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Questions and Answers
What is the primary phase transformation occurring at the eutectoid composition (8%C)?
What is the primary phase transformation occurring at the eutectoid composition (8%C)?
What happens to the carbon solubility of the γ phase as the temperature decreases?
What happens to the carbon solubility of the γ phase as the temperature decreases?
What microstructure is formed when the temperature is reduced quickly under non-equilibrium conditions?
What microstructure is formed when the temperature is reduced quickly under non-equilibrium conditions?
What is the maximum carbon content that can be dissolved in the γ phase at 0.3%C composition?
What is the maximum carbon content that can be dissolved in the γ phase at 0.3%C composition?
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Which property of BCT martensite is primarily affected by the lattice distortion due to carbon atoms?
Which property of BCT martensite is primarily affected by the lattice distortion due to carbon atoms?
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What must be done to martensite before it can be effectively used due to its brittle properties?
What must be done to martensite before it can be effectively used due to its brittle properties?
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Which lattice structure does the α phase have?
Which lattice structure does the α phase have?
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What is the composition threshold below which martensite cannot be obtained?
What is the composition threshold below which martensite cannot be obtained?
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What key characteristic distinguishes alloys from solid solutions?
What key characteristic distinguishes alloys from solid solutions?
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How does the presence of impurities in pure metals typically affect their properties?
How does the presence of impurities in pure metals typically affect their properties?
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What is the primary property that allows metals to conduct heat and electricity?
What is the primary property that allows metals to conduct heat and electricity?
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Which phase transformation corresponds to a liquid changing into two solid phases in the Fe-C system?
Which phase transformation corresponds to a liquid changing into two solid phases in the Fe-C system?
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What is a common characteristic of the intermetallic phase Fe3C?
What is a common characteristic of the intermetallic phase Fe3C?
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What does allotropy in materials refer to?
What does allotropy in materials refer to?
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What is the maximum carbon solubility in the alpha phase (alpha-BCC) at room temperature?
What is the maximum carbon solubility in the alpha phase (alpha-BCC) at room temperature?
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Which of the following transformations occurs at 723 °C in the Fe-C diagram?
Which of the following transformations occurs at 723 °C in the Fe-C diagram?
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Study Notes
Metals and Alloys
- Metals are characterized by their ductility, malleability, high electrical and thermal conductivity, and high corrosion rate.
- Metallic bonding is responsible for the conductivity of heat and electricity due to the presence of free electrons.
- Alloys are composed of at least two different atoms, with at least one being a metal.
- Alloys are generally stronger, harder, more durable, and more corrosion-resistant than their pure metal forms.
Solid Solutions and Allotropy
- A solid solution is a homogeneous mixture of at least two different kinds of atoms in a solid state, with a single crystal structure.
- Allotropy refers to materials with different crystal structures in the solid state, depending on temperature and pressure.
- Iron (Fe), Titanium (Ti), and other materials exhibit allotropy.
Iron Allotropes
- Iron exists in different phases depending on temperature.
- The δ-BCC, γ-FCC, and α-BCC phases have varying lattice parameters and carbon solubility at different temperatures.
Main Transition Mechanisms in Fe-C Diagram
- Eutectic: A liquid phase transforms into two solid phases at constant temperature and concentration.
- Peritectic: One liquid and one solid phase transform into another solid phase at constant temperature and concentration.
- Eutectoid: One solid phase transforms into two different solid phases at constant temperature and concentration.
Fe-C System
- Three key reactions occur in the Fe-C system:
- Eutectic: Liquid Fe → γ + Fe3C
- Peritectic: Liquid Fe + δ → γ
- Eutectoid: γ → α + Fe3C
- These reactions occur at specific temperatures and compositions.
Properties of Fe3C
- Cementite (Fe3C) is a hard and brittle compound.
- It has higher mechanical properties than pure iron due to its unique bonding characteristics.
- Fe3C exhibits metallic, covalent, and ionic bonding.
Fe-C Diagram
- The Acm line represents the carbon solubility of iron as a function of temperature.
- The Led A and Led γ lines identify the transformation pathways of iron and cementite.
Composition 1 (eutectoid composition)
- At eutectoid composition (0.8%C), all carbon is initially dissolved in the γ phase.
- As temperature decreases, the γ phase transforms into pearlite (α + Fe3C).
- At room temperature, the composition is divided between α (0.008%C) and Fe3C (6.67%C).
Lever Rule Application
- The lever rule can be used to determine the phase ratios at room temperature.
- In this case, α accounts for 88.11% and Fe3C accounts for 11.88% of the composition.
Composition 2 (0.3%C)
- At 0.3%C, the composition exists in the γ phase (FCC) with a maximum carbon solubility of 2.06%.
Composition 3 (1.2%C)
- At 1.2%C, the composition exists in the γ phase (FCC), forming a solid solution.
Acm Line and Carbon Solubility
- The Acm line indicates an increase in carbon solubility in the γ phase with increasing temperature.
TTT Diagram
- The TTT diagram (Time, Temperature, Transformation) depicts the microstructure evolution during cooling.
- The cooling rate affects the transformation process, influencing the microstructure or steady-state condition.
Diffusion-Based Transformation (α → BCC)
- The diffusion-based transformation from α to BCC involves short-range movements of iron atoms.
- The process leads to a decrease in lattice volume.
Non-Equilibrium Condition (Quenching)
- Quenching is a rapid cooling process that prevents diffusion-based transformations.
- Due to the rapid cooling, a non-equilibrium condition is achieved.
Martensite
- Martensite is a super-saturated structure of iron with carbon.
- The presence of carbon in the lattice causes lattice distortion, forming a tetragonal (BCT) structure.
- Martensite is characterized by high strength, hardness, and brittleness.
Tempering
- Tempering is a heat treatment applied after martensite formation to improve ductility.
- The tempering temperature depends on the carbon content and other alloying elements.
Mechanical Properties of Martensite
- The carbon content influences the formation of martensite.
- Lath martensite is known for its higher strength and hardness compared to plate martensite.
- Plate martensite exhibits a higher proportion and ductility than lath martensite.
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Description
Test your knowledge on the characteristics of metals and alloys, including their properties and bonding types. Explore concepts such as solid solutions and allotropy, particularly focusing on metals like iron and titanium. Prepare to dive into the fascinating world of materials science!
