While they are both alloys of iron and carbon (as is common steel) with a lot of chromium added which makes them corrosion resistant, depending on their atomic structure and alloy composition (including adding more material) they will be more Corrosion resistant or have other properties that make them better for some applications or others.
For example, austenitic stainless steels, unlike ferritic, martensitic, and duplex stainless steels, are exceptionally resistant to corrosion. They are the most common and are achieved by adding enough austenite stabilizing elements such as nickel, manganese and nitrogen, which makes them less hardenable during heat treatment and non-magnetic. The two most common types of austenitic stainless steel are the so-called 304 stainless steel and 316 stainless steel.
300 Series Austenitic Stainless Steel
Austenitic stainless steels are divided into two main groups, the 200 series and the 300 series. The 200 series are mainly based on manganese and nitrogen to achieve their austenitic structure, although they contain small amounts of nickel, while the 300 series are basically achieved by the addition of nickel.
The 300 series stainless steels are the largest subgroup of austenitic steels, and the most common in this series is type 304, also known as 18/8 or A2 steel.
304 stainless steel and 316 stainless steel, another widely used reference material of the same family, both contain high levels of chromium and nickel (we will see in the next section that the proportion of each element is related to its weight, depending on the type of steel), This makes them particularly resistant to corrosion. They also contain important alloying elements: carbon, manganese, phosphorus, sulfur and silicon, in the same weight ratios as these two steels. The rest of the chemical composition is basically iron.
304 Stainless Steel vs. 316 Stainless Steel: The Difference Between the Two Qualities
To the casual observer, the difference between one type of stainless steel and another is imperceptible, as we have commented on previously. However, for a manufacturer, the difference between stainless steel alloys such as 304 stainless steel and 316 stainless steel can be enormous.
The main difference between the two steel grades is that 316 stainless steel contains molybdenum in addition to all the alloying components of iron, carbon, chromium and nickel and all the elements described in the previous section. Molybdenum significantly improves corrosion resistance, especially in environments with the highest salt content or chlorine exposure.
This is why 316 stainless steel is often referred to as "acid resistant steel", this quality makes it more suitable for application in offshore and even underwater structures, although 304 stainless steel, it has considerable corrosion resistance due to its chromium ratio is slightly higher. In summary, while both 304 and 316 stainless steel are suitable for extreme environments, only the latter can withstand prolonged exposure to chlorides.
Application of 304 stainless steel
As mentioned above, 304 stainless steel is the most common austenitic steel. Its nickel content is usually 8 to 10.5% by weight and its chromium content is usually 18 to 20% by weight. These high percentages give stainless steel 304 high corrosion resistance. In addition, it contains important alloying elements such as manganese, silicon, and carbon, just like stainless steel 316. The rest of the chemical composition is basically iron.
For outdoor furniture such as railings and bollards, stainless steel is an ideal material for corrosion resistance, but can only withstand prolonged exposure if the quality is suitable for its environment. 304 is an economical choice for most environments, but does not have the chlorine resistance of 316.
Other examples of its application are.
Sink and backsplash.
Pots and pans.
Cutlery and crockery.
building panels.
Sanitary ware and sink.
pipeline.
Brewing, dairy, food and pharmaceutical production equipment.
Springs, nuts and bolts.
Application of 316 stainless steel
This is a stainless steel that is very similar to grade 304, also because of the high levels of chromium and nickel in its chemical composition. However, 316 stainless steel contains large amounts of molybdenum, ranging from 2% to 3%, which makes it more corrosion resistant than 304 stainless steel, so it is suitable for extreme applications, such as marine applications, and affects the price of the material.
The slightly higher price of 316 stainless steel compared to 304 stainless steel pays off in areas of high chlorine exposure, especially coastal areas and high salinity infrastructure such as coastal roads. In such applications, 316 stainless steel will last longer than 304 stainless steel, which means many life extensions. However, its molybdenum content has an adverse effect on formability.
Common applications for this steel include.
Food preparation equipment, especially in chlorinated environments.
Countertops and lab equipment.
Coastal architectural panels, grilles and moldings.
boat accessories.
Chemical containers, included for transport.
Heat Exchanger.
Woven or welded screens for mining, quarrying and water filtration.
Threaded fasteners.
spring.
How do you know if the steel is 304 stainless steel or 316 stainless steel?
You cannot tell the difference between 304 stainless steel and 316 stainless steel with the naked eye because there is no discernible difference between two pieces of the same metal, one is polished or textured in exactly the same way by one material or the other. To prove that the stainless steel is inox 304 or inox 316, a Material Test Report (MTR) of the actual material is required. Some small parts made of 316 stainless steel, such as clips and mounting feet, have special markings.
304 Stainless Steel or 316 Stainless Steel: Which to Choose?
Every stainless steel application has unique requirements that require a stainless steel that is up to the task.
In some cases, 304 stainless steel may be the best choice.
Where excellent formability is required.
Where high formability is required.
Those who are on a budget and need affordable materials.
Some situations where 316 stainless steel may be the best choice are.
Environments containing large quantities of corrosive elements.
Where those materials will be placed in or exposed to water on a regular basis.
Those where more resistance and stiffness are needed.
