Stainless steel will always be an excellent choice as a type of material in almost any project given its properties of high resistance to corrosion and durability, among others. However, did you know that there are typologies of this steel? We will be able to choose one or another depending on the needs of our project, and above all to take advantage of all its qualities so that the general quality increases.
That’s why today we will focus especially on dissecting the multiple types of stainless steel to analyse which would be its most common and recommended uses. Will you stay on Initube?
What is stainless steel?
Stainless steel is an iron alloy containing a minimum of 10.5% chromium, an element that gives the base material high corrosion resistance. This element reacts with oxygen in the air to form a thin layer of chromium oxide on the surface of the steel. This is passive, so it regenerates if damaged, protecting the steel from oxidation and corrosion. That’s why it’s often the perfect choice for applications where durability and a clean appearance are required. That’s why it’s often the perfect choice for applications where durability and a clean appearance are required.
In addition to the most outstanding characteristic, which would be the resistance to corrosion, stainless steel has many other properties that make it one of the most demanded materials:
Durability
It has a high resistance to deformation and wear, which allows it to withstand extreme conditions.
Hygiene
It is an easy-to-clean surface, which is why it is the material of choice for applications in the food and medical industry.
Aesthetics
Its bright and clean appearance makes it popular in interior decoration and design.
In addition to iron and chromium, stainless steel may contain other elements, which are added to improve its properties, such as:
– Nickel. Increases corrosion resistance and improves the malleability of steel.
– Molybdenum. Improves corrosion resistance in more aggressive environments, such as those containing chlorides (e.g. salt water).
– Carbon. It is present in small quantities to improve the hardness and strength of the material.
What types of stainless steel are there?
Although stainless steel is grouped into a single type, the truth is that in reality there are various types according to their crystalline structure, chemical composition and mechanical properties. All of them are designed to determine their applications and specific characteristics, that is to say, the type that best suits the project will be the one chosen. Among all of them we can mention:
Austenitic
Its high chromium (16-26%) and nickel (6-22%) content makes it the most widely used due to its high corrosion resistance and excellent ductility. They are also non-magnetic and have good weldability, which is why it is used for cookware, medical equipment, storage tanks and building structures. 304 is the most common and versatile, while 316 has higher corrosion resistance due to the addition of molybdenum, ideal for marine environments.
Series 200
Its composition is similar to the 300 series, but with manganese in place of some of the nickel. It is a cheaper alternative, although with lower corrosion resistance, and is also used in inexpensive cookware and some construction applications.
Ferritic
This type of stainless steel contains between 10.5% and 30% chromium, but with very low nickel or no nickel content. It is magnetic, harder and less malleable than austenitic steel and has moderate corrosion resistance. One of its most interesting properties is that it has good resistance to oxidation at high temperatures.
It is used in the manufacture of household appliances, decorative panels, automotive components and some kitchen utensils. 430 is widely used in decoration and in applications where high corrosion resistance is not essential.
Martensitic
They contain chromium (12-18%) and a higher amount of carbon compared to austenitic and ferritic grades. They are magnetic and can be hardened and tempered by heat treatment. They have high mechanical strength and hardness, but lower corrosion resistance than austenitics.
It can be found in blades, surgical tools, valves, shafts and other applications requiring high wear resistance. 420 is known as the ‘knife steel’ because of its sharpness.
Duplex
This type consists of a mixture of austenitic and ferritic steel, thus containing chromium (18-28%), nickel (4.5-8%) and even molybdenum. They combine the high corrosion resistance of austenitics with the mechanical strength of ferritics. They are also magnetic, but with less ductility than austenitics.
It is in high demand in the oil and gas industries, in chemical plants and in desalination plants, where increased resistance to chloride corrosion (in piping, heat exchangers, etc.) is required.
Superduplex
It is a variant of duplex steel and has higher corrosion resistance and mechanical strength. It seems to be created for sectors where the level of corrosion is very high, such as in the marine industry, on oil platforms and in desalination plants. It is the perfect type of stainless steel if it has to withstand extremely aggressive environments.
Precipitation Hardening (PH – Precipitation Hardening)
They contain chromium and nickel, but also elements such as copper, aluminium and niobium. They are characterised by combining high corrosion resistance with high hardness and mechanical strength. They are hardened through a specific heat treatment that causes the precipitation of hardening particles. The aerospace industry often benefits from this type, as well as the automotive sector and in industrial equipment where high performance is required.
What to consider when choosing the most suitable type of stainless steel?
Choosing the right type of stainless steel for a specific application involves considering a variety of factors that affect its performance and durability. The quality of the final result will depend on this choice, so it is necessary to pay attention and be informed before making any decision. In addition to optimising processes, choosing the right materials will help us in all sectors of our business. Let’s see what to take into account:
Corrosion resistance
It is necessary to assess what the steel of choice will be used for and where. Factors such as humidity, exposure to chemicals (acids, bases, salts) and extreme temperatures can influence the choice.
Another factor to consider is corrosion. We should determine whether the steel will be exposed to crevice corrosion, pitting corrosion or stress corrosion. This will enable us to make a better choice, as, for example, 316 steel has a better resistance to chloride corrosion than 304.
Mechanical properties
Consider whether you need a harder, wear-resistant material (such as martensitic steels) or one that is more malleable and easier to work (such as austenitic steels). If the steel will be used in high temperature conditions, some austenitic stainless steels (such as 321) perform better.
Manufacturing and processing
If the material is to be welded, choose a type with good weldability, such as austenitic steels. Some martensitic steels may be more difficult to weld. Consider the machinability of the steel, as some grades are more difficult to machine due to their hardness and wear resistance.
Regulations and standards
Check the regulations and standards applicable to your industry. For example, in the food or pharmaceutical industry, materials must comply with specific regulations on cleanliness and corrosion resistance.
Cost
Another point to consider is the price. The cost of different types of stainless steel can vary considerably. For example, 316 steel is more expensive than 304 due to its higher nickel and molybdenum content. Consider the total, which includes not only the initial price of the material, but also the costs of maintenance, durability and life cycle.
Aesthetics
In applications where appearance is important (such as furniture, decoration or kitchenware), choose a stainless steel that has a good surface finish and aesthetic properties (bright, polished, etc.).
Cleaning and hygiene requirements
In industries such as food and pharmaceuticals, it is essential to choose a stainless steel that is easy to clean and does not contaminate products. Austenitic steels are ideal because of their non-porous surface.
Durability and service life
Evaluate the expected service life of the material based on its resistance to corrosion, wear and fatigue. A higher quality type of stainless steel may have a higher initial cost, but may be more economical in the long run due to its durability.
The choice of the type of stainless steel will depend entirely on the needs that your project requires from the material. There is not one better than another, but one more suitable than another. We know what we are talking about, because at Initube we have been in the metallurgical sector for more than 40 years.
We specialise in cutting and machining tubes and profiles of all types of ferrous material, so we can say with confidence that we are here to answer any questions you may have about materials or applications in your sector. All you have to do is contact our team so that we can help you to solve your ferrous doubts.
