Magnetic Properties of Steel

Introduction To What Element Is Steel

Steel is a byproduct of iron. Iron is extracted via the blast furnace process, in which the slag floats on the top and the molten iron runs into sand moulds where it solidifies to give pig iron so called because of the shapes of ht solid lumps. Pig iron is not pure iron and contains 3-5% of carbon and 2% of phosphorous, silicon, sulphur, and manganese. Pig iron is brittle and cannot be welded.

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Properties of steel

Removal of part of the carbon and other impurities from pig iron results in steel which is the most common usable form of iron. One of the processes for making steel from pig iron is the Bessemer process. In this process, the molten pig iron from the blast furnace is run into the steel making furnace called the Bessemer converter. The converter is a large pear shaped vessel with holes below. Through these holes, air is blown into the molten metal. The air oxidizes the carbon in pig iron to carbon monoxide which burns at the mouth of the converter. When all the carbon has burnt away, the flames of burning carbon monoxide die out. At this stage, the required amount of carbon and manganese is added to produce the desired type of steel.

The amount of carbon in steels varies from 0.2 to 1.7 percent carbon. When the carbon content is high, the steel is hard and brittle; when low, the steel is soft and tough. Unlike cast iron, steel can be forged, welded, cast tempered, rolled into sheets or drawn into wires. The mechanical properties of steel, example hardness, elasticity, tensile strength, etc., can be varied as desired by proper heat treatment, that is by heating and cooling steel under definite conditions.


Fig1: Atomic structure steel

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Different Classes of Steel

Different classes of steel are Crucible steel, spring steel (low or no alloy), Carbon steel (=2.1% carbon; low alloy), Alloy steel (contains non-carbon elements), Maraging steel (contains nickel), Weathering steel, Stainless steel (contains about =10.5% chromium), and Tool steel (alloy steel that is used for tools)

Magnetic Properties of Steel:

Steel is a ferromagnetic compound. When iron is heated, adding carbon to it and then cooled, the carbon gets incorporated in the atomic structure of the iron, thereby hardening it. The alloy thus formed is steel. Different alloys of iron produce steels with different properties. Steel retains magnetism longer than iron, because of its hardness.

Magnetism is a force of magnetic objects, which allows them to affect some metals and other magnets at a distance. Steel is actually useful as a magnetic material.The ability of a material to hold magnetism, is called magnetic permeability and is indicated by its degree of attraction. Except for the austenitic group, all stainless steels are strongly attracted to a magnet. Hence it has a high permeability, depending on the alloy used. When an external magnetic field is applied, it turns into a permanent magnet. Due to this, the magnetic field inside steel will be 50 times higher than the field applied to it.

Magnetic and non- magnetic steel

Non-magnetic steel (austenitic):

The change in magnetic effect is due to the straining of atomic lattice and formation of marten site. If the nickel to chromium ratio is high, its austenitic structure is more stable. Stainless steel can thus be graded using the magnetic response.

Austenitic grades have low magnetic permeability though magnetic stainless steel does exist. Steel with chromium, but no nickel, does exhibit magnetic qualities, though the degree of magnetic attraction may vary. Magnetic stainless steel does not carry a strong magnetic charge in consumer products, so magnetic attraction has no domestic uses.

Austenitic (non-magnetic) Stainless Steels:

Austenitic stainless steels are non-magnetic or paramagnetic in well-annealed alloys.

Ferritic (Magnetic) Stainless Steels:

Ferritic stainless steels are ferromagnetic and are used as soft magnetic components. Their magnetic properties are not as good as soft magnetic alloys.

Their soft magnetic properties are high magnetic permeability, low residual induction and low coercive force.

Stainless steels vary in their magnetic properties, ranging from paramagnetic, non-magnetic, to hard or permanent magnetic behavior.

Usage of Steel:

There are various applications of steel. Steel can be used to make cutleries, cutting tools, decorative, electromagnets etc. various metals are mixed with steel to change the properties to as desired. So no two alloy of steel will depict the same property. For example when steel is used to prepare electromagnet it has retentivity as its property.

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