This document aims to provide a basic understanding of stainless steel, focusing on its use as a construction material.

For more specialized information or further assistance, please feel free to contact us, and we will be happy to help.

General Knowledge of Stainless Steel

1. Overview of Stainless Steel

1) Stainless steel, known for its excellent corrosion resistance, does not require rust-preventive treatments like painting, unlike carbon steel or aluminum. It also exhibits outstanding strength, heat resistance, and aesthetic appeal.

While stainless steel is more resistant to corrosion than regular carbon steel or aluminum, it is not a completely rust-proof metal like gold or platinum (STAIN+LESS).

2) The reason stainless steel has excellent corrosion resistance is due to the presence of over 11% chromium. When this chromium combines with oxygen, a thin but dense protective oxide layer (referred to as a passive film) forms on the surface. This passive film prevents corrosion.

These exceptional characteristics of stainless steel make it ideal for use in both interior and exterior construction materials. It is used in everything from large buildings to small houses and apartments, and its high strength makes it suitable for structural applications as well.

2. Characteristics of Stainless Steel

1) Compared to carbon steel or aluminum, stainless steel has the following characteristics.

· Its surface is aesthetically pleasing and highly decorative.

· It has excellent internal corrosion resistance, so there are fewer environmental limitations.

· It is lightweight, with high hardness relative to its weight.

· It resists oxidation even at high temperatures, maintaining high strength, making it relatively safe in the event of a fire.

· It has excellent machinability and is easily deformable.

· Its maintenance and management costs are low.

2) Characteristics by Stainless Steel Type

- Stainless steels are developed in various grades based on their physical properties and intended uses.

Among them, the STS304 grade, containing 18% chromium and 8% nickel, is the most widely used in construction.

The STS316 grade is used in coastal areas or industrial zones where corrosion factors like salt, iron, and toxic gases are prevalent.

Economical and weather-resistant steels like STS304N1 and STS304N2 are also used as alternatives, while STS430 is typically used in interior applications or situations where corrosion conditions are not severe.

- Main Stainless Steels Used in Construction

3. Corrosion Resistance of Stainless Steel

1) While stainless steel is much more resistant to corrosion than carbon steel or aluminum, it is not a completely rust-proof metal like gold or platinum.

2) The excellent corrosion resistance of stainless steel is due to the chromium content, which combines with oxygen to form a passive film on the surface, preventing oxidation and protecting the material.

This passive film is extremely thin (around 0.003 mm) and cannot be seen by the naked eye, but it is dense and hard, making it difficult to break or erode.

Even if this film is damaged, the chromium will rebind with oxygen and regenerate the protective layer.

3) Rust in stainless steel occurs when the passive film is destroyed and its regeneration is hindered.

While stainless steel has excellent corrosion resistance, issues like rusting may arise if an inappropriate grade of steel is chosen or if improper maintenance or processing occurs.

4) The main substances that can break down the passive film and prevent its regeneration include chloride ions (from salt, bleach, PVC smoke, hydrochloric acid) and sulfur compounds (from car exhaust, factory emissions, volcanic gases, and steam).

5) Other substances that may not directly destroy the passive film but can interfere with the oxygen supply to the surface or encourage deposition on the surface include soot, dust, and other particulate matter.

○ Environmental Factors Affecting Stainless Steel

Corrosion in Atmospheric Conditions

Stainless steel is highly resistant to corrosion, but in specific environments like coastal areas or industrial zones, it can get dirty or rust. It is important to choose stainless steel grades with excellent corrosion resistance depending on the environmental conditions.

1) Rural and Mountainous Areas

Stainless steel performs exceptionally well in clean, rural, or mountainous environments, with little to no corrosion issues.

2) Urban Areas

Areas with high levels of air pollution, such as automobile emissions or sulfur dioxide from heating systems, can cause chromium-based stainless steel to rust. In such environments, regular maintenance is required to prevent localized rust.

○ Corrosion from Dissimilar Metals

When materials like mild steel, zinc, or aluminum are in contact with stainless steel for extended periods, moisture (like condensation) can lead to galvanic corrosion. This process can cause the dissimilar metals to corrode, which might spread rust to the stainless steel, a phenomenon known as "crevice corrosion".

○ Salt Resistance

Stainless steel may show red rust when exposed to salt from seawater.

In coastal areas, using STS316 or painted stainless steel sheets is recommended for construction.

○ Resistance to Harmful Gases

Stainless steel may experience discoloration or rust when exposed to harmful substances in smoke or exhaust gases, such as from chemical plants, garbage incinerators, or vehicle emissions.

Regular maintenance is necessary in these environments to preserve the appearance and performance of stainless steel.