Lesson 2 - Plain Carbon Steel Flashcards
What does the carbon content of plain carbon steels vary from?
0.04 - 1.70%
What is the rough carbon content of the three subdivisions of plain carbon steels?
Low Carbon: 0.04 - 0.30%
Medium Carbon: 0.30 - 0.60%
High Carbon: 0.60 - 1.70%
What are the three factors affecting steels strength?
- % Carbon
- Microstructure
- Grain size
What is solution hardening
When carbon atoms fill the empty space between the iron atoms.
Carbon atoms interfere with the movement of dislocations.
Plastic deformation becomes difficult due to the movement impedance by carbon, thus, increasing tensile strength
What is the purpose of cold rolling?
Improve tensile strength and hardness
Produce smooth surface finish and exact size
How does ductility change as carbon content increases?
Decreases
How does hardness change as carbon content increases?
Increases
How does tensile strength change as carbon content increases?
Increases up to medium carbon steel then decreases to high carbon steel
How does malleability changer as carbon content increases?
Decreases
Why are higher carbon content steels harder?
Increased interference with dislocation movement, making it harder for dislocations to move.
What relationship does grain size have with dislocation movements?
The smaller the grain size, the larger the amount of grain boundary per unit volume, hence, the more obstacles to dislocation movements.
When does the Hall-Petch relationship not apply? And what happens after this point?
At very small grain sizes ( below 10 nanometres).
Below this limit grain boundary sliding
What is the purpose of heat treatments?
Allow us to put right the following:
- As cast microstructures
- Mechanical damage
- Internal stresses
Also makes fabrication easier
What is Annealing?
A heat treatment where the steel is heated into the austenitic phase region, and then cooled at a controlled rate in a furnace
What is normalizing?
A simple heat treatment where the steel is heated into the austentic phase region, and is then cooled in still air, to produce smaller grain size
What is spheroidising?
A heat treatment where the steel is heated to just below the austenitic change point, then the cementite spheroidises (forms spheres)
What does spheroidising to do a plain carbon steel?
- Makes dislocation movement to be easier
- Mechanical strength of steel is reduced
- However it greatly increases ductility
- May make forming processes much easier
