AME 2 End of Unit

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

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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

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

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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.

B. Grain size decreases and elongated grains form, leading to increased strength.  

1. Effects of Grain Size: Strength, Ductility, Hardness - Vaia

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When aluminum undergoes work hardening, the grains within its structure become smaller and elongated due to the plastic deformation. This change in grain structure increases the strength of the material by hindering the movement of dislocations, which are defects within the crystal lattice that allow for plastic deformation.

Why the other answers are incorrect:

• A. Grain size increases, leading to increased strength. This is opposite to what happens during work hardening. Grain size actually decreases.
• C. The crystal structure remains unchanged, but the metal becomes denser. The crystal structure changes significantly during work hardening, and density is not a primary factor in this process.
• D. The aluminum atoms rearrange to form a new crystal structure. While there is some rearrangement at the atomic level, the overall crystal structure doesn't change dramatically. The primary change is in the grain size and shape.

Work hardening is primarily characterized by a decrease in grain size and the formation of elongated grains, which together contribute to the increased strength of the material.

B. Increased hardness at the surface, while maintaining a tough core.  

1. [Solved] The process of improving the hardness of the outer layers on - Testbook

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Case hardening creates a hard, wear-resistant surface layer while preserving the toughness and ductility of the core material. This combination of properties is essential for components subjected to high wear and stress, such as gears, cams, and bearing surfaces.

Why the other answers are incorrect:

• A. Increased hardness and ductility throughout the entire component. Case hardening specifically increases hardness at the surface, not throughout the entire component. Ductility is generally maintained in the core.
• C. Decreased hardness and increased ductility throughout the entire component. Case hardening increases hardness, not decreases it. Ductility is generally maintained in the core.
• D. No significant change in the properties of the component. Case hardening significantly alters the properties of the component by creating a hard, wear-resistant surface layer.

The primary goal of case hardening is to improve the wear resistance of the component's surface while maintaining the toughness and ductility of the core.

Answer:

C. Increased toughness, decreased brittleness, and refinement of microstructure.

Explanation:

Tempering is a heat treatment process that follows hardening. It involves reheating the hardened steel to a lower temperature, which reduces hardness but significantly increases toughness and ductility. The internal structure is also refined during this process.

Tempering is essential for achieving the desired balance of hardness and toughness in steel components.

Why the other answers are incorrect:

• A. Increased hardness, decreased ductility, and formation of martensite. This describes the hardening process, not tempering. Tempering actually reduces hardness.
• B. Decreased hardness, increased ductility, and formation of pearlite. While tempering does decrease hardness and increase ductility, the formation of pearlite is more associated with the annealing process. Tempering involves the decomposition of martensite into finer structures.
• D. No significant change in mechanical properties or internal structure. Tempering significantly alters the mechanical properties and microstructure of steel, making it tougher and less brittle.

Tempering is a crucial process for achieving the desired balance of hardness and toughness in steel components.

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

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

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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.

C. The increase in strength of aluminum due to plastic deformation.

Work hardening, also known as strain hardening, is the process by which a metal's strength increases as it is subjected to plastic deformation. This occurs because the metal's crystal structure changes as it is shaped, making it more resistant to further deformation.

Why the other answers are incorrect:

• A. A process of heating aluminum to increase its strength. This describes heat treatment, not work hardening. Work hardening occurs through deformation, not heat.
• B. A process of cooling aluminum rapidly to increase its hardness. This describes quenching, a heat treatment process. Work hardening is related to plastic deformation.
• D. The process of adding impurities to aluminum to improve its properties. This describes alloying, not work hardening. Work hardening is a result of the metal's internal structure changing due to deformation.

Work hardening is a physical process that occurs when a metal, like aluminum, is shaped or deformed. It doesn't involve heat treatment or adding impurities.

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:

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

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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

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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.

C. To enhance the wear resistance of the component's surface.

Case hardening is primarily used to increase the hardness and wear resistance of a component's surface while maintaining the toughness of the core. This combination of properties is essential for components subjected to high wear and stress, such as gears, cams, and bearing surfaces.

Why the other answers are incorrect:

• A. To increase the overall ductility of the component. Case hardening actually improves hardness, which can decrease ductility in the hardened layer, although the core remains tough.
• B. To improve the machinability of the component. Case hardening typically makes the surface harder, which can reduce machinability. This process is focused on improving wear resistance.  
  1. What is Case Hardening? | Metal Supermarkets UK

  

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  2. The Use of Case Hardening to Improve Wear Resistance in Metal Components

  

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• D. To reduce the weight of the component. Case hardening does not affect the weight of the component. Its purpose is to modify the properties of the surface.

The primary goal of case hardening is to enhance the wear resistance of the component's surface while maintaining the toughness of the core.

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

  

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• 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

  

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• 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

  

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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.

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

   

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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

  

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