potential is very vulnerable to stress corrosion cracking. Thebranched cracks produced are novel in form. Ni Is selectivelydissolved from the crack walls.

2. Similar cracks are produced in the stressed material inaq. HCI at potentials slightly positive of the free corrosionpotential. The form of the cracks is dependent both uponpotential and upon applied strain.

3. The material is subject to hydrogen embrittlement atlow potentials in aq. HCI.

4. Larger, but fewer cracks were produced in the stressedmaterlal by aq. polythionic acid. Hydrogen embrittlement prob-ably plays a dominant role In this medium.

5. Some differences in cracking behavior were found be-tween the wheel side and the top side of a melt-spun ribbon.

AcknowledgmentR. J. McKlm wishes to thank SERC for financial support

References1. Sedriks, A. J., Corrosion of Stainless Steels, John Wiley

and Sons, New York (1979).2. Shreir, L. L., Ed., Corrosion, Newnes-Butterworths, London

(1979).

3. Waseda, Y., The Structure of Non-Crystalline Materlals,McGraw-Hill (1980).

4. Devine, T. M., J. Electrochem. Soc., Vol. 134, p. 38 (1977).5. Viswanadham, R. K., Green, J. A. S., and Montague, W. G.,

Scripta Met., Vol. 10, p. 229 (1976).6. Masumoto, T. and Kimura, H., Sci. Rep. Res. Inst. Tohoku

Univ., Vol. A27, p. 172 (1979).7. Kawashima, A., Hashimoto, K., and Masumoto, T., Corro-

sion, Vol. 36, p. 557 (1980), and reference therein.8. Latanision, R. M., Turn, J. C., Jr., and Compeau, C. R.,

Third Int. Conf. on Mech. Behavior of Materials, Miller,K. J. and Smith, R. F., Eds., Pergamon Press, Oxford, p. 475(1979).

9. Diegle, R. B., Corrosion, Vol. 36, p. 362 (1980).10. ASTM Standard Recommended Practice, Designation:

G48-76 (1976).11. ASTM Standard Recommended Practice, Designat)on:

G35-73 (1973).12. Brown, B. F., Ed., Stress-Corrosion Cracking in High

Strength Steels and in Titanium and Aluminum Alloys,Naval Research Laboratory, Washington, D.C., p. 10(1972).

13. Ibid, Chapter 3.14. McKim, R. J. and Archer, M. D., unpublished work.

Comparison of Several AcceleratedLaboratory Tests for the Determinationof Localized Corrosion Resistance of

High-Performance Alloys*

P. E. MANNING*

AbstractResults of immersion pitting, immersion crevice, and slow scan potentiodynamic pitting testsare compared to assess the relevance of particular types of accelerated laboratory tests forlocalized corrosion. The alloys examined include 317 L, 20-type alloys, duplex stainless steels,and nickel-base alloys. The solutions utilized are acid chloride-type with and without ferricTons (Fe2(SO4)3J as an oxidizing species. The acids examined include sulfuric, hydrochloric,and mixtures of these two acids. The best accelerated test for rating localized corrosionresistance of alloys is the immersion pitting temperature test. Results from this test pro-cedure best simulate and correlate with the service performance of alloys.

IntroductionAccelerated laboratory tests have been used to rate alloyresistance to localized corrosion for many years. Several ofthe more commonly used electrochemical techniques includethe constant potential test, 1 ' 2 ' 3 potentiodynamic test,4 scratch

test,5 and electrochemical pitting temperature test. 6 ' 7 Anotheroften-used accelerated laboratory test for localized corrosionis the coupon immersion test as a function of solution temper-ature $ ,9 In this test technique, the minimum temperature atwhich localized corrosion will occur in the test solution isdocumented.

In the case of the potentiodynamic test, the experimentaltechnique employed, especially the rate at which the electro-chemical potential is varied with time, strongly influences thetest results. 1,4,1013 Many authors have compared results ofvarious electrochemical tests for localized corrosion. 4,14.24 The

*Presented during Corrosion/82 (Paper 176), March, 1982,Houston, Texas.

*Cabot Corporation, Kokomo, Indiana.

results are conflicting in terms of the test method employedand different alloy/environment combinations.

In immersion tests for localized corrosion, the test solu-tion can be considered as a "chemical potentiostat "

25,26,27

through appropriate additions of oxidizing species. An advan-tage of this test technique over controlled potential tests isthe occurrence of simultaneous anodic and cathodic reac-tions on the test sample. 28'29 By accounting for the cathodiccharacteristics of the alloy, the corrosion potential is not con-strained and shifts in the active direction after initiation oflocalized corrosion.29 ' 30 This more closely simulates in-serviceconditions as compared to controlled potential tests wheremore noble, controlled potential artificially drives the propaga-tion of localized corrosion 30

The most important criteria of any accelerated laboratorytest for localized corrosion is that it must rate alloys consist-ent with service performance case histories in environmentsthat cause localized corrosion. Field test coupon data inspecific service applications are available; 31-37 however, aclear rating of alloy performance from these cases is

0010-931218310000351$3.0010

98 © 1983, National Association of Corrosion Engineers CORROSION-NACE

TABLE 1 - Duplex Alloy Chemistries

C Co Cr Cu Fe Mn Mo N Ni P S SI

3RE60 0.024 0.12 18.77 0.24 70.11 1.60 2.73 0.078 4.92 0.026 0.003 1.53AF22 0.020 - 21.62 0.04 67.20 1.52 2.82 0.120 5.20 0.021 0.004 0.6244LN 0.027 - 24.53 0.01 65.83 1.69 1.51 0.169 6.03 0.007 0.007 0.52FERRALIUM111 alloy 255 0.020 0.16 25.63 1.70 62.07 0.83 3.28 0.190 5.57 0.018 0.004 0.27

I 11 Registered trademark of Bonar Langley Alloys Limited.

TABLE 2 - 20•Type Altoy Chemistries

C Cb Co Cr Cu Fe Mn Mo N Ni P S SI Ti V

Jasnop 700 0.020 0.25 0.23 20.88 0.18 48.25 1.48 4.68 0.035 23.76 0.021 0.012 0.32 - 0.05HASTELLON" alloy M-532 0.004 - 0.57 23.81 0.08 44.95 0.94 4.98 0.026 25.61 0.021 0.008 0.58 0.35 0.04Al 6X 0.019 0.06 0.48 20.21 0.13 45.98 0.62 6.41 0.021 24.95 0.022 0.002 0.34 - 0.08254SM0 0.020 - 0.18 19.45 0.86 54.31 0.39 6.12 0.20 17.80 0.018 0.002 0.54 - 0.042008.30i alloy 0.020 - 0.35 19,65 3.19 39.48 0.34 2.08 0.018 34,13 0.016 0.002 0.39 0.01 0.08254810 0.020 - 0.35 19,65 1.81 46.89 1.39 4.82 0,040 24.53 0.020 0.002 0.48 - 0.06

Unnw B8 0.009 - 0.16 1992. 1.55 4701 1.67 4.57 0.015 24.72 0,031 0.002 0.27 - 0,04

Jassop 777 0.030 0.25 0.26 20.87 2.31 44.41 1.31 4.86 0.030 24,91 0.023 0.012 0.42 - 0.07904E 0.024 - 0.25 20.29 178 45.54 2.96 4,61 0.044 26,54 0021 0.009 0.38 - 0.05

t'IRegistered trademark of Cabot Corporation.'21 Registered trademark of Carpenter Technology Corporation.

TABLE 3 - Other Alloy Chemistries

C Cb Co Cr Cu Fe Mn Mo N Ni P S SI Ti V

3171M 0.016 - - 17.92 0.11 61.16 0.90 3.84 0.047 14.58 0.021 0.020 0.54 - -

SANICROI'I 28 alloy 0.020 0,06 0.04 26.41 1.18 36.02 1.22 2.98 0,046 31.38 0.004 0.002 0.06 - -

825 0.012 NA NA 22.17 1.83 30.00 0.27 2.72 NA 41.64 0.018 0.004 006 0.87 0.04HASTELLOYO elloy G3 0.006 0,15 3.00 22.71 1.84 18.20 0.86 6.95 0.050 45.08 0.014 0.004 0.39 - -HASTELLOY elloy G 0.030 2,09 1.82 22.10 1.78 19.03 1.35 6.52 0.050 42.99 0.026 0.007 0.30 - -

NA - Not Analyzed.I'IRegistered trademark of Sandvikens Jernverks Aktiebolag41Registered trademark of Cabot Corporation.

difficult.38 Nevertheless, Silence, et al., 9 demonstrated verygood correlation among immersion laboratory tests, fieldtests, and service performance in flue gas desulfurizationsystems.

The purpose of this work Is to compare the relevance ofseveral accelerated laboratory tests in rating localized corro-slon resistance and to explain the observed variations in testresults from the examined techniques. The study includes awide range of alloy types including 300 series stainless steels,duplex stainless steels, 20-type stainless steels, and nickel-base alloys.

Experimental ProcedureFour duplex stainless steels (Table 1), nine 20-type

stainless steels (Table 2), 317 LM, SANICRO 28 alloy, and 3nickel-base alloys (Table 3) are examined. The registeredtrademarks of the alloys are listed in Tables 1 through 3.

Electrochemical tests included a 360 mVlh cathodic toanodic polarization procedure and a constant potential test.The 360 mVlh scan rate was chosen on the basis of previouswork.4 Details of the experimental procedure were previouslyreported.4 The electrolyte utilized in all the electrochemicaltests was 4% NaCI with 0.01 M HCI (pH - 2) at a temperatureof 70 C. No purge gas was employed and the solution was ex-posed to air through the condenser outlet.

Immersion tests were used to evaluate pitting and crevicecorrosion resistance. Pitting test samples were 5 cm x 2.5 cmx 0.3 cm with a 120 grit dry belt finish. Crevice corrosion testsamples were 7.5 cm x 2.5 cm x 0.3 cm with mill finish sur-faces, except for the edges which were ground with 120 grit drybeits. A multiple crevice test assembly was used 9 '39 which con-sisted of two serrated TEFLON washers with a total of 24potential crevice sites per sample. The washers were heldagainst the sample with an insulated bolt torqued to 40 in. oz.The environments used for both types of immersion tests were4% NaCI + 0.01 M HCI + 0.1 % Fe2(SO4)3 (oxidizing NaCI-HCIenvironment), 4% NaCI + 0.01 M H 2SO4 + 0.1 % Fe2(SO4)3 (ox-idizing NaCI-H 2SO4 environment), and 4% NaCI + 0.005 M HCI+ 0.005 M H2SO4 + 0.1 % Fe2(SO4)3 (oxidizing NaCI-HCI-H 2SO4

environment). The pH of all three solutions was 1.8. The redoxpotential of the oxidizing NaCI-HCI test environment is 630 mVversus SCE. Reagent grade chemicals and deionized waterwere used in all the experiments.

In pitting immersion tests, the solution temperature wasvaried in 5 C increments to determine the lowest temperatureat which pitting corrosion was detected (observed by a 40X ex-amination of duplicate samples) in 24 hours or in some cases a168-hour exposure period. In crevice corrosion immersiontests, the solution temperature was also varied in 5 C in-crements to determine the lowest temperature at whichcrevice corrosion initiated in a 100-hour exposure period.These lowest temperature values are called the pitting tem-perature and the crevice temperature, respectively.

ResultsIn order to justify an immersion test period, an induction

time study was performed. Immersion pitting tests on severalalloys were conducted for 24-hour and 168-hour periods (Table4). The results show that each alloy's pitting temperature iswithin the ± 5 C accuracy of the test procedure. Therefore, the24-hour immersion pitting test was used for the balance of theimmersion pitting experiments.

A plot of immersion pitting temperature test results in 4%NaCI with 0.01 M HCI and 0.1% Fe 2(SO4)3 as an oxidizingagent, along with slow scan potentiodynamic pitting poten-tials in 4% NaCI with 0.01 M HCI (potentiostat replaces the ox-idizing agent), is given in Figure 1. There is a strong linearcorrelation between the two test techniques with the followingexceptions: 20CB-3 alloy, SANICRO 28 alloy, alloy 825, 254SMO, and Al 6X. These alloys all possess pitting potentialswhich are 200 to 300 mV more noble than the line indicated inFigure 1. In the case of SANICRO 28 alloy, the constant poten-tial test result (16S) lies very near the line. This is 200 mV moreactive than the 360 mV/h potentiodynamic pitting test result. 16

In a previous study, 4 constant potential test results for 316stainless steel, 20CB-3 alloy, alloy 825, FERRALIUM alloy 255,and alloy M-532 were 30 to 70 mV more active than the 360mV/h potentiodynamic pitting test results. Apparently, the pit-

Vol. 39, No. 3, March, 1983 99

TABLE 4 - Induction Time ConsiderationsOxidizing NaCI.HCI Immerslon

Pltting Test

Alloy24-Hoor Test

Pitting Temperature (C)168-Hour Test

Pitting Temperature (C)

3RE60 20 20317 LM 35 30FERRALIUM alloy 255 45 45904L 45 40M-532 60 55SANICRO 28 alloy 60 55

1. 3171M 7. URANUS 86 13. Al 6X

2. 3RE60 8. 254510 14. 2545M0

3. AF22 9. JESSOP 700 15. 825

4. 44LN 10. JESSOP 777 16. "SANICRO - 28 ALLOV

5. "FERRALIUM" ALLOV 255 II. 9041 - I2. G-3

6. - 20C1-3" ALLOY 12. M-532 165 POTENTIOSTATIC PITTING

POTENTIAL - - SANICRO - 28 ALLOV

80,

)a 3

1250 /16s 16 14

so 4 /I3 54 II

40I 7

30

1. 3171M 7. URANUS 86 13.

2. 3RE60 8. 254510 11.

3. AF22 - NO DATA 9. JESSOP 700 15.

4. 44LN 10. JESSOP 777 16.

5. "FERRALIUM" ALLOV 255 II. 9041 17.

6. '2008-3" ALLOV 12. M-532 165

M60

5j 30

NVV PITTING POTENTIAL (mV .. SCE)

FIGURE 2 - Plot of crevice temperature versus pittingpotential for several alloys.

TABLE 5 - Solution Chemistry Considerations

OXidi:ing N.CI.HCI Oxidizing NsCI.H8SO4 OoIdizing N.CI-HCI-H0SO4

4% NaCI + 0.005 M HCII% N.CI + 0.01 M HCI 4% NaG + OA1 M H,50. + 0A05 M H,SOO

+ 0.1% Fs2(S0J, + 0.5% Fa8(S0 + 0.1% Fss(SOJ,PT (°C) C9 (C) PT (C) CT (°C) PT CV

AI 6X

2545M0

825

"SANICRO" 28 ALLOV

G-3

POTENTIOSTATIC P ITTING

POTENTIAL - "SANICRO - 28

ALLOY

Is

20 2 6

5210y

0 I__I 1 I I I I 1 1 I I I I 1 I I 317LM 35 15 30 10 30 15-50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 200 FERRALIUM.Ilay 255 45 45 45 50 45 45

PITTING POT8NTIAL (,V OCT) 904L 45 20 50 10 50 15M•532 60 20 55 15 00 20G3 80 20 80 20 8020

FIGURE 1 - Plot of the pitting temperature versus pit -ting potential for several alloys.

ting potentials of alloy 825 and 20CB-3 alloy are the same asseveral 4 to 5% molybdenum-containing 20-type alloys (alloyslabeled 9, 10, and 11 in Figure 1). This is contradictory to well-documented service performance information32,34,35,36 whichsuggests that the localized corrosion resistance of alloys 825and 20CB-3 is similar to 316 stainless steel. In previousstudies, the pitting potential of 316 stainless steel was -94mV4 and the pitting temperature was 20 C. 9 Note that the pit-ting temperature values for 316 stainless steel (2.06% Mo),alloy 825 (2.72% Mo), and 20CB-3 alloy (2.08% Mo) correlatewell with service experience.

A plot of crevice temperature versus pitting potential isshown in Figure 2. There is essentially no correlation betweenthese test techniques. With the exception of alloys labeled 5,6, and 15 In Figure 2, all the alloys' crevice temperatures arebetween 10 and 30 C, and a 700 mV range of pitting potentialswas observed. The alloys with a low molybdenum content(20CB-3 alloy and 825) demonstrated very 1ow crevice tem-peratures (<_ -5 C, i.e., the solution froze during testing andcrevice corrosion was still observed). In a previous study,9 316stainless steel also had a crevice temperature value of <_ -5C. This correlates well with the ranking from service ex-perience. Note that the crevice corrosion temperature of theduplex stainless steel, FERRALIUM alloy 255, was quite high(45 C). The electrochemical pitting potentials of alloy 825,20CB-3 alloy, and FERRALIUM alloy 255 were nearly identical.

Pitting temperatures and crevice temperatures were de-termined for several alloys in two additional environments, in-cluding an oxidizing NaCl-H 2SO4 solution and an oxidizingNaCI.HCI-H 2SO4 environment. The data are shown in Table 5.The solution pH values were the same (1.8) for all three solu-tions. The results show essentially no differences in alloy per-formance In HCI, H 2SO4, or HCI-H2SO4 mixtures. This is of con-siderable importance in applying the laboratory results to airpollution control corrosion problems where sulfuric acid isknown to exist. Hydrolysis of metal chlorides under scale in

these systems may result in the formation of HCI. Whether theenvironment is a Cl-H 2SO4-type or a Cl-H 2SO4-HCI-type, thelaboratory test rating of alloys applies.

DiscussionIn general, the correlation of results from the immersion

pitting test and the electrochemical pitting test was good;however, there were several notable exceptions shown inFigure 1 (alloy 825, SANICRO 28 alloy, 20CB-3 alloy, Al 6X, 254SMO). In view of previously stated service performance and im-mersion pitting temperature correlation, it appears that theelectrochemical pitting potential test is responsible for thedeviations observed. One cause of the deviation is related toinduction time considerations in pitting potential determina-tion. In potentiodynamic pitting tests, the potential continuesto shift in the noble direction at a specified rate, allowinglimited induction time at a given potential. This tends to yield amore noble pitting potential in the slow scan rate poten-tiodynamic tests as compared to constant potential pittingtests. 4 The difference in pitting potential measured by the twotechniques varies with the alloy tested. For example, alloy 825had a pitting potential difference of 40 mV, 4 20CB-3 alloy had adifference of 70 mV,4 and SANICRO 28 in this study had a dif-ference of 200 mV. The large variation in the SANICRO 28 alloymay be related to the high chromium content of the alloy(26.4l%), which is known to enhance repassivation kineticsand thereby extend induction times. Another problem of elec-trochemical pitting potential data is that the pitting potential(lowest potential at which a pit initiates that will propagate,i.e., potential at which a monotonic increase in current occurs)is determined under artificial propagation conditions. Thepotential is controlled at high anodic values after initiation todetermine whether the pit will repassivate or grow (monotoniccurrent increase). This growth does not represent conditionsthat occur on freely corroding materials. It is presumed thatthe high values of pitting potential (constant potential or

100 CORROSION-NACE

potentiodynamic results) of alloys 825 and 20CB-3 are the re-sult of an inherent resistance to pit propagation under con-trolled, high anodic potentials (i.e., artificial propagation con-ditions). Another more dramatic example of this behavior isthe comparison of pitting potential values for alloys G and G-3(Table 5). In this case, alloy G resisted pit propagation undercontrolled, high anodic potentials to a point where transpas-sivity occurred (670 mV) and pits were not observed on thesample. Alloy G-3 had a pitting potential of 579 mV. A mech-anism for this behavior was not pursued since it is of no prac-tical concern in view of known service experience equivalenceof the two alloys. Furthermore, immersion pitting test resuitshave demonstrated that the localized corrosion resistance ofalloys G and G-3 is equivalent and that alloys 825 and 20CB-3are clearly inferior to the 4 to 5% molybdenum-containing20-type alloys, and in fact are similar to 316 stainless steel inlocalized corrosion resistance. Since alloys Al 6X and 254 SMOwere not tested by the constant potential test, it is unclearwhether the deviation from the majority of the alloys shown inFigure 1 was caused by induction time consideration or artifi-cial propagation conditions which lead to pitting potentialmeasurements that do not relate to service performance.

The correlation of results from the immersion crevice cor-rosion test and the electrochemical pitting test (Figure 2) wasquite poor. The multiple crevice test is not a very sensitive testin view of the limited difference of crevice temperature formany alloys which are known to have varying crevice corrosionresistance. Other workers have discussed the limitations ofmultiple crevice tests.40-43 A mathematical model of crevicecorrosion initiation was developed 44 which discussesvariables that contribute to irreproducibility of crevice corro-sion tests including the crevice gap, crevice depth, and masstransport in and out of the crevice. In a multiple crevice test,the crevice geometry is not welt-controlled, and as soon ascrevice corrosion begins to propagate under one or more crev-ices the crevice geometry changes with time (nonattackedcrevices hold the crevice block in place). For this reason, thetest is only useful in determining whether or not crevice corro-sion will begin to propagate. Propagation rates can not bedetermined by any maximum depth measurement. 40

The Jack of correlation between the crevice temperatureand the electrochemical pitting potential is not surprising. It iswell-known that the mechanism of crevice corrosion 44"7 issimilar to that of pit propagation. 48 Additionally, themechanism of pit initiation49 (pitting potentials are associatedwith pit initiation) is different from that of pit propagation andcrevice corrosion. 28,4144

In view of the above discussion, it is concluded that of thetest methods examined, the best accelerated laboratory testfor rating localized corrosion resistance of alloys is the immer-sion pitting test where a pitting temperature value is deter-mined. Results from this test procedure best simulate and cor-relate with the service performance of the alloys.

The data generated in this work are useful when consider-ing alloying effects on localized corrosion. The beneficial ef-fects of molybdenum additions3,8,11,51 and chromium addi-tions8'51,52,57 for corrosion resistance are well-documented.The detrimental effect of manganese is apparent in severalstudies 8 ,11 ' 56 The role of nitrogen additions on the localizedcorrosion resistance of materials has not been clearlyd e f i n e d .8' 28, 52, 58'58

Several workers8,55.59 have shown that the interaction ofseveral alloying additions is of great importante. Data in thepresent work reinforce this concept. In the case of duplexstainless steels, the least resistant alloy was 3RE60 (18.8 Cr,2.7 Mo, 0.078 N, 1.6 Mn). The remaining duplex alloys displayeda similar behavior, including 44 LN (24.5 Cr, 1.5 Mo, 0.17 N, 1.7Mn), AF22 (21.5 Cr, 2.8 Mo, 0.12 N, 1.5 Mn), and FERRALIUMalloy 255 (25.6 Cr, 3.3 Mo, 0.19 N, 0.83 Mn). It appears thatchromium, molybdenum, and nitrogen are beneficial addi-tions, and the role of manganese is unclear. Note that themolybdenum contents of duplex alloys are considerably lowerthan those of austenitic alloys to provide a similar resistance

to localized corrosion (Figure 1).In the 20-type alloy group, the rating of localized corrosion

resistance by pitting temperature from least to most resistantis as follows:

20CB-3 alloyUranus B6

Jessop 700, Jessop 777, and 904 L254 SLX, M-532, 254 SMO, and SANICRO 28 alloy

Al6X

Considering the chromium, molybdenum, and manganese con-centrations in the above alloys, the beneficial role ofmolybdenum is obvious (Al 6X and 254 SMO versus 20CB-3 al-Ioy).. The interaction of chromium, molybdenum, and manga-nese in the remaining alloys is less clear. In alloys with a 4 to5% molybdenum concentration range, the low-chromium con-tent (Uranus B6) and high manganese-content (904 L) alloystended toward lower pitting temperatures. The high-chromiumcontent (26.4%) and Iow-molybdenum content (3.0%) ofSANICRO 28 alloy resulted in a high pitting temperature.Therefore, very high chromium levels can replace high molyb-denum contents to insure excellent localized corrosionresistance. Alloys with high molybdenum, chromium, andnitrogen contents and a low manganese content gave the bestresuits as a general trend; however, there were exceptions (254SLX and Jessop 777), which reinforce the concept that labora-tory tests as welt as in-service exposures do not easily or con-sistently distinguish properties of alloys with minor chemistrydifferences.

Conclusions1. Results from electrochemical slow scan rate pitting

tests and immersion pitting temperature tests correlate rea-sonably well. The several exceptions to the correlation arerelated to the measurement of pitting potential.

2. Results from pitting potential tests and Immersioncrevice temperature tests show very poor correlation.

3. Immersion test results were essentially identical in ox-idizing NaCl-HCI, oxidizing NaCI-H 2SO4, and oxidizing NaCI-HCI-H 2SO4 solutions.

4. Considering the test methods examined, the best ac-celerated laboratory test for rating localized corrosion resist-ance of alloys is the immersion pitting temperature test.Results from this test procedure best simulate and correlatewith the service performance of alloys.

5. Alloys with high concentrations of chromium, molyb-denum, and nitrogen and low concentrations of manganesetend to have better resistance to localized corrosion.

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