Effect of cold rolling reduction and intercritical annealing ...

journal of materials processing technology 203 (2008) 293–300journal homepage: www.elsevier.com/locate/jmatprotecEffect of cold rolling reduction and intercriticalannealing temperature on the bulk texture oftwo TRIP-aided steel sheetsE. Emadoddin ∗ , A. Akbarzadeh, Gh. DaneshiFaculty of Material Science and Engineering, Sharif University of Technology, P. O. Box 11365-9466,Azadi Avenue, Tehran, IranarticleinfoabstractArticle history:Received 2 November 2006Received in revised form17 September 2007Accepted 12 October 2007Keywords:TextureIntercritical annealingTRIP-aided steelCold rolled sheetChemical compositionHigh strength TRIP-aided steel sheets with high formability and better ductility are of industrialinterest. Texture control and retained austenite characterization are considered as themain factors with respect to the formability and ductility. Processing parameter such asinitial conditions of hot rolling, cold rolling to final size of sheet, intercritical annealingafter cold rolling and subsequent isothermal heat treatment to achieve TRIP specificationin product, affect bulk texture of sheets. Moreover, chemical composition of steel should benoted especially because it can change the intensity of orientation and final macro textureof sheet.In this work, the effect of cold rolling and intercritical annealing on texture developmenthas been investigated for two TRIP-aided steel sheets, which are different in C, Si and Al content.Results show that the cold rolling extends the -fiber on these grades of steel, whereasany intensive -fiber components were not observed by change of cold rolling reduction. Alsothe effect of cold rolling on final texture of experimented materials is different and dependson chemical composition of steel. In contrary, intercritically annealing of cold rolled sheetsdecreases the intensity of -fiber so that the chemical composition of TRIP steel wouldinfluence effectively.© 2007 Elsevier B.V. All rights reserved.1. IntroductionProperties and characterizations of new developed highstrength multi-phase steel sheets with transformationinduced plasticity (TRIP-aided) of retained austenite are studiedin order to optimize the processing conditions and toachieve good mechanical properties and formability. Theeffect of hot deformation process on TRIP behaviour has beenstudied by some researchers (Basuki and Aernoudt, 1999a;Basuki and Aernoudt, 1999b; Chiro et al., 1998). Also the influenceof alloying elements, heat treatment and consequentlyretained austenite characteristics on formability (Lee et al.,2004, 2002), stretch flangeability (Sugimoto et al., 2003, 2000,1999) and mechanical properties of TRIP steels (Kim et al.,2003, 2002, 2001) has been investigated.It is well known the fact that the crystalline texture andpreferred orientation in materials can affect the propertiesand control the formability and deep drawability (Wu et al.,2004; Xie and Nakamachi, 2003, 2002; Verdeja et al., 2003;Asensio et al., 2001; Yazawa et al., 2003; Huh and Engler,2001). Intercritical annealing of cold rolled sheet and thenquenching to an intermediate temperature above M s is per-∗ Corresponding author. Tel.: +98 21 66165242; fax: +98 21 44545101.E-mail address: e.emadoddin@gmail.com (E. Emadoddin).0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2007.10.041

294 journal of materials processing technology 203 (2008) 293–300Table 1 – Chemical composition and critical temperatures of experimented materialsSample code Chemical composition (in wt%) A c1 ( ◦ C) A c3 ( ◦ C)C Mn Si P S AlSi-TRIP 0.12 1.60 1.28 0.015 0.002 0.05 748 897Al-TRIP 0.27 1.48 0.28 0.015 0.001 1.08 746 970Fig.1– ϕ 2 =45 ◦ ODF section of the cold rolled Si-TRIP steelsheets after cold rolling reduction (a) 65%, (b) 76% and (c)84%.Fig.2– ϕ 2 =45 ◦ ODF section of the cold rolled Al-TRIP steelsheets after cold rolling reduction (a) 65%, (b) 76% and (c)84%.

journal of materials processing technology 203 (2008) 293–300 295the austenite phase and the bulk texture of the transformationproduct of some TRIP-aided steels. However, there arenot sufficient studies regarding the texture development duringcold rolling and annealing (Oh et al., 2002; Shin et al.,2002).In this research, the macro texture of two types ofTRIP-aided steels with different chemical compositions isinvestigated and the effect of two important processing factors,i.e. cold rolling reduction and intercritical annealingtemperature on texture development is presented.Fig. 3 – Skeleton lines of (a) the -fiber components and (b)the -fiber for Si-TRIP at different amount of cold rollingreductions that mentioned on the graph.formed to develop the retained austenite in product (Hulka,2007). In this way, for the TRIP-aided cold rolled sheets, bulktexture after cold rolling and intercritical annealing shouldbe studied as the important and effective conditions on thefinal characteristics of the retained austenite and the endtexture. By this means, the TRIP behaviour of steel sheetas well as its mechanical properties and formability can beestimated and controlled. Hutchinson et al. (1998), Verlindenet al. (2001) and Godet (2003) studied hot rolling texture ofFig. 4 – Skeleton lines of (a) the -fiber components and (b)the -fiber for Al-TRIP at different amount of cold rollingreductions that mentioned on the graph.

298 journal of materials processing technology 203 (2008) 293–300Fig. 10 – Intensity of -fiber components for 76% cold rolledSi-TRIP sample with corresponding samples that have beenannealed at different temperature.son of above fact is related to the chemical composition andespecially carbon content of the materials as well as their TRIPcharacteristics.With regard to analysis of two TRIP steels, Table 1, twoimportant points can be concluded:Fig. 9 – Skeleton lines of (a) the -fiber and (b) the -fibercomponents for Al-TRIP steel samples that were cold rolled76% reduction and annealed at intercritical temperature of760 ◦ C, 810 ◦ C and 860 ◦ C.ture components were saturated at reduction of 76% and 84%.This is due to saturation and stabilization of grain rotations athigher deformations. For Al-TRIP, variation of texture intensityby amount of cold deformation is much less than Si-TRIP,Fig. 4a.Comparison of the -fiber for Al-TRIP and Si-TRIP givesremarkable texture information, Fig. 5. It is indicated that atall rolling reductions, the intensity of the texture componentsfor Si-TRIP is higher than Al-TRIP steel sheet. The main rea-Fig. 11 – Comparison of -fiber components for 76% coldrolled Si-TRIP sample with corresponding annealedsamples at different temperature.

journal of materials processing technology 203 (2008) 293–300 299ferrite and small transformation of ferrite to austenite onheating can not change cold rolling texture significantly andbased on this fact, intensity of -fiber texture componentof cold rolled Si-TRIP is close to annealed sample at 760 ◦ C,Fig. 10.The main effect of intercritical annealing temperature isrevealed for -fiber, Figs. 8a and 9a. As it is shown, annealingof Al-TRIP steel at different intercritical region temperatureswould not affect the intensity of -fiber orientations.Although, slightly decrease in the intensity of -fiber textureobserved for annealed sample at 810 ◦ C. In contrary, annealingof Si-TRIP steel cause noticeable deviation of the intensity of-fiber texture. Intensity of -fiber decreases by annealing athigher temperature, Fig. 8a.When cold rolled sheets are heated to intercritical regiontemperature, available pearlite along with some parts offerrite are transformed to austenite by a specific orientationrelationship. In this case, Kurjumov–Sachs (KS) model({111} ||{110} ) can predict the product (austenite phase)crystalline direction corresponding to the initial directionof ferrite phase as a diffusional transformation (Verlindenet al., 2001; Park et al., 2002). However, on quenchingand subsequent austempering treatment of steel, austenitewould transform to bainite (major transformed phase)and retained austenite according to Bain orientation relationmodel ({100} ||{110} Banite )(Hutchinson et al., 1998) whereas,Fig. 12 – Comparison of -fiber components for 76% coldrolled Al-TRIP sample with corresponding annealedsamples at different temperature.(1) There is higher hard phase (Fe 3 C) in Al-TRIP with respectto Si-TRIP steel.(2) There is higher amount of initial retained austenite in hotband prior to cold rolling in Al-TRIP due to its higher carboncontent. This phase was transformed to hard phase ofmartensite by deformation.Due to these two points, grain deformation and rotationwas retarded by surrounding hard phase. The result of thisfact is the weak texture of Al-TRIP with respect to Si-TRIP inFig. 5.3.2. Texture after intercritical annealingFigs. 6 and 7 show ODFs at section ϕ 2 =45 ◦ of annealed Si-TRIP and Al-TRIP steel at different intercritical annealingtemperature. Correspondingly, intensity of texture componentsin annealed sample can be seen as skeleton lines inFigs. 8 and 9.For both TRIP-aided steels, there is not any significantdifference for intensity of -fiber components at differentintercritical annealing temperatures. Also, similar to the coldrolled texture, an orientation is detected at =70 ◦ . Onlyfor Si-TRIP sheet which was annealed at 760 ◦ C, slightlystronger intensity of -fiber with respect to annealed sampleat 810 ◦ C and 860 ◦ C is observed. Indeed, annealing atlower temperature (760 ◦ C) with lack of recrystallization ofFig. 13 – Skeleton lines show -fiber for annealed samplesof Si-TRIP (solid data marks) and Al-TRIP (hollow datamarks) at two intercritical annealing temperaturesmentioned on the graph.

300 journal of materials processing technology 203 (2008) 293–300ferrite phase remain without any orientation change at roomtemperature. Based on these orientation relations that occurduring phase transformation of TRIP-aided steels, it wouldbe expected that cold rolled grains with -fiber (||ND)orientation disappear and the intensity of -fiber texturecomponents decrease. Experimental results indicate that byincreasing the intercritical annealing temperature this fiber isweakened.At lower intercritical annealing temperatures, because oflower volume fraction of ferrite which would contribute intransformation to austenite, orientation change is negligible.However, at higher temperatures higher degree of phase reactionand transformation lead to greater variation of preferredorientation in steel. Fig. 11 presents a comparison of -fiberintensity for cold rolled Si-TRIP and corresponding annealedsamples at different temperatures.For Al-TRIP steel sheets, annealing at different temperatureswill not much affect the intensity of -fiber. In fact,because of higher carbon content of Al-TRIP with respect toSi-TRIP, transformation of ferrite to austenite on heating andbainitic transformation during cooling is more complicated, sothat orientation transformation and texture variation is muchless, Fig. 12.The more intensive -fiber in Al-TRIP compared to Si-TRIPby annealing at practical intercritical annealing temperaturerange, i.e. 800–850 ◦ C, Fig. 13, can be explained by the variantselection models.4. ConclusionThe results of experimental work regarding the effect of coldrolling reduction and intercritical annealing can be summarizedas:(1) While cold rolling develops -fiber in both TRIP-aidedsteels, cold rolling texture in Si-TRIP is sharper than thatof Al-TRIP. Effect of cold rolling on -fiber is negligible.(2) Increasing rate of intensity of texture components byreduction would be decreased due to saturation of grainrotations at higher reductions.(3) Intercritical annealing decreases the probability of formationof -fiber especially in Si-TRIP so higher annealingtemperatures cannot be suitable for -fiber developmentin these steels.(4) Based on the carbon content of Si-TRIP and more transformationfor this material with respect to Al-TRIP, variationof texture components is more probable for it.AcknowledgmentsThe authors would like to thank Prof. L. Kestens and Dr. R.Petrov from Ghent University in Belgium for providing thematerials and Mr. M. M. Saffari at Tarbiat Modarres Universityin Iran for X-ray diffractometery.referencesAsensio, J., Romano, G., Martinez, V.J., Verdeja, J.I., Pero-Sanz, J.A.,2001. Mater. Charact. 47, 119–127.Basuki, A., Aernoudt, E., 1999a. J. Mater. Process. Technol. 89/90,37–43.Basuki, A., Aernoudt, E., 1999b. Scripta Mater. 40 (9), 1003–1008.Chiro, A.D., Root, J.H., Yue, S., 1998. Conference ofThermomechanical Processing in Steel, Vancover, Canada, pp.259–269.Godet, S., Thermomechanical Processing of TRIP AssistedMultiphase Steels. Ph.D. Thesis. Louvain - la - Neuve, Belgium,2003.Huh, M.Y., Engler, O., 2001. Mater. Sci. Eng. A 308, 74–87.Hulka, K., 2007. The Role of Niobium in Multi–Phase steel”, SeeWeb Site: www.us.cbmm.com.br/english/sources/techlib/report/novos.Hutchinson, B., Rede, L., Lindh, E., Tagashira, K., 1998. Mater. Sci.Eng. A 257, 9–17.Kim, S.J., Lee, C.G., Choi, I., Lee, S., 2001. Metall. Mater. Trans. A32, 505–514.Kim, S.J., Lee, C.G., Lee, T.H., Lee, S., 2002. ISIJ Int. 42 (12),1452–1456.Kim, S.J., Lee, C.G., Lee, T.H., Oh, C.S., 2003. Scripta Mater. 48,539–544.Kocks, U.F., Tome, C.N., Wenk, H.R., 1998. Texture and AnisotropyPreferred Orientations in Polycrystals and Their Effect onMaterials Properties. Cambridge University Press, UK.Lee, C.G., Kim, S.J., Song, B.H., Lee, S., 2002. Met. Mater. Int. 8 (5),435–441.Lee, C.G., Kim, S.J., Lee, T.H., Lee, S., 2004. Mater. Sci. Eng. A 371,16–23.Oh, S.T., Park, K.K., Han, H.N., Park, S.H., Oh, K.H., 2002. Mater.Sci. Forum 408–412, 1341–1346.Park, C.M., Bruckner, G., Gottstein, G., 2002. Mater. Sci. Forum408–412, 1191–1196.Shin, E.J., Seong, B.S., Lee, C.H., Balk, S.C., Huh, M.Y., 2002. Mater.Sci. Forum 408–412, 1383–1388.Sugimoto, K.I., Sakaguchi, J., Iida, T., Kashima, T., 1999. ISIJ Int. 39(9), 56–63.Sugimoto, K.I., Nakano, K., Song, S.M., Kashima, T., 2000. ISIJ Int.40 (9), 902–908.Sugimoto, K.I., Iida, T., Sakaguchi, J., Kashima, T., 2003. ISIJ Int. 40(9), 902–908.Verdeja, J.I., Asensio, J., Pero-Sanz, J.A., 2003. Mater. Charact. 50,81–86.Verlinden, B., Bocher, P.H., Girault, E., Aernoudt, E., 2001. ScriptaMater. 45, 909–919.Wu, P.D., MacEwen, S.R., Lloyd, D.J., Neale, K.W., 2004. Mater. Sci.Eng. A 364, 182–187.Xie, C.L., Nakamachi, E., 2002. J. Mater. Proc. Technol. 122,104–111.Xie, L., Nakamachi, E., 2003. Mater. Sci. Eng. A 340, 130–138.Yazawa, Y., Ozaki, Y., Kato, Y., Furukimi, O., 2003. JSAE Rev. 24,483–488.