Carbide-free Rail Steels “Building Bridges in Metallurgy”

Cheap Large dimensions Rolled into shape Wear resistance Rolling contact fatigue Joining

Origin of strength, hardness, toughness

body-centred cubic (a’) face-centred cubic (g)

displacive transformation

Surface 1 Surface 2 50 µm Srinivasan & Wayman

Design Philosophy carbon supersaturated plate carbon partitions into g carbide precipitates from g Design Philosophy

0.4 C 2 Si 3 Mn wt% 1 µm

Very poor toughness!

50 µm

Carbide-free alloys wt %

Impact Energy Charpy impact / J Temperature / °C Test temperature / °C 10 20 30 40 50 60 70 0.4C-3Mn-2Si 0.4C-4Ni -2Si 0.2C-3Mn-2Si Charpy impact / J 200 100 -100 -200 Temperature / °C Test temperature / °C

20 µm

kilocycles to Crack Initiation Pearlite Martensite Bainite 1200 1000 800 600 400 200 kilocycles to Crack Initiation Yates, Jerath

Yates, Jerath

austenite

0.2C 1.25Si 1.55Mn 0.5Cr 0.15V 0.15Mo wt% 15 mm thick plate, without Mo 550°C for 5 h Chang and Bhadeshia

U.K.

Radcliffe et al.

Kaufman

Devnathan & Clayton

Further Developments Fracture toughness / MPa √m 18 wt% Ni 20 40 60 80 100 120 140 160 180 18 wt% Ni maraging steel Fracture toughness / MPa √m QT 2500 2000 1500 1000 Ultimate tensile strength / MPa

Fe-2Si-3Mn-C wt% 800 B 600 Temperature / K 400 M 200 0.2 0.4 0.6 0.8 1 0.2 0.4 0.6 0.8 1 1.2 1.4 Carbon / wt%

Fe-2Si-3Mn-C wt% 1.E+08 1 month Time / s 1.E+04 1.E+00 0.5 1 1.5 1 year 1 month Time / s 1.E+04 1.E+00 0.5 1 1.5 Carbon / wt%

wt% Low transformation temperature Bainitic hardenability Reasonable transformation time Elimination of cementite Austenite grain size control Avoidance of temper embrittlement wt%

g g a a a 200 Å

650-720 HV 10-30% ductility

Stress / GPa Velocity km s-1 Hammond and Cross, 2004

GRP mild steel “superbainite” vehicle steel Peter Brown (DSTL) Dave Crowther (QinetiQ)

“more serious battlefield threats”

www.msm.cam.ac.uk/phase-trans Liou Chun Chang Howard Smith Vijay Jerath (CORUS) Francisca G. Caballero www.msm.cam.ac.uk/phase-trans

French National Railways 0.2C 1.25Si 1.55Mn 0.5Cr 0.15V 0.15Mo wt% UTS > 1100 MPa 320-340 HB elongation > 14% Curve radius 1140 m Cant 124 mm Installed Dec 1998 Traffic Mixed Tonnage 15  106 gt/annum

French National Railways (Howard Smith)

Swiss Railways Curve radius 449 m Cant 120 mm Installed Nov 1999 0.3C 1.25Si 1.55Mn 0.5Cr 0.15Mo wt% UTS > 1200 MPa 360-390 HB elongation > 13% Curve radius 449 m Cant 120 mm Installed Nov 1999 Traffic Freight Tonnage 30  106 gt/annum

Swiss Railways (Howard Smith)

15 mm thick plate, without Mo air-cooled after hot rolling Chang and Bhadeshia

15 mm thick plate, without Mo quenched after hot rolling Chang and Bhadeshia

20 µm

ballistic mass efficiency consider unit area of armour

a g a g g 50 nm

Chatterjee & Bhadeshia, 2004