Effect of Boron Addition and Sintering Atmosphere on Precipitation in Sintered Fe-Mo-C Steels

Abstract:

Sintered steels, with and without boron addition, were prepared from powder compacts of pre-alloyed Fe-1.5Mo powder mixed with varied amounts of graphite (0, 0.1, 0.2, 0.3, and 0.4 wt.%) and hexagonal boron nitride (0 and 0.5 wt.%). Sintering was performed either in hydrogen or in vacuum atmosphere at 1280 °C for 45 minutes. The post-sintering cooling was performed in a furnace that was equivalent to 0.1 °C/s. The sintered boron-free steels showed dual-phase microstructure consisting polygonal ferrite and precipitate-containing grains. Each precipitate-containing grain contained packets, each of which was characterized by lamellar structure with alternating fibrous particles and ferritic laths, when carbon contents were in the range 0.1-0.3 wt.%. All the grains containing fine needle particles decorating ferritic lath boundaries were observed in the sintered Fe-Mo-0.4C steels. Boron addition caused some effects on sintered steels. The action of boron was the formation of grain boundary boride in the vacuum-sintered steels although it was hardly observed in case of hydrogen-sintered steels. Boron also promoted precipitation inside polygonal ferrite grains and along ferritic lath boundaries. The precipitate particle shape was fine needle-like in the sintered boron-containing steels. Due to liquid phase sintering, as a result of eutectic melting, the associated grain growth was observed. Disappearance of grain boundary boride was evidenced in the hydrogen-sintered steels. Without boron addition, hardening of the sintered steels strongly depended on carbon content. With boron addition, all the sintered steels showed high tensile strength and hardness even in the case of no graphite addition. Hardening action by carbon in the sintered boron-containing steels was weaker than that in the sintered boron-free steels.

• Periodical: Key Engineering Materials (Volume 798)
• Pages: 9-16
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.798.9
• Online since: April 2019
• Authors: Nattaya Tosangthum, Prapas Kunnam, Monnapas Morakotjinda, Wantana Koetniyom, Rungtip Krataitong, Pongsak Wila, Ruangdaj Tongsri*
• Keywords: Boride, Carbide, Ferrite, Sinter Hardening, Sintering

References

[1] R. W. K. Honeycome, F. B. Pickering, Ferrite and bainite in alloy steels, Metall Trans. 3(1972) 1099-1112.

[2] C.T. Schade, T. Murphy, A. Lawley, R. Doherty, Microstructure and mechanical properties of micro-alloyed PM steels, Int. J. Powder Metall. 48 (2012) 51-59.

[3] P.K. Sokolowski, B.A. Lindsley, Influence of chemical composition and austenitizing temperature of hardenability of PM steels, Advances in Powder Metallurgy and Particulate Materials, MPIF, New Jersey, USA, (2009).

[4] B. Lindsley, H. Rutz, Effect of molybdenum content in PM Steels, Hoeganaes Corporation, New Jersey, USA, (2009).

[5] R. G. Kamat, E. B. Hawbolt, J. K. Brimacombe, Predicting the onset of transformation cooling conditions: part II application pearlite transformation, Metall Mater Trans A. 26 (1995) 1993-2000.

DOI: 10.1007/bf02670671

[6] S.F.D. Martino and G. Thewlis, Transformation Characteristics of Ferrite/Carbide Aggregate in Continuously Cooled, Low Carbon-Manganese Steel, Metall Mater Trans A. 44 (2013) 3-18.

DOI: 10.1007/s11661-013-2035-x

[7] L.J. Habraken, M. Economopoulos, Transformation and Hardenability in Steels, Climax molybdenum Co., Ann Arbor, Michigan, (1967).

[8] D.N. Shackleton, P. M. Kelly, The crystallography of cementite precipitation in the bainite transformation, Acta Metall. 15 (1967) 979-992.

DOI: 10.1016/0001-6160(67)90263-5

[9] G. Spanos, M. G. Hall, The formation mechanisms, morphology and crystallography of ferrite sideplates, Metall. Trans. A, 27 (1996) 1519-1534.

DOI: 10.1007/bf02649812

[10] M. Skałoń, J. Kazior, Enhanced sintering of austenitic stainless steel powder AISI 316L through boron containing master alloy addition, Arch Metall Mater, 57(2012) 789-797.

DOI: 10.2478/v10172-012-0086-4

[11] A. Molinari, G. Straffelini, T. Pieczonka, J. Kazior, Dilatometry study of the sintering behavior of boron-alloyed Fe-1.5 pct. Mo powder, Int. J. Powder Metall. 31 (2000) 1497-1506.

DOI: 10.1007/s11661-000-0160-9

[12] J. Liu, A. Cardamone, T.J. Potter, R.M. German, F.J. Semel, Boron-enhanced sintering of iron-molybdenum steels, Int. J. Powder Metall. 37(2001) 39-46.

[13] H. Danninger, V. Vassileva, G.M. Christian, Embritting Components in sintered steel, comparison of phosphorous and boron, Powder metall. prog. 17 (2017) 047-064.

[14] J. Karwan-Baczewska, M. Ross, Effect of boron on microstructure and mechanical properties of PM sintered and nitrided steels, Powder Metall. 44(2001) 221-226.

DOI: 10.1179/003258901666374

[15] P. Ninpetch, A. Luechaisirikul, Monnapas Morakotjinda, T. Yotkaew, R. Krataitong, N. Tosangthum, S. Mahathanabodee, R. Tongsri, Effect of boron nitride on microstructure of Fe-Cr-Mo-BN-C steel sintered in vacuum, Mater. Today: Proceedings 5 (2018) 9409-9416.

DOI: 10.1016/j.matpr.2017.10.118

[16] M. Momeni, C. Gierl, H. Danninger, Thermoanalytical sintering studies of Fe-C admixed with ferroboron performed in different atmospheres, Powder Metall. 55 (2012) 54-64.

DOI: 10.1179/1743290111y.0000000020

[17] M. Tsuda, Deboronization phenomena in Fe-Ni alloys, Tetsu-to-Hagane, 82 (1996)153-158.

DOI: 10.2355/tetsutohagane1955.82.2_153

[18] A. Kapito, W. Stumpf, M.J. Papo, The role of alloying elements in bainitic rail steels. The Journal of The Southern African Institute of Mining and Metallurgy 113 (2013) 67-72.

[19] W. Srijampan, M. Morakotjinda, R. Krataitong, T. Yotkaew, N. Tosangthum, A. Wiengmoon, R. Tongsri, Sintered dual-phase steels produced from pre-alloyed Fe-Cr-Mo powder, Chiang Mai J. Sci., 43 (2016) 358-364.

DOI: 10.1016/j.matdes.2015.09.030

[20] M. V. Sundaram, K. B. Surreddi, E. H. Eiga, S. Berg, F.Castro, and L. Nyborg, Enhanced densification of PM steels by liquid phase sintering with boron-containing master alloy, Metall Mater Trans A. 49 (2018) 255-263.

DOI: 10.1007/s11661-017-4383-4

[21] V. Vassileva, H. Danninger, S. Strobl, and C. Gierl, Thermoanalytical sintering studies of Fe-C admixed with ferroboron performed in different atmospheres, Euro PM2007 Congress Proceedings, (2007) 53–58.

DOI: 10.1179/1743290111y.0000000020