| 1. |
- Chasoglou, Dimitris, 1982, et al.
(författare)
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Effect of Atmosphere Composition on the Surface Interactions during Sintering of Chromium-alloyed PM Steels
- 2011
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Ingår i: Proceedings of EURO PM 2011 International Powder Metallurgy Congress & Exhibition, 9th-12th October 2011, Barcelona. - 9781899072231 ; 3, s. 111-117
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Konferensbidrag (refereegranskat)abstract
- Chromium is extensively used today in PM steels, nevertheless its high affinity to oxygen requires strict atmosphere control during the sintering process. Nitrogen-based atmospheres with different hydrogen contents (0, 3 and 10%H2) were used during sintering of chromium-alloyed water atomized steel powders with continuous atmosphere monitoring in the sintering furnace. Fracture surface of pressed and sintered specimens were studied using high resolution scanning electron microscopy (HRSEM) equipped with EDX in order to investigate the development and characteristics of the reaction products formed. The investigation was complemented with thermal analysis using DTA/TG. The formation of particulate reaction products containing strong-oxide forming elements such as Cr, Si and Mn was detected for all conditions. Enhanced oxide reduction was observed in samples processed in hydrogen containing atmospheres independently of the actual content. Obtained results show that significant reduction of the oxygen content can be achieved by adjusting the atmosphere purity/composition.
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| 2. |
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| 3. |
- Hryha, Eduard, 1980, et al.
(författare)
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Carbon Control in PM Sintering: Industrial Applications and Experience so Far
- 2012
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Ingår i: Proc. of EURO PM2012 Congress & Exhibition, 16-19 September 2012, Basel, Switzerland. - 9781899072231 ; 1, s. 265-270
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Konferensbidrag (refereegranskat)abstract
- Challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have tried to address the problem, many of these have rarely come to reality and become an industrial practice.The purpose of this article is to summarize these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. Considering an industrial practice perspective, the paper ensures the PM Industry with a fresh new look into the understanding of the furnace operations and provides recommendations to improve the control of the furnace conditions. As an example, existing furnace installation utilizing Linde SINTERFLEX technology allows monitor and/or control the furnace atmosphere. Article describes reduction of oxides and carbon potentials to enable optimization of the production parameters.
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| 4. |
- Hryha, Eduard, 1980, et al.
(författare)
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Delubrication of PM Components Based on Cr-Prealloyed Steel Powder – Chances and Risks
- 2011
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Ingår i: Proc. of EURO PM2011 Congress & Exhibition, 9-12 October 2011, Barcelona, Spain. - 9781899072231 ; 3, s. 105-110
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Konferensbidrag (refereegranskat)abstract
- Utilization of prealloyed powder grades for production of high-performance PM structural parts require reconsidering of specific stages of sintering process like debinding. Modern lubricants are complex organic compounds, decompositions of which leads to production of a number of species – from complex hydrocarbons to carbon oxides. Composition and amount of decomposition products are strongly determined by the temperature profile and processing atmosphere composition/purity. Uncontrolled delubrication process, especially in the case of the PM components containing elements with high-sensitivity to oxygen, can lead to considerable oxidation. Therefore, in-situ monitoring of the processing parameters during delubrication is presented utilizing commonly used in industry sensors (dew-point, CO2 and O2). Delubrication was monitored in a number of inert and reducing gases of the different purity. Based on the specimens analysis and gas monitoring profiles it is recommended to perform delubrication at the temperatures below 500°C in dry inert atmospheres in the case of ethylenbisstearamide-based lubricants.
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| 5. |
- Hryha, Eduard, 1980, et al.
(författare)
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Oxide Transformation during Sintering of Cr and Mn Prealloyed Water Atomized Steel Powder
- 2011
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Ingår i: Proc. of EURO PM2011 Congress & Exhibition, 9-12 October 2011, Barcelona, Spain. - 9781899072231 ; 1, s. 95-100
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Konferensbidrag (refereegranskat)abstract
- Water atomized steel powders, prealloyed with elements with high oxygen affinity like manganese and chromium, contain small amount of oxides on the initial powder surface and in its interior. Modern powder manufacturing routes allow industrial production of water-atomized steel powders of high purity. However, further oxide products formation and their transformation during consolidation process remain unclear. The present study deals with the modelling of oxides transformation in dependence on sintering atmosphere, temperature profile and powder composition based on the analysis of specimens from interrupted sintering trials using advanced analysis techniques (HRSEM+EDX). Results indicate that composition and especially amount of the oxide products are strongly determined by the conditions during heating stage. Controlled conditions allow to minimize formation of stable oxide products and so to lower sintering temperature/time for obtaining oxide-free sintered parts. Oxide transformation processes occur in accordance with the thermodynamic stability of oxides in the line Fe2O3→FeO→Fe2MnO4→Cr2FeO4→Cr2O3→MnCr2O4→MnO/MnSiOx→SiO2.
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| 6. |
- Oro, Raquel, et al.
(författare)
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Surface Analysis at Different Sintering Stages of Steel Compacts with Mn and Si
- 2011
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Ingår i: Proc. of EURO PM2011 Congress & Exhibition, 9-12 October 2011, Barcelona, Spain. - 9781899072231 ; 1, s. 113-117
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Konferensbidrag (refereegranskat)abstract
- The different stages of sintering have been studied for a gas atomized master alloy containing Fe-Mn-Si-C. Surface characterization and depth profiling of the master alloy powder was performed by meansof XPS. In order to understand the phenomena taking place at surface of the green parts, mixescontaining plain iron powder, master alloy and graphite were heated in high vacuum (10-6 mbar) atincreasing temperatures (400ºC, 600ºC, 800ºC, 1000ºC) and analyzed with XPS. The conditionsduring the heat treatments described seem to be reducing enough to remove part of the manganeseand silicon oxides present at the original surface when the annealing is performed at 800ºC and1000ºC. However, intensive manganese evaporation was observed when heating at 1000ºC. Whilethe amount of silicon cations on the surface decreases importantly from 800 to 1000ºC, the oxygenconcentration in the surface is very similar and this might point out to a recombination of Si cations toform complex Mn-Si oxides. The Mn/Si cations ratio registered indicates that the oxide formed at1000ºC could be the type MnSiO3.
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| 7. |
- Weddeling, Anna, et al.
(författare)
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Characterization of High-Mn-Cr Austenitic Steel Powder Fe-19Mn-18Cr-C-N
- 2011
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Ingår i: Proc. of EURO PM2011 Congress & Exhibition, 9-12 October 2011, Barcelona, Spain. - 9781899072231 ; 2, s. 15-20
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Konferensbidrag (refereegranskat)abstract
- High strength Mn-Cr-austenitic stainless steel offers an appropriate and efficient alternative to Nibasedaustenitic steel. However, high oxygen affinity of manganese (Mn) and chromium (Cr) entailschallenges during manufacturing, handling and further consolidation of Cr- and Mn-rich steel powder.Thus, the composition of the surface of highly alloyed powder is the key parameter that determinespowder properties and usefulness. The surface layer of the gas-atomized high-strength austenitic steelFe-19Mn-18Cr-C-N powder was studied by means of surface analytical techniques (XPS and HR-SEMcombined with EDX). The XPS-study indicates the presence of relatively large manganese-rich oxideislands surrounded by a homogeneous iron-based thin oxide layer on the powder surface. Up to 7 nma zone enriched in chromium in oxide state is observed. HR-SEM images in combination with EDXverify the presence of large Mn-based oxide particulates on the powder surface. Obtained resultsemphasize the substantial effect of a high manganese content on the surface composition.
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| 8. |
- Weddeling, Anna, 1987, et al.
(författare)
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Influence of Nitrogen Atmosphere on Reduction Mechanisms of a High Strength Austenitic Steel
- 2012
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Ingår i: Proceedings EURO PM2012 Congress & Exhibition, 16-19 September 2012, Basel, Switzerland. - 9781899072231 ; 1, s. 375-380
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Konferensbidrag (refereegranskat)abstract
- High C+N-alloyed austenitic steels feature outstanding mechanical properties with tensile strength of more than 1000 MPa and uniform elongation up to 75 %. These properties are achieved by an optimal C/N-ratio. Cast production limits the nitrogen content, since the melt features a significantly lower solubility than the solid state. Current investigations aim to adjust the nitrogen content by sintering atmosphere in the steel FeMn19Cr17C0.4N0.3. The gas-solid interaction is crucial also for the reduction of surface oxides, especially those formed by chromium and manganese, which can deteriorate the toughness of the sintered part. This study clarifies the influence of nitrogen atmosphere on surface properties during the heating stage of the sintering cycle up to 800°C. Investigation was done by surface analytical techniques (XPS and HR-SEM). The influence of nitrogen atmosphere on reduction mechanism and the resulting impact on nitrogen uptake are evaluated under consideration of previous studies.
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