Effect of individual alloying elements, Mechanical Engineering

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Effect of Individual Alloying Elements:

Sulfur

Sulfur is not a needed element in steel since in interferes along with hot rolling and forging resulting in hot-shortness or hot embrittlement. Sulfur however, is useful in rising free cutting nature. Thus sulfur upto 0.33 percent is added in free cutting steel. Or else, sulfur is restricted to 0.05 percent in open hearth or BOF steel and to 0.025 percent in electric furnace steel.

Phosphorous

This produces cold shortness that reduces impact strength at low temperature. Hence its percentage is usually restricted to level of sulfur. This is assists in free cutting steels and is added upto 0.12 percent. This enhances resistance to corrosion also.

Silicon

This is present in all steels but is added upto 5 percent in steels employed as laminates in motors, generators and transformers. For offering toughness this is a significant element in steel utilized for spring, and chisels, punches. It has a good consequence in steel such this combines along with free O2 or oxygen and form SiO2 and raise strength and soundness of steel casting as upto 0.5 percent.

Manganese

1.2 to 1.4% of this produces extremely tough, wear resistant and non-magnetic steel named as Hadfield steel. This is significant ingredient of free cutting steel upto 1.6 percent. Manganese combines along with S, forming MnS. For this reason Mn should be 3 to 8 times the S. Manganese is effective in raising hardness and harden-ability.

Nickel

This is good in raising strength, toughness and hardness whilst maintaining ductility.

0.5% of Nickel is good for parts subjected to impact loads at room and extremely low temperatures. Higher amounts of Nickel assist enhance the corrosion resistance in attendance of Chromium as in stainless steel. This in steel result in excellent mechanical properties after annealing and normalizing and thus large structural, castings and forgings parts are made in Ni-steel.

Chromium

This is common alloying element in tool steels, stainless steel, and corrosion resistant steel as 4% Cr. This forms carbide and usually enhances hardness, wear and oxidation resistant at elevated temperature. This enhances hardenability of thicker sections.

Molybdenum

This is commonly present in carburizing steel, heat resisting steel and high speed tool steel. This forms carbide having high wear resistance and retaining strength on high temperatures. Molybdenum generally raises hardeability and assists enhance the effects of other alloying elements like Mn, Nickel and Chromium.

Tungsten

This is significant ingredient of tool steel and heat resisting steel and commonly has similar effects as Mo but 2 to 3 percent W has same effect as 1 percent Mo.

Vanadium

Similar to Mo, V has inhibiting influence on grain development at high temperature. Vanadium carbide possesses water resistance and highest hardness. It enhances fatigue resistance. It is significant constituent of tool steel and possibly will be added to carburizing steel. Harde-ability is markedly increased because of Vanadium.

Titanium

Addition of this in stainless steel does not allow precipitation of Chromium carbide as Titanium is stronger carbide fixes and former are carbon.

Cobalt

This imparts magnetic property to high Carbon-steel. In the presence of Chromium, Co does not allow scale formation at high temperature with increasing corrosion resistance.

Copper

Steel's atmospheric corrosion resistance is increased via addition of 0.1 to 0.6percent copper.

Aluminium

Aluminium in 1 to 3 percent in nitriding steels is added to enhance the hardness via way of forming Al nitride. 0.01 to 0.06 percent Al added during solidification generates suitable grained steel castings.

Boron

Very minute percentage like 0.001 to 0.005 of B is effective in raising hardness, mostly in surface hardening boriding treatment.

Lead

 Less than 0.35 percent Lead enhances machine-ability.

 The effects of alloying element in respect of several desired effects are summarized underneath:

a.      Hardenability - Si, Manganese, Nickel, Cr, Mo, W, B

b.      Toughness - Si, Ni

c.       High temperature strength - Chromium, Mo, W

d.      Corrosion resistance -Cr, Molybdenum, W

e.      Wear resistance - Chromium, Molybdenum, W, V

f.        Low temperature impact strength - Nickel

g.      Atmospheric corrosion resistance - Copper 

h.      Machin-ability - S, P, Pb

i.        Fatigue strength - V

j.        Surface hardening - Al


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