L E T T E R S TO THE EDITOR

OPTIMAL P.

WORKING

CONDITIONS

M. Dontsov

and

FOR

MATERIALS

IN A C T I V E

A. N. Vereshchagin

MEDIA

UDC 620.194.4.6:620.1981621

The b a s i c p r i n c i p l e of the o p t i m i z a t i o n of the working conditions of a m e t a l in a definite m e d i u m r e d u c e s , w r i t e s G. V. Karpenko [1],t0 the fact that both the m e t a l and the m e d i u m should be in a m i n i m a l l y activated state. T h e r e f o r e , to i m p r o v e the r e s i s t a n c e of a r t i c l e s in an a g g r e s s i v e m e d i u m , the l a y e r of m e t a l a d j a c e n t to the s u r f a c e is s o m e t i m e s annealed (a m i n i m a l t h e r m o d y n a m i c activity of the m e t a l is created) but not quenched, as is g e n e r a l l y done with the work of a r t i c l e s in a n e u t r a l m e d i u m , in an a t t e m p t to i n c r e a s e t h e i r s e r v i c e life. However, the state of m a r t e n s i t e - a g e d s t e e l a f t e r quenching is l e s s active than a f t e r aging. Actually, t e s t s of 18-8 m a r t e n s i t e - a g e d s t e e l in a quenched state and a f t e r quenching and aging (quenching f r o m 900~ aging at 450~ have shown [2] that, in a quenchecl state, it has a c o n s i d e r a b l y ldwer tendency toward b r i t t l e c o r r o s i o n - m e c h a n i c a l failure than in an aged state. In o t h e r words, this e x p e r i m e n t , c o n f i r m i n g the b a s i c p r o p o s i t i o n s of the a r t i c l e by G. V. Karpenko [1], b e a r s witness at the s a m e t i m e that the quenched state of a steel is not always m o r e activated. An investigation was m a d e e a r l i e r [3] of the c o r r o s i o n fatigue of h i g h - s t r e n g t h steel 4140 in v a r i o u s m e d i a as a function of the level of s t r e n g t h (hardness) attained by an a p p r o p r i a t e heat t r e a t m e n t of the m e t a l ( a n nealing of the s t e e l in the d e l i v e r e d state, quenching in oil f r o m 850~ followed by high annealing at various t e m p e r a t u r e s , o r only quenching in oil f r o m 850~ without subsequent annealing). F i g u r e 1 i l l u s t r a t e s the r e s u l t s of this investigation (the m e d i u m was an a e r a t e d 3% solution of NaCI). The g r e a t e r the d e g r e e of loading of the s a m p l e s the lower the n u m b e r of cycles to d e s t r u c t i o n (curve a), which, g e n e r a l l y speaking, is well known; h o w e v e r , s t r o n g e r steel fails at higher s t r e s s e s (curve b). Curve c shows g r a p h i c a l l y that, when the d e g r e e o f loading is c o n s t a n t , the m e t a l has m o r e endurance if it is s t r o n g e r , since in this case with an i n c r e a s e in the s t r e n g t h of the s t e e l the r e l a t i v e level of the loading (a/ao.2) is lowered. But a s t r o n g e r m e t a l can a l s o be r e g a r d e d as m o r e active. However, with a constant e x t e r n a l load, the activation of t h e m e t a l , c o n n e c t e d with the i n c r e a s e in its s t r e n g t h , is c o m p e n s a t e d by an additional lowering o f its r e l a tive loading, i.e., by a d e c r e a s e in the value of ~/%.2.

a

C

7.0

w i t h q~ ~9

.kg/mm2 ,.o.

~z

(O

"a ~v,5 ~ "gl2 i o o [

0-

z~

a~

l

80

~

100

\\~.

-with N:5 10~

170 40

.

0.5

m

~-~e~,,kglmmz

i

I

~p 720 180 eo,,kg/mmz

8P

;'2P

180.

% ~,kg/mrr~

Fig. 1. a) Change in n u m b e r of cycles to d e s t r u c t i o n as a function of d e g r e e of loading of s a m p l e s (the n u m b e r s with the points show the value of the yield point); b) dependence o f the value of the b r e a k ing s t r e s s on the s t r e n g t h of the s t e e l ; c) change in n u m b e r of cycles to d e s t r u c t i o n and of the value of a/%2 with constant cyclic loading as a function of the s t r e n g t h of s t e e l 4140. Zhdanov. T r a n s l a t e d f r o m F i z i k o - K h i m i e h e s k a y a Mekhanika M a t e r i a l o v , Vol. 10, No. 2, pp. 120121, M a r c h - A p r i l , 1974. Original a r t i c l e submitted August 29, 1973.

9 1975 Plenum Publishing Corporation, 227 West 17th Street, New York, N.Y. 10011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $15.00.

230

It can be postulated that an i n c r e a s e in the s t r e n g t h of a m e t a l is p e r m i s s i b l e only up to a c e r t a i n level, which is limited by the possible development of the p r o c e s s of c o r r o s i o n c r a c k i n g . It is c o n s i d e r e d that the above facts m u s t be taken into account in the solution of p r a c t i c a l p r o b l e m s . From

the

Editor

F o r a r i g o r o u s e x p e r i m e n t a l c o n f i r m a t i o n o r r e f u t a t i o n of the p r o p o s i t i o n s advanced in the a r t i c l e of G. V. Karpenko [1], additional e x p e r i m e n t s with a m e t a l having a different e n e r g y level but with a p p r o x i m a t e l y identical m e c h a n i c a l p r o p e r t i e s and homogeneity a r e needed.

LITERATURE 1,

2. 3.

CITED

G. V. Karpenko, Fiz.-Khim. Mekhan. Mater., No. 2 (1973). E. P. Zarubin, Sudostroenie za Rubezhom, No. 7 (1969). H. H. Lee and H. H. Uh|ig, Metallurgical Trans., 3, No. II, 2949-2957 (1972).

.

231