Partial-Isothermally-Treated Low Alloy Ultrahigh Strength Steel With Martensitic/Bainitic Microstructure

Luo, Quanshun; Kitchen, Matthew; Patel, Vinay Kumar; Filleu, Martin; Owens, Dave

doi:10.1002/9781119223399.ch50

Cited by 2 publications

(5 citation statements)

References 10 publications

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“…Such austempering has served as a replacement of conventional oil-quenching, promising ultrahigh strength properties, as shown in our recent work [28].…”

Section: Hardening Mechanism In Austempering Treatmentmentioning

confidence: 85%

“…On each sample, five diffraction peaks were acquired under the θ-2θ (Bragg-Brentano) mode, including the austenite peaks (200) γ , (220) γ and (311) γ , and the ferrite peaks (200) α and (211) α . The obtained diffractions were measured using a self-developed Gaussian peak-fitting technique to determine the peak position (2θ), net intensity (I) and broadening width (β) (FWHM, the full-width at half maximum) [27,28]. These parameters were then used to calculate the volume fraction (V γ ) and carbon content (C γ ) of retained austenite and the micro-strains (ε) of both the martensitic and bainitic ferrite and the retained austenite.…”

Section: Methodsmentioning

confidence: 99%

“…In a recent project, we worked on austempering treatments of a Cr-Ni-Mo-V alloyed spring steel, which led to superior mechanical properties, including ultimate tensile strength of 2100 MPa, yielding strength of 1800 MPa and elongation of 8-10%, along with V-notched Charpy impact toughness of 9-12 J/cm 2 [27,28]. This paper reports the microstructure characterisations of a series of austempered samples, with a focus on the carbon partitioning behaviour at various isothermal soaking times.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

Luo

Kitchen

Abubakri

2017

Metals

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Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 • C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation.

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“…Such austempering has served as a replacement of conventional oil-quenching, promising ultrahigh strength properties, as shown in our recent work [28].…”

Section: Hardening Mechanism In Austempering Treatmentmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

Luo

Kitchen

Abubakri

2017

Metals

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“…Several samples were employed to demonstrate the new approach, including machined cylindrical tensile bars, of 5 mm in diameter, of a high-strength spring steel as well as a TiN coating. The spring steel was strengthened through quenching and tempering heat treatments [37,38]. Two types of machined cylindrical surfaces were made for the residual stress measurement.…”

Section: Methodsmentioning

confidence: 99%

“…It is not the scope of this paper to compare the scales of residual stresses generated in the two different machining operations or to investigate the effect of machining parameters on the residual stresses. However, the precise measurement of machining-induced residual stresses provided a strong support to the research and development of the ultrahigh strength steel [37,38]. The optimised machining process helped to minimise the residual stresses of the turning-and grinding-machined specimens, which contributed to reliable measurements of mechanical properties in tensile and fatigue tests.…”

Section: Residual Normal Stresses Determined Using the New Methods And Conventional Methodsmentioning

confidence: 99%

A modified X-ray diffraction method to measure residual normal and shear stresses of machined surfaces

Luo

2022

Int J Adv Manuf Technol

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X-ray diffraction has been widely used in measuring surface residual stresses. A drawback of the conventional d ~ sin2ψ method is the increased uncertainty arising from sin2ψ splitting when a significant residual shear stress co-exists with a residual normal stress. In particular, the conventional method can only be applied to measure the residual normal stress while leaving the residual shear stress unknown. In this paper, we propose a new approach to make simultaneous measurement of both residual normal and shear stresses. Theoretical development of the new approach is described in detail, which includes two linear regressions, $$\frac{{d}_{\psi }+ {d}_{-\psi }}{2}$$ d ψ + d - ψ 2 ~sin2ψ and {dψ-d-ψ} ~ sin(2ψ), to determine the residual normal and shear stresses separately. Several samples were employed to demonstrate the new method, including turning-machined and grinding-machined cylindrical bars of a high strength steel as well as a flat sample of magnetron sputtered TiN coating. The machined samples were determined to have residual compressive normal stresses at both the axial and hoop directions as well as various scales of residual shear stresses. The TiN coating showed a high scale of residual compressive (normal) stress whereas the measured residual shear stress was extremely low. The new method showed significantly increased precision as compared to the conventional d ~ sin2ψ method.

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Partial-Isothermally-Treated Low Alloy Ultrahigh Strength Steel With Martensitic/Bainitic Microstructure

Cited by 2 publications

References 10 publications

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

A modified X-ray diffraction method to measure residual normal and shear stresses of machined surfaces

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