Steels_ Metallurgy and Applications, Third Edition

Stainless steels 345

140

120

~" e-, 100

so

~ 6O

~ 4O

N.

o 20

301

302

347

321

~1304 310

316

80

A

60

4o

~ 20

(^301 302)
347
304
321
316
0 10 20 30 40 50 60 70 80
Reduction (%)
Figure 4.29 Effect of cold rolling on the 0.2% proof stress and martensite content of
austenitic stainless steels (After Llewellyn and Murray 2s)
(17% Cr, 7% Ni) shows the highest rate of work hardening and this can be
related to the fact that it has the lowest alloy content in the range examined.
Therefore it has the lowest stability and forms the greatest amount of strain-
induced martensite during cold rolling. Conversely, Type 316 (18% Cr, 12% Ni,
2.5% Mo) and Type 310 (25% Cr, 20% Ni) are the most highly alloyed steels
in the series and these show the lowest rates of work hardening because their
alloy content is sufficient to suppress the formation of strain-induced martensite
at ambient temperature. However, if rolling is carried out at a lower temperature,
e.g. -78~ then transformation to martensite can be induced in Type 316 steel
and this results in a higher rate of work hardening than that observed at room
temperature. This is illustrated in Figure 4.30.
Optimization of cold.forming properties
A considerable amount of work has been carded out on the optimization of
composition in austenitic stainless steels in order to promote high levels of stretch
formability in applications such as the production of sink bowls. Up until the early
1970s, the standard Type 304 grade (nominally 18% Cr, 10% Ni) was used in