| 1. |
- Bakshi, S. Das, et al.
(author)
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Dry rolling/sliding wear of nanostructured bainite
- 2014
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In: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 316:1-2, s. 70-78
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Journal article (peer-reviewed)abstract
- The abrasive wear of carbide-free bainitic steel under dry rolling/sliding conditions has been studied. It is demonstrated that this nanostructure, generated by isothermal transformation at 200 °C, has a resistance to wear that supersedes that of other carbide-free bainitic steels transformed at higher temperatures. The experimental results, in combination with a theoretical analysis of rolling/sliding indicates that under the conditions studied, the role of sliding is minimal, so that the maximum shear stresses during contact are generated below the contact surface. Thus, the hardness following testing is found to reach a maximum below the contact surface. The fine scale and associated strength of the structure combats wear during the running-in period, but the volume fraction, stability and morphology of retained austenite plays a significant role during wear, by work-hardening the surface through phase transformation into very hard martensite
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| 2. |
- Ramjaun, T., et al.
(author)
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Effect of interpass temperature on residual stresses in multipass welds produced using low transformation temperature filler alloy
- 2014
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In: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:1, s. 44-51
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Journal article (peer-reviewed)abstract
- Weld filler alloys that exploit transformation plasticity through low austenite to martensite transformation temperatures offer an effective method of reducing residual stresses in strong steel welds. However, in multipass welds, the heat input from later weld passes may be insufficient to retransform prior welding passes, leading to the accumulation of thermally induced strains and elevated residual stresses. In this work, the residual stress distributions produced around arc welds fabricated with a martensitic weld filler alloy that transforms at a low temperature have been studied as a function of the number of passes deposited and the interpass temperature. It is found that when the interpass temperature is above the transformation temperature of the weld metal, the entire multipass weld transforms as a single entity, thus permitting the optimum exploitation of the transformation plasticity. In contrast, the deposition of new metal with a relatively low interpass temperature leads to increased residual stresses in the underlying layers, reducing or eliminating the beneficial stress states previously created.
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| 3. |
- Ramjaun, T., et al.
(author)
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Effects of dilution and baseplate strength on stress distributions in multipass welds deposited using low transformation temperature filler alloys
- 2014
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In: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:6, s. 461-467
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Journal article (peer-reviewed)abstract
- Transformation plasticity can be utilised to control residual stresses in steel welds. This requires special filler alloys that transform at a sufficiently low temperature to compensate for accumulated thermal contraction strains. However, the welding parameters needed to optimise the effect in multipass joints have yet to be established. This topic has been investigated by characterising the residual stress distribution in multipass welds fabricated with different welding alloys and baseplates using neutron diffraction to assess the effects of dilution and baseplate strength. While the use of richly alloyed weld metal does enhance fatigue performance in single pass joints, the extent of stress relief that can be derived from transformation plasticity is reduced due to incomplete martensitic transformation when further layers are deposited. For all cases studied, compressive stresses were measured in the weld metal with balancing tensile stress in the heat affected zone of the plate. The magnitude of the tension was observed to be a function of the strength of the baseplate. Recommendations are also presented for the combination of welding and material parameters that lead to the optimum exploitation of transformation plasticity as a method for boosting the fatigue performance of multipass welded joints.
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| 4. |
- Ramjaun, T., et al.
(author)
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Surface residual stresses in multipass welds produced using low transformation temperature filler alloys
- 2014
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In: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:7, s. 623-630
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Journal article (peer-reviewed)abstract
- Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile transverse stresses were measured in the weld metal.
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