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  • 1.
    Al-Saadi, Munir
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. R&D, AB Sandvik Materials Technology, SE-811 81Sandviken, Sweden..
    Sandberg, Fredrik
    R&D, AB Sandvik Materials Technology, SE-811 81Sandviken, Sweden..
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A study of the static recrystallization behaviour of cast Alloy 825 after hot-compressions2019In: Journal of Physics: Conference Series, 2019, Vol. 1270Conference paper (Refereed)
    Abstract [en]

    The static recrystallization behaviour of a columnar and equiaxed Alloy 825 material was studied on a Gleeble-3800 thermo-simulator by single-hit compression experiments. Deformation temperatures of 1000-1200 °C, a strain of up to 0.8, a strain rate of 1s-1, and relaxation times of 30, 180, and 300 s were selected as the deformation conditions to investigate the effects of the deformation parameters on the SRX behaviour. Furthermore, the influences of the initial grain structures on the SRX behaviors were studied. The microstructural evolution was studied using optical microscopy and EBSD. The EBSD measurements showed a relaxation time of 95 % for fractional recrystallization grains, 𝑡95, in both structures, was less than 30 seconds at the deformation temperatures 1100 °C and 1200 °C. However, fewer than 95% of recrystallized grains recrystallized when the deformation temperature was lowered to 1000 °C. From the grain-boundary misorientation distribution in statically recrystallized samples, the fraction of high-angle grain boundaries decreased with an increasing deformation temperature from 1000 °C to 1200 °C for a given relaxation time. This was attributed to grain coarsening

  • 2. Hou, T. P.
    et al.
    Li, Y.
    Wu, K. M.
    Peet, Mathew James
    Hulme-Smith, Christopher
    Guo, L.
    Magnetic-field-induced magnetism and thermal stability of carbides Fe6-xMoxC in molybdenum-containing steels2016In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 102, p. 24-31Article in journal (Refereed)
    Abstract [en]

    A hybrid method combining first-principles calculations and Weiss molecular field theory with thermodynamic data has been implemented to explore the origin of magnetic-field-induced precipitation behaviors for alloy carbides. The paramagnetic Mo atom disturbed the order of magnetic moment and resulted in a decrease in the Curie temperature for alloy carbide Fe<sub><it>6-x</it></sub>Mo<sub><it>x</it></sub>C. The temperature dependence of magnetic moment and saturation magnetization of Fe atoms at different Wyckoff positions, as well as the saturation or induced magnetization of Fe<sub><it>6-x</it></sub>Mo<sub><it>x</it></sub>C, decreased with increasing temperature. The higher Fe content and external magnetic field greatly increased the magnetization of alloy carbides. Two kinds of stella quadrangula lattices were employed to account for the total magnetism which was derived from the contribution of different Wyckoff sites of Fe atoms and Fe-C distances. The calculated total free energy taking into account magnetic field, temperature and composition was sufficient to provide quantitative agreement with experiment. The investigation of the effects of external field on the carbide precipitation behaviors led to a better understanding of the magnetic-field-induced phase transformation mechanism in heat resistant steels.

  • 3. Hou, T. P.
    et al.
    Peet, Mathew James
    Hulme-Smith, Christopher
    University Of Cambridge.
    Wu, K. M.
    Li, Y.
    Guo, L.
    The determining role of magnetic field in iron and alloy carbide precipitation behaviors under the external field2016In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 120, p. 76-79Article in journal (Refereed)
    Abstract [en]

    A combined approach to calculate the thermodynamic properties of iron and alloy carbides including the thermal and magnetic contribution is derived. Special emphasis is placed on the role of Fe and Mo to the Gibbs free energy. Lower Mo concentration in the carbides corresponds to a higher thermal Gibbs free energy change. The higher Fe content and external magnetic field greatly increase the induced magnetization, reducing the magnetic Gibbs free energy substantially and therefore increase the formation temperature. The stability of M 2 C and M 3 C are mainly determined by the thermal factors, whereas magnetic field has a predominant contribution for M 6 C.

  • 4. Hou, T. P.
    et al.
    Wu, K. M.
    Liu, W. M.
    Peet, M. J.
    Hulme-Smith, Christopher
    University Of Cambridge.
    Guo, L.
    Zhuang, L.
    Magnetism and high magnetic-field-induced stability of alloy carbides in Fe-based materials2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1Article in journal (Refereed)
    Abstract [en]

    Understanding the nature of the magnetic-field-induced precipitation behaviors represents a major step forward towards unravelling the real nature of interesting phenomena in Fe-based alloys and especially towards solving the key materials problem for the development of fusion energy. Experimental results indicate that the a pplied high magnetic field effectively promotes the precipitation of M 23 C 6 carbides. We build an integrated method, which breaks through the limitations of zero temperature and zero external field, to concentrate on the dependence of the stability induced by the magnetic effect, excluding the thermal effect. We investigate the intimate relationship between the external field and the origins of various magnetics structural characteristics, which are derived from the interactions among the various Wyckoff sites of iron atoms, antiparallel spin of chromium and Fe-C bond distances. The high-magnetic-field-induced exchange coupling increases with the strength of the external field, which then causes an increase in the parallel magnetic moment. The stability of the alloy carbide M 23 C 6 is more dependent on external field effects than thermal effects, whereas that of M 2 C, M 3 C and M 7 C 3 is mainly determined by thermal effects.

  • 5.
    Hulme-Smith, Christopher
    University Of Cambridge.
    Improving the thermal stability of bulk nanocrystalline steel2015In: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 2015Conference paper (Refereed)
    Abstract [en]

    A recent innovation in steel metallurgy allows the formation of carbide-free bainite at temperatures below 300 °C, with plates of bainitic ferrite ≈100 nm wide separated by films of carbon-enriched retained austenite ≈50 nm wide, which are inexpensive to make and show an impressive combination of strength and toughness. Heating the material leads to the transformation of austenite to cementite and untempered martensite, rendering the steel weak and brittle. The current work uses thermodynamic modelling to design new alloys with increased resistance to thermal decomposition while retaining desirable mechanical properties. All three alloys studied were found to consist of nanostructured carbide-free bainite using electron microscopy and X-ray diffraction and exhibited improved thermal stability, compared to existing alloys.

  • 6. Hulme-Smith, Christopher
    et al.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Erratum to "Mechanical properties of thermally-stable, nanocrystalline bainitic steels" [Materials Science & Engineering A 700 (2017) 714-720]2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 704, no AugustArticle in journal (Other academic)
  • 7.
    Hulme-Smith, Christopher
    et al.
    University Of Cambridge.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Mechanical properties of thermally-stable, nanocrystalline bainitic steels2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 700, p. 714-720Article in journal (Refereed)
    Abstract [en]

    Two novel, thermally stable bulk nanocrystalline bainitic steels were subjected to a range of mechanical tests. One alloy, containing 0.72 wt% carbon exhibited an ambient-temperature 0.2% proof strength of 1500 MPa and a fracture toughness of 64.6 MPa m<sup>1/2</sup> after the bainite transformation. The other, containing 0.45 wt% carbon and 13.2 wt% nickel, had a 0.2% proof stress of 1000 MPa and a fracture toughness of 103.8 MPa m<sup>1/2</sup> . Both steels showed excellent creep resistance, with a rupture life at 450 ˚C and 700 MPa of 114 h and 94.8 h, respectively. Both displayed fatigue lives consistent with other steels of similar structure in the literature. After thermal exposure at 480 ˚C for 8 d, both steels increased in strength to 1800 MPa, and 1600 MPa, respectively. The latter steel reduced in fracture toughness to 19.6 MPa m<sup>1/2</sup> . These alloys are suitable for a range of engineering applications and remain so after thermal exposure. Combined with impressive high-temperature performance, this

  • 8.
    Hulme-Smith, Christopher
    et al.
    Materials Science and Metallurgy, University of Cambridge, UK.
    Lonardelli, I.
    Materials Engineering and Industrial Technologies, University of Trento, Italy.
    Dippel, A. C.
    Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Materials Science and Metallurgy, University of Cambridge, UK.
    Experimental evidence for non-cubic bainitic ferrite2013In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, no 5, p. 409-412Article in journal (Refereed)
    Abstract [en]

    The first evidence is provided for the existence of a tetragonal or slightly orthorhombic unit cell of bainitic ferrite. It supports the hypothesis that the excess carbon that persists in the ferrite, which is in contact with austenite, is a consequence of an increased solubility due to the change in symmetry from the conventional cubic unit cell. The deviations from the cubic cell are maintained to elevated temperatures, as expected from an increased solubility of carbon in the ferrite.

  • 9.
    Hulme-Smith, Christopher
    et al.
    Materials Science and Metallurgy, University of Cambridge, UK.
    Lonardelli, I.
    Materials Engineering and Industrial Technologies, University of Trento, Italy.
    Peet, Mathew James
    Materials Science and Metallurgy, University of Cambridge, UK.
    Dippel, A. C.
    Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Materials Science and Metallurgy, University of Cambridge, UK.
    Enhanced thermal stability in nanostructured bainitic steel2013In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, no 2, p. 191-194Article in journal (Refereed)
    Abstract [en]

    We report an attempt at increasing the thermal stability of nanocrystalline bainite to tempering heat treatments by enhancing the silicon concentration of the alloy. Validation experiments have been conducted using synchrotron X-irradiation during tempering heat treatment. It is found that the change in alloying successfully stabilizes the austenite at elevated temperatures by retarding cementite formation to temperatures as high as 500 ˚C. Other changes reflected in the lattice parameters of the major phases have revealed further information about the mechanisms involved.

  • 10.
    Hulme-Smith, Christopher
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Ooi, S. W.
    Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Bhadeshia, H. K. D. H.
    Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Intermetallic-strengthened nanocrystalline bainitic steel2018In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 34, no 16, p. 1976-1979Article in journal (Refereed)
    Abstract [en]

    A new thermally stable, nanocrystalline bainitic steel has been developed, rich in nickel and aluminium. During tempering, it is expected that a significant quantity of intermetallic precipitates will form. This was confirmed by X-ray diffractometry, scanning transmission electron microscopy, Fourier transform analysis of atomic column images, energy dispersive X-ray spectroscopy and selected area electron diffraction. These are the first intermetallics to be produced in a nanocrystalline bainitic steel.

  • 11.
    Hulme-Smith, Christopher
    et al.
    Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
    Ooi, Shgh Woei
    Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
    Thermally Stable Nanocrystalline Steel2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48, no 10, p. 4957-4964Article in journal (Refereed)
    Abstract [en]

    Two novel nanocrystalline steels were designed to withstand elevated temperatures without catastrophic microstructural changes. In the most successful alloy, a large quantity of nickel was added to stabilize austenite and allow a reduction in the carbon content. A 50 kg cast of the novel alloy was produced and used to verify the formation of nanocrystalline bainite. Synchrotron X-ray diffractometry using in situ heating showed that austenite was able to survive more than 1 hour at 773 K (500 ˚šC) and subsequent cooling to ambient temperature. This is the first reported nanocrystalline steel with high-temperature capability.

  • 12.
    Hulme-Smith, Christopher
    et al.
    Materials Science and Metallurgy, University of Cambridge, UK.
    Peet, Mathew James
    Materials Science and Metallurgy, University of Cambridge, UK.
    Lonardelli, I.
    Materials Engineering and Industrial Technologies, University of Trento, Italy.
    Dippel, Ann Christin
    Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Materials Science and Metallurgy, University of Cambridge, UK.
    Further evidence of tetragonality in bainitic ferrite2015In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 31, no 2, p. 254-256Article in journal (Refereed)
    Abstract [en]

    There is growing evidence that bainitic ferrite which retains a substantial amount of carbon in solid solution does not have cubic symmetry. We provide additional data on a different nanostructured bainitic steel to support this evidence, based on synchrotron X-ray diffraction experiments. The data are consistent only with a displacive transformation mechanism for bainite.

  • 13.
    Hulme-Smith, Christopher
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. University Of Cambridge.
    Pickering, Ed
    University of Cambridge.
    Steeling the Show2012In: The Naked Scientists: Science Articles and FeaturesArticle, review/survey (Other (popular science, discussion, etc.))
  • 14. Ooi, S. W.
    et al.
    Ramjaun, T. I.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Morana, R.
    Drakopoulos, M.
    Bhadeshia, H. K. D. H.
    Designing steel to resist hydrogen embrittlement Part 2: precipitate characterisation2018In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 34, no 14, p. 1747-1758Article in journal (Refereed)
    Abstract [en]

    A novel, low-alloy steel has been designed for use in the oil and gas industry. Its high strength and hydrogen trapping potential are derived from a martensitic microstructure containing a dispersion of fine vanadium-molybdenum alloy carbides that evolve during tempering. In this second paper, the effect of quench rate from austenitisation and tempering conditions are investigated with respect to the microstructure. The alloy loses its tempering resistance following slow-cooling from austenitisation as a result of MC precipitation, leading to vanadium depletion and significant M2C coarsening. This is predicted using computer simulation and confirmed by high energy X-ray diffraction, combined with electron microscopy.

  • 15. Peet, Mathew James
    et al.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. University Of Cambridge.
    Stone, H. J.
    Partitioning and supersaturation of carbon in low-temperature bainite2015In: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 2015Conference paper (Refereed)
1 - 15 of 15
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