INFLUENCE STEELS

OF

AND

AND

EROSION

ACID

MEDIA

HARDNESS

ALLOYS

ON

OF

CORROSION

RESISTANCE

N. A. Adugina, M. and G. E. Lazarev

STAINLESS

IN SULFURIC

M.

Kristal,

UDC 669.018.8:539.531 ;620 .t 93.4

T h e a v a i l a b l e l i t e r a t u r e d a t a on the i n f l u e n c e of s t e e l and a l l o y h a r d n e s s on c o r r o s i o n and e r o s i o n r e s i s t a n c e in l i q u i d m e d i a c o n t a i n i n g s o l i d p a r t i c l e s a r e quite c o n t r a d i c t o r y . T h i s s t a t e m e n t r e f e r s b o t h to m e d i a t h a t a r e not p a r t i c u l a r l y c o r r o s i v e , s u c h a s p o t a b l e w a t e r , and to s u c h c o r r o s i v e m e d i a a s a c i d , c a u s t i c , o r s a l t s o l u t i o n s . H e r e we a r e p r e s e n t i n g r e s u l t s f r o m a s t u d y of the i n f l u e n c e of the h a r d n e s s of a u s t e n i t i c and a u s t e n i t i c - m a r t e n s i t i c s t a i n l e s s s t e e l s and a l l o y s on the r e s i s t a n c e of t h e s e m a t e r i a l s in s o l u t i o n s of s u l f u r i c a c i d c o n t a i n i n g a b r a s i v e s o l i d p a r t i c l e s . T h e s e s t u d i e s w e r e p e r f o r m e d in two u n i t s with d i f f e r i n g flow v e l o c i t i e s f o r the a g g r e s s i v e m e d i u m . T h e f i r s t unit (UNI-3) s i m u l a t e d the a c t i o n of the w o r k i n g m e d i u m i n v e s s e l s w i t h s t i r r i n g d e v i c e s (flow v e l o c i t y w a s 4.6 m / s e e ) ; the s e c o n d (UN[-1) s i m u l a t e d the i n t e n s e a c t i o n of the w o r k i n g m e d i u m t h a t is o b s e r v e d i n the o p e r a t i o n of the d i s c s of s p r a y d r i e r s , p u m p i m p e l l e r s , and o t h e r e l e m e n t s of c h e m i c a l p l a n t e q u i p m e n t (flow v e l o c i t y 29.0 m / s a c ) . T h e s u l f u r i c a c i d c o n c e n t r a t i o n w a s 1.0-20%, t e m p e r a t u r e s 80 a n d 100~ T h e a b r a s i v e u s e d in t h i s w o r k w a s q u a r t z s a n d with a p a r t i c l e s i z e of 0 . 3 - 0 . 4 m m . T h e U N I - 3 unit c o n s i s t e d of a 3 . 0 - l i t e r v e s s e l ( i n s i d e d i a m e t e r 120 r a m ) w i t h a t u r b i n e - t y p e m i x e r t h a t w a s t u r n e d at 1470 r p m . In t h e s e s t u d i e s , 20 x 80 x 2.0 m m c o u p o n s w e r e a t t a c h e d r i g i d l y , p a r a l l e l to the w a i l s of the v e s s e l . T h e r a t i o of s o l i d to l i q u i d p h a s e w a s 2 : 3 by w e i g h t . T A B L E 1.

W e a r of M a t e r i a l s f r o m A c t i o n of

Water Stream Containing Abrasive Particles Wear

Material

Hardness" in mm/yr lin g/h(flow -l(flow ve loci -t ve~ocky 29.0 ty 4, 6m/sec)~ m/see) i

Khl6N6

H R C 25a

ItRC -lOb

]

0.04~

t),u4~

KhlSN9Yu

H ~ C 10a ItfaC 40b

0.25 (~.2~

o (,I~ 0.o45

Khl8N10T

HZr i 2 o - I 4 0

n,25

13.045

H B 120 -14!1

1.)2~

(.,.,!4.5

ttB

0

OKh 2 3 N 2 8 M 3 D 3 T

140"

/qB 17c)'C

25

0.U4 )

,25

0,045

0Kh N4OMDTYu H B 2F,-,d

~h23

H B 300e

I,.25

Kh2 1N27M4D5S6L

H;~C .Io

--

Kh2 LN27M4D5S8 L

H R C 5o

--

l

).045

O !145 u.~u',

..4n

* Heat-treating regimes: a) quenching; b) quenching + coldtreating at -70~ for 2 h + aging at 850-400~ c) quenching + aging at 750~ d) cold-working; e) cold-working + aging at 650~

In the UNI-1 u n i t , * the a g g r e s s i v e m e d i u m , contain]rig 0.5% q u a r t z s a n d b y w e i g h t , w a s f e d b y m e a n s of a s c r e w p u m p to two h o r i z o n t a l n i p p l e s w i t h d i s t r i b u t o r n o z z l e s a t t h e e n d s . Upon r o t a t i o n o f the s c r e w p u m p w i t h the n i p p l e s , the s l u r r y s t r e a m , u n d e r the i n f l u e n c e of c e n t r i f u g a l f o r c e s , i m p i n g e d on t e s t c o u p o n s t h a t w e r e m o u n t e d at the l e v e l of the n o z z l e s and at a n a n g l e of 30 ~ to the d i r e c t i o n of the l i q u i d s t r e a m . T h e r e s u l t s of the t e s t s in t h e s e u n i t s ( T a b l e 1) s h o w e d that, in a s t r e a m of w a t e r c o n t a i n i n g a b r a s i v e p a r t i c l e s , i n c r e a s i n g the h a r d n e s s of the t e s t s t e e l s f r o m HRC 10 (HB 120-140) to HRC 40 d i d not increase their erosion resistance. This statement a p p l i e s b o t h to m a t e r i a l s of i d e n t i c a l c h e m i c a l c o m p o s i t i o n and s t r u c t u r e (e.g., to the 0 K h N 4 0 M D T Y u a l l o y with a u s t e n i t i c s t r u c t u r e a n d h a r d n e s s e s of HB *E. L . A r o n o v and M. M. T e n e b a u m , " P V - 1 2 unit f o r i n v e s t i g a t i o n of w e a r r e s i s t a n c e of m a t e r i a l s in h y d r o a b r a s i v e w e a r , " Z a v o d . L a b . , 33, No. 6, 764-765 (1967).

Translated from Khimicheskoe i Neftyanoe Mashinostroenie,

No. 9, pp. 20-21, S e p t e m b e r ,

1974.

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 reo@va] system, or transm#ted, b2 an), fiJr~n or by an), means, electro>sic, mechanical, photocopying, micrc~fihnbrg, recording or otherwise, without written permission o f the publisher. A copy o / t h i s article is available from the publisher for 515. 00.

801

ram/yr. ,I00

o

Fig. 1. C o r r o s i o n / e r o s i o n r e s i s t a n c e of diff e r e n t steels in sulfuric acid solutions at 100~ with a flow velocity of 4.6 m / s e e : 1) Kh18N10T (HB 120-140); 2) Kh15N9Yu (HRC 10); 3) Kh15N9Yu (HRC 40),

lO

o

~. 1.o .r

9'1o 2,5 s 7,5. Sulfuric acid concentration

~o

TABLE 2. Influence of H a r d n e s s on C o r r o s i o n / E r o s i o n R e s i s t a n c e of Steels (Flow Velocity 29.0 m / s e e ) in Sulfuric Acid at 80~ Concentration of sulfuric acid, g/liter 60 i ]00 corrosion corrosion Hardness ir.ate, miniwear, g/t~rate, mm iwear,g/h

I

Steel

I/yr Kh18N10T

KhlSN9Yu [(h16N6

HB 120-140

H~c Io HRC 4o ~ 24

"HRC

40

I

[/yr.

6,0

-

0,21

7,~

0:70

10,0

-

0,31

{ I0,0

0,26

54.0 47,0

0,~0

22,0

~2,0

o,ao 0,70

140, 170, 285, and 300) and to m a t e r i a l s identical in c h e m i c a l composition but different in s t r u c t u r e (e.g., to the steels Kht6N6 and Khl5N9Yu, which had a austenitic s t r u c t u r e after quenching but a u s t e n i t i e - m a r t e n s i t i c with 70% m a r t e n s i t e a f t e r a g e hardening). Similarly, no b e t t e r r e s i s t a n c e to e r o sion with a high flow velocity was found for the Kh21N27M4D5S8L steel, with h a r d n e s s up to HRC 50.

0,96

F o r all of the test m a t e r i a l s , the amount of w e a r in water depended solely on the intensity of the mechanical action, i . e . , on the quantity of solid phase, the h a r d n e s s and size of the a b r a s i v e p a r t i c l e s , the flow velocity, and the angle of attack. Thus, with a flow velocity of 4.6 m / s e e during the time of test in the UNI-3 unit, the wear was 0.25 r a m / y e a r ; with a flow velocity of 29.0 m / s e e during the time of test in the UNI-1 unit, it was about 105 r a m / y e a r (0.045 g/h). The data obtained in the tests with water were confirmed by the results of tests with corrosive media. For example, increasing the hardness of the alloy 0KhN40MDTYu from HB 140 to HB 300 did not increase its r e s i s t a n c e to e r o s i o n in 20% sulfuric acid containing solid p a r t i c l e s ; at 80~ (for all h a r d n e s s e s that were examined), the c o r r o s i o n rate of this alloy was about 0.20 r a m / y e a r . In solutions of sulfuric acid with concentrations of 1.0-10.0%, the wear of Khl5N9Yu steel with a h a r d n e s s of HRC 40 was twice that of the s a m e steel with a h a r d n e s s of HRC 10 (see Fig. 1). Likewise, in the t e s t s on the Kh16N6 h i g h - s t r e n g t h steel, no beneficial effect on c o r r o s i o n / e r o s i o n r e s i s t a n c e was observed when the h a r d n e s s was i n c r e a s e d (Table 2). The lower r e s i s t a n c e of the Kh15N9Yu and Khl6N6 steels with h a r d n e s s of HRC 40 to the e r o s i v e action of sulfuric acid containing solid p a r t i c l e s is due to the somewhat lower c o r r o s i o n r e s i s t a n c e of the h a r d e r s t e e l s . The low c o r r o s i o n r e s i s t a n c e of these steels is related to the p r e s e n c e of the second phase ( m a r t e n site) a f t e r a g e - h a r d e n i n g . It should be noted that the alloy 0KhN40MDTYu and the steels Khl6N9Yu and Khl6N6 with m a x i m u m h a r d n e s s (near HRC 40) are less c o r r o s i o n / e r o s i o n r e s i s t a n t than the unhardened s t e e l s with a s i m i l a r d e g r e e of alloying (hardness HB 120-140). This is explained on the basis that they differ in c o r r o s i o n r e s i s t a n c e . F o r example, in operation of the t u r b o m i x e r unit in 10% sulfuric acid, the attrition rate of the Khl5N9Yu s t e e l (HRC 40) was an" o r d e r of magnitude g r e a t e r than that of the KhlSN10T steel (HB 120-140), as indicated in Fig. 1. The attrition rates of the 0KhN40MDTYu (HB 300) and the Kh21N27M4D5S6L (HRC 40} in 20% sulfuric a c i d at 80~ with a flow velocity of 29.0 m / s e e were 0.065 g [ h , and that of the 0Kh23N28M3D3T steel (HB 120-140) was 0.045 g / h . As a result of these investigations, it has been established that increasing the h a r d n e s s of stainless steels f r o m HB 120-140 (HRC t0) to HRC 50 does not i n c r e a s e the r e s i s t a n c e of these steels to the e r o s i v e action of a g g r e s s i v e media containing solid p a r t i c l e s . Hence, in selecting m a t e r i a l s for the v e s s e l s or other,components of appargtus subject to the c o r r o s i o n / e r o s i o n action of a g g r e s s i v e media, steels and alloys with higher c o r r o s i o n r e s i s t a n c e must be used.

802