Austenite In Low Alloy Steel Research Articles

Recent progress in third-generation low alloy steels developed under M3 microstructure control

During the past thirty years, two generations of low alloy steels (ferrite/pearlite followed by bainite/martensite) have been developed and widely used in structural applications. The third-generation of low alloy steels is expected to achieve high strength and improved ductility and toughness, while satisfying the new demands for weight reduction, greenness, and safety. This paper reviews recent progress in the development of third-generation low alloy steels with an M3 microstructure, namely, microstructures with multi-phase, meta-stable austenite, and multi-scale precipitates. The review summarizes the alloy designs and processing routes of microstructure control, and the mechanical properties of the alloys. The stabilization of retained austenite in low alloy steels is especially emphasized. Multi-scale nano-precipitates, including carbides of microal-loying elements and Cu-rich precipitates obtained in third-generation low alloy steels, are then introduced. The structure–property relationships of third-generation alloys are also discussed. Finally, the promises and challenges to future applications are explored.

Enhanced stability of retained austenites in quenched 25SiMn2MoV steel by electro-pulsing current

In this contribution, an electro-pulsing current is applied to 25SiMn2MoV steel to obtain substantial retained austenite contents. Interestingly, after only 440 m s, retained austenite with a volume fraction higher than 10% is obtained via electro-pulsing. In addition, the Ms temperatures of the samples in the different electro-pulsing treated states are all much lower than room temperature, which implies the sufficient stability of this retained austenite. By choosing different initial states, the morphology and content of retained austenite can also be adjusted. It is found that when the initial state is eutectoid, the morphology of the retained austenite formed during electro-pulsing is globular, and the volume fraction is also higher. While the initial state is quenched, the retained austenite exhibits a layered morphology, and the content is relatively low. The mechanical properties indicate that compared with traditionally treated samples, the electro-pulse-treated samples possess a better strength and ductility. In addition, due to the TRIP effect induced by retained austenite, the ability of the resulting materials to prevent crack propagation and work-hardening is also improved. This work proposes a novel method to efficiently obtain adequate contents of retained austenite in low alloy steels and paves a new way for developing new low alloy steels with good properties.

Role of retained austenite in low alloy steel at low temperature monitored by neutron diffraction

In-situ neutron diffraction measurements during tensile tests at low temperatures of a low alloy steel containing retained austenite (γ) have been performed. Evolutions of phase fractions and phase stresses were analyzed and discussed with the progress of deformation. The role of γ in the steel during deformation at low temperatures was observed not to directly in the contribution to the strengths but in the improvement of the elongation by transformation of γ to martensite -and in the increasing of the work-hardening rate by an increase in the phase fraction of martensite and the work hardening of martensite.

Elastic properties of ferrite and austenite in low alloy steels versus temperature and alloying

Models for elastic properties, as a function of temperature, are required when simulating various thermo-mechanical processes. A model for hypoeutectoid steels is proposed that accounts for this temperature dependency as well as the influence of alloying. The model consists of separate parts for the ferrite and austenite phases. The latter also includes a specific contribution due to ferromagnetism. The model is calibrated versus iron and evaluated against various steels.

The influence of austenitization temperature on phase transformations of supercooled austenite in low-alloy steels with high resistance to abrasion wear

The paper presents continuous cooling transformation (CCT) diagram of selected low-alloy steel with high resistance to abrasion. Samples were prepared from examined material in as delivered conditions, then were austenitized at 900, 1000, 1100 and 1200°C for 20min, and then cooled with the rates of V800–500=50, 10, 5, 1, 0.5, 0.1°C/s. During the dilatometric research, the critical temperatures were defined as well as the critical points specified for different cooling rates were designated. In addition, metallographic documentation of received microstructures after dilatometric investigations was prepared and hardness measurement was performed. The increase in the austenitizing temperature caused changes in the temperature of MS and in the size of the martensite laths. What is more, the increase in the austenitizing temperature in the case of the analyzed steel caused a displacement of the bainitic and diffusion transformations to longer times. During the analysis using the TEM and SEM it was found that the size of the austenite grains is largely controlled by precipitates of the nitrides of AlN, TiN and carbides, mainly Cr7C3 and M23C6.

Effect of Carbon Content on Static Recrystallization Behavior of Work-Hardened Austenite in Low Alloy Steel and Its Mechanism

Effect of Carbon Content on Static Recrystallization Behavior of Work-Hardened Austenite in Low Alloy Steel and Its Mechanism

Analysis of Phase Transformations of Supercooled Austenite in Low-Alloy Steel with Boron Additives

Adiagram of transformations in low-alloy boron-containing steel B27 with high resistance to abrasive wear is plotted under continuous cooling. Chemical, metallographic and dilatometric analyses are performed, and the hardness of the steel is measured. Continuous cooling curves are obtained from the temperature of austenitization at a rate of 0.17 – 25 K/sec in the temperature range of 800 – 500°C.

Preventing Abnormal Grain Growth of Austenite in Low Alloy Steels

Abnormal grain growth (AGG) in austenitic state is studied in low alloy steel in relation with precipitation state. It is observed that initial austenite grain size and precipitation state plays more important role in defining the normal or abnormal grain growth condition than the final one obtained after a heat treatment. Precipitate volume fraction evolution with time-temperature having similar quantity at the end but different initial grain sizes, showed different grain growth phenomenon. Arguments are presented to rationalize the presented experience. A simplified AGG model is applied to understand the effects of initial mean austenite grain size and precipitate size distribution on the subsequent AGG occurrence.

Methodological aspects of plotting of thermokinetic diagrams of transformation of supercooled austenite in low-alloy steels

Aspects of plotting of thermokinetic diagrams of transformation of supercooled austenite in low-alloy steels are analyzed critically using published data and results of own studies. Special attention is devoted to the methods of processing and visual representation of experimental data. Recommendations on representation of results for developing unified approaches to plotting and interpreting the diagrams obtained are developed.

Factors Affecting the Grain Growth of Austenite in Low Alloy Steel

Factors Affecting the Grain Growth of Austenite in Low Alloy Steel

Effect of alloying on transformation of supercooled austenite in low-alloy steel of the 14G2S type

Effect of alloying on transformation of supercooled austenite in low-alloy steel of the 14G2S type

Ferrite and bainite in alloy steels

The addition of alloying elements even in small concentrations can alter the properties and structure of ferrite and bainite. The various morphologies of ferrite-carbide aggregates are surveyed including alloy pearlite, fibrous carbide eutectoids and precipitation of fine alloy carbides atγ-α interfaces. Modern ideas on the morphology and growth kinetics of ferrite and upper and lower bainite are also summarized. Using this information, an attempt is made to rationalize subcritical transformations of austenite in low alloy steels. Basic factors influencing the strength of alloy ferrites are discussed, leading to an examination of structure-mechanical property relationships in ferrite and bainite. Finally the exploitation of the ferrite and bainite reactions to produce useful alloy steels by direct transformation of austenite is explored.