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

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 (silicon) and further stabilize austenite (manganese and nickel). However, these elements can interfere in the microstructure development, especially when high partitioning temperatures are considered. In this study, the microstructural development during the Q&P process of four low-carbon, medium-manganese steels with varying contents of silicon and nickel is investigated. During partitioning at 400 °C, silicon hinders cementite precipitation in primary martensite thereby assisting carbon partitioning from martensite to austenite. During partitioning at temperatures of 500 °C and 600 °C, presence of nickel inhibits pearlite formation and promotes austenite reversion, respectively. It is observed that the stabilization of austenite is significantly enhanced through the addition of nickel by slowing down the kinetics of competitive reactions that are stimulated during the partitioning stage. Results of this study provide an understanding of the interplay among carbon, silicon and nickel during Q&P processing that will allow the development of new design strategies to tailor the microstructure of this family of alloys.This research work has been carried out in the framework of the HighQP project (Proposal Number: 709855), funded by the Research Fund for Coal and Steel (RFCS)

Data underlying the paper: "The role of austenite grain size in the martensitic transformation in low carbon steels"

The raw and processed data required to reproduce the findings of the research study "The role of the austenite grain size in the martensite transformation in low carbon steels" are provided within two excel documents for the two experimental techniques used: - Dilatometry (raw data and analysis) - Electron backscatter diffraction (raw data and analysis

Data underlying the paper: "Fracture Mechanisms and Microstructure in a Medium Mn Quenching and Partitioning Steel Exhibiting Macrosegregation"

The raw and processed data required to reproduce the findings of the research study "Fracture Mechanisms and Microstructure in a Medium Mn Quenching and Partitioning Steel Exhibiting Macrosegregation" are provided within two excel documents for the two experimental techniques used: - Dilatometry - Raw data & Analysis - Tensile test

The effect of heating rate and soaking time on microstructure of an advanced high strength steel

This work focuses on the effect of soaking time on the microstructure during ultrafast heat treatment of a 50% cold rolled low carbon steel with initial ferritic-pearlitic microstructure. Dilatometry analysis was used to estimate the effect of heating rate on the phase transformation temperatures and to select an appropriate inter critical temperature for final heat treatments. A thorough qualitative and quantitative microstructural characterization of the heat treated samples is performed using a wide range of characterization techniques. A complex multiphase, hierarchical microstructure consisting of ferritic matrix with embedded martensite and retained austenite is formed after all applied heat treatments. In turn, the ferritic matrix contains recrystallized and non-recrystallized grains. It is demonstrated that the ultrafast heating generally results in finer microstructure compared to the conventional heating independently on the soaking time. There is a significant effect of the soaking time on the volume fraction of martensite of the ultrafast heated material, while in the samples heated with conventional heating rate it remains relatively unchanged during soaking. Recrystallization, recovery and phase transformations occurring during soaking are discussed with respect to the applied heating rate

La descarbonización de la industria siderúrgica empleando hidrógeno como vector energético

La industria siderúrgica necesita reducir drásticamente su huella de carbono para asegurar el bienestar social, económico y medioambiental de nuestra sociedad en el futuro [1]. En el año 2020, por cada tonelada de acero producido, se emitieron 1,85 toneladas de gas dióxido de carbono (CO2), lo que supone alrededor del 8% de las emisiones de CO2 en todo el mundo [2]. Esto se debe al uso extendido de la ruta del alto horno convertidor (de aquí en adelante referida como BF-BOF, del inglés blast furnace-basic oxygen furnace), que supone un 71 % de la producción mundial de acero y se basa en una tecnología dependiente del consumo de combustibles fósiles. Para alcanzar los objetivos fijados desde el Acuerdo de Paris (2015), la Unión Europea (UE) lidera el cambio hacia la neutralidad climática impulsando el uso eficiente de recursos, las energías renovables y la movilidad limpia [3]

Micromagnetic modelling of magnetostriction under uniaxial stress

In the current work we present the results of 3D micromagnetic modelling of magnetostrictive strain and magnetic hysteresis under uniaxial stress in ferrite. The simulations are performed on artificial microstructures with different grain orientations that allow to take into account the anisotropy of magnetic and mechanical properties of iron-based alloys. The obtained results are in reasonable agreement with experimental observations. The proposed method opens a path to predictive modelling of the magnetic properties of different textured steels in the context of in-line non-destructive testing

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

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 redistribution between martensite and austenite upon partitioning conditions of 400 °C and 50 s. Under fixed quenching and partitioning conditions, decreasing the PAGS leads to a more efficient carbon partitioning process through the smaller and more homogeneously distributed phases developed during the first quench. In contrast, the microstructural heterogeneity obtained with larger PAGSs makes it more difficult to control the degree of carbon enrichment in austenite during partitioning and thus the austenite stability. Additionally, large volumes of fresh martensite are more likely to form in the interior of large-scale austenite grains due to the incomplete carbon homogenisation process. To consider the PAGS in the design of Q&P microstructures the selection of an optimum fraction of primary martensite is proposed, which ensures the minimisation of fresh martensite in the final microstructure and the sufficient stabilisation of the austenite phase. This new methodology facilitates the applicability of the Q&P process providing a controlled and reproducible development of optimised Q&P microstructures.(OLD) MSE-3(OLD) MSE-1Materials Science and Engineerin

Influence of biaxial stress on magnetostriction—Experiments and modeling

International audienceThe paper deals with the influence of biaxial stress on the magnetic and magnetostriction behavior of a low carbon steel used for structural pieces in the car industry. Material, specimen, measurement setup and protocol are presented. Anhysteretic measurements are performed, giving results in accordance with literature. A quadratic approximation of magnetostriction vs. induction measurements allows the evaluation of a single magnetostriction parameter per mechanical state. Results are compared to the outputs of a multiscale model, which indicate coherent tendencies but some significant amplitude differences

TAILORING THE MECHANICAL PROPERTIES THROUGH THE CONTROL OF HEAT TREATMENTS IN A PRECIPITATION HARDENING MESTABLE STAINLES STEEL

This research focusses on a complex precipitation (Ni3(Ti,Al)) hardenable metastable stainless steel. Dual phase (austenite/martensite) and ultrafine grained austenitic microstructures obtained after applying isochronal heat treatments (0.1-10 ºC/s) to a cold-rolled (CR) metastable stainless steel have been microstructurally and mechanically characterized using different experimental techniques (Optical microscopy, SEM, TEM, magnetic measurements, tensile tests). A wide range of strength (2.1-1.1 GPa) and elongation (3-25%) values have been obtained using sub-size samples (7 mm in gauge length). The scientific aim is the understanding of those microstructural parameters and mechanisms that influence the achievement of ultra-fine microstructures and control or the mechanical behaviour of different complex microstructures in this type of steels. Whereas the industrial aim would be to expand the applicability of this steel and use this scientific knowledge to design steels with optimized microstructures and mechanical properties