Stainless steel is perhaps one of the most versatile metals used by a wide range of industries and products as it has unique properties that can be used in many applications. When it comes to stainless steel, we noticed there have been a few misconception about its properties and we have decided to work out some of the answers for you!

1. "Stainless steel does not rust "

This is the most common misconception about stainless steel. Perhaps it is due to the word- "stainless steel", many would assume that it is invincible to rusts and therefore, stay "stainless". While the name might suggest that they are rust proof, stainless steel is actually "corrosion-resistant" and will rust in an extreme environment.

Just like steel, stainless steel is composed of the same type of carbon and iron, but it contains an extra magical element that provides resistance protection called chromium. A typical stainless steel usually consists of 12-30% of chromium. When stainless is exposed to oxygen, chromium oxide would form on the surface of the steel and creates a thin coat which glues on the surface and prevents any further oxidation of the stainless steel.

How does stainless steel rust?

According to Polymer Solutions, when stainless steel is scratched and the layer is removed, a new chromium oxide layer will form and protect the rest of the stainless steel beneath and as long as there is enough chromium present, the chromium oxide layer will continue to protect the stainless steel and serves as a shield to rust. 

In other words, the concentration of chromium is the crucial element that prevents the formation of rust. Chromium can protect stainless steel if the localized concentration is in excess of 12%, but if the stainless surface is covered with ample steel particles, it causes the localized concentration of chromium to fall below 12%. The chromium oxide layer would then fail to protect the stainless steel from oxygen attack. Therefore, it is important to provide maintenance to stainless steel by cleaning off all the rust and removing tiny steel particles through cleaning, usually with a solvent to prevent oxidation.

2. "All stainless steel have magnetic properties"

This is another common assumption about the properties of stainless steel. In fact, there are several different families of stainless steels with varied physical properties and its magnetic properties are determined by the chromium and carbon content. However, most of the common stainless steel are "austenitic" in which they have higher amount of chromium and the addition of an extra element known as nickel where it is responsible for altering the physical structure of stainless steel and thereby making it virtually non-magnetic.  

3. "All stainless steel are hard and strong"

Hardness is defined as a material’s ability to resist scratching or indention. Similar to the answer above, the hardness of stainless steel depends on the concentration of chromium and carbon. Increasing carbon content increases hardness and strength as well as improves hardenability. However, it is also important to note that carbon also increases brittleness and reduces weldability.

Stainless Steel Grades

While there are different types of stainless steel, the most widely used stainless steel grades are the 304 and 316 stainless steels:

Type 304

Perhaps the most common and versatile stainless steel, Type 304 grade stainless steel is an austenite steel that has chromium-nickel content and low carbon. It is composed of around 18% chromium and 8% of nickel, which makes it only slightly responsive to magnetic fields. This metal proves to be resistant to oxidation, corrosion and durability. It also exhibits excellent resistance to a wide range of atmospheric chemical, textile, petroleum and food industry exposures. Due to its excellent processing performance and weldability, it is also broadly used in transportation, home appliances and building materials. 304 stainless steel is food-grade stainless steel that is recognized by many countries.

Type 316

The second most popular stainless steel, Type 316 is an austenitic chromium-nickel stainless steel alloy containing molybdenum. The addition of this element increases general corrosion resistance and has greater resistance to chemical attack such as sulfuric acid, chlorides and iodides at high temperature as well as increased strength at elevated temperatures, therefore it is suitable for environments where exposure is to particularly hazardous or corrosive substances commonly seen in the offshore or chemical industry. The fact that it is also negligibly responsive to magnetic fields means that it can be used in applications where a non-magnetic metal is required such as surgical and dental instrumentation.

Similarities

The physical properties of Type 316 are similar to those of Type 304 and share similar characteristics such as:

• They are both austenitic steels and makes up over 70% of total stainless steel production and both cannot be hardened through heat treatment.

•  Both grades offer excellent levels of corrosion resistance especially when compared to other steel types and are quite durable and are easily formed and fabricated.

Differences

• Grade 316 contains an extra element: molybdenum which provides better overall corrosion resistant properties than Grade 304, making it more ideal for more acidic environments.

• Type 316 is also more suitable for sea water environments and marine applications because of its greater resistance to oxidation.

• Type 304 is generally less expensive and is a great choice for kitchen applications and food preparation equipment.

Stainless Steel Bearings

Bearing components made from stainless steel materials have greater corrosion resistance and are non-magnetic because of the low carbon content. As these stainless steel cannot be entirely solid, these bearings is are not suitable to be used in high-load and high-speed environments.

440C Stainless Steel Bearings

AISI Type 440C stainless steel bearing contains high carbon and chromium and is one of the most widely used stainless steel bearings with the advantage of maximum hardness and relatively low cost. Combined with corrosion-resisting and abrasion-resistance properties, they are especially useful in application in severe environmental condition. Grade 440C also provide resistance to crude oil, gasoline, perspirations, foods, fresh water and air.

Slightly magnetic, the high carbon content of Type 440C also allows it to attain the highest hardness levels of any grade of stainless steel bearings when put under heat treatment, which makes them the ideal choice in the heavy industry. Due to the excellent properties of 440C stainless steel bearings, they could be found in numerous products such as food processing machinery, cleaning equipment and other equipment used in high temperature and humidity environments.

Before selecting the appropriate grade of stainless steel bearings, be sure to consider the environment in which you are operating. SLS provides different types of stainless steel bearings and our experienced team is able to provide you with the best solution in selecting the right product and solution for your industry needs.

Want to know more?

If you would like to learn more about the types of stainless steel bearings that SLS has to offer, you can book a consultation with our friendly engineers here: