Effect of pre-existing defects in the parent fcc phase on atomistic mechanisms during the martensitic transformation in pure Fe: A molecular dynamics study

Molecular dynamics (MD) simulations are used to study the effect of different defect configurations and their arrangements in the parent fcc phase on atomistic mechanisms during the martensitic transformation mechanisms in pure Fe. The defect configurations considered are stacking faults (SF) and twin boundaries (TB) in single crystal fcc. Three...

Bainite formation kinetics in steels and the dynamic nature of the autocatalytic nucleation process

Over the years, a quantitative theory to explain bainite formation kinetics has been proposed based on the nucleation kinetics of bainitic sub-units. Although the theory shows acceptable correlation with experimental results, it is observed that the kinetic models show a certain degree of discrepancy with actual kinetics. It is identified...

The role of silicon in carbon partitioning processes in martensite/austenite microstructures

Understanding carbon redistribution in steels is crucial in developing advanced high strength steels. For instance, Quenching & Partitioning (Q&P) processes rely on the partitioning of carbon from martensite into austenite, where at the end of the heat treatment the carbon-enriched austenite shows higher stability at room temperature....

Characterization of bainitic/martensitic structures formed in isothermal treatments below the M_s temperature

Advanced Multiphase High Strength Steels are generally obtained by applying isothermal treatments around the martensite start temperature (M_s). Previous investigations have shown that bainitic ferrite can form from austenite in isothermal treatments below M_s, where its formation kinetics is accelerated by the presence of...

Exploring bainite formation kinetics distinguishing grain-boundary and autocatalytic nucleation in high and low-Si steels

Bainite formation in steels begins with nucleation of bainitic ferrite at austenite grain boundaries (?/? interfaces). This leads to creation of bainitic ferrite/austenite interfaces (?/? interfaces). Bainite formation continues through autocatalysis with nucleation of bainitic ferrite at these newly created ?/? interfaces. The displacive theory...

Molecular dynamics simulations of the mechanisms controlling the propagation of bcc/fcc semi-coherent interfaces in iron

Molecular dynamics simulations have been used to study the effects of different orientation relationships between fcc and bcc phases on the bcc/fcc interfacial propagation in pure iron systems at 300 K. Three semi-coherent bcc/fcc interfaces have been investigated. In all the cases, results show that growth of the bcc phase starts in the areas...

Interaction of carbon partitioning, carbide precipitation and bainite formation during the Q&P process in a low C steel

Theoretical understanding of the “quenching and partitioning” (Q&P) process allowed developing microstructures consisting of carbon-depleted martensite and retained austenite that deliver superior mechanical properties. Most of the models describing the Q&P process are limited to systems in which carbide precipitation in martensite and...

Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

Thermomechanical processing of Advanced Multiphase High Strength Steels often includes isothermal treatments around the martensite start temperature (M s). It has been reported that the presence of martensite formed prior to these isothermal treatments accelerates the kinetics of the subsequent transformation. This kinetic effect is commonly...

Overview of mechanisms involved during the quenching and partitioning process in steels

The application of the quenching and partitioning (Q&P) process in steels involves a microstructural evolution that is more complex than just the formation of martensite followed by carbon partitioning from martensite to austenite. Examples of this complexity are the formation of epitaxial ferrite during the first quenching step and the...

Microstructural development during the quenching and partitioning process in a newly designed low-carbon steel

This paper presents a detailed characterization of the microstructural development of a new quenching and partitioning (Q&P) steel. Q&P treatments, starting from full austenitization, were applied to the developed steel, leading to microstructures containing volume fractions of retained austenite of up to 0.15. The austenite was...

Influence of interface mobility on the evolution of austenite-martensite grain assemblies during annealing

The quenching and partitioning (Q&P) process is a new heat treatment for the creation of advanced high-strength steels. This treatment consists of an initial partial or full austenitization, followed by a quench to form a controlled amount of martensite and an annealing step to partition carbon atoms from the martensite to the austenite. In...

Microstructural Evolution of a Low-Carbon Steel during Application of Quenching and Partitioning Heat Treatments after Partial Austenitization

The “quenching and partitioning” (Q&P) process has been studied in a low-carbon steel containing 1.1 wt pct aluminum by heat treatments consisting of partial austenitization at 900 °C and subsequent rapid cooling to a quenching temperature in the range between 125 °C and 175 °C, followed by an isothermal treatment (partitioning step) at 250 °C...