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A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 2 0 1 9 annealed microstructure when com- pared to spheroidite formed in the same steel by prolonged annealing of pearl- ite. Most notably the chip temperature is appreciably lower, suggesting a lesser build up at the tool edge, which can be correlated to a lower coefficient of fric- tion. ~AM&P Acknowledgment The authors would like to thank Dr. Mihael Brunčko for his support and helpful discussions. For more information: Peter Kirbiš, SIJ Metal Ravne d.o.o., Koroška ces- ta 14, +38651605327 , peter.kirbis@ metalravne.com. Note: This article has been adapt- ed from a full length feature in Metal- lography, Microstructure, and Analysis (2020), DOI 10.1007/s13632-020-00618-5. © ASM International 2020. References 1. N.E. Luiz and Á.R. Machado, “Development Trends and Review of sists of equiaxed ferrite grains and carbides. The ferritic grains can be correlated with the prior bain- itic sheaves as illustrated in Fig. 4, whereas the decomposition process is depicted schematically in Fig. 5. It is predicted that a single sheave of bainite decomposed into two or three newly formed ferrite grains in the case of short/thick and long/thin sheaves respectively, whereas the martensitic phase experienced a conventional tem- pering reaction. In the detail shown in Fig. 4 and Fig. 6a, some of the prior fine plates have coalesced but are still clear- ly visible. After prolonged annealing for 24 h, the decomposition process is complete as seen in Fig. 6b. The dark (graphite) particles are only slightly elongated with a width of between 150-200 nm and a length up to 500 nm. The retained austenite phase on the other hand decomposed rapidly by pre- cipitation of needle like carbides char- acteristic for cementite as shown in Fig. 6c. The decomposition acts as a mechanism of grain refinement al- though it is expected that significant grain coarsening occurs at the austen- itization temperature. CONCLUSIONS It is observed that annealing an initially very fine bainitic microstruc- ture can result in the obtainment of an exceptionally fine annealed micro- structure comprised of equiaxed grains of ferrite with several carbon enriched particles which are most likely graphite. The grain size and particle distribution is remarkably uniform even though the initial continuously cooled bainitic mi- crostructure is known to have a relative- ly wide distribution of bainitic ferrite plate thickness. The annealed micro- structure is in sharp contrast to the one resulting from the prior martensite or retained austenite regions. Machine testing has shown superi- or machining characteristics of the fine Free-machining Steels,” Proc. Inst. Mech. Eng. Part B J. Eng. Manuf. , Vol 222(2), p 347–360, 2008. 2. A. Inam, R. Brydson, and D.V. Edmonds, “Effect of Starting Microstructure upon the Nucleation Sites and Distribution of Graphite Particles during a Graphitising Anneal of an Experimental Medium-Carbon Machining Steel,” Mater. Charact. , Vol 106, p 86–92, 2015. 3. A. Rosen, A. Taub, “The Kinetics of Graphitization,” Acta Metall. , Vol 10, 1962. 4. D. Edmonds, “Acceleration of Graphitisation in Carbon Steels to Improve Machinability,” Super-High Strength Steels , 2005. 5. L.E. Samuels, “Spheroidization and Graphitization,” in Light Microscopy of Carbon Steels , ASM International, 1980. 6. D. V. Edmonds, “The ‘Silicon Age’ of Steel : How Alloying With Silicon Is Playing a Crucial Role in Modern Steel Developments,” Iron Steel Technol. , October, p 157–176, 2015.