Steels_ Metallurgy and Applications, Third Edition

210 Steels: Metallurgy and Applications

7O

6O

rr 1-

50-

r

"2 t~ _

"r"

40-

3O

925oc

845oc

815oc

790~

775oc

I I I I I I I

10 20 30 40 50 60 70

Distance from quenched end (ram)

Figure 3.10 Effect of austenitizing temperature on the Jominy hardenability of 0.55% C

0.84% Mn 0.92% Cr 0.21% Mo steel (After Grange 5)

Alloying elements

Because of their very distinct effects on hardenability, it is convenient to consider
alloying elements in three separate groups:

1. Carbon.


2. General group - Cr, Mn, Mo, Si, Ni, V, etc.


3. Boron.

Carbon must be placed in a special category because it is the element that controls
the hardness of martensite and therefore defines the maximum hardness that can
be achieved in a given steel composition. The relationship between carbon content
and the hardness of martensite is shown in Figure 3.11. The effect is reasonably

70-

60

c)

tr "1" 50

'2 ~"^40

30

20 I

0

Formation

of retained

austenite

I I I I I I I

0.2 0.4 0.6 0.8

Carbon (%)

Figure 3.11 Effect of carbon on the hardness of martensite