Rail steels rely primarily for their properties on wear and rolling-contact-fatigue resistance. These properties, together with toughness, can be optimised by implementing thermo-mechanical processing during rail manufacturing, assisted by controlled additions of strong carbide-forming microalloying elements. Niobium can be used at low concentrations, but the major difficulty is to ensure that niobium does not segregate during casting, especially when rail steels are high in carbon content. The solubility of niobium in ternary Fe–Nb–C austenite is critically assessed to address the issue of segregation. Thereafter, the effect of niobium on medium- and high-carbon (∼0.2–0.8 wt-% C) austenite grain-growth kinetics during reheating or recrystallisation kinetics during hot deformation, and the corresponding effect on pearlitic and bainitic microstructures and mechanical properties are reviewed.
This review was chosen as a runner up of the 2017Materials Literature Review Prize of the Institute ofMaterials,Minerals andMining, run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged
BhadeshiaHKDH. Steels for rails. In: Buschow K, Cahn RW, Flemings MC, Iischner B, Kramer EJ, Mahajan S, editors. Encyclopedia of materials science: science and technology. Oxford: Pergamon Press; 2007. p. 1–7, Elsevier Science, ISBN 0-08-0431526.
2.
HillertM. The formation of pearlite. In: Decomposition of Austenite by Diffusional Processes: Proceedings of a Symposium Held in Philadelphia, PA; 1960 Oct 19; under the sponsorship of the Ferrous Metallurgy Committee of the Institute of Metals Division, The Metallurgical Society, American Institute of Mining, Metallurgical, and Petroleum Engineers; 1962. p. 219–247.
3.
De GraefM, KralMV, HillertM. A modern 3-D view of an ‘Old’ pearlite colony. JOM. 2006;58(12):25–28. doi: 10.1007/BF02748491
4.
TanakaT. Controlled rolling of steel plate and strip. Int Metals Rev. 2013;26(1):185–212.
5.
KlinkenbergC, HulkaK, BleckW. Niobium carbide precipitation in microalloyed steel. Steel Res Int. 2004;75(11):744–752. doi: 10.1002/srin.200405837
6.
MohrbacherH. Niobium microalloyed automotive sheet steel – a cost effective solution to the challenges of modern body engineering. Niobium microalloyed sheet steels for automotive applications edited by TMS. Araxa, Brazil: The Minerals, Metals and Materials Society; 2006. p. 1–23.
7.
NishiokaK, IchikawaK. Progress in thermomechanical control of steel plates and their commercialization. Sci Technol Adv Mater. 2012;13(2):023001. doi: 10.1088/1468-6996/13/2/023001
WilliamsJG, SimpsonID, MacDonaldJK. Niobium in rail steels. Niobium-Proceedings of the International Symposium, Metallurgical Society of AIME, San Francisco, CA; 1984.
10.
De BoerH, MasumotoH. Niobium in rail steel. International Symposium on Niobium; 2001. p. 821–844.
11.
BalasubramanianK. Thermodynamics of microalloyed austenites and nonstoichiometric carbides and nitrides [PhD thesis]. Hamilton, Ontario, Canada: McMaster University; 1988.
12.
TanakaT, OhtaniH, NishizawaT, HasebeH. In: Proc. Japan-Canada Seminar on Secondary Steelmaking; 1985. p. J–7.
13.
DeKazinczyF, AxnasA, PachleitnerP. Some properties of niobium treated mild steel. Jernkont Ann. 1963;147:408.
14.
MoriT, FujitaK, TokizaneM, YamaguchiK. Behavior of niobium carbides and nitrides in steel. Tetsu-to-Hagane. 1964;50(6):911–917.
15.
NaritaK, KoyamaS. The physical chemistry of steels containing vanadium niobium, and tantalum. Tetsu To Hagane. 1966;52(4):788.
SmithRP. The solubility of niobium/columbium/ carbide in gamma iron(solubility of niobium carbide in gamma iron from carbon content of series of iron-niobium alloys equilibrated with hydrogen-methane mixtures). AIME, Trans. 1966;236:220.
18.
AuglandB, ChristensenN, JohansenTH. The solubility of niobium/columbium/ carbide in gamma iron(solubility of niobium carbide in gamma iron determined from experiments using Fe–Nb alloy in equilibrium with hydrogen-methane mixtures). AIME, Trans. 1967;239:1651–1654.
19.
NordbergH, AronssonB. Solubility of niobium carbide in austenite. J Iron Steel Inst. 1968;206(12):1263–1266.
20.
KoyamaS, IshiiT, NaritaK. Effects of Mn, Si, Cr, and Ni on the solution and precipitation of niobium carbide in iron austenite. Japan: Kobe Steel Ltd.; 1971. (Technical report).
21.
LakshmananVK. Thermodynamics of the interstitial phases of niobium in iron austenite [PhD thesis]. Hamilton, Ontario, Canada: McMaster University; 1977.
22.
SharmaRC, LakshmananVK, KirkaldyJS. Solubility of niobium carbide and niobium carbonitride in alloyed austenite and ferrite. Metall Trans A. 1984;15(3):545–553. doi: 10.1007/BF02644979
23.
HuangW. A thermodynamic evaluation of the Fe–Nb–C system. Z Metallkd. 1990;81(6):397–404.
24.
LeeBJ. Thermodynamic assessment of the Fe–Nb–Ti–C–N system. Metall Mater Trans A. 2001;32(10):2423–2439. doi: 10.1007/s11661-001-0033-x
25.
IrvineK, PickeringF, GladmanT. Grain-refined C-Mn steels. Iron Steel Inst J. 1967;205(2):161–182.
26.
BalasubramanianK, KirkaldyJS. Austenite- nonstoichiometric precipitate equilibria in microalloyed steels: part I: Fe–Ti–C and Fe–Nb–C systems. Calphad. 1986;10(2):187–202. doi: 10.1016/0364-5916(86)90021-0
HasebeM, OhtaniH, NishizawaT. to be contributed to Met. Trans. A; Referred in [27].
29.
GustafsonP. A thermodynamic evaluation of the Fe–C system. Scand J Metall. 1985;14(5):259–267.
30.
BalasubramanianK, KroupaA, KirkaldyJS. Experimental investigation of the thermodynamics of Fe–Nb–C austenite and nonstoichiometric niobium and titanium carbides (T=1273 to 1473 K)'. Metall Trans A. 1992;23(3):729–744. doi: 10.1007/BF02675551
31.
SaundersN, GuoUKZ, LiX, MiodownikAP, SchillJP. Using JMatPro to model materials properties and behavior. JOM. 2003;55(12):60–65. doi: 10.1007/s11837-003-0013-2
32.
DaviesRH, DinsdaleAT, GisbyJA, RobinsonJAJ, MartinSM. MTDATA–thermodynamic and phase equilibrium software from the national physical laboratory. Calphad. 2002;26(2):229–271. doi: 10.1016/S0364-5916(02)00036-6
KestenbachHJ, ItmanA, NishiAM, RocaIB, ValentinC. ‘Metallographic studies of eutectics carbides in high niobium microalloyed steels’, In 4 Brazilian Congress on Materials Science and Engineering, Brazil, 1980.
35.
BernetičJ, BradaškjaB, KosecG, BriceljE, KosecB, VodopivecF, KosecL. ‘Centreline formation of Nb(C,N) eutectic in structural steel’. Metalurgija. 2010;49(1):29–32.
36.
VodopivecF, GahrovšekM, RaličB. Solution of eutectic niobium carbonitride in austenite in mild steel. Metal Sci. 1975;9(1):324–326. doi: 10.1179/030634575790444694
37.
ZambergerS, PudarM, Spiradek-HahnK, ReischlM, KozeschnikE. Numerical simulation of the evolution of primary and secondary Nb(CN), Ti(CN) and AlN in Nb-microalloyed steel during continuous casting. Int J Mater Res. 2012;103(6):680–687. doi: 10.3139/146.110688
38.
KumarS, ShuklaS, DeS, SaxenaA, JhaB, MishraB, VermaA, MallikS. API X 70 grade HR coils for ERW pipes. Int J Metall Eng. 2013;2(2):179–187.
39.
DavisCL, StrangwoodM. Segregation behaviour in Nb microalloyed steels. Mater Sci Technol. 2009;25(9):1126–1133. doi: 10.1179/174328409X453262
40.
MingW, DangshenMA, ZhentianL, JianZ, HongxiaoC, JianqingD. Effect of nb on segregation, primary carbides and toughness of H13 steel. Acta Metall Sin. 2014;50(3):285–293.
41.
DenAWB. Characterization of ferroniobium and the thermodynamics and kinetics of dissolution of niobium compounds in liquid iron [Master's thesis]. Hamilton, Ontario, Canada: McMaster University, 2013.
42.
LiuC, HuangY, LiuH, JiangM. Effects and mechanisms of niobium on the fracture toughness of heavy rail steel. Adv Mater Res. 2011;163:110–116.
43.
ColadasR, MasounaveJ, GuerinG, BaïlonJP. Austenite grain growth in medium and high-carbon steels microalloyed with niobium. Metal Sci. 1977;11(11):509–516. doi: 10.1179/030634577790432857
44.
NolascoA, OliveiraEQ, LeonardosG, BordignonPJP. Niobium in Si-Mn rail steel. Proceedings of the Int. Symposium Niobium 81, San Francisco, CA; 1984. p. 1041–1060.
45.
da FonsecaMDGM, de AlmeidaLH, GomesLCFC, Le MayI. Effects of microstructural parameters on the mechanical properties of eutectoid rail steels. Mater Charact. 1997;39(1):1–14. doi: 10.1016/S1044-5803(97)00086-7
46.
KestenbachHJ, MartinsGS. Effect of niobium on austenite recrystallization and pearlite colony size in a microalloyed eutectoid steel. Metall Trans A. 1984;15(7):1496–1499. doi: 10.1007/BF02648581
47.
JanstoSG. Niobium-bearing structural steels for the 21st century. Niobium Bearing Struct Steels. 2010;1–27.
48.
JanstoS. Current niobium developments in high carbon steel applications. MS&T 2011, Materials Science & Technology 2011 Conference and Exhibition (MS&T Partner Societies), Columbus, Ohio; 2011. p. 642–653.
49.
JanstoS. Applied metallurgy of the microniobium alloy approach in long and plate products. In Metal; Brno, Czech Republic, EU; 2012.
50.
JanstoSG. Microniobium alloy approach in medium and high carbon steel bar, plate and sheet products. Metall Mater Trans B. 2014;45(2):438–444. doi: 10.1007/s11663-013-9837-5
51.
JanstoS. Metallurgical mechanism and niobium effects on improved mechanical properties in high carbon steels. In: TMS, editor. HSLA Steels 2015, Microalloying 2015 & Offshore Engineering Steels 2015: Conference Proceedings; John Wiley & Sons, Inc., Hoboken, NJ, USA; 2015. p. 981–986.
52.
ColadasR, MasounaveJ, BallonJP. The hot deformation of austenite, ed. J.B. Balance. New York: AIME; 1977. p. 341–383.
WadaT, FukudaK. Effect of rolling in low temperature austenite region on strength, ductility and toughness of rail steels. Tetsu-to-Hagane. 1987;73(9):1162–1169.
55.
CotrinaE, LópezB, Rodriguez-IbabeJM. Influence of thermomechanical treatment on the austenite-pearlite transformation in a high carbon nb-microalloyed steel. Symposium on the Thermodynamics, Kinetics, Characterization and Modeling of Austenite Formation and Decomposition; 2003. p. 213–225.
56.
SuginoK, KageyamaH, MasumotoH. Development of weldable high-strength steel rails. Proc. Second Heavy Haul Railway Conference, Paper; 1982. p. 187–196.
57.
YangZ, WangH, JiY. Study on Nb microalloying in high carbon pearlite steels for rails. In: TMS, editor. HSLA Steels 2015, Microalloying 2015 & Offshore Engineering Steels 2015: Conference Proceedings; John Wiley & Sons, Inc., Hoboken, NJ; 2015. p. 987–993.
58.
MauritczatL, GroßK, HulkaK, KoerferE, KudielkaE. Niob als mikrolegierungselement in eutektoiden sthlen am beispiel der schienensthle. Berg- und Httenmnnische Monatshefte. 1984;129:25–34.
59.
SinghUP, SinghR, JhaS. Influence of microalloying on fracture toughness and wear resistance of rail steel. Scand J Metall. 1995;24(4):180–186.
60.
MillerSL. Effect of microalloying on pearlite transformation of high carbon wire steels [PhD thesis]. Golden, CO: Colorado School of Mines; 2007.
61.
GuoN, LiuQ. Back-scattered electron imaging combined with ebsd technique for characterization of pearlitic steels. J Microsc. 2012;246(3):221–228. doi: 10.1111/j.1365-2818.2011.03601.x
62.
BhadeshiaHKDH, HoneycombeR. Steels: microstructure and properties. Oxford, UK: Butterworth-Heinemann; 2011.
63.
PickeringFB, GarbarzB. The effect of transformation temperature and prior austenite grain size on the pearlite colony size in vanadium treated pearlitic steels. Scr Metall. 1987;21(3):249–253. doi: 10.1016/0036-9748(87)90207-9
64.
Rodriguez-IbabeJM, LópezB. Thermomechanical processing and role of microalloying in eutectoid steels. In: Weng Y, Dong H, Gan Y, editors. Advanced Steels; Heidelberg: Springer; 2011. p. 475–484.
65.
ParkYJ, BernsteinIM. The process of crack initiation and effective grain size for cleavage fracture in pearlitic eutectoid steel. Metall Trans A. 1979;10(11):1653–1664. doi: 10.1007/BF02811698
66.
MendizabalL, Iza-MendiaA, LópezB, Rodriguez-IbabeJM. Influence of vanadium microaddition on the microstructure and mechanical properties of high strength large diameter wire-rods. In: Rodriguez-Ibabe JM, Gutiérrez I, López B, Iza-Mendia A, editors. Microalloying for New Steel Processes and Applications, Materials Science Forum. Vol. 500; Donostia-San Sebastián, Basque Country, Spaine: Trans Tech Publ.; 2005. p. 761–770.
67.
MagelE. Rolling contact fatigue: a comprehensive review. No. DOT/FRA/ORD-11/24; 2011.
68.
BhadeshiaHKDH. Steels for bearings. Progress Mater Sci. 2012;57(2):268–435. doi: 10.1016/j.pmatsci.2011.06.002
69.
SteeleRK, ReiffRP. Rail: its behavior and relationship to total system wear; Included in Proceedings of FAST (Facility for Accelerated Service Testing) Engineering Conference, Denver, Colorado, 1981, p. 115–164(a).
70.
DanielsLE, BlumeN. Rail corrugation growth performance. Second International Heavy Haul Railway Conference, Colorado Springs, CO; 1982. p. 294–318.
71.
YokoyamaH, MitaoS, YamamotoS, KataokaY, SugiyamaT. High strength bainitic steel rails for heavy haul railways with superior damage resistance; NKK Technical Report – Japanese Edition, Chiyoda, Tokyo: JFE Steel; 2000. p. 17–23.
72.
ReesGI, PerdrixJ, MaurickxT, BhadeshiaHKDH. The effect of niobium in solid solution on the transformation kinetics of bainite. Mater Sci Eng: A. 1995;194(2):179–186. doi: 10.1016/0921-5093(94)09673-2
73.
YakubtsovIA, BoydJD. Bainite transformation during continuous cooling of low carbon microalloyed steel. Mater Sci Technol. 2001;17(3):296–301. doi: 10.1179/026708301773002491
74.
TsuzakiK, UedaT, FujiwaraK, MakiT. Increase in retained austenite by ausforming in an austempered silicon steel. New Mater Process Future. 1989;799–804.
75.
BhadeshiaHKDH. Bainite in steels. London, UK: Institute of Metals; 1992.
76.
MatsuzakiA, BhadeshiaHKDH. Effect of austenite grain size and bainite morphology on overall kinetics of bainite transformation in steels. Mater Sci Technol. 1999;15(5):518–522. doi: 10.1179/026708399101506210
77.
ShipwayPH, BhadeshiaHKDH. Mechanical stabilisation of bainite. Mater Sci Technol. 1995;11(11):1116–1128. doi: 10.1179/mst.1995.11.11.1116
78.
BhadeshiaHKDH. Effect of stress & strain on formation of bainite in steels. Hot Workability Steels Light Alloys-Compos. 1996;543–556.
alloy approach in long and plate products. In Metal; Brno, Czech Republic, EU; 2012