Metallurgy: Cast Iron and Steel Types

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Questions and Answers

What is the main characteristic of grey cast iron?

It is primarily used for high-temperature applications.

It is extremely hard and cannot be machined.

It has a high carbon content that makes it brittle. (correct)

It is resistant to abrasion and wear.

What is the primary purpose of the Open Hearth Furnace in steel production?

To control the temperature during steel casting

To add alloying elements to steel

To determine the correct carbon content in molten iron (correct)

To maximize the production speed of steel

Which statement about white cast iron is true?

It is designed for surfaces requiring abrasion resistance. (correct)

It can be easily machined without grinding.

It cools rapidly in standard conditions to produce a soft material.

It has a lower carbon content than grey cast iron.

What is pig iron primarily composed of?

93% pure iron with carbon and other impurities. (C) Signup and view all the answers

Which material is primarily used to withstand the high temperatures in a crucible furnace?

Graphite or clay (D) Signup and view all the answers

What is a key characteristic of the electric furnace compared to other types of furnaces?

It offers greater control over temperature and alloying elements (B) Signup and view all the answers

Which process leads to the formation of hard cast iron?

Chilling or rapid cooling of liquid cast iron. (D) Signup and view all the answers

How does adding carbon up to approximately 1% affect iron?

It enhances the iron's properties, classifying it as carbon steel. (D) Signup and view all the answers

In the Basic Oxygen Process, what is primarily blown through the molten bath?

Oxygen (D) Signup and view all the answers

Which steel-making process has been mostly replaced by the electric furnace?

Crucible Furnace (B) Signup and view all the answers

What is a common application for grey cast iron?

Producing large pipes and steam radiators. (B) Signup and view all the answers

What additional materials may be included in the crucible when making alloy steel?

Chromium and vanadium (C) Signup and view all the answers

Which of the following best describes the cooling method for producing grey cast iron?

Cooling slowly to maintain its softness. (A) Signup and view all the answers

What is a fundamental characteristic of an alloy?

It is a base metal with small quantities of other metals added. (C) Signup and view all the answers

What kind of structures does the electric arc furnace control best during steel production?

Grain structure (D) Signup and view all the answers

Which material acts as a fluxing agent in the Basic Oxygen Process?

Burnt lime (A) Signup and view all the answers

What is the main purpose of tempering in steel treatment?

To relieve internal strain and increase toughness (C) Signup and view all the answers

Which heat treatment process involves hardening a thin surface layer on steel?

Case Hardening (B) Signup and view all the answers

What does the heat treatment process aim to achieve besides making metals stronger?

It can also make metals softer and more ductile. (A) Signup and view all the answers

At what temperature range is steel typically tempered?

Below the low critical temperature (LCT) (A) Signup and view all the answers

Which method can be used to cool steel after tempering?

Quenching in water, oil, or brine (C) Signup and view all the answers

Why can't all metals and alloys be heat treated?

Because they might not respond to heat treatment (D) Signup and view all the answers

Which heat treatment process is specifically aimed at improving the machinability of hardened steel?

Annealing (C) Signup and view all the answers

Which of the following metals typically responds well to heat treatment?

Aluminum and its alloys (C) Signup and view all the answers

What is the primary purpose of the annealing process?

To relieve internal stress and refine grain structure (B) Signup and view all the answers

During full annealing, at what temperature should the steel be heated?

300-500 C above UCT (B) Signup and view all the answers

What is the cooling process in normalizing?

Cooling in still air (A) Signup and view all the answers

What effect does hardening have on the metal?

Produces fine grain structure and increases hardness (A) Signup and view all the answers

Which method is NOT commonly associated with case hardening?

Hardening (B) Signup and view all the answers

What is the main benefit of case hardening?

To produce a hard surface while maintaining a tough core (D) Signup and view all the answers

What is the purpose of soaking the steel during the annealing process?

To permit recrystallization to occur (A) Signup and view all the answers

Which quenching medium results in the least amount of heat retention?

Air (A) Signup and view all the answers

Which of the following elements is mentioned as being allotropic?

Carbon (B) Signup and view all the answers

What is the primary purpose of hard anodising coating?

To offer electrical insulation (C) Signup and view all the answers

Which type of anodising is known for its dull yellow-green appearance when sealed?

Type 2 – Sulphuric Anodise (B) Signup and view all the answers

What is a characteristic feature of Type 1 cadmium plating?

It is silver-coloured and untreated. (D) Signup and view all the answers

What distinguishes Type 2 cadmium plating from Type 1?

It includes a chrome treatment. (A) Signup and view all the answers

Which application is a known use for hard anodising coating?

In hydraulic cylinders (A) Signup and view all the answers

What is a key feature of Type 3 cadmium plating?

It is used as a paint base. (A) Signup and view all the answers

Which characteristic describes aluminium in relation to allotropism?

It can be hardened through alloying. (C) Signup and view all the answers

Study Notes

Grey Cast Iron

Grey cast iron is produced when liquid cast iron cools slowly
It contains about 3.5% carbon, which makes it brittle
Grey cast iron fractures easily from sharp blows
It has a grey crystalline colour when fractured
Grey cast iron is used for large pipes, steam radiators, water hydrants, and machine frames

White Cast Iron

White cast iron is produced by rapidly cooling or chilling liquid iron
It has a carbon content of 2% to 3.5%
White cast iron is extremely hard and cannot be machined except by grinding
It is used for castings needing abrasion and wear resistance

Pig Iron

Pig iron is formed by pouring melted iron from the blast furnace into sand molds
The molds are parallel trenches with a connecting channel, forming "pigs" connected to a long bar called the "Sow"
Pig iron is about 93% pure iron, 3-5% carbon, and smaller amounts of silicon, phosphorus, sulfur, and manganese

Carbon Steel

Adding 1% or less of carbon to iron produces carbon steel, which is vastly superior to plain iron
An alloy is a base metal (like iron) with small amounts of other metals added to improve its properties
Carbon steel is made by heating pig iron, wrought iron, and scrap metal in an open-hearth furnace
The furnace uses hot air and gas to keep the iron liquid and carbon levels are adjusted before pouring the metal into ingots

Crucible Steel

Crucible steel is high-carbon steel or alloy steel made by melting wrought iron and scrap steel in a crucible
Carbon or other alloying elements are added to the crucible and melted with the iron
The steel is then poured into ingot molds
The electric arc furnace has largely replaced the crucible furnace for making high-quality steel

Electric Furnace Steel

The electric furnace is used when precise temperature control and alloying element addition is crucial
It achieves higher temperatures than other steel-making furnaces
High-carbon steel, special alloy steel, and high-speed steel are produced in electric furnaces
Electric furnaces allow for control of the steel's grain structure

Basic Oxygen Process

The Basic Oxygen Process uses oxygen to quickly refine iron ore, steel scrap, and molten iron
Oxygen is blown down from the top through a lance into the molten metal bath
Burnt lime and other fluxing agents are added during the process to refine the steel

Annealing

Annealing is a softening process that relieves internal stress in steel
It brings the steel into its softest possible condition when cold
Annealing refines the steel's grain structure
Full annealing involves heating the steel above its upper critical temperature, soaking it, and cooling it slowly
Process annealing is similar but involves lower temperatures

Normalizing

Normalizing refines the steel's grain structure and relieves stress
It is used before other heat treatments
Normalizing involves heating the steel above its upper critical temperature, soaking it, and cooling it in still air

Hardening

Hardening produces a fine grain structure and high hardness
It involves heating the steel above its critical temperature, soaking it, and rapidly quenching it in a medium like brine, water, oil, or air

Case Hardening

Case hardening involves producing a hard, wear-resistant surface while keeping the core tough
Common methods of Case Hardening include carburizing, cyaniding and nitriding
Carburizing involves soaking the metal in a carbonaceous material
Cyaniding involves immersing the steel in a molten bath of cyanide salts
Nitriding involves heating the steel in anhydrous ammonia to produce a hard surface

Tempering

Tempering, also called drawing, relieves internal strain in hardened steel, increasing its toughness
It involves heat treating hardened steel below its lower critical temperature, soaking it, and cooling it in air or a quenching medium
Tempering prevents cracking or fracturing under stress

Uses of Different Heat Treated Materials

Ferrous metals (iron and steel) are commonly heat treated
Some aluminum alloys can be heat treated while others require cold working for hardening
Heat treating high-temperature nickel-based alloys is done in some cases depending on composition
The temperatures and process of heat treatment vary among different metals

Heat Treatment

Heat treatment hardens or strengthens metals
It also makes metals softer and more ductile
Heat treatment types include hardening, tempering, annealing, normalizing, and case hardening

Anodic Treatment

Anodic treatment is used to provide corrosion resistance and other properties to aluminum parts
The three types of anodic treatment specified by MIL-A-8625R are Chromic Anodise Coating, Sulphuric Anodise Coating, and Hard Anodising Coating
Chromic Anodise Coating is a dark-grey coating used for sealing and corrosion resistance
Sulphuric Anodise Coating is best for dyeing, has a dull yellow-green appearance, and is used for sealing
Hard Anodising Coating provides electrical insulation and abrasion resistance to parts like hydraulic cylinders and actuator cams

Cadmium Plating

Cadmium plating is a non-porous, electrolytically deposited layer that resists corrosion on steel
Type 1 is pure, silver-coloured cadmium plating
Type 2 is cadmium plating followed by a chrome treatment for improved corrosion resistance
Type 3 is cadmium plating followed by a phosphate treatment, primarily for paint base

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Description

This quiz explores the characteristics and applications of various types of cast iron, including grey, white, and pig iron, as well as carbon steel. You'll learn about their chemical compositions, production methods, and uses in industries. Test your knowledge on these essential materials in metallurgy.