Topic
Bainite
About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.
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TL;DR: In this paper, the effect of ausforming on kinetics, morphology and crystallography of nanobainite steel was examined by electron backscattered diffraction and transmission electron microscopy.
91 citations
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TL;DR: In this article, the influence of the hardness of martensite and ferrite phases in dual phase steel on void formation has been investigated by in situ tensile loading in a scanning electron microscope.
Abstract: The influence of the hardness of martensite and ferrite phases in dual phase steel on void formation has been investigated by in situ tensile loading in a scanning electron microscope. Microstructural observations have shown that most voids form in martensite by evolving four steps: plastic deformation of martensite, crack initiation at the martensite/ferrite interface, crack propagation leading to fracture of martensite particles and void formation by separation of particle fragments. It has been identified that the hardness effect is associated with the following aspects: strain partitioning between martensite and ferrite, strain localisation and critical strain required for void formation. Reducing the hardness difference between martensite and ferrite phases by tempering has been shown to be an effective approach to retard the void formation in martensite and thereby is expected to improve the formability.
91 citations
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TL;DR: In this paper, the effect of second phase lower bainite on lower temperature mechanical properties from ambient temperature (287 K) to 123 K of a commercial Japanese 0.40 pct C-Ni-Cr-Mo ultrahigh strength steel corresponding to AISI 4340.
Abstract: A study has been made of the effect of the second phase lower bainite on lower temperature mechanical properties from ambient temperature (287 K) to 123 K of a commercial Japanese 0.40 pct C-Ni-Cr-Mo ultrahigh strength steel corresponding to AISI 4340. When 25 vol pct lower bainite, which appeared in acicular form so as to partition prior austenite grains, was associated with martensite at 473 K, it provided a better combination of strength and ductility than that achieved using 1133 K direct water quenching irrespective of the test temperature. With the lower bainite, notch tensile strength was dramatically improved over the temperature region studied about 2150 MPa even at 123 K; whereas, in the case of 1133 K direct water quenching, it remained at about 1700 MPa. Similar trends were observed in the relationship between the lower bainite and the Charpy V-notch impact energy at and above 238 K. The lower bainite also produced superior fracture ductility and notch toughness results with decreased temperature of testing as compared to those obtained using a y γ α′ ’ repetitive heat treatment for the same steel. The above beneficial effects of the second phase lower bainite on lower temperature mechanical properties are briefly discussed in terms of metallographic examinations, the law of mixtures, and so on.
91 citations
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15 Feb 2012-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a near Ni-Ni-free, Mn-N bearing duplex stainless steel (D-SS) was developed, which exhibited an excellent strength-ductility combination over 1000 MPa tensile strength and 50% elongation.
Abstract: A near-Ni-free, Mn–N bearing duplex stainless steel (D-SS) that shows transformation induced plasticity was developed. The present D-SS exhibited an excellent strength–ductility combination over 1000 MPa tensile strength and 50% elongation. An analysis of the element partitioning during annealing revealed that the stacking fault energy of austenite was low enough for a strain induced martensite (SIM) transformation to occur. The strain hardening rate began to increase at ∼10% strain with the same manner of SIM fraction. The TEM and EBSD analyses showed that not only the ɛ martensite band intersections but the austenite grain boundaries acted as the SIM nucleation sites. The SIM transformation was saturated because of the austenite grain refinement and the corresponding austenite stabilization. The austenite grain refinement was caused by the mutual impingement of growing SIM and as a result by the engulfment of remaining austenite by SIM. The deformation behavior of the present D-SS was characterized by analyzing the kernel average misorientation (KAM) of the constituent phases with strain. The KAM distribution of austenite, ferrite and SIM exhibited different characteristics. The average KAM of austenite and ferrite increased as the strain increased, but its increasing rate of austenite was higher than that of ferrite. These KAM characteristics were discussed along with the dislocation glide modes of austenite and ferrite. By contrast, the average KAM of SIM was insensitive to strain and higher than that of the other two phases.
90 citations
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TL;DR: In this paper, a set of seven carbide free bainitic steels with a 3 wt% carbon content were proposed for manufacturing and the micro-structural and mechanical characterisation of the steels was investigated.
Abstract: Cementite is responsible of the limited application of conventional bainitic steels, however it has been proof that cementite precipitation during bainite formation can be suppressed by the judicious use of silicon in medium carbon steels In this work, thermodynamic and kinetic models were used to design steels with an optimum bainitic microstructure consisting of a mixture of bainitic ferrite, carbon-enriched retained austenite and some martensite Using these models, a set of seven carbide free bainitic steels with a 03 wt% carbon content were proposed for manufacturing The work presented here is concerned with the microstructural and mechanical characterisation of the steels manufactured Except for the steel with the highest content of alloying elements, all the grades present the same microstructure composed of carbide-free upper bainite and retained austenite after hot rolling and a two-steps cooling Theirs tensile strengths range from 1600 to 1950 MPa while keeping a uniform elongation equal to 4% and a total elongation over 10% Regarding toughness at room temperature, they match quenched and tempered martensitic steels
90 citations