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  • 1.
    Borasi, Luciano
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Investigation of the Effect of Different “Q&P” Parameters on the Mechanical Properties of AHSS2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the present study, the influence of the quenching temperature and partitioning conditions (temperature and time) have been investigated on a 0.6%C-1.2%Mn-1.6%Si-1.75%Cr alloy. Maps of hardness, impact toughness and amount of retained austenite have been developed for three quenching temperatures as a function of partitioning temperature and partitioning time. Results demonstrate that, in this material, the carbon depletion of the martensite and the stabilization of austenite can be achieved significantly faster at high partitioning temperatures, promoting higher retained austenite fractions, lower hardness, and maximizing the energy absorbed in a Charpy V‑Notch test. In addition, the effect of the partitioning time was also analysed, presenting different behaviour at high and low partitioning temperatures. Whereas an increment of time at high partitioning temperatures (>400 ºC) leads to an austenite consumption, at low partitioning temperatures it is effective to retain a higher amount of austenite. 

    Furthermore, tensile properties are shown to be better than in conventional alloys utilized in industry. Whilst, for example, the AISI 52100 alloy achieves 2 GPa of tensile strength and 1‑2% of fracture deformation, in the present study the notable combination of 2.5 GPa of tensile strength and 5.7 % of fracture deformation was achieved in samples quenched until room temperature. Untempered martensite transformed during final cooling in samples quenched until higher temperatures was shown to be detrimental for tensile properties.

    A comparison between the Q&P process and the austempering process on this alloy has been carried out. Results reveal that the quenching and partitioning heat treatment is presented as a promising alternative to reach higher hardness (>700 HV) and similar specific wear rates in dry conditions performing a shorter heat treatment.   

    Finally, a complementary study about the effect of micro-segregation on the Q&P process and an optimization method to minimize the inhomogeneity of the structure by a correct selection of the quenching temperature were established.

  • 2.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Borasi, Luciano
    Luleå University of Technology.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, F.
    Department for Materials Science, Functional Materials, Saarland University, Saarbrücken, Germany.
    Optimization of Quenching Temperature to Minimize the Micro Segregation Induced Banding Phenomena in Quenching and Partitioning (Q&P) Steels2019In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 90, no 1, article id 1800281Article in journal (Refereed)
    Abstract [en]

    Mn, Cr, and Si are favorable elements for designing the quenching and partitioning (Q&P) steels while the microsegregation of them is a common phenomenon in the steels. This segregation makes the bands of enriched and depleted Mn–Cr regions, which affects the Ms temperature of the bands and consequently influence the volume fraction of initial martensite, retained austenite, and secondary fresh martensite in different bands. This issue leads to non-homogeneity in the microstructure and mechanical properties. In this study, the optimization method to minimize the inhomogeneity by selection of the quenching temperature is demonstrated.

  • 3.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Borasi, Luciano
    Luleå University of Technology.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    University of Saarland .
    Process Control Maps to Design an Ultra-High Strength-Ductile Steel2019In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 35, no 10, p. 1173-1184Article in journal (Refereed)
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