Steels_ Metallurgy and Applications, Third Edition

1600

0.11 -

8

1400

~" o.. 1200

E

499 ~

Graphite

+

Liquid

800

!

0.020%

9100C

738~

Liquid

Liquid

2.01% 11152 ~

1146 ~ 4.27%

(stable phase)

I

p (metastable [

0.021% (a + C/mentite)

J [

6000 1 2 3 4 5

Carbon (wt%)

Figure 1.3 The iron-carbon equilibrium diagram, for carbon contents up to 5 per cent 5

Low-carbon strip steels 7

(a) fcc (y iron) (b) bcc (a iron)

Figure 1.4 Atomic arrangement in (a) face-centred cubic structure (austenite) and
(b) body-centred cubic structure (ferrite)

A little below 723~ the remaining austenite may transform to pearlite which
consists of a lamelar structure of alternate laths of ferrite and cementite (Fe3C).
Below the eutectoid temperature, the solubility of carbon in ferrite decreases
rapidly and is approximately given by the following equation 6'

Csoln = 9.65. exp- 12 IO0/RT wt%