Engineering Materials MCQ Questions & Answers | Mechanical Engineering

Chromium is a powerful alloying element in steel. Cr presents in certain structural steels in small amounts.
It is primarily used to increase hardenability of steel and increase the corrosion resistance as well as the yield strength of the steel material.
For that reason often occurs in combination with nickel and copper. Stainless steels may contain in excess of 12% chromium.

In the lower part of the blast furnace (zone of fusion), the temperature is 1200°C to 1300°C

Definition: Annealing is a heat treatment process in which hardened steel is heated to a temperature above its critical point, held for a specific duration, and then cooled slowly, usually in a furnace.

Purpose: The primary aim of annealing is to soften hardened steel, improve its ductility, relieve internal stresses, and refine the grain structure for better machinability.

Reason: Slow cooling during annealing transforms the steel’s microstructure into a softer and more workable form, making it suitable for further machining or shaping operations.

Why not tempering: Tempering also reduces hardness but its main purpose is to reduce brittleness and improve toughness while retaining most of the hardness; it does not fully soften the steel like annealing.

Conclusion: For complete softening of hardened steel, annealing is the correct and standard heat treatment process.

Sulfur is normally regarded as an impurity and has an adverse effect on impact properties when a steel is high in sulphur and low in manganese.
Sulphur improves machinability but lowers transverse ductility and notched impact toughness and has little effects on the longitudinal mechanical properties.

An engineer's hammer is made of High carbon steel

Molybdenum has effects similar to manganese and vanadium, and is often used in combination with one or the other.
This element is a strong carbide former and is usually present in alloy steels in amounts less than 1%.
It increases hardenability and elevated temperature strength and also improves corrosion resistance as well as increased creep strength.
It is added to stainless steels to increase their resistance to corrosion and is also used in high speed tool steels.

Grey cast iron Contains 1.7 to 3.5% carbon in Free State and is obtained by the slow cooling of molten cast iron.

Silicon element results in presence of free graphite in C.I.

Wrought iron is a form of commercial iron containing less than 0.10% of carbon, less than 0.25% of impurities total of sulfur, phosphorus, silicon and manganese, and less than 2% slag by weight. Wrought iron is redshort or hot short if it contains sulfur in excess quantity.

age hardening is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and some steels and stainless steels.
Age-hardening is related with duralumin