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# Understanding the Differences: 4140 vs 4150 Steel

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Understanding the Differences: 4140 vs 4150 Steel

- [February 19, 2025](https://etcnmachining.com/blog/2025/02/19/)
- 1:30 am
- [Dd](https://etcnmachining.com/author/dd/)

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![Understanding the Differences: 4140 vs 4150 Steel](https://etcnmachining.com/wp-content/uploads/2025/02/1.6-2.png)

Having the right alloy steel and comparing its various grades can heavily influence the performance, durability, and cost-effectiveness of an industrial steel application. The two steel grades that are probably the most interchanged are the two very adaptive grades called **4140 and 4150 stee**l. They are both known for their remarkable strength, hardness, and resistance to wear. But what really makes them different? This article illustrates the distinct features, usages, and performance data of 4140 and 4150 steel so that you can make more objective decisions according to your industrial needs. If you belong to the construction, manufacturing, or engineering industry, this guide underscores the debate surrounding these alloys at the center of [material selection](https://etcnmachining.com/blog/injection-molding-materials/) controversies.

## What is the Chemical Composition of 4140 and 4150?

![What is the Chemical Composition of 4140 and 4150?](https://etcnmachining.com/wp-content/uploads/2025/02/1.1-1.png)

The primary distinction between these alloys is best illustrated in their chemical composition. In this case, the difference between carbon content, which affects strength and hardness within 4140 and 4150 steels, stands out. The two remaining elements that greatly impact the designation as low-alloy steels have also been identified.

**4140 Steel:**

- **Carbon:** 0.38–0.43%.
- **Chromium:** 0.80–1.10%.
- **Manganese:** 0.75–1.00%.
- **Molybdenum:** 0.15–0.25%.
- **Phosphorus and Sulfur:** ≤0.035% (each).

**4150 Steel:**

- **Carbon:** 0.48–0.53%.
- **Chromium:** 0.80–1.10%.
- **Manganese:** 0.75–1.00%.
- **Molybdenum:** 0.15–0.25%.
- **Phosphorus and Sulfur:** ≤0.035% (each).

These two alloys differ particularly by carbon content, which has been observed to be higher in 4150 than in 4140. This makes 4150 more appropriate for challenging applications due to greater hardness and strength. 4140, on the other hand, is more machinable and tough. Alloys’ chromium and molybdenum content uniformity greatly increases resistance to wear and corrosion and this is true for both alloys.

### Exploring 4140 Steel Composition and Properties

4140 steel is a type of chromium-molybdenum [alloy steel](https://etcnmachining.com/blog/alloy-steel/) known for its outstanding strength, toughness, and durability. Its constituent components are well-balanced, thus giving it remarkable mechanical attributes. The typical chemical composition of 4140 steel is approximately:

- **Carbon:** 0.38-0.43%.
- **Chromium:** 0.8-1.1%.
- **Molybdenum:** 0.15 – 0.25%.
- **Manganese:** 0.75 – 1.0%.
- **Silicon:** 0.15-0.30%.
- **Sulfur and Phosphorus:**≤0.035% (each).

**Properties and Applications**

The medium carbon content in 4140 gives it an outstanding balance of strength and toughness. The tensile strength of this steel in the annealed state is approximately 655-980 MPa (95-142 ksi), and with heat treatment, it can reach even higher levels. Its hardness at around 197 HBW (Brinell Hardness) in the annealed state can exceed 500 HBW in the quenched and tempered state.

One of the key advantages of 4140 steel is that it is easily altered with heat treatment. It offers high mechanical property enhancement from quenching and tempering. Because of its high versatility, it is used in making components such as gears, axles, crankshafts, and parts that are under heavy loads in machines. In addition, being highly resistant to wear and abrasion contributes to its ability to withstand high-load applications.

**Machinability and Weldability**

Even though 4140 steel is superbly workable, its machinability score is only 65% when compared to AISI 1112 steel, which is considered the standard at 100%. For high-precision machining, a pre-hardening procedure is advised. It has a moderate rating for weldability, and in order to avoid cracking from residual stress, some degree of preheating and post-weld treatment is usually necessary.

For these reasons, 4140 steel is particularly useful for aerospace, automotive, and heavy machinery industries where strength and reliability are paramount.

### Breaking Down 4150 Steel Elements

[Alloy steel](https://etcnmachining.com/blog/alloy-vs-stainless-steel/) 4150 is well known for its capability to withstand high levels of stress and for its strength. Its composition is about 0.48 to 0.55 percent carbon, which increases hardness and wear resistance. In addition, it contains 0.75 to 1.00 chrome, which helps prevent rust and improves hardenability, and 0.70 to 0.90 manganese, which improves toughness and tensile strength. Also, a small percentage of silicon is added, between 0.15 and 0.35, to help increase strength while maintaining flexibility. Phosphorus and sulfur, which help machinability and structural integrity, are usually capped at 0.025 percent. 4150 steel is known to be used in demanding applications, particularly firearm components, shafts, and [machine parts](https://etcnmachining.com/blog/brushing/), due to these carefully balanced components.

### How Does Carbon Content Affect Performance?

While the mechanical properties of steel depend on numerous factors, its carbon content is notably detrimental. Elevated carbon content tends to increase hardness and tensile strength as a result of martensite formation during heat treatment. Steel 4150, with its carbon percentage of 0.4%-0.6%, is renowned for exceptional strength and malleability, making it ideal for gears and shafts that undergo high wear. Yet too much carbon, in excess of 0.8%, creates brittle steel that has low toughness and impact resistance.

The number and studies of materials have suggested, too, that steels with 0.4 – 0.6 percent [carbon are much more difficult to machine and weld when compared to lower carbon steels](https://etcnmachining.com/blog/alloy-steel-and-carbon-steel/). On the other hand, low-carbon steels, those with less than 0.25 percent carbon, are easy to machine and weld but lack these extremely low-weight traits. In this sense, carbon content plays a decisive role in the [steel alloy’s performance](https://etcnmachining.com/blog/4150-alloy-steel/) characteristics.

## What are the Key Differences between 4140 and 4150 Steel?

![What are the Key Differences between 4140 and 4150 Steel?](https://etcnmachining.com/wp-content/uploads/2025/02/1.2-1.png)

### The Primary Difference between 4140 and 4150

The main differentiation of both steels 4140 and 4150 is attributed to their mechanical properties and relevancy, an issue that directly stems from their carbon concentration. The carbon content of 4140 steel is about 0.38%-0.43%, whereas that of 4150 steel has a higher percentage of 0.48%-0.53%. Such differences make different alloys appropriate for distinct engineering and [industrial applications](https://etcnmachining.com/blog/galvanneal-steel/) due to the variations of carbon concentration changing the hardness, tensile strength, and wear resistance.

4140 steel has a very good ratio of strength, toughness, and machinability, making it highly useful in moderate to higher-strength applications needing good ductility, such as structural parts, gears, and crankshafts. The lower carbon content makes machining, welding, and general work easier to do. This can be favorable for parts needing to be precisely manufactured but not so overly hardened that they require excessive machining.

The greater carbon ratio in 4150 steel increases its hardness, making it more difficult to machine using standard methods. This steel is also known for its superior hardenability and increases in tensile strength, making it exceptionally suited for applications in heavy-duty tools, military filed equipment, firearm barrels, and other tools needing extreme heat and wear resistance. The increase in hardness of 4140 steel does reduce machinability, making 4150 harder to work with, thus needing specialized techniques and tools to manufacture the steel.

While making a comparison based on their mechanical performance, it is noted that after heating, the tensile strengths for 4140 are typically in the range of 655-930 MPa (megapascals), with 4150 able to achieve strengths of 760-1080 MPa. Also, with the higher carbon content of 4150, there is a marked improvement of the Rockwell hardness values post-treatment, which is often higher than 4140. Ultimately, the decision for these steel grades rests on the particular details of an application, such as the strength, toughness, machinability, and wear resistance needed. The right choice and treatment of the alloy are key to achieving the best functioning of the product.

### Comparing Mechanical Properties

When analyzing the properties of 4140 and 4150 steel, particular focus must be paid to the tensile strength, [yield strength](https://etcnmachining.com/blog/yield-strength-in-steel/), hardness, and ductility of both options in question to achieve the optimal choice for a specific application.

For the 4140 steel option, the yield strength is identified to fall within the range of 415 to 895 MPa, while the tensile strength appears to change depending on the heat treatment that gets applied, which ranges from 655 to around 1080 MPa. For its Rockwell hardness, while in a normalized or annealed state, it generally measures around 10-30 HRC. However, post-heat treatment can significantly increase up to 35 to 50 HRC. The overall composition offers good strength along with moderate machinability which makes it useful for components such as shafts, gears, and other high-stress [machine parts](https://etcnmachining.com/blog/precision-machining-parts/).

The 4150 steel option offers higher carbon content, resulting in stronger and harder materials. The tensile strength of this steel option is estimated to range between 760-1250 MPa after heat treatment, while the yield strength spans around 565-1100 Mpa. Further, 4150 also sees an increase in Rockwell hardness, which post-treatment typically falls between 50-60 HRC, increasing the wear resistance, which decreases with time. This makes 4150 preferable for heavy-duty applications.

Both alloys show strong fatigue resistance, but the extra carbon in 4150 improves wear resistance and edge retention in tough environments. Unfortunately, this increase in hardness leads to a reduction in machinability compared to 4140. For that reason, the choice of these alloys must follow a careful evaluation of the project’s design requirements, expected mechanical properties, and possible post-processing needs.

### Understanding Strength and Toughness

Strength and toughness are two key mechanical properties of a material that should be analyzed individually. The term strength is associated with a material’s capability to resist an external force without undergoing any deformation or failure. Usually, it is expressed in terms of yield strength, tensile strength, and compressive strength. Toughness refers to how much energy a material can absorb before it fractures and may further be illustrated as the resistance of the material to breaking under impact or stress. Tough materials can absorb energy and tend to crack rather than break, while strong materials can withstand significant loads. Both characteristics are important for any structure or machine that is intended to be reliable and durable; however, the appropriate balance between strength and toughness is customized depending on the requirements of a certain project.

## How Does the Carbon Content Vary in 4140 vs 4150?

![How Does the Carbon Content Vary in 4140 vs 4150?](https://etcnmachining.com/wp-content/uploads/2025/02/1.3-1.png)

### The Impact of Higher Carbon Content in 4150

The key distinction between 4140 and 4150 steel is the carbon content: 0.38-0.43% for 4140 and around 0.48-0.55% for 4150, whose presence greatly affects their mechanical properties and applications. The higher carbon content of 4150 steel makes it tougher and more durable. As a result, it can be used in more demanding applications like heavy-duty shafts, high-impact tools, and firearms, which tend to experience much greater wear and tear over time.

The increased brittleness due to high carbon content makes 4150 steel less suitable for applications that require significant deformation as well as high toughness. Moreover, tools employing such steel would require [advanced machinic techniques](https://etcnmachining.com/blog/automotive-injection-molding/) due to this steel’s increased hardness, thus making it less machinable. Standard material specifications show that the tensile strength for 4140 and 4150 sheets of steel are 160,000 and 180,000 pounds per square inch, respectively. At the more extreme needs, 4150 steel would always outperform, which further affirms the significance of carbon percentage in steel.

Engineers must review strength, toughness, wear resistance, and manufacturability as a checklist when choosing the appropriate grade of steel.

### Carbon Content in 4150 Steel vs 4140

The core distinction between 4150 and 4140 steel is their carbon content, which governs the steel’s mechanical properties and best suits its application. Below is a comprehensive outline of each [steel type’s](https://etcnmachining.com/blog/galvanised-steelwork/) carbon content alongside other relevant compositional constituents:

**4150 steel**

- **Carbon Content:** 0.48% to 0.53% (approximate).
- **Chromium Content:** 0.80% to 1.10% (approximate).
- **Manganese Content:** 0.75% to 1.00% (typical).
- **Molybdenum Content:** 0.15% to 0.25%.

**4140 steel**

- **Carbon Content:** 0.38% to 0.43% (approximate).
- **Chromium Content:** 0.80% to 1.10% (approximate).
- **Manganese Content:** 0.75% to 1.00% (typical).
- **Molybdenum Content:** 0.15% to 0.25%.

**Distinction in Carbon Levels**

Greater toughness and a higher carbon content account for the steel’s increased hardness, tensile strength, and wear resistance, making it favorable to high-stressed applications like firearm barrels and heavy-duty machinery components. The lower carbon content in 4140 steel, on the other hand, allows for better weldability and ductility while still being tough enough to make it favorable to shafts, gears, and other moderate-strength and wear-resistant parts.

Knowing these specific compositional differences allows for informed decisions driven toward the mechanical demands, manufacturing considerations, and project particulars of any professional.

## Applications and Use Cases for 4140 and 4150 Steel

![Applications and Use Cases for 4140 and 4150 Steel](https://etcnmachining.com/wp-content/uploads/2025/02/1.4-1.png)

### Why 4140 Steel is Commonly Used

The wide acceptance of 4140 steel is due to its powerful combination of strength, toughness, and ductility. With a lower carbon percentage, it is more weldable and easier to machine, which is ideal for many industries. It is largely used in the production of shafts, gears, bolts, and forgings, where there is a need for moderate strength and the ability to endure wear and tear. Furthermore, its wide availability and versatility make it an economically favorable option for many engineering endeavors.

### When to Use 4150 for Better Performance

Applications that require improved strength, resistance to wear, and durability against fatigue are particularly suited for the use of 4150 steel. As a result of 4150 steel’s higher carbon allowance when compared to 4140 steel, 4150-grade steel is more easily hardened post-heat treatment, making it ideal for demanding environments. Military-grade firearms barrels, components of heavy machinery, and automotive parts are other examples where this steel grade is used, and extreme performance with the ability to endure damages is a must.

The untempered, heat-treated 4150 steel has a tensile strength between 1860 MPa (270,000 psi) and 1560 MPa (226,000 psi) depending on the positioned tempering, which makes it a remarkable choice for parts that experience extensive loads and abrasion. Its ability to endure different temperatures and still maintain structural integrity is valuable in aerospace and defense applications. 4150 steel has lower carbon content than other types of steel, making it easier to weld, but not having the required pre and post-treatment can result in problems, which is why those methods are preferred.

In conclusion, when exposed to severe operational stress, 4150 steel holds up far better than any other option available. Like any other solution engineered for better performance and durability, it comes with a price, but those drawbacks should be overlooked in exchange for the exceptional results in performance the intended application can expect from it.

### Typical Steel Barrels and Shafts

Barrels and Shafts are often manufactured from alloys of high-strength steel like 4150 because of their remarkable toughness and abrasion resistance. Such components are used in sectors that require accuracy and dependability, like automotive, aerospace, and precision manufacturing. The material also has the capability to endure high amounts of stress and perform while being exposed to extreme thermal changes, which makes it ideal for firearms barrels or heavy machinery shafts. These components undergo specific machining and heat treatment processes so that they fulfill the criteria of their intended use.

## How to Identify and Sort 4140 vs 4150 Steel?

![How to Identify and Sort 4140 vs 4150 Steel?](https://etcnmachining.com/wp-content/uploads/2025/02/1.5-1.png)

### Methods for Sorting and Identification

For specific uses, the proper method of 4140 and 4150 steel differentiation must be implemented in order to work with the correct material. The sorting and identification methods are provided below:

**Chemical Analysis (Spectrometry)**

- The chemical makeup of the steel can be measured accurately with the usage of a spectrometer.
- 4140 steel usually has 0.38-0.43% of carbon, whereas 4150 has 0.48-0.53% of carbon.
- It is very accurate, but it involves specialized implements and skilled personnel.

**Hardness Testing**

- Various methods, such as the Rockwell or Brinell hardness testing, provide a good way of finding out the heat treatment and carbon content of the steel.
- For the most part, 4150 steel is harder due to having more carbon.

**Visual Inspection and Documentation **

- [Alloy steels](https://etcnmachining.com/blog/52100-alloy-steel/) generally have stamped or engraved identifications. Check with the manufacturer’s markings and the documents provided.
- Mill certifications explain fully what grade of steel has been ordered.

**Magnetic Properties Testing **

- With the aid of complex testing machinery, the differences in the magnetic permeability of both 4140 and 4150 steels should be visible. These steels are magnetic. However, their subtle differences in the magnetic properties may be identified.
- This approach is infrequently used, but it can confirm the theory in certain circumstances.

**Response to Heat Treatment**

- The two steels utilize heat treatment differently. In order to determine the make-up of the sample, it can be heated to cycles and the properties studied.
- 41050 steel has a higher carbon content, which helps it resist tempering and increases tensile strength.

**Density Measurement**

- Differences in the carbon content of both steels can lead to differences in the density of the two steel types.
- These differences can be observed through precision weight and volume measures which, however, are less precise than chemical methods.

**Micro-Structural Analysis (Metallography)**

- In detail, the microscopic examination of the steel can provide information on the difference in the carbide morphology and its distribution.
- It is possible that 41050 steel contains more carbide than 41040 steel, which is consistent with the larger amount of carbon it has.

**Spark Test**

- The sample is ground until it produces a spark, which is used to identify the steel sample.
- Less exacting and scientific analogy operators can separate 4140 from 4150 by looking at the sparks produced and gauging their length, brightness, and switchbacks.

These techniques are each a little different from one another and are interchangeable depending on the accuracy needed, tools and equipment needed, and expense factors. To get the best and most reliable results for critical applications, you often use two or more methods.

### Examining the Alloy Steel Properties

Alloy steels are widely used due to their strength, toughness, and multi-purpose nature. The primary characteristics are as follows:

**Strength and Hardness**

- The strength and hardness of alloy steels are improved with the presence of chromium, molybdenum, and vanadium. These elements also provide additional resistance to deformation and wear.

**Improved Toughness**

- The toughness of steel is greatly improved with the addition of alloying elements allowing it to better withstand impact and stress without fracturing.

**Corrosion Resistance**

- Some alloy steels can resist corrosion better than other grades. This is especially true in the presence of chromium or nickel, which makes these steels best suited for harsher environments.

**Machinability and Weldability**

- The ability to machine or weld alloy steels varies with their composition, but more often than not, alloy steels are optimized for industrial processes, ensuring efficient fabrication.

These [properties make alloy steels](https://etcnmachining.com/blog/4130-steel-properties/) essential in industries such as construction, automotive, aerospace, and tool manufacturing. Their specific composition and processing determine their suitability for particular applications.

## Frequently Asked Questions (FAQs)

### Q: What are the two major differences between 4140 and 4150 steel?

A: The difference in carbon content is the distinguishing feature between 4140 and 4150 steel. 4150 steel contains higher carbon, “4150 steel has a higher carbon content (0.48-0.53%) “, than 4140 steel which has low carbon, “4140 steel (0.38-0.43%) “. Because of the higher carbon content of 4150 steel, it exhibits greater strength and hardness. On the other hand, 4140 offers a better balance between toughness and strength.

### Q: What is chromoly steel, and how does it relate to 4140 and 4150?

A: Chromoly steel, also referred to as chrome-moly, is a type of steel that has chromium and molybdenum as part of its alloy composition. Considered chromoly steels, both 4140 and 4150 belong to this category. Unlike carbon steels, these alloying components provide added strength, hardness, and resistance to wear alongside other benefits.

### Q: How does the heat treatment process differ for 4140 and 4150 steel?

A: The heat treatment method for both 4140 and 4150 steel is comparable. However, “4150 steel generally requires more precise temperature control due to its higher carbon content. “4150 steel can achieve higher hardness levels through heat treatment.” A point of difference is that 4140 steel offers more flexibility in achieving a balance between toughness and strength, while 4150 steel is more stringent in its requirements.

### Q: Which type of steel, 4140 and 4150, is preferred for making firearms barrels?

A: The 4140 and 4150 steel grades are both used in the making of firearms barrels. However, 4150 steel is preferred when making rifle barrels due to its increased strength and durability. 4140 chromoly is used for less demanding applications or where there is a need for a balance of strength and toughness.

### Q: How do manufacturers determine what type of steel to use for a specific application, either 4140 or 4150?

A: When choosing between 4140 and 4150 steel, manufacturers take into account the required strength, toughness, wear resistance, and heat treatment possibilities. They also look at the specific application, cost, and the desired balance of properties. It is important to comprehend these differences to understand what steel is appropriate for what purpose.

### Q: Is it possible to use 4140 steel in place of 4150 steel for firearms applications?

A: In certain instances, 4140 steel may adequately fulfill the role of 4150 steel in some firearm parts, but it would be inappropriate for more challenging aspects. However, critical components such as A barrels tend to be made from 4150 steel due to its superior strength and durability. The decision made revolves around the different specifications presented by a specific firearm and what it is primarily designed for.

### Q: How does carbon content impact the properties of 4140 and 4150 steel?

A: The carbon content is responsible for the different properties of both types of steel. Unlike 4140, 4150 possesses a higher carbon concentration, which allows for a higher tempering strength. As a minus, it also makes the 4150 steel more brittle. In comparison with 4140, which has a lower carbon content, this steel is tougher impact resistant.

### Q: Are there any advantages to using 4150 Steel over 4140 Steel?

A: Definitely, in some cases, using 4150 steel has its advantages. 4150 sheets of steel are said to be tougher to machine and weld; heat treats are far more demanding and less forgiving, impact resistance and toughness are lower than 4140, and finally, they are more expensive. Therefore, industries and applications that need affordable materials that do not require higher strength or higher toughness can take advantage of their use.

### Q: How do manufacturers measure and verify the carbon content in 4140 and 4150 Steel?

A: Manufacturers have their own ways to check and verify the carbon content of both 4140 and 4150 steel. Some of the common procedures are optical emission spectroscopy, X-ray fluorescence, and combustion analysis. These systems are able to capture the carbon amounts in more than precise ranges for 4140 (0.38-0.43% carbon) or 4150 (0.48-0.53% carbon) qualifiers for steel.

## Reference Sources

**1. The Role of Carbon in Determining Kinetics and Microstructure of Bainite Transformation of 4140/4150 Steels**

- **Author:** Jian Zhu et al.
- **Published in:** European Scientific Journal
- **Published on:** March 31, 2019
- **Citation Token:** [(Zhu et al.2019)](https://www.semanticscholar.org/paper/Effect-of-Carbon-Content-on-Bainite-Transformation-Zhu-Sun/59db1c74a902503f84c78b07d3566850fb4dd7ae?utm_source=api)
- **Summary:**
- In this paper, the author compares the kinetics and microstructural characteristics of bainite transformation for 4140 and 4150 steels, which primarily differ in their carbon content.
- The research was conducted on isothermal transformation processes at different temperature levels, which allowed for the obtaining of four types of bainite phase matrixes: upper-bainite, mixed, upper-lower-bainite, lower-bainite, and martensite plus lower-bainite.
- **Key findings include:**
- Key results are as follows: The transformation temperatures of upper and lower bainite looked different from each other, with higher amounts of carbon having lower times for the bainite transformation reaction.
- Also, the author constructed TTT diagrams and the kinetics plots of bainite volume fraction to isothermal holding time in order to study the relation between the isothermal holding time and the fraction of the phase obtained.
- With increased carbon content, the amount of activation energy needed for the phase transformations increases, which means that these transformations are more difficult to accomplish. The findings help explain how these steels’ mechanical properties depend on the carbon concentration, which will guide potential development for better purposes.

**2. Examination of Mechanical Properties and Heat Treatment Effects on AISI 4140 Steel**

- **Author:** T. Nagaraja
- **Published In:** IOP Conference Series: Materials Science and Engineering
- **Publication Date:** January 7, 2021
- **Citation Token:** [(Nagaraja, 2021)](https://www.semanticscholar.org/paper/Investigation-of-effect-of-mechanical-properties-of-Nagaraja/c8fa374526f9f6a15c35ae89eddb833c5216da73?utm_source=api)
- **Summary:**
- This research examines the mechanical properties of AISI 4140 steel and its response to different heat treatment metrics.
- This study seeks to improve mechanical properties like hardness, yield strength, and resistance to wear through heat treatment processes.
- **Key findings include:**
- Appropriate heat treatment processes can substantially change the mechanical properties of AISI 4140.
- This research utilized comparative studies between different heat treatment processes to find optimal processes to achieve particular mechanical properties.
- These results will guide the heat treatment processes aimed at improving the functional performance of AISI 4140 steel.

**3. [Steel](https://en.wikipedia.org/wiki/Steel)**

**4. [Carbon steel](https://en.wikipedia.org/wiki/Carbon_steel)**

**5. [41xx steel](https://en.wikipedia.org/wiki/41xx_steel)**

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```