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| 2. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
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Application of Quenching and Partitioning Processes to Welding and Press Hardening
- 2019
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Ingår i: Hot sheet metal forming of high-performance steel. - : Wissenschaftliche Scripten. ; , s. 727-735
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Konferensbidrag (refereegranskat)abstract
- One of the most critical characteristics of welding and press hardening of advanced high strength steels is a low ductility related to a martensitic transformation due to high cooling rate and/or plastic deformation. The present work proposes the application of quenching and partitioning (Q&P) processing to welding and press hardening in a single production step. Using this methodology will not only improve the ductility without losing the ultra-high strength but also accelerate the whole process rate significantly in comparison with austempering treatment in connection to hot pressing and decrease the cost. In this regard, Gleeble simulation of different Q&P cycles beside simulation of deformation at different rates at different temperatures were applied to a medium carbon, Si- alloyed Q&P steel. Samples were characterized using OM, SEM, XRD, hardness, compression and tensile tests. The aim of the project is to establish manufacturing strategies for obtaining components with extreme properties.
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| 3. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
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Effect of Carbon Partitioning, Carbide Precipitation, and Grain Size on Brittle Fracture of Ultra-High-Strength, Low-Carbon Steel after Welding by a Quenching and Partitioning Process
- 2018
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 8:10
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Tidskriftsartikel (refereegranskat)abstract
- To improve the weld zone properties of Advanced High Strength Steel (AHSS), quenching and partitioning (Q&P) has been used immediately after laser welding of a low-carbon steel. However, the mechanical properties can be affected for several reasons: (i) The carbon content and amount of retained austenite, bainite, and fresh martensite; (ii) Precipitate size and distribution; (iii) Grain size. In this work, carbon movements during the partitioning stage and prediction of Ti (C, N), and MoC precipitation at different partitioning temperatures have been simulated by using Thermocalc, Dictra, and TC-PRISMA. Verification and comparison of the experimental results were performed by optical microscopy, X-ray diffraction (XRD), Scanning Electron Microscop (SEM), and Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Scanning Diffraction (EBSD) analysis were used to investigate the effect of martensitic/bainitic packet size. Results show that the increase in the number density of small precipitates in the sample partitioned at 640 °C compensates for the increase in crystallographic packets size. The strength and ductility values are kept at a high level, but the impact toughness will decrease considerably.
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| 4. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
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Effect of tempering on microstructure and mechanical properties of laser welded and post-weld treated AHSS specimens
- 2017
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 891, s. 18-24
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Tidskriftsartikel (refereegranskat)abstract
- An advanced high strength steel (0.08 wt.%C, 1.79 wt%Mn, 0.23 wt%Si) was subjected to different post-weld heat treatments by quenching & tempering treatments (Q&T) after laser welding to reduce the risk of martensite formation in a few seconds based on an idea of quench and partitioning (Q&P), mechanism. The thermal stability of retained austenite, microstructure development and mechanical properties have been studied at 2 tempering temperatures of 440°C (Ms) and 636°C (Bs), both for 15 minutes, by means of electron microscopy, dilatometry, hardness profile and tensile tests. Dilatometer study unveiled that redistribution of carbon atoms and precipitation of transition carbides occur around 150°C and austenite decomposition occur at 600°C. Tempering at 636°C resulted in notable effect on the mechanical properties, while no significant difference was detected at 440°C, except a slight hardness drop. The strength increased up to 12% for the different specimens without significant loss in ductility for all specimens tempered at 636°C, which may be caused by precipitation hardening and recrystallization of martensite lath boundaries during tempering around 600°C.
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| 5. |
- Forouzan, Farnoosh, 1985-
(författare)
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Increasing phase transformation rate in advanced high strength steel applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The bainite transformation rate has been shown to increase by starting the heat treatment with partial martensite transformation after austenitization. Based on this fact, a process very similar to “Quenching and Partitioning” (Q&P) is used to produce a fine-grained complex microstructure of martensite, bainite and retained austenite with outstanding mechanical properties in a very short time. During this process, different mechanisms including bainite transformation, carbon partitioning, carbide precipitation, grain growth may occur. All these mechanisms can affect the mechanical properties such as strength, ductility and toughness. Investigation of the different mechanisms influencing the properties and subsequent optimization of these is important. In this work, different mechanisms of the Q&P heat treatment process and its practical industrial applications have been investigated. Firstly, the implementation of a Q&P method directly after laser welding for a few seconds to substitute any post welding treatment has been studied. To investigate the feasibility, limitations, and advantages of this method for a low-carbon low-silicon high strength steel, the microstructure and mechanical properties by both modelling and experimental approach were studied. Promising results show that this method can decrease the ordinary post-welding treatment time from a few minutes to a few seconds, and in addition improve the mechanical properties of the fusion zone and the heat affected zone to the same or even higher values in comparison with the base material.In the second part of this work, the effect of quenching and partitioning on the microstructure and mechanical properties of a high carbon steel has been studied. The aim with this part was to optimize the phase transformation rate for production of ultra-high strength steel by controlling its microstructural evolution. The results show that it is possible to get good strength values also for high carbon steels by Q&P treatment. In addition, the approach with process control maps can give a good overview of which properties can be achieved by this method. Hardness value of over 700 HV, and tensile strength of up to 2.5 GPa with a relatively good ductility of 4-6% has been achieved by quenching to room temperature and partitioning for less than one minute at 400 °C resulting in a microstructure consisting of martensite and retained austenite. In a nutshell, the approach to bainite transformation with pre-existing martensite shorten the processing time for development of advanced high strength steels significantly. This method is also possible to be used in industrial processes as in welding.
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| 6. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
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Kinetics of Carbon Enrichment in Austenite during Partitioning Stage Studied via In-Situ Synchrotron XRD
- 2023
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 16:4
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Tidskriftsartikel (refereegranskat)abstract
- The present study reveals the microstructural evolution and corresponding mechanisms occurring during different stages of quenching and partitioning (Q&P) conducted on 0.6C-1.5Si steel using in-situ High Energy X-Ray Diffraction (HEXRD) and high-resolution dilatometry methods. The results support that the symmetry of ferrite is not cubic when first formed since it is fully supersaturated with carbon at the early stages of partitioning. Moreover, by increasing partitioning temperature, the dominant carbon source for austenite enrichment changes from ongoing bainitic ferrite transformation during the partitioning stage to initial martensite formed in the quenching stage. At low partitioning temperatures, a bimodal distribution of low- and high-carbon austenite, 0.6 and 1.9 wt.% carbon, is detected. At higher temperatures, a better distribution of carbon occurs, approaching full homogenization. An initial martensite content of around 11.5 wt.% after partitioning at 280 °C via bainitic ferrite transformation results in higher carbon enrichment of austenite and increased retained austenite amount by approximately 4% in comparison with partitioning at 500 °C. In comparison with austempering heat treatment with no prior martensite, the presence of initial martensite in the Q&P microstructure accelerates the subsequent low-temperature bainitic transformation.
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| 7. |
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| 8. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
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Microstructure analysis and mechanical properties of Low alloy High strength Quenched and Partitioned Steel
- 2017
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Ingår i: Solid State Phenomena. - : Trans Tech Publications. - 1012-0394 .- 1662-9779. ; 258, s. 574-578
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Tidskriftsartikel (refereegranskat)abstract
- Gleeble study of the quenching and partitioning (Q&P) process has been performed onDomex 960 steel (Fe, 0.08 %C, 1.79 %Mn, 0.23 %Si, 0.184 %Ti, and 0.038 %Al). The effect ofdifferent Q&P conditions on microstructure and mechanical properties were investigated. The aimof the process is to produce a fine grained microstructure for better ductility and controlled amountsof different micro-constituents to increase the strength and toughness simultaneously. Threedifferent quenching temperatures, three partitioning temperatures and three partitioning times havebeen selected to process the 27 specimens by Gleeble® 1500. The specimens were characterized bymeans of OM, SEM, XRD, hardness and impact tests. It was found that, fine lath martensite withretained austenite is achievable without high amount of Si or Al in the composition although lack ofthese elements may cause the formation of carbides and decrease the available amount of carbon forpartitioning into the austenite. The hardness increases as the quenching temperature is decreased,however, at highest partitioning temperature (640◦C) the hardness increases sharply due to extensiveprecipitate formation.
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| 9. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
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Optimization of Quenching Temperature to Minimize the Micro Segregation Induced Banding Phenomena in Quenching and Partitioning (Q&P) Steels
- 2019
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Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 90:1
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Tidskriftsartikel (refereegranskat)abstract
- Mn, Cr, and Si are favorable elements for designing the quenching and partitioning (Q&P) steels while the microsegregation of them is a common phenomenon in the steels. This segregation makes the bands of enriched and depleted Mn–Cr regions, which affects the Ms temperature of the bands and consequently influence the volume fraction of initial martensite, retained austenite, and secondary fresh martensite in different bands. This issue leads to non-homogeneity in the microstructure and mechanical properties. In this study, the optimization method to minimize the inhomogeneity by selection of the quenching temperature is demonstrated.
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