Steels_ Metallurgy and Applications, Third Edition

346 Steels: Metallurgy and Applications

g c O~

060

I-- 30

150

O4 e-

~

120

9O

30

0

0

_ ~n"-78~

90 c

J I 1 J J ~ J-

A

8~ t

90~

40 !- -78~ ., ..-78~

20 or' 90~

• lld 2~176 I I
  o lO 20 30 40 50 60 70 80
  Reduction (%)

Figure 4.30 Effect of the temperature of rolling on the properties and martensite content
of Type 316 steel (After LleweUyn and Murray 2s)

the UK for this application but the degree of precision required in the pressing
operation, for the consistent production of high-quality bowls, was uneconom-
ical. This related to the fact that the 18% Cr, 10% Ni composition is relatively
stable at ambient temperature and the rate of work hardening was insufficient
to compensate for the reduction in thickness that accompanies the stretching
operation. Failure therefore occurred before the required degree of stretching
(uniform strain) could be achieved. However, in very lean compositions, which
form large amounts of strain-induced martensite at low strain, the rate of work
hardening reaches a maximum at an early stage and decreases when the reaction
is complete. Workers in British Steel 29 therefore focused their attention on iden-
tifying the compositions that would provide the optimum rate of work hardening
and uniform strain via the formation of controlled amounts of strain-induced
martensite. The results of this work are shown in Figure 4.31 which illustrates
the interdependence of composition, stability and uniform strain. In this figure,
the lower diagram shows the relationship between composition and the amounts