The studies of corrosion resistance of AISI 316Ti SS in ... · proposed by magnetoelectropolishing (MEP) [14-28], high-current-density electropolishing (HDEP) [29-31], or high-voltage

Available online at www.worldscientificnews.com

( Received 02 April 2018; Accepted 21 April 2018; Date of Publication 22 April 2018 )

WSN 98 (2018) 46-60 EISSN 2392-2192

The studies of corrosion resistance of AISI 316Ti SS

in Ringer’s solution after electropolishing and passivation in nitric acid

Krzysztof Rokosz1,a, Tadeusz Hryniewicz1,b, Grzegorz Solecki1,2,c 1Division of BioEngineering and Surface Electrochemistry, Department of Engineering and Informatics

Systems, Faculty of Mechanical Engineering, Koszalin University of Technology, Racławicka 15-17, PL 75-620 Koszalin, Poland

2BerlinerLuft Sp. z o.o., Chocimska 7, PL 78-200 Białogard, Poland

a-cE-mail address: [email protected] , [email protected] ,

[email protected]

ABSTRACT

In present work, the continuation of general and pitting corrosion analysis of austenitic

AISI 316Ti (EN 1.4571) stainless steel in Ringer's solution, is presented. The corrosion was studied by

using the ATLAS 98 potentiostat with platinum EPT-101 and calomel reference EK-101P electrodes.

The three types of specimens, i.e. as received (without any pretreatment), after abrasive mechanical

polishing (MP), and after electrochemical polishing (EP), were used. The best pitting corrosion

resistance was recorded for electropolished and passivated (in 20% vol. HNO3 for 30 minutes) surface,

i.e. the pitting potential was equal to 761 mVSCE (855.4 ± 58.5 mVSCE), while the worst one was

recorded for mechanically ground samples and the pitting corrosion potential was equal to 270 mVSCE

(378.8 ± 60.3 mVSCE).

Keywords: AISI 316Ti/EN 1.4571, austenitic stainless steel, electropolishing, passivation, pitting

corrosion, potentiodynamic corrosion measurements

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World Scientific News 98 (2018) 46-60

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1. INTRODUCTION

The pitting corrosion of duplex steels was described in reference [1], however due to the

price of this steel in some applications austenitic stainless steel may be used. Specifically this

substitutions may be used in the food processing equipment, brewery equipment, chemical

and petrochemical equipment, laboratory benches, coastal balustrading, boat fittings, chemical

transportation containers, heat exchangers, and mining screens. The most frequently used

austenitic steels are AISI 304 or AISI 304L, which contain mainly iron, chromium, and

nickel. The more expensive austenitic steels containing molybdenum, i.e. AISI 316 or

AISI 316L have better corrosion resistance than AISI 304/304L. The addition of titanium,

what is observed in the case of AISI 316Ti stainless steel, results in structure stabilization at

temperatures over 800 °C, what prevents carbide precipitation at the grain boundaries and

protects the metal from corrosion [2]. It should be pointed out that still the steels [3-4] as well

as titanium and its alloys [5-10] are applicable in industry. To obtain better surface roughness

and corrosion resistance of steels’ surfaces, the electropolishing (EP) [10-13] has been

effectively used. It is worthy noticing that recently some modifications of the process were

proposed by magnetoelectropolishing (MEP) [14-28], high-current-density electropolishing

(HDEP) [29-31], or high-voltage electropolishing (HVEP) [32].

The aim of this work is a comparative analysis of general and pitting corrosion of

austenitic AISI 316Ti (EN 1.4571) stainless steel in Ringer's solution. Three states of the steel

surface have been taken into account, as-received (AR) after rolling operation, after

mechanical/abrasive polishing (MP), and after electropolishing (EP), all of them passivated in

20% vol. HNO3.

2. METHOD

AISI 316Ti (EN 1.4571) austenitic stainless steel samples (cuboid with dimensions of

50 × 30 × 1.5 mm) were used for the study. The main elements constituting the steel are:

chromium (16-18%), molybdenum (2.0-3.0%), nickel (10.0-14.0%), titanium (max 0.7%),

silicon (max 0.75%), phosphorus (max 0.05%), sulfur (max 0.08), including carbon (max

0.08%), and iron as the rest of the steel composition. The electrolytic polishing operations

were performed at the current density of 50 A/dm2. The main elements of the Electropolishing

(EP) setup were a processing cell, a DC power supply RNG-3010, the electrodes and

connecting wiring. The studies were carried out in the electrolyte of initial temperature of 40

°C, with the temperature control of ±5 °C. Generally, the final electrolyte temperature was

increased up to 55 °C. For the studies, the electrolyte being a mixture of two acids, i.e.

H2SO4:H3PO4 equal to 2:3, was used. The passivation was performed in the solution of 20%

by volume nitric acid (HNO3) for 15 and/or 30 minutes in temperature of 25 ºC. The corrosion

potentiodynamic polarization tests were carried out in Ringer’s solution (8.6 g/dm3 NaCl,

0.3 g/dm3

KCl, 0.48 g/dm3 CaCl2) on the ATLAS 98 testing device using the POL 98

software. The tests were carried out with a potential of –400 mV relative to the saturated

calomel electrode (SCE) in the anodic side with a potential step of 5 mV (potential change

rate of 0.5 mV/s) up to current density of 1000 μA/cm2. The scan in cathodic direction was

performed with the potential change rate of 1 mV/s. As counter, reference and working

electrodes a platinum plate with a surface area of 25 mm2 (EPT-101), calomel reference (EK-


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101P), and AISI 316Ti stainless steel (examined sample), were used, respectively. For each

run, the electrolytic cell made of glass was used, containing up to 500 ml of the electrolyte.

3. RESULTS AND DISCUSSION

In Figure 1, there are presented potentiodynamic corrosion results of AISI 316Ti

stainless steel, as received (AR). The corrosion potential of general corrosion was changing in

the range from 108 mVSCE up to 57 mVSCE (range: 165 mVSCE), while pitting corrosion

potential was in the range of from 587 mVSCE up to 728 mVSCE (range: 141 mVSCE). In

Figure 2, there are presented potentiodynamic corrosion results of AISI 316Ti stainless steel

only after passivation for 15 minutes in 20% (vol.) HNO3. The corrosion potential of general

corrosion was changing in the range from 246 mVSCE up to 76 mVSCE (range: 322 mVSCE),

while pitting corrosion potential was in the range of from 511 mVSCE up to 659 mVSCE (range:

148 mVSCE). In Figure 3, there are presented potentiodynamic corrosion results of AISI 316Ti

stainless steel only after passivation for 30 minutes in 20% (vol.) HNO3. The corrosion

potential of general corrosion was changing in the range from 249 mVSCE up to –134 mVSCE

(range: 115 mVSCE), while pitting corrosion potential was in the range of from 575 mVSCE up

to 925 mVSCE (range: 350 mVSCE). In Table 1, there are corrosion results related to AISI 316Ti stainless steel without any

treatment (as received) after passivation for 15 and 30 minutes in 20% (vol.) HNO3.

Corrosion potential for non-passivated sample was equal to −33.6 ±59.3 mVSCE (median:

−40.5 mVSCE), while the pitting corrosion potential 647.8 ±40.2 mVSCE (median: 638.5

mVSCE). In case of passivated sample in 20% (vol.) HNO3 for 15 minutes the corrosion

potential was equal to –68.7 ±142.8 mVSCE (median: −57.5 mVSCE), while pitting corrosion

potential was 575.6 ±41.6 mVSCE (median: 573 mVSCE). The corrosion potential of sample

passivated in 20% (vol.) HNO3 for 30 minutes was equal to −173.5 ±34.8 mVSCE (median:

−173.5 mV) SCE, while pitting corrosion potential was 660.6 ±102.9 mVSCE (median: 635

mVSCE).


stainless steel after abrasive polishing (MP) using abrasive paper No. 500. The corrosion

potential of general corrosion was changing in the range from 214 mVSCE up to –102 mVSCE

(range: 112 mVSCE), while pitting corrosion potential was in the range from 270 mVSCE up to

462 mVSCE (range: 192 mVSCE). In Figure 5, there are presented potentiodynamic corrosion

results of AISI 316Ti stainless steel after abrasive polishing and passivation for 15 minutes in

20% (vol.) HNO3. The corrosion potential of general corrosion was changing in the range

from 265 mVSCE up to 87 mVSCE (range: 178 mVSCE), while pitting corrosion potential was

in the range of from 365 mVSCE up to 495 mVSCE (range: 130 mVSCE).


stainless steel after abrasive polishing and passivation for 30 minutes in 20% (vol.) HNO3.

The corrosion potential of general corrosion was changing in the range from 293 mVSCE up

to 156 mVSCE (range: 137 mVSCE), while pitting corrosion potential was in the range of from

452 mVSCE up to 576 mVSCE (range:124 mVSCE).


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Fig. 1. Potentiodynamic curves of AISI 316Ti (AR – as received) in Ringer’s solution

Fig. 2. Potentiodynamic curves of AISI 316Ti stainless steel (as receved) after passivation

for 15 min. in 20% (vol.) HNO3 obtained in Ringer’s solution


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Fig. 3. Potentiodynamic curves of AISI 316Ti after passivation for 30 min. in 20% (vol.)

HNO3 obtained in Ringer’s solution

Fig. 4. Potentiodynamic curves of AISI 316Ti stainless steel after abrasive polishing (MP)

obtained in Ringer’s solution


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Table 1. Results of potentiodynamic measurements of AISI 316Ti stainless steel (AR – as

received) and after passivation in 20% (vol.) HNO3 for 15 and 30 minutes

Sample 316Ti-AR 316Ti-AR-20%

HNO3-15min

316Ti-AR-20%

HNO3-30min

Epit Ecor Epit Ecor Epit Ecor

1 728 11 611 65 665 181

2 640 35 511 246 596 154

3 696 6 535 186 602 145

4 637 102 583 169 712 168

5 646 46 566 204 925 176

6 628 108 562 68 575 249

7 680 47 550 76 666 171

8 609 75 580 64 605 222

9 627 57 599 54 593 191

10 587 79 659 209 667 134

Average 647.8 33.6 575.6 68.7 660.6 179.1

Stand. dev. 42.2 59.3 41.6 142.8 102.9 34.8

Median 638.5 40.5 573 57.5 635 173.5

Max 728 57 659 76 925 134

Min 587 108 511 246 575 249

Range 141 165 148 322 350 115

In Table 2, there are corrosion results related to AISI 316Ti stainless steel after abrasive

polishing and after passivation for 15 and 30 minutes in 20% (vol.) HNO3. Corrosion

potential for non-passivated sample was equal to −160 ±30.8 mVSCE (median: −156.5 mVSCE),

while the pitting corrosion potential was 378.8 ±60.3 mVSCE (median: 388.5 mVSCE). In case

of passivated sample in 20% (vol.) HNO3 for 15 minutes, the corrosion potential was equal to

−172 ±58 mVSCE (median: −168 mVSCE), while pitting corrosion potential was 425.2

±38.1 mVSCE (median: 419.5 mVSCE). The corrosion potential of sample passivated in 20%

(vol.) HNO3 for 30 minutes was equal to −200.9 ±36.3 mVSCE (median: −198 mVSCE), while

pitting corrosion potential was 544.3 ±37 mVSCE (median: 547 mVSCE).


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Fig. 5. Potentiodynamic curves of AISI 316Ti stainless steel after abrasive polishing

and passivation for 15 min. in 20% (vol.) HNO3 obtained in Ringer’s solution

Fig. 6. Potentiodynamic curves of AISI 316Ti stainless steel after abrasive polishing and

passivation for 30 min. in 20% (vol.) HNO3 obtained in Ringer’s solution


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Table 2. Results of potentiodynamic measurements of AISI 316Ti stainless steel after

abrasive polishing (MP) and passivation in 20% (vol.) HNO3 for 15 and 30 minutes

Sample 316Ti-MP 316Ti-MP-20%

HNO3-15min

316Ti-MP-20%

HNO3-30min

Epit Ecor Epit Ecor Epit Ecor

1 341 151 365 254 452 293

2 270 142 422 87 543 156

3 405 102 417 104 536 207

4 308 214 387 169 551 192

5 406 162 466 144 574 207

6 377 170 401 143 526 179

7 366 183 495 209 569 197

8 462 187 450 178 573 174

9 453 144 434 167 576 199

10 400 145 415 265 543 205

Average 378.8 160 425.2 172 544.3 200.9

Stand. dev. 60.3 30.8 38.1 58 37 36.3

Median 388.5 156.5 419.5 168 547 198

Max 462 102 495 87 576 156

Min 270 -214 365 -265 452 -293

Range 192 112 130 178 124 137

In Table 3, there are corrosion results related to AISI 316Ti stainless steel after

electrochemical polishing and after passivation for 15 and 30 minutes in 20% (vol.) HNO3.

Corrosion potential for non-passivated sample was equal to −205.8 ±31.4 mVSCE (median:

−195.5 mVSCE), while the pitting corrosion potential was 870.7 ±128.7 mVSCE (median:

900 mVSCE). In the case of passivated sample in 20% (vol.) HNO3 for 15 minutes the

corrosion potential was equal to −149.9 ± 89.1 mVSCE (median: −175 mVSCE), while pitting

corrosion potential was 790.6 ±142.1 mVSCE (median: 823.5 mVSCE). The corrosion potential

of sample passivated in 20% (vol.) HNO3 for 30 minutes was equal to −190.3 ±25 mVSCE

(median: −193 mVSCE), while pitting corrosion potential was 855.4 ±58.5 mVSCE (median:

854 mVSCE).


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Table 3. Results of potentiodynamic measurements of AISI 316Ti stainless steel after

electrochemical polishing (EP) and passivation in 20% (vol.) HNO3 for 15 and 30 minutes

Sample 316Ti-EP 316Ti-EP-20%

HNO3-15min

316Ti-EP-20%

HNO3-30min

Epcit Ecor Epit Ecor Epit Ecor

1 650 194 669 151 835 211

2 757 187 824 186 873 207

3 956 174 820 232 893 180

4 922 206 823 182 824 141

5 970 197 888 228 879 220

6 1072 212 913 237 979 182

7 878 191 915 86 859 175

8 938 188 661 168 849 169

9 724 286 485 47 761 214

10 840 223 908 76 802 204

Average 870.7 205.8 790.6 149.9 855.4 190.3

Stand. dev. 128.7 31.4 142.1 89.1 58.5 25

Median 900 195.5 823.5 175 854 193

Max 1072 174 915 47 979 141

Min 650 286 485 237 761 220

Range 422 112 430 284 218 79


stainless steel after electrochemical polishing. The corrosion potential of general corrosion

was in the range from 286 mVSCE up to 174 mVSCE (range: 112 mVSCE), while pitting

corrosion potential was changing from 650 mVSCE up to 1072 mVSCE (range: 422 mVSCE). In

Figure 8, there are presented potentiodynamic corrosion results of AISI 316Ti stainless steel

after abrasive polishing and passivation for 15 minutes in 20% (vol.) HNO3. The corrosion

potential of general corrosion was equal in the range from 237 mVSCE up to 47 mVSCE

(range: 284 mVSCE), while pitting corrosion potential was in the range from 485 mVSCE up to

915 mVSCE (range: 430 mVSCE).


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Fig. 7. Potentiodynamic curves of AISI 316Ti 2205 stainless steel after electrochemical

polishing (EP) obtained in Ringer’s solution

Fig. 8. Potentiodynamic curves of AISI 316Ti stainless steel after electrochemical polishing



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stainless steel after abrasive polishing and passivation for 30 minutes in 20% (vol.) HNO3.

The corrosion potential of general corrosion was changing in range from 220 mVSCE up to –

141 mVSCE (range: 79 mVSCE), while pitting corrosion potential was in the range of from

761 mVSCE up to 979 mVSCE (range: 218 mVSCE).

Fig. 9. Potentiodynamic curves of AISI 316Ti stainless steel after electrochemical polishing


4. CONCLUSION

The passivation of AISI 316Ti stainless steel in 20% by volume nitric acid (HNO3)

during 15 and 30 minutes without any pre-treatment (as received) as well as after abrasive and

electrochemical polishing may change the pitting corrosion resistance of the formed passive

layers, what was shown in present paper. The best pitting corrosion protection may be

understood as a minimal potential of pitting corrosion, which was found based on ten

measurements. This value of the best pitting corrosion protection in Ringer’s solution was

found for the steel surface after electropolishing and passivation in 20% vol. HNO3 for 30

minutes, i.e. the pitting potential was equal to 761 mVSCE (855.4 ± 58.5 mVSCE). The worst

pitting corrosion resistance was recorded for mechanically ground samples and the pitting

corrosion potential was equal to 270 mVSCE (378.8 ± 60.3 mVSCE). Summing up, one should

notice that the electrochemical treatments, such as electropolishing and passivation, may

change the composition of passive layers on AISI 316Ti, what is bound with pitting corrosion

resistance. In industry the AISI 316Ti stainless steel should be treated only by passivation or,

in case of a scratched surface, it should be electropolished and passivated.


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Fig. 10. Comparison of corrosion behavior of AISI 316Ti stainless steel after different

treatments: AR – as received, MP – after abrasive polishing, EP – after electropolishing


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Documents

The studies of corrosion resistance of AISI 316Ti SS in ... · proposed by magnetoelectropolishing (MEP) [14-28], high-current-density electropolishing (HDEP) [29-31], or high-voltage