Alloy Steels Unit 3

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Questions and Answers

What is the main advantage of alloy steels over carbon steels?

Better electrical conductivity

Enhanced thermal conductivity

Increased corrosion resistance

Improved mechanical properties (correct)

What is the maximum percentage of carbon present in steel?

2.0 %

2.5 %

1.5 % (correct)

1.0 %

Which of the following is NOT a characteristic of low alloy steels?

Has applications similar to plain carbon steels

Requires similar heat treatment to plain carbon steels

Has a different microstructure than plain carbon steels (correct)

Contains up to 3-4% of alloying elements

What is the primary reason for adding nickel to low alloy steels?

To improve fatigue resistance Signup and view all the answers

Which of the following elements is NOT typically added to alloy steels?

Tin Signup and view all the answers

What is the primary characteristic of high alloy steels that distinguishes them from plain carbon steels?

They possess structures and require heat treatments that differ considerably Signup and view all the answers

What is the primary advantage of maraging steels?

Their ability to be worked and machined with comparative ease after solution treatment Signup and view all the answers

Which of the following elements is NOT a carbide stabilizer?

Nickel Signup and view all the answers

What is the effect of nickel on the allotropic transformation temperatures of carbon steel?

Raises the A3 temperature and lowers the A4 temperature Signup and view all the answers

What is the primary function of chromium in stainless steels?

To form a protective film of chromium oxide on the metal surface Signup and view all the answers

What is the primary function of vanadium in OHNS steels?

To enhance wear resistance Signup and view all the answers

What is the purpose of the annealing process in OHNS steels?

To soften the steel for machining Signup and view all the answers

What is the typical hardness range achieved by OHNS steels after oil quenching?

57-62 HRC Signup and view all the answers

What is a unique property of Hadfield's manganese steel?

It remains non-magnetic after work hardening Signup and view all the answers

What is the purpose of the solution annealing process in Hadfield's manganese steel?

To prevent carbide precipitation and ensure the austenitic structure Signup and view all the answers

What is the effect of adding chromium to steel on its crystal growth rate?

It accelerates crystal growth Signup and view all the answers

What is the effect of adding alloying elements to carbon steel on its eutectoid point?

It displaces the eutectoid point to the left Signup and view all the answers

What is the effect of adding alloying elements, such as nickel and chromium, on the transformation rates of austenite to martensite?

They reduce the critical cooling rate Signup and view all the answers

What is the primary reason for alloying steel?

To effect improvements in the mechanical properties Signup and view all the answers

What is the effect of adding chromium on the corrosion resistance of steel?

It substantially improves corrosion resistance Signup and view all the answers

Which element is commonly used in stainless steels, austenitic steels, and some alloy steels, and improves toughness, strength, and corrosion resistance?

Nickel (Ni) Signup and view all the answers

What is the primary effect of Vanadium (V) on steel microstructure?

Refines the grain structure Signup and view all the answers

Which element is a ferrite stabilizer and promotes the formation of ferrite and carbides?

Silicon (Si) Signup and view all the answers

What is the primary effect of Boron (B) on steel properties?

Greatly increases hardenability Signup and view all the answers

Which elements are common carbide formers and enhance wear resistance and high-temperature stability?

Chromium (Cr), Molybdenum (Mo), and Tungsten (W) Signup and view all the answers

What is the primary property of high-speed steels that makes them suitable for cutting tools?

High wear resistance at elevated temperatures Signup and view all the answers

Which of the following heat treatment processes is used to reduce residual stresses and improve toughness in high-speed steels?

Tempering Signup and view all the answers

What is the primary characteristic of ferritic stainless steels that distinguishes them from austenitic stainless steels?

Limited hardenability Signup and view all the answers

Which of the following applications is NOT typically associated with austenitic stainless steels?

Automotive parts Signup and view all the answers

What is the primary advantage of high-speed steels over other types of steels?

Ability to retain hardness at high temperatures Signup and view all the answers

What is the primary reason for the moderate corrosion resistance of martensitic stainless steels?

High carbon content Signup and view all the answers

What is the primary consequence of weld decay in stainless steels?

Intergranular corrosion along the grain boundaries Signup and view all the answers

Which of the following elements is added to martensitic stainless steels to improve toughness?

Nickel Signup and view all the answers

What is the primary purpose of solution annealing in preventing weld decay?

To dissolve the chromium carbides and restore chromium to the grain boundaries Signup and view all the answers

Which of the following is a characteristic of martensitic stainless steels?

High strength and hardness Signup and view all the answers

What is the primary cause of chromium depletion in the heat-affected zone during welding?

Chromium carbide precipitation Signup and view all the answers

What is the purpose of using low-carbon stainless steels in preventing weld decay?

To reduce the tendency for chromium carbide formation Signup and view all the answers

Which of the following tests is used to detect susceptibility to intergranular corrosion in stainless steels?

Strauss test Signup and view all the answers

What is the primary advantage of using stabilized stainless steels in preventing weld decay?

Reduced tendency for chromium carbide formation Signup and view all the answers

What is the primary effect of weld decay on the mechanical properties of stainless steels?

Reduced mechanical strength and toughness Signup and view all the answers

Study Notes

Introduction to Alloy Steels

Alloy steels are a type of steel that contains other elements besides iron and carbon.
The addition of other elements improves the properties of steel, making it suitable for various applications.

Classification of Alloy Steels

Low alloy steels:
- Contain up to 3-4% of one or more alloying elements.
- Similar microstructure to plain carbon steels.
- Used for increasing strength, toughness, and hardenability.
High alloy steels:
- Possess structures and require heat treatments different from plain carbon steels.
- Examples: high-speed tool steels, stainless steels, and maraging steels.

High-Speed Tool Steels

Composition: Tungsten, chromium, vanadium, and carbon.
Properties:
- High hardness and wear resistance.
- Retain hardness at high temperatures.
Applications:
- Cutting tools: drills, taps, end mills, and saw blades.

Stainless Steels

Composition: Chromium (min. 12%) and sometimes nickel.
Properties:
- Corrosion resistance due to chromium oxide film.
- High-temperature resistance.
Applications:
- Kitchen utensils, medical equipment, and architectural features.

Maraging Steels

Composition: Nickel, cobalt, and small amounts of titanium and other elements.
Properties:
- High strength and toughness.
- Low carbon content.
Applications:
- Aerospace and defense industries.

Effects of Alloying Elements

Carbide formers: Cr, W, Ti, V, and Mo.
Austenite stabilizers: Ni, C, and N.
Ferrite stabilizers: Cr, Mo, Si, Ti, and V.
Grain refiners: Al, Ti, and Nb.

Specific Alloying Elements

Carbon (C): increases hardness and strength.
Chromium (Cr): improves corrosion resistance and hardness.
Nickel (Ni): improves toughness and corrosion resistance.
Manganese (Mn): improves strength and deoxidizes the steel.
Molybdenum (Mo): enhances strength, hardness, and corrosion resistance.
Vanadium (V): improves strength, toughness, and wear resistance.

Heat Treatment

Austenitizing: heating to form austenite structure.
Quenching: rapid cooling to achieve desired properties.
Tempering: heating to reduce brittleness and improve toughness.

Specific Steel Types

OHNS (O1) steel: high-speed tool steel with high hardness, toughness, and wear resistance.
Hadfield's manganese steel: high-manganese steel with high toughness and wear resistance.
High-speed steel (HSS): used for cutting tools due to high hardness and wear resistance.### Ferritic Stainless Steels
Magnetic
Good corrosion resistance, particularly in less severe environments
Good ductility and formability, but less than austenitic grades
Lower cost due to lower nickel content
Limited hardenability, only by cold working
Applications: automotive parts, kitchen equipment, industrial equipment, and architecture

Austenitic Stainless Steels

Composition: 16-26% Cr, 6-22% Ni, low C (<0.08%), and other elements like Mn, N, and Mo
Non-magnetic, but can become slightly magnetic when cold worked
Excellent corrosion resistance in a wide range of environments
Good weldability without requiring post-weld heat treatment
Good toughness and ductility at high and low temperatures
Hardenable by cold working
Applications: food and beverage equipment, medical devices, chemical and petrochemical industry, construction, and household items

Martensitic Stainless Steels

Composition: 11.5-18% Cr, higher C (0.1-1.2%), and sometimes Ni for toughness
Magnetic
High strength and hardness, can be significantly hardened by heat treatment
Moderate corrosion resistance, lower than austenitic and ferritic grades
Good wear resistance due to high hardness
Heat treatable to achieve a wide range of hardness and strength levels
Applications: cutlery and blades, turbine blades and engine parts, valves and pumps, and springs and fasteners

Weld Decay

Type of intergranular corrosion that occurs in some stainless steels, particularly austenitic grades
Occurs in the heat-affected zone (HAZ) adjacent to the weld
Caused by chromium carbide precipitation and chromium depletion
Prevention methods: using low-carbon grades, stabilized grades, heat treatment, controlled welding techniques, and proper filler materials
Detection methods: sensitization tests (e.g., Strauss test) and microstructural analysis
Consequences: inter-granular corrosion, reduced mechanical properties, and premature failure

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Description

Learn about the composition and production of alloy steels, including their history and applications in modern industries.