Multiple Choice On the basis of microstructure briefly expla

Multiple Choice On the basis of microstructure, briefly explain why gray iron is brittle and weak in tension. 6. a. The graphite phase is brittle which makes the entire material brittle b. The flake shape of the graphite introduces stress concentration locations which cause the material to become brittle c. The iron-rich phase can form pearlite under some situations which creates a brittle material d. The grain size of the material is small which translates to poor ductility . Which casting method uses a wax pattern? a. Sand casting b. Die casting c. Investment casting d. Continuous casting 8. What is the difference between hot working and cold working? Hot working is done at temps above the recrystallization temperature, clod working is below the recrystallization temperature Hot working is done at termps higher than 100 °C (boiling point of water), cold work is done at temps at or below 100 °C Hot working uses a flame to heat the material during processing, cold working uses a stream of cold water sprayed on the material during processing Hot working is done above the solidus temperature of the alloy, cold work is done below the solidus a. b. c. d.

Solution

6: B

The graphite takes on the shape of a three dimensional flake. In two dimensions, as a polished surface will appear under a microscope, the graphite flakes appear as fine lines. The graphite has no appreciable strength, so they can be treated as voids. The tips of the flakes act as preexisting notches; therefore, it is brittle.

7: C

8: A

9: C

The range of compositions over which these alloys may be precipitation hardened is between
approximately 0.2 wt% Be (the maximum solubility of Be in Cu at about 300°C) and 2.7 wt% Be (the maximum
solubility of Be in Cu at 866°C).