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Bainite and Martensite: Developments and Challenges

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A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 May 2017) | Viewed by 90805

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Dr. Carlos Garcia-Mateo

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Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Avenida Gregorio Del Amo, 8, Madrid, 28040, Spain
Interests: steels; microstructural characterization; phase transformation; mechanical properties; mechanical behavior of materials
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Dear Colleagues,

Nowadays, when modern high strength steels come to play, it is not strange to find that their microstructure contains austenite and either bainite or martensite, a combination of both, or more sophisticated variations such as Q&P and nanostructured bainitic steels.

There is no doubt that there are certain similarities in the mechanisms ruling such transformations, and therefore it is not surprising that parameters at play controlling the mechanical properties also overlap.

The development of new and powerful scientific techniques and equipment (EBSD, APT, HRTEM, etc.) allow us to gain fundamental insights that help to establish some of the principles by which those microstructures are known. The developments accompanying such findings lead to further developments and intensive research providing the required metallurgical support.

There is a very significant number of publications and some scattered conferences and workshops devoted to these type steels. However, there is no forum that brings together the latest developments, taking place in the framework of these microstructures and their properties.

Papers on recent advances and review articles, particularly related to the most challenging aspects of the use of bainitic and martensitic microstructures, in any of their forms, are invited for inclusion in this Special Issue on "Bainite and Martensite: Developments and Challenges".

Dr. Carlos Garcia-Mateo
Guest Editor

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Keywords

Phase transformation
Modelling
Alloy and process design
Thermal treatment
Mechanical and in-use properties
Crystallography
Microstructural (advanced) characterization

Published Papers (13 papers)

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Editorial

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2 pages, 155 KiB

Open AccessEditorial

Bainite and Martensite: Developments and Challenges

by Carlos Garcia-Mateo

Metals 2018, 8(11), 966; https://doi.org/10.3390/met8110966 - 19 Nov 2018

Viewed by 2446

Abstract

Both microstructures, martensite and bainite, although share some common features, when studied in further detail depict a plethora of subtle differences that make them unique. [...] Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

Research

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7902 KiB

Open AccessArticle

In Situ Study of Phase Transformations during Non-Isothermal Tempering of Bainitic and Martensitic Microstructures

by S. Hesamodin Talebi, Hadi Ghasemi-Nanesa, Mohammad Jahazi and Haikouhi Melkonyan

Metals 2017, 7(9), 346; https://doi.org/10.3390/met7090346 - 04 Sep 2017

Cited by 32 | Viewed by 9748

Abstract

Phase transformations during non-isothermal tempering of bainitic or martensitic microstructures obtained after quenching of a medium-carbon low-alloy steel was studied. The microstructures correspond to different locations of an as-quenched large-sized forged ingot used as a die material in the automotive industry. High-resolution dilatometry experiments were conducted to simulate the heat treatment process, as well as to investigate different phenomena occurring during non-isothermal tempering. The microstructures were characterized using optical and scanning electron microscopy. Dilatometry analyses demonstrated that tempering behavior varied significantly from bainitic to martensitic microstructures. Retained austenite, which exists between bainitic ferrite sheaves, decomposes to lower bainite causing a remarkable volume increase. It was found that this decomposition finishes below 386 °C. By contrast, martensite tempering was accompanied with a volume decrease due to the decomposition of medium-carbon martensite to low carbon martensite and carbides. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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10660 KiB

Open AccessArticle

Development of Direct Quenched Hot Rolled Martensitic Strip Steels

by Lieven Bracke, Dorien De Knijf, Christoph Gerritsen, Reza Hojjati Talemi and Eva Diaz Gonzalez

Metals 2017, 7(9), 326; https://doi.org/10.3390/met7090326 - 24 Aug 2017

Cited by 1 | Viewed by 4299

Abstract

Metallurgical concepts for new ultra-high strength martensitic steels have been developed through direct quenching after hot rolling. In addition to the chemical composition, the hot rolling, quenching, and annealing parameters need to be optimized to fulfill the requirements for the demanding applications for which these steels are used. It is also shown that the welding behavior is influenced by the choice of alloying concept. Typical applications also require a high fatigue resistance, especially of formed components. For that reason, a dedicated set-up was developed that allows differentiation between materials, which is illustrated through the effect of inclusions on the fatigue performance of a bent test piece. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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5234 KiB

Open AccessArticle

In-Situ Investigation of Strain-Induced Martensitic Transformation Kinetics in an Austenitic Stainless Steel by Inductive Measurements

by Carola Celada-Casero, Harm Kooiker, Manso Groen, Jan Post and David San-Martin

Metals 2017, 7(7), 271; https://doi.org/10.3390/met7070271 - 13 Jul 2017

Cited by 33 | Viewed by 6604

Abstract

An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α′) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α′-martensite has been found by comparing the results to the ex-situ characterization by magnetization measurements, light optical microscopy, and X-ray diffraction. The sensor has allowed for the observation of the stepwise transformation behavior, a not-well-understood phenomena that takes place in large regions of the bulk material and that so far had only been observed by synchrotron X-ray diffraction. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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5257 KiB

Open AccessArticle

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

by Quanshun Luo, Matthew Kitchen and Shahriar Abubakri

Metals 2017, 7(7), 258; https://doi.org/10.3390/met7070258 - 07 Jul 2017

Cited by 8 | Viewed by 6948

Abstract

Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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10235 KiB

Open AccessFeature PaperArticle

High-Temperature Tempered Martensite Embrittlement in Quenched-and-Tempered Offshore Steels

by Hung-Wei Yen, Meng-Hsuan Chiang, Yu-Chen Lin, Delphic Chen, Ching-Yuan Huang and Hsin-Chih Lin

Metals 2017, 7(7), 253; https://doi.org/10.3390/met7070253 - 06 Jul 2017

Cited by 25 | Viewed by 10537

Abstract

Embrittlement induced by high-temperature tempering was investigated in two quenched-and-tempered offshore steels. Electron backscattering diffraction and analysis of Kernel average misorientation were applied to study the coalescence of martensite; transmission Kikuchi diffraction coupled with compositional mapping was used to characterize the martensite/austenite (M/A) phases. It is suggested that the formation of lenticular martensite along prior austenite grain boundaries or packet boundaries primarily explains the embrittlement in conventional S690Q steel, which has a higher carbon content. This embrittlement can be cured by additional heat treatment to decompose martensite into ferrite and cementite. In a newly designed NiCu steel with reduced carbon content, new lath martensite formed along interlath or inter-block boundaries of prior martensite. This microstructure is less detrimental to the impact toughness of the steel. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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13255 KiB

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Effect of Ausforming Temperature on the Microstructure of G91 Steel

by Javier Vivas, Carlos Capdevila, José Antonio Jimenez, Miguel Benito-Alfonso and David San-Martin

Metals 2017, 7(7), 236; https://doi.org/10.3390/met7070236 - 27 Jun 2017

Cited by 33 | Viewed by 9231

Abstract

The development of thermomechanical treatments (TMT) has a high potential for improving creep-strength in 9Cr-1Mo ferritic/martensitic steel (ASTM T/P91) to operate at temperatures beyond 600 °C. To maximize the number of nanoscale MX precipitates, an ausforming procedure has been used to increase the number of nucleation sites for precipitation inside the martensite lath. Relative to standard heat treatments (consisting of austenitization at about 1040 °C followed by tempering at about 730 °C) this processing concept has enabled achieving a microstructure containing approximately three orders of magnitude higher number density of MX precipitates having a size around four times smaller in ASTM T/P91 steel. On the other hand; this TMT has little effect on the size and number density of M₂₃C₆ particles. The optimized microstructure produced by this TMT route proposed is expected to improve the creep strength of this steel. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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7736 KiB

Open AccessFeature PaperArticle

The Nitrocarburising Response of Low Temperature Bainite Steel

by Daniel Fabijanic, Ilana Timokhina, Hossein Beladi and Peter Hodgson

Metals 2017, 7(7), 234; https://doi.org/10.3390/met7070234 - 26 Jun 2017

Cited by 9 | Viewed by 4587

Abstract

The nitrocarburising response of low transformation temperature ultrafine and nanoscale bainitic steel was investigated and compared with martensite and pearlite from the same steel composition. It was found that the retained austenite content of the bainitic steel dictated the core hardness after nitrocarburising. The refined bainitic structure showed improvements in the nitriding depth and hardness of the nitrocarburised layer, compared to coarser grained martensitic and pearlitic structures, possibly due to the fine structure and the distribution of nitride forming elements. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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1849 KiB

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Effects of Q&P Processing Conditions on Austenite Carbon Enrichment Studied by In Situ High-Energy X-ray Diffraction Experiments

by Sébastien Yves Pierre Allain, Guillaume Geandier, Jean-Christophe Hell, Michel Soler, Frédéric Danoix and Mohamed Gouné

Metals 2017, 7(7), 232; https://doi.org/10.3390/met7070232 - 22 Jun 2017

Cited by 35 | Viewed by 5012

Abstract

We report the first ultra-fast time-resolved quantitative information on the quenching and partitioning process of conventional high-strength steel by an in situ high-energy X-ray diffraction (HEXRD) experiment. The time and temperature evolutions of phase fractions, their carbon content, and internal stresses were determined and discussed for different process parameters. It is shown that the austenite-to-martensite transformation below the martensite start temperature Ms is followed by a stage of fast carbon enrichment in austenite during isothermal holding at both 400 and 450 °C. The analysis proposed supports the concurrent bainite transformation and carbon diffusion from martensite to austenite as the main mechanisms of this enrichment. Furthermore, we give evidence that high hydrostatic tensile stresses in austenite are produced during the final quenching, and must be taken into account for the estimation of the carbon content in austenite. Finally, a large amount of carbon is shown to be trapped in the microstructure. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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5419 KiB

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Evaluating Strengthening and Impact Toughness Mechanisms for Ferritic and Bainitic Microstructures in Nb, Nb-Mo and Ti-Mo Microalloyed Steels

by Gorka Larzabal, Nerea Isasti, Jose M. Rodriguez-Ibabe and Pello Uranga

Metals 2017, 7(2), 65; https://doi.org/10.3390/met7020065 - 22 Feb 2017

Cited by 35 | Viewed by 6702

Abstract

Low carbon microalloyed steels show interesting commercial possibilities by combining different “micro”-alloying elements when high strength and low temperature toughness properties are required. Depending on the elements chosen for the chemistry design, the mechanisms controlling the strengths and toughness may differ. In this paper, a detailed characterization of the microstructural features of three different microalloyed steels, Nb, Nb-Mo and Ti-Mo, is described using mainly the electron backscattered diffraction technique (EBSD) as well as transmission electron microscopy (TEM). The contribution of different strengthening mechanisms to yield strength and impact toughness is evaluated, and its relative weight is computed for different coiling temperatures. Grain refinement is shown to be the most effective mechanism for controlling both mechanical properties. As yield strength increases, the relative contribution of precipitation strengthening increases, and this factor is especially important in the Ti-Mo microalloyed steel where different combinations of interphase and random precipitation are detected depending on the coiling temperature. In addition to average grain size values, microstructural heterogeneity is considered in order to propose a new equation for predicting ductile–brittle transition temperature (DBTT). This equation considers the wide range of microstructures analyzed as well as the increase in the transition temperature related to precipitation strengthening. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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7362 KiB

Open AccessArticle

Phase Equilibrium and Austenite Decomposition in Advanced High-Strength Medium-Mn Bainitic Steels

by Adam Grajcar, Władysław Zalecki, Wojciech Burian and Aleksandra Kozłowska

Metals 2016, 6(10), 248; https://doi.org/10.3390/met6100248 - 20 Oct 2016

Cited by 19 | Viewed by 6868

Abstract

The work addresses the phase equilibrium analysis and austenite decomposition of two Nb-microalloyed medium-Mn steels containing 3% and 5% Mn. The pseudobinary Fe-C diagrams of the steels were calculated using Thermo-Calc. Thermodynamic calculations of the volume fraction evolution of microstructural constituents vs. temperature were carried out. The study comprised the determination of the time-temperature-transformation (TTT) diagrams and continuous cooling transformation (CCT) diagrams of the investigated steels. The diagrams were used to determine continuous and isothermal cooling paths suitable for production of bainite-based steels. It was found that the various Mn content strongly influences the hardenability of the steels and hence the austenite decomposition during cooling. The knowledge of CCT diagrams and the analysis of experimental dilatometric curves enabled to produce bainite-austenite mixtures in the thermomechanical simulator. Light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to assess the effect of heat treatment on morphological details of produced multiphase microstructures. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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Review

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3453 KiB

Open AccessReview

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

by Carlos Garcia-Mateo, Georg Paul, Mahesh C. Somani, David A. Porter, Lieven Bracke, Andreas Latz, Carlos Garcia De Andres and Francisca G. Caballero

Metals 2017, 7(5), 159; https://doi.org/10.3390/met7050159 - 04 May 2017

Cited by 44 | Viewed by 10162

Abstract

The major strengthening mechanisms in bainitic steels arise from the bainitic ferrite plate thickness rather than the length, which primarily determines the mean free slip distance. Both the strength of the austenite from where the bainite grows and the driving force of the transformation, are the two factors controlling the final scale of the bainitic microstructure. Usually, those two parameters can be tailored by means of selection of chemical composition and transformation temperature. However, there is also the possibility of introducing plastic deformation on austenite and prior to the bainitic transformation as a way to enhance both the austenite strength and the driving force for the transformation; the latter by introducing a mechanical component to the free energy change. This process, known as ausforming, has awoken a great deal of interest and it is the object of ongoing research with two clear aims. First, an acceleration of the sluggish bainitic transformation observed typically in high C steels (0.7–1 wt. %) transformed at relatively low temperatures. Second, to extend the concept of nanostructured bainite from those of high C steels to much lower C contents, 0.4–0.5 wt. %, keeping a wider range of applications in view. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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Other

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759 KiB

Open AccessFeature PaperTechnical Note

Tensile Ductility of Nanostructured Bainitic Steels: Influence of Retained Austenite Stability

by Thomas Sourmail, Carlos Garcia-Mateo, Francisca G. Caballero, Lucia Morales-Rivas, Rosalia Rementeria and Matthias Kuntz

Metals 2017, 7(1), 31; https://doi.org/10.3390/met7010031 - 23 Jan 2017

Cited by 24 | Viewed by 5468

Abstract

High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 °C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of strain. Results were correlated with tensile ductility. The role of retained austenite stability is remarkably underlined as strongly affecting the propensity to brittle failure, but also the tensile ductility. A simple quantitative relationship is proposed that clearly delimitates the different behaviours (brittle/ductile) and correlates well with the measured ductility. Conclusions are proposed as to the role of retained austenite fraction and the existence of a threshold value associated with tensile rupture. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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