Metallurgy and Phase Diagrams Flashcards
6 cards from real ME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Metallurgy and Phase Diagrams flashcards as text
Tempering of martensite is performed to:
Answer: Reduce brittleness while accepting some reduction in hardness
Tempering reheats quenched martensite to a temperature below the eutectoid to allow some carbon diffusion, reducing brittleness while sacrificing some hardness.
Austenite in iron-carbon alloys has which crystal structure?
Answer: Face-centered cubic (FCC)
Austenite (gamma-iron) has an FCC crystal structure, which can dissolve significantly more carbon (up to 2.14 wt%) than the BCC ferrite phase.
In the TTT (Time-Temperature-Transformation) diagram, the 'nose' of the curve represents:
Answer: The temperature and time of fastest austenite decomposition
The nose of the TTT curve is where decomposition of austenite is fastest because both the thermodynamic driving force and atomic diffusivity are balanced.
Bainite microstructure in steel is produced by isothermal transformation of austenite at temperatures:
Answer: Between the nose of the TTT curve and the martensite start temperature
Bainite forms by isothermal transformation of austenite at temperatures between the pearlite nose and the martensite start (Ms) temperature.
Which alloying element is added to steel primarily to improve hardenability?
Answer: Chromium
Chromium (and elements like molybdenum, nickel, and manganese) shift the TTT curve to the right, improving hardenability by allowing martensite formation at slower cooling rates.
Stainless steel derives its corrosion resistance primarily from:
Answer: A minimum of about 10.5 wt% chromium forming a passive Cr2O3 surface film
Stainless steel requires at least ~10.5 wt% Cr to form a stable, self-repairing chromium oxide (Cr2O3) passive film that prevents oxidation and corrosion.