ME Metallurgy and Phase Diagrams 2

Question 1

Tempering of martensite is performed to:

Accepted Answer

Reduce brittleness while accepting some reduction in hardness

Answer

Increase hardness and brittleness

Answer

Convert martensite fully to austenite

Answer

Increase carbon content of the steel

Question 2

Austenite in iron-carbon alloys has which crystal structure?

Accepted Answer

Face-centered cubic (FCC)

Answer

Body-centered cubic (BCC)

Answer

Body-centered tetragonal (BCT)

Answer

Hexagonal close-packed (HCP)

Question 3

In the TTT (Time-Temperature-Transformation) diagram, the 'nose' of the curve represents:

Accepted Answer

The temperature and time of fastest austenite decomposition

Answer

The martensite start temperature

Answer

The upper bainite transformation zone

Answer

The eutectoid temperature

Question 4

Bainite microstructure in steel is produced by isothermal transformation of austenite at temperatures:

Accepted Answer

Between the nose of the TTT curve and the martensite start temperature

Answer

Above the eutectoid temperature

Answer

Below the martensite finish temperature

Answer

At the martensite start temperature only

Question 5

Which alloying element is added to steel primarily to improve hardenability?

Accepted Answer

Chromium

Answer

Sulfur

Answer

Lead

Answer

Phosphorus

Question 6

Stainless steel derives its corrosion resistance primarily from:

Accepted Answer

A minimum of about 10.5 wt% chromium forming a passive Cr2O3 surface film

Answer

High carbon content forming a protective carbide layer

Answer

Nickel additions that repel moisture

Answer

Molybdenum forming a thick oxide scale