are some of the most commonly used grades of alloy steel in American standards (AISI):

4130 Steel: Also known as 30CrMo, this grade is known for its strength and versatility. Containing elements such as chromium and molybdenum, which improve its strength and toughness, 4130 steel is commonly used in the aerospace and automotive industries.

4140 Steel: Also known as 42CrMo, similar to 4130 but with higher carbon content, 4140 steel has an excellent balance of strength, toughness, and wear resistance. It is widely used in mining and construction industry, providing parts such as gears, axles, and other high stress parts.

4340 Steel: This nickel-chromium-molybdenum alloy steel is known for its toughness and ability to maintain strength even when overheated. It’s often used in the aerospace industry and for other high-impact applications.

8620 Steel: A low-carbon nickel-chromium-molybdenum alloy steel, 8620 is often used for carburized parts where a harder surface with a tough core is required, such as gears and pinions.

52100 Steel: High in carbon and chromium, this steel is noted for its high hardness and excellent wear resistance. It’s primarily used in bearings and other high-wear environments.

Below is a detailed table showing the standard equivalents for the specific alloy steel grades 4130, 4140, 4340, 8620, and 52100 across different countries and standards:

AISI/SAE (USA)	European EN/DIN	Japanese JIS	Chinese GB	ASTM Equivalent
4130	25CrMo4 / 1.7218	SCM430	30CrMo	ASTM A29 Grade 4130
4140	42CrMo4 / 1.7225	SCM440	42CrMo	ASTM A29 Grade 4140
4340	34CrNiMo6 / 1.6582	SNCM439	40CrNiMoA	ASTM A29 Grade 4340
8620	20NiCrMo2-2 / 1.6523	SNCM220	20CrNiMo	ASTM A29 Grade 8620
52100	100Cr6 / 1.3505	SUJ2	GCr15	ASTM A295 Grade 52100

This table provides a comprehensive view of the equivalence between the selected alloy steel grades in the standards of major industrial countries, along with their corresponding ASTM standards.

Chemical Composition of Alloy Steel Casting

The chemical compositions of alloy steels like 4130, 4140, 4340, 8620, and 52100 vary to give each grade specific properties tailored to their applications. Let me explain what each element does, and then compare each grade of alloy steel casting for a better understanding. As mentioned previously, alloy steel casting involves steel components that have been alloyed with different elements to enhance their mechanical properties. Each element has unique effects; below is a breakdown of what they do.

Carbon (C)

The most fundamental element of alloy steel for casting is carbon. Carbon influences hardness and strength. Higher carbon content increases hardness and strength but reduces ductility. As the primary hardening element, carbon forms carbides with other alloying elements, which increases wear resistance.

Chromium (Cr)

Chromium is added to improve tensile strength, hardness, toughness, wear resistance, and corrosion resistance. In sufficient quantities, chromium can significantly enhance corrosion and oxidation resistance by forming a stable oxide layer on the steel’s surface, known as a passivation layer.

Molybdenum (Mo)

Molybdenum increases hardenability and strength. It helps steel maintain strength at high temperatures. It also improves the steel’s resistance to pitting and crevice corrosion, especially when combined with chromium.

Manganese (Mn)

Manganese improves ductility and wear resistance. It is also crucial for improving the hardenability and strength of steel. Manganese works by deoxidizing the steel during its production and by increasing the toughness of the crystalline structure of the steel.

Nickel (Ni)

Nickel adds toughness and improves corrosion resistance. It also enhances the overall strength and ductility of steel. Nickel is notable for lowering the impact transition temperature, thereby making steel more resilient at lower temperatures.

Silicon (Si)

Silicon is a deoxidizer used to make steel more ductile. It also increases strength and hardness but decreases toughness. In some high-silicon steel alloys, it enhances magnetic properties and corrosion resistance.

Phosphorus (P)

Often considered an impurity, when controlled properly, phosphorus can improve strength, machinability, and hardness. However, it can also make steel more brittle and is usually kept at very low levels in most steel types.

Sulfur (S)

Like phosphorus, sulfur is generally regarded as an impurity. In controlled amounts, it improves machinability but at the expense of ductility and toughness. Sulfur forms manganese sulfide inclusions which enhance machinability but can cause hot shortness (poor hot formability).

Comparison Between Each Grade

These elements are carefully and strategically added in varying proportions depending on the desired properties of the final alloy steel casting components. The exact composition can dramatically affect the performance of the steel in different environments and applications; thus, the careful balance and mixture of these elements are crucial in metal casting.

Now let me show you a comparison table of the chemical composition of each grade of alloy steel used for casting.

Element	4130 (% by weight)	4140 (% by weight)	4340 (% by weight)	8620 (% by weight)	52100 (% by weight)
Carbon (C)	0.28-0.33	0.38-0.43	0.38-0.43	0.18-0.23	0.98-1.10
Chromium (Cr)	0.8-1.1	0.8-1.1	0.7-0.9	0.4-0.6	1.3-1.6
Molybdenum (Mo)	0.15-0.25	0.15-0.25	0.2-0.3	0.15-0.25	–
Manganese (Mn)	0.4-0.6	0.75-1.0	0.6-0.8	0.7-0.9	0.25-0.45
Silicon (Si)	0.15-0.35	0.15-0.35	0.15-0.30	0.15-0.35	0.15-0.30
Nickel (Ni)	–	–	1.65-2.0	0.4-0.7	–
Phosphorus (P)	0.035 max	0.035 max	0.035 max	0.035 max	0.025 max
Sulfur (S)	0.04 max	0.04 max	0.04 max	0.04 max	0.025 max

This table provides a clear breakdown of the primary chemical components found in each steel grade, reflecting their unique compositions and how these influence the material properties suited to different applications.

Mechanical Properties of Alloy Steel Casting

Alloy steel castings exhibit a range of mechanical properties that can be altered through the choice of alloy composition and heat treatment processes. These properties make alloy steels versatile and suitable for various applications across many industries. Below is a breakdown of the key mechanical properties typically found in alloy steel castings:

1. Strength

• High Tensile Strength: Alloy steel castings are known for their high tensile strength, which allows them to withstand significant force without breaking.
• Yield Strength: This is the stress at which a material begins to deform plastically. Alloy steel castings have high yield strengths, making them capable of bearing heavy loads without permanent deformation.

2. Hardness

• Resistance to Deformation: Alloy steel castings can achieve high hardness levels through heat treatment, allowing them resistant to wear and permanent deformation.
• Scratch Resistance: The hardness also contributes to their ability to resist scratching and other surface damages.

3. Toughness

• Impact Resistance: Despite their hardness, properly treated alloy steel castings maintain good toughness, meaning they can absorb energy and withstand impact without fracturing.
• Ductility at Low Temperatures: Certain alloy steels retain their toughness even at low temperatures, making them suitable for cold environments.

4. Wear Resistance

• Durability: Alloy steel casting components resist wear from friction, contact with other metals, and other erosive elements, which is critical for applications in mining, milling, and other heavy industries.

5. Fatigue Strength

• Endurance: Alloy steel casting parts have high fatigue strength, allowing them to endure repeated and varying loads over an extended period without failure.

6. Corrosion Resistance

• Environmental Suitability: While not as resistant as stainless steels, certain alloy steels with elements like chromium and nickel offer improved corrosion resistance against specific environmental conditions.

7. Machinability

• Manufacturing Efficiency: Although high-carbon and high-alloy steels can be challenging to machine, proper alloying and heat treatment can balance hardness and machinability, facilitating easier shaping and finishing.

Now as we can see a comparison table of key mechanical properties of common grades of alloy steel casting.

Property	4130	4140	4340	8620	52100
Tensile Strength (MPa)	670 – 850	750 – 950	780 – 980	530 – 680	700 – 1900
Yield Strength (MPa)	435 – 600	460 – 730	590 – 860	385 – 530	440 – 900
Elongation (%)	15 – 25	13 – 22	13 – 18	18 – 22	10 – 25
Hardness (Brinell)	197 – 237	197 – 302	217 – 302	149 – 212	600 – 700
Impact Strength (J)	Variable (medium)	Variable (high)	Variable (high)	Variable (medium)	Variable (high)
Fatigue Strength (MPa)	450 – 550	480 – 600	600 – 700	300 – 400	500 – 700
Corrosion Resistance	Low – Medium	Low – Medium	Medium	Medium	Low

The mechanical properties listed in the table can vary based on the heat-treating process used, as these processes significantly affect the material’s performance characteristics. The values provided are typical and can differ slightly depending on the manufacturer, specific composition adjustments, and processing variables.

Common Issues of Alloy Steel Castings

Alloy steel castings, while advantageous for their strength and versatility, can face several common issues during the casting process or in service. These problems can affect the quality, performance, and durability of the final products. Here are some of the typical issues associated with alloy steel castings:

Porosity

One of the most common defects in alloy steel castings is the porosity issue, which refers to small holes or voids in the casting caused by trapped gas or shrinkage during solidification. Porosity can often compromise the structural integrity and strength of the casting, making it unsuitable for use, especially in safety-critical applications.

To address this issue, we need to improve the mold and core gas permeability to allow gases to escape. Implementing a proper venting system is another important measure to prevent porosity. We can also control the pouring rate and temperature to minimize turbulence and trapped air.

Shrinkage

Shrinkage often occurs during the casting process; it refers to the contraction of the alloy steel as it solidifies, which can lead to internal voids or external deformations. The impact of shrinkage can be quite severe, as it can cause dimensional inaccuracies and weaken the casting, potentially leading to failure under mechanical stress.

To prevent shrinkage in alloy steel castings, we need to utilize proper riser and gating system designs to ensure adequate feeding of the casting as it solidifies and shrinks. Another solution is to adjust the alloy composition and modify the solidification pathway through directional cooling to minimize areas of isolated hot spots.

Inclusion

Inclusion is a common issue among alloy steel castings; it refers to non-metallic particles such as slag, sand, or oxide films becoming trapped within the casting. The presence of inclusions can significantly reduce the mechanical properties and fatigue life of alloy steel castings, as inclusions often act as stress concentrators.

There are several solutions for preventing inclusions in alloy steel castings. One is to maintain clean melting practices to reduce slag and other contaminants. We could also use filters in the gating system to trap inclusions before they enter the mold cavity. Additionally, proper slag removal before pouring is essential.

Cracking

Another common problem in alloy steel castings is cracking. Cracks form during cooling due to differential contraction rates within the casting or from excessive thermal stresses during processing. Cracks can cause serious issues if not treated properly; alloy steel castings with cracks cannot be used and require costly rework or replacement.

To effectively prevent cracks from occurring, we need to optimize the casting and mold design to reduce thermal stresses. Another effective solution is to control the cooling rate through careful temperature management. Additionally, post-casting heat treatment can be helpful to relieve residual stresses.

Corrosion

Last but not least, corrosion can also be a headache in alloy steel castings, as it can lead to material loss and structural failure over time, particularly in alloys not specifically designed for corrosion resistance.

To prevent corrosion, we must consider implementing alloy modifications to enhance corrosion resistance, such as increasing chromium content for certain applications. Applying protective coatings or surface treatments like passivation can drastically enhance corrosion resistance.

Applications of Alloy Steel Castings

As we discussed at the beginning of this article, alloy steel casting components are among the most widely used metal parts, serving a wide range of industries involved in our day-to-day lives. I have listed some typical industries and applications for your reference.

Automotive Industry

Alloy steel castings are extensively used in the automotive industry due to their strength, durability, and versatility. For engine components, alloy steel is used for manufacturing cylinder heads and blocks, these alloy steel casting components must withstand high temperatures and pressures with high strength and fatigue resistance. Crankshafts and camshafts also rely on the toughness and fatigue strength provided by alloy steel to handle dynamic stresses effectively.

The transmission system incorporates alloy steel in components like gears and bearings that demand exceptional wear resistance and strength to endure continuous stress and friction. Alloy steel casting is also favored for transmission housings, which require robust protection and structural integrity to encase critical mechanical parts securely.

Suspension systems benefit significantly from the ductility and toughness of alloy steels. Components such as control arms, links, and steering knuckles use alloy steel castings to absorb shocks and maintain vehicle stability with enhanced handling and safety. The high strength-to-weight ratio of these materials is particularly advantageous in steering components, supporting vehicle dynamics and safety.

For braking systems, alloy steel’s excellent heat resistance is vital. Brake calipers and discs made from alloy steel perform reliably under high thermal loads, ensuring effective braking performance under various operating conditions.

Structural components like chassis frames and cross members are important parts that rely on the strength and impact resistance of alloy steel castings. These materials are crucial for maintaining the structural integrity of vehicles. Additionally, mounts and brackets that support various mechanical systems are also made from alloy steel, chosen for their ability to handle significant loads with precision.

Alloy steel castings provide the automotive industry with materials that can be precisely cast into complex shapes, allowing for integrated designs and weight reduction without compromising performance. This makes alloy steel an invaluable material in modern automotive engineering, supporting advancements and improvements in vehicle design and functionality.

Railway Industry

Alloy steel castings are widely used in the railway industry, offering robust solutions for various applications that require durability, strength, and resistance to wear and fatigue.

One of the most used applications of alloy steel castings are rail components, including rail, switch and crossing components. The high-strength and durable nature of alloy steel ensures that the rails can withstand wear and deformation over long periods.

The bogie frame, which supports the wheelset and connects to the railcar body, is another critical application of alloy steel castings. These frames bear the weight of the railcar and its cargo, absorbing vibrations and shocks from track irregularities. Alloy steel’s strength and toughness make it an excellent choice for these structural components.

Couplings and draw gears are crucial for the safety and functionality of train operations as they involve the linking mechanisms between railcars. Alloy steel castings are preferred for these components due to their ability to endure the dynamic and static stresses involved, ensuring reliable long-term performance.

In braking systems, especially those involving discs and other critical braking components, alloy steel castings are used because of their ability to handle high thermal stresses and resist wear under harsh operating conditions.

The casting of alloy steel is also utilized in the manufacture of various suspension parts, including springs and damping systems that help in managing the stability and comfort of rail travel. The material’s properties ensure that these components can last long and perform well even under the constant strain of heavy loads and speed.

Components under the carriage, such as bearing housings and axle boxes, are made from alloy steel castings. These parts must be exceptionally robust to support the axle assembly and wheelsets, ensuring safe and smooth operations.

Lastly, alloy steel castings find applications in signal and track equipment where durability and resistance to environmental wear are paramount. These components need to reliably function in outdoor environments, making alloy steel’s corrosion resistance valuable.

In the railway industry, the use of alloy steel castings is driven by the need for materials that can withstand the rigors of heavy-duty use and adverse conditions while maintaining safety and efficiency. Alloy steel’s mechanical properties make it an indispensable material in maintaining and advancing rail infrastructure and vehicle technology.

Aerospace Industry

Alloy steel castings are integral to the aerospace industry, where they are employed in a variety of applications that demand strength, durability, and resistance to extreme conditions. These materials are essential for ensuring the reliability and safety of both aircraft and spacecraft.

For engine parts, alloy steel castings such as turbine blades and vanes must endure high temperatures and stresses during operation. The ability of alloy steel to maintain its strength at high temperatures makes it ideal for these applications. In addition, engine gear components and exhaust system parts, such as exhaust manifolds that require heat and corrosion resistance, are also typically made from alloy steel.

The landing gear of aircraft, including struts and actuation systems, relies heavily on alloy steel castings for their strength and shock resistance, which are vital for safe take-offs and landings. Wheels and brake systems also use alloy steel for its high load-bearing capacity and wear resistance, ensuring durability and safety under the rigorous conditions of landing and taxiing.

Structural components of aircraft, such as internal frames and support structures, benefit from the high strength-to-weight ratio of alloy steel castings. This property is crucial for maintaining the overall structural integrity of the aircraft while keeping weight to a minimum. Alloy steel is also used in the manufacture of seat tracks and fittings, which need to withstand the forces experienced during flight and any potential impact events.

Alloy steel castings are also used in the production of aerospace fasteners, including bolts and other securing components. These fasteners holds various parts of the aircraft together and must resist loosening under the constant vibrations and dynamic loads encountered during flight.

Components in the fuel systems of aircraft, such as pumps and valves, are made from alloy steel due to its corrosion resistance and strength. These characteristics prevent leaks and maintaining the integrity of the fuel system under pressure.

Control systems within aerospace applications also depend on alloy steel for parts like hydraulic actuators and fittings. These components must handle high pressures and resist fatigue over time, making alloy steel a preferred material due to its robust properties.

Mining and Construction Machinery

Alloy steel castings are extremely useful in both the mining and construction machinery industries due to their strength, toughness, and wear resistance. These properties make alloy steel an amazing choice for equipment that must endure harsh operating conditions and heavy loads.

In the mining industry, equipment is subjected to extreme wear and tear, heavy loads, and corrosive environments. Alloy steel castings are extensively utilized to manufacture components such as excavator buckets and teeth, which encounter intense wear as they dig through hard soil and rock. Drill bits and holders, made from alloy steel, are crucial for their toughness and ability to withstand the stress of drilling through tough materials. Additionally, crusher components like jaws, mantles, and hammers are also crafted from alloy steel to handle the demanding task of breaking down rocks.

Similarly, in the construction industry, machinery must be robust enough to handle heavy materials and operate under diverse environmental conditions. Alloy steel castings are integral to the production of load-bearing components such as booms, arms, and chassis parts found in cranes, excavators, and bulldozers. These components benefit significantly from the high strength and fatigue resistance of alloy steel. Gears, pinions, and shafts within power transmission systems are also manufactured from alloy steel to endure the stresses of operating heavy machinery. Furthermore, hydraulic system components like cylinders and pistons are typically made from alloy steel to withstand the high pressures encountered in these systems.

The durability of equipment made with alloy steel components ensures longer operational life under tough working conditions, which is important for reducing downtime and maintenance costs. Enhanced material strength allows for the design of machinery that can handle greater capacities, thereby improving operational efficiency. Moreover, the safety of machinery is significantly enhanced by the use of alloy steel, a critical consideration in industries where equipment failure can result in serious hazards.

Energy Sector

In the energy sector, alloy steel castings play a pivotal role due to their strength, high-temperature resistance, and corrosion resistance, which are essential qualities for equipment used in harsh and demanding environments. Alloy steel castings are extensively used in oil and gas extraction and processing, where components such as valves, pumps, and drill bits must withstand high pressures, abrasive materials, and corrosive substances. These materials are crucial for ensuring operational reliability and safety, particularly in offshore drilling rigs and refineries where failure can lead to significant environmental and safety hazards.

In the power generation industry, alloy steel castings are fundamental in the construction of components for both traditional and renewable energy systems. For traditional power plants, including coal, natural gas, and nuclear facilities, alloy steel is used to manufacture boiler parts, turbine blades, and other machinery that must handle high temperatures and pressures efficiently. In the realm of renewable energy, such as wind turbines, alloy steel castings are employed to create the turbine housings and other structural components that require durability to withstand variable and harsh weather conditions over long periods.

The application of alloy steel castings in the energy sector is critical for building and maintaining the infrastructure required to produce and process energy reliably and safely. Their use ensures that equipment can operate under the extreme conditions typical of this industry, maintaining efficiency and minimizing downtime.

Alloy Steel Casting Manufacturer

All in all, we have discussed the grades, chemical compositions, mechanical properties, common issues, and applications of alloy steel casting. If you’ve followed along, you probably have a good idea of where they are used. So, if you are a supplier in the aforementioned industries, great! That means you know you need them. Please contact us today to get a free quotation!

At Taiyuan Simis Investment Casting Co., Ltd, we are a professional precision casting manufacturer specializing in manufacturing all types and grades of alloy steel castings, using various processes—investment casting, sand casting, shell mold casting, lost foam casting, and more. If you are from an industry not mentioned, don’t worry. We provide alloy steel casting services and produce all kinds of bespoke alloy steel parts and components; with 40 years of manufacturing experience in the foundry industry, we know our business well. Please share this article if you find it useful, and contact us for any inquiries.