Steels_ Metallurgy and Applications, Third Edition

Low-carbon strip steels 27

0.30

0.25

~

0.20

0.15

0.10

0.05

200

~

l phase

-"~,-,,,,._...,"~.- SolU ~iutio n

~ strengthened

"grain refinement /" ~-,= ~ ansformatiov

_ ~~ gthened

Partially annealed "~' ~n

_- cold work ~-,,,~

, ,,| , II ,, _ ~ J

400 600 800

Tensile strength (MPe)

Figure 1.25
Goodwin 45)

Relationship between n value and tensile strength (After Dasarathy and

.8 -

n=O

0.2

.2

0 .2 .4 .6 .8

Polar height / radius of diaphragm

Figure 1.26 Variation of calculated polar thickness strain versus polar height for
different values of n for rm -- 1 (After Wang 46)

that the polar thickness strain for a given bulge height decreases as the n value
increases. The implication is that the strain becomes more uniformly distributed
as the n value increases. Figure 1.27(a) shows that the polar thickness strain at
instability increases with increasing n value and the result is that the maximum
bulge height at instability also increases with increasing n value (Figure 1.27(b)).
As with rm value, equivalent effects are obtained with the more complicated
pressings that are needed across the engineering industry. In practice, it is found
that success with any particular pressing may be dependent on a high value of
one or other of the parameters r or n, whereas success with another pressing
may depend on high values of both parameters. 47