Microstructure formation during solidification

• What is steel made of?
• What is the difference between steel and cast iron regarding their composition?
• Why is carbon used as an alloying element for steel?
• Why do further phase transformations take place in the already solidified state in steels?
• In which lattice structure does steel crystallize first?
• Which lattice structure does steel (usually) have at room temperature?
• What is the steel part in the phase diagram?
• How does the carbon content influence the solidification range of steels?
• What is austenite and ferrite?
• How does the carbon content affect the transformation of $$\gamma$$-iron into $$\alpha$$-iron?
• Which microstructural changes occur in the stable or metastable system during the $$\gamma$$-$$\alpha$$-transformation?
• What promotes the respective systems?
• Which system is relevant for steel and which for cast iron?
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Phase transformations in solidified state (metastable system)

• What is the carbon content of a eutectoid steel?
• Why is virtually no carbon soluble in ferrite?
• What phases does pearlite consist of and at what temperature does it form?
• What is the structure of pearlite under the microscope?
• What is the difference in the name between eutectic and eutectoid?
• Why does the solubility of carbon in austenite decrease with decreasing temperature?
• What is the maximum percentage of carbon that can be dissolved in austenite and at what temperature?
• What is an undersaturated, supersaturated and saturated state?
• How is the insoluble carbon precipitated from austenite?
• What does the microstructure of a hypereutectoid steel look like?
• How is carbon precipitated in hypoeutectoid steels during $$\gamma$$-$$\alpha$$-transformation?
• What does the microstructure of a hypoeutectoid steel look like?
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Summary of phase transformations

• What microstructural transformations does a hypoeutectoid steel undergo during cooling?
• How does the microstructure of a hypereutectoid steel develop?
• At what temperature is pearlite formed?
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Comparison of phase transformations

• What analogy can be found between the iron-carbon phase diagram and the phase diagram of an alloy whose components are insoluble in one another?
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Determination of microstructure and phase fractions

• How can the microstructure fraction of a steel be determined from the iron-carbon phase diagram?
• How is the phase fraction of a steel determined from the iron-carbon phase diagram?
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Influence of carbon on hardness and strength of steels

• Why does the hardness of steel increase with increasing carbon content?
• How do the cementite lamellae in pearlite increase the strength of steels?
• Why does unalloyed steel become brittle from a carbon content of 0.8 %?
• Why do phase diagrams only apply to infinitely slow cooling rates?
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