Question

1A. Which equilibrium phase on the Fe-Fe

phase diagram changes to Martensite when cooled quickly enough?

A. Austenite B. Ferrite C. Bainite D. Cementite

1B. For a tapered cross section metal bar that contracts when cooled, what is the stress status when the part is quenched to room temperatures (25 pts)?

A. The edge is in compression and the heavier section is in tension B. The edge is in tension and the heavier section is in compression C. No residual stresses will be built in the component

1C. A cylindrial carbon steel ingot is cooled from austenite temperatures to room temperatures, what is the stress status in the ingot (25 pts)?

A. The surface of the ingot is incompression and the center of theingot is in tension B. The surface of the ingot is in tension and the center is in compression C. No residual stresses will be built in the component

Answer 1

1A Answer

A.Austenite

Reason:

If the austenite is cooled at a very fast rate, i.e. athermally, the morphology formed is known martensite. This microstructure appears like a rod/needle type is referred as Martensite.

1B. Answer

A. The edge is in compression and the heavier section is in tension

Reason:

The edges will cool at a faster rate because of less cross sectional area. So there will be compression in edges and this compression will create tension on the other section

1C Answer

A. The surface of the ingot is in compression and the center of the ingot is in tension

Reason:

This is because the surface gets cooled at a faster rate than the center as it is in contact with the cooling medium i.e. air . So due to this the surface will be in compression and the compression on surface will create tension in the center.