Engineering Materials MCQ Questions & Answers | Mechanical Engineering

A specimen of aluminium metal when observed under microscope shows F.C.C. crystal structure

Machinability refers to the ease with which a material can be cut or machined to the desired surface finish and accuracy.

Grey cast iron has the best machinability among the three because the presence of graphite flakes in its structure acts as a lubricant and reduces tool wear.

Low carbon steel has moderate machinability. It does not have graphite, so cutting is tougher compared to grey cast iron.

Wrought iron has the least machinability due to its fibrous structure and slag inclusions, which make cutting more difficult.

Thus, the descending order of machinability is Grey cast iron > Low carbon steel > Wrought iron.

Toughness is the ability of a material to absorb energy and plastically deform without fracturing.
Toughness is the amount of energy per unit volume that a material can absorb before rupturing.

Substitutional solid solution strengthening occurs when the solute atom is large enough that it can replace solvent atoms in their lattice positions.
Brass (alloy of copper and zinc) is an example of Substitutional solid solution.

The atoms crowd into the interstitial sites, causing the bonds of the solvent atoms to compress and thus deform.
Carbon in iron is an example of Interstitial solid solution.

Manganese increases hardenability and tensile strength of steel, but to a lesser extent than carbon.
It is also able to decrease the critical cooling rate during hardening, thus increasing the steels hardenability much more efficient than any other alloying elements.
Manganese is used to make the blades of bulldozers, bucket wheel excavators and other earth moving equipment contain iron.

Pig Iron
Chemical Composition: C: 3.5 - 4.5%, Mn: 0.4 - 1.0%, Si: 0.5 - 1.2%, P: 0.15% Max, S: 0.04% Max.

Pig Iron
Chemical Composition: C: 3.5 - 4.5%, Mn: 0.4 - 1.0%, Si: 0.5 - 1.2%, P: 0.15% Max, S: 0.04% Max.

Cast iron is a ferrous alloy which has more than 2% carbon in it. Though it can have any percentage of carbon between 2% to 6.67%, but practically it is in between 2% to 4% only.

High silicon iron-based alloys are excellent corrosion resistant materials with advantages of superior corrosion resistant properties, low cost and saving on noble metals such as nickel and chromium.
When containing 14.5% or more silicon, the corrosion resistance of these iron-based alloys is better than that of some cast irons containing a significant amount of chromium, nickel and/or molybdenum, and even than that of certain nickel based alloys in some severe corrosion conditions.