All of us use products made of stainless steel in our daily lives. But have you ever wondered why we use it instead of steel?
Well, stainless steel is highly resistant to rusting, making it highly resourceful for industrial purposes. Ever wondered about its electrical conductivity?
Does stainless steel conduct electricity? Yes, it does. Because stainless steel is a metal alloy, it has the property to conduct electricity but is not as strong as copper or aluminum. Therefore, stainless steel is a poor conductor of electricity. While carbon steel offers a resistivity that is eight times higher than copper, stainless steel has a resistivity that is 40 times higher than copper.
Did you know that stainless steel can be of various types?
Every kind of stainless steel has its specialty. In this article, we’ll discuss stainless steel’s characteristics as an electricity conductor.
But before we get to that, we’ll also tell you what it is chemically composed of. Also, do you exactly know what electrical conductivity is?
Stay with us till the end to satisfy your curiosity.
What is Stainless Steel?
Stainless steel is an alloy that consists mainly of iron and chromium along with other elements like nickel. It consists of about 10 to 30 percent of chromium.
The exact components of stainless steel depend on the type of stainless steel we want as well as the purpose for which it is required.
Few of the other elements added to this alloy are – aluminum, copper, titanium, nickel, molybdenum, nitrogen, sulfur, phosphorous, and selenium.
These additives enhance its property of corrosion resistance, induce special characteristics, and keeps the stainless steel rust-free.
Did you know that stainless steel is almost 100 percent recyclable? It can be recycled an infinite number of times. It is this quality of the alloy that makes it a “green material.”
Stainless steel is a green material because it’s an inert alloy and is, therefore, environmentally neutral.
Additionally, it doesn’t release any toxins that pollute the environment either.
You could say that stainless steel is a boon to both Nature and humans. It has an excellent aesthetic appeal, long durability, strength, and easy maintenance, making it an ideal material to be used in industries, buildings, transportation, research, and logistics.
Now, let’s dive into the various types and grades of stainless steel and learn how they differ from one another.
Types of Stainless Steel
Most of you know must already know that stainless steel is mainly used for its property of corrosion resistance and being rust-free.
But if it has only this purpose, why does it need to have different kinds? That’s what we are going to figure out in this section.
There are five major categories of stainless steel to make it suitable for withstanding different situations and conditions.
These categories are classified on the basis of their microstructures.
1. Austenitic Stainless Steel
Austenitic stainless steel is a kind of stainless steel that has the primary microstructure made up of austenite. Do you have an idea about what austenite means?
Austenite is a solid solution containing iron and carbon. This solution comes into existence when the critical temperature rises above 723 degrees centigrade.
This stainless steel is 70 percent austenitic and contains a minimum of 16 percent chromium and 6 percent nickel. For the formation of the austenite microstructure, austenitic stabilizers are used. It is a non-magnetic alloy.
Its impressive properties include its resistance to extremely high temperature and display of a high level of strength and toughness.
2. Ferritic Stainless Steel
Ferritic stainless steel is a type of stainless steel that has only chromium as its additive. It contains 10.5 percent to 18 percent of chromium. In comparison to the austenitic stainless steel, it displays poor fabrication
characteristics and poorer corrosion resistance.
Then what’s so great about it? Well, in terms of engineering abilities, it is better than austenitic stainless steel, and also it is magnetic. Additionally, its resistance to stress corrosion is pretty good.
3. Duplex Stainless Steel
Duplex stainless steel is a combination of austenitic and ferritic stainless steel. This stainless steel contains high amounts of chromium and low amounts of nickel.
As duplex stainless steel is a combination of both austenitic and ferritic stainless steel, it contains the attributes of both types of stainless steel.
Because of the power of this combination, it has properties of both high tensile strength and good weldability.
Even though duplex stainless steel exhibits good stress corrosion resistance, ferritic stainless steel is better in this field. Its toughness is lower than the austenitic type but higher than the ferritic type.
4. Martensitic Stainless Steel
Martensitic stainless steel is a kind of stainless steel that contains high amounts of carbon and low amounts of chromium.
Even if austenitic, ferritic, and martensitic stainless steel have the same amount of chromium and alloy content, martensitic stainless steel displays a lower corrosion resistance.
It has an impressive property of high hardenability. Guess what? Its properties can even improve when it is heat-treated.
5. Precipitation Hardening Stainless Steel
Precipitation hardening stainless steel is a kind of stainless steel that has properties of both austenitic and martensitic stainless steel.
The perfect proof of this combination is its ability to harden and its ability to develop high tensile strength through heat treatment.
Hardening in this type of stainless steel is achieved by adding one or more additives like copper, aluminum, and titanium.
Nickel and chromium are present as alloying elements in this kind of stainless steel. It’s specially is in high-speed applications like turbine blades.
Grades of Stainless Steel
The American Iron and Steel Institute (AISI) system is used to name different stainless steel grades.
This system numbers the different metal alloys in 3-digit numbers starting with 2, 3, and 4.
The 200 series consists of austenitic stainless steel containing manganese. This grade has a low nickel content (below 5 percent).
200 series is used for producing cutleries, washing machines, etc.
The 300 series finds its use in austenitic stainless steels containing nickel, carbon, and molybdenum.
While molybdenum improves its resistance to corrosion in acidic surroundings, nickel improves its ductility.
300 series finds its use in the automobile industry, jewelry, etc.
The 400 series of stainless still consists of martensitic and ferritic stainless steel. It can undergo heat treatment and provides high strength and corrosion resistance. However, its ability to resist corrosion is lower than 300 series.
400 series is used as decorative steel as well as for automotive trim.
What is Electrical Conductivity?
In layman’s words, electrical conductivity is the ability of the material to carry current.
It is an attribute that tells us how well any given material can conduct electricity.
Electrical conductivity is also defined by the amount of voltage required for a certain amount of electric current to flow.
It is represented by the symbol σ and measured in Siemens per meter or S/m.
Substances that have high electrical conductivity, such as aluminum and copper, are called conductors, while those that have a lesser or no conductivity, such as rubber, are known as insulators.
Electrical conductivity and electrical resistivity are closely related. It is because electrical conductivity is the inverse or reciprocal of electrical resistivity.
The following formulae can explain their relation:
σ = 1/ρ
where σ is electrical conductivity and ρ is electrical resistivity.
Now, for material with a uniform area of the cross-section, the resistivity is:
ρ = RA/l
where R is electrical resistance, A is the area of cross-section, and l is the length of the material.
The following is a list of metals and metal alloys ranked from best to worst in terms of electrical conductivity:
If you go through the list carefully, you can deduce that stainless steel has the lowest conductivity among all the metals mentioned above and metal alloys.
The Electrical Conductivity of Stainless Steel
Even though stainless steel is a metal alloy, it is a poor conductor of electricity, unlike most metals. It has an electrical conductivity that is a lot lesser than the value of conductivity of silver and copper.
At 20 degrees Celsius, silver and copper have a conductivity of 6.30×10 7 S/m and 5.96×10 7 S/m, respectively, while stainless steel has an electrical conductivity of 1.45×10 6 S/m.
Therefore, the most conductive metal, i.e., silver, has an electrical conductivity almost 60 times higher than that of stainless steel.
The electrical conductivity of stainless steel might be low, but it gives rise to electrical contact resistance (ECR) because of the presence of protective oxide layer limiting its functions in applications as electrical connectors.
Mostly, copper alloys and connectors coated with nickel with lower ECR values are used as electrical connectors.
Stainless steel connectors are used only when the design criteria are low, and high corrosion resistance is required in conditions, such as in highly oxidizing environments and high temperatures.
You might be wondering what contact resistance means? It is the resistance of a material to the flow of electricity because of surface contacts.
From the above list of ranked metals and metal alloys, you can see that even carbonized steel has a higher conductivity than stainless steel.
Did you know that Type 304 and Type 316 are the most common grades of stainless steel used in the electronic industry for their high corrosion resistance?
Stainless steel is also used in electrical enclosures for floor mounts, freestanding junction boxes, and wall mounts.
As we reach the end of the article, we can conclude the initial question by saying that stainless steel is a poor conductor of electricity compared to other metals and metal alloys. Grades 304 and 316 of stainless steel are used as electrical connectors.
Even though it has a low electrical conductivity, stainless steel is highly useful and has been successfully replacing steel in various industries. Steel can rust, but stainless steel doesn’t. This results in the longer shelf life of all stainless steel products.
Its longevity, as well as its ability to be recycled, makes it highly crucial for us to use it more instead of depleting our essential resources.