Steel is one of the most fundamental and important materials in modern industry, used in various applications and seen in many of the buildings and structures around us every day. According to data from the World Steel Association, global steel production is expected to approach 1.9 billion tons in 2024. Thousands of years ago, humans began exploring how to extract stronger and more durable metals from iron ore. With advancements in metallurgy, steel gradually became a material stronger, tougher, and more versatile than pure iron. At the same time, these advancements led to the development of a variety of steel types.
Among these, two of the most common types are carbon steel and alloy steel. While they may appear similar at first glance, key differences set them apart, making one more suitable than the other for certain applications. We’ll explain more about each type of steel in the following passage, and provide a clear comparison to help you choose the right one.
What Is Alloy Steel?
Alloy steel is primarily composed of iron and carbon, with additional alloying elements such as chromium, nickel, molybdenum, manganese, or vanadium added in varying proportions. These additional elements lend their advantages to the alloy steel, enhancing properties like strength, hardness, corrosion resistance, wear resistance, and toughness.
Depending on whether the total weight percentage of alloying elements is below or above 5%, alloy steel generally falls into two categories: low-alloy steel and high-alloy steel. Low-alloy types are the most commonly used. The alloying elements they commonly include, such as manganese and silicon, primarily enhance structural strength and weldability while maintaining good ductility and machinability. With relatively low production costs, they are popular in general engineering applications.
Besides carbon, manganese, and silicon, high-alloy steel incorporates higher proportions of elements like chromium, nickel, molybdenum, tungsten, and vanadium, along with rare elements such as titanium and niobium. These elements improve properties such as corrosion resistance, high-temperature strength, and wear resistance, making the material essential for demanding engineering scenarios.
Now, let’s take a look at five of the most commonly used elements in alloy steels.
Chromium: A key component in stainless steel and some tool steels. The right amount of chromium can significantly improve corrosion resistance and positively affect hardness and wear resistance.
Nickel: Improves toughness, especially in low-temperature environments. Pure nickel or high-nickel alloys, such as Monel and Inconel, offer excellent corrosion resistance. When combined with chromium, as seen in 304 stainless steel, the corrosion resistance is further enhanced, especially in oxidative environments like humid air or acidic solutions.
Molybdenum: Primarily enhances toughness and strength under high-stress and high-temperature conditions. It also reduces creep, improves resistance to pitting and crevice corrosion. Moreover, it increases the hardenability, allowing for deeper hardening, which is particularly important for large components.
Manganese: Improves hardenability during heat treatment and reduces the likelihood of cracking during the process. Additionally, as a deoxidizer, manganese helps remove oxygen from steel, enhancing its quality and workability.
Vanadium: Vanadium helps control grain growth during heat treatment, ensuring finer grain structures. This enhances material strength while maintaining ductility. Additionally, vanadium significantly improves the high-temperature performance of steels and is commonly used in high-temperature applications such as engine components and heat exchangers.
What Is Carbon Steel?
Carbon steel, as the name suggests, is a type of steel primarily composed of iron mixed with varying concentrations of carbon. Unlike alloy steel, carbon steel contains only trace amounts of other elements such as manganese, silicon, or sulfur. Its properties vary significantly depending on the carbon content, which ranges from very low levels (less than 0.05%) to relatively high levels (up to 2.0%). Generally, the higher the carbon content, the greater the hardness and strength, but it becomes more brittle, with reduced ductility and weldability.
Due to its simple composition, carbon steel is generally easier to produce and more cost-effective than alloy steel. Additionally, it is highly responsive to heat treatment processes, offering great flexibility and can be processed using various manufacturing methods, including those offered by Chiggo, such as CNC machining, sheet cutting, sheet metal fabrication, and welding. As the most important group of engineering alloys, carbon steel accounts for the majority of steel applications in industries ranging from construction to manufacturing.
Carbon steel is typically divided into four categories based on its carbon content:
Low-Carbon Steel (or Mild Steel)
Contains up to 0.3% carbon and is the most common form of carbon steel. It is soft, ductile, and easy to weld. It is widely used in applications such as rebar, automotive and household appliance bodies, steel wires, fences, and various sheet metal components.
Medium-Carbon Steel
With carbon content ranging from 0.3% to 0.6%, medium-carbon steel has higher strength and hardness than low-carbon steel but lower formability and ductility. It is often used in machine gears, shafts, crankshafts and drive shafts in automotive.
High-Carbon Steel
High-carbon steel, with a carbon content between 0.6% and 1.0%, is extremely hard and wear-resistant, though brittle. It is highly responsive to heat treatment, which allows significant performance improvements but demands precise processing and carries higher risks. Typical applications include cutting tools, springs, and wear-resistant components.
Ultra-High Carbon Steel
Contains around 1.5% to 2% carbon and bridges the gap between high-carbon steels and cast iron. Due to its high hardness and brittleness, it is extremely difficult to machine and form. As a result, it is rarely used except in specialized fields requiring exceptional performance, such as molds and cutting tools.
It’s important to note that for carbon content exceeding 2.0%, the material typically transitions into the category of cast iron, which has a lower melting point and excellent fluidity, allowing it to be well-suited for casting complex shapes. Additionally, these ranges are approximate guidelines rather than strict rules, and classifications may vary between sources. Instead, they are intended to provide a general understanding of how different groups of carbon steel alloys behave.
What’s the Difference Between Alloy Steel and Carbon Steel?
As discussed above, alloy steel and carbon steel differ significantly in their composition, which serves as the basis for their distinct properties. To provide a clearer understanding of these differences, we will analyze their distinctions across key characteristics step by step.
Strength
Alloy steel is generally stronger than carbon steel due to the addition of alloying elements like chromium, molybdenum and nickel. However, the strength of alloy steel can vary significantly depending on the type and concentration of alloying elements. In some cases, the strength of certain low-alloy steels may be comparable to or even lower than that of high-carbon steel after heat treatment.
Hardness
In its untreated state, alloy steel typically has higher hardness than plain carbon steel. This is due to alloying elements like tungsten and vanadium, which enhance hardness by directly strengthening the matrix and forming hard carbides. However, after heat treatment, high-carbon steel can achieve hardness levels (e.g., above HRC 60) comparable to or even exceeding certain standard alloy steels. For example, tool-grade high-carbon steel can rival the hardness of tungsten- or vanadium-containing tool steels. Despite the increased hardness of carbon steel after heat treatment, its wear resistance and hot hardness are generally inferior to those of alloy steel.
Toughness
Alloy steel generally has better toughness than carbon steel, especially under extreme conditions like high or low temperatures. Alloying elements such as nickel, chromium, and molybdenum enhance its low-temperature impact resistance and high-temperature creep resistance, making it suitable for aerospace, bridges, and pressure vessels.
Carbon steel performs well at room temperature, particularly low-carbon steel, which offers good ductility and impact absorption. However, its low-temperature brittleness and reduced high-temperature toughness limit its applications.
Ductility
Ductility, the ability of a material to deform without breaking, varies greatly between alloy steel and carbon steel depending on their composition and treatment. Low-carbon steel typically has better ductility than most alloy steels, being a preferred material for forming and welding applications. However, as carbon content increases, the ductility of carbon steel decreases significantly.
In extreme conditions, such as high or low temperatures or under high stress, alloy steel often surpasses carbon steel in ductility. This is due to the addition of alloying elements like nickel and molybdenum. Conversely, carbon steel tends to fracture more easily in low-temperature conditions or deform under high heat.
Wear and tear resistance
Alloy steel typically offers better wear resistance than carbon steel, particularly in high-temperature, impact load, or corrosive environments. Low-alloy steels, such as manganese steel, combine high toughness and wear resistance, which suit applications like mining equipment and heavy machinery. High-alloy steels, such as tool steel, achieve significantly higher hardness and wear resistance after heat treatment, meeting the demands of cutting tools and molds.
In contrast, carbon steel provides good wear resistance at room temperature, especially high-carbon steel. However, it has lower impact resistance and is prone to failure in high-temperature or humid conditions.
Corrosion resistance
Alloy steel, containing elements like chromium, nickel, or molybdenum, forms a passive film—a protective oxide layer on its surface—that greatly enhances corrosion resistance. It performs exceptionally well in humid, high-temperature, or acidic environments. Common grades, such as stainless steel, are widely used in chemical equipment and marine engineering.
By comparison, carbon steel has poor corrosion resistance and is prone to rust in humid or corrosive environments. It typically requires coatings, galvanization, or other surface treatments to slow down corrosion.
Thermal conductivity
The thermal conductivity of alloy steel is generally lower than that of carbon steel. This is due to the addition of alloying elements such as nickel, chromium, and molybdenum, which hinder heat flow. Unlike alloy steel, carbon steel relies primarily on its ferritic matrix for thermal conductivity, as it contains minimal or no alloying elements. Although the conductivity slightly decreases with higher carbon content, the change is relatively small. As a result, carbon steel is better suited for applications requiring efficient heat transfer, such as boiler pipes and radiators.
Machinability
Carbon steel is more machinable, particularly in low-carbon and medium-carbon types, due to their lower hardness and reduced cutting resistance. As for high-carbon steel, its hardness greatly increases after heat treatment, facing some challenges in machining.
The machinability of low-alloy steel is near that of medium-carbon steel. However, high-alloy steels, such as stainless steel, have poorer machinability due to the presence of alloying elements like chromium and nickel. They often require high-performance cutting tools and optimized machining parameters to handle the challenges like higher cutting resistance and increased tool wear.
Weldability
The weldability of carbon steel is generally better than that of alloy steel, particularly for low-carbon steel, which is easy to weld with a low risk of cracking. However, as the carbon content increases in medium- and high-carbon steels, weldability decreases due to higher hardening tendencies and increased sensitivity to cracking.
In comparison, low-alloy steel has weldability similar to that of medium-carbon steel. High-alloy steels, such as high-strength steels and stainless steels, present more welding challenges because of their alloying elements and typically require specialized welding techniques and strict heat input control.
Cost
Carbon steel is more cost-effective due to its simpler composition and easier processing requirements. Therefore, if enhanced performance in demanding environments is not required, carbon steel is definitely a more economical alternative to alloy steel.
Alloy Steel vs. Carbon Steel: Which One Is Better?
With a deeper understanding of what distinguishes alloy steels from carbon steels, it’s natural to wonder, “Which one is better?” Unfortunately, this question have no a definitive answer. But here are some helpful considerations when you make the choice:
1. If cost is a primary concern, carbon steel is often the preferred option. It provides sufficient performance for general structural uses where corrosion resistance is not that much critical. Additionally, for simpler fabrication processes, carbon steel is an excellent choice as it is easier to cut, weld, and shape, particularly in low-carbon varieties.
2. In the following situations, alloy steel is the better choice.
When your project demands superior tensile strength, hardness, and wear resistance, such as gears and suspension components in automotive, cutting tools, and industrial molds, alloy steel provides the necessary durability.
If the material will be exposed to moisture, chemicals, or marine environments, alloy steel with the addition of elements like chromium and nickel is better suited for these conditions.
When the application involves extreme temperatures, such as high-temperature environments in boilers, turbines, and pressure vessels, or low-temperature environments in cryogenic tanks and refrigeration systems, alloy steel provides superior thermal stability and toughness.
If your project requires materials with specialized properties, such as magnetic components, fatigue-resistant parts, or heat-resistant equipment, certain alloy steels are specifically engineered to meet these needs, ensuring long-term performance and reliability.
Work with a Trusted Partner for Steel Machining
Choosing the right material, whether alloy steel or carbon steel, is just the first step to a successful project. At Chiggo, we offer a wide range of metal machining services and treatment processes to meet your needs. With a foundation built on expert knowledge, premium-quality materials, and precision engineering, Chiggo ensures every project achieves excellence. Whether you look for enhanced performance, cost-effective solutions, or expert material guidance, we are here to help. Let’s create something exceptional together!
FAQ
Are there alternative materials to alloy and carbon steel?
Yes, there are several alternatives to alloy and carbon steel, each offering unique benefits for specific applications. Here are the key options:
Nickel Alloys: Excellent corrosion resistance with good strength and malleability, favored in chemical processing, marine environments, and high-temperature uses.
Aluminum Alloys: Lightweight with excellent corrosion resistance and a high strength-to-weight ratio, commonly used in aerospace, automotive, and structural applications.
Titanium: Strong, lightweight, and durable, often used in aerospace and medical implants, though it is costly and difficult to process.
Cast Iron: Durable and wear-resistant, suitable for engine blocks, heavy machinery, and pipes, but limited by its brittleness.
Copper and Copper Alloys: Renowned for excellent electrical and thermal conductivity, corrosion resistance, and antimicrobial properties, widely used in wiring, plumbing, and decorative applications.
Composites: Materials like carbon fiber and glass fiber offer high strength and corrosion resistance, favored in aerospace, automotive, and sports equipment despite their higher costs.
Ceramics: Highly resistant to corrosion and wear, suitable for electronics and medical devices, but their brittleness restricts use in high-impact applications.
Why are stainless steel, tool steel, and high-speed steel often separated from alloy steel?
Although they are technically types of alloy steel, they are separated due to:
High Alloy Content: These steels contain significantly more alloying elements than regular alloy steel.
Specialized Properties: Each has unique characteristics, like stainless steel's corrosion resistance, tool steel's hardness, and high-speed steel's performance at high temperatures.
Targeted Applications: These steels are designed for specific industries, such as medical, aerospace, or cutting tools, making them distinct from general-purpose alloy steels.
Industrial Practice: For clarity and ease of understanding, they are often classified independently in standards and markets.
