Although stainless steel is commonly used in many industries, thanks to its high corrosion resistance, hygiene, and strength with over 150 grades available, it becomes quite challenging to pick the right grade during the selection process.
Since stainless steel is an incredible metal that offers a variety of alloys, picking the right grade can go a long way to ensuring that your job is done seamlessly. There are many factors you can consider while selecting a grade of stainless steel.
The amount and type of corrosion resistance desired
Usually, stainless steel is chosen for its corrosion-resistant properties. But you have to consider the amount and the type of corrosion resistance that is desired. Different grades come with different amounts of corrosion resistance.
For instance, Austenitic stainless steels can give you the most corrosion resistance since high amounts of chromium are present. Thus, you can opt for grade 304 when corrosion resistance is vital. Grade 316 and grade 304 are comparable, but since grade 316 has molybdenum as part of its chemical makeup, its corrosion resistance is more.
If you are looking for a more affordable grade, you can settle for Ferritic and Martensitic stainless steel. Still, their corrosion resistance is low owing to the presence of less nickel and sometimes less chromium.
To avoid stress corrosion cracking that comes with Austenitic stainless steel, you can opt for Duplex stainless steel.
Consider your operating environment
You will have to consider your operating environment before investing in a stainless steel grade. Think about the environment where you will use your final product. While it will be okay to use stainless steel to make a door frame in your home or offices, regular stainless steel can’t sustain extremely low pH, high temperatures, high stresses, and crevice corrosion.
Go for stainless steels in the austenitic T3XX series, such as 316 and 304 alloys.
They can retain their strength, toughness, and corrosion-resistant properties over the broadest temperature range. Type 316 can even resist chloride ions that you find in marine and chemical processing applications.
Note that you can’t weld all types of stainless steel grades. Stainless steels that are prone to hot cracking and stress corrosion cracking cannot be used to weld. For instance, Martensitic stainless steels are high in carbon content, making any type of change difficult. Thus, this stainless steel type is bad for welding.
You can opt for grades such as 304 or 304L as they come with little carbon in comparison to other stainless steel grades. Generally, austenitic stainless steel grades are best for welding and formation though stress cracking can occur.
Using little ferrites is recommended to protect the material from cracking. This is the exact reason why duplex steels exhibit great weldability and formability properties. As long as you choose the right grade, such as Grade 430 and 407 Ferritic stainless steel can also be welded. But consider the fact that many ferritic steel grades are bad for welding owing to their poor HAZ (heat affected zone) toughness. They can crack in the wrong temperature range.
Give importance to the mechanical qualities
Strength, ductility, and toughness are the three top mechanical qualities that should be given importance. Stainless steel comes with 10–30% chromium as its alloying element. It is this element that helps it resist corrosion.
When it comes to austenitic grades, the presence of nickel provides the highest toughness and ductility among stainless grades. Stainless steel grades that are most resistant to corrosion are those rich in chromium, molybdenum, and nickel.
Moreover, make sure that you should not be focusing solely on the alloy content when choosing a grade of stainless steel. How the material is processed will also affect its mechanical response.
How long the steel is held at different temperatures as part of its cooling process and the total speed at which it is cooled will affect its overall quality. It is true that heat treatment can increase the hardness of carbon steels, but austenitic stainless steel is hardened by cold working operations, including bending, rolling, swaging, or drawing at temperatures lower than the re crystallization temperature.
Note that when hardness is increased by cold working operations, it will decrease other properties such as elongation and impact resistance.
Consider the magnetic response
You will find different families of stainless steels with different physical properties. The magnetic properties of stainless steel are determined by the elements added into the alloy.
Basic stainless steel displays a ‘ferritic’ structure and is magnetic as a result of the addition of chromium.You can harden it by adding carbon, thus making it ‘martensitic.’
On the other hand, the most common stainless steels are austenitic as they come with higher chromium content. You will also find nickel, which modifies the physical structure of the steel, making it non-magnetic.
Austenitic grades have a low magnetic reaction or ‘relative magnetic permeability.’ The stainless steel grades rich in nickel content like the 316 or 310 grades are non-magnetic in any situation.
Thus, you can use them in applications where you require a non-magnetic metal. If you are looking for stainless steel grades with high magnetic response, opt for the ferritic and martensitic stainless steel grades (400 series). They come with high permeabilities and are classified as ‘ferromagnetic.’ Also, consider the Duplex grades like 2101 and 2205 while looking for ferromagnetic stainless steel grades.
Winding-Up Since there are a plethora of grades of stainless steel to choose from, displaying different properties, you have to determine which type of stainless steel you require depending on its application. Going for the right stainless steel grade will help you complete your project seamlessly while also saving you money.
Source: Construction Review Online
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