Past research projects 2002-2013

• Design against brittle failure for duplex stainless steels
• Formation of particles during long time ageing and their influence on mechanical properties in stainless steels
• Fatigue properties of friction stir welded joints in aluminium alloys
• Materials Design of Creep Resistant Steels  
• Composition-microstructure-property relations (CMPR)
• Friction stir welding of copper
• Fundamental modelling of flow and creep deformation in phosphorus doped copper
• FEM modelling of creep deformation in copper canister in power law breakdown regime
• Influence of notches on the creep deformation and rupture of copper

Design against brittle failure for duplex stainless steels

Research leader: Rolf Sandström.
PhD student: Henrik Sieurin, Johan Pilhagen
Keywords: Duplex stainless steel, pressure vessel, welding, fracture toughness, design principle,
Project period: 2004–2013

Project description:

Both specific rules as well as proper materials data have been lacking concerning design against brittle failure. This has been of major concern particularly in safety classed components such as pressure vessels. To solve this problem, new methods for design against brittle failure based on fundamental principles in fracture mechanics have been developed. Elasto-plastic fracture mechanics is fully implemented by taken failure limit diagrams into account. A unique feature is that both primary and secondary stresses such as residual stresses are considered. By using the Master curve approach basic relations between the fracture toughness and the impact toughness can be established. This implies that the code requirements can be based on impact toughness values and expensive fracture mechanics testing can be avoided in engineering applications. A critical issue is the minimum crack size that can be safely detected by non-destructive measuring techniques. By analysis of available scientific literature, relations between the minimum safely detectable crack size and the component thickness have been set up. The new approach has been verified experimentally with the help of a large number of fracture mechanics tests. The tests have also demonstrated that duplex stainless steels can be applied safely down to very low temperatures also in the welded condition that was not known before. The role of austenite and sigma phase formation has been carefully analysed. The new design principles are now implemented in the European pressure vessel code EN 13445, part 2, Materials.

Publications:

• R. Sandström, P. Langenberg, H. Sieurin, New brittle fracture model for the European pressure vessel standard, International Journal of Pressure Vessels and Piping 81 (2004) 837–845
• R. Sandström, P Langenberg, G Baylac, P Bocquet, A, Design by analysis of high strength steel pressure vessels: input of ecopress, Europ. Symp on pressure equipment ESOPE 2004, Paris, 28-30 Sept 2004
• R. Sandström, P. Langenberg, H. Sieurin, Analysis of the brittle fracture avoidance model for pressure vessels in European standard, Int J Pressure Vessel and Piping 82, Issue 11 (2005) 872-881
• H. Sieurin, R. Sandström, Fracture toughness of a welded duplex stainless steel, Engineering Fracture Mechanics, Volume 73, Issue 4, March 2006, Pages 377-390.
• H. Sieurin, R. Sandström, Fracture toughness of a welded duplex stainless steel, Engineering Fracture Mechanics, Volume 73, Issue 4, March 2006, Pages 377-390.
• H. Sieurin, R. Sandström, E. M. Westin, Fracture toughness of the lean duplex stainless steel LDX 2101, Metallurgical and Materials Transactions A: v 37, n 10, October, 2006, p 2975-2981.
• H. Sieurin, R. Sandström, Austenite reformation in the heat-affected zone of duplex stainless steel 2205, Materials Science and Engineering: A, Volume 418, Issues 1-2, 25 February 2006, Pages 250-256.
• R. Sandström, P. Langenberg, E. M. Westin, H. Sieurin, Design against brittle failure for duplex stainless steels, Int. conf. Duplex 2007, Grado, Italy (2007)
• H. Sieurin, E. M. Westin, M. Liljas, R. Sandström, Fracture toughness of welded commercial duplex stainless steel, Int. conf. Duplex 2007 (2007)
• H. Sieurin, R. Sandström, Sigma phase precipitation in duplex stainless steel 2205, Materials Science and Engineering: A, 444, Issues 1-2, 25 January 2007, 271-276.
• R. Sandström, P. Langenberg, Design against brittle failure for stainless steels in the European pressure vessel code EN 13445, 6th European Stainless Steel Conference, Helsinki, Finland, 2008
• Sieurin H, Westin EM, Liljas M, Sandstrom R. Fracture Toughness of Welded Commercial Lean Duplex Stainless Steels. Weld World. 2009;53:R24-R33

· Johan Pilhagen, Rolf Sandström, Influence of lattice orientation on the fracture toughness of duplex stainless steel 2205, Duplex World 2010, Beaune, France, 2010

Source of funding: EU, Outokumpu Stainless, Sandvik Materials Technology

Formation of particles during long time ageing and their influence on mechanical properties in stainless steels

Research leader: Rolf Sandström.
Scientist: Lai-Zhe Jin; PhD student: Muhammad Farooq
Keywords: Long term ageing, particle precipitation, mechancal properties, modelling, austenitic stainless steel
Project period: 2005–2012

Project description:

During service of stainless steels with larger amounts of alloying elements, coarse intermetallic particles and carbides are formed. These coarse particles impair the mechanical properties. Increased service temperature and more corrosive biofuels in power plants have had the consequence that the use of higher alloyed materials has increased with the effect that the role of coarse particles becomes more crucial. In the present project long term ageing is studied for the austenitic stainless steels 253 MA and 309/310. The particle formation is characterised with microscopy and in parallel the particle structure is modelled. Also the effect of the particles on the tensile properties and toughness is measured and modelled.

Publications

· Rolf Sandström, Lai-Zhe Jin, The role of precipitation after long time ageing in an austenitic stainless steel, 6th European Stainless Steel Conf., Helsinki, Finland, June 2008, p. 471-482

· M. Farooq, R. Sandström and M. Lundberg, Precipitation during long time ageing in the austenitic stainless steel 310, High Temp. Mtrls. 2012, in press.

· R. Sandström, M. Farooq and B. Ivarsson, Influence of particle formation during long time ageing on mechanical properties in the austenitic stainless steel 31, High Temp. Mtrls. 2012, in press

· M. Farooq, R. Sandström, Influence of long time ageing on ductility and toughness in the stainless steel 310 in the presence of banded microstructure, 7th European stainless steel conference, Como, 2011

Source of funding: KME, Outokumpu Stainless, Sandvik Materials Technology

Fatigue properties of friction stir welded joints in aluminium alloys

Research leader: Rolf Sandström.
PhD students: Mats Ericsson, Meysam Shahri
Keywords: AlMgSi - Alloys, Welding, Extruded Profiles, Mechanical Properties, Fatigue, Component Testing
Project period: 2000–2011

Project description:

Thin-walled components of extruded aluminium alloys can effectively be assembled into high strength, rigid and light structures. The maximum width of extruded profiles is limited to 30-50 cm in the largest presses. Friction stir welding (FSW) is very well suited for seam-welding (alongside joining) of long extruded profiles to create large (built-up) beams and to connect several profiles to large connected areas e.g. floors in trucks, ferries and container ships; bridge-decks platforms (heli-decks), etc. Hardenable AlMgSi-alloys loose considerable strength in conventional welding. In the project it has been demonstrated that FSW joints have much improved static and dynamic strength properties. The behaviour of the joints has successfully been modelled.

Publications:

• M Ericsson, R Sandström, Fatigue of friction stir welded AlMgSi-alloy 6082, Materials Science Forum Vols. 331-337 (2000) 1787-1792
• M Ericsson, R Sandström, Fatigue performance of friction stir welded AlMgSi-alloy 6082, Aluminium, vol. 77, no. 7-8, (2001) 572-575
• M Ericsson, R Sandström, Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG, International Journal of Fatigue, 25 (2003) 1379-1387
• M Ericsson, R Sandström, Fatigue of FSW Overlap Joints in Aluminium Welded with Different Tool Designs, 5th Int Symp on Friction stir welding, Metz (2004)
• M Ericsson, R Sandström, Fatigue crack propagation in friction stir welded and parent AA6082, Steel Research International, v 77, n 6, June, 2006, p 450-455
• M Ericsson, L Z Jin, R Sandström, Fatigue properties of friction stir overlap welds, Journal of Fatigue, 29, Issue 1, January 2007, 57-68
• M M Shahri, R Sandström, Fatigue Strength of Friction Stir Welded Aluminium Profile for Train Car Application, 7th Int. Symp. on Friction Stir Welding, Awaji Island, Japan (2008)
• Shahri MM, Sandstrom R. Fatigue analysis of friction stir welded aluminium profile using critical distance. Int J Fatigue. 2010;32:302-9

· Mahdavi Shahri M, Sandström R. Influence of fabrication stresses on fatigue life of friction stir welded aluminium profiles. J Mater Process Tech. 2012;212:1488-94.

· Mahdavi Shahri M, Sandström R, Osikowicz W. Critical distance method to estimate the fatigue life time of friction stir welded profiles. Int J Fatigue. 2012;37:60-8.

Source of funding: SkanAluminium, Oslo; Sapa Technology, SSF

Materials Design of Creep Resistant Steels

Research leader: Rolf Sandström
PhD student: Hans Magnusson
Project period: 2004–2012
Keywords: 9 and 12% Cr-steels, creep, particle strengthening, solid solution hardening, substructure, cavitation

Objectives: 

To find relationships between microstructure and creep deformation and strength for heat resitant 9 and 12% chromium steels.

Results: 

Factors that control the creep deformation and strength are studied. Models for particle strengthening have been developed taking dislocations in the subgrain interior as well as in the boundaries into account. The deformation rate is controlled by the time it takes for dislocations to climb across the particles. The coarsening of MX, M23C6 and Laves is described with thermodynamic modelling. A model for solid solution hardening has been developed based on solid drag of alloying elements. By adding the contributions from particles strengthening, substructure and solid solution hardening the creep deformation of 9% Cr-steels have successfully been predicted. To handle the rupture nucleation and growth of creep cavities have been modelled.

Publications:

• H Magnusson, R Sandström, Modelling of the influence of Laves phase on the creep properties in 9% Cr steels, CREEP8 Conference, San Antonio, Texas, USA, Jul 22-26, 2007
• H Magnusson, R Sandström, Dislocation climb of particles at creep conditions in 9-12% Cr steels, Metallurgical and Materials Transactions A 38A (2007) 2428-2434
• H Magnusson, R Sandström, Creep strain modelling of 9-12% Cr steels based on microstructure evolution, Metallurgical and Materials Transactions A 38A (2007) 2033-2039
• Magnusson H., Sandström R., Growth of creep cavities in 12% Cr steels, ECCC Creep & Fracture in High Temperature Components Design & Life Assessment, Dübendorf, Switzerland, April 21-23, 2009

  Magnusson H, Sandstrom R. Influence of aluminium on creep strength of 9-12% Cr steels. Mat Sci Eng a-Struct. 2009;527:118-25.

· Magnusson H, Sandstrom R. Modeling Creep Strength of Welded 9 to 12 Pct Cr Steels. Metall Mater Trans A. 2010;41A:3340-7.

Source of funding: CROX (SSF), Brinell Centre (SSF)

Composition-microstructure-property relations (CMPR)

Research leader: Rolf Sandström
PhD students: Henrik Sieurin, Johan Zander
Project period: 2005–2012
Keywords: Aluminium alloys, stainless steels, mechanical properties, technological properties

Project description: 

To be able to perform material grade optimisation, composition-microstructure-property relations (CMPR) must be available. Mechanical, physical and technological properties as well as environmental loading are all considered, since lack of relations for important properties would disable the optimisation.

Solid solution hardening of Al-, Cu-, Ni-alloy systems has been analysed applying the Labusch-Nabarro theory. Data on solid solution hardening has been collected and compared with lattice misfit parameters from King and Pearson. Successful results have been obtained for Cu- and Ni-alloys. In addition the yield strength values in the collected commercial stainless data have been investigated. In turns out that the strength variation between different grades of steels can be represented accurately. This is quite an important result industrially since the strength of most austenitic and duplex stainless steels is primarily controlled by solid solution hardening.

By analysing microstructure mechanisms, CMPR for mechanical properties have been set up for non-hardenable and hardenable aluminium alloys. Properties covered include yield strength, tensile strength, fatigue strength and hardness. CMPR for three technological properties general corrosion resistance, machinability and weldability have been formulated for aluminium alloys using data from AluSelect.

Publications:

• Sieurin H., Zander J., Sandström R., Modelling solid solution hardening in stainless steels, Materials Science and Engineering A. vol. 415, 2006, pp. 66-71.
• J. Zander, R. Sandström, L. Vitos, Modelling of mechanical properties for non-hardenable aluminium alloys, Computiational Materials Science, Volume 41, Issue 1, November 2007, Pages 86-95
• J. Zander, R. Sandström, One parameter model for strength properties of hardenable aluminium alloys, Materials & Design, Volume 29, Issue 8, 2008, Pages 1540-1548.
• J. Zander, R. Sandström, Modelling Technological Properties of Commercial Wrought Aluminium Alloys, Materials & Design (2009)

· Zander J, Sandström R. Merit exponents and control area diagrams in materials selection. Mater Design. 2011;32:4850-6.

· Zander J, Sandström R. Materials selection for a cooling plate using control area diagrams. Mater Design. 2011;32:4866-73.

· Zander J, Sandström R. Materials selection with several sizing variables taking environmental impact into account. Materials and Design. 2012;37:243-50.

Source of funding: Brinell Centre (SSF), Sapa Technology, Outokumpu Stainless, Sandvik Materials Technology

Fundamental modelling of flow and creep deformation in phosphorus doped copper

Research leader: Rolf Sandström
PhD students: Henrik Östling (former Andersson)
Project period: 2002–2013
Keywords: Copper, creep, slow strain rate tensile test, phosphorus

Project description:

The Swedish spent nuclear fuel will be encapsulated in an insert made of iron with a surrounding copper canister. The iron insert provides the mechanical strength and the copper canister gives corrosion protection. The material in the canister will be oxygen free copper alloyed with phosphorus, Cu-OFP, to have sufficient creep ductility. A model based on solute drag has been developed for the influence of the phosphorus. In spite of the low P-content, the effect on the creep strength is dramatic, which the model can fully explain. Constitutive equations for the creep rate for P-free and P-doped copper have been formulated. The equations that take into account both climb and glide can describe the creep rate from 20 to 400 ºC. A model has also been established for primary creep.

A model has also been developed for slow rate tensile flow curves. The model can accurate represent flow curves in the temperature interval 20 to 175 ºC for strain rate between 10-7 to 10-1. All the models developed in this project are fundamental in the sense that they can describe experimental data without the use of any fitting parameters.

Publications:

• Sandström R., Andersson H.C.M., The effect of phosphorus on creep in copper, Journal of Nuclear Materials, 372 (2008) 66-75
• Sandström R., Andersson H.C.M., Creep in phosphorus alloyed copper during power-law breakdown, Journal of Nuclear Materials 372 (2008) 76-88
• Sandström R., Andersson H.C.M., Creep during power-law breakdown in phosphorus alloyed copper, CREEP8 Conference, San Antonio, Texas, USA, July 22-26, 2007.
• Sandstrom R. Basic model for primary and secondary creep in copper. Acta Mater. 2012;60:314-22.
• Sandström R, Hallgren J. The role of creep in stress strain curves for copper. J Nucl Mater. 2012;422:51-7.

Source of funding: SKB

FEM modelling of creep deformation in copper canister in power law breakdown regime

Research leader: Rolf Sandström
Scientist: Lai-Zhe Jin
Project period: 2007–2013
Keywords: Copper, creep, FEM, waste package

Project description:

A copper canister for the disposal of nuclear waste according to the KBS-3 concept is studied. The nuclear fuel waste is placed in a cast iron insert that is put in the canister. The canister is exposed to an external pressure of 15 MPa at a temperature of about 348 K after the disposal. This implies that creep deformation is well inside the power law break down regime with a creep exponent of about 65. These conditions have been simulated with FEM-modelling. The material model is a climb-glide equation where primary creep is taken into account according to the F-model. The computations demonstrate that the lid and the bottom of the canister are deformed almost instantly until they reach the insert. For the cylindrical part the same process takes about 10 years. The dominating contribution to the deformation comes from primary creep.

Publications:

• Jin L-Z., Sandström R., Creep of copper canisters in power-law breakdown, Computational Materials Science,Volume 43, Issue 3, September 2008, Pages 403-416
• Jin L-Z., Sandström R., Non-stationary creep simulation with a modified Armstrong-Frederick relation applied to copper canisters, Computational Materials Science, 2009;46:339-46.
• Jin L-Z., Sandström R., Modified Armstrong-Frederick relation for handling back stresses in FEM computations, Proceedings 2nd international ECCC conference. Creep & fracture in high temperature components - design & life assessment issues, Dübendorf, Switzerland, eds I. A. Shibli, S.R: Holdworth, 2009, pp. 836-847 .
• Jin LZ, Sandström R. Numerical simulation of residual stresses for friction stir welds in copper canisters. Journal of Manufacturing Processes. 2012;14:71-81

Source of funding: SKB

Influence of notches on the creep deformation and rupture of copper

Research leader: Rolf Sandström
Scientists: Lai-Zhe Jin, Rui Wu (Swerea-KIMAB)
Project period: 2006–2013
Keywords: Copper, creep, notches

Project description:

Phosphorus alloyed oxygen free copper (Cu-OFP) canisters are planned to be used for spent nuclear fuel in Sweden. The copper canisters will be subjected to creep under multiaxial stress states in the repository. Creep tests have been carried out using cylindrical specimens with different notch acuities at 75°C. The creep lifetime for notched specimens is considerably longer than that for the smooth one, indicating that the investigated Cu-OFP is insensitive to the presence of notches (notch strengthening). The notch strengthening factor in time exceeds 100 if extrapolated results are compared with uniaxial data. Using the fundamental creep models formulated in another project, the notch strengthening can be fully explained with the help of finite element modelling.

Publication:

· Wu R, Jin LZ, Sandstrom R. Influence of multiaxial stresses on creep properties of phosphorus alloyed oxygen free copper. American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP. PART B ed, 2009. p. 1525-32

Source of funding: SKB