UPPER BAINITE (High Temperature) LOWER BAINITE (Low Temperature) Carbon supersaturated plate Carbon diffusion into austenite Carbon diffusion into austenite and carbide precipitation in ferrite Carbide precipitation from austenite

0.2 µm

with carbides

Carbide-free alloys wt %

1 µm

Very poor toughness!

50 µm

T-zero curves

50 µm

0.4C-3Mn-2Si 0.4C-4Ni -2Si 0.2C-3Mn-2Si Impact Energy Test temperature / °C

20 µm

Pearlite Martensite Bainite kilocycles to Crack Initiation Yates, Jerath

Advances in carbide-free bainitic steels Ultimate tensile strength / MPa Fracture toughness / MPa √m 18 wt% Ni maraging steel QT

an apple weighs 1 Newton 1 m = 1 Pa

Cooking temperature? 180 to 220 °C

200 °C for 20 days Caballero, Mateo & Bhadeshia 2.5 GPa

50 nm     

20 nm     

Low temperature transformation: 0.25 T/T m Fine microstructure: 20 nm thick plates Carbide-free Designed using theory alone Typical mechanical properties:

Very Strong, Low Temperature Bainite Ultimate tensile strength / MPa Fracture toughness / MPa m 1/2 18 wt%Ni maraging steel QT