As part of our deep dive series, today we're going to take a detailed look at one of our favourite metals at Webforge, stainless steel.
This versatile and popular material is behind some of the most common products you'll interact with on a daily basis in industrial settings, so it's important you understand what makes it so effective.
In this article, we'll look at where stainless steel comes from, its different types and applications and how Webforge has put it to use in some of our flagship offerings.
What is stainless steel?
Stainless steel isn't one metal, but rather a name given to a group of steel alloys. The key factors binding these different substrates together is their corrosion resistance, and the fact they contain at least 10.5% of chromium in their makeup.
To make stainless steel, the different elements go through a multi stage process that follows these steps:
- Melting and casting - For around eight to twelve hours, the raw materials are intensely heated in an electric furnace. This results in molten steel, which can be cast into a variety of forms, including rods, slabs, blooms and billets.
- Forming - The semi-finished steel is now formed - a process that involves hot rolling, where the substrate is heated and passed through rollers. Depending on the desired application for the stainless steel, a number of other processes take place to shape the metal accordingly.
- Heat treatment - Often, once the stainless steel is formed, it needs to be heated and cooled in controlled conditions to soften it and relieve internal stresses to the metal. This stage, also called annealing, needs to be particularly closely monitored, as the changing temperatures can impact the metal's properties. Generally speaking:
- Aging steel at a higher temperature means it will have low fracture toughness and higher strength.
- Aging steel at a lower temperature means it will be tougher, but less strong.
- Descaling - During the annealing stage, scale often builds up on the steel's surface. This can be removed in a number of ways, including electropolishing and anodising.
- Cutting - The metal is cut to attain the correct trim or size for the finished product. Again, a variety of methods can be employed here, the most common being mechanical cutting, followed by flame cutting.
- Finishing - Stainless steel is known for its smooth, glossy texture, making finishing a vital final phase. The exact measures taken here depend on the type of finish required, but they all usually involved the use of heat and/or grinding with abrasive materials.
While fabricators may add additional stages when adopting stainless steel into their own products, these six steps are the key parts of the manufacturing process.
What are they key properties of stainless steel?
- Corrosion resistance - The chromium element of stainless steel is responsible for a protective oxide layer that forms on the surface of stainless steel. This forms a barrier against corrosion, even if the product is damaged.
- High strength - Stainless steels generally have higher tensile strengths when compared to mild steels.
- Quality aesthetics - The descaling and finishing stages in the manufacturing process make for a visually attractive product, that's also easy to clean.
- Work hardening - Certain grades of stainless steel can be significantly strengthened simply by cold working (look back at the heat treatment point above).
- Chemically customisable - As an alloy, manufacturers can tease different properties out of stainless steel simply by varying the ratios of the various component. There are over 100 grades of this metal, giving great flexibility for applications.
- Temperature resistance - The range of grades also mean that you can find stainless steels that will perform well in extreme heat, and others that will do the same in extreme cold.
What are the different types of stainless steel?
We're not going to go through every single type, or grade, of stainless steel, but here are some of the most common:
1. Austenitic stainless steel
According to the Australian Stainless Steel Development Association, austenitic stainless steel accounts for over 70% of stainless steel production. It gets its name from the austenite crystal structure achieved by adding nickel to the metal's composition. The percentage ratio of nickel to chromium in austenitic steel is 8:18.
In industrial sectors, this steel is seen most commonly in chemical plant equipment and general architectural applications. Core specific characteristics include:
- High ductility formability and fabricability.
- High corrosion resistance.
- High weldability.
- Hardenable only through cold working.
2. Ferritic stainless steel
These are your plain chromium stainless steels that feature low carbon content.
The main advantage of ferritic steel is a moderate to good corrosion resistance which improves as chromium levels increase. However, when compared to austenitic stainless steel, this material isn't as ductile or weldable, and can't be hardened by heat treatment.
As such, ferritic steel is commonly used in car manufacture, especially in trims and exhaust pipes. That said, it does have uses for the industrial sector, and can frequently be found in colliery equipment and hot water tanks.
3. Duplex stainless steels
A combination of the two above types, duplex stainless steels contain medium levels of nickel, a significant amount of chromium and often some molybdenum.
The hybrid properties of this category of metal includes:
- Higher yield and tensile strengths than either austenitic of ferritic stainless steels.
- Solid resistance to corrosion stress cracking.
- Good weldability.
As a result, duplex stainless steels have a wide variety of uses, including everything from heat exchangers and desalination plants to marine applications
4. Martensitic stainless steel
Martensitic stainless steels were the first to be commercially developed, with their primary usage being as cutlery. They have similar chromium levels as ferritic stainless steels, but with a much higher carbon content. They're not used in the industrial sector, as a result of properties such as poor weldability and only moderate corrosion resistance.
While they're not naturally as strong as other groupings, this feature can be improved through heat treatment.
Today, you'll still find martensitic stainless steels in cutlery, as well as surgical equipment, spindles and pins.
Examples of stainless steel industrial products
The easiest way to show how this versatile material is deployed in the industrial sector is to look at some examples of real life products. Here are examples from across the industry:
1. Walkway grating
You need to know that your staff and equipment can move safely around your site, making walkways a key industrial consideration. While gratings have the clear advantage of allowing water and detritus to pass through external walkways, thus not creating slip hazards, exposure to such elements require these features to be corrosion resistant.
Stainless steel ticks this box while also being easy to clean - making maintenance quick and easy. The other advantage of stainless steel gratings, is their strength, while aluminium may have a higher strength:weight ratio, when you're looking for heavy duty flooring, steel is the answer.
Stanchions are often used to support handrails and safety barriers - an application which also requires strength and corrosion resistance, but also one that usually needs to be aeshetically pleasing. As these features are often found at entrance ways, they form part of a building's visual statement and so need to be clean and professional looking.
Webforge's Monowills Link™ is a modular handrail system that can be manufactured from stainless steel. This site feature is available as preassembled stanchions or in complete systems and is often chosen because of its long life and ease of installation.
3. Desalination plant equipment
Stainless steel can be found in many different components in desalination plants. These include:
Rust resistance is of elevated importance here due to the nature of working with high quantities of salt water. However, some stainless steels have the further advantage of being able to cope with high temperatures, a factor which can extend their lifespan in this setting.
4. Colliery facilities
Duplex stainless steel is often favoured for coal mining facilities, thanks to its combination of high tensile strength and extreme corrosion resistance. However, depending on the specific requirements of coal mining plant, you will also find other stainless steels used in a variety of different functions.
Hopefully this article has given you an insight into the origins of stainless steel, its properties and where it can be deployed. At Webfoge, we work with a variety of different metals, with an emphasis on tailoring our offerings to each clients' individual needs. For more information on our stainless steel products, or to talk about your requirements, get in touch with our team today.