Material Science - short answer questions from AMIE exams

Why are cutting tools manufactured from high-carbon steel in preference to low or medium carbon?
High carbon steels contain more carbon and are therefore harder both initially and after heat treatment. In most instances, the cutting tool must be harder than the material being cut.

Suggest whether low, medium or high-carbon steel should be used for the following applications. 
  1. nails 
  2. ball bearings
  3. car bodies
  4. crankshafts
  5. heat-treatable machine parts
  6. drills
  1. Low
  2. High
  3. Low
  4. Medium
  5. Medium
  6. High.
State whether the carbon contents below relate to low,  medium or high carbon steels.
  1. 0.29% 
  2. 0.65%
  3. 0.87%
  4. 0.08%
  5. 1.32%
  6. 0.31%
  7. 0.59%
  1. Low
  2. High
  3. High
  4. Low
  5. High
  6. Medium
  7. Medium
In which way does the normalising treatment differ from the annealing treatment. 
The only difference between annealing and normalising treatments is the way in which they are cooled. Material that is being annealed is cooled in the furnace whilst normalising cooling is done in still air.

Explain case hardening.
Case-hardening is a method of hardening a ferrous alloy so that the outer portion or case is made substantially harder than the inner portion or core. Its purpose is to produce a material that can resist abrasion and wear due to the hard surface and resist shock loading due to the softer core.

Give one example to show where normalising would be preferred to annealing, giving reasons to support your answer.
The main reason for preferring normalizing to annealing a ferrous material is when improved machinability is desired. A material in its softest state is not necessarily in its most machinable state. To facilitate machining the material must allow chip cracks to propagate and not spread on the too; point. Annealing a ferrous material produces a soft material that may not machine as easily as normalized steel.

List any three applications of copper used in the home. 
Typical applications include: domestic water tanks, rubbing for central heating, ornamental canopies above fires, jugs, vases.

Explain why brass is not as good an electrical conductor as copper.
The addition of zinc to produce brass, together with other elements and impurities, drastically reduces the conductivity of the material.

State the difference in composition of brass and bronze.
Both are alloys of copper. Brass is mainly a combination of copper and zinc, whereas bronze is an alloy of copper and tin. Each can contain other elements in smaller quantities.

State two typical applications for
  1. Copper
  2. Brass
  3. Bronze.
Typical applications include
Copper - electrical conductors, pipes, architectural cladding, boiler tubes. 
Brass - jewellery, presswork and marine applications
Bronze - bearings (light and heavy-duty), pumps, valves, etc. coins.


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