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Forouzan, F., Surki Aliabad, R., Hedayati, A., Hosseini, N., Maawad, E., Blasco, N. & Vuorinen, E. (2023). Kinetics of Carbon Enrichment in Austenite during Partitioning Stage Studied via In-Situ Synchrotron XRD. Materials, 16(4), Article ID 1557.
Open this publication in new window or tab >>Kinetics of Carbon Enrichment in Austenite during Partitioning Stage Studied via In-Situ Synchrotron XRD
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2023 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 16, no 4, article id 1557Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
advanced high strength steels, high-carbon steel, high-resolution dilatometry, in-situ synchrotron XRD, martensitic/bainitic phase transformation, quenching and partitioning (Q&P)
National Category
Metallurgy and Metallic Materials Other Materials Engineering
Research subject
Engineering Materials; Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-95858 (URN)10.3390/ma16041557 (DOI)2-s2.0-85149208737 (Scopus ID)
Funder
The Kempe Foundations
Note

Validerad;2023;Nivå 2;2023-03-14 (joosat);

Licens fulltext: CC BY License

Available from: 2023-03-14 Created: 2023-03-14 Last updated: 2023-03-14Bibliographically approved
Mishra, P., Åkerfeldt, P., Svahn, F., Nilsson, E., Forouzan, F. & Antti, M.-L. (2023). Microstructural characterization and mechanical properties of additively manufactured 21-6-9 stainless steel for aerospace applications. Journal of Materials Research and Technology, 25, 1483-1494
Open this publication in new window or tab >>Microstructural characterization and mechanical properties of additively manufactured 21-6-9 stainless steel for aerospace applications
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2023 (English)In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 25, p. 1483-1494Article in journal (Refereed) Published
Abstract [en]

The alloy 21-6-9 is a nitrogen-strengthened austenitic stainless steel often used in aerospace applications due to its high strength, good fabrication properties, and toughness at cryogenic temperatures. However, minimal research has been conducted on alloy 21-6-9 using the additive manufacturing process laser powder-bed fusion (L-PBF). The L-PBF technique has been seen as a key to reducing production time and avoiding costly machining. Therefore, there is an interest in investigating L-PBF-processed 21-6-9 to determine the effects of L-PBF on properties at elevated and cryogenic temperatures. In this study, prior to tensile testing the alloy 21-6-9 underwent heat treatments that simulated aerospace applications and the alloy was analyzed and characterized to evaluate phase stability. The effects of elevated and cryogenic temperatures (77K) on the tensile behavior and microstructure were investigated using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The tensile tests showed that the yield strength and ultimate tensile strength improved, while ductility varied depending on the conditions and test environment. The ultimate tensile strength was approximately 80% higher at 77K than at room temperature, although the elongation decreased by around 90%, possibly due to the formation of strain-induced martensite.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
L-PBF, 21-6-9 stainless steel, elevated temperature, cryogenic temperature, microstructural characterization, mechanical properties
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-97925 (URN)10.1016/j.jmrt.2023.06.047 (DOI)2-s2.0-85162113914 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-06-30 (hanlid)

Available from: 2023-06-06 Created: 2023-06-06 Last updated: 2023-09-05Bibliographically approved
Zohrevand, M., Aghaie-Khafri, M., Forouzan, F. & Vuorinen, E. (2022). An investigation on microstructure and mechanical properties of 316 stainless steel: a comparison between ultrasonic treatment and thermal annealing. Philosophical Magazine, 102(14), 1321-1343
Open this publication in new window or tab >>An investigation on microstructure and mechanical properties of 316 stainless steel: a comparison between ultrasonic treatment and thermal annealing
2022 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 102, no 14, p. 1321-1343Article in journal (Refereed) Published
Abstract [en]

The effect of ultrasonic treatment (UST) and thermal annealing (THA) post-processes on the mechanical properties and the related microstructural mechanisms of the tensile pre-strained 316 stainless steel was investigated. It was shown that both processes reduce the microhardness and the yield point as well as increasing the elongation of the pre-deformed alloy. A 10% reduction of the yield point and 28% increase in the elongation was observed after the higher power UST (500 W), while an enhanced ductility of 56% and 41% reduction of the yield point was measured for the high-temperature THA (800°C) treated steel. The increased ductility was related to de-twinning and dislocation annihilation mechanisms, which increase the mean free path distance of dislocations. The de-twinning mechanism was proposed as the boundary migration mechanism and reverse gliding of the partial dislocations by cyclic shear stress for the THA and UST processes, respectively. Unlike the UST process, the high-temperature thermal annealing was associated with the formation of M23C6 precipitates, which causes depletion of alloying elements from the vicinity of grain boundaries and makes the alloy more prone to intergranular corrosion. Compared with THA, the advantages of the UST process are as follows: a rapid and straightforward process, low energy consumption, enhanced ductility without significant reduction in strength, and inhibition of grain boundary precipitation.

Place, publisher, year, edition, pages
Taylor & Francis, 2022
Keywords
Ultrasonic treatment, thermal annealing, stainless steel, ultrasonic softening, EBSD
National Category
Metallurgy and Metallic Materials
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-89840 (URN)10.1080/14786435.2022.2048113 (DOI)000766999300001 ()2-s2.0-85126467178 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-08-19 (sofila);

Funder: Iran National Science Foundation [Grant no. 96000917]

Available from: 2022-03-24 Created: 2022-03-24 Last updated: 2022-08-19Bibliographically approved
Hosseini, N., Forouzan, F. & Vuorinen, E. (2022). In-situ microstructural evolution during quenching and partitioning of a high-carbon steel by high-temperature X-Ray diffraction. Materials Today Communications, 31, Article ID 103503.
Open this publication in new window or tab >>In-situ microstructural evolution during quenching and partitioning of a high-carbon steel by high-temperature X-Ray diffraction
2022 (English)In: Materials Today Communications, ISSN 2352-4928, Vol. 31, article id 103503Article in journal (Refereed) Published
Abstract [en]

Carbon partitioning from martensite to austenite is essential for austenite stabilization during quenching and partitioning (Q&P), while a few competitive phenomena, such as bainitic transformation and carbide precipitation, alter the microstructural evolution. So, there is a need of using in-situ in combination with ex-situ characterisation techniques to understand the C partitioning at high temperature in relation to simultaneous competitive phenomena that might occur during the partitioning stage.

In this study, microstructural evolutions of a medium carbon steel ( 0.6C–1.6Si–1.25Mn–1.75Cr wt%) during Q&P treatment were investigated by using an in-situ High-Temperature X-Ray Diffraction (HTXRD) equipment at three partitioning temperatures. Results confirmed that carbon enrichment of austenite at 280 and 400 ℃ originates from partial carbon depletion from martensite and bainitic transformation, while partitioning at 500 ℃ results in the complete depletion of carbon from initial martensite and ferrite formation. Short diffusion distance (~0.13 µm) of carbon at 280 ℃ caused a poor carbon homogenization of austenite and formation of 8 vol% fresh martensite after final quenching. High Si content of the steel stabilized transitional carbides and, concurrently, suppressed Fe3C formation during Q&P. The outcome of this study could contribute to the design of suitable chemistry and process parameters for producing quenched and partitioned steels.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Advanced high strength steels, Quenching and Partitioning, In-situ XRD
National Category
Metallurgy and Metallic Materials
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-90160 (URN)10.1016/j.mtcomm.2022.103503 (DOI)000797464400004 ()2-s2.0-85129472748 (Scopus ID)
Funder
The Kempe Foundations
Note

Validerad;2022;Nivå 2;2022-06-01 (johcin)

Available from: 2022-04-12 Created: 2022-04-12 Last updated: 2022-06-01Bibliographically approved
Lundholm, E., Akerström, P., Jonsén, P., Forouzan, F. & Sala, R. (2022). Numerical Modelling of the Mechanical Properties of Press Hardened Boron Steels. In: Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson (Ed.), Svenska Mekanikdagar 2022: . Paper presented at Svenska Mekanikdagarna 2022, Luleå, Sweden, June 15-16, 2022. Luleå tekniska universitet
Open this publication in new window or tab >>Numerical Modelling of the Mechanical Properties of Press Hardened Boron Steels
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2022 (English)In: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Luleå tekniska universitet, 2022
National Category
Applied Mechanics
Research subject
Solid Mechanics; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-95111 (URN)
Conference
Svenska Mekanikdagarna 2022, Luleå, Sweden, June 15-16, 2022
Available from: 2022-12-30 Created: 2022-12-30 Last updated: 2023-09-05Bibliographically approved
Zohrevand, M., Aghaie-Khafri, M., Forouzan, F. & Vuorinen, E. (2021). Internal stress relief and microstructural evolution by ultrasonic treatment of austeno-ferritic 2205 duplex stainless steel. Materials Science & Engineering: A, 815, Article ID 141290.
Open this publication in new window or tab >>Internal stress relief and microstructural evolution by ultrasonic treatment of austeno-ferritic 2205 duplex stainless steel
2021 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 815, article id 141290Article in journal (Refereed) Published
Abstract [en]

The microstructure and mechanical properties of 2205 dual-phase pre-strained stainless steel following the high-power ultrasonic treatment (UST) were investigated. Mitigation of the deformation fiber texture, decrease in dislocation density, XRD peak shifting, and hardness reduction corroborated that the ultrasonic treatment can effectively reduce the internal stress of the duplex structure. The EDS and XRD results showed no brittle intermetallic phases were formed after the UST process, unlike conventional thermal treatment methods. Around 18% reduction in microhardness value and a significant ductility improvement of 54% can be achieved using an intermediate amplitude (power) vibration. The microstructure and mechanical properties variation caused by the UST process and the related mechanisms have been discussed in detail. New microstructural mechanisms have been proposed for the interpretation of the observed acoustic stress relief in both α and γ-phases.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Ultrasonic treatment, stress relief, mechanical properties, EBSD, Duplex stainless steel
National Category
Metallurgy and Metallic Materials
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-83675 (URN)10.1016/j.msea.2021.141290 (DOI)000651214800002 ()2-s2.0-85104659525 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-05-03 (alebob)

Available from: 2021-04-14 Created: 2021-04-14 Last updated: 2021-06-07Bibliographically approved
Mishra, P., Åkerfeldt, P., Forouzan, F., Svahn, F., Zhong, Y., Shen, Z. & Antti, M.-L. (2021). Microstructural Characterization and Mechanical Properties of L-PBF Processed 316 L at Cryogenic Temperature. Materials, 14(19), Article ID 5856.
Open this publication in new window or tab >>Microstructural Characterization and Mechanical Properties of L-PBF Processed 316 L at Cryogenic Temperature
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2021 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 19, article id 5856Article in journal (Refereed) Published
Abstract [en]

Laser powder bed fusion (L-PBF) has attracted great interest in the aerospace and medical sectors because it can produce complex and lightweight parts with high accuracy. Austenitic stainless steel alloy 316 L is widely used in many applications due to its good mechanical properties and high corrosion resistance over a wide temperature range. In this study, L-PBF-processed 316 L was investigated for its suitability in aerospace applications at cryogenic service temperatures and the behavior at cryogenic temperature was compared with room temperature to understand the properties and microstructural changes within this temperature range. Tensile tests were performed at room temperature and at −196 °C to study the mechanical performance and phase changes. The microstructure and fracture surfaces were characterized using scanning electron microscopy, and the phases were analyzed by X-ray diffraction. The results showed a significant increase in the strength of 316 L at −196 °C, while its ductility remained at an acceptable level. The results indicated the formation of ε and α martensite during cryogenic testing, which explained the increase in strength. Nanoindentation revealed different hardness values, indicating the different mechanical properties of austenite (γ), strained austenite, body-centered cubic martensite (α), and hexagonal close-packed martensite (ε) formed during the tensile tests due to mechanical deformation.

Place, publisher, year, edition, pages
MDPI, 2021
Keywords
316 L stainless steel, cryogenic temperature, martensite, strain-induced martensite, L-PBF process
National Category
Metallurgy and Metallic Materials
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-87561 (URN)10.3390/ma14195856 (DOI)000707229400001 ()34640252 (PubMedID)2-s2.0-85116707993 (Scopus ID)
Funder
Luleå University of Technology, 220004, 2283003
Note

Validerad;2021;Nivå 2;2021-10-20 (alebob)

Available from: 2021-10-20 Created: 2021-10-20 Last updated: 2023-09-05Bibliographically approved
Zohrevand, M., Aghaie-Khafri, M., Forouzan, F. & Vuorinen, E. (2021). Microstructural Evolutions under Ultrasonic Treatment in 304 and 316 Austenitic Stainless Steels: Impact of Stacking Fault Energy. Steel Research International, 92(9), Article ID 2100041.
Open this publication in new window or tab >>Microstructural Evolutions under Ultrasonic Treatment in 304 and 316 Austenitic Stainless Steels: Impact of Stacking Fault Energy
2021 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 92, no 9, article id 2100041Article in journal (Refereed) Published
Abstract [en]

The influence of ultrasonic treatment (UST) on the microstructure of AISI‐304 and AISI‐316 stainless steels as two common commercial grades with similar properties but different levels of stacking fault energy (SFE) are compared in this study. The softening effect of the ultrasonic wave on the pre‐deformed structure is demonstrated by microhardness measurements, while the relaxation of tensile residual stresses is affirmed through the X‐ray diffraction (XRD) peak shifting. Electron and optical microscopy revealed a significant impact of ultrasound on the reduction of deformation twins’ fraction. A new mechanism for de‐twinning under the action of ultrasonic vibration is proposed using electron backscatter diffraction (EBSD) analysis. The reduction of 25% and 34% are detected in dislocation density of 10% pre‐deformed tensile sample after 300 W UST for 304SS and 316SS alloys, respectively. The effect of SFE is discussed, and it turned out that cross‐slip is the main mechanism of dislocation annihilation as a result of UST. Observation of the low‐deformation regions close to the grain boundaries indicated the occurrence of the recrystallization phenomenon during UST. Dislocation annihilation, de‐twinning, dislocation absorption to grain boundaries, and recrystallization are regarded as the softening and relaxation mechanisms of UST for austenitic stainless steels.

Place, publisher, year, edition, pages
John Wiley & Sons, 2021
Keywords
ultrasonic treatment, stress relaxation, stacking fault energy, EBSD, stainless steel
National Category
Metallurgy and Metallic Materials
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-83676 (URN)10.1002/srin.202100041 (DOI)000646083100001 ()2-s2.0-85104961991 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-09-10 (beamah);

Finansiär: Iran National Science Foundation (INSF) (96000917)

Available from: 2021-04-14 Created: 2021-04-14 Last updated: 2021-12-09Bibliographically approved
He, H., Forouzan, F., Volpp, J., Robertson, S. M. & Vuorinen, E. (2021). Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry. Materials, 14(2), Article ID 456.
Open this publication in new window or tab >>Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry
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2021 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 2, article id 456Article in journal (Refereed) Published
Abstract [en]

The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried out. The welded joints (WJ) comprised of similar/dissimilar steels with similar/dissimilar thickness were consisted of different zones and exhibited similar microstructural characteristics. The trend of microhardness for all WJs was consistent, characterized by the highest value at hardening zone (HZ) and lowest at softening zone (SZ). The degree of softening was 20 and 8% for the DP1000 and DP800 WJ, respectively, and the size of SZ was wider in the WJ combinations of DP1000 than DP800. The tensile test fractures were located at the base material (BM) for all DP800 weldments, while the fractures occurred at the fusion zone (FZ) for the weldments with DP1000 and those with dissimilar sheet thicknesses. The DP800-DP1000 weldment presented similar yield strength (YS, 747 MPa) and ultimate tensile strength (UTS, 858 MPa) values but lower elongation (EI, 5.1%) in comparison with the DP800-DP800 weldment (YS 701 MPa, UTS 868 MPa, EI 7.9%), which showed similar strength properties as the BM of DP800. However, the EI of DP1000-DP1000 weldment was 1.9%, much lower in comparison with the BM of DP1000. The DP800-DP1000 weldment with dissimilar thicknesses showed the highest YS (955 MPa) and UTS (1075 MPa) values compared with the other weldments, but with the lowest EI (1.2%). The fatigue fractures occurred at the WJ for all types of weldments. The DP800-DP800 weldment had the highest fatigue limit (348 MPa) and DP800-DP1000 with dissimilar thicknesses had the lowest fatigue limit (<200 MPa). The fatigue crack initiated from the weld surface.

Place, publisher, year, edition, pages
MDPI, 2021
Keywords
laser welding, dual phase steel, similar/dissimilar welded joints, microhardness, tensile properties, fatigue
National Category
Manufacturing, Surface and Joining Technology Other Materials Engineering
Research subject
Engineering Materials; Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-82628 (URN)10.3390/ma14020456 (DOI)000611382200001 ()33477790 (PubMedID)2-s2.0-85099781493 (Scopus ID)
Funder
Carl Tryggers foundation
Note

Validerad;2021;Nivå 2;2021-01-25 (alebob);

Finansiär: EC Research Fund for Coal and Steel (800726, 754155)

Available from: 2021-01-25 Created: 2021-01-25 Last updated: 2021-02-19Bibliographically approved
Heidarzadeh, A., Neikter, M., Enikeev, N., Cui, L., Forouzan, F. & Taherzadeh Mousavian, R. (2021). Post-treatment of additively manufactured Fe-Cr-Ni stainless steels by high pressure torsion: TRIP effect. Materials Science & Engineering: A, 811, Article ID 141086.
Open this publication in new window or tab >>Post-treatment of additively manufactured Fe-Cr-Ni stainless steels by high pressure torsion: TRIP effect
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2021 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 811, article id 141086Article in journal (Refereed) Published
Abstract [en]

High pressure torsion (HPT) at room temperature was used for post-treatment of additively manufactured Fe-Cr-Ni stainless steel with 12.9 wt. % Ni as a very strong austenite stabilizer. The results showed that HPT caused a considerable increase in nanohardness of the additively manufactured samples. In contrast with thermodynamic equilibrium-state modeling, a phase transformation from FCC to HCP structure occurred, leading to the formation of ε-martensite during HPT on high angle boundaries, low angle boundaries, and dislocation cells with no detection of deformation twins. It was demonstrated that the combination of additive manufacturing thanks to the high density of dislocations after solidification and HPT process expands the opportunities of both methods to control deformation mechanisms in stainless steels leading to different phase and microstructural features. Thus, the outcome of this study provides a fundamental basis to design advanced structural materials.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Additive manufacturing (AM), High pressure torsion (HPT), Nanoindentation, Electron back-scattered diffraction (EBSD), stainless steel, phase transformation (PT)
National Category
Manufacturing, Surface and Joining Technology
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-83305 (URN)10.1016/j.msea.2021.141086 (DOI)000636780500001 ()2-s2.0-85102877302 (Scopus ID)
Funder
European Regional Development Fund (ERDF)
Note

Validerad;2021;Nivå 2;2021-04-08 (alebob);

Finansiär: Science Foundation Ireland  (16/RC/3872); I-Form industry partners; Saint Petersburg State University (26130576)

Available from: 2021-03-18 Created: 2021-03-18 Last updated: 2021-05-03Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5390-7701

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