Stainless steel is a popular material in modern construction due to its durability and resistance to corrosion, but not all stainless steel is created equal. Understanding the different types and their properties is crucial for ensuring the longevity and quality of your projects, especially in environments like Bali, where specific challenges exist.
The Story Behind Stainless Steel
The journey to modern stainless steel was a long one. Early attempts to prevent rust in iron involved various techniques, including plating with silver and nickel. However, the real breakthrough came with the discovery that adding chromium to steel could create a truly rust-resistant alloy. Harry Brearley is generally credited with this in 1911, realizing that at least 10.5% chromium and less than 0.15% carbon in steel resulted in what was originally called “rustless steel”. This discovery led to the development of the 400 series stainless steel, specifically grade 430. Later, the addition of nickel by Guillet and Guissen resulted in the 300 series “Austenitic” stainless steels.
Different Types of Stainless Steel
Today, there are many types of stainless steel, but the most common fall into two main categories:
- 300 series (Austenitic): These are the most widely used, with around 18% chromium and 8% nickel. The nickel is what makes them “Austenitic”. Within this series, grades 304 and 316 are the most common.
- Grade 304: The most popular grade accounting for around 50% of all stainless steel applications. It’s widely used in kitchens, food processing, and appliances.
- Grade 316 (Marine Grade): Similar to 304 but with more nickel (2-3%) and added molybdenum, making it resistant to chlorides. Grade 316 is ideal for severe environments and industrial chemicals.
- 400 series (Ferritic): These are generally easier to machine than the 300 series. However, they may not be as corrosion-resistant.
The Science Behind Rust Resistance
The secret to stainless steel’s rust resistance lies in its crystal structure. When chromium is added to steel, it fills the gaps in the iron crystal structure, preventing oxygen molecules from reaching the iron and causing rust. Additionally, a thin layer of corrosion forms on the surface, acting as a barrier and further protecting the metal. To be considered true stainless steel, there must be a minimum of 10.5% chromium.
- Pure iron is “ferrite”, having a body-centered cubic crystal structure.
- When heated above 1000 degrees C it becomes “austenite”, with a face-centered cubic structure.
- Adding nickel keeps this “austenite” structure even at room temperature, which is more resistant to rusting and is not magnetic.
Challenges with Stainless Steel in Bali
Despite its benefits, stainless steel can still face challenges, especially in places like Bali. One of the most common issues is the presence of chlorides.
- Seawater and groundwater, often high in chlorides, can cause pitting corrosion, where small holes form on the surface of the steel.
- This is particularly problematic for 304 stainless steel.
- While 316 is more resistant, it’s also harder to find in some areas.
- Additionally, the desire to cut costs often leads to poorer quality stainless steel being used, which is more prone to rusting.
How to Identify Genuine Stainless Steel
Magnetism is a simple yet effective way to test if stainless steel is genuine.
- The “ferrite” structure of pure iron is magnetic.
- Austenitic stainless steel (304 and 316) does not contain any ferrite, and is not magnetic.
- If a magnet sticks to a piece of steel, it is likely not a genuine 304 or 316 grade stainless steel.
- Beware of products with trade names that sound respectable but are made of poorer quality materials.
Conclusion
When specifying stainless steel for your construction projects, be sure to choose appropriate grades that meet the needs of the environment. Be aware that not all stainless steel is the same, and take measures to ensure you are using the correct type for its intended purpose. By understanding these key points, you can make informed decisions and ensure the durability and longevity of your builds.
