The image shows the microstructure of brass.
What type of grain structure does this image represent?
- Deformed
- Dendritic
- Equiaxed
- Stressed
ENGINEERING, PPT 2016 HSC 26c
Structural steel `text{I}`-beams are used to make a crane were hot-rolled then normalised.
Explain why normalising was chosen as the heat treatment process. Support your answer with a labelled sketch of the resulting microstructure. (4 marks)
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Advantages of normalising:
→ An increase in strength. Grain size strengthening is achieved due to the fine uniform grain structure produced by normalising.
→ When compared to other strengthening methods it is relatively economical.
→ Normalising relieves stress.
Show Worked Solution
Advantages of normalising:
→ An increase in strength. Grain size strengthening is achieved due to the fine uniform grain structure produced by normalising.
→ When compared to other strengthening methods it is relatively economical.
→ Normalising relieves stress.
♦ Mean mark 43%.
ENGINEERING, PPT 2017 HSC 25b
A small truck chassis rail has been made from rectangular hollow section (RHS) steel. The RHS has been cold formed from an alloy steel with a yield strength of 500 MPa. A manufacturer's sign on the chassis rail is shown below.
- Explain why the chassis rail should normally not be drilled or welded. (3 marks)
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- A large reinforcing plate that supports a new attachment is to be welded onto the chassis rail according to the manufacturer's specifications.
- Use the diagram below to draw and label the macrostructure of the weld area, including the surrounding chassis rail and reinforcing plate. (2 marks)
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i. Welding
→ The chassis rail steel becomes molten when welded at temperatures exceeding the A1 temperature.
→ Columnar grains may form on some parts of the weld upon cooling.
→ Martensite may form on cooling, creating a brittle, hard microstructure with less strength than that of the steel chassis (500 MPa).
Drilling
→ Stress raisers are produced by drilling the flanges.
→ Fatigue failure is initiated by surface roughness that can occur around the drill hole.
♦♦ Mean mark (i) 39%.
ii.
♦♦ Mean mark (ii) 27%.
ENGINEERING, PPT 2019 HSC 24b
Normalised high-tensile steel has been chosen for the manufacture of a wing support beam.
- Draw and label the microstructures of a normalised high-tensile steel and an annealed high-tensile steel. (2 marks)
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- Explain how the microstructure produced by normalising high-tensile steel improves the steel's suitability for this application. (2 marks)
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i. Microstructures
ii. → The strength of the steel is markedly increased.
→ Normalising produces finer and more uniform grains.
Show Worked Solution
i. Microstructures
♦♦♦ Mean mark (i) 26%.
ii. → The strength of the steel is markedly increased.
→ Normalising produces finer and more uniform grains.
♦ Mean mark (ii) 41%.
ENGINEERING, PPT 2022 HSC 23c
Steel `text{I}`-beams have been used when large, open spans need to be created inside buildings.
Explain how microstructural changes take place in steel when an `text{I}`-beam is formed using the process of hot rolling. You may use a drawing to support your answer. (4 marks)
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→ During hot rolling the steel is heated to above its recrystallisation temperature.
→ Therefore, due to the pressure of the rollers, the grains change from their original state to become elongated.
→ However, as the steel exits the rollers it is still above recrystallisation temperature, resulting in the recrystallisation of the elongated grains to create finer, equiaxed grains.
Show Worked Solution
→ During hot rolling the steel is heated to above its recrystallisation temperature.
→ Therefore, due to the pressure of the rollers, the grains change from their original state to become elongated.
→ However, as the steel exits the rollers it is still above recrystallisation temperature, resulting in the recrystallisation of the elongated grains to create finer, equiaxed grains.
♦ Mean mark 48%.
ENGINEERING, PPT 2020 HSC 18 MC
The grain structure of a material has changed over time from that shown in microstructure `A` to that shown in microstructure `B`.
What heat treatment process has the material undergone to cause this change?
- Tempering
- Normalising
- Quench hardening
- Precipitation hardening