Steels_ Metallurgy and Applications, Third Edition

212 Steels: Metallurgy and Applications

Figure 3.13

CooP)

a00 I-- 0.a0% c

/ ....... -- - o.9o% c

r0o 1-- 0.70,/, c

/ ~ ~o.6o% C

ooo1-

400 0.49*/0 C

200 -- 0.19"/, C

I I t t I I t t t t

5 10 15 20 25 30 35 40 45 50

Distance from quenched end (ram)

Effect of carbon on hardenability of SAE 8600 steels (after Llewellyn and

by Siebert et al., 4 who include information on the effects of elements such as
copper, tungsten and phosphorus as well as the five common alloying elements.
Work by deRetana and Doane 7 evaluated the effects of the major alloying
elements on the hardenability of low-carbon steels of the type used for case
carburizing. Their information is shown in Figure 3.14, where the change in
hardenability is expressed by means of a multiplying factor, calculated as follows:

Multiplying factor =

hardenability of (base steel + alloying element)

hardenability of base steel

The data shown in Figure 3.14 were derived from Jominy tests on a variety
of commercial and experimental casts of carburizing grades in which only one
element was varied in the initial part of the work. The multiplying factors were
tested subsequently in multi-element steels and modified empirically to provide
more widely applicable, averaged factors. However, the authors were unable to
develop a single factor for molybdenum due to interactive effects and therefore
separate factors are shown for this element for use in low- and high-nickel steels.
Although the effects can vary significantly with the carbon content and base
composition, a guide to the potency of elements in the general group in promoting
hardenability is shown below:

Vanadium

Molybdenum

Chromium

Manganese

Silicon

Copper

Nickel

decreasing effect

However, carbon could be placed at the top of this list and elements such as
phosphorus and nitrogen, although present in small amounts, appear to produce