Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

Cui, Z.; Patel, Jay; Palmiere, E.J.

doi:10.1002/9781119223399.ch30

Cited by 3 publications

(2 citation statements)

References 79 publications

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“…Reproduced with permission from Springer [46]. Owing to the competing effect of recrystallisation and austenite grain boundary pinning at the onset of deformation-induced NbC precipitation, partial recrystallisation occurs during hot deformation [9,53]. Hot torsion testing of C–Mn–Cr–Nb rail steel at BHP Melbourne Research Laboratories, Australia (Ref 23 in [9]) indicated that austenite recrystallisation becomes sluggish during deformations at 1000C starting from 0.015–0.035 wt-% Nb, dissolved in 0.4–0.8 wt-% C steels reheated at 1260–1300C.…”

Section: Effect Of Niobium On Prior Austenite Grain Structurementioning

confidence: 99%

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Niobium microalloying in rail steels

Ray

2017

Materials Science and Technology

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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

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Section: Effect Of Niobium On Prior Austenite Grain Structurementioning

confidence: 99%

“…It was suggested to confine the rolling to C to minimise these problems. More recently, Cui et al [53] also showed partial recrystallisation of hot deformed austenite at finish deformation temperatures of 950–1000C for 0.6C–0.018Nb (wt-%) steel.…”

Section: Effect Of Niobium On Prior Austenite Grain Structurementioning

confidence: 99%

Niobium microalloying in rail steels

Ray

2017

Materials Science and Technology

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Effect of Niobium Supersaturation in Austenite on the Static Recrystallization Behavior of Carbon Structural Steels

Rakshe

Patel²,

Palmiere

2022

Metall Mater Trans A

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This work describes the effect of Nb supersaturation in austenite on the suppression of static recrystallization of austenite during an isothermal holding period following hot deformation. The investigation involved three carbon structural steels with varying Nb concentration at constant C (0.20 pct) and N (0.007 pct) levels. The isothermal double-hit deformation technique led to the determination of T5 pct and T95 pct (recrystallization-stop and full recrystallization temperatures, respectively) as a function of a true strain and interpass time. The results indicate that the T5 pct increases with increasing Nb supersaturation in austenite at a rate of 40 °C per 0.006 pct Nb supersaturation for a true stain ε=0.40. At each respective T5 pct, all tested steels exhibited an Nb supersaturation ratio ≥ 7.5 in austenite. A high, localized strain-induced precipitation of Nb(CN) was observed at the austenite subgrain boundaries in the unrecrystallized microstructure. This translated into higher values for local precipitate-pinning forces (FPIN), which were significantly higher than that predicted from equilibrium thermodynamics. The critical FPIN for retardation of static recrystallization was found to be 1.6 MPa at the respective T5 pct for each steel. The present study has contributed to advancing our knowledge of the interplay between Nb solute supersaturation and volume fraction of Nb(CN) precipitation in particular for carbon structural steels. It has also highlighted an opportunity to apply niobium, even an ultra-low addition (i.e., < 100 ppm) to commodity-grade structural steels to reduce overall alloying costs.

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Bridging the gap: enabling lower carbon footprint and creating economic value from application of modern high strength niobium steels

Patel¹

2018

IABSE Reports

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<p>This paper presents examples from a bridge and tall-building structure to demonstrate how important it is from the outset that engineers select the correct type of steels (beyond just grade selection), its alloy design and manufacturing route is in bringing about a combination of environmental (savings of >1,000t of CO2) and economic value (savings of >$100,000s) that is felt throughout the supply chain. It will discuss the advantages niobium micro-alloyed steel systems bring and highlights how to extract maximum contribution from them. Attention is given to the individual and distinct metallurgical role it plays and how judicious additions, only costing a few dollars per tonne of steel, can leverage significant value.</p><p>The paper concludes, that in today’s market driven environment it is of growing necessity that engineers do take in consideration the advantages that modern niobium micro-alloyed high strength steels can bring through their correct selection at the very start of the design process.</p>

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Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

Cited by 3 publications

References 79 publications

Niobium microalloying in rail steels

Niobium microalloying in rail steels

Effect of Niobium Supersaturation in Austenite on the Static Recrystallization Behavior of Carbon Structural Steels

Bridging the gap: enabling lower carbon footprint and creating economic value from application of modern high strength niobium steels

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