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Mandziej S.T.,Advanced Materials Analysis | Ruggeri M.,Dynamic Systems Inc.
Materials Science Forum | Year: 2013

Grain refinement should increase strength of metallic materials in a predictable manner. However, in applications of severe plastic deformations for this purpose, limits have been observed due to self-recovery and strain-induced precipitation assisted by generation of adiabatic heat. Pure metals and single-phase alloys have not been the best candidates for achieving ultrafine-grained microstructures therefore more often precipitation-hardening multi-phase alloys have been used in SPD experiments. To generate ultrafine-grained microstructures by accumulated multiple compressive strains executed at various strain rates during programmed thermal cycles the MaxStrain™ device was developed for Gleeble™ physical simulator. This paper deals with processing of Al-6061 wrought alloy and Al-319 cast alloy by the MaxStrain device, and describes obtained microstructures. © (2013) Trans Tech Publications, Switzerland.


Mandziej S.T.,Advanced Materials Analysis | Vyrostkova A.,Slovak Academy of Sciences | Solar M.,Elektrode Jesenice
Welding in the World | Year: 2011

In the course of 5thFP "SmartWeld" EU R&D project, welding consumables of P24 grade were developed with the aim of reaching adequate combination of creep strength and fracture toughness, eventually without post-weld heat treatment. All-weld metal samples, showing evidences of "smartness" in various creep tests, were subjected to thorough metallographic and micro-analytical study, to explain changing of their properties. In particular, scanning and transmission electron microscope observations concentrated on evolution of microstructure and transformations of carbides, which were leading to nucleation of voids and cracks in various creep tests. Three different types of creep tests were carried out, i.e. the constant load short-term/ creep rupture test, the small punch accelerated creep test and the simulative (Gleeble) accelerated creep test. The transformed microstructures after these creep tests were compared with the initial microstructures of the weld metals. In this article are presented two different manual metal arc weld metals of P24 grade, in as-welded and post-weld heat-treated states, manufactured by Metrode Ltd, Chertsey, UK and by Elektrode, Jesenice, SI.


Mandziej S.T.,Advanced Materials Analysis | Vyrostkova A.,Slovak Academy of Sciences | Chovet C.,Air Liquide
Welding in the World | Year: 2011

The search for new more creep-resistant materials for supercritical components of modern power plants stimulates also welding research to provide joints adequate to withstand highly demanding operation conditions. Seeking for improvement of existing welding consumables, experimental Ti-doped P92 grade weld metals were developed of exceptionally long life in creep rupture tests. In response to this request SEM and TEM investigations were carried out to identify the features of microstructure, which could be responsible for so different behaviour in the creep rupture tests. In this research the microstructures of the Ti-doped FCAW P92 weld metals were also compared with these of a standard P92 pipe material as well as with the submerged arc weld metal deposit W0 manufactured by flux-cored consumable containing no addition of Ti. Transformation of microstructures of this "reference" P92 pipe material and of the Ti-free P92 weld metal was accomplished in the accelerated creep tests on Gleeble physical simulator. An attempt has been made to correlate the fracture appearance of the creep-ruptured samples with the fine structure in their head/grip and gauge portions. In the microstructure of non-affected by the creep strain head portions of the creep- ruptured samples appeared numerous delta-ferrite grains with no carbide precipitates. Evidences were found that creep voids and cracks formed fast in the initially precipitate-free delta-ferrite grains of the sample W1, while in sample W2 during the creep test a peculiar strain-induced precipitation hardening of the delta-ferrite appeared, however no Ti was identified there in the ultra-fine precipitates.


Mandziej S.T.,Advanced Materials Analysis
Procedia Engineering | Year: 2010

An accelerated creep test (ACT) has been developed for ferritic/martensitic creep resistant steels and weld metals, aiming to speed-up the microstructure transformation to the same extent like it occurs during real multi-year creep. Using low-cycle thermal-mechanical fatigue on Gleeble physical simulator, the compositions of precipitated phases, mainly carbides, could reach in less than 30 hours the state near to the thermodynamic equilibrium, as predicted by Thermocalc. Accordingly the equivalent depletion of alloying elements occurred in the steel's / weld metal's matrix, resulting in decrease of creep strength prior to failure by elevated temperature fracture. Based on TEM observations discussed are precipitation processes related to changes in creep behaviour as well as dislocations interactions with the precipitates resulting in the acceleration of creep. A particular role in the acceleration of the carbide precipitation and the steel's matrix transformation was ascribed to meta-stable mobile edge dislocations of a<001> Burgers vector, which were found to effectively transport interstitial elements. The thermalmechanical fatigue procedure of the ACT consists of compression-tension cycles containing steps of generating these edge dislocations as reaction products between intersecting families of a/2<111> screw dislocations saturated with interstitials and dragging the interstitials dissolved in cores of the a<001> edge dislocations to finally dispose the interstitials at grain boundaries or phase boundaries while annihilating these edge dislocations. The developed ACT procedure obeys the following principles: The basic temperature and applied strains prevent odd transformations like secondary dissolution of carbides or intensive formation of non-equilibrium phases.The final deformation at fracture is like at real creep just a few pct in total.The depletion of weld metal or steel matrix in alloying elements is achieved similar to that of crept steels and the carbide phases at onset of cracks are not different. This ACT procedure was already effectively applied in 2001-04 within 5thFP EU R&D project "SmartWeld" (G1RD-CT-200100490) to development of new generation weld metals for power generation applications, and most recently was implemented in studies on new materials for super-critical power-generation components and on determining of remnant lifetime of power plants, in the course of EU collaboration actions COST-536 and COST-538. Actually the ACT is included into research/technical services provided to interested customers by the manufacturers of the Gleeble series physical simulators, i.e. the DSI company from Poestenkill, NY, USA. © 2010 Published by Elsevier Ltd.


Jenko D.,Slovenian Institute of Metals And Technology | Mandziej S.,Advanced Materials Analysis | Toffolon-Masclet C.,French Atomic Energy Commission | Sustarsic B.,Slovenian Institute of Metals And Technology | Jenko M.,Slovenian Institute of Metals And Technology
Materiali in Tehnologije | Year: 2014

Specimens of duplex stainless steel (DSS, the 258-alloy type) were isothermally annealed (aged) at 300 °C and 350 °C for 10000 h and 30000 h. Spinodal decomposition of the solid solution in ferrite occurs during the thermal ageing of this material with a redistribution of mainly Cr and Ni and a formation of nanocellular domains. This causes significant changes in the mechanical properties (the hardness and the tensile strength increase, while the ductility and the notch toughness decrease). The change in the mechanical properties may be related to the changes in the material's internal structure (stacking faults, the morphology and density of dislocations) or/and internal stresses. Therefore, non-aged and aged specimens were studied using transmission electron microscopy (TEM).


Mandziej S.T.,Advanced Materials Analysis
METAL 2010 - 19th International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2010

The accelerated creep test on Gleeble physical simulator was developed as a response to the need for fast gaining of reliable physical data for long-term behaviour of materials operating at elevated temperatures. The design of components and lifetime estimation for power generating or chemical processing plants relies on long-term creep data, which are available for plates and pipes of creep resisting steels. Hoiwever such components are usually manufactured by welding and for the factory-made welded joints such data are seldom while for any later repair welds generally not available. On such demand a low-cycle thermal-mechanical fatigue test was developed, in which the sub-structural processes characteristic of creep occur rapidly, changing the initial microstructure of steels and welds to the nearto-equilibrium one in less than 50hours. This procedure relies on controlled generation of dislocation configurations, which can transport interstitial elements at high rates, a few orders of magnitude faster than the normal diffusion in conventional creep, while the sequences of carbide precipitation and coagulation appear unchanged. The developed accelerated creep test, next to its short duration, characterizes by the following: The temperature and applied strains in ACT prevent odd transformations of carbides or intensive formation of non-equilibrium phases. The final deformation at fracture is like at real creep -just a few pct in total. The depletion in alloying elements of matrix of ACT samples is similar to that of crept steels and carbide phases at onset of cracking are identical. To meet these requirements a low-cycle thermal-mechanical deformation-relaxation test was developed, during which the sub-structural processes characteristic of creep occurred much faster, transforming the initial microstructure of the creep resisting steels and welds to the near-to-equilibrium one in less than 30hours. The formation of dislocation configurations and the sequence of carbide precipitation and coagulation, as confirmed by TEM investigations, well resembled these of the conventional creep, so the testing procedure, hence called the simulative accelerated creep test -ACT, has been verified this way. © 2010 TANGER Ltd., Ostrava.


Mandziej S.T.,Advanced Materials Analysis | Vyrostkova A.,Slovak Academy of Sciences | Solar M.,Elektrode Jesenice
Welding in the World | Year: 2010

New creep-resisting weld metals of P91 grade were manufactured by manual metal arc (MMA) process producing multi-bead multi-layer test coupons, from which specimens were taken for accelerated creep testing on Gleeble physical simulator. The recently developed accelerated creep testing (ACT) procedure on Gleeble allows transforming in a relatively short time (less than 100 h) the microstructure of creep-resisting materials to the near to thermody-namic equilibrium state, resembling that of multi-year application at creep condition. Such advanced transformation of microstructure in the investigated weld metals after ACT was confirmed by microscopic and microanalytical study. The results also appeared in agreement with Thermocalc calculations. By an optimum combination of chemical compositions of the electrodes with welding procedure and post-weld heat treatment, advantageous mechanical properties were achieved as well as results of ACT indicating potentially long creep life in service exposure conditions. In discussion of the ACT results, comparisons with results of conventional creep testing have been made. The ACT procedure appears useful in fast screening of newly developed creep-resisting materials.


Mandziej S.T.,Advanced Materials Analysis
Materiali in Tehnologije | Year: 2010

Worldwide demand of better and more efficient metallurgical processes, leading to low costs of their products, stimulates intensive research to reach these goals. In this respect, any full-scale industrial experiments appear non-acceptable. Cutting off the R&D costs and fast introducing of new technologies is possible when physical and numerical simulations are used. The computer simulation can be only correct when exact data of materials behaviour at processing conditions are known. To obtain the data, physical simulation is needed and it must be executed on multi-purpose thermal-mechanical testing devices accurately reproducing the real industrial processing conditions. For continuous casting or metal forming, individual phases of processes or multi-step operations must be followed, characterized by their time, temperature, and by applied forces, strains and strain rates. Actually the physical simulation, as compared with full-scale industrial testing, allows in a fraction of time for a fraction of cost an improvement of existing technology or development of a new one for modern materials and products. It can be used for solving production problems due to solidification phenomena or deformability limits, which result in hot cracking and rejection of the product. In this paper several examples of physically simulated procedures are given and their physical background discussed.

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