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Questions and Answers
What is the composition of the intermediate solid compound found in the Iron-Carbon phase diagram?
Which type of carbon steel has the highest machinability?
What temperature does the eutectoid reaction occur in the Iron-Carbon phase diagram?
Which type of carbon steel is typically used for structural steels and machine parts?
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What is the composition of the microstructure of hypoeutectoid steel?
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What type of alloy consists of a principal metal element and another element that can be metallic or non-metallic?
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In which type of alloy does the solute occupy the interstitial sites of the solvent metal?
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What type of alloy involves fixed compositions and is made up of metals, similar to Fe3C?
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In the Cu-Ni phase diagram, what does the phase field extending from 0 to 100 wt% Ni represent?
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What is the graphical representation that shows the phases present in a material under varying system conditions?
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Study Notes
Iron-Carbon Phase Diagram
- The iron-carbon phase diagram is obtained for temperature and composition while maintaining a constant pressure of 1 atm.
- The diagram contains 1.3% carbon, which is a eutectic composition, and shows the presence of various phases, including α (ferrite), γ (austenite), and δ (delta ferrite) iron, as well as Fe3C (cementite).
Invariant Reactions
- There are three invariant reactions in the iron-carbon phase diagram:
- Eutectic reaction at 4.3%C, 1130°C
- Eutectoid reaction at 0.8%C, 723°C
- Peritectic reaction at 1492°C
Microstructure of Steel
- Pearlite is a microstructure that forms through the eutectoid reaction, consisting of alternating layers of α (ferrite) and Fe3C (cementite).
- Hypoeutectoid steel has a microstructure that consists of ferrite and pearlite, while hypereutectoid steel has a microstructure that consists of pearlite and cementite.
Lever Rule
- The lever rule is used to find the proportions of the phases present in a two-phase region.
- The rule is applied by calculating the relative amounts of the phases based on the composition of the alloy.
Steel Classification
- According to AISI, plain carbon steel is defined as steel with a composition that does not exceed the following limits: Mn < 1.65%, Si < 0.6%, Cu < 0.6%.
- Alloy steel is defined as steel with a composition that exceeds these limits.
Types of Plain Carbon Steel
- Low carbon steel: 0.3%C, with a microstructure consisting of ferrite and pearlite, possessing good formability, weldability, and machinability.
- Medium carbon steel: 0.3-0.8%C, with a microstructure consisting of ferrite and pearlite, possessing good toughness, ductility, and machinability.
- High carbon steel: 0.8-2.0%C, with a microstructure consisting of pearlite and cementite, possessing good hardness and wear resistance.
Alloys
- An alloy is a metallic material consisting of two or more elements, with the principal element being a metal.
- Alloys can be formed in three ways: interstitial solid solution, substitutional solid solution, and intermediate compound formation.
Interstitial Solid Solution
- In an interstitial solid solution, atoms of the solute element occupy the interstitial sites of the solvent element's lattice.
Substitutional Solid Solution
- In a substitutional solid solution, atoms of the solute element replace atoms of the solvent element in the lattice.
Intermediate Compound
- An intermediate compound has a fixed composition, and its properties are different from those of the constituent elements.
- Example: Fe3C (cementite), with a weight percentage of carbon of 6.67%.
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Description
Explore the world of metallic materials through the study of phase diagrams and alloy classification. Learn about the different types of alloys such as interstitial solid solutions and substitutional solid solutions.
