| 1. |
- Alshahrani, M. A.M., et al.
(author)
-
High-Temperature Hydrogen Attack on 2.25Cr-1Mo Steel: The Roles of Residual Carbon, Initial Microstructure and Carbide Stability
- 2022
-
In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 54, s. 3682-
-
Journal article (peer-reviewed)abstract
- High temperature hydrogen attack is a damage mechanism that occurs in critical steel components in petrochemical plants and refineries when the hydrogen penetrates the steel and reacts with the carbides within to produce pores containing methane. With the motivation of understanding the role of carbide stability on the reaction with hydrogen, samples of a classic 214Cr-1Mo steel were subjected to a variety of heat treatments that generate a corresponding variety of precipitates, prior to exposure to high-pressure hydrogen in an autoclave. Using quantitative carbide, porosity and microstructural characterisation, it has been possible to demonstrate the roles of four variables: (a) the carbon residue present in the ferrite; (b) the non-equilibrium chemical composition of carbide; (c) the fraction of the carbide that is closest to the thermodynamic equilibrium state and (d) the initial microstructural state, i.e., whether it is martensitic or bainitic prior to heat treatment.
|
|
| 2. |
- Bakshi, S. Das, et al.
(author)
-
Dry rolling/sliding wear of nanostructured bainite
- 2014
-
In: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 316:1-2, s. 70-78
-
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
|
|
| 3. |
- Bakshi, S. Das, et al.
(author)
-
Dry rolling/sliding wear of nanostructured pearlite
- 2015
-
In: Materials Science and Technology. - 0267-0836 .- 1743-2847. ; 31:14, s. 1735-1744
-
Journal article (peer-reviewed)abstract
- The dry rolling-sliding wear behaviour of pearlite that has an interlamellar spacing of just 85 nm has been characterised. Its wear resistance is found to be comparable to that of much harder bainitic steels. Microstructural observations indicate that there is substantial plastic deformation of both ferrite and cementite components of pearlite in the vicinity of the wear surface. Plasticity is not expected from Hertzian analysis that assumes a smooth contact surface. Instead, it is likely to be a consequence of exaggerated stresses due to surface roughness. The material remains ductile to shear strains in the order of 4. Diffraction data indicate that the coherent domain size is reduced to about half the interlamellar spacing and that some of the cementite may dissolve and contribute to the expansion of the lattice parameter of ferrite
|
|
| 4. |
- Bhadeshia, H K D H, et al.
(author)
-
Coalesced bainite
- 2006
-
In: Transactions of the Indian Institute of Metals. ; 59, s. 689-694
-
Journal article (peer-reviewed)
|
|
| 5. |
- Hulme-Smith, Christopher, 1989-, et al.
(author)
-
Intermetallic-strengthened nanocrystalline bainitic steel
- 2018
-
In: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 34:16, s. 1976-1979
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 6. |
|
|
| 7. |
- Ooi, S. W., et al.
(author)
-
Designing steel to resist hydrogen embrittlement Part 2 : precipitate characterisation
- 2018
-
In: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 34:14, s. 1747-1758
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 8. |
- Ramjaun, T., et al.
(author)
-
Effect of interpass temperature on residual stresses in multipass welds produced using low transformation temperature filler alloy
- 2014
-
In: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:1, s. 44-51
-
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.
|
|
| 9. |
- Ramjaun, T., et al.
(author)
-
Effects of dilution and baseplate strength on stress distributions in multipass welds deposited using low transformation temperature filler alloys
- 2014
-
In: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:6, s. 461-467
-
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.
|
|
| 10. |
- Ramjaun, T., et al.
(author)
-
Surface residual stresses in multipass welds produced using low transformation temperature filler alloys
- 2014
-
In: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:7, s. 623-630
-
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.
|
|
