See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/216681352Effect of cryogenic treatment on distribution ofresidual stress in case carburized En 353 steel.Mater Sci Eng AARTICLEinMATERIALS SCIENCE AND ENGINEERING A APRIL 2008Impact Factor: 2.41 DOI: 10.1016/j.msea.2007.07.035CITATIONS50DOWNLOADS446VIEWS2206 AUTHORS, INCLUDING:Bensely Albert16 PUBLICATIONS 307 CITATIONS SEE PROFILENagarajan GovindanAnna University, Chennai124 PUBLICATIONS 1,554 CITATIONS SEE PROFILEArunachalam RajaduraiAnna University, Chennai42 PUBLICATIONS 359 CITATIONS SEE PROFILEKrzysztof JunikWroclaw University of Technology3 PUBLICATIONS 65 CITATIONS SEE PROFILEAvailable from: Arunachalam RajaduraiRetrieved on: 13 August 2015Materials Science and Engineering A479 (2008) 229235Effect of cryogenic treatment on distribution of residual stressin case carburized En 353 steelA. Benselya,, S. Venkatesha, D. Mohan Lala, G. Nagarajana,A. Rajaduraib, Krzysztof JunikcaDepartment of Mechanical Engineering, College of Engineering, Anna University, Guindy, Chennai 600025, IndiabDepartment of Production Engineering, Madras Institute of Technology, Anna University, Chromepet, Chennai 600044, IndiacInstitute of Materials Science and Applied Mechanics, Department of Mechanics, Wroclaw University of Technology, PolandReceived 6 July 2006; received in revised form 14 June 2007; accepted 16 July 2007AbstractThe effect of cryogenic treatment on the distribution of residual stress in the case carburized steel (En 353) was studied using X-ray diffractiontechnique. Two types of cryogenic treatment: shallow cryogenic treatment (193 K) and deep cryogenic treatment (77 K) were adopted, as asupplement to conventional heat treatment. The amount of retained austenite in conventionally heat-treated, shallow cryogenically treated anddeep cryogenically treated samples was found to be 28%, 22% and 14%, respectively. The conventionally heat-treated, shallow cryogenicallytreated and deep cryogenically treated samples in untempered condition had a surface residual stress of 125 MPa, 115 MPa and 235 MPa,respectively. After tempering the conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples had a surfaceresidual stress of 150 MPa, 80 MPa and 80 MPa, respectively. A comparative study of the three treatments revealed that there was an increasein the compressive residual stress in steel that was subjected to cryogenic treatment prior to tempering. The experimental investigation revealedthat deep cryogenically treated steel when subjected to tempering has undergone a reduction in compressive residual stress. Such stress relievingbehaviour was mainly due to the increased precipitation of ne carbides in specimens subjected to DCT with tempering. 2007 Elsevier B.V. All rights reserved.Keywords: Case carburized steel; Cryogenic treatment; Grinding; Residual stress; Retained austenite1. IntroductionScientists and engineers have been successful in improvingtheimpact andfatiguepropertiesofmetalsbyintentionallyintroducing residual stresses into the surface of these materi-als. Residual stress exists in an elastic solid body in the absenceof, or in addition to, the stresses caused by virtue of load ortemperature or both. Such stresses can arise from deformationduring cold working, in welding from weld metal shrinkage,and in changes in volume due to thermal expansion. In recentyears, there has been a considerable interest in the properties anddevelopment of compressive residual stress. Knowledge of thenature of residual stresses is of paramount importance since theycan lead to creep failure, fatigue and stress corrosion cracking insensitive materials. Mack Alder and Olsson [1] have observedCorresponding author. Tel.: +91 44 22203262.E-mail address: benzlee5@yahoo.com (A. Bensely).that after case hardening, the gear tooth would experience com-pressive residual stresses, which are benecial in maintainingan appreciable endurance limit. But these benecial stresses arecounter acted by detrimental tensile residual stresses in the core.The explanation of this phenomenon is based on the uneven vol-umetric expansion in the core and at the surface layer duringphase transformation. Hence, it is an important consideration inthe heat treatment of steel.Various methods are used to improve the behaviour of steel.Carburizing is one of the prevalent methods used for this pur-pose. It is a thermo chemical diffusion process used to produce ahard wear resistant case. Due to carburization, the percentage ofcarbon in the case will increase to the carbon potential applied.Carburizing is benecial to the component but the increase incarbon content leads to retention of austenite after hardening,which is not desirable. In some steels, those with higher carboncontent and alloy steels, the martensite nish temperature (Mf) isbelow 273 K, which means that at the end of the heat treatment,there is as much as 515% of austenite remaining [2].0921-5093/$ see front matter 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.msea.2007.07.035230 A. Bensely et al. / Materials Science and Engineering A479 (2008) 229235The amount of retained austenite exhibits signicant effectson the magnitude of compressive stresses formed and ultimately,on dimensional stability. Some of the factors affecting retainedaustenite formation include chemical composition, quenchingtemperature, quenchingcoolingrates, austenitizingtemperature,grain size and tempering. The effects of retained austenite on theproperties of steel includes decrease of tensile strength and yieldstrength, reduction of maximum attainable surface compressivestresses and this is proportional to the amount of retained austen-ite present. Also, strength and compressive residual stresses arereduced by the presence of retained austenite, thereby reducingfatigue resistance [3]. Tempering process reduces the percent-age of retained austenite. But it may not always be the effectiveway to reduce the amount of retained austenite, because of themarked decrease of hardness, mechanical strength, and wearresistance that partially cancels the positive effect of retainedaustenite transformation.For this reasons a more effective method could be cryogenictreatment. The transformation of austenite to martensite wouldinuencetheresidual stress, whichinturnwouldaffect thebehaviour of the material. The material under investigation isEn 353, which nds applications in heavy-duty gears, shafts,pinions, rocker arms, camshafts, gudgeon pins, push rod leads,levers, bushes and other small arm components. The objectiveof the present study is to examine the distribution of residualstress in En 353 due to cryogenic treatment.2. Standpoints in researchAlot of research has been going on over the past fewdecades,in the eld of cryogenics. Ioan Alexandru and Vasile Bulancea[4] have concluded that the residual stresses play a very impor-tantrolebothduringandafterthecryogeniccooling. Thesestresses constitute the main cause for the continuation of thetransformation of retained austenite to martensite, within thecryogenic eld. It is surprising to see the fact that after cryogeniccooling the value of the residual stresses becomes even lowercompared with classical quenching, either in water or in oil, tothe ambient temperature. When quenched steel is cryogenicallytreated, the retained austenite will transformto martensite. Thenthe size of the component will have only a little expansion andthe stability of the component will increase. Also, it has beenobserved that the structure of cryogenically cooled materialsproved to be much more uniform and dense. In addition, cryo-genic cooling has induced the occurrence of very ne carbideswith dimensions less than 1 m, which occupy the micro voidsand contribute to the increase of both density and coherencewith the metal. Molinari et al. mentioned that carbide precip-itation occurs with a higher activation energy thus leading toa higher nucleation rate and in turn to ner dimensions and amore homogeneous distribution. Anewphenomenon referred astempered martensite detwining was observed. Deep cryogenictreatmentcanstronglyreducethewearrateofthehotworktool steel. This result was interpreted on the basis of increasedtoughness, because in the presence of delamination the abilityofmaterialstoopposecrackpropagationcanreallyincreasethe mechanical stability on the wear surface and the load bear-ing capacity. Therefore, even if the deep cryogenic treatmentdoesnot inuencethehardness, it increasesbothtoughnessandwearresistance[5]. Barronconductedpreliminaryteststo determine the effect of cryogenic treatment on lathe tools,end mills, zone punches and concluded that an increase in toollife from 50% to more than 200% was observed for the toolswhich had been soaked in liquid nitrogen for 12 h [6]. FanjuMeng et al. have studied the effect of cryogenic treatment onthewearbehaviourofFe12CrMoV1.4Ctool steel. Theresults have shown a dramatic increase in wear resistance espe-cially at high sliding speeds [7]. Microstructural analysis of thesample after cryogenic treatment has shown ne carbide pre-cipitates of size in the range of 10 nm, which are characterizedas-carbide. Thisformationof -carbideshelpstoimprovethe wear resistance. Mohan Lal et al. [8] studied the effect ofcryogenic treatment on T1 type-high speed material and foundthat soaking at 203 K can attain the maximum hardness of 67HRC.Theeffect of cryogenictreatment ontheresidual stressbehaviour of En 353 prior to tempering and after tempering isnot yet reported. Hence the present study deals with the mea-surement of residual stress distribution, which in turn helps toknow whether cryogenic treatment helps in improving the lifeof the component.3. Experimental3.1. Sample preparationCommercially available 30 mm diameter bar stock of En 353raw material was procured. In order to conrm the composi-tion of the material procured, elemental analysis was carriedout using optical emission spectroscope (OES), the results ofwhich are shown in Table 1. The raw sample conforms to thechemical requirements of En 353 specications, as far as theconstituents are concerned. It was also found that weight per-centage of carbon has increased from 0.16 to 0.75 in the caseTable 1Chemical composition of the untreated En 353 steel (weight %)Sample description Carbon Silicon Manganese Phosphorus Sulphur Chromium Nickel MolybdenumNominal composition 0.120.18 0.10.35 0.61.0 0.035 0.00250.05 0.751.25 1.01.5 0.080.15Raw material 0.16 0.21 0.68 0.022 0.028 0.76 1.19 0.10Case composition after conventional heat treatment 0.75 0.20 0.67 0.021 0.022 0.76 1.19 0.09Uncertainty 0.011 0.013 0.013 0.011 0.002 0.007 0.006 0.020A. Bensely et al. / Materials Science and Engineering A 479 (2008) 229235 231after case carburizing, which shows that the carbon potentialemployed for carburizing is 0.75. After conrming the com-position the 30 mm diameter bar stock was machined down to25 mm diameter rod and nally cut down into six equal piecesoflength15.2 mm. En353iswidelyusedinmakingcrownwheel and pinion, which undergoes carburizing treatment. Thiscomponent requires a case depth of 1 mm after nal grindingoperation before it is put into application. In order to ensure asimilar case depth of 1 mm, a case depth of 1.2 mmwas achievedduring carburizing process. This in turn can be made to reach1 mm after the various treatments by performing nal surfacegrinding operation to remove the excess 0.2 mm before resid-ual stress measurements. Thus six specimens each of 25 mmdiameter and 15.2 mm length were obtained along with a blankspecimen (25 mm diameter 15.2 mm length) of En 353. Theywere subjected to liquid carburizing at 1183 K until the blankspecimen reached a case depth of 1.2 mm. Conrmation wasmade by cutting and examining the blank specimen under opticalmicroscope. Then the six samples were air-cooled, followed byhardening at 1093 Kfor 30 min. All the six specimens were thenquenched from1093 Kin oil at 313 K. Immediately after quenchhardening one sample was segregated from the six and it wasdesignated as conventionally heat-treated untempered specimen(CHTUT). One of the remaining ve samples was subjectedto tempering at 423 K for 1.5 h and was designated as conven-tionally heat-treated tempered specimen (CHTT). Meanwhilethe remaining four samples were segregated into two groups oftwo specimens each. Both the samples of one group, which hadalready undergone quench hardening, were subjected to shal-lowcryogenic treatment. In shallowcryogenic treatment the twosamples were kept in a mechanical freezer at 193 Kfor 5 h. After5 h both were removed from freezer and exposed to room tem-perature. One of the two shallow cryogenically treated sampleswas kept as such and it was designated as shallow cryogeni-cally treated untempered specimen (SCTUT), while the otherone was immediately tempered at 423 K for 1.5 h and it wasdesignated as shallow cryogenically treated tempered specimen(SCTT). Similarly the two specimens of the other group, whichhad already undergone quench hardening process, were imme-diately subjected to deep cryogenic treatment. In deep cryogenictreatment the two specimens were cooled from room tempera-ture to 77 Kin 3 h, soaked at that temperature for 24 h and heatedback to room temperature in 6 h. These very low temperatureswere achieved using computer controls in a well-insulated treat-ment chamber with liquid nitrogen (LN2) as working uid. Afterreaching the room temperature, one of the samples was kept assuch and it was designated as deep cryogenically treated untem-pered specimen (DCTUT) and the other specimen was subjectedto tempering at 423 Kat 1.5 h and it was designated as deep cryo-genically treated tempered specimen (DCTT). After completingthe treatments all the six specimens were subjected to conven-tional surface grinding so that a case depth of 1 mm similar tothat in the actual component was attained. Surface grinding wascarried out at 2800 revolutions per minute with a feed of 50 musing a CUMI make green silicon carbide abrasive wheel having13 mmthickness and 60-grit. Cutting oil was used as the coolantduring grinding.3.2. X-ray diffraction methodX-raydiffraction(XRD) measurementsarebasedonthechange in the interplanar spacing (strain) by virtue of load ortemperature or both. Diffraction effects are produced when abeam of X-rays of specic wavelength passes through the three-dimensional array of atoms, which constitutes the crystal [9].Each atom scatters a fraction of the incident beams, and if therequired conditions are fullled then the scattered waves rein-force to give a diffracted beam. These conditions are governedby the Bragg equation:n = 2dhkl sin (1)where n is the integer denoting the order of diffraction, thewavelength of the incident beam, dhkl the interplanar spacing ofthe hkl planes, and is the angle of incidence on the hkl planes.Metallurgical applications of XRDtechnique include identica-tion and quantitative analysis of crystalline chemical compounds(phase analysis and quantication, e.g. retained austenite deter-mination), residual macro- and micro-stress analysis.In the present study, X-ray diffraction measurementswereperformedonXStress3000diffractometer (StresstechOy/Finalnd). Xstress 3000 X-Ray analyzer is based on solid-state linear sensor technique (MOS, Dual 512pixels) andgoniometer in modied geometry (symmetrical side inclina-tion). XRD analysis was performed at room temperature usingCr K( =2.2909 A) radiation for residual stress measurementsand retained austenite content also was determined (by usingvanadium lters). Accuracy obtainable using a diffractometer isin the region of 0.5% for the range above 1 to 2 volumes per-centage of austenite. Samples of 25 mm diameter and 15 mmheight wereusedforthemeasurements. Volumefractionofretained austenite was determined by X-ray phase analysis using{2 0 0, 2 1 1} peaks of martensite and {2 0 0, 2 0 0} peaks ofaustenite. Themainobjectiveoftheworkwastodetermineresidual stress distribution both prior to and after conventionalheat treatment, shallow cryogenic treatment and deep cryogenictreatment conditions. Residual stresses can be divided into twogeneral categories, macro-stresses, where the strain is uniformover relatively large distances and micro-stresses produced bynon-uniformstrain over short distances, typically a fewhundredA. Both types of stresses can be measured by X-ray diffractiontechniques. In the current study, macro-stresses were measured.The basis of stress measurement by X-ray diffraction is the accu-rate measurement of changes in interplanar d spacing caused bythe residual stress. When macro-stresses are present the latticeplane spacinginthe crystals (grains) change correspondingtotheresidual stress and the elastic constants of the material. This pro-duces a shift inthe positionof the correspondingdiffraction, i.e. achange in Bragg angle . The determination of interplanar spac-ing depends on the accurate measurement of the corresponding.Thedatawereacquiredinseveral angles(inrangeof045) and the stresses were calculated by the classical sin2method. Thepeakpositionwascalculatedbythecrosscor-relation method. The parameters selected for experimentation232 A. Bensely et al. / Materials Science and Engineering A479 (2008) 229235Table 2Experimental inputs for residual stress analysisMiller indices hkl 211Diffraction angle () 156.4Angular resolution () 0.029Poissons ratio 0.3Exposure time (s) 4Penetration depth (m) 4Youngs Modulus (GPa) 200are listed in Table 2. Due to the limited penetration (4 m forchromiumradiation in steel) of X-ray only surface stresses couldbe measured. Hence stresses at shallow points in the sampleswere determined by repeating the measurements after removing(electro polishing) layers of known thickness. When performinglayerremoval forresidual stressdepthprolingit isimpor-tant to consider any redistribution or relaxation in the residualstress in the exposed surface. Ageneralized solution proposed bySikarskie based on the original solutions of Moore and Evanswas used [10,11]. For electro polishing, the electrolyte used,consistedof80 cm3perchloricacid(70%), 700 cm3ethanol,100 cm3butoxyethanol and 120 cm3-distilled water. The jet pol-ishing was performed at temperatures ranging from 253 K to263 Kat avoltagebetween20 Vand30 Vandat acurrentof about 600900 mA. The specimens were jet polished usingthe electrolyte at 283 K. The peaks on the XRD patterns wereindexed with the X-ray polycrystalline powder diffraction les(International Center for Diffraction Data (ICDD)).4. Results and discussion4.1. Retained austeniteThe retained austenite present in the specimens of En 353subjectedtoconventional heat treatment, shallowcryogenictreatment and deep cryogenic treatment prior to and after tem-pering was measured using X-ray diffractometer with vanadiumlters. The results are shown in Table 3.Afterconventionalquenchhardeningofcarburizedspeci-mens (i.e. CHTUT), it was found that there was 28.1% retainedaustenite. This, on tempering (i.e. CHTT) does not yield anyreduction in retained austenite content because the temperatureemployed for tempering is just 423 K, which cannot decom-posetheavailableaustenite. Thedecompositionofausteniteoccursfrom513 Kto593 K[12]. HencethereisnochangeinretainedaustenitepriortoandaftertemperingincaseofTable 3Retained austenite content by X-ray measurementsType of treatment Retained austenite (%)CHTUT 28.1 3.5CHTT 28.5 6.1SCTUT 22.0 7.6SCTT 22.8 5.9DCTUT 14.9 5.8DCTT 14.3 4.1conventional heat treatment. The conventional quench hardenedspecimen (i.e. CHTUT) when kept in a mechanical freezer at193 Khasresultedinareductionofretainedaustenitefrom28.1%to 22%(i.e. SCTUT). As the temperature applied for tem-pering is not sufcient to decompose the austenite into ferriteand cementite, 22.8%remains even after tempering (i.e. SCTT).This clearly indicates that shallow cryogenic treatment does notcompletely transform the retained austenite into martensite butit has reduced the percentage of retained austenite available incomparison with conventional heat treatment. When the conven-tionally quench hardened carburized specimens (i.e. CHTUT)were subjected to deep cryogenic treatment, a 50% reductionof available retained austenite (28.1% austenite in CHUT) wasobserved in DCTUT specimens. Increasing carbon content ofsteel increases the potential for retained austenite on quench-ing. This is because Ms temperature decreases with increasingcarbon content. The effect of carbon content can be calculatedusing the Steven and Haynes equation for steel containing up to0.5% carbon [13].Ms (C) = 561 474C 33Mn 17Cr17Ni 21Mo (2)Mf = Ms215 (3)where carbon, manganese, nickel, chromium and molybdenumare concentrations of these elements in percent. For carbon con-centration more than 0.5% corrections must be made. Since thecarbon concentration in the surface of En 353 after carburiz-ing is 0.75% correction curve was used. It was found that 20 Khas to be added to the Mstemperatures derived using Stevenand Haynes equation. 100% martensite transformation can beexpected to happen at a temperature of 226 K for a carbon con-tent of 0.75% in case. The present study clearly indicates that100% removal of retained austenite was not obtained even aftercooling the samples to a very low temperature of 77 K. Thus,some amount of retained austenite exists in deep cryogenicallytreated samples and shallow cryogenically treated samples also.4.2. Residual stress distributionFig. 1 shows the distribution of residual stress in samplestestedpriortotempering. Auniformdifferenceinvaluesofresidual stress is observed corresponding to the measured depthfromthe surface. The gradient of residual stress is the same, irre-spective of which treatment is employed but the range of valuesvaries with respect to the treatment. This can be attributed tothe transformation of retained austenite to martensite. A reduc-tionofaround6%retainedaustenitefromCHTUTsamplesdoes not induce compressive residual stress in SCTUT sam-ples, whereas a tremendous increase in compressive residualstress is observed in DCTUT samples and is due to 50% trans-formationofavailableretainedaustenite(28.1%inCHTUTsamples) to martensite. The process of subjecting samples toshallow cryogenic treatment is totally different from deep cryo-genic treatment apart from the level of temperature reduction.A. Bensely et al. / Materials Science and Engineering A 479 (2008) 229235 233Fig. 1. Distribution of residual stress in En 353 steel specimens prior to temper-ing.In shallow cryogenic treatment the CHTUT samples availableat room temperature are suddenly exposed to 193 K, similarly itis immediately taken out of the mechanical freezer and exposedto room temperature. In the case of deep cryogenic treatmentprocess the CHTUT samples were slowly taken to 77 K fromroom temperature and slowly brought back to room tempera-ture. Hence whatever stress developed during the process has notbeen relieved. This mechanism need to be validated by carryingout a detailed investigation on the effects of lattice parametersc and a with respect to the rate of cooling to 193 K and 77 Kand rate of warming to room temperature. Lower the tempera-ture of cryogenic treatment, greater will be the transformation ofaustenite to martensite and hence, greater will be the compres-sive residual stress induced. This compressive residual stress isbenecial with respect to wear and fatigue [3]. This was evi-dent in the earlier research on wear resistance of cryogenicallytreated En 353 steel [14].Cryogenic treatment cannot represent a nal heat treatmentsince subsequent tempering is absolutely necessary to achievene carbide precipitation. Tempering reduces residual stresses,increases ductility, toughness and ensures dimensional stability.Fig. 2 shows the distribution of residual stress in conventionalheat treatment, shallow cryogenic treatment and deep cryogenicFig. 2. Distribution of residual stress in En 353 steel specimens after tempering.treatment after tempering. The untempered conventionally heattreated and shallow cryogenically treated samples, which whensubjectedtotempering(CHTT, SCTT)seemedtoretaintheresidual stress after tempering; while those subjected to deepcryogenic treatment followed by tempering (DCTT) showed aremarkable stress relief. This indicates that the extent to whichthe metal is cooled below room temperature plays an importantrole. The distribution trend is not uniform and the stress band isalso altered. The substantial relief of compressive residual stressin the DCTT specimens may be due to the occurrence of nerprecipitates throughout the matrix and the loss of tetragonality ofmartensite. The mechanism behind the large change in residualstress can be due to atomic level change during the cool down,soak and ramp up process of deep cryogenic treatment as wellas the immediate tempering process. The cool down process ofdeep cryogenic treatment causes the transformation of retainedaustenite to freshly formed martensite, which has different lat-ticeparameter(higherc/aratio)thantheoriginalmartensite[15]. Owing to volume contraction in the DCT process, the crys-talline lattice tends to decrease. However, due to the difcultyin diffusion of carbon atoms at lowtemperature, precipitation ofultra ne carbides will not take place at a very low temperatureof 77 K. But increased holding time at cryogenic temperatureinvolves localized diffusion of carbon leading to cluster forma-tion. These clusters act as nuclei for the formation of ultra necarbides on subsequent warm up and tempering. These changesin lattice parameter are conrmed by a recent in situ neutrondiffraction study, which indicated that the lattice parameters aand c of the martensite behave differently during the cool-ing and warming-up processes [16]. The lattice parameter achanges with the temperature almost linearly, following almostthe same curve during the cooling and warming-up process, indi-cating a pure thermal elastic effect. The lattice parameter c, onthe other hand, rst decreases with the cooling temperature, but itdoes not followthe same slope while warming-up, and increasesonly very slightly during the warming-up process, indicating it isnot only a pure thermal effect. It is inferred fromthe above resultthat carbon atoms segregation did occur during the cold treat-ment process. Because the carbon atoms predominantly occupythe octahedral or tetrahedral sites in the martensitic lattice, thesegregation of carbon atoms from the octahedral or tetrahedralsite to the defect regions mainly affects the c lattice param-eter. The capacity of carbon atoms to diffuse increases as thetemperaturerisesbacktoroomtemperature. Duringthisthecarbon atoms move a short distance to segregate on the twincrystal surfaceor onother defects, formultranecarbidesof diameter 2660 A [17] leading to greater relief of residualstress.4.3. Grinding effectsFigs. 35 show the CHTUT, SCTUT and DCTUT samplesafter grinding, respectively, whereas Figs. 68 show the CHTT,SCTT and DCTT samples after grinding, respectively. On com-parison, grinding cracks are visible in all the specimens prior totempering. As the samples are exposed to low temperature, theconversion of retained austenite to martensite has manifested234 A. Bensely et al. / Materials Science and Engineering A479 (2008) 229235Fig. 3. Optical photograph showing the inuence of grinding on CHTUT spec-imen.as cracks during the subsequent grinding operation. The inten-sity of cracks visible is different for all the samples and canbe related to the amount of untempered martensite available,which is highly brittle in nature. The presence of grinding cracksin SCTUT and DCTUT is more when compared to CHTUT.This could be attributed to the conversion of retained austen-ite to martensite at low temperatures. The cracks visible in thetempered specimen can be related to the ne carbide precipita-tion. As cryogenic treatment facilitates ne carbide precipitationduring tempering, no visible cracks are observed in SCTT andDCTT specimen. This clearly indicates that the toughness ofthe matrix holding the carbides has improved. Low temperatureconditioning of martensite accelerated the precipitation of neFig. 4. Optical photograph showing the inuence of grinding on CHTT speci-men.Fig. 5. Optical photograph showing the inuence of grinding on SCTUT spec-imen.carbides during tempering. This resulted in large relaxation incomparison with CHTT. Since there is little carbide precipita-tion in CHTT and due to partial transformation of austenite tomartensite, brittleness is more in CHTT samples. In SCTT andDCTT samples, uniform relaxation has occurred in every nedomain of the matrix resulting in reduced brittleness comparedtoCHTTsamples. Duringsubsequent temperingofconven-tionally heat-treated samples, no appreciable change in residualstress is noticed. This clearly shows that there is not much necarbide precipitation and hence a fewcracks are still visible evenafter tempering. The number of cracks available after temperingin CHTT samples is larger than in the case of tempered SCTTFig. 6. Optical photograph showing the inuence of grinding on SCTT speci-men.A. Bensely et al. / Materials Science and Engineering A 479 (2008) 229235 235Fig. 7. Optical photograph showing the inuence of grinding on DCTUT spec-imen.Fig. 8. Optical photograph showing the inuence of grinding on DCTT speci-men.and DCTT samples, but DCTT samples does not show any signof cracking after grinding operation.5. ConclusionThestudyconrmsthatcryogenictreatment(i.e. shallowcryogenic treatment and deep cryogenic treatment) should befollowed by tempering. Untempered specimens of shallowcryo-genictreatment anddeepcryogenictreatment havesurfacecracks, whichisnotbenecialtothelifeofthecomponent.The retention of residual stress in samples subjected to conven-tional heat treatment and shallow cryogenic treatment, followedby tempering can lead to better fatigue properties, as comparedto the specimen subjected to DCT. The decrease in the tempera-ture increases the lattice defects and thermodynamic instabilityofthemartensite, whichdrivesthecarbonandalloyingele-ments to nearby defects. These clusters act as nuclei for theformation of ne carbides on subsequent tempering. The inten-sity of carbide precipitation depends on the extent to which thespecimens are cooled below room temperature. The large relax-ation of residual stress in DCTT specimens indirectly reectsabout the amount of carbide precipitation. Based on relaxationphenomenon it is concluded that DCTT exhibit the maximumcarbide precipitation than SCTT and CHTT specimens. Thishas reected in an earlier study on the improved wear resistanceobtained for En 353 after deep cryogenic treatment with temper-ing [14]. The study clearly shows that En 353 when subjectedto deep cryogenic process has attained the maximum compres-sive stress (235 MPa) before tempering. This aids the carbideprecipitation during the subsequent tempering process resultingin large relaxation (80 MPa).AcknowledgementsThe authors wish to thank the support of Ministry of Sci-ence and Computerization, Poland, towards residual stressmeasurements. The authors also gratefully acknowledge M/s.Chennai MetcoPrivate Limited, for extendingtheir metal-lurgical facilitiesforthesuccessful completionofthework.The authors gratefully acknowledge the nancial support fromDepartment of Science and Technology, India, under FIST pro-gram (SR/FST/ETI-053/2002) for setting up a state of the artcryogenic treatment facility, which enabled for the successfulcompletion of the project.References[1]M. Mack Aldener, M. Olsson, Proceedings of the 4th International Con-ference of the Engineering Intergrity Society, Cambridge, UL, 2000, 371.[2]P. Mayr, Residual Stresses in Science and Technology, vol. 1, Garmisch-Partenkirschen, FRG, 1986.[3]G. Parrish, Carburizing: Microstructure and Properties, ASMInternational,1999.[4]IoanAlexandru, VasileBulancea, HandbookofResidual Stress, ASMInternational, 2002.[5]A. Molinari, Pellizzari, Mater. Process. Technol. 118 (2001) 350.[6]R.F. Barron, Prog. Refrigeration Sci. Technol. 1 (1973) 529.[7]Fanju Meng, Kohsuke Tagashira, Ryo Azuma, Hideaki Sohma, ISIJ Int. 34(1994) 205.[8]D. Mohanlal, Renganarayanan, S. Kalanidhi, Indian J. Cryogenics 219 (2)(1996) 41.[9]W.F. Gale, T.C. Totemeier, SmithellsMetalsReferenceBook, 8thed.,Butterworth-Heinemann, 2004.[10]D.L. Sikarskie, AIME Trans. 239 (1967) 577580.[11]M.G. Moore, W.P. Evans, SAE Trans. (1958) 66.[12]Trobert E. Reed-Hill, Reza Abbaschhian, Physical Metallurgy Principles,3d ed., Thomson, 2003.[13]Failure Analysis and Prevention, ASM handbook, 11, 2002, 192.[14]A. Bensely, A. Prabhakaran, D. Mohan Lal, G. Nagarajan, Cryogenics 45(2005) 747.[15]P.-Li Yen, Ind. Heat. (1997) 40.[16]J.Y. Huang, Y.T. Zhu, X.Z. Liao, I.J. Beyerlein, M.A. Bourke, T.E. Mitchell,Mater. Sci. Eng. A 339 (12) (2003) 241.[17]Dong Yun, Xiaoping, Xiao Hongshen, Heat Treat. Met. 3 (1998) 55.