Effect of Rolling in Low Temperature Austenite Region on Strength, Ductility and Toughness of Rail Steels

Niobium in Microalloyed Rail Steels

“…Therefore, for refined or unrecrystallised austenite, strength may decrease due to the coarsening of the lamellar spacing [72]. This trend is confirmed as illustrated in Figure 2.14 by Wada et al [80] for non-microalloyed 0.78C-1Mn (wt%) steel. But for the Nb-microalloyed 0.81C-1Mn-0.018Nb (wt%), though the transformation temperature increases with decreasing finish rolling temperature, the yield strength tends to increase.…”

“…Niobium addition is said to increase the no-recrystallisation temperature (T nR ). Wada et al [80] carried out a detailed analysis for the effect of 0.02 wt% Nb microalloying and controlled finish rolling at low temperature (710-960 o C) austenite region for eutectoid rail steel compositions. Increased T nR at 870-890 • C for Nbmicroalloyed steels (Nb, Cr+Nb, Si+Nb in ref [80]) were reported compared to 760-800 • C T nR for the non-microalloyed steels (BA, Cr, Si steels in ref [80]).…”

“…Wada et al [80] carried out a detailed analysis for the effect of 0.02 wt% Nb microalloying and controlled finish rolling at low temperature (710-960 o C) austenite region for eutectoid rail steel compositions. Increased T nR at 870-890 • C for Nbmicroalloyed steels (Nb, Cr+Nb, Si+Nb in ref [80]) were reported compared to 760-800 • C T nR for the non-microalloyed steels (BA, Cr, Si steels in ref [80]). Cotrina et al [81] carried out multi-pass hot torsion tests on 0.78C-0.03Nb (wt%) steels and showed recrystallised austenite grains of size 60-80 µm with finish rolling temperature (FRT) of 1060 o C while austenite remains un-recrystallised for FRT 870 o C. Figure 2.13a attempts to summarise the T nR temperatures reported in literature with increasing niobium content.…”

“…But for the Nb-microalloyed 0.81C-1Mn-0.018Nb (wt%), though the transformation temperature increases with decreasing finish rolling temperature, the yield strength tends to increase. Strain induced precipitation of niobium carbo-nitride (NbCN) was attributed to the strength increase despite coarser lamellar spacing due to higher transformation temperature [80]. Liu et al [68] observed fine niobium rich precipitates in both ferrite and cementite lamellae of pearlite ( Yang et al [83] also reported increasing interlamellar spacing (ILS) with increasing niobium content [Steel 6700: 148 nm, Steel 6704: 178 nm, Steel 6910: 193 nm] 5 during normalizing from 850 o C. For similar heat-treated austenite grain sizes, Gomes et al [71] reported about 10% increase in mean true ILS for 0.76C-0.045Nb (wt%) steel compared to its non-microalloyed counterpart.…”

Study on Wear and Fatigue Performance of Two Types of High-Speed Railway Wheel Materials at Different Ambient Temperatures

“…Contact points of the rail and wheel in a variety of paths [4]. As early as the 1980s, some scholars have studied the material properties of ferritic steel at low temperature by means of mechanical experiments and material preparation methods [19][20][21][22][23][24]. The results showed that extreme temperatures can cause the degradation of various ferritic steel properties, such as strength and toughness, before the formation of macroscopic cracks, affecting the safety of wheel/rail services [25][26][27].…”