Alloy Steel vs Carbon Steel: Understanding the Differences and Their Applications

The manufacturing, industrial, and infrastructural segments heavily depend on steel as a core resource. Yet, a higher grade of steel for every purpose does not exist. The most common forms are alloy steel and carbon steel, both of which differ quite remarkably in many aspects. Understanding these distinctions and their implications on performance in differing conditions is vital for choosing the correct type of steel for each individual project. This article is designed to equip professionals and interested parties with the knowledge necessary to identify the most important distinguishing features of alloy and carbon steel. The differences in these materials head towards their microstructure composition and, ultimately, to their practical application. So why do the differences in these alloys matter in the outcome of your projects? Let’s take a closer look.

What is Alloy Steel?

Alloy steel is steel that has been enhanced by the addition of other elements such as chromium, nickel, manganese, or vanadium. These other elements are included to achieve certain steel characteristics like elevated strength, impressive hardness, enhanced corrosion resistance, and stiffness. The remarkable adaptability of alloy steel’s particular constituents to fulfill relevant desires makes it fully customizable for wished attributes. Because of these qualities, alloy steel can be used in construction, automotive components, and industrial machinery.

What Are the Alloying Elements?

Manganese, chromium, nickel, molybdenum, vanadium, silicon, and boron are all present in alloy steel and are deemed the primary elements of alloying. Every element comes with a particular defined trait written below:

• Strengthening toughness and wear resistance are enhanced by manganese.
• Corrosion resistance, hardness, and durability are improved with the addition of chromium.
• Extreme temperatures, along with added toughness and strength, are resisted due to nickel.
• Increased resistance to heat, along with increased strength and hardness, is caused by molybdenum.
• Overall strength, along with wear resistance, is contributed by vanadium.
• Strength alongside improved magnetic properties is enhanced by silicon.
• Hardenability and resistance to wear are enhanced by boron.

The selection of these elements is done on the basis of the mechanical properties along with the performance requirements of the applications.

How Does Alloy Steel Compare to Carbon Steel?

Like carbon steel, alloy steel also comprises iron and carbon, but its alloying elements in the form of chromium, nickel, molybdenum, and manganese set it apart. Unlike carbon steel, which contains 2.1% carbon by weight, alloy steel can contain up to 1% carbon, giving the steel added elasticity. Although both types are cost-efficient in their own regard, the presence of chromium and nickel in alloy steel raises its cost. The presence of these additional elements in alloy steel enhances its strength and is useful when creating aerospace components or machinery that are exposed to extremely harsh conditions.

Alloy steel has superior toughness, strength, and resistance to wear when compared to carbon steel; for alloys, this can range between 600 and 1200 MPa, while the average for carbon steel stays between 400 to 750 MPa. Although low in strength, the molybdenum present in alloy steel does increase its strength at higher temperatures, making it useful when creating power plant turbines. However, these added benefits come with a price as they increase the complexity of production and require the use of rare elements, making the alloy steel more expensive.

The ability to resist corrosion is another major differentiator. Carbon steel, alloy steel, and stainless steel all have mechanical strength. However, carbon is the least expensive and most susceptible to weakening if not properly maintained. On the other hand, alloy, and ss steel with a chromium percentage exceeding 10% have remarkable oxidation and corrosion resistance and, therefore, must be used when in locations subject to chemicals, moisture, or salt.

Why Choose Alloy Steel?

The selection of alloy steel is primarily for its strength, durability, and resistance to mechanical and chemical wear. The enhancement of these properties makes it specific for use in heavy-duty construction, automotive, and industrial machinery. Moreover, its versatility allows modifications for specific performance requirements which make it dependable and economical across many sectors.

Understanding Carbon Steel: What Makes It Unique?

Types of Carbon Steel

Carbon steel is subdivided according to its carbon level, with every subdivision having unique properties and functions. The main types of carbon steel are:

Low Carbon Steel (Mild Steel)   

• Low-carbon steel is ductile and can be easily worked into various shapes, making it useful in industries where flexibility and weldability are essential. It has carbon levels of less than 0.25%. Low-carbon steel is typically employed in the production of construction materials like structural beams, as well as in automobile body parts. The tensile strength of low-carbon steel typically ranges from 400 to 550 MPa.

Medium Carbon Steel   

• Medium carbon steel has a carbon content ranging from 0.25% to 0.60% and has adequate ductility as well as strength. It is often utilized in mechanical components such as gears, axles, and shafts. This type of steel has moderate wear resistance compared to low-carbon steel, and during post-heat treatment, its tensile strength increases up to 550 to 700 MPa, which is typically achieved after appropriate heat treatment.

High Carbon Steel   

• High carbon steel is the category of steel with the most carbon content with levels ranging from 0.60%-1.25%. It is well known for its strength and hardness but has low ductility. High carbon steel is used to manufacture cutting tools, springs, and wire ropes due to their wear resistance. During machining and welding, precautions have to be taken due to the steel’s brittleness.

Ultra-High Carbon Steel

• With a 1.25% or more carbon content, this type of carbon steel’s strength and hardness are unmatched. This makes it exceptional for use in knives, punches, and industrial tools. The tensile strength of ultra-high carbon steel exceeds 1200 MPa, while its low ductility makes it challenging to use and handle properly.

By classifying carbon steel according to its carbon content, manufacturers and engineers are able to choose the appropriate type for specific application performance requirements with guarantees of reliability and efficiency.

Properties of Carbon Steel

Tensile Strength

• The maximum tensile strength of high-carbon steel is over 1200 MPa, making it exceptionally hard and durable for extreme applications.
• Low-carbon steel is more ductile and easier to work with, having a range of 400 to 550 MPa.

Hardness

• With higher carbon content, the hardness of carbon steels increases as well. For instance, high carbon steel can Brinell range from 200 to 650 HBs and is ideal for wear-resistant tools and components.

Ductility

• Low-carbon steels can be easily ducted without cracking, having an approximate range of 25-40% elongation.
• Medium- and high-carbon steels are less ductile, usually ranging from 5-20%, depending on the treatment.

Thermal Conductivity 

• Carbon steels exhibit moderate thermal conductivity, as is the case with most steel, from 45-65 W/m·K, which influences the rate of heat loss in machinery and during operational use.

Machinability

• Lower carbon steels are easier to machine and are often more desirable for cutting and welding.
• While high-carbon steel is harder, and is more difficult to machine, requiring specialized tools and techniques.

Wear Resistance 

• Older carbon steels are easier to abrade making these steels ideal for parts that undergo constant friction, such as gears and cutting tools.

Corrosion Resistance

• For carbon steel, protection against corrosion is not straightforward, as it does not have any in-built resistance properties. It usually goes through a treatment process, such as galvanization or paint, to coat the carbon steel and prevent rust from forming.

Density

• Carbon steel has a steady and consistent density of approximately 7.85 g/cm³, which is essential in weight-sensitive operations.

Melting Point

• Carbon steel’s average melting point is between 1425-1540°C (2600-2800 °F) which is impacted a little bit by the alloying elements.

Electrical Conductivity

• Carbon steel can most certainly not be used for electric applications, especially the high carbon variants with an electrical conductivity value of around 1.43% of IACS. Copper and aluminum are vastly superior when it comes to electric conduction.

Elastic Modulus

• Carbon steel uses a modulus of elasticity value of around 200 GPa (29,000 ksi) which provides it the necessary stiffness to avoid deformation under a load.

These features provide additional flexibility to carbon steel, making it useful as a component metal as well as allowing it to be modified through alloy or heat treatments and coatings to meet the specific requirement of an application.

When to Use Carbon Steel?

Because of its reasonable cost and helpful in achieving the required strength and reliability, carbon steel is much preferred for many applications. Carbon steel is utilized in structural parts and components, automotive applications, pipelines, and cutting tools, which demand high strength and wear resistance. Due to its stiffness and high modulus of elasticity, it is also suitable for construction, particularly beams and columns in load-bearing structures in bearing frames. However, it should be avoided for application in corroding environments without proper coating or treatment.

Alloy Steel vs Carbon Steel: Which is Stronger?

Understanding Tensile Strength

The term “tensile strength” refers to the greatest degree of tensile stress that a material can carry before fracturing. Due to the incorporation of chromium, nickel, or manganese, alloy steel normally has higher mechanical properties and, therefore, greater tensile strength when compared to carbon steel. As carbon steel does offer some strength, the greater resistance to stress and deformation under load offered by alloy steel gives it the upper hand in the more demanding applications.

How Do Hardness and Durability Compare?

Both hardness and durability stand apart as unique properties, but they each play an inherent role in material selection as well as in engineering applications. Hardness defines the ability of a material to resist deformation, mostly in the form of scratching, indentation, or abrasion. This feature can, in most cases, be captured in quantitative terms such as the Mohs scale, Brinell hardness test (BHN), or Vickers hardness test (VHN), depending on the sort of material and its use.

On the contrary, durability is concerned with a material’s ability to sustain use over a period of time with minimal wear, pressure, or damage. While hardness contributes directly toward one’s ability to endure by resisting external forces aimed at damaging the surface, durability is a broader term and includes corrosion, fatigue, and other forms of environmental stress.

Alloy steel provides an example; it has a significantly higher Brinell hardness number in the range of 200-600BHN, while carbon steel averages 120-200. This makes alloy steel more desirable for use in construction and the automotive industry. On the other hand, stainless steel is known to outperform both in long-term durability when subjected to harsh environmental conditions due to its unparalleled toughness and corrosion resistance. These differences illustrate the need to focus on both hardness and durability depending on the requirements of any given project.

Corrosion Resistance in Alloy vs Carbon Steel

Due to the addition of elements like chromium, nickel, and molybdenum, alloy steel normally showcases better corrosion resistance than carbon steel. These elements help in forming an oxide protective layer around the surface which diminishes the effects of environmental variables like moisture or chemicals. Carbon steel, in contrast, is more susceptible to rust and degradation due to environmental circumstances unless the steel is coated or treated. For purposes that require higher corrosion resistance, alloy steel is generally the more reliable option.

What are the Key Differences Between Alloy and Carbon Steel?

Differences in Chemical Composition

Alloy steel possesses traits that make it stand out due to the presence of additional constituents like chromium, nickel, or molybdenum to name a few. This is in stark contrast with carbon steel, which is composed of iron and carbon, which means that carbon steel has no or very few constituents that combine with alloying elements. These distinctions, both in the ratio of constituents, are the ones that define the difference, which then leads to distinct performance characteristics and the applicability of the alloy steel and some other kinds.

How Manufacturing Processes Differ

The processes involved in the production of alloy steel and carbon steel differ greatly because of the alloy’s chemical compounds and their uses. For alloy steel, other constituent elements such as chromium, nickel, and molybdenum are added in precise amounts while the steel is in liquid form. This step is crucial to achieve the target material attributes, which include greater strength, better resistance to corrosion, and enhanced wear resistance. The purity and homogeneity of the alloying constituents are crucial. These latter methods of deoxygenation of molten steel, vacuum degassing, and argon oxygen decarburization are often necessary in alloy steel production.

Carbon steel, on the other hand, follows a simpler production cycle as it consists mostly of iron and carbon with no significant alloying additives. This makes it cheaper to produce, especially when basic oxygen furnaces or even electric arc furnaces are used. Carbon steel is less costly to produce compared to alloy steel due to the lower complexity of its constituents.

Alloy steel comprises a small share of the global steel production market due to its high production cost, coupled with its specialized application in the aerospace and automotive industries. Carbon steel, which dominates the steel production market, has a wider utility in construction and infrastructure developments. The comparison highlights the differences in the use and availability of both types of steel.

Impacts on Applications of Carbon and Alloy Steel

Applications of Carbon Steel

Civil Construction

• Carbon steel is one of the most commonly used materials in construction. The primary reason for this is that it is strong, cheap, and easy to manufacture. It is the principal material used in structural parts like beams, columns, and frames of buildings and bridges. As per industry estimates, about 50% of the carbon steel made in the world is used in construction.

Infrastructure Development

• Carbon steel is essential for the construction of roads, railways, pipelines, and other infrastructure. Its strength and low cost make it appropriate for massive undertakings where cost and durability are essential. Carbon steel Pipelines, for instance, are said to make up 70% of the total installed pipelines.

Consumer Products

• Carbon steel is also used in making tools and other appliances like kitchen and hardware items. Its ability to serve the applicable needs of residential as well as commercial industries makes it a highly useful product.

Alloy Steel Applications

Automobile Industry

• Alloy steel is commonplace in the automobile industry for the production of gears, engines, axles, chassis, and other pieces of the automobile. With better wear resistance and toughness, it is certainly suited for highly stressed and exposed parts and components. Research indicates that close to 60% of the total demand for alloy steel comes from the automobile industry.

Aerospace and Defense

• Turbine engines, aircraft components, and defense equipment utilize alloy steel due to its superior strength, heat resistance, and precision in engineering. This industry accounts for approximately 20% of the total global alloy steel consumption.

Industrial Machinery

• Alloy steel is greatly needed in the construction of heavy machinery used in the energy, mining, and manufacturing sectors. These include drills, power tools, and turbine components which require the strength and durability of alloy compositions.

Energy Sector

• Offshore drilling platforms, wind turbines, and nuclear reactors are included in the applications of the energy industry that make use of alloy steel. Its strength under extreme operating conditions ensures safety and efficiency for operational purposes, which accounts for about 15% of alloy steel consumption.

The international applications of carbon and alloy steel vividly portray their roles in the economy, which is powered by the functioning of various industries. High-level knowledge of their consequences makes it possible to choose materials economically while still meeting performance goals.

Real-World Applications of Carbon and Alloy Steel

Common Uses of Alloy Steel

Automotive Industry

• Alloy steel is used for the manufacturing of different automotive parts such as gears, crankshafts, and axles due to their strength and resistance to abrasive wear.

Construction

• Bridges and skyscrapers are constructed with alloy steel because they can withstand high levels of stress and are durable, which allows them to function in structural applications.

Aerospace

• Alloy steel is utilized in the production of aircraft parts, such as the landing gear and engine, due to its performance at high temperatures and harsh conditions.

Machinery and Tools

• Alloy steel is employed in the production of industrial tools, cutting devices, and mechanical parts due to its hardness and the ability to endure strenuous usage.

Common Uses of Carbon Steel

Construction and Infrastructure

• Carbon steel is preferred in the construction sector for structural frames, pipelines, and reinforcing bars. The material’s impressive strength-to-weight ratio enables the construction of vise and heavy skyscrapers, bridges, and tunnels. For instance, nearly 60% of steel produced worldwide is allocated for construction and infrastructure indicating its tremendous importance in city development.

Automobile Manufacturing

• Carbon steel is a constituent material for several automotive parts such as body panels, chassis, and safety reinforcements. The low carbon structural variant is particularly favored for being easy to work with, while the higher carbon grade offers better strength and rigidity where it is needed most.

Energy Sector 

• Carbon steel finds application in the energy sector in the construction of oil and gas pipelines, storage tanks, and components of power plants. The carbon steel’s resistance to high pressure and temperature makes it an important material in this industry. Some industrial statistics show that up to 15% of the entire world’s carbon steel demand comes from energy-related ones.

Industrial Equipment 

• Carbon steel is often used in heavy machinery and industrial equipment such as boilers, pressure vessels, and conveyor systems due to the wear resistance of the material and harsh operating conditions. The material’s availability in different grades meets specific property demands in extreme environments.

Household and Consumer Goods

• The manufacturing of kitchen utensils, such as knives, cookware, and other related items, heavily depends on carbon steel, as it is hard and can retain a sharp edge. Also, it is economically used in appliances and furniture due to its strength and low cost. Professional kitchen users, for example, prefer carbon steel knives for their precise cutting ability.

Choosing the Right Steel for Your Project

The choice of steel hinges on the unique needs of your project. First off, determine required mechanical properties like strength, flexibility, or resistance to wear. For example, carbon steel is superb for applications where durability as well as load-bearing capacity are necessary such as construction and industrial equipment. Opt for stainless steel, if the corrosion resistance or visual appeal matters more. In addition, analyze the budget, surrounding environment, and need for maintenance over time. Talking to suppliers or experts in the field can help make sure the steel you choose offers the right performance and cost.

Frequently Asked Questions (FAQs)

Q: What is the primary difference between carbon steel and alloy steel?

A: Carbon steel and alloy steel differ primarily in their composition. Carbon steel primarily consists of iron and carbon with trace amounts of other components, while alloy steel has other additional alloys like chromium, nickel, or molybdenum. The disparity in composition results in differences in the strength, durability, and applicability of the two carbon steels.

Q: Is alloy steel stronger than carbon steel?

A: In general, yes. Alloy steel is typically stronger than carbon steel due to the additional elements within its composition. With these additional components come enhanced mechanical properties such as improvement in strength, hardness, and toughness. However, other factors like the composition and heat treatment of the steel will determine its exact strength. High-alloy steels greatly surpass the strength of plain carbon steel, which makes them ideal for use in applications needing greater strength and durability.

Q: What is the usual utilization of carbon steel?

A: Carbon steel has the ability to be used in an array of applications and systems, which makes it very versatile. It is broadly used in construction activities such as buildings and bridges, as well as making automotive parts, tools, pipelines, and even household appliances. Low-carbon steel is commonly and frequently utilized in general-purpose applications, whereas Medium carbon steel is accepted in the field for machine parts and axles. High carbon steel is widely accepted and is the most useful tool steel due to its hardness, which makes it suitable for tools and cutting equipment.

Q: What are the different categories of alloy steel?

A: Some of the siles of alloy steel due to its composition and traits are: 1. Low-alloy steel – Has minor amounts of alloying materials, usually under 5%. 2. High-alloy steel – Noted for having higher proportions of alloying elements, more than 5%. 3. Stainless steel – An alloyed metallic material that has a minimum of 10.5% chromium for better resistance against corrosion. 4. Tool steel – Intended for pieces utilized in cutting or drilling tools. 5. HSLA (High Strength Low Alloy) steel – Notable due to its durability and formability.

Q: What sets apart low-alloy steel from high-alloy steel?

A: The distinction between low-alloy and high-alloy steel comes with the quantity of added alloying materials. Low-alloy steel has under 5% alloying materials, while high-alloy has over 5% added. Compared to carbon steel, low-alloy steel has enhanced traits without being overly pricey. On the other hand, high-alloy steels such as stainless steel are known for their strength in resisting corrosion alongside the inherent special features utilized in advanced engineering.

Q: What are steel properties influenced by the carbon content?

A: Carbon percentage is a determining factor that impacts the properties of steel. As carbon content increases, the steel becomes harder and stronger but less flexible. Low-carbon steel (less than 0.30% carbon) is soft and ductile, which aids in forming and welding. Medium-carbon steel (0.30 to 0.60 percent of carbon) is strong with some ductility. High-carbon steel (0.60 to 1.00 percent of carbon) is very hard and strong, but because of its low ductility, it is limited to tools and cutting implements.

Q: What alloy is best for the chemical processing equipment?

A: In most cases, alloy steel, specifically stainless steel, is used instead of carbon steel for chemical processing equipment. Stainless steel is a high alloy steel characterized by high corrosion resistance due to the presence of chromium. This allows stainless steel to handle corrosive chemicals while maintaining the purity needed in chemical processes. Different grades of stainless steel can be selected depending on the desired chemical environment and the applicable temperature of the process.

Q: Which is more prevalent in common goods, carbon steel or alloy steel?

A: Common day-to-day items utilize carbon steel because it’s cheaper than alloy steel and more readily available. It is present in numerous household items, construction supplies, and the automobile industry. Nonetheless, alloy steel is gaining popularity in more advanced applications such as sophisticated kitchen knives, aerospace parts, and high-end manufacturing tools. The use of either carbon steel or alloy steel is determined by how strong, durable, and cheap the item needs to be.

Reference Sources

1. An investigation into the wear and friction of oil seals for rubbing with flame-sprayed alloy and ceramic on lower carbon steel

• By: Chao-Ping Huang et al.
• Published in: Solid State Phenomena, Volume 319, Pages 52 – 57.
• Date published: June 14, 2021.
• Abstract:  
• The primary goal of this research is to analyze the influence of sprayed coatings on the surface of oil seals and their corresponding friction and abrasion values. The study also attempts to test the performance of the uncoated AISI 52100 against various anti-wear coating materials.
• Methodology: The authors measured the friction coefficients for five rubber seals against four different coating layers of bearing steel using a block vs. ring tester. The steel was for both wet and dry conditions. The coatings were Ni-Cr-B-Si alloy, Ni-Cr-WC alloy, and ceramics.
• Important discoveries:  
• HNBR rubber has better resistance to wear and reduced friction.
• More brittle materials, such as ceramics, have greater resistance to wear and higher friction due to their hardness.
• The study assessed the performance of coatings and concluded that Ni-Cr-B-Si alloy and ceramic powder were more beneficial than other coatings for surface wear resistance on oil seals(Huang et al., 2021, pp. 52–57).

2. Structure and Hardness of Coatings Wear Resistant Deposited on Low Carbon Steel Vias Low-Frequency Current Modulation.  

• By: Y. Saraev et al.
• Published in: Steel in Translation Volume 50, Pages 387–390
• Publication Date: June 1st, 2020
• Summary:
• The present research is devoted to studying the structure and hardness of wear-resistant coatings applied to low-carbon steel and produced using low-frequency current modulation techniques.
• Methodology: The authors applied a number of metallurgical approaches to studying the microstructure and hardness of the coatings.
• Key Findings: The coatings were proven to enhance the low-carbon steel’s hardness and wear resistance considerably, which indicates their possible use in sectors that deal with robust materials (Saraev et al. 387-390).

3. Efficient Synthesis of 6,7-Dihydro-5H-cyclopenta[b]pyridine-3-carbonitrile compounds and their applicability as inhibitor films for corrosion of steel alloys

• Authors: H. A. Abd El‐Lateef et al.
• Published in: ACS Omega Volume 7 Pages 24727 – 24745
• Publication date: July 8th, 2022
• Summary:
• This work is aimed towards the synthesis of new compounds which has the ability to work as a corrosion protective of steel alloys especially in acidic medium.
• Methodology: The study applied corrosion electrochemical measurements and surface morphology studies to examine the effectiveness of the synthesized compounds as corrosion inhibitors.
• Key findings: The inhibition efficiency of the synthesized compounds was found to be very high, confirming their relevance to corrosion protection of steel alloys (El-Lateef et al. 2022 24727-24745).

4. Carbon steel

5. Alloy steel

6. Steel