PROPERTIES OF AUSTENITIC STEEL WITH NICKEL
AND NITROGEN AT LOW TEMPERATURES
E. A. Ul'yanin, N. A. Sorokina, UDC 669.15-194.56:620.172.251.1
and Ya. M. Zaretskii
We investigated the effect of nickel on the p r o p e r t i e s of austenitic steels containing 18% Cr, with and
without nitrogen (Table 1), at t e m p e r a t u r e s f r o m +20 t o - 2 5 3 ~ The addition of nitrogen makes it possible
to i n c r e a s e the strength of austenitie steel, while nickel provides fairly high ductility at low t e m p e r a t u r e s .
The low carbon content of the steel lowers its susceptibility to e m b r i t t l e m e n t at low t e m p e r a t u r e s
after heating at 800-700~ which must be taken into account for welded p a r t s [1, 2].
Figure 1 shows the amount of strain m a r t e n s i t e f o r m e d in tensile strength samples tested a t - 1 9 6 ~
Nitrogen is an effective austenite stabilizer, and t h e r e f o r e the steels investigated may have a purely
austenitic s t r u c t u r e after testing at -196~ depending on the concentrations of nickel and nitrogen.
In the steels without nitrogen the ultimate strength i n c r e a s e s sharply with d e c r e a s i n g t e m p e r a t u r e s ;
the yield strength also i n c r e a s e s , but to a l e s s e r extent (Fig. 2). The addition of 0.23-0.25% N i n c r e a s e s
the strength substantially. The strengthening effect of nitrogen i n c r e a s e s with d e c r e a s i n g t e m p e r a t u r e s .
While the difference between the yield strengths of melts with and without nitrogen is 15 k g / m m ~ at 20~ it
a v e r a g e s 50 k g / m m 2 a t - 2 5 3 ~
An i n c r e a s e of the nickel concentration by even 5% (melts N13A
and N18A) has noeffect on the ultimate or yield strengths at any of the
r eo
9~ 70
t e m p e r a t u r e s investigated. The addition of nitrogen simultaneously in-
eo c r e a s e s the strength and lowers the ductility, although the ductility r e -
N mains s a t i s f a c t o r y even at low t e m p e r a t u r e s (> 30%).
The strength was d e t e r m i n e d for smooth and notched s a m p l e s
(notch depth 1.7 mm, root radius 0.25 ram, angle 37~ This f o r m of
gl notch e n s u r e s a s t r e s s - c o n c e n t r a t i o n f a c t o r K t = 3.04 [calculated by
L)
lO lZ 1o 16 % N i f o r m u l a (3)].
Fig. 1. Effect of nickel and Nitrogen i n c r e a s e s the sensitivity of the steel to s t r e s s c o n c e n -
n i t r o g e n on the amount of trators at-253~ This is manifest in the sharp i n c r e a s e in the value
strain martensite formed of abn for melts with nitrogen (Table 2) and also in the g r e a t e r d i f f e r -
in the steel tested a t - 1 9 6 ~ ence between ab n and crb for melts without nitrogen. F o r all c o m p o s i -
. . . . ) Steel without nitrogen; tions investigated r b > 1, which indicates sufficient r e s e r v e duc-
) steel with nitrogen. tility of the steel in the notch. With d e c r e a s i n g stability of the aastenite
TAB LE i
Composition, % T A B LE 2
Steel
c ICrlNi N Mn n
ob Ob
N10 0,04 17,05 10,2 0,07 0,,54 Steel Ob
N12 0,03 17,9 t 11,9 0,06 0,48 kg/mm z
N14 0,03 17,8 I 1a,8 0,06 0,08
N15 0,04 16,0 14,5 0,06 0,41 N10 185 170 1,08
N20 0,04 17,2 20,1 0,07 0,47 N15 181 139 1,29
N20 164 117 1,38
N13A 0,0251 18,5 12,7 0,22 1,51 N13A 264 182 1,4
N14A 0,0251 18,8 14,1 0,25 1.51 N14A 293 183 1,6
N15A 0,025] 18,9 15,0 0,25 1,57 N15A 281 182 1,54
N16A 0,025 19,0 16,0 0,24 1,52 N16A 287 182 1,58
N18A 0,025 t8,7 17,9 0,24 1,57 N18A 244 169 1,60
Central Scientific R e s e a r c h Institute of F e r r o u s Metallurgy. Translated f r o m Metallovedenie i
T e r m i c h e s k a y a Obrabotka Metallov, No. 9, pp. 8-10, September, 1969.
681
o b, kg/mra 2 00. 2, kg/mrn2 6,%
, otL 720,
100, lO0
7gO 80 8O x-.-"
88 *0
20 :~- 2O
*0 0 o
~
-250 -1SO -SD 50 -250 -150 -50 50 -250 1150 150
Testing temperature
Fig. 2. T e m p e r a t u r e dependence of strength and ductile c h a r -
a c t e r i s t i c s as a function of nickel and nitrogen contents.
in the steel at -253~ (at lower nickel concentrations) the value
an, kg/cm2 of crbn/O'b at this t e m p e r a t u r e d e c r e a s e s .
We also investigated the effect of heating at 800~ for 2 h
on the f r a c t u r e toughness a t - 1 9 6 ~ The steel containing n i t r o -
gen h a s a f a i r l y high notch s e n s i t i v i t y , which i n c r e a s e s with the
70 l~ N tC, -t8 2.0t2 l~ g~
a b
nickel concentration (Fig. 3).
Fig. 3. F r a c t u r e toughness a t - 1 9 6 ~ The sensitivity of the s t e e l s investigated to heating in the
in relation to heat t r e a t m e n t and alloy- range of precipitation of e x c e s s p h a s e s is somewhat higher than
ing, a) Steel without nitrogen; b) steel that of steel 000Kh21G7AN5 [1]. Evidently this is due to the
with nitrogen. - - ) Quenched f r o m higher nickel content, which lowers the solubility of c a r b o n and
1050~ . . . . ) quenched f r o m 1050~ nitrogen in austenitic steel and intensifies the decomposition of
+ heating at 800~ for 2 h. the solid solution.
CONCLUSIONS
1. Nickel i n c r e a s e s the ductility and f r a c t u r e toughness of austenitic steel at low t e m p e r a t u r e s due
to the higher stability with r e s p e c t to the m a r t e n s i t i c t r a n s f o r m a t i o n .
2. The addition of 0~ N r a i s e s the strength of the steel, the ductility and f r a c t u r e toughness
r e m a i n i n g f a i r l y high.
LITERATURE CITED
1, E. A. Ul'yanin and A. A. Babakov, Metal. i T e r m . Obrabotka Metal., No. 5 (1966).
2. H. J e s p e r et al., Stahl und Eisen, No. 21 (1966).
3. G. V. Uzhik, R e s i s t a n c e to F r a c t u r e and Strength of Metals [in Russian], Izd. AN SSSR (1950).
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