New Ms-formula for exact microstructural prediction of modern 3rd generation AHSS chemistries

Kaar, Simone; Steineder, Katharina; Schneider, Reinhold; Križan, Daniel; Sommitsch, Christof

doi:10.1016/j.scriptamat.2021.113923

Cited by 37 publications

(15 citation statements)

References 18 publications

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“…The values presented in parenthesis correspond to the standard deviation of at least 2 measurements. These experimental results are in good agreement with the calculated MS of 335 °C [33]: On the other hand, the dilatation measured during the isothermal step at 400 °C is to a large extent generated by the transformation of austenite to bainite (Figure 2a,b). Based on the dilatometric results, a set of samples were subjected fast cooling and isothermal at 400 °C for 600 s to induce the stabilization of austenite via carbon redistribution during bainite formation [34].…”

Section: Methodssupporting

confidence: 88%

The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels

Durán

Corallo

Ros-Yanez

et al. 2021

Metals

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This study focuses on the effect of non-conventional annealing strategies on the microstructure and related mechanical properties of austempered steels. Multistep thermo-cycling (TC) and ultrafast heating (UFH) annealing were carried out and compared with the outcome obtained from a conventionally annealed (CA) 0.3C-2Mn-1.5Si steel. After the annealing path, steel samples were fast cooled and isothermally treated at 400 °C employing the same parameters. It was found that TC and UFH strategies produce an equivalent level of microstructural refinement. Nevertheless, the obtained microstructure via TC has not led to an improvement in the mechanical properties in comparison with the CA steel. On the other hand, the steel grade produced via a combination of ultrafast heating annealing and austempering exhibits enhanced ductility without decreasing the strength level with respect to TC and CA, giving the best strength–ductility balance among the studied steels. The outstanding mechanical response exhibited by the UFH steel is related to the formation of heterogeneous distribution of ferrite, bainite and retained austenite in proportions 0.09–0.78–0.14. The microstructural formation after UFH is discussed in terms of chemical heterogeneities in the parent austenite.

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Section: Methodssupporting

confidence: 88%

The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels

Durán

Corallo

Ros-Yanez

et al. 2021

Metals

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“…transformation. When the manganese content was increased, the incubation time also increased to 15 and 50 s. The same results were reported by Llopis [24], which determine that Mn retards bainite transformation like Ni and Cr. It means that the manganese decreases the driving force of phase transformations and therefore longer incubation times are needed.…”

Section: Theoretical Calculationssupporting

confidence: 83%

Effect of Mn on the chemical driving force and bainite transformation kinetics in medium-manganese alloys

Morawiec

Opara

García‐Mateo³

et al. 2022

J Therm Anal Calorim

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This work presents insights into the manganese influence on the driving force and bainite transformation kinetics. Three different medium-Mn steels were subjected to theoretical calculations and dilatometric study in order to determine the Mn impact on bainite formation. The theoretical approach shows that the increase of manganese leads to a lower bainite fraction formed during the isothermal stage. This implicates the carbon enrichment of the austenite during thermal treatment. The less bainite is formed, the higher is the fraction of residual austenite which enrichment of carbon is globally low. Meanwhile, the manganese influences the incubation and transformation time. As the manganese content increases, the incubation period and formation time of bainite are longer because the chemical driving force essential to start and complete austenite into bainite transformation decreases. This was proved by theoretical calculations and dilatometric analysis, which show that even a small increase in manganese content leads to a longer time necessary to occur the bainitic transformation. For the steel containing 5% manganese, the driving force was too small that the transformation could occur even after 3 h. Additionally, the XRD analysis was conducted to determine the retained austenite fraction and its carbon enrichment. These results were compared with the theoretical values to determine the accuracy of the applied model.

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“…This corresponds to the observations in other studies [ 34,37 ] and can be explained by two main factors. First, an increase in C generally reduces the M s temperature, [ 24,38 ] as we have confirmed by means of dilatometry (Table 1), and second, elevated C contents contribute to a more pronounced chemical stabilization of RA, preventing the formation of α ′ sec . [ 39–41 ]…”

Section: Resultsmentioning

confidence: 69%

“…The tangent method described in another study [ 24 ] was used to derive the M s temperature of the investigated steels from dilatometry (Bähr Dil 805 A D −1 ). Therefore, the samples were heated with 10 K s −1 to the austenitizing temperature ( T A ) given in Table 1 and isothermally held for 120 s, followed by subsequent cooling to room temperature (RT) with 50 K s −1 .…”

Section: Methodsmentioning

confidence: 99%

Tailoring the Ductility Characteristics of Lean‐Medium Mn Quenching and Partitioning Steels with Varying C Contents

Kaar

Križan

Schneider

et al. 2023

steel research int.

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During recent years, quenching and partitioning (Q&P) steels have gained strong interest due to their promising lightweight potential and crashworthiness. With their microstructure consisting of tempered martensite (α″) and C‐enriched retained austenite (RA), they are characterized by balanced ductility, combining the formability properties of conventional dual‐phase and complex‐phase steels at elevated strength levels. This study thoroughly examines three chemical compositions with 4.0 wt% Mn, 1.5 wt% Si, and varying C contents between 0.10 and 0.20 wt% with regard to their structure–properties relationship. In this context, various parameters are derived from tensile testing to assess the formability behavior of the investigated steels. The results clearly demonstrate a strong effect of the RA fraction and its mechanical stability on the ductility characteristics of lean‐medium Mn Q&P steels. Generally, the optimum exploitation of the transformation‐induced plasticity effect favors high global ductility, but the resulting heterogeneities in the microstructure remarkably impair the local one. By increasing the C content, larger RA fractions can be stabilized, shifting the ductility characteristics from rather local toward global. For this reason, medium C content of 0.15 wt% allows for the adjustment of the optimum microstructure leading to desired balanced ductility.

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New Ms-formula for exact microstructural prediction of modern 3rd generation AHSS chemistries

Cited by 37 publications

References 18 publications

The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels

The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels

Effect of Mn on the chemical driving force and bainite transformation kinetics in medium-manganese alloys

Tailoring the Ductility Characteristics of Lean‐Medium Mn Quenching and Partitioning Steels with Varying C Contents

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