Stainless Steel

General information about stainless steel

There are five main families of stainless steel, namely austenitic, martensitic, ferritic, precipitation hardening and duplex stainless steel. Stainless steel is a steel alloy containing a minimum of 10.5% Chromium. When the chromium content on the steel’s surface reacts with the surrounding atmosphere a passive layer of chromium oxide is created which protects the steel from corrosion. In total over 250 grades of stainless steel exist, each with differing mechanical, physical, thermal and anti-corrosive qualities.

What are the characteristics of stainless steel?

The characteristics of stainless steel vary by family and grade. Generally it is said that stainless steel is corrosion resistant, however the level of resistance is determined by the levels of chromium which form the passive protective layer. Oftentimes nickel is added to austenitic stainless steels, typically around 8%, to enhance favourable characteristics such as toughness. The addition of molybdenum further enhances corrosion resistance to pitting and crevice corrosion.

In comparison to austenitic, ferritic stainless steels tend to be less corrosion resistant due to lower carbon contents and the absence of nickel. While not as strong or corrosion resistant ferritic stainless steel is magnetic and exhibits good engineering qualities such as being more weldable.

How is stainless steel manufactured?

There are three key stages in the production of flat stainless steel products.

The first stage is the production of slab, in which raw materials, often recycled scrap metals, are molten together commonly in an electric arc furnace (EAF). The alloy composition of the molten steel is tailored by removing elements in line with a required balance. This is done in an Argon Oxygen Decarburization Converter (AOD). Depending on the steel manufactured, a Vacuum Oxygen Decarburization (VOD) process may be applied. Following this process the molten steel is poured in to a ladle where final chemical adjustments can be undertaken.

The steel slab is then cast, converting the molten steel into manageable pieces. Every slab is fully traceable. The slabs form the feed stock for further processing such as hot rolling.

During hot rolling slabs are heated and passed through rollers which adjust the width and thickness of the slab according to prespecified measurements. This is followed by the removal of surface scale through a pickling and annealing process.

The rolling process continues but at room temperature until the desired material thickness has been reached.

What are the benefits of stainless steel?

Due to its corrosion- and weather- resistance stainless steel is suitable for both indoor and outdoor application.

Stainless steel is an extremely durable and well ageing material. Its long life cycle -over a hundred years in some applications if the right grade is selected- keeps maintenance costs to a minimum. Hence stainless steel is a very cost effective material.

Stainless steel is generally corrosion resistant if the correct grade for the desired application has been selected.

Stainless steel is widely used in catering and medical sectors as it is easy to keep clean and therefore more hygienic than other materials.

Stainless steel has numerous architectural applications and is often specified by designers for its aesthetics and the range of appearances (colours and finishes) available.

Stainless steel is fully recyclable. Approximately 90% of end-of-life stainless steel products are collected and recycled, making it a sustainable and environmentally friendly choice.

Which sectors utilise steel sheets in their manufacture?

Stainless steel is a universal material which is used in many different industries, amongst others in:

• Construction
• Automotive / transportation
• Petrochemical industry
• Ship Building
• HEVAC
• Domestic appliances / goods
• Medical industry