Carbon concentration of austenite in austempered ductile iron (ADI)

• Autorzy: Ławrynowicz Z. , Dymski S.
• Języki publikacji: EN

Abstrakty

EN

The investigation was carried out to examine the influence of temperature and times of austempering process on the maximum extend to which the bainite reaction can proceed and the carbon content in retained austenite. It should be noted that a small percentage change in the austenite carbon content can have a significant effect on the subsequent austempering reaction changing the volume fraction of the phases present and hence, the resulting mechanical properties. Specimens were prepared from an unalloyed ductile cast iron, austenitised at 950oC for 60 minutes and austempered by the conventional single-step austempering process at four temperatures between B_S and M_S, eg., 250, 300, 350 and 400oC. The samples were austempered at these temperatures for 15, 30, 60, 120 and 240 minutes and finally quenched to ambient temperature. Volume fractions of retained austenite and carbon concentration in the residual austenite have been observed by using X-ray diffraction. Additionally, carbon concentration in the residual austenite was calculated using volume fraction data of austenite and a model developed by Bhadeshia based on the McLellan and Dunn quasi-chemical thermodynamic model. The comparison of experimental data with the T_0, T_0' and Ae_3' phase boundaries suggests the likely mechanism of bainite reaction in cast iron is displacive rather than diffusional. The carbon concentration in retained austenite demonstrates that at the end of bainite reaction the microstructure must consist of not only ausferrite but additionally precipitated carbides.

Słowa kluczowe

EN

retained austenite; bainite; austempering; ductile iron

PL

austenit szczątkowy; bainit; hartowanie izotermiczne; żeliwo sferoidalne

• Wydawca: Komisja Odlewnictwa Polskiej Akademii Nauk Oddział w Katowicach
• Czasopismo: Archives of Foundry Engineering
• Rocznik: 2007
• Tom: Vol. 7, iss. 3
• Strony: 93--98
• Opis fizyczny: Bibliogr. 16 poz., rys., tab.

Twórcy

autor

Ławrynowicz Z.

autor

Dymski S.

• University of Technology and Life Sciences, Mechanical Engineering Faculty, al. Kaliskiego 7, 85-796 Bydgoszcz, Poland,

Bibliografia

• [1] M.A. Yescas, H.K.D.H. Bhadeshia, D.J. Mac Kay, Estimation of the amount of retained austenite in austempered ductile irons using neural networks, Materials Science and Engineering, A311 (2001) 162-173.
• [2] Z. Ławrynowicz, S. Dymski, Application of the mechanism of bainite transformation to modelling of processing window in ductile iron ADI, Archives of Foundry Engineering, PAN, Vol.6, No 19, (2006) 177-182. (in Polish).
• [3] J.W. Christian, Theory of transformations in metals and alloys, 778, Oxford, Pergamon Press, 1965.
• [4] H.K.D.H. Bhadeshia, Bainite in Steels, Institute of Materials, 1-458, London, 1992.
• [5] A. Hultgren, Jernkontores Ann., vol. 135 (1951) 403
• [6] S.H. Zahiri at al., Application of bainite transformation model to estimation of processing window boundaries for Mn-Mo-Cu austempered ductile iron, Materials Science and Technology Vol.17 (2001) 1563-1568.
• [7] Z. Ławrynowicz, S. Dymski, Mechanism of bainite transformation in ductile iron ADI, Archives of Foundry Engineering, PAN, Vol.6, No 19, (2006) 171-176. (in Polish).
• [8] H.K.D.H. Bhadeshia, Bainite: Overall Transformation Kinetics, Journal de Phys., Vol. 43 (1982) C4 443-447.
• [9] H.K.D.H. Bhadeshia, A Rationalisation of Shear Transf. In Steels, Acta Metall., Vol.29 (1981) 1117-1130
• [10] R.B. McLellan, W.W. Dunn, J. Phys. Chem. Solids. Vol.30 (1969) 2631.
• [11] Z. Ławrynowicz, Materials Science and Technollogy, Vol 18 (2002) 1322-1324.
• [12] H.K.D.H. Bhadeshia, Diffusion of carbon in austenite, Metal Science, Vol.15 (1981) 477-479.
• [13] Z. Ławrynowicz, A. Barbacki, The mechanism of bainite transformation in Fe-Cr-Mn-Si-C steel. Proc. of the Scientific Con. AMTECH'95, Rousse, Bułgaria, 19-21 April 1995, 1-8
• [14] Z. Ławrynowicz, Transition from upper to lower bainite in Fe-Cr-C steel, Mat. Sci. Techn., Vol.20 (2004) 1447-1454.
• [15] M. Takahashi, H.K.D.H. Bhadeshia, A Model for the Microstructure of Some Advanced Bainitic Steels, Materials Transaction, JIM, Vol.32 (1991) 689-696.
• [16] R.C. Thomson at al., Modelling microstructural evolution and mechanical properties of austempered ductile iron, Materials Sci. and Technology, Vol. 16 (2000) 1412-1419.