— Some of the popular alloy steels are:
(a) Silicon steel
(b) Silicon-Manganese steel
(c) Nickel steel
(d) Chrome-Nickel steel
(e) Chrome-Vanadium steel
(g) Chrome-Molybdenum steel
(h) Chrome steel
(i) Manganese steel
(j) Tungsten steel
(k) Vanadium steel
(l) Cobalt steel.
(a) Silicon Steel
— Silicon steel contains
C 0.10%, Mn 0.60% and Si 1.00%.
— Silicon imparts strength and fatigue resistance and improves electrical properties of steel.
— Many bridges have been built of what is called Silicon Structural Steel. This is stronger than carbon steel of equal ductility.
(b) Silicon-Manganese Steel
— Silicon-manganese steels contain
C 0.40-0.55%, Si 0.04-1.8%, Mn 0.9-1.0%.
— Such steels are used for springs in the hardened and tempered condition (55 Si 2 Mn 90 steel), and for making punches and chisels.
(c) Nickel Steel
— Nickel steel contains
C 0.35% Ni 3.5%
— Addition of nickel to structural steel results in an increase of strength, without a proportionality great decrease of ductility.
— Nickel steels are used for storage cylinders for liquefied gases and for other low temperature applications.
— Other uses of nickel steels are for heavy forgings, turbine blades, highly stressed screws, bolts and nuts (40 Ni 3 steel).
(d) Chrome-Nickel Steel
— Chrome-nickel steel contains
C 0.35% Ni 1.25% Cr 0.60%
— Chrome-nickel steel will have, after heat treatment, almost the same strength and ductility as 3.5% Nickel steel which has also been heat-treated, but it will not cost as much.
— Chrome-nickel steels combine the effect of nickel (in increasing the toughness and ductility) and chromium (in improving hardenability and wear resistance).
(e) Chrome-Vanadium Steel
— Chrome-vanadium steel contains
C 0.26% Cr 0.92% V 0.20%
— Chromium and vanadium are added to low alloy steel to increase its hardenability and to impart a grain structure that is finer than that of the standard chromium low-alloy steels.
— Chrome-vanadium steel is used for making axles and shafts of automobiles, aeroplanes and locomotives.
(f) Molybdenum Steel
— Molybdenum steel contains
C 0.35% Mo 0.76%
— Molybdenum steel, when heat-treated, produces a structural steel which has increased elastic limit without correspondingly decreased ductility. Molybdenum improves hot hardness and strength of steel. Molybdenum steels are less effected by temper brittleness.
— Molybdenum steels are used for making:
Aircraft landing gear Coil and leaf springs
Fuselage Pressure vessels
Transmission gear, etc.
(g) Chrome-Molybdenum Steel
— Chrome-molybdenum steel contains
C 0.35% Cr 1.06% Mo 0.36%
— Chrome-molybdenum steel has not as good a combination of strength and ductility as nickel, chrome-nickel and chrome-vanadium steels, but it is quite easy to roll and draw into tubes, to fabricate, and to weld, so that it is very popular for airplane structural parts.
(h) Chrome Steel
— Chrome steel contains
C 0.36% Cr 0.57%
— Chromium intensifies the effect of rapid cooling on steel. Therefore chromium is used only in steels which are to be heat-treated.
— Chromium forms carbides and thus gives high hardness and good wear resistance. In addition, chromium increases tensile strength and corrosion resistance of low alloy steels.
% of Cr in steel Uses
8% Electrical purposes
15% Springs, ball and roller bearings.
(i) Manganese Steel
— Manganese low alloy steels are characterized by:
Mn 1.6-1.9% C 0.18-0.48%
Si 0.2-0.35% S and P < 0.040% each.
— Manganese increases hardness and tensile strength. A secondary effect is an increased resistance to abrasion. The steel also withstands the shock test excellently.
— Manganese steels are used for making
Power shovel buckets
Grinding and crushing machinery
Railway tracks, etc.
(j) Tungsten Steel
— Tungsten low alloy steels are tool steels containing approximately 2% tungsten, 1.70% chromium and 0.50% carbon. This is hard tough tool steel that is commonly used for making cutting tools.
— Tungsten forms carbides and prevents softening of the alloy at high temperatures.
— The tungsten steel may contain upto 15% tungsten. Tungsten steel is used for making high speed cutting tools and permanent magnets.
(k) Vanadium Steel
— Vanadium is one of the most powerful scavengers that can be added to liquid steel for the special purpose of removing oxygen. Vanadium has the effect of increasing the strength and hardness of the metal. It produces a very small grain size.
— Except for castings, vanadium is seldom used as the sole alloying element in steel. It is used together with chromium and other elements when high strength and anti-fatigue properties are essential, as in springs, gears, shafts and heavy forgings.
(l) Cobalt Steel
— Cobalt tool steels are used where high frictional heats are developed. Cobalt imparts additional red hardness to steel and cutting ability of tool is maintained at elevated temperatures.