Weathering Steel Landscaping: A Quick Selection Guide

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Metals possess high strength, excellent plasticity, and a distinctive metallic luster. They are wear-resistant, durable, and easily harmonize with earth, wood, stone, and cement. Lighter than stone, metals reduce load, offer ductility, and are efficiently processed in factories with high precision. This minimizes labor costs, shortens construction periods, and supports high recycling rates, making them environmentally friendly. Landscape architects are drawn to the unique texture, luster, and natural beauty of metals. Today, let's explore the recent favorite in outdoor landscape metal materials—weathering steel.

Natural Beauty of Corten Steel

1. Introduction to Corten Steel

Weathering steel, also known as atmospheric corrosion-resistant steel, originated from Corten steel in North America. It belongs to a low-alloy steel series situated between standard steel and stainless steel. Weathering steel is created by incorporating small amounts of copper, nickel, and other corrosion-resistant elements into ordinary carbon steel. Possessing high-quality steel attributes such as strength, plasticity, shaping, welding and cutting capabilities, abrasion resistance, and tolerance to high temperatures, weathering steel exhibits 2 to 8 times the weather resistance and 1.5 to 10 times the paintability of ordinary carbon steel. Additionally, it provides rust resistance, enhancing component longevity, reducing consumption, and offering benefits like labor and energy savings.

Corten steel specification: Following the addition of phosphorus, copper, chromium, nickel, and other weather-resistant elements, a dense and strongly adherent oxide layer forms between the rust layer and the matrix. This unique oxide layer provides stability, and its uniform natural rust-red color prevents oxygen and water from penetrating into the substrate. Consequently, it protects the substrate beneath the rust layer, slowing down its corrosion rate.

2. Corten Steel Properties

(1) Unique Performance Characteristics: Weathering steel boasts outstanding visual expression, evolving in appearance over time. Its color, brightness, and saturation surpass those of ordinary structural materials, making it easily distinguishable against the backdrop of garden greenery.

(2) Strong Shape-Shaping Ability: Weathering steel is relatively easy to shape into diverse and intricate forms while maintaining excellent structural integrity.

(3) Distinctive Space Definition Ability: Utilizing very thin steel plates, weathering steel can clearly and precisely delineate spaces, creating a site that is concise, vibrant, and impactful.

3. Corten Steel Process and Classification

Rust Stabilization Treatment Method: The rust stabilization treatment involves using chemical methods, such as rust liquid, to gradually dissolve the film on the steel plate's surface. This process induces rusting and stabilization, forming a uniform rust layer. This layer acts protectively, suppressing rust from the steel's initial use.

Color changes caused by rust treatment of corten steel

4. Common Parameters of Corten Steel Sheet

Weathering steel thin plates typically range in thickness from 1.5mm to 4mm, medium plates from 4mm to 20mm, thick plates from 20mm to 60mm, and extra thick plates can reach up to 80mm. Standard widths include 0.5m, 1m, 1.2m, 1.5mm, 2m, etc. (These values may vary among manufacturers in the market and are provided for reference purposes only).

5. Corten Steel Price Range

corten steel price = steel plate raw material price + rust treatment price.

The cost of rust treatment about 4$/㎡, depending on the process. Taking a 3mm thick weather-resistant steel plate as an example, the raw material cost is approximately 16.80 $/㎡. Hence, the price of weather-resistant steel plates falls about 21 $/㎡. It's important to note that variations in plate thickness and quality will impact the price of weathering steel accordingly. (This pricing represents ordinary mid-range products and is provided for reference purposes only; Click to obtain the latest pricing of corten landscape).

6. Design Considerations

(1) Natural Site Conditions: Consider the natural conditions of the site, both indoor and outdoor, inland and coastal. Factors such as salt content, air humidity, sunlight, architectural shape, and orientation influence the growth rate and composition of the rust layer on weathering steel. This may result in varying degrees of uneven rust conditions. For a uniform color appearance, attention should be given to drainage outlet placement and ensuring consistent lighting and water exposure throughout the structure.

(2) Avoiding Water Accumulation: Rust layers on weathering steel are prone to delamination and corrosion when exposed to water. Pay careful attention to drainage design near the bottom of the weathering steel elements. For instance, when weathering steel is used in a planting pond, consider filling height and internal drainage channels during design to prevent muddy water from overflowing during rainfall, which could lead to contamination and corrosion.

(3) Sample Color as Reference: The sample color of weathering steel may not be a reliable reference. In a general natural environment, it takes 6 months to 1 year (when a rust accelerator is used) to develop a stable and dense rust-red protective layer from a new steel plate. This duration may be longer in some dry areas or indoors. Even if aiming for a simple and uniform rust-yellow color, it can take about a month. The color transition during this process progresses from bright yellow to earthy yellow, orange, orange-red, reddish-brown, and brown. When designing weathering steel landscapes, focus on the final color, and clearly communicate the anticipated color changes during the initial stages with the involved parties.

(4) Slow Corrosion and Lifespan: Weathering steel corrodes slowly, and the lifespan of high-quality weathering steel is eight times that of ordinary steel (with an annual corrosion rate on one side being 0.097mm). Consider a small thickness corrosion allowance during the design phase.

8. Distinguishing True and False Weathering Steel

To authenticate weathering steel, it is essential to comprehend the rusting processes of both weathering steel and ordinary steel. The following two tables distinctly illustrate the disparities between these two types of steel.

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Table1:Rusting Process of Corten Steel

Characteristic	Weathering Steel	Ordinary Steel
Initial Appearance of Rust	Rapid rusting, typically within a few weeks	Gradual rusting, often noticeable over time
Rust Color	Progresses from bright yellow to deep brown	Usually a uniform brown or red-brown color
Surface Texture	Develops a textured surface with variations	Often smoother, less textured rust surface
Stability of Rust Layer	Stable and adherent, forming a protective layer	May have less stability and prone to flaking
Rust Accumulation Rate	Slower after the initial rapid phase	Generally consistent corrosion over time

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Table2:Physical Characteristics of Weathering Steel vs. Ordinary Steel

Characteristic	Corten Steel	Ordinary Steel
Composition	Alloyed with elements like copper and nickel	Standard carbon steel composition
Purpose	Designed for enhanced weather resistance	General-purpose construction material
Surface Finish	Exhibits a unique and varied surface texture	Typically smoother surface finish
Weight	Comparable or slightly lighter than ordinary steel	Typically heavier than weathering steel
Lifespan	Generally longer due to enhanced corrosion resistance	May have a shorter lifespan depending on corrosion rate

Understanding these distinctions will aid in accurately identifying true weathering steel, ensuring that the material selected aligns with its intended characteristics and benefits.

It can be seen from the table that the difference between the rust appearance of ordinary steel and weather-resistant steel is not obvious within 6 months after the rust begins. The reason is that the dense protective rust layer of weather-resistant steel has not really grown up 6 months ago. Therefore, it is difficult to distinguish the authenticity of weathering steel from fake weathering steel with the naked eye in the early stage, which is also an important reason for the phenomenon of confusion in the market.

(The left side is weather-resistant steel, and the right side is ordinary steel. The color and texture after rusting for 7 days are almost the same)

(Dense rust spots are formed in the later stage of weathering steel)

(Ordinary steel later forms a flaky and fluffy rust layer)

To sum up, ordinary observation in the early stage cannot identify the authenticity of weathering steel, and the following methods can be used for detection.
Corten steel authenticity detection method:

Submit it to a third-party testing agency to test the content of several precious metal elements such as Cu (copper), Ni (nickel), Cr (chromium), etc. through spectrum testing, and compare it with the warranty reference. The Cu and Ni content of ordinary steel plates The content of several precious metal elements such as Cr and Cr will be 10 times or more less than the corresponding content on the weathering steel warranty.
Sampling the weathering steel plate, divide the sample into two halves, use a grinder or sandpaper to destroy the original rust surface on one half, and then spray water for observation. Because the real weather-resistant steel plate is made of excellent material, even if one layer is removed, good rust will still naturally grow inside.