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Austenitic Stability and Strain-Induced Martensitic Transformation Behavior of Nanocrystalline FeNiCrMoC HSLA Steels

Park Jungbin, Jeon Junhyub, Seo Namhyuk, Kim Gwanghun, Son Seung Bae, Jung Jae-Gil, Lee Seok-Jae

Archives of Metallurgy and Materials

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2023

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Vol. 68, iss. 1

77--80

EN

The austenitic stability and strain-induced martensitic transformation behavior of a nanocrystalline FeNiCrMoC alloy were investigated. The alloy was fabricated by high-energy ball milling and spark plasma sintering. The phase fraction and grain size were measured using X-ray diffraction. The grain sizes of the milled powder and the sintered alloy were confirmed to be on the order of several nanometers. The variation in the austenite fraction according to compressive deformation was measured, and the austenite stability and strain-induced martensitic transformation behavior were calculated. The hardness was measured to evaluate the mechanical properties according to compression deformation, which confirmed that the hardness increased to 64.03 HRC when compressed up to 30%.

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Cold unidirectional/cross‑rolling of austenitic stainless steels: a review

Mohammadzehi Sara, Mirzadeh Hamed

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 3

art. no. e129

EN

The effects of cold unidirectional/cross-rolling on the development of substructure, strain-induced martensitic transformation, crystallographic texture (preferred orientation), and mechanical properties, as well as the microstructure after subsequent annealing of metastable austenitic stainless steels were overviewed. First, the deformed state was discussed. Compared to unidirectional rolling, it was revealed that cross-rolling leads to the formation of a greater amount of deformation-induced martensite, which is related to the generation of numerous intersecting shear bands and nano-twins, as well as a higher dislocation density in the austenite phase (activation of higher number of slip/twinning systems). It was concluded that these effects are more pronounced at low reductions in thickness. Regarding texture evolution, cross-rolling tends to strengthen the Brass component in the retained austenite phase. Subsequently, the mechanical properties were reviewed, where it was concluded that a more rapid work-hardening and higher strength/hardness at low strains can be obtained due to the effects of cross-rolling on the microstructure. Moreover, while the effects of cross-rolling on the strength at high rolling reductions might not be significant, it is possible to decrease the anisotropy of the sheet due to the alternate change in the rolling direction. Afterward, the annealing of cold-rolled sheets was discussed. It was deduced that cross-rolling might be used for more intense grain refinement based on the thermomechanical processing of cold-rolling and reversion/recrystallization annealing, where the activation of greater number of slip systems, higher dislocation density, and greater martensite content in the deformed state are responsible in this regard. Finally, the suggestions for future works were proposed.

3

Modelling of the DP and TRIP micro-structure in the CMnAlSi automotive steel

Lis A. K., Gajda B.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 15, nr 1-2

127--134

EN

Purpose: The CMnAlSi steel is a new grade of TRIP steels with 1wt % of Al and Si. It is important to determine the usability of the CMnAlSi for production of sheets for automotive applications. Design/methodology/approach: The effect of cooling rate and austenitization temperature on phase transformations was investigated. The dilatometric experiments of the steel were done for the full austenitization temperature 1200°C, and for (α+γ) temperature ranges: 1100°C, 1000°C, 900°C and 800°C. Steel was also processed to achieve TRIP grade by continuous annealing with modeled vertical hot dip galvanizing line. The microstructures were investigated by light optical microscopy and SEM with EDX attachment. The amount of retained austenite in the obtained microstructures was investigated with X-ray diffraction. Findings: There is possibility to produce “dual-phase” CMnAlSi steel grade with controlled rolling at finishing temperature below 900°C to 800°C and fast cooling. Steel CMnAlSi is well suited for production of TRIP grade via heating cycle which correspond to vertical hot dip galvanizing process. Practical implications: This steel is suitable for production of automotive applications. Originality/value: The new procedure of control rolling from the (α+γ) temperature range of CMnAlSi steel was presented.