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Is carbon steel the same as blue steel?

Steel is one of the most widely used materials in the world due to its strength, durability, and versatility. While carbon steel and blue steel sound similar, they actually refer to different types of steel with unique properties and applications.

Steel is an alloy composed mainly of iron with added carbon for strength. While steels can contain a variety of alloying elements like chromium, nickel, and manganese, the primary distinction between types of steel comes from their carbon content.

Carbon steel and blue steel represent two different classifications of steel based on their carbon composition and how the steel is processed. While both contain carbon as a key alloying element, the amount of carbon present and the effects it has on the steel’s properties are quite different between the two.

Carbon Steel

Carbon steel is one of the most common types of steel, making up about 90% of all steel production. As the name suggests, it is defined by its carbon content. Specifically:

Carbon Steel Type Carbon Content
Low carbon steel 0.05-0.25% carbon
Medium carbon steel 0.25-0.60% carbon
High carbon steel 0.60-1.00% carbon

The carbon content has a direct impact on the steel’s properties:

– **Strength:** Increasing carbon content increases yield and tensile strength. High carbon steel is harder and stronger than low carbon steel.

– **Weldability:** Higher carbon content lowers weldability. Low carbon steel can be welded easily while high carbon steel requires special welding techniques.

– **Corrosion Resistance:** Low carbon steel is more corrosion resistant than high carbon steel.

– **Machinability:** Low carbon steel is easier to machine, while high carbon steel is more difficult due to its hardness.

– **Cost:** Simple carbon steels are relatively inexpensive compared to alloyed steels.

Blue Steel

Blue steel refers specifically to types of steel that develop a blue tint when oxidized. This is achieved through unique heat-treating processes that control the oxide layer formation on the surface. Two main types of blue steel are commonly produced:

Blued Mild Steel

Mild steel is a form of low carbon steel with a carbon content less than 0.25%. When put through a bluing process, it develops a thin oxide layer that provides a protective patina and gives the steel a distinct blue appearance.

The bluing process involves:

– Heat the mild steel to around 300°F.

– Remove from heat and rub clean.

– Return to heat to oxidize the surface and form blue iron oxide.

– Allow to cool gradually.

– Repeat heating and cooling process multiple times to deepen the blue color.

– Apply oil or wax coating to seal the blued surface.

Blued mild steel has an attractive, unique appearance but the bluing doesn’t significantly impact the steel’s properties or performance.

Blued High Carbon Steel

High carbon steel can also be blued through a similar process. However, with higher carbon content (0.6-1.0%), the bluing produces some different effects:

– The blue oxide layer forms more readily compared to mild steel.

– The oxidation process hardens the steel’s surface slightly through heat-treating.

– Provides added corrosion resistance.

Common applications of blued high carbon steel include:

– Firearms – Bluing protects the gun barrel and metal components from corrosion and provides an attractive finish. The slight surface hardening also improves wear resistance.

– Cutting tools – Blued tool steels help resist corrosion and enhance performance.

– Springs – Bluing slightly increases yield strength and corrosion protection.

– Decorative uses like sculptures, metalwork, and kitchen knives.

Key Differences Between Carbon Steel and Blue Steel

While carbon steel and blue steel sound similar, there are some important distinctions between the two:

Carbon Steel Blue Steel
Refers broadly to all steels containing 0.05-1.0% carbon as an alloying element. Specifically refers to mild steel or high carbon steel that has been blued or oxidized to produce a blue appearance.
Carbon is added to increase strength. Other alloying elements may also be present. Mild steel contains less than 0.25% carbon. High carbon blue steel typically contains 0.6-1.0% carbon.
No specific appearance. Has a regular steel gray/silver color. Distinct blue finish achieved through controlled oxidation of the steel surface.
A broad classification of one of the most widely produced types of steel. A niche type of heat-treated steel known for its unique blued aesthetic.

In summary:

– Carbon steel is a broad term referring to all steels containing varying amounts of carbon as an alloying element.

– Blue steel is a specific classification of mild steel or high carbon steel that has gone through a bluing process to produce an oxidized blue finish.

– While blue steel is always a type of carbon steel, not all carbon steel can be classified as blue steel. The difference comes down to the bluing treatment that gives blue steel its characteristic appearance.

Uses of Carbon Steel vs Blue Steel

Due to the differences in their properties and production, carbon steel and blue steel find applications in different areas:

Typical Applications of Carbon Steel

– Structural steel – Used in buildings, bridges, and construction. Both low and high carbon steel is used depending on the needed strength.

– Mechanical parts – Carbon steel can be machined into gears, shafts, screws, and other components. Low carbon is easier to machine.

– Rail tracks – High strength and wear resistance make carbon steel ideal for railroad tracks.

– Wire rope – Relies on the strength of high carbon steel while remaining flexible.

– Pipe and tubing – Used for plumbing, oil/gas, fire sprinklers, etc.

– Automotive components – A mix of high strength parts along with easier to shape mild steel.

– Appliances – Stainless steel is popular but carbon steel is often used for high temperature parts and panels.

Typical Applications of Blue Steel

– Firearms – Bluing helps prevent corrosion and adds an attractive finish to guns.

– Cutting tools – Blued tool steels maintain hardness while resisting corrosion. Ideal for knives, swords, chisels, etc.

– Clock springs – Bluing enhances yield strength and corrosion resistance.

– Jewelry – Provides a unique, eye-catching blue color for rings, watches, bracelets, etc.

– Sculptures and decorative metalwork – An oxidized blued finish creates an appealing aesthetic.

– Kitchen knives – Combines stainless steel corrosion resistance with a stylish blued finish.

– Historical pieces – Bluing was used to protect and decorate older metal items and weapons.

Cost Comparison

There is some cost difference between plain carbon steel and blued steel products:

– Simple carbon steel is relatively inexpensive, with cost largely based on the type of steel grade used.

– Blued steel finishes add some additional processing which increases cost.

– However, bluing is still a relatively economical process compared to more complex treatments like nitriding or chroming.

Some example cost differences:

Product Carbon Steel Price Blued Steel Price
Grade 8.8 Bolts $2.50/lb $4.50/lb
Hunting Knife Blade $8 $12
Decorative Steel Panels $25 $35

As seen above, blued steel usually commands around a 50-100% price premium over untreated carbon steel. The extra cost accounts for the additional processing time required.

However, for products where appearance and finish are critical like decorative items, knives, or firearms, the appeal of the blued steel aesthetic makes the cost increase worthwhile for many consumers.


While carbon steel and blue steel refer to different types of steel altogether, they also overlap in the case of blued high carbon steel. The key distinction lies in the unique bluing process that gives blue steel its characteristic appearance.

Carbon steel encompasses a wide range of steels based simply on their carbon content, making it a versatile, economical, and widely used material. Blue steel, on the other hand, occupies a more niche category where the oxidized, heat-treated finish is the defining quality.

So in summary:

– Carbon steel is defined by its carbon alloy content as a broad classification of steels.

– Blue steel refers specifically to carbon steel that has undergone an oxidizing bluing treatment to produce a unique finish.

– Blued mild steel and blued high carbon steel are the two main types of blue steel produced.

– While they overlap, carbon steel and blue steel are not interchangeable terms. Blue steel brings specific properties and aesthetics from its processing that carbon steel does not possess on its own.

Hopefully this breakdown helps provide a better understanding of how these two types of steel are related, how they differ, and when each one is the right choice for the job!