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4140 vs 4340-which one is better for your project ?

Author: Yaozu Deng
Published on: 2023-08-23

Steel, the backbone of modern construction and manufacturing, has an array of compositions, each tailored for specific applications. In our pursuit to identify the best materials for any given project, we often find ourselves entangled in the intricate web of comparisons. Among these numerous face-offs, the one between 4140 and 4340 steel stands out. Both are revered for their strength and versatility, yet subtle nuances distinguish them.

This article aims to dissect the properties, applications, and characteristics of these two alloys, unraveling the tapestry of their similarities and disparities.


Understanding the Basics: What are 4140 and 4340 Steel?

4140 Vs 4340 steel

Both 4140 and 4340 steels are part of the vast family of alloy steels, distinguished by the specific elements they are alloyed with and their respective amounts. These alloying elements impact everything from the steel’s weldability and hardenability to its strength and resistance to wear.

Basics of 4140 Steel

4140 steel, colloquially known as “chromoly” steel, is a blend of chromium and molybdenum alloyed with iron, resulting in a material that boasts significant strength and resilience. The naming convention here is quite logical – “chrom” denotes the presence of chromium, while “moly” points to molybdenum.

Table: Chemical Composition of 4140 Steel

Element Percentage
Carbon 0.38-0.43%
Chromium 0.8-1.1%
Molybdenum 0.15-0.25%
Manganese 0.75-1.00%
Silicon 0.15-0.30%
Phosphorus Max 0.035%
Sulfur Max 0.040%

With its components, 4140 steel is designed to offer a balance between toughness, wear resistance, and strength. It’s steel commonly used in applications that require higher tensile strength. Additionally, it can be tempered and hardened to customize the properties.


Basics of 4340 Steel

4340 steel stands in its own league, being nickel-chromium-molybdenum alloy steel. This steel is recognized for its superior toughness, especially when in heat-treated conditions. The presence of nickel introduces a level of deep hardening, ensuring that the steel remains robust even when worked extensively.

Table: Chemical Composition of 4340 Steel

Element Percentage
Carbon 0.38-0.43%
Chromium 0.7-0.9%
Nickel 1.65-2.00%
Molybdenum 0.20-0.30%
Manganese 0.60-0.80%
Silicon 0.15-0.35%
Phosphorus Max 0.035%
Sulfur Max 0.040%


4140 Steel Properties – A Deep Dive

4140 steel, with its unique blend of elements, has created a niche for itself in various industries. Understanding its properties is key to recognizing why it’s revered and where its strengths lie.

1. Physical Properties

The inherent features of 4140 steel, which are a result of its composition, can be observed even before it’s subjected to any external forces or treatments.

Table: Basic Physical Properties of 4140 Steel

Property Value
Density 7.85 g/cm^3
Melting Point 1416°C (2580°F)
Thermal Conductivity 42.6 W/m·K
Coefficient of Expansion 12.3 µm/m°C

The density gives us an idea about the compactness of the material, while the melting point provides insights into its heat resistance capabilities.

2. Mechanical Properties

These properties depict how the material behaves under applied forces or in specific conditions.

Table: Key Mechanical Properties of 4140 Steel

Property Value
Tensile Strength 655 MPa
Yield Strength 415 MPa
Modulus of Elasticity 205 GPa
Hardness (Brinell) 197 HB
Impact (Izod) 54 J

The tensile strength indicates the steel’s resistance to being pulled apart, while yielding strength points to the force it can withstand without permanent deformation.

3. Applications based on Properties

Given the comprehensive physical and mechanical properties, the high tensile and yield strength make 4140 ideal for heavy-duty machinery parts. Its hardness ensures longevity and resistance to wear, marking it apt for tools. Furthermore, the combination of strength and toughness makes it suitable for structural purposes.


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4340 Steel Properties – A Comprehensive Analysis

When we shift our focus to 4340 steel, we’re met with a material that exhibits a different set of characteristics. The presence of nickel, coupled with chromium and molybdenum, imparts this steel with attributes that are sought after in high-stress applications.

1. Physical Properties

Delving into the basic physical properties of 4340 steel provides insights into its inherent nature.

Table: Basic Physical Properties of 4340 Steel

Property Value
Density 7.85 g/cm^3
Melting Point 1425°C (2597°F)
Thermal Conductivity 44.5 W/m·K
Coefficient of Expansion 12.5 µm/m°C

2. Mechanical Properties

The mechanical properties of 4340 steel underline its resilience and strength.

Table: Key Mechanical Properties of 4340 Steel

Property Value
Tensile Strength 745 MPa
Yield Strength 470 MPa
Modulus of Elasticity 210 GPa
Hardness (Brinell) 217 HB
Impact (Izod) 61 J

3. Applications rooted in Properties

4340 steel’s mechanical and physical properties make it an ideal choice for several high-stress applications, including aerospace components, heavy-duty shafts, and gears and crankshafts. Its high tensile strength makes it a prime choice for aerospace applications, while its ability to withstand stress makes it perfect for heavy-load shafts. The combination of strength, toughness, and heat resistance marks it suitable for vital components such as gears and crankshafts.


Key Applications: Where are 4140 and 4340 Steel Used?

Both 4140 and 4340 steels have carved out significant roles in numerous industries, primarily due to their stellar mechanical and physical properties. By understanding where these materials are employed, we get a holistic view of their indispensability and the confidence industries place in their characteristics.

4140 Steel Applications

Various parts that made with 4140 steel

Various applications of 4140 steel

As discussed earlier, 4140 steel’s unique balance of strength, hardness, and wear resistance, while being relatively easy to machine, makes it an ideal choice for several applications.

Table: Detailed Applications of 4140 Steel

Category Component Rationale
Machinery Parts & Components Bearings Often used to make large and medium-sized bearings due to its high fatigue strength; sustains heavy loads.
  Spindles Suitable for spindles in machinery because of its high torsional strength; key for rotational components.
  Cylinder Rods Used in hydraulic cylinder rods for its wear resistance.
Structural Uses Frames & Foundations Resilience and strength make it ideal for structural frames and foundations in construction.
  Studs & Bolts Commonly heat-treated and used for high-strength bolts and studs.
  Connection Rods Valued in machines and engines where components need robust integration and resistance to stress.
Tools & Dies Punches Hardness post heat-treatment makes it a material of choice.
  Cutters Preferred for its hardness after heat-treatment.
  Drill Jigs Chosen for its post heat-treatment hardness.
  Gauges Hardness post heat-treatment is beneficial.
Other Notable Applications Firearm Receivers Its malleability combined with strength is preferred for firearm receivers.
  Couplings & Joints In machinery, it’s used where seamless integration is necessary; its tensile strength is a major advantage.

The Applications of 4340 Steel

Custom 4340 steel part

The properties of 4340 steel – especially its strength and deep hardening – makes it stand out for high-stress applications.

Table: Applications of 4340 Steel Across Various Industries

Industry Component/Application Rationale
Aerospace & Aviation Landing Gear 4340 steel’s ability to withstand tremendous stress upon landing makes it a prime choice.
  Axles Apt for aircraft axles due to its resilience to torsional stress.
  Engine Components Used for parts like connecting rods which need to be strong and tough.
Automotive Axles and Shafts Preferred for shafts and axles in automobiles, especially high-performance ones, for its ability to withstand high stress.
  Gears Wear resistance and strength of 4340 steel make it ideal for gears, especially in racing cars.
Energy Sector Drilling Equipment Strength and toughness make it ideal for components like drill bits.
  Oil Extraction Tools The steel’s resistance to wear and tear is crucial for tools used in the extraction of oil and gas in potentially corrosive environments.
Military & Defense Armor Plating Resilience of 4340 steel makes it suitable for armor plates, ensuring paramount protection.
  Weapon Components Critical nature of defense requires consistent performance, making 4340 steel a choice for weapon components, similar to its use in aerospace.


4340 vs 4140 Steel – The Showdown

When it comes to choosing an alloy for a particular application, the decision often boils down to comparing the properties and advantages of available materials. In the realm of steel alloys, 4340 and 4140 are two contenders that often find themselves in a face-off due to their popularity and versatility. Let’s compare these two steel grades in depth.

Chemical Composition

Understanding the chemical makeup of these two steels is crucial as it underpins many of their characteristics.

Table: Chemical Composition of 4140 and 4340 Steel

Element 4140 Steel (Percentage) 4340 Steel (Percentage)
Carbon (C) 0.38 – 0.43% 0.38 – 0.43%
Manganese (Mn) 0.75 – 1.00% 0.60 – 0.80%
Silicon (Si) 0.15 – 0.35% 0.15 – 0.35%
Chromium (Cr) 0.80 – 1.10% 0.70 – 0.90%
Molybdenum (Mo) 0.15 – 0.25% 0.20 – 0.30%
Nickel (Ni) 1.65 – 2.00%

It’s evident that the primary difference lies in the nickel content found in 4340 steel, which greatly enhances its toughness.

Mechanical Properties

Mechanical properties are pivotal when choosing a steel alloy for specific applications. Factors like tensile strength, yield strength, and elongation determine how a material will behave under stress.

Table: Mechanical Properties of 4140 and 4340 Steel

Property 4140 Steel 4340 Steel
Tensile Strength 655 MPa 745 MPa
Yield Strength 415 MPa 470 MPa
Elongation at Break 25.7% 22.3%
Hardness (Brinell) 197 217

From the above table, it’s evident that 4340 steel typically possesses a higher tensile and yield strength compared to 4140. However, 4140 has a slightly better elongation at break.

Heat Treatment and Hardening

Both steels are amenable to heat treatment, which significantly influences their final properties.

  • 4140 Steel: Responds well to annealing, hardening, and tempering. Post-quenching, it’s hardened to achieve certain mechanical properties, then tempered to reduce brittleness.
  • 4340 Steel: Known for its deep hardenability due to nickel content. It can be heat-treated, hardened, and tempered in thicker sections without losing properties.

Other Comparison Aspects

Other aspects to consider when comparing 4140 and 4340 steel include weldability, individual applications, and budget constraints. Weldability is a critical factor for those intending to weld these steels. While we have already explored the individual applications of these steels, it is useful to compare them side by side. Lastly, budget constraints are always important to consider, as 4340 steel is typically more expensive due to its superior properties and nickel content.

Table: Comparative Analysis of 4140 and 4340 Steel

Attributes/Properties 4140 steel 4340 steel
Weldability Offers good weldability. Preheating is advised to avoid cracking. More challenging due to nickel content. Preheat and post-heat are essential for a strong weld.
Applications Axles, bolts, hydraulic shafts, tool holders. Known for toughness & wear resistance. Preferred in aircraft landing gears, axles, and high-performance auto systems for strength & hardenability.
Cost Factor More affordable & widely available. Typically more expensive due to superior properties and nickel content.


Machinability: Which Steel is Easier to Work With?

CNC turning process

metalworking industry. cutting tool making metal worm shaft at machining center

Steel CNC machining

In industrial applications, the ease of machining a material determines productivity, quality of the finished product, and the tool wear rate. Both 4140 and 4340 steels are often the materials of choice for various industries, but their machinability can differ based on their properties and compositions.

Machinability refers to the ease with which a material can be cut. It’s often gauged by factors such as surface finish, tool wear rate, and cutting speed.

  • Surface Finish: The final appearance and smoothness of the machined surface.
  • Tool Wear Rate: The rate at which the machining tool degrades. A lower wear rate means the material is more machine-friendly.
  • Cutting Speed: The speed at which the material can be machined without compromising the tool or the quality of the finish.

Table: Machinability Comparison of 4140 and 4340 Steel

Factors 4140 Steel 4340 Steel
Cutting Process Suitable for conventional and high-speed cutting. More challenging, especially when hardened.
Tool Wear Moderate wear. Higher wear due to nickel content. Carbide tools recommended.
Surface Finish Typically smooth with right tools & parameters. Requires precise machining parameters and tool choice for a smooth finish


Heat Treatment and Hardening Comparison

Heat treatment significantly influences the final properties of steel alloys. Both 4140 and 4340 steels are amenable to various heat treatments, which can modify their hardness, ductility, and strength.

Heat treatment involves heating and cooling a material under controlled conditions to achieve desired mechanical properties. The primary heat treatments are:

  • Annealing: Softens steel and improves its ductility.
  • Quenching: Hardens steel by cooling it rapidly.
  • Tempering: Reduces brittleness in quenched steel by reheating it to a specific temperature and then cooling it.

Table: Heat Treatment Processes for 4140 and 4340 Steel

Treatment Process 4140 steel 4340 steel
Annealing Heat to 830-850°C, hold for uniform temperature, cool in furnace. Heat to 800-850°C, and cool in the furnace.
Hardening Heat to 830-850°C, quench in oil or water to increase hardness and strength. Heat to 830-860°C, quench in oil or water. Nickel ensures hardening in thick sections.
Tempering Heat between 450-700°C based on desired hardness, then cool. Heat between 540-680°C for optimal balance of toughness and hardness, then cool.


Prolean’s Steel Machining Services: Ensuring the Precision

Prolean, as a pioneer in the industry, has developed a reputation for delivering top-notch steel machining services. Our expertise extends beyond mere manufacturing, as we integrate advanced technologies and expert methodologies to ensure that each product is of the highest quality.

Advanced Machining Techniques

Prolean employs state-of-the-art machinery that is capable of handling both 4140 and 4340 steel. With computer-aided design (CAD) and computer-aided manufacturing (CAM) systems, we ensure precision in every cut, drill, and weld, resulting in parts that are both functional and durable.

Custom Solutions

Understanding that every client has unique requirements, we offer tailored solutions. Whether it’s a specific design, finish, or heat treatment, our team collaborates closely with clients to bring the visions to reality.

Quality Assurance

Quality is not just a buzzword at Prolean; it’s a guarantee. Our rigorous quality control processes, combined with regular audits and inspections, ensure that every product that leaves our facility meets the highest industry standards.



In the world of metallurgy, both 4140 and 4340 steel hold prominent positions due to their unique properties and wide range of applications. Whether it’s the automotive, aerospace, or construction industry, these steels have proven to be indispensable. While they share similarities, the distinct differences between them make each type suitable for specific applications.

Prolean’s Steel Machining Services further accentuates the importance of selecting the right steel and ensuring that it’s processed with precision and care, guaranteeing products that are both reliable and long-lasting.



What are the main differences between 4140 and 4340 steel?

The primary differences lie in their composition and properties. 4140 is a medium-carbon alloy, while 4340 has high nickel content, affecting their heat treatment responses and applications.

Which industries predominantly use 4340 steel?

Aerospace, automotive, energy, and defense sectors predominantly use 4340 steel due to its high strength and deep hardenability.

How does Prolean ensure the quality of its machined products?

Prolean employs advanced machinery, CAD/CAM systems, rigorous quality control processes, and regular audits to ensure top-quality products.

Can 4140 steel be used for aerospace applications?

While 4140 steel is versatile and has various applications, 4340 steel is often preferred in aerospace due to its superior strength and deep hardenability.

Why is heat treatment essential for these steels?

Heat treatment processes like annealing, hardening, and tempering modify the properties of steel, enhancing its strength, hardness, or ductility, depending on the application’s requirement.

Does Prolean offer customized machining solutions?

Yes, Prolean provides tailored solutions, collaborating closely with clients to meet specific design, finish, or heat treatment requirements.


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