Corrosion testing of stainless steels

Corrosion testing of stainless steels

Corrosion testing of stainless steels Testing for corrosion resistance is an important part of stainless s t e e l manufacture. The existing standards...

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Corrosion testing of stainless steels Testing for corrosion resistance is an important part of stainless s t e e l manufacture. The existing standards, however, are often inappropriate for testing sintered stainless steels. Professor Ernst Mahn and Troels Mathieson of the Technical University of Denmark, Lyngby, have investigated the use of hexacyanoferrate solutions for this specific role.

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M m a n u f a c t u r i n g of s t a i n l e s s steel is in m a n y ways an a t t r a c t i v e p r o c e s s which offers several advantages c o m p a r e d to c o n v e n t i o n a l m a n u f a c t u r i n g of s t a i n l e s s steels. These include efficient use of r a w m a t e r i a l , low energy c o n s u m p tion, s h o r t p r o d u c t i o n t i m e a n d achievem e n t of n e a r - n e t s h a p e w i t h i n few p r o c e s s steps. The a p p l i c a t i o n s of s i n t e r e d s t a i n l e s s steel is, however, l i m i t e d due to difficulties in achieving p r o p e r t i e s c o m p a r a b l e to t h o s e of w r o u g h t s t a i n l e s s steel. The corrosion r e s i s t a n c e is t h e m o s t i m p o r t a n t p r o p e r t y a n d a t t h e s a m e t i m e t h e limiting factor. The c o r r o s i o n r e s i s t a n c e of s i n t e r e d s t a i n l e s s steel is d e p e n d e n t on t h e quality of t h e raw p o w d e r s as well as t h e p r o c e s s c o n d i t i o n s which d i r e c t l y d e t e r m i n e t h e s t r u c t u r e of t h e s i n t e r e d material. S i n t e r e d s t a i n l e s s steel is not a new m a t e r i a l a n d therefore well d o c u m e n t e d , however, it is o f t e n difficult to a c h i e v e u n i f o r m a n d a c c e p t a b l e p r o p e r t i e s . V a r i a t i o n s in t h e q u a l i t y of one t y p e of p o w d e r b e t w e e n d i f f e r e n t v e n d o r s is one c r i t i c a l a s p e c t m e n t i o n e d in literature. Reduced corrosion p r o p e r t i e s can also occur d u e to c h a n g e s of t h e m e t a l l u r g y r e l a t e d to t h e sintering cycle.

42 MPR April 1994

Insufficient removal of t h e b i n d e r or b a d sintering a t m o s p h e r e with a high d e w p o i n t can c o n t r i b u t e to i n c r e a s e d c o n t e n t s of N, O a n d C. If at t h e s a m e t i m e t h e cooling is too slow, t h e f o r m a t i o n of i n t e r g r a n u l a r precipitates, e.g. c h r o m i u m oxide, n i t r i d e and carbide, can p o s s i b l y occur, which m i g h t r e s u l t in significant i n t e r g r a n u l a r corrosion resistance. The i n h e r e n t p o r o s i t y of s i n t e r e d steels is a critical factor as well. On this basis it a p p e a r s t h a t corrosion of s i n t e r e d s t a i n l e s s steel is c a u s e d by a c o m p l e x of m e c h a n i s m s . In o r d e r to achieve uniform quality of t h e m a t e r i a l s it is therefore necessary to control t h e sintering p r o c e s s carefully to be able to characterize t h e corrosion p r o p e r t i e s of t h e s i n t e r e d material. This is, however, difficult in t h e a b s e n c e of a s t a n d a r d corrosion test m e t h o d which a c c o m m o d a t e s for t h e special case of corrosion in p o r o u s s t a i n l e s s steels. The existing s t a n d a r d s for convent i o n a l w r o u g h t s t a i n l e s s steel a r e often c o m p l i c a t e d a n d too aggressive to s p l i t u p t h e p r o p e r t i e s into convenient groups. The need for a corrosion t e s t for q u a l i t y control of s i n t e r e d s t a i n l e s s s t e e l is t h e r e f o r e obvious. The p r i m a r y i n t e n t i o n h a s been to set u p a s i m p l e m e t h o d w h e r e whole s i n t e r e d c o m p a c t s can be tested. An e x p o s u r e t e s t involving chloride i n d u c e d corrosion was obvious since this form of corrosion is quite c o m m o n in p r a c t i c a l a p p l i c a t i o n s of sint e r e d stainless steel. The chosen m e t h o d uses d i l u t e s o l u t i o n s of p o t a s s i u m h e x a c y a n o f e r r a t e with different levels of chloride c o n t e n t , a n d it is d e s c r i b e d e a r l i e r by Herbsleb a n d Schwenchk. P o t a s s i u m h e x a c y a n o f e r r a t e (III) w o r k s a s a c o r r o s i o n i n d i c a t o r b e c a u s e b l u e dye, T u r n b u l l ' s blue, is f o r m e d in the p r e s e n c e of ferro ions. This p r o p e r t y is also utilized in t h e feroxyl test, ASTM A780, to prove iron c o n t a m i n a t i o n of s t a i n l e s s steel surfaces. The relevant r e a c t i o n is: K + ( a q ) + F e 2 + ( a q ) + [Fe(CN6)] 3" --~ (aq) KFemFe II (CN) 6 (S) P o t a s s i u m h e x a c y a n o f e r r a t e is also an oxidizing a g e n t which is utilized in t h e t e s t m e t h o d . By using solutions of equal p a r t s of hexacyanoferrate(II) and hexacyanoferrate(III), a redox potential corresponding to t h e corrosion p o t e n t i a l of passive stainless steels in a q u e o u s s o l u t i o n s is achieved

0026-0657194157.00 © 1994, Elsevier Science Ltd.

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(app. 170 mV SCE). The r e d o x system is also c h a r a c t e r i z e d by being s t a b l e with t i m e a n d t h e p o t e n t i a l is n o t significant affected by t h e a d d i t i o n of chloride. The c o r r o s i o n r e s i s t a n c e can h e r e b y be c h a r a c t e r i z e d by defining a critical c h l o r i d e content. This article d i s c u s s e s t h e r e s u l t s a n d p e r s p e c t i v e s by u s i n g t h i s t e s t m e t h o d , which is referred to as t h e feroxyl test. The c o r r e l a t i o n with o t h e r c o r r o s i o n meas u r e m e n t m e t h o d s is t r e a t e d , including s a l t spray test and electrochemical corrosion test. The t e s t m a t e r i a l s include s i n t e r e d s t a i n l e s s steels, all b a s e d on AISI 316L powder, b u t w i t h different c o r r o s i o n p r o p e r ties d u e to different s i n t e r i n g conditions. The s i n t e r e d m a t e r i a l s are c o m p a r e d to w r o u g h t s t a i n l e s s steels t h a t cover q u a l i t i e s from AISI 431 to AISI 316.

Experimental A l l the sintered materials were produced from the same charge of a conventional

AISI 316L (-100 m e s h ) powder. The powd e r a d d e d w a s 1% l u b r i c a n t (Metallub or A c r w a x ) a n d p r e s s e d with a p r e s s u r e of 540 MPa in o r d e r t o f o r m ISO 2 7 4 0 c o m p a c t s . D e b i n d e r i n g a n d sintering were p e r f o r m e d in i n d u s t r i a l b e l t - t y p e furnaces or in a l a b o r a t o r y tube-furnace. The a d d i t i o n a l e x p e r i m e n t c o n d i t i o n s a r e shown below in t h e r e s u l t s section. The t e s t e d w r o u g h t steels a r e listed in Table 1. In t h e feroxyl t e s t s a b a s e s o l u t i o n potassium hexacyanoferrate (II/III) was u s e d . T h i s is m a d e by a d d i n g 0.99 g K ~ [ F e ( C N ) 6 ] a n d 1.27 g K 4 [ F e ( C N ) 6 ] 3H20 to 1000 ml d e i o n i z e d water. F r o m t h i s s o l u t i o n o t h e r s o l u t i o n s with c h l o r i d e c o n c e n t r a t i o n s of 0.05, 0.1 a n d 0.5% Cl- were mixed, w h i c h gives a r e d o x p o t e n t i a l of 160,

SPECIAL

FEATURE

165 a n d 180 mV SCE ( + 5 mV) respectively a t t h e t e s t t e m p e r a t u r e of 25°C. Whole s i n t e r e d s p e c i m e n s w i t h o u t c u t t i n g surfaces were e x p o s e d . The w r o u g h t steels were t u r n e d into cylindrical ~ 1 0 x 10 m m samples a n d d e g r e a s e d before exposure. There is no a g i t a t i o n in t h e e x p o s u r e vessel a n d t h e s a m p l e s were p l a c e d on i r r e g u l a r bed, e.g. a grid or a r o d m a d e of plastics, in o r d e r to minimize t h e c o n t a c t a r e a between t h e h o l d e r a n d t h e s a m p l e (see Figure 1 a n d F i g u r e 2). The p r o p o r t i o n b e t w e e n t h e v o l u m e of s o l u t i o n a n d e x p o s e d surface a r e a was at l e a s t 25 m l / c m 2. The s a m p l e s were e v a l u a t e d after 24 h o u r s of e x p o s u r e a n d a visual m a r k was given after a g r a d i n g scale from 0 to 3. The scale i n c l u d e s t h e following marks: 0: No attack. No blue spots. 1: L i g h t a t t a c k . Very w e a k b l u e s p o t s w i t h o u t growth. 2: M o d e r a t e attack. Blue s p o t s with slow growth. No needle growth of large accumulation of blue dye. 3: Severe attack. Blue s p o t s with growth. N e e d l e g r o w t h o r a c c u m u l a t i o n of t h e c o r r o s i o n p r o d u c t on t h e surface. The m a t e r i a l s have also been e x p o s e d to a n e u t r a l salt s p r a y t e s t which is p e r f o r m e d on t h e basis of t h e ISO 3768 s t a n d a r d . The e x p o s u r e p e r i o d is 1500 h o u r s a n d at l e a s t two whole s a m p l e s from each e x p e r i m e n t are tested. During t h e e x p o s u r e t h e condition of each s a m p l e is e v a l u a t e d within fixed intervals a n d a visual m a r k is given a c c o r d i n g to a g r a d i n g scale from 10 to 0. The value 10 r e p r e s e n t s no visible corrosion w h i l e 0 c o r r e s p o n d s to a s u r f a c e h a l f covered with c o r r o s i o n p r o d u c t s . The timet o - c o r r o s i o n h a s been c h o s e n a t t h e t i m e until m a r k 8 is achieved.

(3

............

~............!i¸.......

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FIGURE 1: Samples exhibiting severe attacks characterized by the.mark 3 in the feroxyl test. 316L PIM (a and b) and wrought 304 steel with an artificial crevice formed by an o-ring (c).

a

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No.

Sintering

SPECIAL

FEATURE

Feroxyl Test (%cr)

1120°C 20 min D.A.d)(-27°C) 1160°C 45 min H2(-27°C) 1250°C 30 min H2(? )

0.05%

0.1%

3 1 1

3 3 2

Salt Spray Test

0.5%

Epit c)

Time hr a)

Visual mark b)

mV SCE

20 30 24

0 1 1

65 455 230

1250°C 30 min H2(-30°C) 1250°C 120 min H2(-30°0)

1 1

3 3

31 13

1 1

243 333

6 7 8 9 10

1120°C30 min H2 (-70°C) 1120°C 120 min H2 (-70°C) 1250°C30 min vacuum 1120°C30 min vacuum 1120°C 120 min vacuum

0 0 0 0 0

3 3 3 3 3

1305 1206 1134 1284 1008

9 7 8 8 8

365 370 330 368 410

11 12 13 14

1160°C 45 min H2(?) 1250°C 120min H2 (-70°C) 1250°C 120min H2 (-70°0) 1250°C 120min H 2 + 5%N2(-70°C)

0 0 0 0

1 1 0 0

500 855 114 564

5 8 .7 6

423 605 490 550

a) Time-to-corrosion in Neutral Salt Spray test c) Pitting potential in 0.1%cr, 308c, pH5, 5 mV/min

b) Pitting potential in 0.1%C1-, 30°C, pH5, 5 mV/min d) Dissociated ammonia

Electrochemical testing by cyclic polarization has been performed in order to c h a r a c t e r i z e t h e r e s i s t a n c e to localized corrosion. The test e n v i r o n m e n t is a solution of 0.1% chloride at 30°C with pH 5 (acetate buffer). The solution is d e a e r a t e d with n i t r o g e n before the anodic polarization starts at -600 with a scan rate of 5 mV/min. From the polarization curve the critical potential, Epit, is d e t e r m i n e d as a m e a s u r e of the resistance to pitting. As a s u p p l e m e n t to the corrosion tests some other tests of the sintered specimens were performed. This includes NOC-analysis, m e a s u r e m e n t of d i m e n s i o n a l change, d e t e r m i n a t i o n of d e n s i t y a n d open porosity as well as tensile tests.

Results The results of the feroxyl tests are all b a s e d o n a v i s u a l j u d g e m e n t of t h e a p p e a r a n c e of the corrosion attack. The attack can, however, vary to some e x t e n t a n d it is d e p e n d e n t on the chloride c o n t e n t a n d the type of sample. Figure 1 shows two sintered tensile c o m p a c t s exposed in 0.1% Cl-, b o t h with severe a t t a c k s which is characterized by growth of needle s h a p e d precipitates of blue dye. Figure l b shows s i m i l a r s a m p l e s exposed in the 0.5% C l solution a n d the attack is here less localized b u t more severe. These s a m p l e s e x h i b i t severe attacks with large a c c u m u l a t i o n of

44 MPR April 1994

blue dye as well as light attack characterized by small spots with slow growth. The smallest spots are not corrosion but d e p o s i t i o n of blue dye as a result of the n a t u r a l c o n v e c t i o n in t h e solution. All sintered materials in Figure 1 are given t h e m a r k 3 which r e p r e s e n t s a severe a t t a c k . The w r o u g h t s t a i n l e s s steel in Figure lc. is also characterized with the m a r k of 3. Normally the corrosion of these steels a p p e a r s as localized attack at the crevice u n d e r the o-ring or between the s a m p l e a n d the holder. The corrosion properties of the sintered steels are shown in Table 2 whereas other properties of practical interest are shown in Table 3. The m a t e r i a l s are a r r a n g e d in 4 groups with increasing resistance to the feroxyl test downwards. The first group includes materials t e n d i n g to corrode in the 0.05% Cl- solution a n d e x h i b i t i n g severe corrosion in the 0.1% Cl- solution. These steels were sintered in i n d u s t r i a l furnaces in which the d e w p o i n t of the s i n t e r i n g atmos p h e r e was too high a n d c o n s e q u e n t l y caused high c o n t e n t s of N, O a n d C. The salt spray test also indicates poor corrosion resistance as all the steels corrode w i t h i n 30 hours. The r e m a i n i n g materials were all sintered in a laboratory furnace u n d e r wellcontrolled conditions. This also includes the two steels in the second group which were

i! ~

No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

!i

Dim Change %

Density glcm 3

Open Porosity %

-0.03 0.08 0.95 0.68 1.27 0.32 0.61 0.74 0.50 0.83 0.54

6.53 6.61 6.78 6.71 6.84 6.62 6.68 6.71 6.67 6.73 6.70

15.6 15.0 13.0 13.9 12.2 14.8 14.1 13.9 14.7 13.9 14.0

1.22 1.09

6.86 6.85

12.4 2.2

sintered in h u m i d hydrogen. These steels e x h i b i t a light a t t a c k in t h e 0.1% Cl ~ solution a n d severe corrosion a p p e a r s in the 0.5% C1 solution. The t h i r d group include m a t e r i a l s where no a t t a c k is observed in t h e 0.1% Cl solution whereas all the steels show severe corrosion in the 0.5% Cl- solution. The sintering of these m a t e r i a l s was carried out in a reducing a t m o s p h e r e of either dry hydrogen or v a c u u m with a r g o n / h y d r o g e n backfilling. The improved corrosion resist a n c e achieved by this process, also a p p e a r s from larger values of the time-to-corrosion a n d the p i t t i n g potentials. All m a t e r i a l s in the fourth group resist the highest chloride w i t h o u t severe attack. A p a r t from one steel, the rest were sintered u n d e r intensified c o n d i t i o n s at high temp e r a t u r e for a long time in a reducing s i n t e r i n g atmosphere. The w r o u g h t materials show corrosion properties in a g r e e m e n t with the c o n t e n t s of the alloying elements, Cr, Mo a n d S (see Table 4). Corrosion is observed for the m a r t e n s i t i c AISI 431 steel a n d the sulfuralloyed a u s t e n i t i c AISI 303 in the weakest chloride solution. The a u s t e n i t i c steels with higher alloying contents, AISI 304 a n d AISI 316, show a b e t t e r corrosion resistance a n d do not corrode before the 0.1% a n d 0.5% C1 level respectively. Moreover it a p p e a r s t h a t the resistance to p i t t i n g expressed by Spi t complies with the results of the ferroxyl test for these materials.

Discussion For a long time the d e v e l o p m e n t of a quick corrosion test for quality control of sintered stainless steel has been requested by producers as well as by users of this

Tensile Strength MPe

Yield Strength MPa

182 186 239 184 300 140 190 213 205 253 192 317 291 347

180 145 152 136 149 126 145 142 156 153 149 144 144 218

0.5 0.4 10.0 4.7 19.7 2.2 5.1 8.6 4.0 10.7 5.3 23.7 18.0 10.9

Type

AISI AISI AISI AISI

Elonggation %

N

O

C

ppm

ppm

ppm

2730 2100 2500 2240 1470 1970 2010 1920 2160 2150 2830 270 720 1480

930 1300 300 190 130 170 260 170 60 60 300 20 50 40

3030 330 150 220 60 360 190 110 410 220 260 20 30 1350

0.05%

Feroxyl 0.1%

0.5%

Test Epit mV SCE

431 303 304 316

3 3 1 1

3 3 3 2

270 325 470 590

material. On this basis the suitability of the feroxyl test has been investigated, since this m e t h o d is quite simple a n d quick c o m p a r e d to other m e t h o d s such as salt spray tests a n d e l e c t r o c h e m i c a l tests. It was also i m p o r t a n t t h a t Herbsleb, who has used t h i s m e t h o d for t h e i n v e s t i g a t i o n of wrought stainless steel, in general found a r e a s o n a b l e a g r e e m e n t to the electrochemical m e a s u r e m e n t methods. Our work exa m i n e s w h e t h e r the m e t h o d can be used for the characterization of sintered stainless steel, a n d w h e t h e r a n acceptable a g r e e m e n t with the salt spray test a n d the electrochemical m e t h o d is obtained. The results in Table 2 seem to show t h a t there is a certain correspondence between the results of the feroxyl test a n d those of the salt spray test. The materials with poor corrosion resistance all show some corrosion in the 0.05% s o l u t i o n a n d severe corrosion in the 0.1% solution. At the same time a low resistance to the s p r a y t e s t is m e a s u r e d . The m a t e r i a l s w i t h o u t attack in the 0.1% solution show a resistance t h a t is significantly b e t t e r in the salt spray test. However, the resistance to the salt spray test of the m a t e r i a l s in the

MPR April 1994 45

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a

SPECIAL

FEATURE

b

FIGURE 2: Correlation between results of the feroxyl test in 0.1%C1 and the time-to-corrosion in salt spray (a) and the pitting potential (b). The investigation includes 41 materials produced from AlSl 316L powder with 1% Metallub or 1% Acrawax added to it and pressed at a pressure of 540 MPa.

b e s t group is p o o r e r t h a n e x p e c t e d on t h e basis of t h e feroxyl test. It does, however, a p p e a r t h a t in general t h e 0.1% C1- level can reveal defects t h a t will also cause corrosion in t h e s a l t s p r a y test. F u r t h e r m o r e this s t a t e m e n t is proved by t h e overall t r e n d shown in Figure 2a, which i n c l u d e s a l a r g e r group of e x p e r i m e n t s t h a n t h o s e p r e s e n t e d in Table 2. Regarding t h e p i t t i n g p o t e n t i a l of t h e s i n t e r e d m a t e r i a l s , a t e n d e n c y to i n c r e a s i n g p i t t i n g p o t e n t i a l with i n c r e a s i n g r e s i s t a n c e to t h e feroxyl t e s t is observed. A p a r t from o n e m a t e r i a l , it c a n be s e e n t h a t no c o r r o s i o n in t h e 0.1% C1- s o l u t i o n is o b s e r v e d w h e n t h e p i t t i n g p o t e n t i a l is g r e a t e r t h a n 330 mV SCE. The overall c o n n e c t i o n between t h e s e two e x p r e s s i o n s of corrosion r e s i s t a n c e is shown in Figu r e 2b, a n d a n a c c e p t a b l e a g r e e m e n t between t h e two m e t h o d s is seen, a l t h o u g h t h e d i s p e r s i o n is q u i t e wide. This t e n d e n c y is m o r e obvious for t h e w r o u g h t steels a c c o r d i n g t o T a b l e 4. It is, h o w e v e r , remarkable that the pitting potentials m e a s u r e d in a 0.1K% C1- s o l u t i o n , a r e g r e a t e r t h a n t h e value e x p e c t e d on t h e basis of t h e results of t h e feroxyl t e s t in t h e corresponding chloride solution with a r e d o x p o t e n t i a l of 165 mV SCE. The r e a s o n is p r o b a b l y t h a t t h e p i t t i n g p o t e n t i a l is m e a s u r e d with a relative high scan rate, which m i g h t r e t a r d t h e t i m e d e p e n d e n t i n i t i a t i o n of pitting. When c o m p a r i n g t h e c o r r o s i o n p r o p e r ties of t h e s i n t e r e d steel to well-known w r o u g h t steels it a p p e a r s t h a t t h e m a t e r i a l s s i n t e r e d in d r y h y d r o g e n o r v a c u u m a r e c o m p a r a b l e to or b e t t e r t h a n t h e sulfur alloyed free-cutting steel. By using intensified s i n t e r i n g c o n d i t i o n s in a dry a t m o sphere of hydrogen (with nitrogen

46 MPR April 1994

a d d i t i o n ) , s i n t e r e d AISI 316L steel can achieve a corrosion r e s i s t a n c e at t h e s a m e level as t h a t of conventional AISI 304, a n d in s o m e cases as c o n v e n t i o n a l ASISI 316. It a p p e a r s clearly from t h e above results t h a t t h e feroxyl t e s t reveals defects arising from an i m p r o p e r sintering cycle causing corrosion. However, only a m o d e r a t e agreem e n t with t h e o t h e r m e t h o d s is obtained, which also applies to the correlation between the salt spray test and the e l e c t r o c h e m i c a l test. This is p r o b a b l y because of different corrosion m e c h a n i s m s in t h e different m e a s u r e m e n t m e t h o d s . The feroxyl t e s t is b a s e d on s o l u t i o n s with a relative low c o n t e n t of chloride a n d t h e s a m p l e is p o l a r i z e d to p o t e n t i a l s close to t h e r e d o x p o t e n t i a l of t h e solution. Even t h o u g h c o r r o s i o n is p a r t l y c o n t r o l l e d by t h e oxidizing agent, it is still a d y n a m i c process. The salt s p r a y t e s t uses a s t r o n g e r c h l o r i d e c o n c e n t r a t i o n (5% NaC1) a n d t h e condit i o n s are at t h e s a m e t i m e less oxidizing, which i m p l i e s t h a t corrosion develops a t a low potential. In t h e e l e c t r o c h e m i c a l t e s t t h e corrosion is c o n t r o l l e d by a p o t e n t i o stat. A c o m p l e t e a g r e e m e n t between t h e m e t h o d s can therefore not be e x p e c t e d . At t h e s a m e t i m e this e m p h a s i z e s t h e i m p o r t a n c e of k n o w i n g t h e a c t u a l c o r r o s i o n s i t u a t i o n w h e n t h e corrosion r e s i s t a n c e is characterized. In r e l a t i o n to t h i s t h e feroxyl t e s t fairly r e p r e s e n t s a p r a c t i c a l s i t u a t i o n in a e r a t e d a q u e o u s e n v i r o n m e n t s with a low c o n t e n t of chloride. A m o n g t h e o t h e r a d v a n t a g e s t h e feroxyl t e s t offers it s h o u l d be m e n t i o n e d t h a t t h e corrosion a t t a c k can easily be l o c a t e d a n d corrosion d e p e n d i n g Upon the g e o m e t r y can p o s s i b l y be identified. F u r t h e r m o r e it is p o s s i b l e to define a q u a l i t y level by choosing a p r o p e r c h l o r i d e c o n t e n t which m a k e s t h e t e s t s u i t a b l e for quality control. Conclusion O u r w o r k f o u n d t h a t e x p o s u r e in hexacyanoferrate (II/III) solutions with different chloride c o n t e n t s is a r a p i d a n d s i m p l e m e t h o d for c o r r o s i o n t e s t i n g of s i n t e r e d s t a i n l e s s steel. The m e t h o d can reveal corrosion-like defects d u e to iron c o n t a m i n a t i o n or i m p r o p e r sintering conditions. The m e t h o d shows a m o d e r a t e agreement with other corrosion measuring m e t h o d s in c h l o r i d e - c o n t a i n i n g environments, such as salt the s p r a y t e s t a n d e l e c t r o c h e m i c a l m e a s u r e m e n t of t h e p i t t i n g p o t e n t i a l . By using optical p r o c e s s conditions, s i n t e r e d AISI 316L steel can achieve p r o p e r t i e s c o m p a r a b l e to t h o s e of t h e c o r r e s p o n d i n g w r o u g h t steel. Overall, t h e m e t h o d s e e m s s u i t a b l e for quality c o n t r o l by m a n u f a c t u r e r s a n d users of s i n t e r e d s t a i n l e s s steels •