Brittle fracture

Question 1

What are favorable conditions for brittle fracture?

Answer 1

Cold temperatures - raise the yield limit
High deformation rate - less opportunity for deformation
3d stress condition - no opportunity for shear stress
BCC and some HCP crystal structure - present brittle-to-ductile transition
Higher carbon composition
Larger grains - increase the risk

Question 2

How can brittle fractures be reduced?

Answer 2

C < 0.2% - yield limit and tensile strength decrease
Add Mn < 2% - remove S at grain boundary forming ductile MnS (instead of brittle Fe sulphides)
Add Si & Al - remove O (otherwise formation of more harmful Fe oxides)
Add Al - grain size reduction
Add Ni - toughness increases, coarsens carbides/ nitrides
Grain size reduction - Mn, Ni, Mo, Nb, Vi or NORMALIZATION