Explain fully what is meant by the following as applied to plain carbon steels

Explain fully what is meant by the following as

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22. Explain fully what is meant by the following, as applied to plain carbon steels and how the‘Jominy end-quench test’ can be used to assess hardenability: (a) limited ruling section;(b) mass effect; and(c) hardenability. 23. Name and describe the three (3) parts involved in a heat treatment cycle. 24. How would the mechanical properties of 0.6% carbon steels differ if the following heat treatments where applied? (a) Heat and soak at 800 °C and then quench in cold water. (b) Heat and soak at 800 °C and then quench in oil. (c) Heat and soak at 800 °C and then slowly cool in the furnace. 25. State the form of heat treatments needed to effect the following changes: 26. Explain why steels with carbon content below 0.3% cannot be significantly hardened by quenching unless other alloying elements are added. 27. Why is the ruling section quoted in material specifications? 28. Explain what is meant by a heat treatment cycle, and the functions of the heating, holding (soaking) and cooling parts of the cycle. 29. Explain how the hardening of a steel surface can be affected by changing the surface composition. 30. Compare the surface hardening processes of nitriding and carburising.
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~ Page 52 of 73 ~ Polymers A polymeric solid can be thought of as a material that contains many chemically bonded parts or units which themselves are bonded together to form a solid. The word polymer literally means "many parts." Two industrially important polymeric materials are plastics and elastomers. Plastics are a large and varied group of synthetic materials which are processed by forming or moulding into shape. Just as there are many types of metals such as aluminium and copper, there are many types of plastics, such as polyethylene and nylon. Elastomers or rubbers can be elastically deformed a large amount when a force is applied to them and can return to their original shape (or almost) when the force is released. Polymers have many properties that make them attractive to use in certain conditions. Many polymers: o are less dense than metals or ceramics, o resist atmospheric and other forms of corrosion, o offer good compatibility with human tissue, or o exhibit excellent resistance to the conduction of electrical current. The polymer plastics can be divided into two classes, thermoplastics and thermosetting plastics, depending on how they are structurally and chemically bonded. Thermoplastic polymers comprise the four most important commodity materials – polyethylene, polypropylene, polystyrene and polyvinyl chloride. There are also a number of specialized engineering polymers. The term ‘thermoplastic’ indicates that these materials melt on heating and may be processed by a variety of moulding and extrusion techniques.
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