The growth of acicular ferrite in Fe-Mn

Annika Borgenstam

• Fe - 0.92, 1.81, 3.67, 5.54, 7.60 mass% Ni• Fe – 0.99, 1.98, 3.92, 5.66 mass% Cr• Fe – 0.71, 1.69, 2.60, 5.46 mass% Mn• Fe - 0.27, 0.51, 1.00, 2.00 mass% V• Fe - 0.5, 0.99, 2.01, 3.01 mass% Mo• Carburized• Isothermal heat treatment • Microstructure studied by LOM• Measurements of the composition gradients with

ASEM

Experimental work

Distance from surface

Car

bon

cont

ent

Distance from surface

The gradient technique

Measurement of the carbon gradient with ASEM

Linje 3, Prov Fe-1%Mn, 2h, 051124

0,00000

0,10000

0,20000

0,30000

0,40000

0,50000

0,60000

0,70000

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0,90000

1,00000

0,00 200,00 400,00 600,00 800,00 1000,00 1200,00 1400,00 1600,00 1800,00 2000,00

Avstånd, my

% C

Correlation between micro-hardness and carbon content for 2% Mn

1%Mn 725oC

6% Mn 350oC

Temperature as function of critical carbon content in Fe-Mn alloys

Growth controlled by:• Constant thermodynamic barrier• Carbon diffusion• Paraequilibrium conditions

One model for lengthening of Widmanstätten ferrite, upper bainite

and lower bainite

Comparison of experimental data with WBs

0.71%

1.69%

2.60%

Critical temperature for Fe-Mn alloys with 0.1 mass% C

Critical temperature as function of Mn content for Fe-Mn alloys with 0.1 mass% C

Critical temperature as function of Mn content for 0.1 mass% C compared with WBs calculation

Critical temperature as function of Mn content for Fe-Mn alloys with 0.2 mass% C

Critical temperature as function of Mn content for 0.2 and 0.6 mass% C compared with WBs

calculation

The themodynamic barrier