10+ Hitachi Hi-Rel Power Electronics Interview Questions and Answers

The temperature range for various heat treatments in metallurgy varies depending on the specific process.

• Annealing temperature range: 300-1200°C

• Quenching temperature range: Room temperature to 200°C

• Normalizing temperature range: 800-950°C

• Austempering temperature range: 250-450°C

• Other heat treatments have their own specific temperature ranges

• Temperature ranges can also vary depending on the type of metal being treated

The diameter of the DI pipes continuously casted at NML was 100mm.

• DI pipes were continuously casted at NML

• The diameter of the pipes was 100mm

Heat treatment processes differ in temperature, time, and cooling rate to achieve desired material properties.

• Annealing: heating and slowly cooling to reduce hardness and increase ductility

• Quenching: rapid cooling to increase hardness and strength

• Tempering: heating and cooling to increase toughness and reduce brittleness

• Normalizing: heating and cooling to refine grain structure and improve machinability

• Hardening: heating and cooling to increase hardness and wear resistance

• Sph...read more

Hardness and strength are related but not the same. Hardness is a measure of resistance to indentation while strength is a measure of resistance to deformation.

• Hardness is a measure of a material's ability to resist scratching, cutting, or penetration.

• Strength is a measure of a material's ability to resist deformation or fracture under an applied load.

• Hardness and strength are related because materials that are harder tend to be stronger, but this is not always the case.

• For e...read more

Heat treatments include annealing, tempering, quenching, and case hardening. Each process has unique properties and uses.

• Annealing involves heating and slowly cooling to soften metal and improve ductility.

• Tempering involves heating and cooling to increase toughness and reduce brittleness.

• Quenching involves rapid cooling to increase hardness and strength.

• Case hardening involves adding a hard outer layer to a softer metal.

• Each process has specific temperature and time requireme...read more

The diameter of DI pipes used during the continuous casting process varies depending on the specific application.

• The diameter of DI pipes used in continuous casting can range from 100mm to 1000mm or more.

• The diameter is determined by factors such as the size of the casting machine, the type of metal being cast, and the desired output.

• For example, a smaller diameter pipe may be used for casting smaller products like rods or bars, while a larger diameter pipe may be used for ca...read more

Cryogenic process of heat treatment involves cooling materials to extremely low temperatures to improve their properties.

• Materials are cooled to temperatures below -150°C using liquid nitrogen or helium.

• This process improves the wear resistance, toughness, and dimensional stability of materials.

• Common applications include treating tool steels, aerospace alloys, and superconducting materials.

• The process can also be used for stress relieving and improving the magnetic propertie...read more

Fe-C diagram with peritectic or eutectic lines

• Fe-C diagram shows the phases of iron-carbon alloys at different temperatures and carbon concentrations

• Peritectic line separates the liquid and solid phases during cooling

• Eutectic line separates the two-phase region from the three-phase region

• Peritectic reaction occurs when a solid phase reacts with a liquid phase to form a new solid phase

• Eutectic reaction occurs when a liquid phase transforms into two solid phases at a specific c...read more

Strength and hardness are related but not the same. Strength is the ability to withstand force while hardness is resistance to deformation.

• Strength refers to the ability of a material to withstand an applied force without breaking or deforming.

• Hardness refers to the resistance of a material to deformation, scratching, or abrasion.

• A material can be strong but not hard, such as rubber, or hard but not strong, such as glass.

• The relationship between strength and hardness depends ...read more

Heat treatment includes annealing, tempering, quenching, and normalizing.

• Annealing involves heating the material to a specific temperature and then cooling it slowly.

• Tempering involves heating the material to a specific temperature and then cooling it quickly.

• Quenching involves heating the material to a specific temperature and then cooling it rapidly.

• Normalizing involves heating the material to a specific temperature and then cooling it in still air.

• Each form of heat treatme...read more

Continuous cooling curves show the cooling behavior of a material during solidification.

• Continuous cooling curves are used to determine the cooling rate required for a material to achieve a desired microstructure.

• They are plotted by cooling a sample at a constant rate and measuring its temperature as a function of time.

• The curves can be used to predict the formation of different phases and microstructures in the material.

• Examples of materials that can be analyzed using contin...read more

Fe-C diagram shows the phases of iron-carbon alloys at different temperatures and carbon concentrations.

• The diagram is also known as the iron-carbon phase diagram.

• It is used to understand the behavior of steel and cast iron.

• The diagram shows the different phases of iron and carbon at different temperatures and carbon concentrations.

• The diagram has three main regions: austenite, ferrite, and cementite.

• The eutectoid point is an important feature of the diagram.

• Bifurcations occu...read more

Le Chatelier's principle states that when a system at equilibrium is subjected to a change, it will adjust to counteract the change.

• Le Chatelier's principle is a fundamental concept in chemical equilibrium.

• It states that when a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will shift in a way that counteracts the change.

• For example, if the concentration of a reactant is increased, the equilibrium will shift towards the p...read more

Minerals are naturally occurring inorganic substances with a definite chemical composition, while metals are a type of mineral that have high electrical conductivity and luster.

• Minerals are inorganic substances found in nature, while metals are a subset of minerals with specific properties.

• Metals have high electrical conductivity, malleability, and luster, distinguishing them from other minerals.

• Examples of metals include iron, copper, gold, and silver, while examples of non-...read more

WHRB in rotary kiln stands for Waste Heat Recovery Boiler, which is used to recover heat from the exhaust gases of the kiln.

• WHRB is a type of boiler that captures and reuses the heat energy from the exhaust gases of a rotary kiln.

• It helps in improving the overall energy efficiency of the kiln operation.

• The recovered heat can be used for various purposes such as preheating combustion air or generating steam for power generation.

• WHRB systems are commonly used in industries like...read more

Iron smelting process is a method of extracting iron from its ore using heat and reducing agents.

• Iron ore is heated in a blast furnace with coke (carbon) and limestone as reducing agents.

• The coke burns to produce carbon monoxide, which reacts with the iron ore to release the iron metal.

• The limestone helps to remove impurities from the iron ore, forming slag as a byproduct.

• The molten iron is then collected at the bottom of the furnace and cast into molds to form ingots or othe...read more

Sponge iron is a metallic product produced through the direct reduction of iron ore in the form of lumps, pellets, or fines.

• Sponge iron is also known as direct reduced iron (DRI).

• It is produced by removing oxygen from iron ore through a chemical reaction using natural gas or coal as a reducing agent.

• Sponge iron is used as a raw material in the production of steel through the electric arc furnace (EAF) or basic oxygen furnace (BOF) processes.