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Fracture toughness properties of duplex stainless steels
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Good toughness properties in base and weld material enable the use of duplex stainless steels (DSS) in critical applications. DSS offer high strength compared to common austenitic stainless steels. The high strength can be utilized to reduce the wall thickness and accordingly accomplish reduction of cost, welding time and transportation weight, contributing to ecological and energy savings. Although DSS have been used successfully in many applications the last decades, the full utilisation in pressure vessels has been restricted due to conservative design rules. The consequences of failure in a pressure vessel are often very severe and it is accordingly important to verify a high ductility and fracture toughness.

In this study fracture toughness data has been generated that has been used to analyse the brittle failure model in the European pressure vessel code EN 13445. The evaluation of the results has been made successfully by the master curve analysis, previously applied to ferritic steels. The master curve analysis includes calculation of a reference temperature, which can be correlated to an impact toughness transition temperature. A correlation between fracture and impact toughness results is necessary for a practically applicable design code. The heat distribution and austenite reformation have been modelled to verify satisfactory toughness properties in the heat affected zone. A similar model was used to evaluate the nucleation and diffusional growth of sigma phase during isothermal heat treatment or continuous cooling.

For future stainless steel development, the availability of satisfactory correlations between composition, microstructure and mechanical properties are essential to optimize alloy design. Stainless steel data has been analysed to find approximate relations between mechanical properties and the chemical composition, grain size, ferrite content, product thickness and solution hardening size misfit parameter. The solution hardening effect was successfully predicted by the Labusch-Nabarro relation and multiple regression analyses were used to evaluate hardening equations for stainless steel.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 46 p.
Keyword [en]
duplex stainless steel, fracture toughness, austenite reformation, sigma phase, material optimisation
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3964ISBN: 91-7178-354-7 (print)OAI: oai:DiVA.org:kth-3964DiVA: diva2:10204
Public defence
2006-05-24, F3, Lindstedtsv. 26, KTH, 13:30
Opponent
Supervisors
Note
QC 20100920Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2010-09-20Bibliographically approved
List of papers
1. Fracture toughness of a welded duplex stainless steel
Open this publication in new window or tab >>Fracture toughness of a welded duplex stainless steel
2005 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 73, 377-390 p.Article in journal (Refereed) Published
Abstract [en]

The present work includes fracture toughness testing on 30 and 50 mm thick duplex stainless steel 2205 (22% Cr, 5.5% Ni, 3% Mo, 0.15% N). Base metal and submerged arc weldments (SAW) at subzero temperatures have been tested using full size three point bending. The evaluation of the results has been carried out using J-integral calculations and correlations to Charpy impact values. It is shown that the temperature dependence of the fracture toughness can be described by a transition temperature curve, the master curve. The reference temperature was evaluated to -143 and -101 degrees C for base and weld material respectively.

Keyword
duplex steel, fracture toughness, K-JC, master curve, SAW
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5732 (URN)10.1016/j.engfracmech.2005.03.009 (DOI)000234725800001 ()2-s2.0-29844442045 (Scopus ID)
Note
QC 20100920Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2010-09-20Bibliographically approved
2. Fracture toughness of the lean duplex stainless steel LDX 2101
Open this publication in new window or tab >>Fracture toughness of the lean duplex stainless steel LDX 2101
2006 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 37A, no 10, 2975-2981 p.Article in journal (Refereed) Published
Abstract [en]

Fracture toughness testing was performed on the recently developed lean duplex stainless steel LDX 2101 (EN 1.4162, UNS S32101). The results were evaluated by master curve analysis, including deriving a reference temperature. The master curve approach, originally developed for ferritic steels, has been used successfully. The reference temperature corresponds to a fracture toughness of 100 MPa √m, which characterizes the onset of cleavage cracking at elastic or elastic-plastic instabilities. The reference temperature, To, was -112 °C and -92 °C for the base and weld materials, respectively. In addition, the fracture toughness is compared with impact toughness results. Complementary crack tip opening displacements (CTODs) have also been calculated. The toughness properties found in traditional duplex stainless steels (DSS) are generally good. The current study verifies a high fracture toughness for both base and weld materials and for the low alloyed grade LDX 2101. Even though the fracture toughness was somewhat lower than for duplex stainless steel 2205, it is still sufficiently high for most low-temperature applications.

Keyword
Crack tip opening displacements, Duplex stainless steels, Master curve analysis
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5733 (URN)10.1007/s11661-006-0179-7 (DOI)000241000400008 ()2-s2.0-33749586464 (Scopus ID)
Note
QC 20100915. Uppdaterad från Manuskript till Artikel (20100915)Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2010-09-15Bibliographically approved
3. Crack detection performance and other assumptions for implementation in a model for avoidance of brittle fracture in pressure vessel steels
Open this publication in new window or tab >>Crack detection performance and other assumptions for implementation in a model for avoidance of brittle fracture in pressure vessel steels
2003 (English)In: Proceeding of the 29th MPa Seminar, Stuttgart, Oct 9-10, 2003., 2003Conference paper, Published paper (Refereed)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5734 (URN)
Note
QC 20100920Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2010-09-20Bibliographically approved
4. Austenite reformation in the heat-affected zone of duplex stainless steel 2205
Open this publication in new window or tab >>Austenite reformation in the heat-affected zone of duplex stainless steel 2205
2006 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 418, no 1-2, 250-256 p.Article in journal (Refereed) Published
Abstract [en]

 The aim of the present work was to evaluate the amount of reformed austenite in the heat-affected zone (HAZ) of submerged arc welded (SAW) duplex stainless steel 2205. The model is based on calculations of the nucleation and growth of austenite. The present results are compared with other studies to evaluate the toughness properties and the probability of precipitation of brittle, intermetallic sigma phase. The results indicate that cooling the weld in air provides a satisfactory amount of reformed austenite and prevents formation of sigma phase.

Keyword
Austenite reformation, Cooling rate, Duplex stainless steel, Heat-affected zone
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5735 (URN)10.1016/j.msea.2005.11.025 (DOI)000235769400032 ()2-s2.0-32244438159 (Scopus ID)
Note
QC 20100831Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2010-08-31Bibliographically approved
5. Sigma phase precipitation in duplex stainless steel 2205
Open this publication in new window or tab >>Sigma phase precipitation in duplex stainless steel 2205
2007 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 444, no 1-2, 271-276 p.Article in journal (Refereed) Published
Abstract [en]

Sigma phase precipitation is known to embrittle duplex stainless steel. Accordingly, heat treatment and welding must be performed carefully. Nucleation and diffusional growth of sigma phase in the duplex stainless steel 2205 have been analysed in order to ensure the high toughness shown in previous studies for both base and weld material. A quasi-static growth model has been modified in order to take into account interactions with neighbouring particles due to overlapping diffusion fields (soft impingement). The model gives a satisfactory estimate of sigma phase precipitated both during isothermal aging and continuous cooling.

Keyword
duplex stainless steel, sigma phase, precipitation, toughness
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5736 (URN)10.1016/j.msea.2006.08.107 (DOI)000243624000036 ()2-s2.0-33845267739 (Scopus ID)
Note
Uppdaterad från manuskript till artikel: 20100920 QC 20100920Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2010-09-20Bibliographically approved
6. Modelling solid solution hardening in stainless steels
Open this publication in new window or tab >>Modelling solid solution hardening in stainless steels
2006 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 415, no 1-2, 66-71 p.Article in journal (Refereed) Published
Abstract [en]

The solid solution hardening of stainless steels is studied by using the Labusch-Nabarro relation. Models are evaluated in order to predict the mechanical properties from chemical composition, solution hardening misfit parameters, grain size, ferrite content and product thickness. A data source of six grades of steels is used for the modelling. Both austenitic and duplex stainless steels are covered including more than 1100 batches, which are subjected to multiple regression analyses. The models are compared with earlier studies and can be used as tools in material optimisation.

Keyword
stainless steel, material optimisation, solution hardening, mechanical properties, multiple regression
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5737 (URN)10.1016/j.msea.2005.09.031 (DOI)000234270400009 ()2-s2.0-29244466485 (Scopus ID)
Note
QC 20100920Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2011-08-17Bibliographically approved

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