BRIEF

EFFECT FATIGUE

COMMUNICATIONS

OF

IMPACT

WAVES

STRENGTH

OF

A. G. Teslenko, A. B. Kuslitskii, and R. P. Didyk

ON STEEL

THE IN

LOW-CYCLE WORKING

MEDIA UDC 539.4.015 +534.141.2

I. P. Pistun, G. V. Karpenko,

At the p r e s e n t time a significant amount of t h e o r e t i c a l m a t e r i a l has been accumulated on the action of impact waves of various intensities on metal and alloys [1, 2, and o t h e r s ] . However, the use of explosive strengthening in machine c o n s t r u c t i o n is impossible without a thorough and c a r e f u l study of the effect of impact waves on the s e r v i c e p r o p e r t i e s of steels. Although c o n s i d e r a b l e work has been done in investigating the fatigue strength [3] and w e a r r e s i s t a n c e [4, 5] of steels a f t e r explosive strengthening, the data on this problem is still insufficient. We have limited o u r s e l v e s to a study of the l o w - c y c l e fatigue s t r e n g t h of explosively strengthened steels in working media. As the t e s t subjects we chose 2.5 m m thick rolled sheet steel of two types, St. 10 low c a r b o n steel and KhlSN10T s t a i n l e s s . The strengthening was done with an elastic explosive [6]. The m e c h a n i c a l p r o p e r t i e s w e r e d e t e r m i n e d before and after strengthening on flat samples with a c r o s s section of 1.5 x 1.5 m m under static load on an RM-500 tensile machine. As a r e s u l t of the explosive strengthening the ductility of the investigated steels dropped by 50% (St. 10) and 20% (KhlSNi0T) while the s t r e n g t h i n c r e a s e d c o r r e s p o n d i n g l y by 5-9% (Khl8N10T) and 45-80% (St. 10) (Table 1). The m i c r o h a r d n e s s (Fig. 1) was m e a s u r e d on a PMT-3 t e s t e r with a load of 50 g gradually moving in depth to the s u r f a c e of contact of the plate with the metal b a s e . The l o w - c y c l e fatigue testing was done on flat s a m p l e s . The pieces for the s a m p l e s w e r e cut on a milling machine f r o m the unstrengthened and explosively strengthened steel plates. At all stages of machining s i m i l a r i t y of the m e t h ods was s t r i c t l y o b s e r v e d . Special attention was paid to the condition of the edges of the gauge lengths of the s a m p l e s . The = St~S~~~ ' l o w - c y c l e fatigue s t r e n g t h of the original and strengthened steel ~2m was d e t e r m i n e d on a type IP-2 machine [7] at a f r e q u e n c y of 50 c y c l e s / m i n . The t e s t s were made with a pulsating cycle s t a r t Original 1 ing f r o m z e r o . In all c a s e s the tension was applied to the side which was in contact with the explosive. The c o r r o s i v e medium 10 20 30 .0 ~r Distance fromthe sample's surface,% of depth was a 3% w a t e r solution of sodium chloride, and the same soluFig. 1. Change in the m i e r o h a r d n e s s tion with cathodic polarization was used as the hydrogen abof Kh18N10T steel samples. sorption medium. TABLE

1

Steel

Original Strengthened Original elongation, %

KhI8NIOT KhI8NIOT

St. 10

48,8 33,7 31,4

37,8 26,4 13,1

_Strengthened Original Strengthened

Y.S., kg/mmz - 63,0 74,3 24,0

68,5 78.0 43,9

T.S., kgTmm'z-

,

74,2 80,7 33,8

80,1 85,3 48,9

D n e p r o p e t r o v s k Mining Institute. The P h y s i c a l and Mechanical Institute of the A c a d e m y of Sciences of the Ukrainian SSR, Lvov. 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 c h e s k a y a Mekhanika Materialo% Vol. 9, No. 6, pp. 96-97, N o v e m b e r - D e c e m b e r , 1973. Original a r t i c l e submitted 'March 30, 1973. 9 19 75 Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part of 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.

711

2,0

Y rrosive

z

z ~3

~2

II

g 1,2 I

I

/a

,I

0,8 P,~ 8,% Fig. 2

o,4

I

I,

o,6 0,8 8,'/, Fig. 3

Fig. 2. The effect of explosive strengthening on the low cycle fatigue r e s i s t a n c e of KhlSN10T s t e e l in working m e d i a . Fig. 3. The effect of a c o r r o s i v e (a) and a hydrogen a b s o r p t i o n (b) m e d i u m on the l o w - c y c l e fatigue r e s i s t a n c e of unstrengthened (1) and explosive s t r e n g t h e n e d (2) K b / S N t 0 T steel.

Fig. 4. The m i c r o s t r u c t u r e of St. 10 (x500) e x p l o s i v e l y s t r e n g t h e n e d u n d e r too int e n s e conditions.

The r e s u l t s of the low-cycle fatigue testing show that explosive strengthening affects the fatigue r e s i s t a n c e of s t e e l in different ways. W h e r e a f a v o r a b l e distribution of r e s i d u a l s t r e s s e s is c r e a t e d (Fig. 1), strengthening i n c r e a s e s the fatigue r e s i s t a n c e of the steel. It is c h a r a c t e r i s t i c that in a c t i v e liquid m e d i a the fatigue r e s i s t a n c e i n c r e a s e s m o r e than in a i r . In a i r the low-cycle fatigue r e s i s t a n c e of s t e e l i n c r e a s e d by 20-30%, the c o r r o s i v e m e d i u m i n c r e a s e was 30-75%, and in the hydrogen a b s o r p t i o n m e d i u m it was 1.8-2.1 t i m e s (Fig. 2). Consequently, the strengthening of m e t a l s is an i m p o r t a n t r e s e r v e f o r i n c r e a s i n g the r e l i a bility and life of steel, e s p e c i a l l y in active liquid media. As Fig. 3 shows, the negative action of active liquid m e d i a on the e x p l o s i v e - s t r e n g t h e n e d s t e e l is significantly l e s s .

However, it should be mentioned that positive r e s u l t s in the explosive strengthening of m e t a l m a y be obtained only when the o p t i m u m p r o c e s s conditions such a s quantity and distribution of explosive, b a s e m a t e r i a l , etc. a r e chosen. In addition, it m u s t be t a k e n into c o n s i d e r a t i o n that it is i m p o s s i b l e to draw conclusions on the b e s t conditions on the b a s i s of static t e n s i l e t e s t data. T h e s e positive r e s u l t s w e r e obtained on Khl8N10T steel. L e s s intense explosive strengthening on the s a m e Khl8N10T s t e e l of a n o t h e r heat did not i n c r e a s e its l o w - c y c l e fatigue r e s i s t a n c e although its s t r e n g t h w a s higher than that of the o r i g i n a l m e t a l (Table 1). E x c e s s i v e explosive t r e a t m e n t intensity p r o duces d a m a g e . As the r e s u l t of such a t r e a t m e n t the m e t a l is d e s t r o y e d (Fig. 4), which s h a r p l y r e d u c e s the low-cycle fatigue r e s i s t a n c e of the s t e e l in working m e d i a although the static tensile data (Table 1) is completely acceptable. LITERATURE

1. 2. 3. 4.

712

CITED

A. A. D e r i b a s , The 1)hysics of E x p l o s i v e Strengthening and Welding [in Russian], Nauka, N o v o s i b i r s k (1972). Metal B e h a v i o r and the Strength of M a t e r i a l s [in Russian], Collected W o r k s of the Volgograd 1)olytechnic Institute, Volgograd (1968). V. M. Grebennik, R. 1). Didyk, A. G. T e s l e n k o , and V. K. Tsapko, P r e b l . P r o c h n o s t i , No. 8 (1972). R. 1). Didyk, G. T. Lipitskii, A. G. T e s l e n k o , and V. 1). Borodulina, A b s t r a c t Information on C o m pleted S c i e n t i f i c - R e s e a r c h W o r k in the Colleges of the Ukrainian SSR during 1966-1967 [in Russian], Kiev (1968).

5.

6.

7.

V. K. Tsapko, V. M. Grebennik, A. S. Malkin, R. P. Didyk, and A. G. Teslenko, Metallurg. i Gornorud. l>romyshlen., No. 4 (1969). L. V. Dubnov and V. A. Pukov, Zh. P r i k l . Mekhan. i Tekh. F i z . , No. 9 (1966), No. 6 (1964). V. I. Tkachev and Yu. I. Babel, Zh. l>rikl. Mekhan. i Tekh. Fiz., No. 2 (1966).

713