Development of New High-Strength Carbide-Free Bainitic Steels
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In this paper, an attempt was made to optimize the mechanical properties by tailoring the process parameters for two newly developed high-strength carbide-free bainitic steels with the nominal compositions of 0.47 pct C, 1.22 pct Si,1.07 pct Mn, 0.7 pct Cr (S1), and 0.5 pct was obtained.Abstract:
An attempt was made to optimize the mechanical properties by tailoring the process parameters for two newly developed high-strength carbide-free bainitic steels with the nominal compositions of 0.47 pct C, 1.22 pct Si, 1.07 pct Mn, 0.7 pct Cr (S1), and 0.30 pct C, 1.76 pct Si, 1.57 pct Mn, and 0.144 pct Cr (S2) (wt pct), respectively. Heat treatment was carried out via two different routes: (1) isothermal transformation and (2) quenching followed by isothermal tempering. The results for the two different processes were compared. The bainitic steels developed by isothermal heat treatment were found to show better mechanical properties than those of the quenched and subsequently tempered ones. The effect of the fraction of the phases, influence of the transformation temperatures, the holding time, and the stability of retained austenite on the mechanical properties of these two steels was critically analyzed with the help of X-ray diffraction, optical metallography, scanning electron microscopy, and atomic force microscopy. Finally, a remarkable combination of yield strength of the level of 1557 MPa with a total elongation of 15.5 pct was obtained.read more
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Fundamentals and application of solid-state phase transformations for advanced high strength steels containing metastable retained austenite
Zongbiao Dai,Hao Chen,Ran Ding,Qi Lu,Chi Zhang,Zhigang Yang,Sybrand van der Zwaag,Sybrand van der Zwaag +7 more
TL;DR: In this paper, the authors provide a brief review of the desired microstructures for Transformation-induced plasticity (TRIP), Carbide-free Bainitic (CFB), Quenching & Partitioning (Q&P), and Medium Manganese steels followed by comprehensive discussions on the phase transformations to be used in their creation.
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Characterization of microstructures and tensile properties of TRIP-aided steels with different matrix microstructure
TL;DR: In this article, three different heat treatment processes have been proposed as a fundamental method to produce three kinds of TRIP-aided steels with polygonal ferritic matrix (F-TRIP), bainitic matrix (B-Trip), and martensitic matrix, and the work hardening of the samples was evaluated by calculating the instantaneous n value as a function of strain.
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Development of continuously cooled low-carbon, low-alloy, high strength carbide-free bainitic rail steels
TL;DR: In this article, an analytical approach for understanding the effects of different alloying elements on the thermodynamic and kinetic aspects of bainite transformation and the resultant microstructure and mechanical properties is presented.
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Critical Assessment 22: bainitic forging steels
TL;DR: In this article, a critical assessment is performed concerning the most important influencing parameters and processing routes for bainitic steels, and cooling concepts are discussed regarding their optimal chemical composition, achievement of homogeneous microstructure and a low sensitivity to processing parameters.
References
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I and i
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Journal ArticleDOI
Very strong bainite
TL;DR: A steel with an ultimate tensile strength of 2500 MPa, a hardness at 600-670 HV and toughness in excess of 30-40 MPa/m 1/2 is the result of exciting new developments with bainite as discussed by the authors.
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The bainite transformation in a silicon steel
Abstract: An experimental silicon steel has been used in a detailed kinetic and structural study of the bainite transformation in an attempt to resolve some of the controversies concerning the reaction mechanism. Distinct reaction ‘C’ curves and transformation mechanisms were observed for the upper and lower bainite reactions. The observed set of three minima in transformation kinetics were found to be incompatible with the solute drag explanation of the kinetic Bs temperature. Transmission electron microscopy indicated the growth of both upper and lower bainite by the propagation of displacive subunits, with adjacent nucleation in the latter case. Definite evidence for carbon supersaturation was obtained for the lower bainitic ferrite. The results are best explained in terms of a shear mechanism for the ferritic component of bainite rather than a ledge mechanism (as is observed in Widmanstatten ferrite growth). Carbide precipitation events were also characterized and the evidence suggested that precipitation resulted from the aging of a supersaturated matrix in lower bainite. The evidence also suggests that carbide precipitation events are of secondary importance to the essence of bainite formation. It was further proven that the concept of a metastable equilibrium1 controlling the transition from upper to lower bainite was not applicable to the present steel and indeed, if any metastable equilibrium does exist in any other steel, it does not constitute a general phenomenon and hence is not essential to the bainite transformation mechanism.
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The mechanism of bainite formation in steels
TL;DR: In this article, microstructural evidence, together with a thermodynamic analysis, of the bainite reaction in steels are presented in support of a growth mechanism involving the propagation of displacive sub-units.