Bainite

Question 1

What temperature ranges do bainite, pearlite and martensite happen in?

Answer 1

Pearlite - high temp (550-720)
Bainite - mid temp
Martensite - low temp (<250)

Question 2

What is bainite?

Answer 2

Contains ferrite and cementite like pearlite but it is non-lamella. It uncleared and grows by displacive transformation but does involve diffusion of carbon.

Question 3

How could you recognise bainite on a microscope?

Answer 3

Etches are darker due to a large number of fine carbides.

Question 4

How do bainite grains grow?

Answer 4

They grow from austenite boundaries into fine plates and grow into clusters with carbides in between the clusters. Units are called ‘sub units’ and clusters are called sheaves.

Question 5

What are the two types of Bainite?

Answer 5

Upper - 550-400C - diffusion of carbon is fast and Fe3C forms between ferrite plates
Lower - 250-400C - diffusion of carbon is slower and Fe3C forms within the ferrite plates