Steels_ Metallurgy and Applications, Third Edition

Stainless steels 313

at high tempering parameters. The addition of vanadium (Figure 4.9(c)) produces
a similar effect and the stabilization of M2X maintains a high level of hardness,
even after tempering at 650~
Irvine and Picketing 6 also demonstrated the beneficial effects of carbon,
nitrogen and niobium on the tempering resistance of 12% Cr steels. As illustrated
in Figure 4.10, carbon and nitrogen increase the hardness throughout the
tempering range and in the tempered 650~ 1 h condition, the 0.2% PS values of
12% Cr-Mo-V steels can be expressed by means of the following parameter:

0.2% PS = 710 + 772 (C + 2N) N/mm 2

Carbon and nitrogen also have the further benefit of being austenite formers
and therefore do not require compensating additions to preserve the required
martensitic structure.

6~176 r

500 -~'~~N~

400 - \~,~ ,-s

Steel no.C, % N, % ~~.~4

4 0.127 0.020

> -1- 5 0.133 0.031

= 300 - 6 0.130 0.044

7 0.129 0.062

= i i I _ I I I I

-I- (a)

500 - ~'"~"~ Steel no.C, % N, %

0.096 0.033

0.133 0.031

1 O. 155 0.039

400 -

300 - 2

200 I I I 1 I I I

13 14 15 16 17 18 19 20

(b) T (20 + Log t) x 10-3

I i ~ I I i I

400 450 500 550 600 650 700

1 hour at temperature (~

Figure 4.10 Effect of (a) nitrogen and (b) carbon on the tempering characteristics of a
12% Cr-Mo-V steel (After Irvine and Picketing ~)