QUESTION THREEa. List the four classifications of steels and briefly describe the properties of each.(10 marks)b. What property of titanium makes it attractive for use in race-car and jet-enginecomponents? (2 marks)c. Why is magnesium often used as a structural material in power hand tools? Why are itsalloys used instead of pure magnesium? (3 marks)d. List two examples of refractory materials. Which property of the refractory metalsdefines their most useful applications? (2 marks)e. What are shape-memory alloys (SMAs)? (3 marks)SECTION CQUESTION FOURa. Cite the four factors that influence corrosion. (2 marks)b. Briefly describe the following forms of corrosion, and for each, cite measures that can betaken to prevent or control it. (8 marks)i. Galvanic corrosionii. Crevice corrosioniii. Intergranular corrosioniv. Erosion–Corrosionc. A piece of corroded metal alloy plate was found in a submerged ocean vessel. It wasestimated that the original area of the plate was 800 cm2 and that approximately 7.6 kg hadcorroded away during the submersion. Assuming a corrosion penetration rate of 4 mm/yr forthis alloy in seawater, estimate the time of submersion in years. The density of the alloy is4.5 g/cm3. (3 marks)a. Compare the effectiveness of quenching in moderately agitated water and oil by graphing ona single plot radial hardness profiles for cylindrical specimens of an 8630 steel of diameter65 mm that have been quenched in both media. Use Figure 2 and Figure 3. (7 marks)

a. The four classifications of steels are carbon steels, alloy steels, stainless steels, and tool steels.

• Carbon steels: These steels primarily contain carbon as the main alloying element. They have good strength and hardness, but low corrosion resistance.

• Alloy steels: These steels contain additional alloying elements such as manganese, nickel, chromium, or molybdenum. They have improved strength, toughness, and wear resistance compared to carbon steels.

• Stainless steels: These steels contain a high percentage of chromium, which provides excellent corrosion resistance. They also have good strength and heat resistance.

• Tool steels: These steels are specifically designed for use in cutting tools, molds, and dies. They have high hardness, wear resistance, and toughness.

b. Titanium is attractive for use in race-car and jet-engine components because of its high strength-to-weight ratio. It is lightweight but has excellent strength, allowing for improved performance and fuel efficiency.

c. Magnesium is often used as a structural material in power hand tools because of its low density, which makes the tools lightweight and easy to handle. However, pure magnesium is too soft and prone to corrosion, so its alloys, such as AZ31 and AZ91, are used instead. These alloys have improved strength, corrosion resistance, and better mechanical properties.

d. Two examples of refractory materials are tungsten and molybdenum. The most useful property of refractory metals is their high melting point, which allows them to withstand high temperatures without melting or deforming. This property makes them suitable for applications in high-temperature environments, such as in furnaces and aerospace components.

e. Shape-memory alloys (SMAs) are a class of materials that can "remember" their original shape and return to it when subjected to certain stimuli, such as temperature or stress. They exhibit a unique property called shape memory effect, which allows them to undergo reversible shape changes. SMAs find applications in various fields, including biomedical devices, aerospace engineering, and robotics.