Edward Giovanni Rodriguez Arias | Universidade Estadual de Campinas (original) (raw)

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Papers by Edward Giovanni Rodriguez Arias

Although high carbon martensitic steels are well known for their industrial utility in high abras... more Although high carbon martensitic steels are well known for their industrial utility in high abrasion and extreme operating environments, due to their hardness and strength, the compressive stability of their retained austenite, and the implications for the steels' performance and potential uses, is not well understood. This article describes the first investigation at both the macro and nano scale of the compressive stability of retained austenite in high carbon martensitic steel. Using a combination of standard compression testing, X-ray diffraction, optical microstructure, electron backscattering diffraction imaging, electron probe micro-analysis, nano-indentation and micro-indentation measurements, we determined the mechanical stability of retained austenite and martensite in high carbon steel under compressive stress and identified the phase transformation mechanism, from the macro to the nano level. We found at the early stage of plastic deformation hexagonal close-packed (HCP) martensite formation dominates, while higher compression loads trigger body-centred tetragonal (BCT) martensite formation. The combination of this phase transformation and strain hardening led to an increase in the hardness of high carbon steel of around 30%. This comprehensive characterisation of stress induced phase transformation could enable the precise control of the microstructures of high carbon martensitic steels, and hence their properties. For many years, high carbon steels have proved useful for industrial application in extreme operation conditions due to their hardness, strength and relatively low cost compared to high alloy steels. High carbon martensi-tic steels are favoured when high abrasion resistance is required. These steels contain plate and lath martensite which is formed from austenite during quenching, although this transformation is rarely complete, and some austenite remains. An inverse relationship exists between the strength of the martensite formed in the quenching process and the amount of residual austenite; the martensite's strength increases as the amount of retained austenite decreases. Hence retained austenite is generally considered deleterious in low-carbon steel 1–5. However, the retained austenite can subsequently be transformed to the more stable martensite phase with the application of high stresses and temperatures; thereby increasing the toughness and ductility of the substrate. This means that under extreme operating conditions, when the pressures on the substrate, and the temperature to which is it exposed, are high enough, the transformation of retained austenite will be triggered, thereby achieving additional work hardening of the steel in-situ. This work hardening may be very desirable in industrial applications in which the steel's surface wears due to the application of stresses, but the material remains hard due to the transformation of retained austenite to martensite. Depending upon its chemical composition, retained austenite can be meta-stable phase and will transform to martensite by passing the phase transformation barrier energy. Martensitic transformation is achieved by the cooperative shear movement of atoms; applied compressive stress involving compression deformation aids the transformation 6. If the steel is subjected to high compression or if it is heated

Retained austenite fractions, predicted to be stable at room temperature assuming ortho-equilibri... more Retained austenite fractions, predicted to be stable at room temperature assuming ortho-equilibrium solute distribution during intercritical annealing, were calculated for ''medium-Mn'' steels with varying Mn, C, Al, Si, and Cr additions using SSOL 2 and TCFE 7 Thermo-Calc Ò databases. While Mn additions increase retained austenite levels, increased C levels are not predicted to greatly impact austenite fractions. Additions of Si reduce the levels, whereas opposing trends are predicted for Al additions by the employed Thermo-Calc Ò databases. Chromium significantly reduces the dependence of retained austenite fraction on annealing temperature. Alloying effects are explained through four critical phase transformation temperatures.

Although high carbon martensitic steels are well known for their industrial utility in high abras... more Although high carbon martensitic steels are well known for their industrial utility in high abrasion and extreme operating environments, due to their hardness and strength, the compressive stability of their retained austenite, and the implications for the steels' performance and potential uses, is not well understood. This article describes the first investigation at both the macro and nano scale of the compressive stability of retained austenite in high carbon martensitic steel. Using a combination of standard compression testing, X-ray diffraction, optical microstructure, electron backscattering diffraction imaging, electron probe micro-analysis, nano-indentation and micro-indentation measurements, we determined the mechanical stability of retained austenite and martensite in high carbon steel under compressive stress and identified the phase transformation mechanism, from the macro to the nano level. We found at the early stage of plastic deformation hexagonal close-packed (HCP) martensite formation dominates, while higher compression loads trigger body-centred tetragonal (BCT) martensite formation. The combination of this phase transformation and strain hardening led to an increase in the hardness of high carbon steel of around 30%. This comprehensive characterisation of stress induced phase transformation could enable the precise control of the microstructures of high carbon martensitic steels, and hence their properties. For many years, high carbon steels have proved useful for industrial application in extreme operation conditions due to their hardness, strength and relatively low cost compared to high alloy steels. High carbon martensi-tic steels are favoured when high abrasion resistance is required. These steels contain plate and lath martensite which is formed from austenite during quenching, although this transformation is rarely complete, and some austenite remains. An inverse relationship exists between the strength of the martensite formed in the quenching process and the amount of residual austenite; the martensite's strength increases as the amount of retained austenite decreases. Hence retained austenite is generally considered deleterious in low-carbon steel 1–5. However, the retained austenite can subsequently be transformed to the more stable martensite phase with the application of high stresses and temperatures; thereby increasing the toughness and ductility of the substrate. This means that under extreme operating conditions, when the pressures on the substrate, and the temperature to which is it exposed, are high enough, the transformation of retained austenite will be triggered, thereby achieving additional work hardening of the steel in-situ. This work hardening may be very desirable in industrial applications in which the steel's surface wears due to the application of stresses, but the material remains hard due to the transformation of retained austenite to martensite. Depending upon its chemical composition, retained austenite can be meta-stable phase and will transform to martensite by passing the phase transformation barrier energy. Martensitic transformation is achieved by the cooperative shear movement of atoms; applied compressive stress involving compression deformation aids the transformation 6. If the steel is subjected to high compression or if it is heated

Retained austenite fractions, predicted to be stable at room temperature assuming ortho-equilibri... more Retained austenite fractions, predicted to be stable at room temperature assuming ortho-equilibrium solute distribution during intercritical annealing, were calculated for ''medium-Mn'' steels with varying Mn, C, Al, Si, and Cr additions using SSOL 2 and TCFE 7 Thermo-Calc Ò databases. While Mn additions increase retained austenite levels, increased C levels are not predicted to greatly impact austenite fractions. Additions of Si reduce the levels, whereas opposing trends are predicted for Al additions by the employed Thermo-Calc Ò databases. Chromium significantly reduces the dependence of retained austenite fraction on annealing temperature. Alloying effects are explained through four critical phase transformation temperatures.