14-15 Flashcards
What is a continuous cooling diagram?
A temperature-time diagram that has the constant cooling of steels, this means that some steel alloys cannot be made.
Normally the graph with less components.
What is critical cooling rates?
The minimum rate at which steel can be cooled to prevent steel decomposing from austinite.
What is annealing?
Reheating the steel above its recrystallisation temperature, then cooling of metal above the critical cooling point by 30-50.
Advantages of annealing?
Reduced internal stress which makes it more ductile.
Enhances toughness.
Increases grain size.
Disadvantages of annealing?
Reduces hardness.
What is normalizing?
Heating the steel just above its upper critical point, then soaking it for a short period and allowing it to cool in air.
Purpose of normalising?
Removes impurities and improves its strength and hardness.
How is an alloy steel made?
By combining steel with one or more elements such as silicon, nickel and titanium.
What is stainless steel?
Has a low carbon content, chromium and molybdenum.
Is strong and can withstand high temperatures.
What is hardenability?
How easy it is for an object to harden when it is rapidly cooled.
E.g Jominy
What is a Jominy test?
Firstly, heat a rod uniformly and place in a Jominy test machine.
Next, the machine will squirt water constantly on the bottom of the rod.
Once, the colour is homogeneous you will have a metal with different hardness, as it has been continuously cooled.
Finally, a diagram can be made of distance from quenching to hardness. The values closer away should have a high hardness.
What is Flame hardening?
Used to make gears, as they require very hard teeth and high toughness on the inside to counter the stress placed on the gear.
What is an induction hardening?
An inductor will go close to the gear teeth to cause thermal energy through an electric current and allowing the core stays the same.
Then quench.
What is gas carburisation?
Increases the amount of concentration of carbon.
Place the low carbon steel in a high-temperature furnace, which has a carbon-rich atmosphere.
Man factor the change the hardness of steel is the time and temperature of the furnace.
How would carburising be different from nitriding and nitrocarburizing?
Nitriding/nitrocarburizing- thicker grains and higher hardness.
