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Optimization of Quenching Temperature to Minimize the Micro Segregation Induced Banding Phenomena in Quenching and Partitioning (Q&P) Steels
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.ORCID-id: 0000-0002-5390-7701
Luleå tekniska universitet.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.ORCID-id: 0000-0002-9100-7982
Department for Materials Science, Functional Materials, Saarland University, Saarbrücken, Germany.
2019 (Engelska)Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 90, nr 1, artikel-id 1800281Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
John Wiley & Sons, 2019. Vol. 90, nr 1, artikel-id 1800281
Nyckelord [en]
banding, hardness, microsegregation, microstructure, quenching and partitioning (Q&P)
Nationell ämneskategori
Annan materialteknik
Forskningsämne
Materialteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-71024DOI: 10.1002/srin.201800281ISI: 000454790200006Scopus ID: 2-s2.0-85053542723OAI: oai:DiVA.org:ltu-71024DiVA, id: diva2:1251935
Anmärkning

Validerad;2019;Nivå 2;2019-01-25 (johcin) 

Tillgänglig från: 2018-09-28 Skapad: 2018-09-28 Senast uppdaterad: 2019-03-04Bibliografiskt granskad
Ingår i avhandling
1. Increasing phase transformation rate in advanced high strength steel applications
Öppna denna publikation i ny flik eller fönster >>Increasing phase transformation rate in advanced high strength steel applications
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Ökning avfasomvandlingshastigheten för avancerade höghållfasta stål
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2019
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nyckelord
Advanced high strength steel, Quenching and partitioning, welding
Nationell ämneskategori
Metallurgi och metalliska material Annan materialteknik
Forskningsämne
Materialteknik
Identifikatorer
urn:nbn:se:ltu:diva-72569 (URN)978-91-7790-324-6 (ISBN)978-91-7790-325-3 (ISBN)
Disputation
2019-05-10, E231, Luleå, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

This thesis is the result of a collaboration between Luleå University of Technology and Saarland University that aims toward a double degree.

Tillgänglig från: 2019-03-05 Skapad: 2019-03-04 Senast uppdaterad: 2019-04-16Bibliografiskt granskad

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