Practice Questions

The temperature at which austenite-to-pearlite eutectoid transformation occurs is called the lower critical temperature

Chilled cast iron is produced by cooling molten cast iron at a specific rate to form both white and gray cast iron. It is used for surface preparation and as an aggregate in high-density concrete.

From white cast iron by annealing process

An iron-carbon alloy with 4.3% carbon is known as eutectic cast iron. Cast iron with carbon content above 4.3% is hyper- eutectic, while that below 4.3% is hypo-eutectic. Plain carbon steels with less than 0.8% carbon are hypo-eutectoid, while those with more than 0.8% carbon are hyper-eutectoid. A 0.84% carbon steel is known as pearlite steel and is stronger than ferrite or cementite.

Duralumin is an alloy made up of 93% Aluminum, 3% Copper, 2% Magnesium, and 2% manganese. It is used for making airplane blades, wire, bar and rods, forgings, and auto body panels. Alloys are homogenous mixtures of two or more metals or metals and non-metals, which prevent corrosion and give strength to the metal. Other commonly used alloys include brass, bronze, and solder.

Silicon steel with 5% silicon content is widely used in the electrical industry due to its magnetic properties. It increases permeability, resistivity, and decreases hysteresis losses. The addition of silicon to steel improves its soundness and reduces eddy current losses. Therefore, it is used in generators, motors, and transformers.

The crystal structure of α-iron is body centered cubic (BCC) which has one atom at the center and one atom at each corner of the unit cell. BCC is used for brittle materials such as ferrite or α-iron. Face centered cubic (FCC) is used for ductile materials and has one atom at the center, one atom at each corner, and one atom on each face of the unit cell. The iron- carbon diagram shows the crystal structures for different phases.

Martensite is the hardest constituent of steel due to internal strains and plastic deformation. The rate of cooling and carbon percentage directly affect the hardness achieved in martensitic transformation.

Steel with 0.8% carbon and 100% pearlite is known as eutectoid steel. It is much stronger than ferrite or cementite. Hypo-eutectoid steel has less than 0.8% carbon while hyper- eutectoid steel has more than 0.8% carbon. Steel with carbon composition up to 2.1% is considered as steel and beyond this, it is considered as cast iron.

Ferromagnetic materials exhibit permanent magnetism and attractive powers. Nickel, Iron, Cobalt, and Alloys are examples of ferromagnetic materials. Copper, Tungsten, and Aluminium are not ferromagnetic. Ferrimagnetism is another magnetic behavior where the net magnetic moment is achieved due to partial cancellation between ions with different magnetic moments.

Steel with up to 0.15% carbon is known as mild steel. Dead mild steel has a carbon content of 0.05 to 0.15% and is very ductile. Mild steel has a carbon content of 0.15 to 0.3% and is soft and ductile, Medium carbon steel has a carbon percentage of 0.3 to 0.8% and has better strength than mild steel, but is less ductile. High carbon steel has a carbon percentage of 0.8 to 1.5% and is very hard and strong. High- speed steel is a high alloy steel used for cutting tools with a composition of 18-4-1 (tungsten 18%, chromium 4%, vanadium 1%).

Gun metal is a type of bronze, typically composed of 88% copper, 10% tin, and 2% zinc. This alloy is known for its durability and resistance to corrosion, making it ideal for applications in steam and hydraulic systems. Its specific composition allows it to withstand high pressures and temperatures, which is why it is commonly used in the manufacturing of valves, gears, and bearings.

Creep is time-dependent deformation in materials under constant load at high temperature. It occurs in three stages - primary, secondary, and tertiary. The creep rate decreases in primary creep, becomes linear in secondary creep, and increases in tertiary creep leading to necking and fracture.

3. The lower critical temperature of all steels is 723°C, the temperature of Pearlite to Austenite transformation, below which austenite does not exist. Hypo-eutectoid steels have carbon content from 0-0.83% with primary ferrite and Pearlite. Eutectoid steel with 0.83% carbon entirely consists of pearlite. Hyper-eutectoid steels have carbon content from 0.83-2.06% with primary cementite and pearlite. Upper critical temperature (Point A3) is the temperature below which ferrite starts to form in hypo-eutectoid alloys. Upper critical temperature (Point Acm) is the temperature below which cementite starts to form in hyper-eutectoid alloys.

Invar, an alloy of Nickel and Iron, has the nearly zero coefficient of expansion. The coefficient of expansion is the ratio of increase in length, area or volume to its original length, area or volume when the material is heated by 1 degree Celsius or Kelvin.

Austenitic stainless steel contains a minimum of 16% chromium and 6% nickel. It is one of the three types of stainless steel alloys, the other two being ferritic and martensitic. Ferritic stainless steel contains chromium from 10.5 to 18%, while martensitic stainless steel has high carbon and lower chromium content. The given option 1, which states that austenitic stainless steel contains 18% chromium and 8% nickel, is the correct answer.

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