CWB Level 3 Module 20 Practice questions & answers graded A+ 2023/2024

CWB Level 3 Module 20 Practice questions Which of the following metals has the highest thermal conductivity? C (a) carbon steel (b) stainless steel ( (c) aluminum - correct answer (c) aluminum The Ellingham diagram C (a) is a plot of thermal conductivity against temperature. (b) shows the free energy of oxide formation against temperature. (c) shows the rate of oxidation of metals against temperature. - correct answer (b) shows the free energy of oxide formation against temperature. True or False? A metal with a high negative free energy of oxide formation will generally require greater shielding from the atmosphere during welding. - correct answer True Electricity can be conducted by: (a) atoms and electrons. (b) electrons and ions. C (c) only ions. - correct answer (b) electrons and ions. C Which of the following elements is often present in submerged arc fluxes to improve arc stability? (a) copper ( (b) potassium ( (c) nickel C (d) tungsten - correct answer (b) potassium ( Thoria is added to tungsten electrodes for what purpose? - correct answer To increase thermionic emission by lowering the work function. True or False? All pure metals have the same crystal structure. - correct answer False. Metals generally have one of three basic structures. Which crystal structure(s) is (are) composed of close-packed planes? - correct answer FCC and HCP The real strength of metals is lower than the theoretical value because: (a) real crystals always fracture along specific crystal planes. (b) grain boundary sliding occurs. (c) the presence of dislocations facilitates slip. - correct answer (c) the presence of dislocations facilitates slip. Multiplication and subsequent congestion of moving dislocations causes: (a) elastic extension. (b) work or strain hardening. (c) a drop in the yield stress. - correct answer (b) work or strain hardening. Which of the following elements are most likely to form interstitial solid solutions? (a) copper (b) nickel (c) carbon - correct answer (c) carbon If FCC iron has a denser structure than BCC iron, why does it have a higher solubility for carbon? - correct answer The preferred site for carbon in BCC iron is smaller than that in FCC iron. If two metals have complete mutual solid solubility how many phases are formed in the solid— one ortwo? - correct answer One How many phases are there in a eutectic—one or two? - correct answer Two Without referring to the text, draw the phase diagram for a eutectic system with limited mutual solid solubility of the two components. - correct answer Refer to Figure 6.6. Using the portion of the iron—carbon phase diagram in Figure 6.10, use the lever rule to determine the percentage of ferrite and eutectoid pea rlite present in a slowly cooled 0.2% carbon steel. - correct answer About 25% pearlite and 75% ferrite. Here the tie line begins at 0.0%C (a ferrite) and ends at 0.08%C (pearlite). The fulcrum for the lever rule is at 0.2%C % pearlite = (0.2%C — 0.0%C)I(0.8%C — 0.0%C) x 100% % pearlite = (0.2/0.8) x 100% % pearlite = 25% Which of the following metals has the highest work hardening coefficient? (a) 70/30 brass (b) aluminum (c) copper (d) low carbon steel - correct answer a True or False? Recrystallization always involves the formation of a new phase. - correct answer False To get recovery and recrystallization the metal must have been previously