Steels_ Metallurgy and Applications, Third Edition

Engineering steels 273

fractions. In the absence of pearlite, try = txa and in the absence of ferfite, try =
t~p. The index n in the above equation allows the yield strength to vary with
pearlite content in a non-linear manner and, as indicated below, it was given the
value of ~. The full quantitative equations for yield and tensile strengths are as
follows:

1 l 1 1

YS (N/ram 2) = f~ [35+58.5%Mn+ 17.4d-[ ]+(1 -f~ )[17.8+3.85So ~ ]

+ 63.1%Si + 426~/%N

1 1 1

TS (N/mm 2) = fa3 [247 + 1146~/%N + 18.2d-[] + (1 - f~)

l

[721 + 3.55So [ ] + 97.3%Si

where So = inteflamellar spacing of pearlite (ram).
Thus in high-carbon steels the volume fraction of pearlite (1 - f~) and the
interlamellar spacing (So) have a significant effect on both the yield and tensile
strengths. The major difference between the two equations is the value of the
constants, namely 35 and 178 N/ram 2 for yield strength and 247 and 721 N/mm 2
for tensile strength. Manganese in solid solution appears to have no significant
effect on tensile strength, but this element appears in the equation for yield
strength. The components of yield strength in medium-to high-carbon steels,
containing 0.9% Mn, 0.3% Si and 0.007% N, are shown in Figure 3.40. This

9 Experimental data 9

4OO

.-, ~eadlte

r

i

200

50 Peadlte (wt%) 100

Figure 3.40 Components of yield strength in high-carbon steels (After Gladman et al. 42)