| 1. |
- Hosseini, Seyed, 1981, et al.
(författare)
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A Methodology for Temperature Correction When Using Two-Color Pyrometers : Compensation for Surface Topography and Material
- 2014
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Ingår i: Experimental mechanics. - : Springer Science and Business Media LLC. - 0014-4851 .- 1741-2765. ; 54:3, s. 369-377
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, the applicability of the two-color pyrometer technique for temperature measurements in dry hard turning of AISI 52100 steel was studied, where both machined surfaces as well as cutting tools were considered. The impacts of differing hard turned surface topography on the two-color pyrometer readings was studied by conducting temperature measurements on reference samples created using cutting tools with different degrees of tool flank wear. In order to conduct measurements in a controlled environment, a specially designed furnace was developed in which the samples were heated step-wise up to 1,000 °C in a protective atmosphere. At each testing temperature, the temperatures measured by the two-color pyrometer were compared with temperatures recorded by thermocouples. For all materials and surfaces as studied here, the two-color pyrometer generally recorded significantly lower temperatures than the thermocouples; for the hard turned surfaces, depending on the surface topography, the temperatures were as much as 20 % lower and for the CBN cutting tools, 13 % lower. To be able to use the two-color pyrometer technique for temperature measurements in hard turning of AISI 52100 steel, a linear approximation function was determined resulting in three unique equations, one for each of the studied materials and surfaces. By using the developed approximation function, the measured cutting temperatures can be adjusted to compensate for differing materials or surface topographies for comparable machining conditions. Even though the proposed equations are unique for the hard turning conditions as studied here, the proposed methodology can be applied to determine the temperature compensation required for other surface topographies, as well as other materials. © 2013 Society for Experimental Mechanics.
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| 2. |
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| 3. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Atomic-scale investigation of carbon atom migration in surface induced white layers in high-carbon medium chromium (AISI 52100) bearing steel
- 2017
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 130, s. 155-163
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the Ac1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ-carbides (cementite). The APT results reveal that the original θ-carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (
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| 4. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Characterization of the Surface Integrity induced by Hard Turning of Bainitic and Martensitic AISI 52100 Steel
- 2012
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 1:1, s. 494 - 499
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Konferensbidrag (refereegranskat)abstract
- Depending on the process parameters and the tool condition, hard turned surfaces can consist of a “white” and a “dark” etching layer having other mechanical properties compared to the bulk material. X-ray diffraction measurements revealed that tensileresidual stresses accompanied with higher volume fraction of retained austenite are present in the thermally induced white layer. While compressive residual stresses and decreased retained austenite content was found in the plastically created white layer. The surface temperature was estimated to be ~1200 C during white layer formation by hard turning.
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| 5. |
- Hosseini, Seyed, 1981
(författare)
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Characterization of White Layers induced by Hard Turning of AISI 52100 Steel
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hard turning is a machining process applied to metallic materials with hardness above 45 HRC. The process offers high production flexibility and sustainable manufacturing since it allows performing both rough and finishing machining of complex geometries in one single setup. With respect to surface integrity, hard turning can generate beneficial compressive residual stresses and good surface quality with small dimensional variation. However, deterioration of the cutting tool generates tensile residual stresses and also alters the surface microstructure, i.e. leads to formation of white layers. Since the mechanisms for white layer formation are not yet fully understood, there is limited understanding of whether there exists different types of white layers possessing different mechanical properties. Therefore, additional processing steps are often added to remove the white layers and to generate compressive residual stresses. By hard turning at different cutting speeds, 30 m/min to 260 m/min, and different tool conditions, it was possible to generate surface integrities with and without white layers on AISI 52100 steel. After hard turning with fresh cutting tools, only discontinuous and thin white layers were detected, while in case of turning with cutting tools with excessive flank wear, white layers up to 3 μm in thickness were observed. White layers formed at 30 m/min are characterized by reduced retained austenite content, deformed M3C carbides and compressive or low tensile residual stresses. In contrast, when white layers created at higher cutting speeds e.g. 260 m/min, significantly increased retained austenite contents, un-affected M3C carbides and high tensile residual stresses were measured. Temperature measurements with a novel two-color pyrometer at the cutting edge revealed large differences in cutting temperature for the studied cutting conditions, i.e. cutting temperatures higher than 900°C were measured at a cutting speed of 260 m/min, while during machining at 30 m/min, temperatures of about 550°C were measured. Microstructural characterization by use of transmission electron microscopy showed that the white layers consist of nanocrystalline and sub-microsrystalline grains ranging from 10 to 200 nm in diameter. The results show that there are different types of white layers, which are predominantly thermally or mechanically induced. Hence, depending on the formation mechanisms, different mechanical properties can be obtained.
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| 6. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Cutting temperatures during hard turning : Measurements and effects on white layer formation in AISI 52100
- 2014
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 214:6, s. 1293-1300
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns the temperature evolution during white layer formation induced by hard turning of martensitic and bainitic hardened AISI 52100 steel, as well as the effects of cutting temperatures and surface cooling rates on the microstructure and properties of the induced white layers. The cutting temperatures were measured using a high speed two-colour pyrometer, equipped with an optical fibre allowing for temperature measurements at the cutting edge. Depending on the machining conditions, white layers were shown to have formed both above and well below the parent austenitic transformation temperature, Ac1, of about 750 C. Thus at least two different mechanisms, phase transformation above the Ac1 (thermally) and severe plastic deformation below the Ac1 (mechanically), have been active during white layer formation. In the case of the predominantly thermally induced white layers, the cutting temperatures were above 900 C, while for the predominantly mechanically induced white layers the cutting temperatures were approximately 550 C. The surface cooling rates during hard turning were shown to be as high as 104-105 C/s for cutting speeds between 30 and 260 m/min independent of whether the studied microstructure was martensitic or bainitic. Adding the results from the cutting temperature measurements to previous results on the retained austenite contents and residual stresses of the white layers, it can be summarised that thermally induced white layers contain significantly higher amounts of retained austenite compared to the unaffected material and display high tensile residual stresses. On the contrary, in the case of white layers formed mainly due to severe plastic deformation, no retained austenite could be measured and the surface and subsurface residual stresses were compressive. © 2014 Elsevier B.V.
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| 7. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Determination of Stresses and Retained Austenite in Carbon Steels by X-rays - A Round Robin Study
- 2011
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Ingår i: Experimental Mechanics. - : Springer Science and Business Media LLC. - 1741-2765 .- 0014-4851. ; 51:1, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- Residual stresses and retained austenite are twoimportant process-related parameters which need to becontrolled and monitored carefully during production andheat treatment of products. X-ray diffraction techniques arenormally used in this context, and the purpose of thepresent study was to investigate the reproducibility andaccuracy of these methods for medium and high carbonsteels. The work was carried out as a round robin studyincluding nine different laboratories in Sweden and Finland.Stress measurements were carried out on three specimens etched to three different depths, 0 μm, 230 μm and 515 μm. Retained austenite measurements were carried out on three specimens containing approximately 11, 17 and 30 vol.-% of this phase. The stress measurements showed good reproducibility with standard deviations of typically 4% on flat and smooth surfaces and not more than about 8% on etched surfaces. Estimations revealed that specimen misalignment and improper X-ray spot location were the main sources behind the variation in the stress recordings. The determination of retained austenite showed a standard deviation of typically 15% between the different contributors. However, by using identical evaluation methodsfor all raw data, the data spread could be narrowed by afactor of 3 to 4 despite the fact that different experimental settings were used in the individual laboratories.
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| 8. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Dissolution of iron-chromium carbides during white layer formation induced by hard turning of AISI 52100 steel
- 2014
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 14, s. 107-112
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Konferensbidrag (refereegranskat)abstract
- The (Fe, Cr)3C carbide morphology in the surface region of hard turned bainitic AISI 52100 steel was investigated using both experimental techniques and simulations, where microstructural analysis was correlated with analytical studies of the carbide dissolution kinetics using DICTRA1. The experimental results showed that for both predominantly thermally and mechanically induced white layers no significant carbide dissolution took place down to a depth of 20 μm below the machined surfaces. This was confirmed by the analytical results from DICTRA, which showed that no significant carbide dissolution should take place during hard turning given the short contact times. Within the hard turned surfaces up to ∼12% of the carbides were elongated, indicating plastic deformation of the carbides during machining.
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| 9. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Formation mechanisms of white layers induced by hard turning of AISI 52100 steel
- 2015
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454. ; 89, s. 258-267
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns the formation mechanisms of white layers (WLs) induced by machining of through-hardened (martensitic and bainitic) AISI 52100 steel. The microstructures of different types of WLs were investigated using transmission electron microscopy; those that had been predominantly mechanically induced (M-WL) and those that had been predominantly thermally induced (T-WL). Independent of the process parameters and the starting microstructure, the WLs consisted of a randomly oriented nano- and submicron-sized microstructure with an average grain size in the order of several tens of nanometres. The M-WLs were characterised as bcc-(α) ferrite and orthorhombic-(θ) cementite where the initial martensite/bainite platelets had been reoriented along the shear direction and broken-down into elongated sub-grains through dynamic recovery. The T-WLs were shown to consist of fcc-(γ) austenite, bcc-(α) martensite, and orthorhombic-(θ) cementite. Here the elongated sub-structure was found to coexist with equiaxed grains, meaning that the formation was initiated by dynamic recovery, which advanced to dynamic recrystallisation at the increased temperatures caused by the higher cutting speeds. Although times and temperatures are considered to be insufficient to dissolve the secondary carbides, carbide refinement was observed independently on the type of WL. The carbide refinement was controlled by (i) deformation and fragmentation of the carbides via dislocation movement along the {1 1 0} and {1 0 0}, (ii) precipitation of nano-sized carbides and (iii) diffusion-based carbide refinement by carbon depletion via dislocations in the nano-sized grains and grain boundaries, which act as high diffusivity paths.
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| 10. |
- Hosseini, Seyed, 1981, et al.
(författare)
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Microstructure characterization of white layer formed by hard turning and wire electric discharge machining in high carbon steel (AISI 52100)
- 2012
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Ingår i: Advanced Materials Research. - 1662-8985 .- 1022-6680. ; 409, s. 684-689
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Konferensbidrag (refereegranskat)abstract
- White layers, formed during hard turning and wire electric discharge machining, werecharacterized by means of X-ray diffraction, scanning electron microscopy and transmissionelectron microscopy. Different cutting speeds and flank wear were utilized in order to obtaindifferent thermally and/or plastically deformed white layer. Since the white layer after wire electricdischarge machining is mainly thermally induced, it was used as a reference structure. In theinvestigation, both bainitic and martensitic structures were studied. With a constant flank wear of0.175 mm the thickness of the white layer increased from 1.5 μm to 3 μm as the cutting speed wasincreased. In both processes the white layer were characterized by nano-sized grains and surfacetensile residual stresses. M3C carbides were observed in the hard turned white layer, indicating thatthe time and temperature needed for completely dissolving the carbides were not reached duringcutting. For both materials the white layers formed by wire electric discharge machining consistedof ~ 30 vol. % of retained austenite. Observation regarding the volume fraction of the retainedaustenite in the white layer formed by hard turning for martensitic material showed an increase inthe volume fraction of retained austenite from ~ 2 - 3 vol. % to ~ 6 vol. %, while this observationwas not seen in the white layer formed in the bainitic material.
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