Low vs Medium vs High Carbon Steel: Applications and Differences

Table of Contents > 1. What Is Carbon Steel?     1.1 Types of Carbon Steel 2. Low Carbon Steel Properties and Applications     2.1 Properties of Mild Steel     2.2 Weldability of Low-Carbon Steel     2.3 Most Common Low-Carbon Steel Grades     2.4 Low-Carbon Steel Applications 3. Medium Carbon Steel Basics     3.1 Medium-Carbon Steel Properties     3.2 Weldability of Medium-Carbon Steel     3.3 Typical Medium-Carbon Steel Grades     3.4 Applications of Medium-Carbon Steel 4. High-Carbon Steel Properties, Weldability & Applications     4.1 Properties of High-Carbon Steel     4.2 Weldability of High-Carbon Steel     4.3 Common High-Carbon Steel Grades and Applications 5. Low-Carbon Vs Medium-Carbon Vs High-Carbon Steel Comparison Table 6. Final Thoughts 7. 🧐Low vs Medium vs High Carbon Steel: Applications and Differences FAQ

Carbon steel is a versatile metal that is fundamentally an alloy of iron and carbon. Although it also contains elements like manganese, silicon, sulfur, and phosphorus, carbon is the primary alloying element, giving it its name, carbon steel.

Depending on the amount of carbon, carbon steel can be soft and ductile or hard and strong. These properties will also impact its weldability, so it is crucial to understand the differences before undertaking any project.

In this article, we will thoroughly explain the properties, differences, and applications of low-carbon, medium-carbon, and high-carbon steel. Let's learn which one is the easiest to weld and which is the hardest.

TIG Welding Carbon Steel on 6-inch Pipe
Source:https://www.youtube.com/watch?v=DNVPsbXOy6Q

What Is Carbon Steel?

Carbon steel is an iron alloy that contains up to 2.1% carbon by weight. Carbon is the primary alloying element, ergo the name carbon steel. Besides carbon, it also contains other components, such as silicon, manganese, sulfur, and phosphorus, but in smaller amounts or as impurities. 

Due to its relatively low cost, widespread availability, and ease of fabrication, carbon steel is one of the most widely used metals in the global industry. Its properties vary with the carbon content, ranging from soft and ductile to hard and strong.

Carbon steel can rust if it lacks a protective layer, which limits its real-life applications. Adding carbon can improve corrosion resistance, but it does not entirely protect it from oxidation. Nonetheless, it remains one of the most widely used metals.

Besides the applications, properties also affect the weldability of carbon steel. You'll need a different approach when welding each type, so it is crucial to understand the properties of each carbon steel type.

Carbon steel is an iron alloy that contains up to 2.1% carbon by weight.
Source: https://www.youtube.com/watch?v=U5D9fkUxtYQ

 

Types of Carbon Steel

Carbon steel is typically categorized into three groups based on its carbon content. These are known as:

• Low-carbon steel (Mild steel) 0.05-0.3% carbon

• Medium-carbon steel 0.3-0.6%

• High-carbon steel over 0.6%, commonly up to 1.5%

Characteristics of Low vs Medium vs High Carbon Steel

The more carbon steel has, the harder and stronger it gets. That's advantageous in components such as springs, knives, cutting tools, or bearings. However, it also makes the steel less ductile, so it can crack when subjected to heat.

Organizations such as the American Iron and Steel Institute (AISI) and the American Society for Testing and Materials (ASTM) facilitate the identification of steel grades. AISI typically uses a four-digit system, in which the first two digits indicate the alloy, and the second two denote the carbon content. ASTM uses an "A" to indicate ferrous materials, followed by an arbitrarily assigned number for each alloy.

Each grade has slightly different properties, but grouped types share similar characteristics. Let's explore each group.

AISI and AISI Steel Designation System
Source: https://www.youtube.com/watch?v=gXXRGjddQOM

Low Carbon Steel Properties and Applications

Low-carbon steel, as its name suggests, has the lowest weight-to-carbon ratio among other carbon steel types. Typically, low-carbon steels contain 0.05-0.30% of carbon.

Such low carbon content makes low-carbon steel more malleable and ductile compared to other types. However, it is also the softest of the three carbon steels. As a result, it is the easiest to weld, cut, bend, or shape, which is why it is also known as mild steel.

Due to low carbon content, mild steel is less expensive than other types of steel. Additionally, it is easier to produce and work with, which makes it one of the most widely available options on the market.

Some Low-Carbon Steel Applications
Source: https://www.slideshare.net/

Properties of Mild Steel

The exact properties of low-carbon steels vary depending on the specific grade of the mild steel. But some general rules apply to the entire type.

In general, mild steel has a moderate tensile strength of 20300 - 347000 psi. This is enough for some structural applications, but not for heavy-duty uses, where high-carbon steels shine.

Low-carbon steel is ductile and malleable. Therefore, it can be stretched, rolled, and bent into various forms without breaking. It can also absorb impact and shock well.

The melting point of low-carbon steel reaches 2600°F. It offers good thermal conductivity, which, combined with other properties, makes it highly weldable.

Mild steel is highly magnetic due to its high iron content. Although it may contain chromium or manganese, it is not inherently resistant to corrosion, and therefore, it can rust.

Weldability of Low-Carbon Steel

Low-carbon, or mild steel, is the most weldable and forgiving among the three types of carbon steel. It has a low carbon content that improves ductility and prevents embrittlement.

As a result, you can easily weld mild steel with any of the most popular arc welding methods, including MIG, TIG, Stick, or Flux-cored welding. When heated, mild steel doesn't form a hard, martensitic structure, so it is less likely to crack. Ductility and flexibility allow mild steel to deform without fracturing during welding. 

Due to low carbon content, mild steel typically doesn't require any heat treatment before or after the welding. Rapid heating or cooling usually does not cause cracking, and the metal itself is fairly forgiving. Of course, defects can happen if you are not careful enough, but they are not caused by the properties of the metal, but rather by operator errors.

TIG Welding Mild Steel Pipe on 3F Position
Photo by @lornafae (TikTok)

Most Common Low-Carbon Steel Grades

There are dozens of mild steel grades, but here are some general examples of the most widely used mild steel grades.

Low-Carbon Steel Applications

General construction and infrastructure:

• Beams, columns, structural shapes

• Rebars in concrete

• Steel plates and sheets for bridges, buildings, and pipelines

Low Carbon Steel Structure
Source: https://www.steels-structure.com/

The automotive industry:

• Car body panels, chassis parts, bumpers, and wheels

• Exhaust systems (when combined with coatings)

Pipes and tubing:

• Water, gas, and sewage pipelines

• Tubes for HVAC systems and general engineering

Low Carbon Steel Pipelines
Source: https://www.octalsteel.com/

Machinery and equipment:

• Frames, enclosures, and housings

• Agricultural equipment and storage tanks

Sheet metal products:

• Appliances, cabinets, furniture

• Cans and packaging (often coated or galvanized)

Fasteners and hardware:

• Bolts, nuts, nails, wires, chains, and fences

Low Carbon Steel Fasteners
Source: https://htecfast.com/

Medium Carbon Steel Basics

Medium carbon steel has a carbon content ranging from 0.3 to 0.6% of its weight. Besides carbon, medium-carbon steels contain small amounts of manganese, ranging from 0.060 to 1.65%. Manganese helps medium-carbon steel achieve desirable properties during heat treatment, such as quenching and tempering.

Generally, medium carbon steels provide a balance of ductility and hardness. They are less ductile than mild steel, but still offer better formability than high-carbon steel. The metal is also harder than low-carbon steel due to higher carbon content, but it has lower hardness than high-carbon steel.

Example of Medium Carbon Steel 
Source: https://metalzenith.com

Medium-Carbon Steel Properties

Medium-carbon steel has moderate strength and hardness. It exhibits lower ductility and toughness than mild steel, but responds well to heat treatment, such as quenching and tempering, which improve its properties.

Increased hardness provides improved wear resistance. However, the properties affect the weldability, making medium-carbon steel much more challenging to weld than mild steel.

Furthermore, increased carbon content increases the tensile strength to 35500 – 252000 psi. However, it has lower ductility and toughness compared to low-carbon steels, meaning it is less formable and more brittle. 

Medium-Carbon Steel Properties

 

Weldability of Medium-Carbon Steel

As the carbon content rises, the medium-carbon steel becomes more challenging to weld. Increased amounts of carbon and manganese can lead to the formation of martensite in the heat-affected zone (HAZ) due to rapid heating or cooling during welding.

The martensite structure is brittle, and any diffusible hydrogen can bind to it, causing hydrogen-assisted cracking. Additionally, rapid heating and cooling can induce residual stress, which compromises the overall strength of the weld and potentially leads to cracking.

Diagram of Martensite Structure 
Source: https://www.researchgate.net/

To weld medium-carbon steel, you will need to preheat and undergo post-weld heat treatment (PWHT). Preheating reduces the risk of rapid heating and the formation of a hard martensite structure. PWHT involves slow cooling or stress relief to reduce the risk of cracking.

Heat control and low-hydrogen filler will also help reduce thermal stress and hydrogen diffusion. Nonetheless, medium-carbon steels still have some ductility and malleability, making them more weldable than high-strength steels. You can still use methods such as MIG, TIG, or Stick welding.

Stick Welding the Medium-Carbon Steel Paper Cutter Tie Rod
Source: https://www.youtube.com/watch?v=ke83tx89p0A&t

Typical Medium-Carbon Steel Grades

The most common medium carbon steel grades include the standard AISI/SAE 10xx series, such as 1030 through 1055. Here are some examples:

Applications of Medium-Carbon Steel

The automotive and transportation industry:

• Axles, crankshafts, camshafts, connecting rods,

• Gears, sprockets, couplings, and shafts,

• Wheels and rails in railway systems.

Source: https://www.slideshare.net/

Repairing and building heavy machinery and equipment:

• Press tools, machine parts, and spindles,

• Industrial shafts, keys, and fasteners under stress,

• Agricultural machinery components.

Construction and heavy-duty parts:

• Pressure vessels, pipelines (with proper heat treatment),

• Structural parts demanding higher strength than mild steel.

Medium Carbon Steel Structural Parts
Source: https://steelprogroup.com/medium-carbon-steel/

Energy and aerospace (primarily alloyed steel):

• Power transmission components,

• Aircraft landing gear, propeller shafts, and bolts,

• Oil and gas drilling equipment.

Wear-resistant tools and products:

• Hammers, wrenches, springs,

• High-strength wires and cables.

Medium Carbon Steel Wire for Spring Use

High-Carbon Steel Properties, Weldability & Applications

High-carbon steel, as the name suggests, contains the highest amount of carbon among the three, typically ranging from 0.60% to 1.5% of its total weight. High carbon content provides exceptional hardness, wear resistance, and high-temperature performance. That's why it is also called tool steel.

Due to their properties, high-carbon steels are commonly used in applications that require high resistance to wear and tear. Based on its composition, it is a plain high-carbon steel, primarily consisting of iron and carbon. These are the metals used to make springs, knives, cutting tools, and brake components.

However, it can also contain other alloying elements that improve performance in specific conditions. For example, adding chromium and manganese can aid in the hardening process while enhancing the steel's resistance to corrosion.

Image of High Carbon Steel Alloy
Source: https://energosteel.com/en/library/high-carbon-alloy-steel/

Properties of High-Carbon Steel

As noted, due to increased carbon content, high-carbon steel is extremely hard. It provides high tensile strength and resistance to wear and tear. High abrasion resistance makes it suitable for cutting tools and industrial equipment.

Although advantageous, high carbon content also has its drawbacks. High-carbon steels have low ductility, which reduces machinability. They also have low malleability, making them more challenging to work with. Simply put, high-carbon steels are so hard that they cannot deform without breaking.

Depending on the grade, high-carbon steel has a tensile strength of 39,900–484,000 psi. The melting point ranges from 2,800 to 2,900°F, making it valuable in high-temperature applications.

Properties of High-Carbon Steel

Weldability of High-Carbon Steel

High carbon content also affects the weldability. High-carbon steels are very challenging to weld, as they form hard, brittle martensite when heated, which makes the steel prone to cracking.

Rapid heating and cooling create residual stresses that can lead to the formation of cracks during solidification. Additionally, any added hydrogen can bind to the newly formed microstructure. Once hydrogen diffusion starts, it can create internal stress, which leads to hydrogen-included-cracking (HIC).

Hydrogen-induced cracking (HIC) Explained
Source: https://whatispiping.com/hydrogen-induced-cracking-hic/

Therefore, try to weld high-carbon steel only when necessary. If you decide to weld it, use heat treatment, low-hydrogen filler (electrode), and control the heat.

Preheating and post-weld heat treatment (PWHT) are mandatory with high-carbon steel. Preheating reduces the thermal stress that the heat of the arc can cause and hydrogen migration. PWHT relieves residual stresses and reduces the risk of hydrogen cracking.

Preheating before High Carbon Steel Welding
Source: https://www.youtube.com/watch?v=5ocKjyVWhak&t=72s

Low-hydrogen electrodes will lower the risk of HIC. Low amounts of hydrogen usually won't be so harmful to welds, but with hard, brittle high-carbon steels, even the most minor amounts can produce stress.

Finally, track and control the heat. Detailed control of starting and interpass temperatures, as well as slow cooling, is mandatory in achieving desirable results. Nonetheless, even if you do everything right, high-carbon steel welds can crack, which is why it can be a hit-or-miss task.

Stick Welding High Carbon Steel 
Source: https://www.youtube.com/watch?v=5ocKjyVWhak&t=72s

Common High-Carbon Steel Grades and Applications

Low-Carbon Vs Medium-Carbon Vs High-Carbon Steel Comparison Table

To summarize everything we learned, here is a comparison table that highlights the most essential properties and differences between low-carbon, medium-carbon, and high-carbon steels.

Final Thoughts

Carbon steels comprise a vast group of metals that primarily contain iron and carbon, often supplemented by other alloying elements. Depending on the carbon content, there are three primary types: Low-carbon, medium-carbon, and high-carbon steels.

Low-carbon steels are inexpensive, ductile, and highly weldable, making them ideal for general fabrication and construction. Medium-carbon steels balance strength and toughness. Thus, they find wide use in automotive parts, shafts, gears, and machinery components.

High-carbon steels, while less ductile and more difficult to weld, excel in hardness and wear resistance. These properties make them ideal for cutting tools, springs, and high-strength wires.

Understanding their properties is crucial in making the right choice for your applications. Additionally, they will provide hints on weldability. Knowing the challenges that await you will prepare you to tackle any welding task in front of you.

🧐Low vs Medium vs High Carbon Steel: Applications and Differences FAQ

1. What are the main classification standards for carbon steel?

Carbon steel is mainly classified according to its carbon content, which is divided into three categories: low-carbon steel (with a carbon content of 0.05%-0.30%), medium-carbon steel (with a carbon content of 0.30%-0.60%), and high-carbon steel (with a carbon content of 0.60%-1.5%). In addition, organizations such as AISI and ASTM have formulated corresponding steel grade identification standards for unified classification and identification.

2. Is medium-carbon steel used for?

Medium-carbon steel is strong and tough, ideal for automotive parts (axles, shafts, gears), machinery, construction components, energy and aerospace parts, as well as durable tools like hammers and springs.

 

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