So, is Steel magnetic? Some grades of steels are magnetic and some are non-magnetic. Martensitic steel consists of ferritic microstructure due to which it shows magnetic behavior whereas austenitic grades have nickel present in it and they do not show magnetic behavior. Therefore, different steels have different answers regarding magnetic properties. Let us read more about this variation of magnetic properties with different grades of steel in more detail! There cannot be a straightforward answer to this question. There are various grades of steel present in the market, where some of them are magnetic while some of them are not. Therefore, there is no direct conclusion that can be made on this question. A more general outlook towards this question can help in answering the question with a ‘No’ that is the steel is not a magnetic material. There are many more interesting questions that can be raised here, which are summarized as follows –
Why are some materials magnetic?
We can find the answer to this question when we dive deep right to the atomic level. In each atom, there are electrons present which are orbiting the positively charged nucleus in an atom. Electrons, the negatively charged subatomic particles, are identified with three inherent properties namely, mass, charge, and the spin of electrons. The spin of an electron refers to the angular momentum gained during rotation on its own axis. Most of the elemental atoms have electrons whose spins have been paired or coupled. These types of atoms are not useful for the generation of magnetic character. In elements like iron (Fe), there are unpaired electrons and thus unpaired spins present. One such metal is tungsten having weaker magnetic behavior. Read out the article regarding magnetism in tungsten. This ensures that the overall summation of the angular momentum is non-zero and therefore can interact with a magnetic field. Therefore, the presence of unpaired electrons in an atom is the prerequisite for a material to exhibit magnetic properties.
Magnetic Properties of Austenitic, Ferritic and Duplex Stainless Steel
There are different grades of steel and stainless present in the market, depending upon the percentage of constituents present in the final mixture or alloy. It is very difficult to comment as some types of steel will be magnetic as well as some of them will not be magnetic. In the alloy making process, magnetic properties of the core elements such as iron are hampered because of the changes in the microstructure. Some microstructures still exhibit magnetic properties while others cease the same.
- Ferritic: The ferritic type of microstructure is magnetic originally because of which the martensitic steel shows magnetic properties. Ferritic grades behave similarly to the carbon steel grade of steel.
- Austenitic: The presence of nickel in some types of stainless steel disturbs the overall structure and magnetic properties are ceased to nonexistent. These types of steel grades are called as austenitic grades. Austenitic microstructures are not very stable and tend to undergo a phase transition to exist as ferritic structures. But the nickel present makes the austenitic microstructures stable thus restraining any phase transition to take place even at room temperature. Austenitic grades show more corrosion resistance as compared to that ferritic grade. This observation has published a myth that corrosion resistance and magnetism are inversely related to each other. However, this is not true and these two things are not related to each other.
- For Duplex, there are two microstructures present namely ferritic and austenitic, this makes duplex steel diamagnetic in nature because of the equal and opposite magnetic dipole or moment.
The Magnetic Properties of Stainless Steel 304 and Stainless Steel 316
The main difference in the magnetic properties arises because of the core microstructure which is dependent upon the composition and the constituents as well. Within the allowed ranges of variation of Ni and Cr, significant differences in magnetic properties may be observed for a given alloy. If we look at the typical composition, we can summarize the following –
The other major aspect is the alloying process. During the preparation of 304 and 316, at high temperatures, the austenitic microstructure is preferred when cooled as compared to the ferritic, which gives the magnetic properties. Some crystals might also take crystallize with the ferritic type of structures however it will not be very significant in comparison to the austenitic. Hence, they might have better magnetic properties than diamagnetic materials but cannot be regarded as magnetic as well.
The Different Types of Magnetic Materials
Magnetic materials are further classified depending upon the interaction they have with the external magnetic field and are listed as follows – Diamagnetic materials – Non-magnetic materials are called diamagnetic in nature. For example – Glass. Paramagnetic materials – Materials that get weakly magnetized when exposed to an external magnetic field are called paramagnetic materials. We can regard elements such as aluminum as paramagnetic materials. Ferromagnetic materials – Materials that get strongly magnetized when exposed to an external magnetic field and can sustain this induced magnetism either temporarily or permanently are called ferromagnetic materials. Elements like iron and cobalt fall under this category. Ferrimagnetic materials – Materials that get moderately magnetized when exposed to an external magnetic field are called ferromagnetic materials. They cannot this induced magnetism for a long period.
Can Magnetism be Induced?
Yes, magnetism can be induced into a material by bringing it close to a strong permanent magnet. However, a popular idea to induce magnetism is to introduce the magnetic material into a changing electric field. This induced magnetism subsides as soon as we remove the external factor responsible for it. We can differentiate permanent magnets and induced materials using a very preliminary property that the permanent magnets attract a magnetic material but do not repel it, while a material with induced magnetism will not behave in the same fashion.
Properties of Steel
The most important properties of steel are associated with durability and strength. In the case of stainless steel, the prime property is the resistance to corrosion. Steel has a higher strength to weight ratio ie; 1/16. It can carry a load multiple times its own weight. This property of steel is quite instrumental in making the complete building structure lightweight. The steel has a value of its coefficient of linear thermal expansion around 12 ×10-6 °K-1. All of these can be summarized that – steel has high strength, durability, corrosive resistance, and good thermal coefficient as well.
Conclusion
Magnetism is a very important physical phenomenon that is governed by the movement of subatomic particles. Talking about magnetism regarding steel cannot be pinpointed because some grades or types of steel show magnetic properties and some do not. Therefore, it is better to talk about individuality as it depends on the microstructures. There are boundless applications to magnets and magnetic materials, it still allocates a large number of funds for research and understanding magnetism in a detailed manner.
