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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 article, it is shown that the tendency of the martensite to crack in a mixed microstructure of austenite and martensites depends on its absolute size.
Abstract: Modern TRIP assisted steels contain retained austenite with carbon concentrations in excess of 1 wt-%. Some of their mechanical properties, in particular the toughness and ductility, rely on the diffusionless transformation of this austenite into high-carbon martensite, induced by stress and strain. The properties can be excellent in spite of the fact that freshly formed high-carbon martensite is brittle. This contradictory behaviour has yet to be explained. In the present paper, the authors propose and show experimentally that the tendency of the martensite to crack in a mixed microstructure of austenite and martensite depends on its absolute size. It is demonstrated that in these mixtures, it is more difficult to crack fine martensite. It is the fine scale of the retained austenite in TRIP assisted steels that permits the martensite to be tolerated without endangering their mechanical properties.
73 citations
15 Jul 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, an extensive experimental program was conducted to investigate the strain rate dependent mechanical properties of TRIP steel and its constituent phases. And the results showed clearly that the excellent mechanical properties are not only preserved at higher strain rates, but they are still improved.
Abstract: In the automotive industry a lot of effort is put into the development of lightweight car body structures. Therefore, complex multiphase steel grades have been developed with exceptional mechanical properties: they combine high strength values (yield strength, tensile strength, etc.) with an excellent ductility. TRansformation Induced Plasticity steels (TRIP steels) show these properties pre-eminently. To guarantee a controlled dissipation of the energy released during a crash it is essential to characterize and understand the impact-dynamic material properties. In this paper, results are presented of an extensive experimental program to investigate the strain rate dependent mechanical properties of TRIP steel and its constituent phases. These different phases (ferrite, bainite and austenite) were prepared separately to obtain a clear understanding of their individual behaviour within the multiphase steel. A split Hopkinson tensile bar set-up was used for the experiments and microstructural observation techniques such as SEM and XRD revealed the mechanisms governing the observed high strain rate behaviour. The results show clearly that the excellent mechanical properties are not only preserved at higher strain rates, but they are still improved. As in the static case the ferrite phase is responsible for the large deformation in the TRIP steel and bainite causes the high strength levels. The martensite/austenite constituent is responsible for the excellent combination of high stress and strain in the TRIP steel as well as for the important strain hardening.
73 citations
TL;DR: In this paper, a series of iron-carbon and iron-nickel-carbon steels have been investigated in order to assess the relative contribution of the following to the strength of martensite: 1) solid solution hardening by carbon, 2) carbon in the form of precipitates or segregates, and 3) the substructure of the martensites, i.e. dislocation tangles or internal twinning.
72 citations
TL;DR: In this article, it was shown that the critical step to bring about the transformation is for the precipitate to be cut by the moving matrix dislocation, and on this basis it is shown that there is a critical size of martensite nucleus which is only a few atoms in thickness.
72 citations
TL;DR: In this article, microstructures and Charpy impact properties have been examined in two microalloyed steels following heat treatments to simulate weld heat affected zone (HAZ) structures over a range of heat input conditions, characterised by the cooling time from 800 to 500°C ( Δ t 8/5 ).
72 citations