| 1. |
- Ashby, M. F., et al.
(författare)
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A first report on diagrams for grain growth in welds
- 1982
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 30:11, s. 1969-1978
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Tidskriftsartikel (refereegranskat)abstract
- Data for carbide dissolution, grain growth and martensite formation in the heat-affected zone of a weld can be assembled into a diagram showing the extent of each, for different weld cycles, and at different points in the zone. The diagrams are based on elementary kinetic models for grain growth and carbide dissolution, integrated over the weld cycle; and on experimental data. The sets of poorly-known kinetic constants which appear in such a treatment are determined by fitting the equations to data from real or simulated welds, at certain fixed points. Diagrams are presented for six steels. As well as summarising much data they allow the effect of change in weld procedure, or of preheat, to be predicted.
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| 2. |
- Ashby, M.F., et al.
(författare)
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The transformation hardening of steel surfaces by laser beams-I. Hypo-eutectoid steels
- 1984
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 32:11, s. 1935-1948
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Tidskriftsartikel (refereegranskat)abstract
- Surfaces can be treated with a scanning laser beam to modify their properties. The beam subjects the near-surface to a thermal cycle with an amplitude and shape which depends on the process variables: the beam size, energy, scan rate and on whether the laser is pulse or continuous, and the chemistry and metallurgy of the steel. Approximate solutions to the equations of heat flow are combined with kinetic models to predict the near-surface structure and hardness of plain carbon steels after laser treatment. The results are assembled into diagrams which show immediately the combination of process variables for a desired surface structure and the associated hardness profile
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| 3. |
- Easterling, K.E., et al.
(författare)
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On the growth of martensite in steel
- 1980
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 28:9, s. 1229-1234
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Tidskriftsartikel (refereegranskat)abstract
- Criteria based on minimum energy and maximum stress considerations have been developed for the first stages of growth of martensite in steel. It is shown that the critical size of nucleus at which dislocation-assisted growth can occur is about 25 nm diameter. The mode of growth governing low carbon lath martensite forming on {111} austenite habit planes is found to be fundamentally different from that of plate martensite which forms on irrational habit planes. A mechanism for lath thickening and growth is advanced in which dislocations nucleate at the thickest section of the lath and then follow after the coherent leading edge of the lath to generate ledges. Plate growth on the other hand can occur by the formation of twins which nucleate and thicken laterally behind the coherent leading edge of the plate.
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| 4. |
- Easterling, K.E., et al.
(författare)
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The nucleation of martensite in steel
- 1976
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 24:4, s. 333-341
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Tidskriftsartikel (refereegranskat)abstract
- Calculations of the total energy for transforming austenite to martensite in the form of thin ellipsoidal plates, fully coherent with the austenite, show that the process may be spontaneous in the presence of pre-existing dislocations. It is found that dislocations, or groups of dislocations, in the austenite are suitable sites for martensite nucleation in that their strain fields may interact favourably with the strain field associated with the Bain deformation thereby eliminating the energy barrier to nucleation. The driving force for twinning to occur virtually simultaneously with nucleation is large and when this happens energy is released for thickening and growth of the nucleus. It is also found that the strain energy of coherent plates of martensite, whether twinned or untwinned, is a function of their orientation in the austenite, although the lowest strain energy case occur nevertheless over a relatively wide range of orientations
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| 5. |
- Helle, A.S., et al.
(författare)
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Hot isostatic pressing diagrams : new developments
- 1985
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 33:12, s. 2163-2174
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Tidskriftsartikel (refereegranskat)abstract
- The equation and procedures for constructing hot-isostatic pressing diagrams are simplified and clarified. In earlier work, three classes of mechanism were modelled: plastic yielding, power-law creep and diffusional densification. In this paper two further mechanisms are added: diffusional deformations of particles when the grain size is smaller than the particle size, and separation of pores from boundaries when grain growth occurs. Application of HIP diagrams to tool steels, alumina and copper are discussed
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| 6. |
- Ion, John C., et al.
(författare)
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A second report on diagrams of microstructure and hardness for heat-affected zones in welds
- 1984
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 32:11, s. 1949-1962
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Tidskriftsartikel (refereegranskat)abstract
- The paper improves and extends kinetic models to include: precipitate coarsening; the use of semi-empirical equations including carbon-equivalence to predict microstructure and hardness; a comparison between the theory and data obtained from different types of real welds; and an alternative, more easily used diagram.
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| 7. |
- Li, C-H., et al.
(författare)
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A lattice resolution study of the martensitic transformation of small iron particles in a copper matrix
- 1985
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 33:2, s. 317-328
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Tidskriftsartikel (refereegranskat)abstract
- The martensitic transformation of small, fully coherent, gamma iron precipitates in an epsilon copper matrix, brought about by the bombardment of thin foils with argon ions, has been studied using lattice fringe imaging. It is found, in general, that only partial transformation of individual particles occurs, this corresponding to a simple homogeneous shear (a Bain strain). In addition, the transformation is limited to particles located within about two particle diameters of the foil surface. It is established that the mere presence of a Frank (or Shockley) loop in a particle, due to the bombardment, is insufficient to trigger the transformation. The implications of this result are discussed with reference to bulk martensite. In the present case, it is concluded that transformation may simply initiate at sites of local decohesion or microslip at the matrix/particle boundaries brought about by vacancy condensation following ion bombardment, these sites being most effective in the vicinity of free surfaces
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| 8. |
- Li, W-B., et al.
(författare)
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Laser transformation hardening of steel : II. Hypereutectoid steels
- 1986
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 34:8, s. 1533-1343
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Tidskriftsartikel (refereegranskat)abstract
- For pt.I see ibid., vol.32, p.1935 (1984). The properties of surfaces can be modified by heat-treatments using a scanning laser beam. In pt.I it was shown that the hardness and the depth of the laser-hardened layer in hypereutectoid steels could be predicted, with reasonable accuracy, from a model which combined an analysis of heat flow with one of the kinetics of pearlite dissolution, carbon redistribution in austenite, and subsequent transformation to martensite. In the present study the model is extended to include the case of hypereutectoid steels. A new approximate solution for carbide dissolution is developed, which allows both the changes in particle size and volume fraction, and in carbon content of the austenite, to be estimated. Reasonable agreement between measured and predicted hardness for a laser treated 1% C steel are obtained. The results are presented as laser processing diagrams which show how the case depth and hardness depend on the process variables
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| 9. |
- Li, Wen-Bin, et al.
(författare)
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On densification and shape change during hot isostatic pressing
- 1987
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Ingår i: Acta Metallurgica. - Cambridge : Elsevier BV. - 0001-6160. ; 35:12, s. 2831-2842
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Tidskriftsartikel (refereegranskat)abstract
- When the temperature of a powder compact is raised, heat diffuses inwards from the surface. If the compact is under pressure (as it is during HIPing), the surface layers start to densify, increasing the local thermal conductivity. Under certain conditions a densification front then propagates into the powder, and this leads to changes of shape of the compact, which is no longer identical to the preform shape. The conditions which lead to non-uniform densification are analysed and the consequences are discussed, and compared with experiments
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| 10. |
- Porter, D.A., et al.
(författare)
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Dynamic studies of the tensile deformation and fracture of pearlite
- 1978
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Ingår i: Acta Metallurgica. - : Elsevier BV. - 0001-6160. ; 26:9, s. 1405-1422
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Tidskriftsartikel (refereegranskat)abstract
- High resolution 200 kV scanning electron microscopy has been used to study in situ the tensile deformation and fracture of a range of pearlites, from relatively coarse mean interlamellar spacing of about 400 nm, to very fine mean spacing of about 90 nm. It was found that there were considerable differences in the tensile deformation behaviour between fine and coarse pearlites. A model is proposed to account for the differences based upon a combination of pile-up and fibre loading stresses, in which the operating deformation mode is largely determined by which type of mechanism is dominant
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