Carbon Steel vs Black Steel

Carbon steel is mainly composed of iron and carbon. By adjusting the carbon content and processing, different strengths, hardness, and toughness can be obtained. Due to its good comprehensive mechanical properties, low cost, and ease of processing and manufacturing, it is widely used in construction, machinery manufacturing, and energy transportation (such as oil and gas). It should be noted that ordinary carbon steel has poor corrosion resistance, and anti-corrosion measures must be considered during use.

Black steel is not an independent steel grade, but rather a description of its surface condition. It specifically refers to carbon steel products (such as black steel plates and black steel pipes) that have been hot-rolled and have a black iron oxide scale on the surface, without final anti-corrosion treatment such as galvanizing or painting. This condition is a natural result of the production process, not for aesthetic purposes, but to provide raw materials or blanks at the lowest cost. 

Common "black iron pipes" belong to this category of products, often used in fire protection systems or as low-pressure fluid pipelines requiring on-site corrosion protection. Their biggest drawback is their extreme susceptibility to corrosion; therefore, they should never be used in their raw state in applications with a risk of corrosion or requiring long-term maintenance-free operation.

Difference Between Carbon Steel and Black Steel:

Difference	Carbon Steel	Black Steel
Definition	This refers to steel materials with a carbon content between 0.02% and 2.11%, primarily composed of iron and carbon.	Specifically, it refers to carbon steel products with a black iron oxide scale on the surface, without any surface finishing treatments such as galvanizing, painting, or polishing.
Surface Finish	Carbon steel is silver-gray in its raw state. Depending on its intended use and the manufacturer's specifications, it may or may not have a protective coating. It has various surface characteristics: such as a black oxide scale from hot rolling, a bright surface from cold rolling, a galvanized layer, a painted layer, and a polished mirror finish.	Black steel is the natural result of a hot rolling process, with a black oxide layer covering the steel surface.
Scope	Extremely broad. Classified according to carbon content into low-carbon steel, medium-carbon steel, and high-carbon steel. Diverse forms: steel plates, steel bars, steel pipes, steel billets, castings, etc.	Narrower scope. A subset of carbon steel products. Primarily refers to hot-rolled plates, bars, structural profiles (such as I-beams and angle steel), and some steel pipes.
Advantages	Wide performance range, high cost-effectiveness, and good machinability. It can provide specific mechanical properties (strength, hardness, toughness).	It has the lowest cost among carbon steels and is suitable as a blank requiring secondary processing or painting. Users can perform secondary processing (such as rust removal and painting, galvanizing, and machining) according to the end use.
Galvanization	Requires galvanization because this steel is susceptible to corrosion.	Is a non-galvanized steel.

1. Chemical Composition

Carbon steel is a type of steel with iron and carbon as its main elements (carbon content typically between 0.02% and 2.1%). Based on carbon content, it can be classified into low-carbon steel, medium-carbon steel, and high-carbon steel. Its strength and hardness increase with increasing carbon content, while its plasticity decreases.

Black steel is not a separate steel grade, but rather a description of its surface condition. It specifically refers to carbon steel products that, after hot rolling and other processes, have a layer of black iron oxide scale (mainly composed of iron(III) oxide, Fe₃O₄), and have not undergone any plating or coating treatment. Therefore, its chemical composition is exactly the same as its corresponding carbon steel base material, and there is no independent composition standard. The "black steel plate" and "black steel pipe" we commonly refer to are carbon steel products in this state.

2. Production Process

Carbon steel is produced through basic processes such as smelting, continuous casting, and rolling (hot or cold rolling). The "black steel" state is usually a natural result of the hot rolling process.

After high-temperature rolling, the steel is cooled in air, and the surface reacts with oxygen to form a dense black iron oxide scale. Compared painted or galvanized carbon steel products, "black steel" products eliminate the need for subsequent surface plating or coating processes, resulting in lower costs. They are supplied as raw materials or blanks requiring secondary processing.

3. Corrosion Resistance

Both materials are inherently prone to corrosion, depending on surface treatment.

Carbon steel is susceptible to electrochemical corrosion in humid or corrosive environments, exhibiting poor corrosion resistance. The black iron oxide scale on the surface of black steel is thin and easily damaged, providing only very limited short-term protection. It corrodes rapidly in humid, acidic, alkaline environments or after mechanical damage. Therefore, black steel products cannot be used directly in corrosive environments and must undergo specialized anti-corrosion treatment (such as painting, galvanizing, or asphalt wrapping) before or after installation and use. This is precisely the main drawback of its low cost.

4. Strength

The mechanical properties (strength, toughness) and weldability of carbon steel and black steel are primarily determined by their chemical composition and heat treatment state, and are not directly related to whether they are "black steel" or not. When welding "black steel," the oxide scale at the weld bead must be removed to ensure weld quality.

5. Application Areas

Carbon steel is commonly used as a basic material, with applications covering almost all industrial fields, including construction, machinery, automobiles, and home appliances.

Black steel products are mainly utilized for their low cost and availability as raw materials. Common applications include:

Building Structures: As raw materials for steel structural beams and columns requiring overall coating (such as H-beams).
Pipeline Systems: As low-pressure fluid transport pipes requiring on-site anti-corrosion treatment (such as some fire water pipes).
General Manufacturing: As raw materials for parts requiring further machining or heat treatment.

Note: For applications requiring corrosion resistance, high aesthetics, or immediate use (such as outdoor railings, appliance housings, and precision parts), galvanized, color-coated, and stainless steel materials are often chosen instead of black steel.

Frequently Asked Questions:

1. Is black steel steel with a higher carbon content?
No. "Black" refers only to its surface color and is unrelated to its carbon content. Black steel can be low-carbon or medium-carbon steel.

2. Why isn't black steel made rust-proof, but instead allows it to rust?
This is for cost and process balance. Natural cooling after hot rolling will form an oxide scale. Galvanizing or painting requires additional production lines, chemical treatments, and energy consumption, significantly increasing costs and selling prices. Many applications (such as internal structures of large structures or parts requiring rework) actively choose black steel as the raw material.

3. Are "black steel" and "hot-rolled steel" the same thing?
Almost identical, but with slight differences.

Almost all "black steel" products are produced through hot rolling because hot rolling produces an oxide scale. However, "hot-rolled steel" is a term that emphasizes the process, and the resulting product is usually in a "black steel" state. Therefore, the two are often used interchangeably when referring to sheet metal and profiles.

4. Is "black steel" a competitor to "white steel"?
In business terms, yes.

"White steel" typically refers to:
Stainless steel (due to its silvery sheen).
Galvanized steel (with a silvery-gray zinc coating).
The contrast between "black steel" and "white steel" vividly illustrates the difference between having and not having an anti-corrosion coating.

5. Should I choose black steel or other carbon steel products?
This depends on your end use, budget, and processing capabilities:

Choose black steel: If you need low-cost raw material and plan on extensive secondary processing (such as overall painting after cutting and welding, or embedding in concrete as a building structural component), or for short-term, temporary projects.

Choose galvanized/painted carbon steel products: If you need ready-to-use material and do not have the means or desire for surface anti-corrosion treatment, and require a longer maintenance-free lifespan (such as outdoor railings, roofs).

Read more: Carbon Steel vs. Stainless Steel or MS and GI Pipe Difference