stress corrosion cracking - properties of uns s32101

8/9/2019 Stress Corrosion Cracking - Properties of UNS S32101

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Dear Reader

This issue of Acom contains a contribution concerned with stress

corrosion cracking (SCC). This corrosion form is a subgroup of

phenomena normally denoted environmentally induced cracking

(EIC), that also includes corrosion fatigue, hydrogen embrittlement

and liquid metal embrittlement. The field of SCC deals with corrosion

under applied static stress, as opposed to corrosion fatigue whichtreats the effect of corrosion under cyclic mechanical loads.

Failure due to stress corrosion is characterized by a brittle behavior

in combination with a certain time to failure after being taken into

operation. Cracks can be intra- as well as transgranular. Transgranular

cracks normally show a highly branched characteristic, as shown in

the paper. For duplex stainless steels, crack propagation is often halted

at a phase boundary. This is one of the explanations to their superior

resistance to SCC.

For the newly developed lean duplex grades, stress corrosion cracking

poses additional problems to the testing engineer, since it is difficult to

find environments where the failure is explicitly due to stress corrosion

cracking and not some other form of corrosion, e.g. uniform attacks or

pitting. The paper in this issue of Acom presents data from a series of

different lab tests on the lean duplex grade LDX 2101, which, as expected,

performed very well under stressed conditions. I hope you will find

the paper interesting and that it will answer some of the questions

related to lean duplex stainless steels in load bearing applications.

Yours sincerely,

Claes Olsson, PhD

Acom editor

Stress Corrosion CrackingProperties of UNS S32101 A new Duplex StainlessSteel with low NickelContent

acom2 - 2007

A corrosion management and applications engineering magazine from Outokumpu


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Stress Corrosion CrackingProperties of UNS S32101

A new Duplex Stainless Steelwith low Nickel Content

E. Johansson

Outokumpu Stainless AB, Avesta Research Center

PO Box 74, SE-774 22 Avesta, Sweden

T. Proek

Institut de la corrosion / French Corrosion Institute

220 Rue Pierre Rivoalon, F-29200 Brest, France

Abstract

UNS S32101 is a general-purpose lean duplex stainless steel with low nickel content.

The stress corrosion cracking properties of UNS S32101 were investigated under constant

strain conditions. Both evaporative and immersion test methods were used. The results

for UNS S32101 were compared with those of a standard austenitic stainless steel and

other duplex grades. Immersed in concentrated chloride solutions, UNS S32101 exhibited

similar resistance to stress corrosion cracking as other duplex grades. In the wick test

UNS S32101 was not susceptible to stress corrosion cracking and was comparable to other

duplex grades while the austenitic grade tested failed due to stress corrosion cracking.

When exposed to chloride deposits under atmospheric conditions UNS S32101along with

other duplex grades, did not suffer from stress corrosion cracking while the austeniticgrade did. Thus, the chloride stress corrosion cracking resistance of UNS S32101 was shown

to be far superior to that of austenitic grade UNS S30400. Moreover, UNS S32101 displays

behaviour similar to other duplex steel grades tested. With the test methods used, it was

not possible to obtain an individual ranking of the different duplex stainless steel grades.

Keywords:stress corrosion cracking, chloride stress corrosion cracking, stainless steel,

duplex stainless steel, wick test, constant strain

Introduction

Chloride induced stress corrosion cracking (SCC) is a form of corrosion that standard

austenitic stainless steel grades are susceptible to. In order to avoid chloride induced SCC,duplex stainless steels can be used instead of austenitic grades. The duplex structure of

these steels has proved to be very resistant to chloride induced SCC. In this study the

SCC properties of a new duplex stainless steel grade with low nickel content LDX 2101 (1)

(UNS S32101) are presented and compared with a standard austenitic stainless steel

grade and with other duplex stainless steel grades.

UNS S32101 is a general-purpose lean duplex stainless steel with low nickel content.

Substituting nickel for manganese and nitrogen is used to balance the duplex microstructure

to approximately equal amounts of ferrite and austenite [1]. Due to the duplex micro-

structure and the high nitrogen content UNS S32101 has high mechanical strength.

Earlier studies have shown that the corrosion resistance of UNS S32101 is equal or better

than that of austenitic grade UNS S30400 for uniform corrosion, intergranular corrosion

and localized corrosion (pitting and crevice corrosion) [2]. It has been demonstrated that

UNS S32101 can provide considerable weight savings and be cost efficient if its combination

of excellent mechanical properties and good corrosion resistance are utilised [3].

Other studies of the stress corrosion properties of duplex stainless steel with low nickel

(1) Outokumpu Registered Trademark

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content, and high manganese content, showed that in a 25% boiling sodium chloride

solution grade UNS S32001 provided superior stress corrosion cracking resistance

compared to UNS S30400 [4]. Further, tests in saturated chloride solution showed that

UNS S32003 exhibited a higher stress corrosion cracking limit than grades UNS S30400

and UNS S32205 [5]. However, UNS S32101 differs from these two investigated steels

with its combination of high manganese and high nitrogen content.One difficulty when testing the susceptibility to SCC is that the ranking of steel

grades varies depending on test method. The relative performance of different steel

grades depends on both the choice of chloride environment and the loading method.

Thus, testing in a standard environment might give the wrong ranking compared to a

real service environment. One major difference between test methods for SCC is the

means by which the test specimen is exposed to the chloride containing solution. Exposure

can be achieved by immersing the specimen in the solution, dripping solution onto the

specimen, or by exposure to a soaked insulation material. Usually, chloride induced SCC

becomes a concern at temperatures above 50 60C. However, there are certain cases

when SCC can occur at lower temperatures, e.g. in swimming pool atmospheres [6, 7, 8].

By placing drops of a chloride solution on a stressed specimen at a controlled temperature

and humidity, this type of SCC can be tested. In this study the SCC resistance is tested

by fully immersing specimens, by exposure to a soaked insulation material and by placing

drops of chlorides on samples under atmospheric conditions. Also the stress condition

under which the material is exposed to the corrosive environment is an important factor.

The stress can be applied by a constant load, constant strain or constant strain rate.

Initially, a constant load or constant strain specimen are stressed equally. However, in the

constant strain case relaxation causes a lowering of the stress with time. Usually constant

strain tests involve bending of a specimen with rectangular cross section resulting in both

tensile and compressive stresses. Thus, only one side of the specimen is exposed to tensile

stresses and this stress varies along the specimen surface. U-bends expose the material to

both plastic and elastic deformation, while four-point bend specimens are only deformed

elastically. In this study specimens are stressed with constant strain either by U-bend testor by four point bend test (with a maximum stress of 90% of the yield stress).

Experimental

Material

The materials investigated in this study were lean duplex stainless steel grade S32101,

duplex grades S32304, S32205 and S32750, and austenitic grade S30400. The typical

chemical compositions, pitting resistance equivalent (PREN) values and microstructure

for the materials are presented in Table 1. PREN roughly estimates the resistance to

pitting corrosion in chloride environments. The higher the PREN value, the better the

corrosion resistance. The PREN value can be calculated according to:

PREN = %Cr + 3.3 x %Mo + 16 x %N (1)

All the materials were received in cold rolled, heat-treated and pickled condition. The sheet

thickness ranged from 1.0 to 3.0 mm. The minimum mechanical properties of the tested

material are shown in Table 2.

Steel grade Typical chemical composition [wt%] Micro-

UNS EN1) Cr Ni Mo C N Other PREN structure

S30400 1.4301 18.1 8.3 0.04 18 Austenitic

S32101 1.4162 21.5 1.5 0.3 0.03 0.22 5Mn 26 Duplex

S32304 1.4362 23 4.8 0.3 0.02 0.10 26 Duplex

S32205 1.4462 22 5.7 3.1 0.02 0.17 35 Duplex

S32750 1.4410 25 7 4 0.02 0.27 42 Duplex

1)European Norm

Stainless steel grades Table 1

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Stressing of U-bend specimens

U-bend specimens were shaped according to ASTM G30-97 [9]. Specimens with dimension

127x13 mm were cut from sheets parallel or transverse to the rolling directions. The

specimens were stressed using a two-stage method around a mandrel with a 25.4 mmdiameter, and secured with nuts and bolts. Before the final stressing stage the specimens

were degreased in acetone. The time between the two stressing stages, and between the

final stressing stage and the start of the test was kept as short as possible.

Test in concentrated calcium chloride

Both U-bend and four-point bend (4-PB) specimens were exposed in concentrated

calcium chloride solution.

The 4-PB specimens were stressed according to ASTM G39-99 [10]. The mechanical

properties, yield stress and elastic modulus, were measured at 100C. Specimens were

cut from sheets parallel to the rolling direction, 65x10 mm. After degreasing in acetone,

specimens were placed in special holders and a stressing jig was used to strain the specimensto the desired stress level.

The materials were tested in the as-received conditions. U-bend specimens had a sheet

thickness of 1.5 mm for grades S32101, S32304 and S32205, and 1.0 mm for grades

S30400 and S32750. Totally six U-bend specimens were tested for each material, three

specimens were stressed parallel and three specimens stressed transverse to the rolling

direction. The 4-PB specimens had a sheet thickness of 3.0 mm and were stressed parallel

to the rolling direction.

A solution with 40 wt% CaCl2was prepared and the pH adjusted to 6 using a slurry

of calcium oxide. The stressed specimens were placed in the solution and the solution

was heated to 100C. Throughout the test period, the temperature was maintained at

Steel grade ASTM, min values

Rp0.2

Rm A

2

UNS EN1) [MPa] [MPa] [%]

S30400 1.4301 205 515 40S32101 1.4162 530 700 30

S32304 1.4362 400 600 25

S32205 1.4462 450 655 25

S32750 1.4410 550 795 15

1) European Norm

Key mechanical properties Table 2

Specimens U-bend 4-PB

Surface finish As received

Temperature 100C

Solution CaCl2

Concentration 40 wt%

Test duration 500 8 h (or until failure)

Stress ratio (% of Rp 0.2

) 60 and 90%

Relaxation time beforestress applications1) 0 2 days

Relaxation time before test start2) 0 4 h 0 4 h

1) The time difference between preliminary bending and application of stress.2) The time difference between stress application and test start.

Experimental parameters for concentrated calcium chloride Table 3

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100C and the pH measured every second day and adjusted to 6 if necessary. When possible,

the time to cracking was observed and if cracking occurred before the end of test period,

i.e. after 500 h, the test was terminated. After exposure the specimens were evaluated by

visual inspection and by light optical microscopy. Table 3 summarises the experimental

parameters for the calcium chloride test.

Test in concentrated magnesium chloride

The test was performed according to ASTM G36-94 Standard Practice Evaluating

Stress-Corrosion-Cracking Resistance of Metals and Alloys in a Boiling Magnesium

Chloride Solution [11]. This is an accelerated test method for ranking the relative degree

of stress corrosion cracking susceptibility for stainless steel. A 45% (7M) MgCl2solution

has a boiling point of 155C and adding small amounts of distilled water or MgCl2

crystals controls the concentration of MgCl2in order to reach a the right temperature.

The materials were tested in the as-received conditions and the sheet thickness was

1.5 mm for grades S32101, S32304 and S32205, and 1.0 mm for grades S30400 and

S32750. All specimens were stressed parallel to the rolling direction.

The stressed parts of U-bend specimens were exposed to the boiling solution for 24

hours and the temperature was maintained at 155C. The specimens were evaluated byvisual inspection, light optical microscopy and scanning electron microscopy (SEM).

Table 4 summarises the experimental parameters for the magnesium chloride test.

Wick test

The wick test was developed to simulate evaporative conditions by embedding a heated

stainless steel in an insulation material wetted with a dilute chloride solution [12]. In thisinvestigation a modification of the ASTM C692 Standard Method for Evaluating Stress

Corrosion Effect on Wicking Type Thermal Insulation on Stainless Steels [13] was used

to assess the SCC resistance under evaporative conditions.

The dimensions of the test coupons were 200x50 mm. Sheet thickness was 3.0 mm

for S30400 and 1.5 mm for S32304 and S32205. S32101 was tested with sheet thickness

of 1.5 and 3.0 mm. The mechanical properties, yield stress and elastic modulus, were

determined for the tested materials. The specimens were stressed parallel to the rolling

direction. Holes were drilled for the tightening bolt and heating connectors. The surface

facing the thermal insulation during testing was dry ground parallel to the longest

dimension on a 120-grit belt grinder. Stressing of the specimen was done in a two-stage

operation. The coupon was bent to produce a U-shape, radius 25.4 mm, with parallel legs

before a stress was applied by a screw joint. Before the final stressing stage the specimens

were degreased with acetone and rinsed with distilled water.

A thermo-electric couple was spot welded to the specimen in the centre of the concave

surface for temperature control. The specimen was fitted into the U-shaped groove of the

Specimens U-bend

Surface finish As received

Temperature 155 1C

Solution MgCl2

Concentration 45 wt%

Test duration 24 h

Relaxation time before stress applications1) 0 2 days

Relaxation time before test start2) 0 4 h

1) The time difference between preliminary bending and application of stress.2)The time difference between stress application and test start.

Experimental parameters for concentrated magnesium chloride Table 4

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insulation material, which was placed in aqueous NaCl solution. By applying an AC

current, the specimen was heated to 100C. The level of the solution was controlled and

stabilised with an external solution container and a float switch. The test duration was

672 hours. The specimens were evaluated by visual inspection and light optical

microscopy. Table 5 summarises the experimental parameters for the wick test.

Test with chloride deposits

It was shown by Shoji and Ohnaka [14] and later by other authors that stainless steels

covered with chloride salt deposits have the highest susceptibility to stress corrosion

cracking when exposed in air at the relative humidity corresponding to the deliquescence

point of the chloride salt. This is because the chloride concentration of the solutionformed on the surface is the highest at the deliquescence point. If the relative humidity

of the air is lower than the deliquescence point of the particular salt, the deposit is in a

dry state and no solution is formed. With the relative humidity above the deliquescence

point, the surface solution becomes more diluted. Thus, the chloride concentration and

the aggressiveness of the solution decrease at higher relative humidity.

To simulate the most aggressive conditions for the initiation of stress corrosion crack-

ing in terms of tensile stress, chloride deposits and climatic parameters, magnesium and

calcium chloride spots were applied to U-bend specimens. The sheet thickness of the

materials was 2.8 mm for S30400, 1.4 mm for S32101, 2.0 mm for S32304 and S32205,

and 3.0 mm for S32750. All specimens were stressed parallel to the rolling direction.

Chloride deposits were formed according to a modified procedure used by Shoji and

Ohnaka [14]. Six droplets of saturated magnesium chloride (340 g/l) or calcium chloride

solution (380 g/l) were deposited on the top of U-bend specimens.

The specimens were placed in desiccators with respective saturated salt solutions to

keep the relative humidity at the deliquescence point and exposed at 50C for 4 and

22 weeks. The relative humidity inside the desiccators was recorded during the whole

exposure time. It was 31% and 17% for MgCl2and CaCl2, respectively.

One specimen of each alloy was exposed for 4 weeks and two specimens were exposed

for 22 weeks. After exposure, the specimens were inspected visually and by light optical

microscopy. From selected specimens, cross sections were cut in the longitudinal direction,

embedded into resin, polished, and examined with light optical microscopy. Table 6

summarises the experimental parameters for the chloride deposits test.

Specimens U-bend

Surface finish 120 grit

Temperature 100 6C

Solution NaCl

Chloride concentration 1500 ppm

Test duration 672 8 h

Stress ratio (% of Rp 0.2

) 100%

Relaxation time before stress applications1) 0 2 days

Relaxation time before test start2) 04 h

1) The time difference between preliminary bending and application of stress.

2) The time difference between stress application and test start.

Experimental parameters for the Wick test Table 5

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Results and discussion

Concentrated calcium chloride

Table 7 gives a summary of the results from the calcium chloride test. None of the duplex

(S32101, S32304 and S32205) U-bend specimens showed any evidence of stress corrosioncracking, neither in the parallel nor in the transverse direction after an exposure time

of 500 hours. On the S32101 and S32205 materials there were a few cases of pitting

corrosion on the stressed surface. All duplex grades exhibited corrosion attacks on the

ground edges of the specimens. The most severe case of edge attack was found on S32101

and the least severe on S32205. For the S30400 grade, the first cracks were visible after

less than 48 hours of exposure. The test was cut short after 96 hours as the material then

showed severe stress corrosion cracks on all specimens. Five of the specimens were cracked

through the cross section of the U-bends, whereas the sixth specimen had several large

cracks across the surface.

Specimens U-bend

Surface finish As recived

Temperature 50C

Solution MgCl2 CaCl2

Chloride concentration 340 g/l 380 g/l

Relative humidity 31 1 % 17 1 %

Test duration 4 and 22 weeks

Experimental parameters chloride deposits Table 6

After exposure for 500 hours, none of the duplex 4-PB specimens showed any signs of

stress corrosion cracks. All of the duplex grades exhibited edge attacks on the ground

edges of the specimens. Most severe was the edge attack on grade S32304 and least severe

on grade S32750. The test of grade S30400 was cut short after 340 hours and stress

corrosion cracks were found on all specimens, stressed to both 60 and 90% of the yield

stress, when they were examined in a light optical microscope. The cracks were extended

across the thickness of the specimen and were generally found in the area around the two

inner supports.

Concentrated magnesium chloride

The results from testing in boiling 45% MgCl2solution are summarised in Table 8.

There were no signs of pitting attack on the specimens after exposure. However, the

surface appearance was generally greyish and dull except for grade S32750 that was still

Summary of test results for concentrated calcium chloride Table 7

Number of specimens

Exposure U-bend 4-PB

Material time Failed due Failed due

UNS No. [h] Tested to SCC Tested to SCC

S30400 96 6 6

340 4 4

S32101 500 6 0 2 0

S32304 500 6 0 2 0

S32205 500 6 0 2 0

S32750 500 2 0

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quite shiny. While all specimens of S30400, S32205 and S32750 were cracked through

the specimen thickness after exposure for 24 hours, two of the S32101 specimens and

one of the S32304 specimens showed no evidence of stress corrosion cracks when the

surface was examined. However, after grinding and polishing cross sections of the speci-

mens, cracks were detected in all specimens. Thus, all specimens had failed due to stress

corrosion cracking in boiling magnesium chloride. Cross sections of all grades werefurther investigated by SEM and Figures 14 illustrate the differences in crack size and

morphology of the duplex grades.

Figure 1 shows that S32101 has cracks extending to around 0.7 mm into the cross section

and the cracks are wide, discontinuous and exhibited minor branching. Grades S32304

(Figure 2) and S32205 (Figure 3) both have cracks extending about 1 mm into the material

while the crack in grade S32304 is less branched than grade S32205. S32750 has narrow

and branched cracks that cut across the whole specimen thickness (1.0 mm) of the specimens.

When the crack reaches the specimen centre, the cracks extend parallel to the rolling

direction (Figure 4).

The wide appearance of the cracks in grade S32101 suggests that corrosion of thecrack walls is taking place. Corrosion of the crack walls could also account for the less

branched appearance of the cracks in S32101. Andersen et. al. showed that selective

dissolution of the ferrite phase occurred in S31803 when testing the SCC susceptibility

under evaporative conditions [15]. In this study, it was difficult to detect whether one

phase has been selectively dissolved and it appears that both phases have been subjected

to corrosion in this aggressive environment. The severity of the attack on the crack walls

makes it difficult to distinguish the original crack path in S32101.

Higher magnification reveals that the crack path is mainly transgranular in both ferrite

and austenite (Figures 1 4) in the duplex grades. However, there are tendencies that

the crack prefers a transgranular propagation mode in the austenitic and in the interface

Summary of test results for concentrated magnesium chloride Table 8

Exposure Number of specimens

Material time Failed due

UNS No. [h] Tested to SCC

S30400 24 3 3

S32101 24 3 3

S32304 24 3 3

S32205 24 3 3

Fig. 1 Backscattered Electron Micrographs of representative cracks in S32101, 45% MgCl2155C after 24 hours.

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between the ferrite and austenite phase. This gives rise to the staircase path that is particularly

visible in S32205 (Figure 3).

The materials are tested under extremely severe conditions in this test and it is not veryrealistic when compared to normal operating environments. Nevertheless, the magnesium

chloride test has continued being used because of its simplicity.

Fig. 2 Backscattered Electron Micrographs of representative cracks in S32304, 45% MgCl2155C after 24 hours.

Fig. 3 Backscattered electron micrographs of representative cracks in S32205, 45% MgCl2155C after 24 hours.

Fig. 4 Backscattered electron micrographs of representative cracks in S32750, 45% MgCl2155C after 24 hours

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Wick test

After removal of salt deposits and corrosion products, visual inspection revealed stress

corrosion cracks in the austenitic material S30400. Discoloration of the specimens

indicates that some general corrosion has occurred underneath the salt deposits during

exposure. Cross sections were cut from selected specimens and ground and polished

for metallurgical examination. The examination by optical light microscopy did notreveal any cracks in the duplex specimens. A summary of the results for the wick test

is tabulated in Table 9.

Previously, Andersen et. al. [15] performed wick test on stainless steel grades

S30400, S32304 and S31803 (S32205). The results are shown in Table 10 and shows

that S30400 failed due to SCC while none of the S32304 specimens failed. Regarding

S31803 (S32205) one out of four specimens failed due to SCC. Thus, Andersens results

are in agreement with the results presented in this study.

Chloride deposits

A summary of the results after exposure with chloride deposits at 50C and at thedeliquescence point is presented in Table 11.

Stress corrosion cracks were found on all specimens of stainless steel grade S30400. Specimensexposed for 22 weeks were cracked completely and the crack depth was over 1 mm on

specimens exposed for 4 weeks. The first cracks were observed as early as after 7 days

of exposure. Specimens with MgCl2spots had cracks in each of the six droplet zones

and few pits were found on the surface. Further examination of the crack morphology

showed that the cracks were branched and transgranular.

Summary of test results for

the Wick test Table 9

Number of specimens

Material Failed due

UNS No. Tested to SCC

S30400 2 2

S32101 6 0

S32304 2 0

S32205 2 0

Summary of test results for

the Wick test from Andersen et. al. [15] Table 10

Number of specimens

Material Failed due

UNS No. Tested to SCC

S30400 3 3

S32304 4 0

S31803 4 1

Number of specimens

Exposure MgCl2 CaCl

2

Material time Failed due Failed due

UNS No. [weeks] Tested to SCC Tested to SCC

S30400 4 1 1 1 1

22 2 2 2 2

S32101 4 1 0 1 0

22 2 0 2 0

S32304 4 1 0 1 0

22 2 0 2 0

S32205 4 1 0 1 0

22 2 0 2 0

S32750 4 1 0 1 0

22 2 0 2 0

Summary of test results for chloride deposits Table 11

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Pitting was observed on all specimens of lean duplex grade S32101 after exposure. The

pitting density was usually high and in some cases the entire surface was covered with

pits. The pits were small and often elongated in perpendicular direction. These pits could

be interpreted as cracks initiating from the top view. However, metallographic examination

did not confirm the presence of any cracks and only shallow pits were identified. The pit

depth after 4 weeks of exposure was typically in the order of 10 mm. As shown in Figure 5,the ferritic phase was the more continuous in the alloy and it is possible that although

SCC was initiated in the austenitic phase, cracks were subsequently blocked by the ferrite

phase. Etched areas were also found on the surface of S32101. MgCl2seemed to be

slightly more aggressive than CaCl2for this grade.

Duplex stainless steel grades S32304, S32205 and S32750

were all corroded in a similar manner. All specimens of these

grades showed etched areas on the surface and in some places

this superficial attack was deeper and had the character of

pitting. Metallographic examination revealed that these

etched areas were places of selective corrosion attack (Figure

6). However, the corrosion was generally superficial and the

extent of corrosion did not vary significantly for specimens

exposed for 4 and 22 days. Specimens with MgCl2drops

were slightly more corroded than those of with CaCl2drops,

and this difference was more pronounced for the lower

alloyed duplex grade S32304.

Fig. 5 Pit morphology of grade S32101 exposed with MgCl2(left) and CaCl2(right) deposits for 4 weeks

(the ferritic phase appears as brighter contrast and is indicated by arrows).

Fig. 6 Selective attack on grade S32304 exposed with

MgCl2deposits for 4 weeks.

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Conclusion

In this study, the stress corrosion cracking properties of lean duplex stainless steel UNS

S32101 have been investigated under constant strain loading. Both evaporative and

immersion test methods have been used. The following can be concluded regarding the

stress corrosion cracking resistance of UNS S32101:

In concentrated (40%) calcium chloride solution UNS S32101 did not suffer stresscorrosion cracking when stressed by U-bend or four-point bend loads. None of

the duplex grades were susceptible to stress corrosion cracking while UNS S30400

cracked well before the test ended.

In concentrated (45%) magnesium chloride solution all the materials investigated

failed due to stress corrosion cracking. The crack morphology of UNS S32101 suggests

that corrosion takes place inside the crack giving it a less branched appearance than

in grades UNS S32205 and UNS S32750.

In the wick test UNS S32101 was not susceptible to stress corrosion cracking and

was comparable to the other duplex grades while grade UNS S30400 failed due to

stress corrosion cracking.

Exposed to chloride deposits at 50C and relative humidity at the deliquescence point

none of the duplex grades suffered from stress corrosion cracking within 22 weeks

while grade UNS S30400 cracked within 4 weeks of exposure. All grades exhibited

pitting and selective attack of the austenitic phase was found on duplex grades

UNS S32304, UNS S32205 and UNS S32750. The aggressiveness of calcium

chloride and magnesium chloride deposits were found to be comparable.

Thus, the chloride stress corrosion cracking properties of UNS S32101 was shown to be

far superior to that of austenitic grade UNS S30400. UNS S32101 showed behaviour

similar to the duplex steel grades. With the test methods used, it was not possible to

obtain an individual ranking of the different duplex grades regarding their resistance to

stress corrosion cracking.

References

[1] Johansson P., Liljas M., A New Lean Duplex Stainless Steel for Construction

Purposes, 4thEuropean Stainless Steel Science and Market Congress, p. 153157.

(Paris, France: ATS, 2002)

[2] Bergquist A., Iversen A., Qvarfort R., Corrosion Properties of UNS S32101

A New Duplex Stainless Steel With Low Nickel Content Tested For Use As

Reinforcement in Concrete. CORROSION/2005, paper no. 05260.

(San Diego, CA: NACE , 2005)

[3] Benson M., Applications Utilizing the Adventageous Properties of LDX 2101

(EN 1.4162, UNS S32101), Stainless Steel World 2005, p. 171176.

(Maastricht, The Netherlands)

[4] NITRONIC 19D Stainless Steel, Product Data Bulletin, AK Steel.

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2003TM (S32003) Welds, Stainless Steel World 2005, p. 168 170.

(Maastricht, The Netherlands)

[6] Oldfield J.W., Todd B., Room temperature stress corrosion cracking of stainless

steels in indoor swimming pool atmospheres, British Corrosion Journal 26,

No. 3, p. 173 182, 1991.

[7] Fielder J.W., Lee B.V., Dulieu D., Wilkinson J., The corrosion of stainless steels

in swimming pools, Proc. Applications of Stainless Steel 92, Stockholm, Sweden,

June 911, Vol. 2, p. 762772, 1992.

[8] Faller M., Richner P., Material selection of safety-relevant components in indoor

swimming pools, Materials and Corrosion 54, No. 5, p. 331338, 2003.

[9] ASTM G30-97 Standard Practice for Making and Using U-Bend Stress-Corrosion

Test Specimens.

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Reproduced with permission from NACE International, Houston TX. All rights reserved.

Paper 07475 presented at CORROSION/07, Nashville, TN NACE International 2007.

[10] ASTM G39-99 Standard Practice for Preparation and Use of Bent-beam

Stress-Corrosion test Specimens.

[11] ASTM G36-94 Standard Practice Evaluating Stress-Corrosion-Cracking

Resistance of Metals and Alloys in a Boiling Magnesium Chloride Solution.

[12] Dana A.W., Delong W.B., Corrosion, Vol. 12, No. 7, July 1956, pp. 1920.

[13] ASTM C692-71. Standard Method for Evaluating Stress Corrosion Effect on

Wicking Type Thermal Insulation on Stainless Steels.

[14] Shoji S., Ohnaka N., Effects of Relative Humidity and Kinds of Chlorides on

Atmospheric Stress Corrosion Cracking of Stainless Steel at Room Temperature,

Boshoku Gijutsu 38, p. 9297, 1989.

[15] Andersen H., Arnvig P., Wasielewska W., Wegrelius L., Wolfe C.: SCC of Stainless

Steel under Evaporative Conditions, Corrosion 98, p. 251/1251/17.

(San Diego, CA: NACE 1998)

13acom |2 - 2007


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