AME 2 End of Unit

B. Flame hardening.

Flame hardening is a simple onboard process for case hardening steel components. It involves heating the surface of the component with an oxy-acetylene flame to the austenitizing temperature, followed by rapid quenching with water or oil. This process creates a hard, wear-resistant surface layer.

Why the other answers are incorrect:

• A. Induction hardening: This process involves heating the surface using high-frequency currents, which requires specialized equipment and is not as simple as flame hardening.  
  1. Inductive Hardening | Aalberts ST

  

  www.aalberts-st.com

• C. Nitriding: This process involves diffusing nitrogen into the surface, requiring a controlled atmosphere and longer processing times. It is not a simple onboard process.  
  1. All you need to know about gas nitriding - Thermi-Lyon

  

  www.groupe-thermi-lyon.com

• D. Carburizing: This process involves diffusing carbon into the surface, requiring a controlled atmosphere and longer processing times. It is not a simple onboard process.  
  1. Effect of the Atmosphere for Heat Treatment on Carbon Flux in Ultra-Rapid Carburizing

  

  www.jstage.jst.go.jp

Flame hardening is a relatively simple process that can be performed on-board using readily available equipment, making it a suitable choice for many applications.

Answer:

C. To increase the wear resistance of the journal surface.

Explanation:

Case hardening is a process that hardens the surface of a metal while maintaining a softer core. For bearing journals, this is crucial as it provides a hard, wear-resistant surface to withstand friction and load, while the softer core maintains toughness and absorbs shock.

Why the other answers are incorrect:

• A. To increase the core hardness of the journal. Case hardening specifically targets the surface of the material, not the core.
• B. To improve the machinability of the journal. Case hardening typically makes the surface harder, which can reduce machinability. This process is focused on improving wear resistance, not machinability.
• D. To reduce the weight of the journal. Case hardening does not affect the weight of the material. Its purpose is to modify the properties of the surface.

Case hardening is primarily used to enhance the wear resistance of the surface of a component, such as a bearing journal, without significantly affecting the properties of the core material.

Answer:

C. Normalizing is a heat treatment process that refines the grain structure and improves toughness.  

1. Normalizing: Definition, Purpose, How It Works, and Stages - Xometry

www.xometry.com

Explanation:

Normalizing is a heat treatment process that involves heating the metal to a specific temperature above the critical point, holding it there for a sufficient time, and then allowing it to cool in air. This process refines the grain structure, reduces internal stresses, and improves the overall mechanical properties of the metal, including toughness and ductility.  

1. Difference between normalizing, tempering, annealing, quenching - JC casting

www.investmentcastingpci.com

2. Anneal, Normalize, & Stress Relieve - Clifton Steel

www.cliftonsteel.com

While it doesn't soften the metal as much as annealing, it still improves its machinability and formability.

Why the other answers are incorrect:

• A. Normalizing is a heat treatment process that increases hardness and brittleness. Normalizing actually refines the grain structure and improves toughness, leading to a balance of strength and ductility.
• B. Normalizing is a heat treatment process that softens the metal and increases ductility. While normalizing does improve ductility, it primarily focuses on refining the grain structure and improving overall mechanical properties.
• D. Normalizing is a process to increase the conductivity of a metal. Normalizing primarily affects the mechanical properties of a metal, not its electrical conductivity.

Normalizing is a heat treatment process that primarily aims to refine the grain structure of the metal, which leads to improved toughness, ductility, and machinability.

A. Annealing to relieve stresses and improve ductility.  

1. Annealing vs. Stress Relieving Heat Treatment: What's the Difference? - Paulo

www.paulo.com

 

A used copper washer would likely have internal stresses from being deformed during installation and removal. Annealing would soften the copper, relieving these stresses and making it more pliable for reuse.

Why the other answers are incorrect:

• B. Hardening to increase strength and wear resistance. Hardening is not suitable for a used copper washer as it would make it brittle and prone to cracking.
• C. Carburizing to increase surface hardness. Carburizing is a process for steel, not copper.  
  1. Carburizing - Wikipedia

  

  en.wikipedia.org

   

• D. No heat treatment is necessary. While a new copper washer might not require heat treatment, a used one often has internal stresses which can be relieved through annealing.

Annealing is the most suitable process for a used copper washer to restore its ductility and remove internal stresses.

Answer:

B. Hardening is a heat treatment process to increase hardness and reduce ductility.

Explanation:

Hardening is a heat treatment process that involves heating steel to a specific temperature (austenitizing) and then rapidly cooling it (quenching). This process dramatically increases the hardness of the steel but at the expense of ductility, making it more brittle.  

1. Metallurgy - Hardening, Treatments, Heat - Britannica

www.britannica.com

2. How does the process of hardening steel work and what is its purpose? | Sacher CNC

sacher-cnc.com

Hardening is often followed by tempering to improve toughness without significantly reducing hardness.

Why the other answers are incorrect:

• A. Hardening is a heat treatment process to soften steel. Hardening actually increases the hardness of the steel.
• C. Hardening is a process to improve the machinability of steel. While the hardening process might make the steel more difficult to machine, its primary purpose is to increase hardness.
• D. Hardening is a process to reduce the strength of steel. Hardening significantly increases the strength of steel, especially its resistance to wear and deformation.

Hardening is a heat treatment process specifically designed to increase the hardness of steel, often at the expense of ductility.

B. By heating the aluminum to a specific temperature, holding it there, and then cooling it slowly.

Annealing is a heat treatment process that involves heating a metal to a specific temperature, holding it there for a sufficient time, and then cooling it slowly. This process softens the metal and improves its ductility. While it's challenging to achieve precise temperature control and slow cooling on a moving vessel, it's theoretically possible with careful planning and equipment.

Why the other answers are incorrect:

• A. By rapidly cooling the aluminum from a high temperature. This describes quenching, which is used to harden metal, not anneal it.

   

  1. Metal Hardening | Metal Quenching | Metal Tempering - Metlab | Heat Treating

  

  www.metlabheattreat.com

• C. By deforming the aluminum to increase its strength and ductility. This describes work hardening, which is the opposite of annealing.
• D. By adding impurities to the aluminum to change its properties. This describes alloying, not annealing. Annealing is a heat treatment process.  
  1. Annealing is a heat treatment process which alters the microstructure... - Bodycote

  

  www.bodycote.com

Annealing involves heating the metal to a specific temperature, holding it there, and then cooling it slowly to soften it and improve its ductility.

Answer:

C. Increasing carbon content increases strength but decreases ductility.  

1. Exploring the Impact of Carbon Content on Steel Strength and Ductility - AZoM

www.azom.com

Explanation:

As the carbon content in steel increases, it forms a harder carbide structure within the metal matrix. This hardening process increases the steel's strength. However, this increased hardness comes at the expense of ductility, making the steel more brittle.  

1. How does the addition of carbon affect steel's properties? - TutorChase

www.tutorchase.com

2. Does Increasing Hardness Increase Strength? - Technische veren specialist | Tevema.com

www.tevema.com

3. Carbon metal content, Classification of Steel and Alloy Steels - The Fabricator

www.thefabricator.com

Therefore, while carbon is essential for enhancing steel's strength, it's a trade-off as it reduces the material's ability to deform without fracturing.

Why the other answers are incorrect:

• A. Increasing carbon content increases ductility and decreases strength. This is incorrect as increasing carbon content typically increases strength but decreases ductility.
• B. Increasing carbon content increases both strength and ductility. While strength increases with carbon content, ductility decreases.
• D. Carbon content has no significant effect on steel properties. This is incorrect as carbon is a key alloying element in steel and significantly affects its properties.

Increasing carbon content primarily increases the strength of steel but at the expense of ductility, making it more brittle.

Answer:

B. Annealing is a heat treatment process that softens the metal and increases ductility.  

1. Annealing / Normalising - Heat Treatment - Bodycote plc

www.bodycote.com

Explanation:

Annealing is a heat treatment process that involves heating a metal to a specific temperature, holding it there for a period of time, and then cooling it slowly. This process softens the metal, making it more ductile and easier to form or machine.

Why the other answers are incorrect:

• A. Annealing is a heat treatment process that increases hardness and brittleness. This is incorrect. Annealing actually softens the metal and reduces brittleness.
• C. Annealing is a process to increase the strength of a metal. While annealing can improve the machinability of a metal, it generally reduces its strength.
• D. Annealing is a process to improve the conductivity of a metal. Annealing primarily affects the mechanical properties of a metal, not its electrical conductivity.

Annealing is specifically used to soften and improve the ductility of a metal, making it easier to form or machine.

A. Annealing to improve ductility, followed by hardening to increase strength.

Valve springs undergo a two-step heat treatment process:

1. Annealing: This softens the wire material, making it easier to coil into the desired spring shape.  
   1. Understanding the Difference Between Annealing and Tempering

   

   www.ulbrich.com

    

2. Hardening: This increases the strength and elasticity of the spring, enabling it to withstand repeated cycles of compression and extension.

This combination of processes ensures the spring has the necessary properties to perform its function effectively.

Why the other answers are incorrect:

• B. Normalizing to refine grain structure, followed by tempering to improve toughness. While normalizing is a heat treatment process, it's not typically used for valve springs. The focus is on annealing and hardening for these components.
• C. Hardening to increase wear resistance, followed by tempering to improve toughness. This sequence is correct for many components, but not for valve springs. Valve springs require high ductility to withstand repeated cycles.
• D. Patenting to increase ductility, followed by cold working to increase strength. Patenting is a specific heat treatment process not typically used for valve springs. Cold working would increase strength but decrease ductility, which is undesirable for a valve spring.  
  1. Annealing to Increase Metal Ductility - Industrial Metallurgists

  

  www.imetllc.com

   

Annealing improves ductility for coiling, and hardening provides the necessary strength and elasticity for spring action.

C. Hardening to increase wear resistance, followed by tempering to improve toughness.

A crankshaft undergoes a two-step heat treatment process:

1. Hardening: This increases the surface hardness of the crankshaft, making it resistant to wear and tear from high loads and friction.
2. Tempering: This process follows hardening to reduce brittleness and improve toughness, preventing the crankshaft from fracturing under stress.

This combination of hardening and tempering provides the optimal balance of hardness, strength, and toughness required for a crankshaft.

A. Annealing to improve machinability, followed by hardening to increase strength.

This sequence is incorrect because annealing softens the metal, which is counterproductive to the goal of increasing strength for a crankshaft.

B. Normalizing to refine grain structure, followed by tempering to improve toughness. Normalizing is a step in the right direction, but tempering is typically done after hardening, not normalizing.  

1. Tempering (metallurgy) - Wikipedia

en.wikipedia.org

D. Carburizing to increase surface hardness, followed by quenching to improve core strength. Carburizing increases surface hardness, but quenching is done immediately after heating to achieve the hard surface, not after carburizing.

The correct sequence is hardening followed by tempering to achieve the desired combination of surface hardness and core toughness for a crankshaft.

Answer:

B. Low-carbon steels

Explanation:

Annealing is a heat treatment process used to soften and improve the ductility of steel. It is particularly effective on low-carbon steels as they are more prone to hardening and becoming brittle during processing.  

1. Annealing is a heat treatment process which alters the microstructure... - Bodycote

www.bodycote.com

By annealing low-carbon steels, you can restore their original softness and make them easier to form or machine.

Why the other answers are incorrect:

• A. High-carbon steels: High-carbon steels are typically hardened and tempered to achieve desired properties. Annealing would reverse this process, making them softer and less suitable for applications requiring high strength and hardness.
• C. Stainless steels: Stainless steels often undergo annealing to improve machinability or ductility before further heat treatments, but they are not primarily annealed for softening purposes.
• D. Tool steels: Tool steels are typically hardened and tempered to achieve high hardness and wear resistance. Annealing would soften them, making them unsuitable for their intended purpose.

Low-carbon steels are the primary candidates for annealing as they are more prone to hardening during processing and benefit greatly from the softening and ductility improvement provided by this heat treatment.

B. A heat treatment process where only the surface of the workpiece is rapidly heated using high-frequency currents, followed by quenching.  

1. How to Choose the Best Heat Treatment – Process Guide - meviy

de.meviy.misumi-ec.com

Induction hardening involves using electromagnetic induction to rapidly heat the surface of a metal part to its austenitizing temperature. This is followed by immediate quenching, creating a hard, wear-resistant surface layer while preserving the toughness of the core.

Why the other answers are incorrect:

• A. A heat treatment process involving heating the entire workpiece to a high temperature, followed by quenching. This describes a full hardening process, not induction hardening.
• C. A chemical process where carbon is diffused into the surface of the workpiece to increase hardness. This describes carburizing, another case hardening process, but not induction hardening.
• D. A process of adding a hard coating to the surface of the workpiece. This describes a coating process, not a heat treatment process.

Induction hardening specifically uses electromagnetic induction to rapidly heat the surface of the workpiece, creating a hard layer through quenching.