In contemporary high-pressure die casting foundries, the mastery of each sequence in the production cycle is more and more important. In the paper, an example of virtual analysis of gearbox casting from Al alloy will be presented. It includes a large variety of parameters, as follows: choosing of appropriate foundry technology, calculation of computer simulation of casting process which takes into account the filling process of cold chamber and filling of cavity, model description of three phases in high-pressure die casting, flow of molten metal, solidification, formation of stress and deformations. Additionally, the optimization of cooling and heating systems will be compared with calculated volume defects, dimensions of castings and their deformations with experimentally obtained values.
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Purpose: Among many disciplines within engineering, welding is probably one of the most inexact – rather more of an art than a science. As weldment is meant the complete joint comprising the weld metal, heat affected zones (HAZ) and the adjacent parent metal and should have the same properties as the parent metal. This paper aims provides a basic understanding of the metallurgical principles involved in how aluminium alloys achieve their strength and how welding can affect these properties. The most important and applied welding processes to Al alloys are here shortly introduced, as well as the preparation of parent metals prior to welding and good welding practice to avoid and/or keep under control defects and failures. Some case studies with possible failures will be introduced together with actions and suggestions to solve the observed problems. Design/methodology/approach: Two sheets of the EN AW 5454 (AlMg3Mn) alloy were weld with resistance welding process and after a mechanical processing of lamination was observed the presence of the defect. The microstructure of the defect as well as the welded part were evaluated with stereomicroscope (LEICA MS5), optical microscope (LEICA MEF4M), and with SEM analysis (LEO 1540 VP equipped with an energy dispersive X-ray spectroscope Oxford Link Pentafet). Findings: The well welded part was analysed with optical microscopy and electronic microscopy resulting with the attended mechanical properties. Micro-hardness indentations on the joint demonstrated the good mechanical properties of the joint while with the microscopic observations were identified the orientation and presence of precipitates typical of this alloy. In the defect, microscopically observations showed the presence of oxide inclusions. Research limitations/implications: There are a number of problems associated with the welding of aluminium and its alloys that make it difficult to achieve this ideal. The features and defects that may contribute to the loss of properties comprise the following: gas porosity, oxide inclusions and oxide filming, solidification (hot) cracking or hot tearing, reduced strength in the weld and HAZ, lack of fusion, reduced corrosion resistance and reduced electrical resistance. Originality/value: This case study illustrated clearly the importance of the cleaning on the surfaces to obtain a well welded joint ensuring the desired mechanical properties.
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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.
The present work investigates the possibility of using powder metallurgy processing for producing a metal matrix composite. Materials were prepared from AlSi5Cu2 chips with reinforcement of 10, 15, 20 wt. % silicon carbide. Aluminum alloy chips were milled with SiC powder in a high-energy ball mill by 40 hours. Mechanical alloying process lead to obtain an uniform distribution of hard SiC particles in the metallic matrix and refine the grain size. The consolidation of composite powders was performed by vacuum hot pressing at 450°C, under pressure of 600 MPa by 10 min. The results shows that the addition of SiC particles has a substantial influence on the microstructure and mechanical properties of composite powder as well as consolidated material. Hot pressing is an effective consolidation method which leads to obtain dense AlSi5Cu2/SiC composite with homogeneous structure and advanced mechanical properties.
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Of this paper is to give an overview concerning some alternative methods for the production of enhanced performance light alloys components for critical industrial applications and to present an analysis of a new rheocasting process suitable fpr the manufacturing of high performance industrial components. Design/methodology/approach: Innovative design of some automotive parts, their characterization throught radiographic analysis to verify the integrity of the samples from metallurgical point of view. OM and SEM microstructural characterization, optical microscope, mechanical characterization based on samples machined from the produced parts. Findings: Semi-solid metal (SSM) processes demonstrated their capability to reduce the existing gap between casting and forging and during such a processes there are the opportunity to better control the defect level. Research limitations/implications: The produced parts possess excellent properties, some criticises are related to the use of ceramic cores. There is the need of innovation in industrial design to open the mentalities to new advantageous solutions. Practical implications: The principal goal to improve the competitiveness and energy savings associated to the production in high performance cars was fully accomplished. Originality/value: A study on the feasibility was included opening the route for prototype production characterized by an adequate strength as well as by higher esthetical appearance than the element produced by gravity casting process. The presence of the defects does not negatively influence or compromise the employment of the callipers neither in extreme condition, favouring their use on a very high performance cars. In the future, extension of the proposed process for the production of other important applications are expected.
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Purpose: of this paper is to review the effect of heat treatments and of strain hardening on microstructure and properties of superduplex stainless steels. Design/methodology/approach: Annealing and strain hardening treatments influences microstructures and properties. Findings: The characteristics and the properties of the industrially employed superduplex grade has been discussed, moreover the presence and the precipitation of sigma phase has been highlighted through ageing treatments. Research limitations/implications: : Based on the up to date achieved outcomes, it appears that a quite homogeneous and good mechanical properties can be obtained controlling the composition and the heat treatment and strain hardening parameters. Practical implications: The major implication is related to the transfer toward the proper choice of correct parameters for working the duplex grades. Originality/value: to supply deeper information with respect to those available in literature, which does not clearly indicate what amount of secondary phases existing in duplex stainless steel microstructure can be acceptable.
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.
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Purpose: The main goal of this study is to develop and obtain some competitive products, with high added value. In particular, the attention will be focused on the possibility to obtain a new class of Cobalt based alloy by Ti addition. Design/methodology/approach: Modification of the composition by Ti addition can increase the corrosion resistance, processing and at the same time can improve the alloy biocompatibility. Findings: Addition of these elements has a positive effect on the alloy hardness. Up to 6% of Ti or combining Ti and Zr as alloying elements there are no significant differences as hardness concerns. As corrosion resistance in a simulated oral cavity environment concerns, no significant release of metal ions was observed, the pH value and the weight loss fulfil the conditions required by the Standard ISO 10271/2011. However, the best behaviour was obtained employing CoCrMoTi6 alloy. Research limitations/implications: Based on the up to date achieved outcomes, it appears that a quite homogeneous and good mechanical properties have been obtained modifying the original alloy with 6% of Ti. The future research work will be oriented to get additional and detailed data on the biocompatibility of the alloy. Practical implications: The central issue is the valid transfer to dentistry application. Originality/value: The aim of the paper is to obtain a new class of Co based alloy by the modification of the original chemical composition.
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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.
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Purpose: The paper proposes an overview of the actual most important and applied rheocasting technologies for the manufacturing of high performance Al components. Some excellent results recently attained in industrial applications are presented and discussed. Design/methodology/approach: Samples were machined from the produced parts and mechanical tests, i.e. tensile and impact, were executed on series of samples; moreover, microstructure features and the morphology of fractures were observed to check the quality of alloys and of produced castings. Findings: Despite the numerous rheocasting processes recently developed, it appears that their industrial application is still limited and some only are really interesting for the production of high performance component. The done investigations show that the use of a very simple and well controlled process leads to produce parts having excellent properties and reliability. The results obtained up to now suggest that the rheocasting route can be considered an attractive fabrication technology to produce high quality products, especially for aluminium alloys. Research limitations/implications: A lot of rheocasting processes are proposed, but for the final success it is necessary to choice a really valid process and to maintain all the steps under a strict control. Practical implications: The obtained results can be used for searching the appropriate way of improving the performance of highly stressed parts, using a very competitive and simple rheocasting process, contributing to make aluminium and its alloys still more attractive for light-weighting components for structural, as well as for automotive and aeronautic/aerospace applications. Originality/value: The main SSM technologies and future trends are presented and discussed. The properties of A356 and A357 aluminium alloys were investigated to establish the influence of the adopted Rheocasting process on the final performances and reliability of the produced parts.
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Purpose: Purpose of this paper is presenting the state-of-the-art and the mechanism of Al continuous casting process and to improve the microstructure of the Al sheets reducing the morphological differences between the surface layer and the core of the considered alloy. Design/methodology/approach: After a short illustration of some techniques which are presently employed for the production of Al alloy sheets for packaging applications, the development of the grain structure and the effect of the homegenization treatment and rolling on the microstructurural evolution has been presented and discussed. Findings: The positive effect of the homogenization treatment and rolling on the microstructure has been demonstrated. The homogenized alloy presents improved workability and machinability. Research limitations/implications: Based on the up to date achieved outcomes, it appears that homogeneous, fine microstructure and quite uniform distribution of the particles allow obtaining higher mechanical properties. The future research work will be oriented to get additional and detailed data on the performance of the alloy. Practical implications: The continuous increase of Al-based alloys in different applications involves manufacturing high integrity and superior performance components using cost-effective and safely processes. In this direction the research communities together with manufacturing industries are focusing their attention to develop new and enhanced products using innovative procedures. The central issue is the technological transfer to industry for affordable mass production. Originality/value: Obtaining a fine and homogenous microstructure for Al sheets by reducing the morphological differences between the surface layer and the core of the alloy improved mechanical performances and enhanced workability and machinability has been obtained. High performance end-product make this type of alloy very attractive for packaging material production.
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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.
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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.
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Purpose: The main goal of this paper was the examination of the role of W addition on properties of two sinter-hardened alloys with two different carbon levels. Additionally the influence of sinter-hardening process has been evaluated. Microstructural characteristic and mechanical properties of Ni-Mo steels with increasing amount of tungsten (from 0 to 0.3% wt.) were taken under consideration. Design/methodology/approach: Powder mixes have been compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at 1120 °C for 60 minutes. Rapid cooling has been applied with an average cooling rate of 2.5 °C/s. Obtained steels were analyzed by scanning microscopy with energy dispersive spectroscopy (EDS) for phase distribution and mapping and light optical microscopy for observations of the microstructure. Charpy impact test, three-point bending, microhardness, pin-on-disk and disk-on-disk tests were used. Findings: The outcome of implemented vacuum sintering with rapid cooling as well as chemical composition were studied in terms of mechanical properties, focusing in particular on impact energy, hardness and wear resistance. The results achieved after the investigation of Ni-Mo and Ni-Mo-W sinter-hardened steels with low and high carbon content proved that applied process of sintering under vacuum and rapid cooling brought expected outcome. Research limitations/implications: The characteristics of powders and the applied cooling rate were found be a good compromise for mechanical properties and microstructures, though further researches should be carried out in order to examine different cooling rates and parameters of tempering process. Originality/value: The effect of W and/or WC additions to highly alloyed steels is well known. In the work the effect of small additions of W and WC to low alloyed steels, especially in terms of hardenability and wear resistance, was investigated.
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Purpose: Purpose of this paper was to apply a computer method of open porosity analysis for determination of porosity in sintered Astaloy CrL and CrM powders. Design/methodology/approach: The powders used in the present papier are pre-alloyed iron-base powders containing low amounts of chromium and molybdenum. The amount of graphite which is mixed with the iron-base powder is 0.6% and lubricant is 0.75%. Green compacts were sintered in a vacuum furnace at 1120°C for 30 minutes in vacuum and rapidly cooled in nitrogen at four different rates: high cooling (7°C/s and 6.5 °C/s) and medium cooling (1.6°C/s) low cooling (0.3 °C/s). Next the samples were tempered in vacuum in the same furnace at 200°C for 60 minutes and cooled in nitrogen, with the exception of low cooling. Obtained samples were examined by light optical microscopy (LOM) for microstructure observation and scanning electron microscopy (SEM). Findings: The investigations of porosity in the pre-alloyed steels were performed using ”Image-Pro Plus 4.5” computer program. Leica light microscope (MEFA4) was applied to prepare series of micrographs. The microstructures were observed at 100x magnification and recorded as*jpg files. After calibration of the digital images, the perimeter, area, diameter, roundness, Feret max were calculated. Practical implications: The program has some limitations (built in mathematical functions), which made difficult to obtain some results automatically. Originality/value: The obtained results prove that this program is very useful in the statistical analysis of microstructures, because it saves the time during calculations and is well suited for checking sintered materials.
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Purpose: The purpose of this paper was to describe the sintered duplex stainless steels manufactured in sinterhardening process and its usability in field of stainless steels and moreover using computer software to calculate the powder mix composition. Design/methodology/approach: In presented paper duplex stainless steels were obtained through powder metallurgy starting from austenitic or ferritic base powders by controlled addition of alloying elements powder. In the studies besides the preparation of powder mixes, computer software based on Schaeffler’s diagram was studied. Findings: It has been demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition and sintering cycle. Research limitations/implications: According to the alloys characteristic applied cooling rate and powder mix composition seems to be a good compromise to obtain balanced duplex stainless steel microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and sintering parameters. Practical implications: Applied producing method of sintered duplex steels and used sintering cycle as well as developed computer software to calculating powder mix composition proves his advantage in case of obtained microstructures and additionally it seem to be very promising for obtaining a balanced duplex structure, also working with cycles easy to be introduced in industries. Originality/value: The utilization of sinter-hardening process combined with use of elemental powders added to a stainless steel base powder shows its advantages in terms of good microstructural homogeneity and especially working with cycles possible to introduce in industrial practice.
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Purpose: Purpose of this paper was to present the benefits of powder metallurgy technology and development of sinter-hardening process applied to different steels including pre-alloyed Ni-Mo steels with W addition, Astaloy CrM and experimental sintered duplex stainless steels. The mechanical properties, focusing in particular on hardness and wear resistance, of two different sinter-hardened steels were described. Microstructure characteristic of produced sinter-hardened steels was taken under consideration. Design/methodology/approach: Different compositions have been tested in order to investigate the influence of sinter-hardening of steels under different cooling rates on microstructure and properties. As a first group of materials Ni-Mo pre-alloyed steel powders were used, differing with the addition of tungsten and amount of carbon. Green compacts were sintered at the temperature 1120 degrees centigrade for 1 hour. The next set of investigated materials was produced by mixing the Astaloy CrM powder with carbon amount of 0.6% and then compacted and sintered in the same conditions. Under sinter-hardened conditions, experimental sintered duplex stainless steels were also evaluated. After sintering, different cooling rates were applied. Findings: The applied sinter-hardening process resulted with achievement of material characterized by proper microstructure. The investigation of sinter-hardened steels proved that applied process of sintering under vacuum and rapid cooling brought expected outcome. Research limitations/implications: Considering the achieved outcome, it was revealed that chemical composition and applied process of steels preparation, sinter-hardening with rapid cooling, results in achievement of materials with relatively high apparent hardness and significant resistance to abrasion. Anyhow, further researches should be performed. Originality/value: The paper contributes to better understanding advantages of sinter-hardening process applicable to different sintered steels.
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Purpose: of this paper was to describe sintered duplex stainless steels manufactured in sinter-hardening process and its usability in field of stainless steels. Design/methodology/approach: In presented study duplex stainless steels were obtained through powder metallurgy starting from austenitic, ferritic base powders by controlled addition of alloying elements, such as Cr, Ni, Mo and Cu. In the studies apart from the preparation of mixes, Schaeffler's diagram was taken into consideration. Prepared mixes have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at temperatures from 1200 to 1285 degrees centigrade for 0.5, 1 and 2 h. After sintering different cooling cycles were applied using nitrogen under pressure from 0.6 MPa to 0.002 MPa in argon atmosphere. Produced duplex stainless steels have been studied by scanning and optical microscopy and EDS chemical analysis of microstructure components. Findings: Obtained microstructure and mechanical properties of sintered duplex stainless steel strictly depend on the density and the pore morphology present in the microstructure and especially on cooling rate directly from sintering temperature in sinter-hardening process. The lowest cooling rate - applied gas pressure, the mechanical properties and corrosion resistance decrease due to precipitation of sigma phase. Proper bi-physic microstructure was obtained using nitrogen under pressure of 0.6 and 0.2 MPa. Research limitations/implications: Applied fast cooling rate seems to be a good compromise for mechanical properties and obtained microstructures, nevertheless further tests should be carried out in order to examine its influence on corrosion properties. Originality/value: The utilization of sinter-hardening process combined with use of elemental powders added to a stainless steel base powder shows its potentialities in terms of good microstructural homogeneity and especially working with cycles possible to introduce in industrial practice.
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Purpose: Purpose of this paper was to present the benefits of powder metallurgy technology and development of sinter-hardening process. The mechanical properties, focusing in particular on hardness and wear resistance, of two different carbon levels pre-alloyed steel powders processed with sinter-hardening method, were described. Microstructure characteristic of produced sinter-hardened Ni-Mo steels with increasing amount of tungsten (from 0 to 0.3% wt.) was taken under consideration. Design/methodology/approach: Different compositions have been tested in order to investigate the influence of various tungsten additions into low (0.4%) and high (0.6%) carbon content of pre-alloyed steel powders. Powders, with addition of 0.7% lubricant, were pressed in a 2000 kN hydraulic press. De-waxing process at 550 degrees centigrade for 60 minutes in a fully nitrogen atmosphere was performed before the sintering. Sinering was carried out in vacuum furnace with argon backfilling. The furnace was equipped with a cooling zone to provide accelerated cooling from the sintering temperature. Green compacts were sintered at the temperature 1120 degrees centigrade for 1 hour and rapidly cooled with a rate 2.5 degrees centigrade/s. Findings: The applied sinter-hardening process with achievement of material characterized by good wear resistance. The investigation of Ni-Mo and Ni-Mo-W sinter-hardened steels with low and high carbon content proved that applied process of sintering under vacuum and rapid cooling brought expected outcome. Research limitations/implications: Considering the achieved outcome, it was revealed that chemical composition and applied process of steels preparation, sinter-hardening with the cooling rate 2.5 degree centigrade/s, results in achieving materials with relatively high hardness and significant resistance to abrasion. Anyhow, further research should be performed. Originality/value: Sinter-hardening of Ni-Mo pre-alloyed powders with the addition of different additions of tungsten, especially in terms of hardenability and wear resistance, was investigated.
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Purpose: of this paper was to examine the influence of sintering parameters like time, temperature, atmosphere and gas pressure under cooling stage on the mechanical properties of duplex stainless steels. 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, such as Cr, Ni, Mo and Cu. In the studies behind the preparation of mixes, Schaeffler's diagram was taken into consideration. Prepared mixes have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at temperatures from 1200 to 1285 degrees centigrade for 0,5, 1 and 2 h. After sintering different cooling cycles were applied using nitrogen under pressure from 0.6 MPa to 0.002 MPa in argon atmosphere. Produced duplex stainless steels have been studied by scanning and optical microscopy and EDS chemical analysis of microstructure components. Mechanical properties have been studied through tensile test. Findings: Mechanical properties of sintered stainless steels are strictly connected with the density and the pore morphology present in the microstructure too and especially of cooling rate directly from sintering temperature. The lowest cooling rate - applied gas pressure, the mechanical properties decrease due to precipitation of sigma phase. Mechanical properties of studied steels depends on austenite/ferrite ratio in the microstructure and elements partitioning between phases too. Research limitations/implications: Applied fast cooling rate seems to be a good compromise for mechanical properties and obtained microstructures, nevertheless further tests should be carried out in order to examine it influence on corrosion properties. 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 microstructural homogeneity and first of all good mechanical properties was achieved, also working with cycles possible for industries.
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