Difference Between Mild Steel and Corten Steel
In the world of steel products, understanding the distinctions between Mild Steel and Corten Steel is crucial for informed decision-making. Drawing on over 40 years of combined experience in the Steel Industry, we aim to clarify these differences to assist our customers in selecting the appropriate material for their requirements.
Mild Steel vs. Corten Steel
Mild Steel, also known as carbon steel, and Corten Steel, often referred to as weathering steel, differ significantly in their composition, properties, and applications. Let’s explore their key differences:
- Composition:
- Mild Steel: Predominantly composed of iron and carbon, with small amounts of manganese, sulfur, and phosphorus.
- Corten Steel: Includes additional alloys like copper, chromium, nickel, and phosphorus, enhancing its resistance to weathering.
This blog post will continue to examine these differences further, covering aspects such as weather resistance, applications, and maintenance requirements for each steel type.
What is Steel and How is it Made?
Let’s start with the basics. Metals can be broadly categorized into two types: Pure Metals and Alloys. Pure Metals, as the name suggests, are metals that are at least 99% pure in their natural state, without any alloying elements. Examples include Gold, Aluminum, Copper, Lead, and Iron. Alloys are formed when Pure Metals are combined with each other or other chemicals.
Steel is an alloy made primarily from the Pure Metal Iron, combined with other chemical elements. If you recall from your science classes, Steel can be classified into three main types: 1. Carbon Steel, 2. Tool Steel, and 3. Stainless Steel.
For the purposes of this blog post, we’ll focus on Carbon Steel. Both Mild Steel and Corten Steel fall under the category of Carbon Steels.
What is Corten Steel?
Corten Steel, also known as Weathering Steel, is a type of high-strength, low alloy Carbon Steel. It was patented in 1933 by the United States Steel Corporation. Typically, Corten Steel contains 0.2-0.5% copper, 0.5-1.5% chromium, and 0.1-0.2% phosphorus.
The name “Cor-Ten” is derived from two words that highlight Corten Steel’s qualities: COR-rosion resistance and TEN-sile strength. This means it offers high resistance to corrosion and exceptional strength and durability.
How Does Corten Steel Resist Corrosion?
Corten Steel’s ability to resist corrosion is primarily due to its chemical composition. The metal forms a distinctive orange, red, and brown patina over time, creating a protective outer layer. This layer slows down the degradation and corrosion of the material.
An interesting feature of Corten Steel is its self-healing property. If the surface of the protective layer gets scratched, the exposed area begins to develop its own protective patina, helping to maintain the steel’s durability over time.
How Long Does Corten Steel Take to Weather?
The protective patina on Corten Steel develops over time through cycles of wet and dry weather conditions. If your Corten product is installed indoors or under cover where it’s not exposed to rain, the patina formation will either be delayed or may not occur naturally. Alternatively, a solution can be applied before delivery to ensure the product arrives with a patina already formed.
Under normal outdoor conditions, you can expect the patina to begin forming within days, especially after the first rainfall. A complete patina typically develops over approximately 6 to 9 months, depending on local atmospheric factors such as heat, humidity, rainfall, proximity to water bodies, and coastal winds. Over about 36 months, the patina will continue to mature, stabilizing in color and finish.
It’s generally advised not to use Corten Steel in very wet environments or within 2 kilometers of the coast, as salt from sea winds can retain moisture on the steel’s surface, potentially slowing the formation of the protective layer. However, Corten Steel is widely used in applications like shipping containers and coastal bridges due to its resilience and protective properties against corrosion.
Why is Corten Steel Used in Landscaping and Garden Design?
Corten Steel is favored for its striking aesthetic appeal. The contemporary designs and shapes of our products, combined with the natural colors of the patina, create a visually stunning effect that complements the greens and floral hues commonly found in gardens and landscaping schemes. It serves as a year-round canvas and backdrop for outdoor spaces, enhancing their elegance and modern appeal.
For an added touch of sophistication in your landscape or garden design, Moongates are an excellent choice. These structures feature Corten Steel, providing a contemporary twist to traditional metal arches. What sets them apart is the unique design illusion where each leg appears to vanish into the ground, making Moongates a truly distinctive addition to any outdoor environment.
Will the Patina from Corten Steel Stain?
Corten Steel and Mild Steel can produce what is known as “Run Off” during the early stages of patina development. This runoff carries some of the patina color and may stain surfaces on which the products are placed.
This phenomenon is common with all-natural steel products. There are steps you can take to manage this issue. Placing the product on or surrounded by loose stone or chippings that can be periodically turned over or replaced with a fresh top layer can help mitigate runoff. Alternatively, placing the product on a protective slab or layer that can be removed or replaced once the patina is fully developed is another effective approach.
What is Mild Steel?
Mild Steel is the most commonly used material in industries such as Construction, Manufacturing, and Automotive. It typically contains approximately 0.05% to 0.25% Carbon. Due to its widespread availability, Mild Steel is more cost-effective compared to Corten Steel.
Despite its lower cost, our Mild Steel products use structural-grade materials, ensuring comparable tensile strength to Corten Steel. This makes them a practical choice for various applications.
How long does Mild Steel take to Weather?
Mild Steel generally develops a patina similar to Corten Steel but over a slightly longer period. The atmospheric conditions mentioned earlier still affect Mild Steel. Typically, the patina begins to form within a few weeks and progresses to its full development over 12 to 18 months.
Is there a difference in color finish between Mild Steel and Corten Steel?
There are minimal differences in the aesthetic appearance of Mild Steel and Corten Steel. As mentioned earlier, both types of carbon steel develop rust. The variation in appearance is primarily due to their chemical compositions. Corten Steel tends to start with yellowish and orangish hues because of its copper content.
Mild Steel develops a patina that leans towards orange, red, and brown tones. Over time, both steels will achieve a similar appearance when they reach full patination. The key distinction is that Corten Steel maintains its patina finish once fully developed, while Mild Steel may continue to evolve in coloration over a longer period.
If desired, a clear rust varnish can be applied to Mild Steel once it achieves the desired aesthetic to preserve the finish. Despite differences in finish, our products are crafted using the same methods by our skilled and qualified fabricators.
How sustainable are Corten and Mild Steel products?
It’s undeniable that steel production consumes a significant amount of energy, and its strength makes it a heavy material to transport. However, steel is highly sustainable as it is a circular product. This means it is 100% recyclable, and this recycling process can be repeated indefinitely.
Uses of Corten Steel vs. Mild Steel
Corten Steel’s exceptional resistance to corrosion makes it well-suited for outdoor applications, including sculptures, building facades, fences, cladding, roofing panels, bridges, and other structures exposed to harsh weather conditions such as snow or sea salt. Its ability to withstand extreme temperatures also makes it suitable for industrial settings like furnaces or boilers, ensuring durability against high heat exposure over time.
On the other hand, Mild Steel’s malleability makes it ideal for indoor use, such as furniture frames or kitchen appliances, where flexibility is crucial for design purposes. Its low carbon content also reduces health risks associated with long-term exposure compared to other metals like lead or copper, ensuring a non-toxic environment.
Corten Steel Vs Mild Steel Price
The price disparity between Corten steel and mild steel can vary significantly depending on the specific product. Corten steel, a distinctive metal composed of alloying elements that resist corrosion while retaining strength and durability, generally commands a higher price point. This is attributable to the increased costs associated with sourcing and manufacturing Corten steel.
For large-scale industrial applications such as structural framing or outdoor sculptures, the added expense of Corten steel may be justified by its superior longevity and resilience to harsh environmental conditions. Even for smaller items like outdoor furniture or decorative pieces, Corten steel remains a viable choice if the desired aesthetic and durability warrant a higher initial investment.
Conclusion
Both Corten steel and mild steel present unique advantages depending on the specific application. Despite their differences, they share some similarities. It’s crucial to carefully evaluate all factors before choosing between these materials to ensure optimal project outcomes, while also considering budget constraints if applicable. Professionals in the metal and steel industries should weigh factors such as cost-efficiency, durability, flexibility, and health considerations to make informed decisions that align with their specific application needs.
