Journal ArticleDOI
Effect of tempering on the microstructure and mechanical properties of a medium carbon bainitic steel
TLDR
In this paper, the effect of tempering on the microstructure and mechanical properties of a medium carbon bainitic steel has been investigated through optical microscopy, electron back-scattered diffraction, transmission electron microscopy and X-ray diffraction analyses.Abstract:
The effect of tempering on the microstructure and mechanical properties of a medium carbon bainitic steel has been investigated through optical microscopy, electron back-scattered diffraction, transmission electron microscopy and X-ray diffraction analyses. A nano-level microstructure containing plate-like bainitic ferrite and film-like retained austenite is obtained by isothermal transformation at Ms+10 °C followed by tempering within 240–450 °C. Results show that the sample tempered at 340 °C occupies the optimal balance of strength and toughness by maintaining a certain level of plasticity; samples tempered at 320 °C and 360 °C with low and high yield ratio come second. The microstructure of the steel is not sensitive to tempering temperatures before 360 °C. When the temperature is increased to 450 °C, the significantly coarsened bainitic ferrite plate and the occurrence of a small quantity of carbide precipitation account for its low toughness. The amount of retained austenite increases with the tempering temperature before 400 °C, followed by decreasing with further increase in the temperature. This behavior is related to the competition between retained austenite further transforming into bainite and decomposing into carbide during tempering.read more
Citations
More filters
Journal ArticleDOI
Effects of austempering temperature on bainitic microstructure and mechanical properties of a high-C high-Si steel
TL;DR: In this paper, a high-C high-Si bainitic steel, by austempering around the nose-tip temperature of the TTTT diagram, revealed multiple lengths of nanobainite plates and various sizes and shapes of retained austenite.
Journal ArticleDOI
Evolution of microstructure and mechanical properties during tempering of M50 steel with Bainite/Martensite duplex structure
TL;DR: In this article, the evolution of microstructure and mechanical properties during tempering of M50 steel with bainite/martensite (B/M) duplex structure have been investigated.
Journal ArticleDOI
Effect of retained austenite on impact toughness and fracture behavior of medium carbon submicron-structured bainitic steel
TL;DR: In this article, the effects of retained austenite on the crack propagation behavior of a submicron-structured bainitic steel under impact fracture were studied using scanning electron microscopy (SEM), TEM, and electron back-scattering diffraction (EBSD).
Journal ArticleDOI
Effect of tempering conditions on adiabatic shear banding during dynamic compression and ballistic impact tests of ultra-high-strength armor steel
TL;DR: In this article, the roles of strain-hardening rate on susceptibility of adiabatic shear band (ASB) formation and subsequent cracking were investigated in two ultra-high-strength armor steel plates heat-treated differently.
Journal ArticleDOI
Inconsistent effects of austempering time within transformation stasis on monotonic and cyclic deformation behaviors of an ultrahigh silicon carbide-free nanobainite steel
TL;DR: In this paper, the effects of transformation stasis after the incomplete transformation of carbide-free bainite have been studied, and the best combination of strength and ductility was obtained through a longer austempering time within transformation stabilization, which did not result in longer fatigue life.
References
More filters
Journal ArticleDOI
Structure–properties relationship in TRIP steels containing carbide-free bainite
TL;DR: In this article, the authors review the current knowledge about the relationship between the micro-structure of cold rolled intercritically annealed low-alloy TRIP-aided sheet steels and their mechanical properties from a materials engineering point of view.
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.
Journal ArticleDOI
Tempering of steel
G. R. Speich,W. C. Leslie +1 more
TL;DR: In this article, the authors present an understanding of the processes involved in the tempering of iron-carbon martensites and how they are affected by alloying elements, and how these processes overlap and occur on such a fine scale.
Journal ArticleDOI
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.
Journal ArticleDOI
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.