Plastic deformation

Question 1

Why is the strain-rate in hot deformation more important to look at than the strain applied?

Answer 1

Because if the strain is given to the material at a very fast rate, the material will not be able to deform properly.

Question 2

What is hot brittleness?

Answer 2

The reduction in workability during an intremediate temp. Lacking from approx. 700-1000 C.

Question 3

Why does hot brittleness occur?

Answer 3

Because this is the area where the steel starts transforming from austenite to ferrite. At these temps ferrite is softer than austenite. A thin layer of ferrite starts occurring at the grain boundaries.

Question 4

What can failure mechanism maps show us?

Answer 4

The response of a metallic alloy to hot working. It is roughly visualized showing the different mechanisms active under specific conditions of strain rate and temperature.

Question 5

What is the deformability of cast metals is generally limited of?

Answer 5

The deformability of cast metals is generally limited by
- the solidification defects
- the coarse structure
- the presence of micro-segregants at grain boundaries

Question 6

When can cold working occur?

Answer 6

Because of the limitations of deformability in cast metals due to defects, structure and segregants, the metals are first subjected to hot working and only when their structure is improved, they can successfully be cold deformed

Question 7

The grain size resulting from hot-working strongly affects sensitivity for cracking and ductility in alloys. The grain size in a hot worked metal is ruled by:

Answer 7

• Time at high temp
• Strain and strain-rate
• Temp and strain gradients in the volume
• Secondary alloying elements can also limit grain growth

Question 8

Variation in the hard ability in banded regions (in hot-worked fibrous elements) can

Answer 8

generate cracks in some of the phases/particles/compositions.

Question 9

Which phase is brittle, and cracks once we do extra cold/hot-working

Answer 9

Martensite

Question 10

Failure analysis practical approach:

Answer 10

1. Measurement of a sample
2. Find the actual loading condition
3. Identify the theoretical failure condition based on this load.
4. Compare the failure with the result of the theoretical analysis.