The transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are introduced. The metastable austenitic stainless and multiphase TRIP-assisted steels, as well as the more recent third generation AHSS grades, namely the medium-Mn and quenching and partitioning (Q&P) steels, are critically discussed. These steels utilize the TRIP effect and the enhanced work-hardening rate through the transformation of (retained) austenite in their microstructures to martensite during plastic deformation for the improvement of strength-ductility balance, which make them especially suitable for the automotive industry to be used in the lightweight car body for addressing the safety, fuel consumption, and air pollution issues. The kinetics of strain-induced martensitic transformation (SIMT) as well as the effects of chemical composition, grain size, deformation temperature, strain rate, and deformation mode on the austenite stability are reviewed. The effects of holding temperature and time during the isothermal bainitic transformation (IBT) in TRIP-aided steels, during the austenite-reverted-transformation (ART) annealing in medium-Mn steels, and during the quenching and partitioning steps in the Q&P steels are critically discussed towards enhancement of the amount of retained austenite and optimization of strength-ductility trade off. The alternative thermomechanical processing routes as well as the modified grades such as δ-TRIP and quenching-partitioning-tempering steels are also introduced.

Transformation-induced plasticity (TRIP) in advanced steels: A review

Enhanced ductility and toughness in an ultrahigh-strength Mn-Si-Cr-C steel: The great potential of ultrafine filmy retained austenite

The recent developments in the field of hot dip zinc coating are reviewed with special reference to different industrial applications. The improvements in physical and chemical structural composition due to pre- and post-modification processes are discussed. The present review has the focus mainly on the readership of young researchers engaged in this field. Very recent developments on the hot dip galvanization processes are highlighted. Their industrial competencies with aluminium dipping are also briefly discussed. The scopes for immediate future developments are also highlighted then and there.

A review on recent approaches in the field of hot dip zinc galvanizing process

The Transformation-Induced-Plasticity (TRIP) effect is used for enhancing the formability of cold formable sheet steels. While the first observation of this phenomenon dates back to the 1930's, the industrial usage of the TRIP steels started after 1950. First fully austenitic steels, later on multiphase steels have been developed with a meta-stable austenitic phase that can transform stress-assisted or strain-induced into ϵ- or α′-martensite during deformation. The historic development, the principles of the TRIP effect, and the different groups of steels using the TRIP effect are described. For the already commercialized TRIP steels, characteristic chemical compositions and microstructures are discussed; the requirements for the process design as well as new annealing concepts after cold rolling are explained.

The TRIP Effect and Its Application in Cold Formable Sheet Steels

Over many decades, significant efforts have been made to improve the strength-elongation product of advanced high strength steels (AHSSs) by creating tailored multi-phase microstructures. Successive solid-state phase transformations for steels with a well selected chemical composition turned out to be the key instrument in the realisation of such microstructures. In this contribution, we first provide a brief review of the desired microstructures for Transformation-induced plasticity (TRIP), Carbide-free Bainitic (CFB), Quenching & Partitioning (Q&P) and Medium Manganese steels followed by comprehensive discussions on the phase transformations to be used in their creation. The implications for the steel composition to be selected are addressed too. As the presence of the right amount and type of metastable retained austenite (RA) is of crucial importance for the mechanical performance of these AHSSs, special attention is paid to the important role of successive solid-state phase transformations in creating the desired fraction and composition of RA by suitable element partitioning (in particular C and Mn). This critical partitioning not only takes place during final cooling (austenite decomposition) but also during the back transformation (austenite reversion) during reheating. This review aims to be more than just descriptive of the various findings, but to present them from a coherent thermodynamic / thermo-kinetic perspective, such that it provides the academic and industrial community with a rather complete conceptual and theoretical framework to accelerate the further development of this important class of steels. The detailed stepwise treatment makes the review relevant not only for experts but also metallurgists entering the field.

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Fundamentals and application of solid-state phase transformations for advanced high strength steels containing metastable retained austenite

The “quenching and partitioning” (Q&P) process has recently been substantiated to be a unique technological route for the production of high strength steels with significant amounts of retained austenite, and thus to provide better combination of strength and ductility. In this work, intercritically annealed specimens followed by Q&P treatment have been applied to low-carbon steel with chemical composition typical for conventional TRIP-assisted steels. Microstructure of the steel treated by the Q&P process was characterized by means of optical microscope, SEM, TEM and XRD. The study suggests that microstructure is mainly composed of ferrite, lath martensite, martensite–austenite islands, retained austenite and a small amount of bainite formed during partitioning. The fraction of bainite formed during partitioning is proportional to quenching temperature. The mechanical property of specimen treated by the Q&P process exhibits an improved combination of strength and ductility than that of the Q&T process. Two schemes of hot-dipping galvanization processes were designed. The results indicate that both hot-dip galvanizing schemes present a limited reduction in tensile strength and a slight enhancement of ductility. The scheme of galvanizing and partitioning after the quenching progress shows a better combination of strength and ductility.

Microstructure development and mechanical properties of quenching and partitioning (Q&P) steel and an incorporation of hot-dipping galvanization during Q&P process

This paper presents a detailed characterization of the microstructural evolution of quenching and partitioning (Q&P) steel by dilatometer, X-ray diffraction and scanning electron microscopy. Influence of partitioning time on mechanical properties was investigated and the relationship between microstructures and mechanical properties was established. The results indicate that bainite transformation occurs at the preliminary stage of partitioning and the amount is proportional to quenching temperature. Martensite softening, bainite transformation kinetics, amount and stability of retained austenite collaboratively have effects on mechanical properties. The purpose of the EBSD investigation is to study the changes in the microstructure of the Q&P steel during deformation and obtain a better understanding of collaborative deformation-transformation behavior. During deformation, plastic deformation preferentially occurred in the vicinity of ferrite–martensite interfaces and spread to the interior of ferrite grain with strain increasing. Plastic deformation started to occur in martensite after large strain. Furthermore, grain rotation occurred in some austenite grains or divided into subgrains during deformation.

Study of microstructural evolution, microstructure-mechanical properties correlation and collaborative deformation-transformation behavior of quenching and partitioning (Q&P) steel

Jing Sun

Papers

Microstructure development and mechanical properties of quenching and partitioning (Q&P) steel and an incorporation of hot-dipping galvanization during Q&P process

Study of microstructural evolution, microstructure-mechanical properties correlation and collaborative deformation-transformation behavior of quenching and partitioning (Q&P) steel