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Microstructures in a carburized steel after isothermal pearlitic treatment

Abraham Mathews, J. (author), Farahani, H. (author), Sietsma, J. (author), Petrov, R.H. (author), Mecozzi, M.G. (author), Santofimia, Maria Jesus (author)

The influence of carbon concentration variations on pearlite formation (20 h at 600 °C) in a case-carburized steel is investigated. The resultant microstructure shows three distinct regions: carburized case, a transition region, and the original core. The microstructural transition from the case to the core regions is observed to be...

journal article 2023

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Austenite formation from a steel microstructure containing martensite/austenite and bainite bands

Abraham Mathews, J. (author), Sietsma, J. (author), Petrov, R.H. (author), Santofimia, Maria Jesus (author)

In many commercial steel processing routes, steel microstructures are reverted to an austenitic condition prior to the final processing steps. Understanding the microstructure development during austenitization is crucial for improving the performance and reliability of the microstructure that forms from austenite. In this work, austenite...

journal article 2023

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Fundamental study of nonclassical nucleation mechanisms in iron

Ou, X. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Nucleation is the re-arrangement of a small number of atoms in the structure of a material leading to a new phase. According to the classical nucleation theory, a nucleus will grow if there is an energetically favourable balance between the stability of the newly formed structure and the energy costs associated to the formation of strains and...

journal article 2022

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Influence of chemical segregation on bainitic microstructures in a carburized bearing steel

Abraham Mathews, J. (author), Sietsma, J. (author), Petrov, R.H. (author), Santofimia, Maria Jesus (author)

Bainite to austenite reversal is one of the grain refinement techniques employed in carburized steels. However, chemical segregation influences the homogeneity of the bainitic structure, which is seminal to exploit the advantages associated with austenite reversal. It is therefore important to understand the influence of chemical segregation...

journal article 2022

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Role of planar faults in martensite formation in nano-polycrystalline iron by molecular dynamics simulation

Karewar, Shivraj (author), Hidalgo Garcia, J. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

The martensitic transformation in pure Fe and its alloys has been studied over many decades. Several theoretical models have been proposed to describe the atomic motion that leads to the fcc-to-bcc martensitic transformation. However, such models do not account for the effect of pre-existing planar defects such as twin boundaries and stacking...

journal article 2022

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Analysis of work hardening mechanisms in Quenching and Partitioning steels combining experiments with a 3D micro-mechanical model

Celada-Casero, Carola (author), Vercruysse, Florian (author), Linke, Bernd (author), Smith, Ali (author), Kok, Piet (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Quenching & Partitioning (Q&P) steels owe their good strength-ductility combinations to the martensite/austenite (α’/γ) mechanical interactions and to the formation of mechanically-induced martensite (α′_mech) through the transformation-induced plasticity (TRIP) effect. An essential role is played by carbon, whose...

journal article 2022

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Microstructural Impact of Si and Ni During High Temperature Quenching and Partitioning Process in Medium-Mn Steels

Ayenampudi, S. (author), Celada-Casero, Carola (author), Arechabaleta, Z. (author), Arribas, M. (author), Arlazarov, A. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Austenite stabilization through carbon partitioning from martensite into austenite is an essential aspect of the quenching and partitioning (Q&P) process. Substitutional alloying elements are often included in the chemical composition of Q&P steels to further control the microstructure development by inhibiting carbide precipitation ...

journal article 2021

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The Thermal Stability of Quenched and Partitioned Steel Microstructures

Koopmans, T.T.W. (author), Sietsma, J. (author), Zhao, L. (author), Santofimia, Maria Jesus (author)

The quenching and partitioning (Q&P) process is a heat treatment process, aiming at the creation of steel microstructures composed of martensite and retained austenite. Herein, the thermal stability of the microstructure is investigated upon reheating steel microstructures, created with different Q&P settings, in different thermal...

journal article 2021

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Influence of martensite/austenite interfaces on bainite formation in low-alloy steels below M_s

Ravi, A.M. (author), Navarro Lopez, A. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Bainite formation in steels typically starts at austenite grain boundaries and continues through nucleation of bainite at newly formed bainitic ferrite/austenite interfaces. Recent experimental evidence has pointed out that austenite to bainite transformation can also proceed in the presence of martensite. Studies suggest that the presence of...

journal article 2020

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Impact of austenite grain boundaries and ferrite nucleation on bainite formation in steels

Ravi, A.M. (author), Kumar, A. (author), Herbig, Michael (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

The rate of bainite formation depends on several factors such as austenite grain size, decomposition of austenite into other phases and austenite composition. Although studies have been carried out to understand various factors affecting bainite formation, open lines of investigation still remain. In this work, the effect of ferrite formation...

journal article 2020

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The role of grain-boundary cementite in bainite formation in high-carbon steels

Ravi, A.M. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Low temperature bainite formation in high-carbon steels leads to highly refined microstructures. However, the rate of bainite formation becomes impractically low as the bainite formation temperature decreases. Thus, it is important to create strategies to accelerate the low-temperature bainite formation kinetics in high-carbon steels. In this...

journal article 2020

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Coalescence of martensite under uniaxial tension of iron crystallites by atomistic simulations

Ou, X. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Molecular dynamics simulations are used to study the effects of tensile loading on nucleation and subsequent growth of bcc phase in pure fcc iron. The results show that orientation variant selection occurs during the stress-induced fcc-to-bcc transformation, which leads to the coalescence of neighbouring bcc platelets with identical...

journal article 2020

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Unravelling the mechanical behaviour of advanced multiphase steels isothermally obtained below M_s

Navarro Lopez, A. (author), Hidalgo Garcia, J. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

The initial formation of athermal martensite was proven to accelerate the subsequent bainite formation kinetics during isothermal holdings below the martensite-start temperature (M_s). The presence of prior athermal martensite (PAM) within the phase mixture is expected to modify the overall mechanical response of these newly...

journal article 2020

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The role of the austenite grain size in the martensitic transformation in low carbon steels

Celada-Casero, Carola (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

There is sufficient experimental evidence to propose that the formation kinetics of athermal martensite directly depends on the austenite grain structure from which the martensite forms. Yet, this dependence is frequently ignored. The present study investigates the role of the prior austenite grain size (PAGS) in the martensitic...

journal article 2019

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Microstructure evolution during high-temperature partitioning of a Medium-Mn Quenching and Partitioning steel

Ayenampudi, S. (author), Celada-Casero, Carola (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Medium-Mn Quenching & Partitioning (Q&P) steels have been recently considered as potential candidates for the 3rd generation advanced high-strength steels. The processing of these steels aims to induce the partitioning of substitutional alloying elements from martensite to austenite during an isothermal treatment at high temperature,...

journal article 2019

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Theoretical aspects of spinodal decomposition in Fe-C

Kim Lee, B.N. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Carbon redistribution is known to occur during room temperature aging of Fe-C martensite. One of the proposed mechanisms in the literature by which carbon redistributes is spinodal decomposition, a thermodynamically driven reaction in which the alloy undergoes separation into carbon-rich and carbon-poor regions, giving rise to modulations in...

journal article 2019

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Effect of C on the martensitic transformation in Fe-C alloys in the presence of pre-existing defects: A molecular dynamics study

Karewar, S.V. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

Molecular dynamics simulations are used to investigate the atomic effects of carbon (C) addition in Fe on the martensitic phase transformation in the presence of pre-existing defects such as stacking faults and twin boundaries. The pre-existing defect structures in Fe-C alloys have the same effect on the atomistic mechanisms of martensitic...

journal article 2019

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The influence of the austenite grain size on the microstructural development during quenching and partitioning processing of a low-carbon steel

Celada-Casero, Carola (author), Kwakernaak, C. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

The influence of the prior austenite grain size (PAGS), varying between 6 and 185 μm, on the microstructural development of a low carbon steel during quenching and partitioning (Q&P) processing is investigated. The effect on the size and morphological aspects of the microconstituents is discussed based on the kinetics of carbon...

journal article 2019

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Influence of the prior athermal martensite on the mechanical response of advanced bainitic steel

Navarro Lopez, A. (author), Hidalgo Garcia, J. (author), Sietsma, J. (author), Santofimia, Maria Jesus (author)

The accelerated formation of bainite in presence of martensite is opening a new processing window for the steel industry. However, for a feasible industrial implementation, it is necessary to determine the mechanical behaviour of the steels developed under such conditions. This study focuses on analysing the effects of the formation of...

journal article 2018

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Influence of bainite reaction on the kinetics of carbon redistribution during the Quenching and Partitioning process

Nishikawa, A.S. (author), Santofimia, Maria Jesus (author), Sietsma, J. (author), Goldenstein, Hélio (author)

In the present study the microstructural evolution and kinetics of carbon redistribution during the partitioning step of the Quenching and Partitioning process are investigated by means of a modeling approach that simultaneously considers the martensite-austenite carbon partitioning and the decomposition of austenite into bainitic ferrite....

journal article 2018