When it comes to versatile, high-strength steels, 4140 steel stands out as a popular choice in various industries. Its unique balance of toughness, wear resistance, and machinability makes it a go-to material for applications requiring durability under stress. In this article, we’ll dive into what makes 4140 steel so special, covering its common uses, standards, chemical composition, and key properties.
What is 4140 Steel?
4140 steel is a low-alloy steel primarily composed of iron, with added carbon, chromium, and molybdenum, which classifies it as “chromoly” steel. These elements give 4140 its high strength, excellent wear resistance, and moderate corrosion resistance. Commonly used in the automotive industry, 4140 steel is ideal for components that need to endure significant stress and strain, such as drive shafts, gears, axles, and crankshafts. Its superior durability also makes it a top choice for load-bearing stationary parts like bolts and chains.
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How Exactly is 4140 Steel Made?
4140 steel is created by melting iron with carbon, chromium, molybdenum, and other elements in an electric or basic oxygen furnace at temperatures above 1500°C. Once fully melted and mixed, the molten steel is poured out to cool. After cooling, the steel undergoes annealing—reheating and controlled cooling—to soften it for easier processing.
The next step involves dipping the steel in hydrofluoric acid to remove surface rust and impurities. The cleaned steel is then melted again and cast into molds to form billets or slabs. Finally, these billets or slabs are hot- or cold-worked through rollers to achieve the desired shapes and sizes.
4140 Steel Chemical Composition
The properties of 4140 steel are largely determined by its chemical composition. It is a low-alloy steel, meaning it has a relatively small amount of alloying elements. The typical composition includes:
| Element | Percentage (%) |
|---|---|
| Carbon (C) | 0.38 – 0.43 |
| Manganese (Mn) | 0.75 – 1.00 |
| Phosphorus (P) | 0.035 max |
| Sulfur (S) | 0.040 max |
| Silicon (Si) | 0.15 – 0.35 |
| Chromium (Cr) | 0.80 – 1.10 |
| Molybdenum (Mo) | 0.15 – 0.25 |
4140 Steel Properties
The unique blend of elements in 4140 steel gives it a set of properties that make it incredibly versatile. Here’s a breakdown of its key properties:
| Property | Value |
|---|---|
| Melting Point | 1416 – 1471°C (2581 – 2680°F) |
| Boiling Point | 3000°C (5432°F) |
| Tensile Strength | 850 – 1000 MPa (123,000 – 145,000 psi) |
| Yield Strength | 655 – 862 MPa (95,000 – 125,000 psi) |
| Hardness (Annealed) | 28 – 32 HRC |
| Hardness (Hardened & Tempered) | Up to 54 HRC |
| Elongation at Break | 20 – 25% |
| Modulus of Elasticity | 205 – 210 GPa (29,700 – 30,500 ksi) |
| Density | 7.85 g/cm³ (0.284 lb/in³) |
| Magnetism | Magnetic |
What Are the Common Forms of 4140 Steel?
4140 alloy steel is available in several forms, each suited to specific applications:
- Sheets: Typically 1 to 10 mm thick, 4140 alloy steel sheets are used for flat sheet cut parts.
- Cold Drawn: Cold-drawn bars, available in round, flat, or square shapes, are treated to form a ductile, softer pearlite microstructure.
- Annealed: The most common form, annealed 4140 steel is cold-formed into bars or plates for enhanced flexibility.
- Plates: Commonly 20–120 mm thick, though they can be up to 300 mm, 4140 plates are often annealed, polished, and coated for various applications.
- Hot Rolled: Round, flat, hex, and square bars often come in hot-rolled form, with a different surface finish and generally lower strength than cold-rolled steel.
- Bars: Available in flat, square, or round cross sections, with square and round bars being the most common, ranging from 6 mm to 120 mm. These are often used for CNC machined parts.
What Are the Equivalent Steels to 4140?
4140 steel, known for its high strength and versatility, is recognized under different names across various global standards:
- China: GB/T 3077, equivalent to 42CrMo
- USA: ASTM A29, standard for 4140
- Japan: JIS G4105, equivalent to SCM440
- Great Britain: BS 970, equivalent to 42CrMo4
- Germany: DIN 17200, equivalent to 1.7225 or 42crmo4
These equivalents are used in different regions to match the properties and applications of 4140 steel.
What is 4140 Steel Standard?
4140 steel is governed by several international standards that ensure its quality and performance. Key standards include:
| Standard | Description |
|---|---|
| ASTM A29 | Specifies requirements for general steel bars, including 4140. |
| SAE J404 | Provides chemical composition and mechanical properties for carbon and alloy steels, including 4140. |
| AISI 4140 | Designation by the American Iron and Steel Institute for 4140 steel. |
| DIN 1.7225 | European standard equivalent to 4140, widely used in Europe. |
These standards outline the necessary composition, heat treatment, and mechanical properties for 4140 steel, ensuring it meets industry requirements.
What is 4140 Steel Used For?
4140 steel is widely used in industries like automotive, aerospace, oil and gas, and heavy machinery. Some of the common applications include:
Automotive Parts
In the automotive industry, 4140 steel is used for manufacturing high-strength components such as drive shafts, axles, and crankshafts. Its durability makes it ideal for parts that need to withstand significant stress and wear.
Machinery Components
4140 steel is often used in machinery for parts like gears, spindles, and structural components that require high strength and resistance to impact and fatigue.
Oil and Gas Industry
Components such as drill collars, downhole tools, and other high-stress parts are made from 4140 steel due to its excellent toughness and resistance to harsh operating conditions.
Tooling and Dies
The steel’s hardness and wear resistance make it suitable for tooling applications, including forging dies, mold bases, and cutting tools.
Aerospace
In aerospace, 4140 steel is utilized in parts that require a balance of strength, toughness, and weight. Components such as landing gear and structural supports benefit from the steel’s ability to maintain performance under high stress.
Advantages and Disadvantages of 4140 Steel
| Advantages | Disadvantages |
|---|---|
| High strength | Higher cost |
| Good toughness | Welding difficulties |
| Excellent wear resistance | Limited corrosion resistance |
| Heat treatable | Hardness variability |
| Versatile | Machining challenges |
| Good machinability in certain conditions | Thermal sensitivity |
What Temperature is 4140 Normalized At?
Normalizing 4140 steel at 1600°F (870°C) enhances its mechanical properties by refining the grain structure and relieving internal stresses. This process improves the steel’s strength, toughness, and machinability while providing a more uniform microstructure.
4140 Steel vs Tempering Temperature
4140 steel hardens in a temperature range of 1525° to 1625° F (830° to 885° C) and is typically quenched in oil. The mechanical properties of 4140 steel can be significantly adjusted by tempering it at temperatures ranging from 400° to 1300° F (200° to 705° C).
4140 Steel Annealed at 1600°F Properties and Oil Quenching
When 4140 steel is annealed at 1600°F (871°C), it undergoes a process that softens the material, making it easier to machine and work with. After annealing, if the steel is oil quenched, it is rapidly cooled to harden the steel.
Does 4140 Steel Rust?
Yes, 4140 steel can rust. Although it’s a low-alloy steel with good hardness and strength, it is still susceptible to corrosion because it contains iron, which is prone to rust when exposed to moisture and oxygen.
To mitigate rusting, 4140 steel can be coated with protective finishes, such as plating or painting, or treated with rust inhibitors.
Is 4140 Stainless Steel?
No, 4140 is not stainless steel. It is an alloy steel, specifically a low-alloy steel, which means it contains iron along with small amounts of carbon, chromium, and molybdenum.
4140 vs 4130 Steel
4140 steel generally offers higher tensile and yield strength compared to 4130 steel, making it more suitable for high-stress applications. When hardened and tempered, 4140 steel has a hardness range of 28 to 32 HRC. In contrast, 4130 steel has lower tensile and yield strength.
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Conclusion
4140 steel is a reliable and versatile alloy steel that’s been a staple in various industries for decades. Its balance of strength, toughness, and wear resistance, combined with its ability to be heat treated to specific requirements, makes it a preferred material for a wide range of applications. Whether you’re manufacturing gears, tooling, or critical oil and gas components, 4140 steel is a solid choice that delivers performance and durability.
FAQ
4140 steel is widely used for manufacturing high-stress components due to its excellent strength and durability. Its robust properties make it ideal for applications requiring high resistance to wear and impact.
Yes, 4140 steel is harder than mild steel. While mild steel typically has a hardness of around 120-180 Brinell, 4140 steel can achieve hardness levels of 28-32 HRC when hardened and tempered.
To weld 4140 steel, use low hydrogen rods such as E7018 or E8018. These rods are preferred because they help minimize hydrogen-induced cracking and provide good weld quality.
Catalog: Materials Guide
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
