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ThefutureofTEMishere.TheHT7700DigitalTEMHitachiHigh-TechnologiesEuropeGmbHTel.+44(0)1628585200Tel.+49(0)21516435310eminfo@hht-eu.comwww.hht-eu.comSimple&seamlessimagingupto64mp.ThefirstTEMdesignedfromthegrounduptobefullydigital..Highsensitivitydigitalimagingatalltimes-withfully-integratedscreenandcapturecameras.Quickandeasyimagingatupto64megapixels-withHitachi'sprecisemulti-framecapturesystem.Perfectlysuitedtoelectrontomography-withHitachi'scalibration-freeandmarker-lesstiltacquisitionsystem.Thehighestcontrastandresolutioninoneinstrument-withthepatenteddual-focal-lengthobjectivelens.Flexibilityassured-optionsfor3dvisualisation,cryoimaging,EDXmicroanalysisandmoreIfyouutiliseTEMforbiomedicalresearch,pathology,neuroscience,pharmaceuticals,nanotechnology,polymersorplantsciencecontactusnowtoseehowtheHT7700cantransformyourlab.Patenteddualfocallengthobjectivelens-highcontrastmode(unstainedsciaticnerve).Patenteddualfocallengthobjectivelens-highresolutionmode(carbonnanotube)Hitachi'suniquetomographicalgorithms(leftimage)ensureprecisereconstructioncomparedtoconventionalmethods(rightimage).CIRCLE NO. 7 OR ONLINE: www.microscopy-analysis.com

site and austenite, as measured by opticalmicroscopy. Nikbakht et al. [7] showed that astabilized alloy 193 (Fe-8%Mn with 0.17%Ti,0.18%Al and 0.018%C) exhibited brittle cleav-age on ice brine quenching from 900°C, basedon clear fracture surface examination. This is inagreement with a much earlier but convincingfracture profile analysis [8] and thermody-namic calculations on alloy 193 showed thatthere is less than 0.03 ppm N in solid solution.On tempering alloy 193 for 6 min at 450°C, theDBTT rose from 27 to 125°C, giving intergran-ular failure. This indicated that embrittlementis due to segregation of Mn per se to prioraustenite grain boundaries.In the last five years, there have been manycreditable studies in related subjects. Forexample, Vaynman et al. [9] have found thatthe increase in strength in a low-carbon, Fe-Cu-based steel was derived from a large num-ber density of copper-iron-nickel-aluminum-manganese precipitates, characterized bystate-of-the-art atom-probe tomography.Sathiya et al. [10] found using cross-sectionimaging that the shape of the fusion zone,generally characterized by a few geometricalfeatures, namely bead width, bead height anddepth of penetration, depended upon a num-ber of parameters such as gas flow rate, volt-age, travel speed and wire feed rate. Recentresearch in ferrous materials in general hasbeen well reviewed in a recent book by Bernsand Theisen [11]. However, there has been lit-tle research reported on the steels studiedhere.MATERIALS AND METHODSSteelsIn the present research, two cryogenic steelswith around 20% manganese were investi-gated: Fe-19.7%Mn (VM339A) and Fe-19.7%Mn stabilized with 0.056%C, 0.19%TiBIOGRAPHYWei Sha obtained a BEngat Tsinghua University in1986. He was awarded in1992 a PhD by OxfordUniversity and in 2009 aDSc by Queen's Univer-sity Belfast. He previouslyworked at Imperial College and CambridgeUniversity. He is presently Professor of Mate-rials Science, with research interests in phasetransitions and SEM.ABSTRACTTwo manganese steels were investigated:Fe-19.7%Mn (VM339A) and Fe-19.7%Mnstabilized with 0.056%C, 0.19%Ti and0.083%Al (VM339B). The toughness ofVM339A was higher than VM339B, butVM339B had higher hardness. Temperingdoes not affect the toughness of the alloys.SEM images of the fracture surface for boththe alloys revealed ductile fractures. A fur-ther alloy with a lower manganese content,Fe-8.46%Mn-0.24%Nb-0.038%C, and thuseven lower cost than the conventional 3.5Nicryogenic steel, was tested for its impacttoughness after heat treatment at 600°C,giving promising results.KEYWORDSscanning electron microscopy, hardnessmeasurement, mechanical characterization,steel, fractureAUTHOR DETAILSProfessor Wei Sha, School of Planning, Architecture and CivilEngineering, Queen's University Belfast, Belfast BT7 1NN, UKTel: +44 28 90974017Email: w.sha@qub.ac.ukMicroscopy and Analysis25(7):15-19 (EU), 2011ANALYSISOFSTEELSINTRODUCTIONNickel raises the yield strength of iron, asfound many decades ago by Roberts andOwen [1] by measuring the strength of manyFe-Ni alloys. Nickel also lowers the ductile brit-tle transition temperature (DBTT, cleavage) ofiron, as proved by Floreen et al. [2] by measur-ing the impact properties of Fe-Ni alloys withdifferent Ni contents. Both results have beenverified in the extensive steel research that fol-lowed, so nickel is an established alloy methodof raising strength and increasing toughness. As shown by Avery and Parsons [3] withsome real examples, nickel has been widelyused in cryogenic steels, but the high cost ofnickel now demands a second thought on theactual amounts of this element required inthese steels. Oshima et al. [4] have vividly illus-trated the sharp rise of nickel price on the Lon-don Metal Exchange. Oshima et al. [4] alsoexplored the ways of nickel saving, by adetailed property comparison between lownickel stainless steels and conventional stain-less steels. Based on their findings, nickel-freehigh-manganese steels could have a combina-tion of good tensile strength and ductility andso could provide a great potential in applica-tions for structural components in industry. In recent years, numerous attempts havebeen made to improve the performance ofmanganese steels by modifying their composi-tion and by applying heat or thermomechani-cal treatments. For example, by examining themicrostructure and the performance [5] it wasconcluded that the capability of work harden-ing and impact abrasion resistance wereenhanced greatly after rolling. The cold asyn-chronous rolling technique taken was only oneway of achieving potential property improve-ment.In their classical work, Holden et al. [6]reported that 15-20%Mn steels, with around0.02% carbon, contain mostly epsilon marten-Fracture Surface, Impact Energy andHardness of Ni-Free High-Mn SteelsWei Sha,1H. H. Haji Talib,1Eric A. Wilson,2Raj Rajendran,3Savko Malinov,4Harvey R. Charlesworth,5Lee Ibbitson61. School of Planning, Architecture and Civil Engineering, Queen's University Belfast, UK. 2. Faculty of Arts, Computing, Engi-neering and Sciences, Sheffield Hallam University, UK. 3. School of Mechanical and Building Sciences, B. S. Abdur RahmanUniversity, India. 4. School of Mechanical and Aerospace Engineering, Queen's University Belfast, UK. 5. London & Scandi-navian Metallurgical Co. Ltd., UK. 6. Tata Steel Speciality, UKTable 1: Hardness (HV1) of theexperimental alloysunder various heattreatment conditions.MICROSCOPY AND ANALYSISNOVEMBER 201115Heat TreatmentVM339AVM339B850oC 1h, air cooled222±2281±12850oC 1h, water quenched (WQ)226±2288±2WQ + 450oC 0.1 h230±2299±11WQ + 450oC 1 h263±17-WQ + 450oC 10 h270±7294±9WQ + 450oC 100 h274±9-