Wyniki wyszukiwania - Biblioteka Nauki

1

High density sintered stainless steels with improved properties

100%

Rosso M. , Actis Grande M.

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tom Vol. 21, nr 2

97-102

EN

Purpose: of this paper is the study of the properties of sintered ALSI 316L (1.4404 according to EN 10088. Sintered stainless steels occupy a prominent position in the high alloyed steels, however their properties are limited by the presence of porosity. The improvement of quality and performances of products coupled with a reduction of manufacturing costs calls for high compacting pressures, as well as high sintering temperatures. However, the possibility to fill the open porosity of sintered parts by infiltration process with a metal alloy or by the use of reactive sintering techniques can favour the production of stainless steel parts with enhanced mechanical properties and good corrosion resistance). Design/methodology/approach: Sintered AISI 316L (1.4404 according to EN 10088) stainless steel samples have been manufactured using different combinations of compacting pressure and sintering parameters (time, temperature, atmosphere), or a modified composition able to allow reactive sintering process, as well as the contact infiltration with bronze. Findings: the studies have been forwarded towards the statistical and dynamic mechanical properties, as well as the corrosion behavior. Lowering the porosity level and increasing the sintering degree, by use of higher compacting pressure or sintering temperature, is of great effectiveness, especially from the point of view of mechanical properties and fatique endurance. Practical implications: the obtained results demonstrate the benefits of contact infiltration and of reactive sintering techniques to sinter stainless steels components having higher density and better mechanical and corrosion resistance properties than the traditional compositions, compacted at high pressure and sintered at elevated temperature. Originality/value: very promising results have been also obtained with a modified composition able to allow reactive sintering process.

2

Corrosion resistance of sintered duplex stainless steel evaluated by electrochemical method

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Dobrzański L. A. , Brytan Z. , Actis Grande M. , Rosso M.

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tom Vol. 17, nr 1-2

317--320

EN

Purpose: Purpose of this paper was to examine the corrosion resistance of duplex stainless steels using electrochemical methods in 1M NaCl solution. The influence of powder mixes preparation and cooling cycle after sintering on corrosion properties was evaluated. Design/methodology/approach: In presented study duplex stainless steels were obtained through powder metallurgy starting from austenitic, martensitic base powders by controlled addition of alloying elements. In the studies behind the preparation of mixes, Schaffler’s diagram was taken into consideration. Prepared mixes have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at 1260°C for 1h. After sintering two different cooling cycles were applied: rapid cooling with an average cooling rate of 245°C/min and slow cooling of 5°C/min in argon atmosphere. Findings: According to achieved results, it was affirmed that applied sintering method as well as powder mixes preparation allows for manufacturing the sintered duplex steels with good corrosion properties. Corrosion resistance of sintered stainless steels is strictly connected with the density and the pore morphology present in the microstructure too. The highest resistance to pitting corrosion was achieved for composition with approximate balance of ferrite and austenite in the microstructure. Research limitations/implications: According to the powders characteristic, the applied fast cooling rate seems to be a good compromise for corrosion properties and microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and sintering temperatures. Originality/value: The use of elemental powders added to a stainless steel base showed its potentialities, in terms of fair compressibility and final sintered density. In addition a good structural homogeneity and first of all corrosion resistance was achieved, also working with cycles possible for industries.

3

A comparative study of Ti-Al and Ti-Nb alloys for advanced technological applications

80%

Peter I. , Rosso M. , Castella C.

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tom Vol. 73, nr 2

199--205

EN

Purpose: of this paper is to compare some properties of Ti-Al and Ti-Nb alloys to investigate on the possibility to jointly employed them industrially. Ti-Al alloys have been proposed because they present challenging characteristics for high temperature purposes and β type Ti-Nb alloy has specific mechanical properties at room temperature. Ti-Al alloys are very attractive materials and represent one of the most important materials employed for aero jet engines. The most promising alloy belonging to the above mentioned classes are predominantly based on simultaneously presence of two phases, namely γ-TiAl (gamma titanium aluminides) and α2-Ti3Al both with a fully lamellar microstructure and could replace Ni-based superalloys in some high temperature applications in aerospace and automotive industries. The most important advantages of such alloys compared to some superalloys consist in their low density correlated to their superior efficiency in service and reduced gas emission. Design/methodology/approach: The Ti-Al alloy have been produced by gravity casting, using a vibrating furnace, while the Ti-Nb alloy samples have been realized by the cold crucible levitation melting (CCLM) casting technology. Microstructural and mechanical characterization have been performed. Findings: The microstructural analysis for the Ti-Al alloy reveals a fully-lamellar microstructure with alternate plates of α2-(Ti3Al) and γ-(TiAl) plates. The grains have an average size of about 200 μm. For the Ti-Nb based alloy only a β mono-phase has been detected. This alloy has a equiaxed microstructure with an average grain dimension of about 170 μm. The Ti-Nb alloy presents a high mechanical strength while on the contrary that of the Ti-Al has been deleteriously affected by the presence of large gas porosities. Superior hardness values have been reached with Ti-Al alloy, due to the presence of hard γ-TiAl. Practical implications: The most important implication is related to the transfer toward the proper choice of the correct parameters during manufacturing. Originality/value: Investigation on the influence of the elemental composition enriched by other elements and casting processes on the defect development, the microstructural characteristics and on the mechanical behaviour of the alloys.

4

Coastal Area Prone to Extreme Flood and Erosion Events Induced by Climate Changes: Study Case of Juqueriquere River Bar Navigation, Caraguatatuba (Sao Paulo State), Brazil

80%

Arasaki E. , Alfredini P. , Pezzoli A. , Rosso M.

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tom Vol. 6, no. 4

571--577

EN

According to the IPCC, the forecast for the year 2100 is an increasing of global average temperature, whose impacts in winds, waves, tides, currents and bathymetry will produce real risks of extreme events due to climate changes. Juqueriquere River is Sao Paulo State (Brazil) North Coastline major waterway. Due to minimum channel depths in the coastal bar, navigation is only possible for small leisure crafts and fishing boats and some cargo barges during higher tidal levels. This study case has been evaluated according to the relative sea level and wave climate scenarios forecasting, based on the meteorological recognition patterns of the last decades data for tides and waves. The impact of climate changes is obtained from this knowledge. The main goal of this paper is to have the initial conceptual description about the impacts on the bar navigation conditions of Juqueriquere to obtain guidelines for master nautical plans.

5

The challenge of PM tool steels for the innovation

80%

Rosso M. , Ugues D. , Actis Grande M.

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tom Vol. 18, nr 1-2

175--178

EN

Purpose: The economical impacts and complexity of tool steels justify the lot of efforts for their development, processing and application. In particular the main goal is the attainment of isotropic microstructures characterised by homogeneous distribution of fine carbide particles and segregation free. The paper offers a review of the Powder Metallurgy tool steels currently manufactured, their properties are discussed with particular regard to their main application and attained performances. Design/methodology/approach: Powder Metallurgy is the way to make the goal, its alloying flexibility allows the production of new tool steels that cannot be made by conventional processes, because of segregation and related hot workability problems. Findings: In practice, through the Powder Metallurgy route it is possible to achieve the highest levels of properties, specifically related to toughness, mechanical behaviour, wear and corrosion resistances of the produced alloys. Research limitations/implications: The use of Powder Metallurgy route allows, through the HIP consolidation from tiny powder particles, to facilitate the production of tool alloy grades able to reach very high performances. Moreover the application of coatings can determin e further advantages. Practical implications: When using thin coatings, like PVD deposited layers, the PM steels more uniformly distributed and fine carbide structure was found to give a clear improvement in the interface quality of the relative coated systems. Conversely, the less uniform traditional steels carbide distribution resulted in a less continuous contact between the substrate and the coating. Originality/value: The paper demonstrate the superior value and perfomances of PM tool steels and their better adaptability to PVD coatings. In particular, cold working, plastics and high speed applications are the main interested and advantageously affected by the uniqueness of PM tool steels. Some comparison between equivalent traditional and PM tool steel grades are presented.

6

The influence of sintering time on the properties of PM duplex stainless steel

80%

Brytan Z. , Dobrzański L. A. , Actis Grande M. , Rosso M.

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2009

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tom Vol. 37, nr 2

387-396

EN

Purpose: The purpose of this paper is to analyse the effect of sintering time on the pore morphology, microstructural changes, tensile properties and corrosion resistance of vacuum sintered duplex stainless steel. Design/methodology/approach: In presented study PM duplex stainless steels were obtained through mixing base ferritic stainless steel powder with controlled addition of elemental alloying powders and then sintered in a vacuum furnace with argon backfilling at 1250°C for different time periods. Produced materials were studied by LOM/SEM metallography and the pore morphology was characterized. The mechanical properties were studied in tensile, hardness and Charpy impact tests. The corrosion resistance was evaluated by means of salt spray test and immersion in sulfuric acid. Findings: Prolongation of sintering time influenced on increase of density thus on the mechanical properties and microstructure balance. Practical implications: Mechanical properties of obtained PM duplex stainless steels are very promising, especially with the aim of extending their field of possible applications. Originality/value: The possibility of obtaining balanced austenitic-ferritic microstructure of stainless steel using elemental powders added to a stainless steel base powder. The vacuum sintering of such powder mixture results in good microstructural homogeneity.

7

Characteristic of vacuum sintered stainless steels

80%

Brytan Z. , Dobrzański L. A. , Actis Grande M. , Rosso M.

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tom Vol. 33, nr 2

126-134

EN

Purpose: In the present study duplex stainless steels were sintered in vacuum. using rapid cooling form the mixture of prealloyed and alloying element powders The purpose of this paper was to describe the obtained microstructures after sintering as well as the main mechanical properties of sintered stainless steels. Design/methodology/approach: In presented work duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed stainless steels powders by controlled addition of alloying elements powder. Prepared mixes were sintered in a vacuum furnace in 1250°C for 1h. After sintering rapid cooling (6°C/s) using nitrogen under pressure was applied. Sintered compositions were subjected to structural examinations by scanning and optical microscopy and EDS analysis as well as X-ray analysis. Mechanical properties were studied through tensile tests and Charpy impact test. Findings: It was demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition as well as sintering cycle with rapid cooling rate. Obtained sintered duplex stainless steels shows good mechanical properties which depends on phases ratio in the microstructure and elements partitioning (Cr/Ni) between phases. Research limitations/implications: Basing on alloys characteristics applied cooling rate and powder mix composition seems to be a good compromise to obtain balanced sintered duplex stainless steel microstructures. Practical implications: Mechanical properties of obtained sintered duplex stainless steels structures are rather promising, especially with the aim of extending their field of possible applications. Originality/value: The utilization of vacuum sintering process with rapid cooling after sintering combined with use of elemental powders added to a stainless steel base powder shows its advantages in terms of good microstructural homogeneity.

8

Struktura i własności spiekalnych stali typu duplex

80%

Dobrzyński A. L. , Brytan Z. , Grande M. A. , Rosso M.

Inżynieria Materiałowa

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2006

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tom Vol. 27, nr 3

580-583

PL

Rosnące zainteresowanie wielu gałęzi przemysłu spiekanymi stalami odpornymi na korozje wiąże sie z koniecznością prowadzenia prac badawczych nad optymalizacją składu chemicznego i technologii wytwarzania spiekanych stali ferrytyczno-austenitycznych w celu uzyskania materiału charakteryzującego sie najkorzystniejszymi własnościami mechanicznymi i odpornością na korozje, a także atrakcyjnego ze względów ekonomicznych i możliwości łatwego zastosowania w praktyce produkcyjnej. W pracy przedstawiono wyniki badań składu fazowego, struktury oraz własności mechanicznych spiekanych ferrytyczno - austenitycznych stali typu duplex, uzyskanych w wyniku wprowadzenie do proszku bazowego stali austenitycznej X2CrNiMo17-12-2 oraz stali martenzytycznej X6Cr13, proszków dodatków stopowych takich jak Cr, Ni, Mo i Cu w stężeniach zapewniających uzyskanie struktury o składzie chemicznym, odpowiadającej dwufazowej stali austenityczno - ferrytycznej. Ponadto przygotowano mieszaninę proszków stali austenitycznej i ferrytycznej X6Cr17 w udziale 1 / 1 (tab. 2). Połączone procesy spiekania w próżni i chłodzenia konwekcyjnego zostały realizowane w temperaturze 1260°C i czasie 60min. W celu uzyskania prędkości chłodzenia umożliwiającej uzyskanie jednorodnej struktury dwufazowej bez wydzieleń faz wtórnych zastosowano azot pod ciśnieniem 0,6MPa. Przeprowadzone badania struktury (rys. 6) i własności mechanicznych (tab. 4) otrzymanych stali umożliwiają optymalizacje parametrów procesu spiekania w celu uzyskania stali dwufazowej charakteryzującego się najkorzystniejszymi własnościami mechanicznymi i zwiększoną odpornością na działanie środowisk korozyjnych. Odporność na korozje zbadano w środowisku kwasu H2SO4 i mgły solnej o stężeniu 5% NaCl (rys. 7).

EN

The growing interest of many industrial branches of sintered stainless steels is connected with necessity of conducting research works over optimization of chemical composition and the production technology of sintered austeno-ferritic stainless steels. The main goal is to obtain the material characterized by the most profitable mechanical properties, corrosion resistance, attractive in economical aspects and easy to introduce in productive practice of sintered steels. This work presents the investigation results phase composition, microstructure and mechanical properties of sintered austeno-ferritic duplex stainless steels obtained through technology of powder metallurgy starting from austenitic X2CrNiMo17-12-2, martensitic X6Cr13 powders by controlled addition of alloying elements, such as chromium, nickel, molybdenum and copper in the right quantity to obtain the chemical composition of the structure similar to biphasic austeno-ferritic. Moreover the ferritic stainless steel X6Cr17 has been mixed with austenitic stainless steel in the ratio of 1 / 1 in order to exam the structure deriving after sintering (tab. 2). The combined processes of vacuum sintering and convective cooling were realized in temperature 1260°C and time 60min. In order to achieve the cooling speed enabling the obtainment of homogeneous biphasic structure without precipitates of secondary phases the nitrogen under pressure of 0,6MPa was applied. The conducted investigations of microstructure (fig. 6) and mechanical properties (tab. 4) of produced sintered steels make possible the optimization of parameters of sintering process in aim to obtain duplex steels characterized by the most profitable mechanical properties and the improved corrosion resistance in the corrosive environments. Corrosion resistance was evaluated in the environment of H2SO4 5% NaCl concentration slat spray fog with (fig. 7).

9

Structure investigation of ball milled composite powder based on AlSi5Cu2 alloy chips modified by SiC particles

71%

Suśniak M. , Karwan-Baczewska J. , Dutkiewicz J. , Actis Grande M. , Rosso M.

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tom Vol. 58, iss. 2

437--441

EN

The paper is focused on the processing of aluminum alloy chips using powder metallurgy. Chips obtained from recycled AlSi5Cu2 alloy were ball milled with the addition of silicon carbide powder with an average size of 2μm. Mechanical alloying process was employed to obtain homogeneous composite powder. The effect of processing time (0 - 40h) on the homogeneity of the system was evaluated, as well as a detailed study of the microstructure of AlSi5Cu2 aluminum chips and SiC particles during MA was carried out. Addition of silicon carbide (10, 20wt%) to recycled aluminium chips and application of MA lead to fragmentation of the homogeneous composite powder down to particle size of about 3μm and spheroidization. The addition of hard SiC particles caused reinforcement and reduced the milling time. Higher content of silicon carbide and longer processing time allowed to obtain AlSi5Cu2/SiC powders with microhardness ~500HV0,025. The results of MA were investigated with SEM, EDS, LOM, XRD and showed that relatively homogeneous distribution of SiC reinforcements in the matrix as well as grain refinement of aluminum solid solution down to 50nm can be obtained after 40h of processing.

PL

W artykule przedstawiono metodę otrzymywania proszku kompozytowego na osnowie wiór stopu aluminium AlSi5Cu2 pochodzących z recyklingu z dodatkiem węglika krzemu (SiC-α, 2μm). Określono wpływ czasu mielenia oraz dodatku SiC na mikrostrukture i właściwości proszku kompozytowego.Dodatek SiC (10, 20%mas) do wiór stopu aluminium i zastosowanie mechanicznej syntezy pozwala na otrzymanie jednorodnego i drobnoziarnistego proszku o wielkości 3μm i kształcie zbliżonym do sferycznego. Dodatek twardych cząstek SiC powoduje umocnienie proszku oraz skrócenie czasu mielenia. Dodatek SiC i zastosowanie 40h mielenia pozwala otrzymać cząstki proszku o mikrotwardości około 500 HV0,025. Badania proszku kompozytowego przeprowadzone na mikroskopie optycznym, SEM oraz TEM potwierdziły jednorodne rozmieszczenie cząstek SiC w osnowie oraz zmniejszenie wielkości ziarna do 50nm po 40 godzinach procesu.