Stainless Steel：Features and Benefits
Stainless steel is a relatively new material and invented early in the 1900s. It was initially called ‘rustless steel’. Over the past century, many researches and experiments have been conducted, which has led to dramatic improvement in its productivity and quality.
What is Stainless Steel?
Stainless steel is an alloy steel containing more than 50% iron and a minimum of 10.5% chromium. It is known for excellent corrosion resistance, durability and long-life.
In general, iron oxidizes and rusts easily when exposed to water and oxygen over time. However, why does stainless steel have a high resistance to corrosion even its main component is iron? This is largely to do with chromium.
Chromium reacts strongly with oxygen and produces a very thin oxide film (only three millionth of millimeter) on the surface of the stainless steel known as the ‘passive layer’. Although extremely thin and invisible, it is very hard, tightly adherent to the surface and super protective.
Even if it is damaged by abrasion or cutting, this passive layer develops on the surface slowly as the chromium reacts with oxygen in the air. Then it repairs itself naturally to prevent oxygen and moisture from reaching the iron underneath and stops further corrosion.
Types of Stainless Steel
There are over 150 grades of stainless steel and each has its own unique properties that make them ideal in specific working environments.
Among them, most commonly used stainless steel is 18-8 which is also known as SUS304. It is an austenitic type of stainless steel and is not attracted by a magnet. About 60% of all stainless steel used in the world is this grade.
The term ‘18-8’ is referring to the 18% chromium, 8% nickel alloy mixture of the steel.
When more than 10.5% of chromium is added to iron, passive layer is formed. Increasing the amount of chromium makes passive layer more stable and gives it a better self-healing mechanism.
On the other hand, adding nickel in stainless steel makes the surface harder and stronger, and slows the rate of oxidation and rusting. Therefore, the higher the chromium and nickel content, the more resistant the stainless steel is to corrosion.
Next most common are ferritic stainless steels which are magnetic like pure iron. 18-0 stainless steel known as SUS430 is one which contains 18% of chromium and 0% (actually 0.75%) of nickel.
The lack of nickel leads to a reduced corrosion resistance and is more likely to rust than 18-8 stainless steel. It doesn’t cost as much as 18-8 steel and is used where corrosion resistance is not too demanding as an alternative to the 18-8 stainless steel.
Sustainability of Stainless Steel
Today, stainless steel is actively recycled on a large scale around the world by recyclers who collect and process scrap for re-melting. This is because it can be recycled easily and economically and also the demand for stainless steel is increasing every year to keep up with the expansion of its use.
The International Stainless Steel Forum (ISSF) released figures for 2017 showing that global crude stainless steel production reached an all-time high total of nearly 48.1 million tonnes. In 2018, the global output has grown by a further 5%, to achieve a new record high mark of around 50.7 million tonnes.
This figure has increased significantly over the past decade, when the yearly global stainless steel production was well below 30 million tonnes.
Stainless steel is infinitely recyclable and can be used forever. This is a great example of the sustainability.
Using stainless steel may cost a little more initially but considering the length of its valuable life, it is more cost effective choice than other alternatives. Additionally, it is very exciting to think that your choice is helping reduce the impact on the environment and contributing to a greener future.