Magnetic Alloy Steels:
These steels are divided into two sets. Such which retain their magnetism and that which do not. The steels which retain their magnetism are termed as hard magnetic steels. The other group is magnetically soft.
1 percent plain carbon steel in its entirely hardened situation was the earliest permanent magnetic material. Later improvements occurred whilst W, Cr and cobalt were added like alloying elements. The most helpful of permanent magnetic steels contain high proportions of Nickel, Co, and Al, along with small amount of W. Alnico is an excellent example that comprises 10% Al, 18% Nickel, 12% Co, 6% Copper, Rest Fe.
Magnetically soft materials are needed to demagnetise rapidly. In prior days soft iron was utilized as a soft magnetic material but later iron-silicon alloys containing upto 4.5 percent Si were improved. Though, modern high duty soft magnetic materials are iron-nickel alloys as like: Permalloy that contains 78 percent Ni. Another soft magnetic material is mumetal having 75% Ni. These alloys are employed for transformer cores and as shield material for submarine cables.
Alloy steels calculate a wide range of application and a few of them are explained in Table.
Table: Application of Alloy Steels
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Sl. No.
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Application
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Desired Properties
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Composition (% )
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1
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Rail steel
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Strength, ductility, impact and fatigue strength
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C - 0.4 to 0.6 Mn and
Cr - upto 1
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2
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Spring steel (tension compression, torsion)
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Good elongation high elastic limit (20 to 30%, 1200-1400 MPa). Good surface finish for fatigue strength
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(a) C - 0.6, Mn - 0.9, Si - 2.0
(b) C - 0.5, Mn - 0.8, Cr - 1.0, V - 0.15
(c) C - 0.5, Ni - 0.9, Cr - 0.5, Ni - 0.6, Mo - 0.2
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|
3
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Structural steel (bridges, building, cars, gears, clutches, shafts)
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High strength, toughness, high temperature strength, corrosion resistance
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Wide range of alloy steels containing several alloying elements
|
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4
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Weldable steel for welded structures
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Weldability, high resistance to atmospheric corrosion, resistance to brittle fracture
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C - 0.15 to 0.3 with some
Cu and V
|
|
5
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Concrete reinforcing steel
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Bend 90o - 180o, tor-steel with ribs for greater surface area.
Elongation = 16%, UTS = 500-650 MPa, Y. S. = 35 MPa.
Elongation = 13%,
UTS = 600 MPa, Y. S. = 350 MPa
|
C - 0.3 to 0.4, Mn - 0.5 to 0.8
C - 0.45 to 0.6, Mn - 0.7 to 1.1
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6
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High speed steel for cutting tools
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Resist temperature upto
550-600oC. Cutting tools requiring high hardness at working temperature 18 : 4 : 1 steel and
6 : 5 : 4 : 2 steel
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C - 0.8, W - 18, Cr - 4, V - 1,
C - 0.8, W - 6,
Mo - 5, Cr - 4, V - 2
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7
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Creep resisting steel
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Application in pipelines upto
400-550oC. Other parts upto
550oC
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Mo - 0.4 to 6
V - 0.25 to 1.0
Cr - upto 6.0, C - low
|
|
8
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Hadfield Mn steel, excavating and crushing m/c. rail road crossing, oil well, cement, mining industries. Used as casting and hot rolled
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Resistance to abrasion and shock, high toughness strength and ductility
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C - 1 to 1.4,
Si - 0.3 to 1.0, Mn - 10 to 14
|
|
9
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High strength low alloy steel (HSLA) for automotive parts
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High strength/weight ratio. Balanced properties such as toughness, fatigue strength, weldability and formability
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C - 0.07 to 1.3, Ti, V, Al, Co less than 0.5
|
|
10
|
Ball bearing steel
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Rolling element, inner and outer races. High hardness
61-65 Rc high fatigue strength
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C - 0.9 to 1.1, Cr - 0.6 to 1.6, Mn - 0.2 to 0.4
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