Metallurgy - Hardenability, Strengthenability, Surface Treatment

Front 1

What is hardenability?

Back 1

Depth up to which a material is hardened as a result of heat treatment

Front 2

What three things does the hardenability of steel depend on?

Back 2

Composition of steel

Grain size

Quenching medium/method

Front 3

What are examples of liquid and gaseous quenchants.

Back 3

Liquid - Oil, Water/Brine

Gaseous - Air, Helium, Argon

Front 4

Quenching has 3 stages - what are these?

Back 4

A - Vapour Blanket Stage (Slow Cooling)

B - Nucleate Boiling Stage (Fast Cooling)

C - Convective or Liquid Cooling Stage

Front 5

What mechanical properties do fine grains affect?

Back 5

Increase impact toughness

Improve machining finishes

Mitigate quenching cracks

Front 6

What mechanical properties do course austenite grains affect?

Back 6

Raise hardenability

Raise Tensile Strength

Improve rough machinability

Front 7

What 6 factors affect grain size?

Back 7

Nature/Extent of Deoxidizers

Chemical Composition of Steel

Method of Manufacture

Alloying Elements

Metallic/Non Metallic Inclusions

Heat Treatment Processes

Front 8

What does increasing %C do to hardenability?

Back 8

Increases it

Front 9

Do any other alloy additions increase hardenability?

Back 9

Yes

Cr, Mn, Mo, Si, Ni, B

Front 10

Best way of increasing strength?

Back 10

Placing obstacles in paths of dislocations

Front 11

Why are polycrystalline materials stronger?

Back 11

Slip directions vary from crystal to crystal - some grains unfavourably oriented.

Dislocations cant easily cross grain boundaries.

Front 12

What are 3 types of strengthening mechanisms?

Back 12

Solid Solution Strengthening

Grain Size Reduction

Strain Hardening

Front 13

There are two types of grain boundries (low angle and high angle) which are more effective at improving strength?

Back 13

High Angle

Front 14

What equation shows that reducing grain size increases strength?

Back 14

Hall Petch

Front 15

How does solid solution strengthening work? (How do impurities work too?)

Back 15

Interstitial/Substitutional Impurites cause lattice strain and interact with dislocation strain field.

Impurities diffuse and segregate around dislocation - reduces strain energy and anchors dislocation

Front 16

Why surface hardening?

What can be done by surface hardening?

Back 16

Can improve a lot of properties of material

Can form hard wear resistant surface, fracture resistant cores etc.

Front 17

What is wear resistance influenced by?

Back 17

Hardness

Volume fraction/distribution of high hardness precipitated (high volume and uniform distribution is preferred)

preferred)

Front 18

What are the two main surface hardening mechanisms?

Back 18

Carburising

Nitriding

Front 19

What is carburising (the process)?

Back 19

Introducing carbon into layer of steel.

Steel heated and held at temp above upper critical temperature

Quenched rapidly to produce hardened surface layer

Steel tempered

Front 20

What three types of carburising processes are there?

Back 20

Pack carburising

Gas carburising

Liquid carburising

Front 21

Why is nitriding carried out on the finished product?

Back 21

Because it is a low temperature process

Front 22

What elements are common in nitriding steels?

Back 22

Cr, Al, V and Mo