High-resolution characterization of the martensite-austenite constituent in a carbide-free bainitic steel

Hofer, Christina; Bliznuk, Vitaliy; Verdiere, An; Petrov, Roumen; Winkelhofer, Florian; Clemens, Helmut; Primig, Sophie

doi:10.1016/j.matchar.2018.07.011

Cited by 23 publications

(13 citation statements)

References 61 publications

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“…TKD offers better spatial resolution (< 10 nm) than EBSD, allowing the resolution of nanoscale microstructural constituents having 10-30 nm in size [26,27]. It has been successfully used to analyze oxides and nitrides in aluminium alloys [28] and stainless steels [29,30], as well as martensite and retained austenite in bainitic steels [31]. In this work, for TKD and TEM studies, the samples were ground to a thickness…”

Section: Microstructural Characterizationmentioning

confidence: 99%

The effect of heating rate and soaking time on microstructure of an advanced high strength steel

Valdes-Tabernero

Celada-Casero

Sabirov

et al. 2019

Materials Characterization

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This work focuses on the effect of soaking time on the microstructure during ultrafast heat treatment of a 50% cold rolled low carbon steel with initial ferritic-pearlitic microstructure.Dilatometry analysis was used to estimate the effect of heating rate on the phase transformation temperatures and to select an appropriate inter-critical temperature for final heat treatments. A thorough qualitative and quantitative microstructural characterization of the heat treated samples is performed using a wide range of characterization techniques. A complex multiphase, hierarchical microstructure consisting of ferritic matrix with embedded martensite and retained austenite is formed after all applied heat treatments. In turn, the ferritic matrix contains recrystallized and non-recrystallized grains. It is demonstrated that the ultrafast heating generally results in finer microstructure compared to the conventional heating independently on the soaking time. There is a significant effect of the soaking time on the volume fraction of martensite of the ultrafast heated material, while in the samples heated with conventional heating rate it remains relatively unchanged during soaking.Recrystallization, recovery and phase transformations occurring during soaking are discussed with respect to the applied heating rate.

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Section: Microstructural Characterizationmentioning

confidence: 99%

The effect of heating rate and soaking time on microstructure of an advanced high strength steel

Valdes-Tabernero

Celada-Casero

Sabirov

et al. 2019

Materials Characterization

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“…TEM images of M–A constituent showed clearly that the M–A constituent was an irregular polygon with sharp edge, which was generally harmful for the impact performance. For example, several studies reported that the sharp edge M–A constituent is easy to induce stress concentration during impact process and hence accelerate the fracture of the steels …”

Section: Resultsmentioning

confidence: 99%

“…For example, several studies reported that the sharp edge M-A constituent is easy to induce stress concentration during impact process and hence accelerate the fracture of the steels. [29][30][31] Figure 4 shows the continuous cooling transformation (CCT) curves of the three steels simulated using JMatPro software. One can see that the ferrite and bainite transition temperature was 755 and 590 C under the 10 C s À1 cooling rate, and which was 700 and 560 C under the 100 C s À1 cooling rate in 0.6 wt% Ni steel.…”

Section: Microstructure Characterizationmentioning

confidence: 99%

Improved Toughness of a High‐Strength Low‐Alloy Steel for Arctic Ship by Ni and Mo Addition

et al. 2020

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The effect of Ni and Mo addition on the microstructures of a high strength low alloy (HSLA) steel under the thermo-mechanical control processing (TMCP) process is currently unknown, which is herein explored by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). As the Ni increase from 0.6 to 0.9 wt%, the volume fraction of bainitic ferrite increase from 30% to 50%, the average size decrease from 3 to 2 μm, and the size of the martensiteaustenite (M-A) constituent decrease from 1.2 to 0.7 μm. The volume fraction of bainitic ferrite increases from 30% to 85%, and grain size increases from 3 to 5 μm with increasing Mo from 0 to 0.2 wt%. The size of M-A constituent decreases from 1.2 to 0.3 μm. Impact absorbed energy at À100 C increases from 50 to 70 J as the Ni increase from 0.6 to 0.9 wt%, which decreases from 50 to 10 J with increasing Mo from 0 to 0.2 wt%. The improved impact toughness mainly results from the decreasing size of the grain and the M-A constituent with the increase in Ni from 0.6 to 0.9 wt%.

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“…The small, round islands within the bainitic matrix are retained austenite. The larger, angular regions show a slight substructure at higher magnification and are a combination of austenite and martensite, the so-called MA-islands [27]. The occurring zones of sample I min are characterized in the following.…”

Section: Microstructural Characterization Via Semmentioning

confidence: 98%

Microstructural characterization of a double pulse resistance spot welded 1200 MPa TBF steel

et al. 2019

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In the automotive industry resistance, spot welding is the dominant technology in sheet metal joining of advanced high strength steels (AHSS). In order to improve the mechanical performance of AHSS welds, in-process tempering via a second pulse is a possible approach. In this work, two different double pulse welding schemes were applied to a 1200 MPa transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) steel. The different microstructures in the welds were characterized via light optical and scanning electron microscopy. Additionally, hardness mappings with several hundred indents were performed. It is shown that the second pulse, following a low first pulse which is high enough to produce a weld nugget that fulfills the quality criterion of a minimum spot weld diameter of 4*√t, leads to partial reaustenitization and consequently to a ferritic/martensitic microstructure after final quenching. Hardness mappings revealed that this inner FZ is harder than the surrounding FZ consisting of tempered martensite. In contrast, if the highest current without splashing is chosen for the first pulse, the same second pulse does not reaustenitize the FZ but only temper the martensite.

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High-resolution characterization of the martensite-austenite constituent in a carbide-free bainitic steel

Abstract: High-resolution characterization of the martensite-austenite constituent in a carbide-free bainitic steel

Cited by 23 publications

References 61 publications

The effect of heating rate and soaking time on microstructure of an advanced high strength steel

The effect of heating rate and soaking time on microstructure of an advanced high strength steel

Improved Toughness of a High‐Strength Low‐Alloy Steel for Arctic Ship by Ni and Mo Addition

Microstructural characterization of a double pulse resistance spot welded 1200 MPa TBF steel

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