| 1. |
- Chasoglou, Dimitris, et al.
(författare)
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Computational predictions with coupled experimental investigations of the effect of alloying elements on microstructure in PM-HIP alloys
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013. - : European Powder Metallurgy Association (EPMA). - 9781899072408
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Konferensbidrag (refereegranskat)abstract
- Steel produced by the PM-HIP route has a more homogenous microstructure compared with that obtained in conventionally produced material. This is an important advantage in many applications, and is therefore of interest to predict. The homogeneity of the microstructure is possible due to the rapid solidification of the powder grains in the atomization and the small size of the powder grains. Computational predictions of the variations of composition in powder grains, compacted material and conventionally produced material are compared with microstructure investigations. The microstructure is investigated in SEM with coupled composition analysis by EDS/WDS. The computational predictions are based on a description of the equilibria in the steel, and of the kinetics of segregation on solidification. The effect of alloying elements is discussed, and the effect in a stainless steel and in a tool steel is calculated.
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| 2. |
- Chasoglou, Dimitris, 1982, et al.
(författare)
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Effect of reducing agents on the sintering of chromium alloyed PM steels
- 2013
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Ingår i: Proceedings EURO PM2013 Congress & Exhibition, 15-18 September 2013, Gothenburg, Sweden. - : European Powder Metallurgy Association (EPMA). ; 2, s. 297-302
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Konferensbidrag (refereegranskat)abstract
- The control of the surface chemistry during sintering is the key factor for the successful and efficientproduction of PM parts, especially for powders containing elements with high affinity to oxygen such as chromium.The effect of different reducing agents was investigated by performing sintering trials on water atomized steel powder pre-alloyed with 3 wt.% Cr with and without the addition of graphite as well as using atmospheres with varying hydrogen content. The use of thermal analysis and photoacoustic spectroscopy in combination with results from fractographic investigation showed that oxide reduction is enhanced with the presence of hydrogen even if the main reduction mechanism is the carbothermal reactions. Oxides rich in Cr, Mn and Si were formed during sintering for all appliedconditions. The findings are summarized in a simple model describing the enclosure of oxides during the sinter-neckdevelopment and the changes in surface chemistry during the process.
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| 3. |
- Chasoglou, Dimitris, 1982, et al.
(författare)
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Optimisation of sintering atmospheres for controlled sintering of PM steels
- 2013
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Ingår i: Proceedings EURO PM2013 Congress & Exhibition, 15-18 September 2013, Gothenburg, Sweden. - : European Powder Metallurgy Association (EPMA). ; 2, s. 339-346
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Konferensbidrag (refereegranskat)abstract
- The use of elements with high oxygen affinity such as Cr or Mn in PM steels has been met with skepticism although such grades are attractive options for structural applications. They require strict control of the used atmosphere during the sintering process. Various techniques such asphotoacoustic spectroscopy (PAS) and continuous CO/CO2/H2O measurements have been implemented for atmosphere monitoring during sintering trials of Cr-alloyed steel powder. The used atmospheres were nitrogen-hydrogen blends (0,3,10 and 100% H2) as well as vacuum. The progress of the oxidation/reduction processes was also followed with thermogravimetric studies. The pressed and sintered samples were examined using optical and electron microscopy in combination with EDX in order to evaluate the formed reaction products. The presence of hydrogen, even in smallamounts, is positive for the oxide reduction. Results show that careful adjustment of the used atmosphere leads to efficient production of steel components based on Cr -prealloyed powders.
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| 4. |
- De Oro Calderón, Raquel, 1982, et al.
(författare)
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Introduction of Oxidation-Sensitive Elements in Low Alloyed Steels using the Master Alloy Route: Key Aspects for Success
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013; Gothenburg; Sweden; 15 September 2013 through 18 September 2013. - 9781899072408 ; 3, s. 337-342
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Konferensbidrag (refereegranskat)abstract
- Defining the proper conditions for sintering of steels containing oxidation-sensitive elements requires a deep understanding of the overall gas-gas and solid-gas reactions taking place especially during the heating stage of the sintering process. In this work, Mn and Si have been introduced in sintered steels in the form of a master alloy powder specifically designed to form a liquid phase. The effect of sintering atmosphere (Ar, H2 or N2-10H2) and carbon content on both reduction/oxidation reactions and dimensional stability were studied by advanced thermal techniques. Two different types of base powders (plain iron and Cr-prealloyed steel) were considered with the aim of understanding the effect of chemical interaction between base powder and master alloy. The results show how heterogeneity in chemical activity between the components of the mix modifies the overall reduction reactions, and how dimensional changes are importantly affected by the presence of reducing agents: either H2 from the atmosphere or carbon introduced as graphite.
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| 5. |
- De Oro Calderón, Raquel, 1982, et al.
(författare)
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New alloying systems for PM-steels: opportunities for the Mn-Si master alloys
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013; Gothenburg; Sweden; 15 September 2013 through 18 September 2013. - 9781899072408
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Konferensbidrag (refereegranskat)abstract
- Low alloyed steels containing innovative combinations of alloying elements have been produced though the master alloy route. Fe-Mn-Si master alloy systems were designed to enhance sintering by creating a liquid phase, and were manufactured by gas atomizing in N2. This paper presents an overview of the characteristics of steels modified with Fe-Mn-Si master alloys. Special focus is given to defining the proper conditions for sintering, and to analyzing the level of mechanical properties achievable with standard processing conditions. Although high temperatures (>1300 ºC) are required for reducing highly stable Mn-Si oxides, standard sintering cycles at 1120 and 1250 ºC yielded oxygen contents below 0.1 wt.% and 0.02 wt.% respectively, combined with competitive mechanical properties in the as sintered condition. UTS values around 600 MPa, elongations between 1-3%, hardness values of 200-350 HV10 and impact energies around 10-30 J can be obtain with less than 3 wt.% of alloying elements. Besides, a proper balance of swelling upon liquid phase formation and isothermal shrinkage provides dimensional changes below 0.1 %
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| 6. |
- De Oro Calderón, Raquel, 1982, et al.
(författare)
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Synthesis of Nanostructured Tungsten Carbide Powders from Mechanically Activated Mixes of Tungsten Oxide with Different Carbon Sources
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013; Gothenburg; Sweden; 15 September 2013 through 18 September 2013. - 9781899072408 ; 1, s. 89-94
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Konferensbidrag (refereegranskat)abstract
- Nanostructured WC powders which provide fine microstructures after sintering, can significantly improve mechanical properties of WC-based hard materials. Synthesis of such nanostructured WC powders from tungsten oxide has been achieved in presence of carbon by a two-step process: Mechanical Activation of initial powders (by milling), followed by Thermal Activation of the mixes. In the second step, the necessary reduction reactions followed by carburization reactions take place. The effect of both milling parameters and carbon source type on the effectiveness of the reduction-carburization reactions is studied in this work. The efficiency of the carburization process for synthesis of nanostructured tungsten carbide powders is discussed based on the effect of the type of carbon source used, and the characteristics of the milled powders.
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| 7. |
- Lyckfeldt, Ola
(författare)
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Powder rheology of steel powders for additive manufacturing
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013. - : European Powder Metallurgy Association (EPMA). - 9781899072408 ; , s. 29-36
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Konferensbidrag (refereegranskat)abstract
- The recent development of advanced rheometers for dry powders characterization has opened opportunities to accurately determine a variety of powder properties to be related to function in specific powder processes. In this study, steel powders aimed for additive manufacturing (AM) were exposed to various types of measurements such as basic flow ability, compressibility, aeration response and shear using a powder rheometer. The results showed that different batches of the same quality of stainless steel (316L) powders, with similar particle size distribution, vary significantly regarding the dry flow properties with critical impact on the function in AM. Differences in specific surface areas indicated variation in particle shape/roughness that could be correlated to rheometer data. Low compressibility, high aeration response and low shear resistance related to low degree of powder cohesivity was identified as favorable characteristics. Hence, powder rheology provides a powerful tool for powder quality control and to confirm processing performance.
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| 8. |
- Magnusson, Hans, et al.
(författare)
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An experimental and computational technique suitable for characterisation of oxides
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013. - : European Powder Metallurgy Association (EPMA). - 9781899072408
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Konferensbidrag (refereegranskat)abstract
- Understanding of oxide stability is important for processing of sintered steels. The stability of an oxide depends on the alloy composition, temperature and environment for oxidation. The type of oxide and its range of stability can be predicted by thermodynamic calculations. The reactive character of oxygen with metal is a natural difficulty for a thermodynamic study of oxides. In this work, an experimental and computational technique has been developed, allowing for an evaluation of oxide stability. Oxidation results of Fe-Cr-Mn-Si alloys in Ar/H2 atmospheres will be presented, and compared with calculations. Oxidised Fe-6Cr-3Mn-(0-0.1)Si alloys show mainly a spinel oxide with the formula (Fe,Mn)Cr2O4. Silicon is found in separate oxides, rather than combined Cr-Mn-Si oxides. At low partial pressures it appears to be quartz types of oxide SiO2, and at higher partial pressures olivine (Fe,Mn)2SiO4.
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| 9. |
- Tahir, Abdul Malik, et al.
(författare)
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Investigation of Cu distribution and porosity in Fe-2Cu and Fe-2Cu-0.5C compacts
- 2013
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Ingår i: International Powder Metallurgy Congress and Exhibition, Euro PM 2013. - : EPMA. - 9781899072408
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Konferensbidrag (refereegranskat)abstract
- The distribution of the alloying element Cu in steel compacts is important in determining the properties of the sintered products. In this work, mixtures of Fe-2Cu and Fe-2Cu-0.5C were compacted at 600 MPa and sintered at 1120oC for the holding times of ts= 3, 13, 23, and 33 min. Dilatometry and light optical microscopy is used to investigate porosity, Cu distribution and its effect on the dimensional changes during sintering. The result shows that the molten Cu penetrates into the Fe interparticle and grain boundaries in less then 3 min holding time at 1120°C, however C addition hinders the liquid penetration of Cu. Furthermore, it is found that the C-added compact has lower volume expansion and porosity compared to the C-free system, after 33 min of holding time at 1120°C.
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