INTRODUCTION

The 200 series of stainless steels was developedin the early 1930’s. Although the first chemicalanalysis investigated where of 205 kind (Nicontent close to 1% and austenitic phasestabilized due to simultaneously high Mn andNitrogen additions - see Table I - ), the firstgrades which received the AISI label in the mid-fifties were the 201 and 202 grades ( Ni contentaround 4 to 6 % and nitrogen additions lowerthan .25 % ).They became more popular duringthe Korean War to conserve the nickel. In thattime due to Nickel shortage, nickel uses weremainly restricted to military applications. TheTenelon grade / AISI 214 grade with less than2% Ni and about .35%N were produced at theend of the fifties. The Mn-austenitic gradescontaining Mo to improve the corrosionresistance properties appeared in the mid-sixties both in US and Europe. SimultaneouslyMn + Cu containing grades were developedwhich made it possible to produce 4 / 6 %Niaustenitic grades (AISI 211 and 203) havingrelatively low nitrogen content (< 0.06 %).Equivalent drawing properties than 304 could beachieved . The grades started to be popular in theearly 70’s due to new Ni shortage phenomenon’s.With the new AOD technology nitrogen additionsin the 200 series were made easier and on amore cost-effective way. Expensive nitridedferrochromium, ferromanganese or eventually

nitrides manganese were replaced by blowinggaseous nitrogen in the molten steel in the AODvessel. Once again nickel shortage ended andwith high level of availability Ni price wasreduced. For more than 30 years the 304 gradestarted to be the standard of the stainless steelfamily. His well know properties whenconsidering corrosion resistance, formabilityand weldability made it possible to achieve aaverage yearly growth of 6%. 200 series stillhad in the eighties and nineties marginalapplications where there attractive properties –combination of strength (30% higher than 304)and high ductility - are used. Furthermore somenew grades with very high nitrogen levels ( 0.5to 1% and more) were developed by a new ESRprocess. The small size ingots are obtained bymelting under high nitrogen pressure. Thosealloys are considered for marginal applications.

Indian government, for economical reasons,decided to limit the Ni importations. As a resultlocal producers, including Jindal, started toproduce huge quantities of so-called 200 seriesgrades for local uses. Specific grades weredeveloped. This includes 4 and 1 %Ni grades withand without Copper. Most of the production wasrestricted to local applications. A real knowledgeconcerning their in service properties wasdeveloped so that material selection experiencewas build up. With the new century, a new periodof high volatility of nickel price started.

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THE NEW 200-SERIES : AN ALTERNATIVE ANSWER TO NI. SURCHARGE ? DREAM OR NIGHTMARE?

Dr. Jacques CHARLES.

U&A, ARCELOR. Immeuble PACIFIC-11,13 cours Valmy F-92070 La Defense cedex. jacques.charles@arcelor.com

AbstractFor more than 50 years manganese additions have been considered to replace nickel in austeniticstainless steels. As a result, reductions in alloy surcharge particularly when nickel price are jumpingcan be expected. This has result in the development of the so-called 200 series. The grades areknow to have complementary nitrogen additions in order to further stabilize the austenitic phase.Copper additions have also been successfully considered in order to provide a stable austenite. Withcopper additions, nitrogen additions can be reduced providing softer manganese austenitic grades.The grades until end of last century, with a few exceptions like in India, had only very limitedapplications and where selected mainly for their combination of high strength and ductility ( possiblestrengthening by very high nitrogen additions and / or by cold deformations ) More recently hugeamount of 200 series have been produced in Asia. The grades have modified chemical compositions– low chromium additions, extra low nickel additions, ... – and high residual elements like sulfur whichare know to have detrimental effects on localized corrosion resistance ( pitting ). The paper willpresent a review of the 200 – series grades and point out the specificities of the new developedgrades. Chemical compositions, mechanical properties, corrosion resistance properties andapplications are presented. The lack of international codes , references for those grades are pointedout. Finally warnings are addressed for improper uses of those grades which might lead on end-users.

Simultaneously China became a major consumerof stainless steel. Part of the tonnage wasproduced locally. The continuous pressure toobtain low cost grades resulted in thedevelopment of cheaper grades with always lessalloying elements like nickel and even lesschromium. Due to low cost manufacturing routesor less performing facilities grades with veryhigh sulfur and carbon containing grades weresold on the market. Those productions from amarginal production level moved to hundred ofthousands tons production.

Now about two millions of so-called 200 seriesgrades are consumed in Asia – mainly China(Figure 1). Some of the grades are not covered byinternational codes or specifications. Someother are in the international standards or atleast are manufactured with up to dateequipments with a control of the residualelements like sulfur and carbon which have aclear impact on the in service properties of thegrades. Several new austenitic manganesegrades were developed recently by majorstainless steel producers . They are designed forspecific applications. The purpose of this paperis to present mechanical properties, corrosionresistance properties and manufacturingproperties of the new developed grades (TableII). Their properties are also compared to thoseof the more classical 200 series.

PHASE DIADRAMS / MECHANICALPROPERTIES

Figures 2 and 3 provide some data concerningthe austenitic phase stability. It is observed thatlower nickel, even with high manganesecontents, reduces the solubility limit ofchromium in the austenitic phase. Hopefully themanganese additions increase the solubility ofthe nitrogen in the austenitic phase which , bythe way, has a powerful effect on austenitic

phase stability and make it possible to increasesomewhat the chromium content of the low Ni.grades.

Figure 1. Stainless Steel Crude Production bycategories in %.

The experimental data provided are issued fromtests performed on industrial plates collected indifferent countries. Chemical analysis arepresented Table II. Figure 4 presents thedifferent grades plotted versus

Mn. and Ni. contents. Most of the 200-seriesgrades are plotted on a line joining 10%Ni and16%Mn.

Almost complete replacement of Nickel ispossible by combined Mn. and Nitrogen + Carbonadditions. Lower nickel addition requires moremanganese and nitrogen to stabilize theaustenitic phase. To conclude, austeniticmanganese stainless steels with a nickel contentof 1% or less requires about 10 %Mn with andmore than 0.25% N. to stabilize the austeniticphase. The strength of the grades due to high N.contents is about 30% higher than a 304 grade.Higher draw ability properties may be obtainedwith lower nitrogen additions but than chromiumcontent must be reduced down to 14-15% inorder to preserve the austenitic phase.

2Table I. Chemical analysis of different 200 series grades.

Type Standard Cr Ni Mn N C S OTHERS201 S20100 16.0 - 18.0 3.5 - 5.5 5.5 - 7.5 0.25MAX 0.15MAX 0.030MAX -201LN S20153 16.0 - 17.5 4.0 - 5.0 6.4 - 7.5 0.10 - 0.25 0.03MAX 0.015MAX Cu 1.0MAX 202 S20200 17.0 - 19.0 4.0 - 6.0 7.5 - 10.0 0.25MAX 0.15MAX 0.030MAX -204L S20400 15.0 - 17.0 1.5 - 3.0 7.0 - 9.0 0.15 - 0.3 0.03MAX 0.030MAX

S20430 15.5 - 17.5 1.5 - 3.5 6.5 - 9.0 0.05 - 0.25 0.15MAX 0.030MAX Cu 2.0 - 4.0205 S20500 15.5 - 17.5 1.5 - 3.5 14.0 - 15.5 0.32 - 40 0.12 - 0.25 0.030MAX214 S21400 17.0 - 18.5 1.0MAX 14.0 - 16.0 0.35MIN 0.12MAX 0.030MAX216 S21600 17.5 - 22 5.0 - 7.0 7.5 - 9.0 0.25 - 0.5 0.08MAX 0.030MAX Mo 2.0 - 3.0

S24000 17.0 - 19 2.25 - 3.75 11.5 - 14.5 0.2 - 0.4 0.08MAX 0.030MAXS32001 19.5 - 21.5 1.0 - 3.0 4.0 - 6.0 0.05 - 0.17 0.03MAX 0.030MAX Cu 1.0MAX

EN 1.4371 16.0 - 17.0 3.5 - 5.5 6.0 - 8.0 0.15 - 0.20 0.03MAX 0.015MAX -EN 1.4372 16.0 - 18.0 3.5 - 5.5 5.5 - 7.5 0.05 - 0.25 0.15MAX 0.015MAXEN 1.4373 17.0 - 19.0 4.0 - 6.0 7.5 - 10.5 0.05 - 0.25 0.15MAX 0.030MAX

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Table II. Chemical analysis of different 200 series industrial plates and sheets.

Country Cie Usual name UNS Cr Ni Mn Cu C N S (ppm) Rp0.2 Rm MdEurope U&A 16-4Mn S20100 16,3 4,1 6,5 0,09 0,16 40 400 770 39,99

U&A 16-7Mn † S20400 16 1,6 7,5 2,9 0,05 0,19 < 10 390 710 28,92KTN H400 18 3,8 6,8 0,035 0,16 7 450 770 48,35

USA Nitronic 30 S20400 16 2,5 8,5 0,02 0,17 390 830 101,82Nitronic 19D * S32001 20 1,6 5 0,5 0,02 0,13 500 850 105,8

Allegheny 219 S21904? 21 6 9 0,03 0,25 460 780 -113,86S.Amer. Acesita P201A - 15,2 1,1 9 1,7 0,1 0,1 <10 370 870 95,36

Acesita P202A - 15,1 4 7,2 1,6 0,06 0,05 <10 310 730 71,87Acesita P300A † S20400 16,1 1,5 7,4 2,9 0,05 0,18 3 370 745 35,89

Asia Jindal J1 - 15 4 7 1,6 0,06 0,05 60 300 700 74,88Jindal JI - 16,1 4 7,1 1,7 0,06 0,07 31 46,85Jindal J4 - 15,5 1 10 1,6 0,09 0,14 60 470 820 74,99Jindal J4 - 15,9 1 9,7 1,6 0,1 0,15 82 62,73NTK D10 - 17,5 4,8 3,7 2,8 0,06 0,15 10 355 675 -36,51

Posco 204M S20400 16 2,5 8 0,03 0,25 480 840 64,34Posco 202 2D - 15,5 4,8 7,4 1,2 0,06 0,07 10 43,91Posco 204 2D - 14,4 1,04 10,3 1,2 0,05 0,16 5 107,28CHX1 - - 15 1,1 9,6 1,7 0,1 0,14 123 74,7CHX2 - - 11,3 1,1 12,8 0,08 0,13 0,045 60 176,16

Figure 2. Effect of Cr and Mn on nitrogen solubility.

Figure 3. Austenite stability at 1075 °C (Franks)

Figure 4. Ni and Mn contents in stainless steelsalloys

Figure 5. Mechanical properties of several S.S.

Combining high manganese, high nitrogen andchromium additions, make it possible to design afamily of grades having very high mechanicalproperties ( Figure 5 : yield strength ) . Thosegrades have limited draw ability properties.

Copper additions have been considered for theiraustenite forming properties. Those coppercontaining 200 series can be designed for anequivalent level of nickel, manganese andchromium with lower nitrogen additions. Thegrades are softer and deep drawing properties,without needing high power equipments, can beachieved. An alternative solution for the copperadditions, instead of decreasing the nitrogenadditions, is to make a further decrease of thenickel content – from 4 to 1 % Ni. ( substitutionof nickel by copper, an austenite formingelement ).

DEFORMATION AND PHASESTABILITY

Isothermal tensile tests were performed on anInstron 8082 machine at room temperature and60°C. The strain rate was 1% per min. Automaticmeasuring system of strain ( ASAME) was used.The sigma-meter was used to quantify themagnetism. Figure 6 presents the % ofmartensite versus the strain %. Testingtemperature is very sensitive since the Mdtemperature is close to room temperature. J1and J4 grades tested had a more stableaustenite. This can be correlated to their relativehigher content in nitrogen compared to theequivalent grades.

Figure 6. Volume fraction of martensite alphaversus % of deformation. Tests performed at20°C.

All grades were free of martensite in the asreceived conditions and tested samples at 60°Cexhibited very few martensite after 40%

elongation even for the grades having hugetransformation at room temperature (figure 7).Although several Md formula are available, noone is really designed for such compositions.Indicative Md temperatures are provided table II( Nohara kind formula ).

Figure 7. Volume fraction of martensite alphaversus % of deformation. Tests performed at60°C.

The very sensitive effect of temperature explainwhy testing conditions may greatly modify themeasured martensite level in the grades.Heating effects due to deformation in nonisothermal conditions may reduce significantlythe amount of transformed austenite. No epsilonmartensite was detected by X-ray investigations.

To conclude 200 series grades are sensitive tomartensitic transformations particularly whennitrogen and or carbon contents are reduced inorder to reduce the strength of the grades. As aresult higher draw ability properties are oftencorrelated to unstable microstructures .

DEEP DRAWING AND DELAYEDCRACKING

Figure 8 presents the risk of delayed crackingversus deep drawing ratio for several stainlesssteels. It is observed that unless the austenitic304 grade is know to undergo a partial alphamartensitic transformation during deformation,the grade in those conditions do not presentcold cracking phenomenon’s. On the opposite, 4% Ni 200 series grades and, even more, the1%Ni grade are sensitive to cold crackingphenomenons. To conclude, the 1%Ni grade evenwith copper additions is very sensitive to coldcracking phenomenon’s. When necessary postheat treatment must be considered in order toavoid such undesirable phenomenon.

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Figure 8. Delayed cracking tests data.

CORROSION RESISTANCE PROPERTIES

Figures 9 presents current density datarecorded on several stainless steels (ferritic,manganese austenitic and nickel austeniticgrades ) being immersed in sulfuric 2M acidsolution at 23°C. Corrosion resistance is directlylinked to the chromium content. The currentdensity data are plotted on a logarithmic scale.This underlines the powerful effects ofchromium content on the corrosion resistance ofstainless steels in acidic conditions.

High corrosion rates

Figure 9. Current density data measured onferritic 430, 441 and austenitic grades in a 2MH2SO4 solution at 23°C.

Figures 10 to 12 presents some data concerningthe resistance to pitting for several stainlesssteels. Data are recorded by polarization curves.Higher voltage for pit initiation means betterresistance to pitting.

Figure 10. Pitting potential of several stainlesssteels performed in a NaCl 2M solution at 23°C.

It is clearly observed that pitting corrosionresistance is directly related to the chromiumcontent of the grades. Higher sulfur contentshave a negative effect on pitting corrosionresistance (Figure 11). This is a well knowphenomenon since sulfide inclusions arepreferential sites to initiate pits. The gradesnewly manufactured particularly in China havethe worst pitting corrosion resistance and in nocase may perform as an austenitic 304 grade. Figure 12 presents data performed on a multipitcell. About 20 samples per plate have beentested. It is confirmed that the new developedgrades of 4 and 1 Ni. families are more sensitiveto pitting than a 304 grade even if the testingconditions are not severe.

Figure 11. Pitting potential of 1Ni and 4 Ni manga-nese containing austenitic stainless steels. Testsperformed in NaCl 2M solution at 23°C.

When increasing the temperature from room to50°C we observe that pitting corrosion is asexpected reduced but that the 1% Ni grades aremore affected than the 4%Ni grades (figure 13 ).

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Figure 12. Pitting corrosion resistance of severalstainless steel grades. ( 20 samples per platetested) .

Figure 13. Effect of temperature on the pittingcorrosion resistance. Tests performed in NaCl2M sol.

Crevice corrosion resistance of the differentgrades has been also investigated by means ofpolarization curves. Tests were performed in a2M NaCl solution at various Ph in order toinvestigate the depassivation pH – pH underwhich the grade is no more passive – as well asthe kinetics of corrosion of the different gradesunder the depassivation potential. Those dataprovide us useful information concerning theeffects of alloying elements and structure on thecrevice corrosion resistance. Data are providedfigures 14 and 15.

It is observed once again that the 4 Ni and 1Nigrades do not perform like a 304 grade. The 1 Niparticularly with low chromium and high sulfurcontent are the worth. The grade are reallysubject to crevice corrosion in relatively nonsevere conditions. It is obvious that the use ofsuch grades in acidic conditions likeencountered In process industry is prohibited.The alloys are also not to be considered for usesin sea water or sea shore conditions.

Complementary salt spray tests have beenconducted on 304, 4 Ni, 1 Ni and 439 ferriticgrades. The two austenitic 4 Ni and 1 Ni exhibitedcorrosion marks. Corrosion was particularly

spectacular on the edges. Clearly the grades donot perform equally to 304 austenitic grades.The grades are not suitable for sea shoreapplications.

Figure 14. Typical depassivation pH of StainlessSteel grades. Data obtained by means of polari-zations curves in 2M NaCl solution at several pH.

Figure 15. Crevice corrosion propagation rate.Tests performed in a 2M NaCl solution at pH of1.5.

Inter granular corrosion tests have also beenperformed on several plates issued from theChinese market. Strauss-test and red. Strauss-test (35°C) testing conditions have beenselected. TIG welds and spot welds structureshave been considered. It is clearly observed thatin those conditions grades having more than0.09 carbon present in both base and welddeposit areas cracks. When welding such gradeswith high carbon level, at least for thicknesses

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higher than 2 mm., PWHT must be considered toobtain satisfactory inter granular corrosionresistance properties.

304 4 Ni 1 Ni 439

Figure 16. Salt spray tests performed during 575Hours on several stainless steels.

Figure 17. Inter granular corrosion resistancetest results performed on 1 and 4 Ni gradesissued from the Chinese market.

DISCUSSION

The partial or almost total substitution of Ni bycombined Mn and nitrogen additions in thestainless steel grades makes it possible toproduce austenitic grades with lower Ni.content. Furthermore, manganese additionshave a beneficial effect on the increase of thenitrogen solubility in the austenitic structure.This has lead, for now many years, to thedevelopment of high strength austenitic grades.Nowadays more than 1 % N is considered. Hotand cold rolling are more difficult due to thestrengthening effect of nitrogen additions. Mostof those grades concern a very marginaltonnage and are dedicated to specificapplications.

Some thousands of tons of grades equivalent to201, 202 or 205 grades with lower nitrogenlevels ( 0.12/0.25) are produced by big players inthe stainless steel business. This concerns US,Europe and Asia. The classical production route– electrical furnace, AOD, continuous casting,

hot rolling with a steckel mill or tender mill pluscold rolling on ZS – is selected with somespecificities ( capture of the fumes, … morepower needed for rolling, specific conditions forpickling… ) which explain that some extraproduction costs must be considered. Their mainadvantage is an increase of the mechanicalproperties of nearly 30 % which allows thedesigners to cut weight. The grades had more orless successes taking in to account the nickelprice. Once again the grades are well definedand used for many years in specific applicationslike transport industry.

India, for many decades, decided to restrictsharply the imports of nickel metal to saveforeign currency and by the way develop internalmining resources. This resulted in localproduction of Mn austenitic grades for the Indianmarket. 304 grades were selected only when inservice applications including safety aspectsrequested their use. With time and experiencesseveral applications could be considered aspotential areas for the use of Mn containingaustenitic grades. ( non critical applicationswhen considering corrosion resistance, internalbuilding and architecture stainless steel uses,household applications..).In the nineties Indiastarted to produce huge quantities of the socalled 4 and 1 Ni grades with copper - anotheraustenite stabilizing element - which made itpossible to achieve a further decrease of thecostly nickel or with the same Ni level, reducethe nitrogen content. This latest possibilitymade it possible to develop grades withimproved drawing properties. Some grades werealso developed in order to reduce the costlyalloying elements. Grades with 1 Ni and even lessstarted to be more and more popular since withthe new century since nickel price jumped tonew records. The need of low cost austeniticgrades equivalent to 304 to fill up the growingdemand in Asia started to be a strong drivingforce for new material selection. Deep drawingproperties were requested as well as “ soft “grades because the manufacturing equipmentswere designed for the 304 grades. The 1 Ni gradewith copper additions started to be the bestcandidate. Unfortunately has earlier presentedthe chromium content of 18% is not compatiblewith such low nickel grade without formingferrite. Chromium content was thus reduceddown to 16 % … 15% and now even for someproducers 14 %... 13 %! Clearly those gradeshave not equivalent corrosion resistance than304 grades! The chromium content is the keyfactor for the corrosion resistance. Furthermoremanganese and to some respect copper mayhave specific detrimental effects. Repassivation

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properties are lowered and particularly inacidified conditions which are developing underdeposit corroded areas or in crevices their rateof dissolution is 10 to 100 time higher than thatof the 304 grades. The 1 Ni grades are also knowto be much more sensitive to stress corrosioncracking. The grades particularly with lownitrogen content have an unstable austenitewhich transforms in to alpha martensite whendeformed. In such conditions the grades arevery sensitive to cold cracking phenomenons.Cracks easily develop. And on top of all thisdetrimental aspects, hundred of thousands oftons are produced in China with poorequipments. Chemistry is not preciselycontrolled, carbon level exceed the acceptableranges, sulfur contents reach 80 .. even morethan 100 ppm. … This affect the corrosionresistance properties of the grades! Theirproperties are much closer to than of a 409grade than a 304!!!!

Development takes place at an extraordinaryspeed and production has rose to more than amillion of tons. Most of the grades do not fulfillinternational standards, traceability do not existand grades are provided to distributors with“black” marketing : cheaper and equivalent to304 !!! Such development is a real nightmare forour stainless steel industry since it may ruin theimage of confidence of our products. Somefailures have already occurred ( petrochemicalplant ) and many outdoor applications presentsan unusual rusty appearance for stainless steel!More will occurred since part of that productionwill be included in final products for export. Setof 4 pans issued from China and sold in Europepresented 4 different chemistries : from 301 to 4and 1 Ni grades! More will have to be done intraceability and international rules! In thefuture, recycling the scraps will be complicatedand scrap dealers will have to certify the real Nicontent of the grades. Copper when used as astandard alloying element in 4Ni. and 1Ni. gradeswill pollute the standard 304 chemistry….

Definitively we need to stay professional in ourbusiness and keep on the safety area. Traceabilitymust be a general goal and teaching all the actors– producers, suppliers, layers, transformators, endusers...- concerning the real properties of thedifferent stainless steel grades a need.

CONCLUSION

The paper has presented the so-called Mn austeniticstainless steels of which Ni is partially replaced – upto 90% - by combined Mn and nitrogen additions.The main following conclusions can be addressed :

- Austenitic stainless steels with lower Nicontents – down to 1Ni max – can be producedthanks to combined Mn. and N. additions .

- Several grades were developed for many years,at a marginal scale, with success for theircombined high strength and ductilityproperties. This include the “classical” 200-serie grades as well as extra high nitrogencontaining grades ( 0.5….1,2 %N ). Their usesare well controlled and their low tonnage donot affect the scrap recycling business.

- India at a “country scale” has developed a localeconomy were Mn austenitic grades play amajor role. Grades are specified for specificapplications; mainly non critical and non highlycorrosive applications. With time, learningabout their restricted uses has growth. Thegrades are not called “equivalent to 304”.

- With the new century, the booming Asian andparticularly the Chinese economies combinedwith a jump to new record of Ni prices, hasencouraged the uses of cheaper austeniticstainless steels. Hundred thousands of tons ofmainly 1 Ni but also 4 Ni grades were imported.Local producers started also to produce thegrades with low cost driven approachconducting to melt grades with lower alloyingelements – including Cr.- and no control ofresidual elements like S, C, O. Grades werecalled “ equivalent to 304 and cheaper”!

- Corrosion resistance of such grades isdrastically lower than a 304 kind material.This concerns the general, pitting, crevice,stress corrosion and inter granular corrosionresistance! They are clearly not designed forcorrosive conditions encountered in processindustry, sea shore applications and even willrust if used in water systems!

- The products will through exports of finalproducts reach all countries around the world.Since they behave not like 304 rusty andcorroded products will be observed after fewmonths when improperly used. Recycling willbe more difficult since stainless steel scrapmay be contaminated. ( Cu, Mn... ).

- Traceability and conformity to standards, codesand norms must be a common habit. Materialspecification must be written taking in toaccount the real properties of the products andin service conditions. If not , uses should beprohibited. Poor quality products should berestricted to marginal local applications if notbanished.

- Education is of first concerns! Scientific datashould be provided to all the actors in order topreserve the image of the stainless steelindustry.

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ACKNOWLEDGEMENTS

Many thanks to the team of U&A RC for makingmany of the data here presented. This includesP.O. SANTACREU, J.D. DENIS, A. MORIZOT and L.PEGUET.Thanks also to TKN R&D and particularly DrKRAUTSCHICK for the data provided withregards to the delayed cracking and intergranular corrosion.I would like also to express many tanks’ to DrSINGHAL of Jindal for the useful informationsprovided concerning the Mn. austenitic gradesproduced in India as well as his work on thehistory of the Mn austenitic grades.My acknowledgements are also addressed tomembers of the ISSF team and particularlyStaffan Malm for his continuousencouragements.

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