Studying the Progress of Sintering in Ferrous Powder Compacts by In-Situ Measuring the Thermal Conductivity

Danninger, Herbert; Leitner, G.; Gierl‐Mayer, Christian

doi:10.1515/pmp-2018-0009

Cited by 11 publications

(17 citation statements)

References 18 publications

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“…In contrast to the pronounced differences of the nitrogen content (by a factor of about 250), the oxygen content is virtually identical, proving that carbothermal reduction of the oxides is not affected by the atmosphere, which agrees with previous experiments (see e.g. [5,24]). Tab.1.…”

Section: Sintering Studiessupporting

confidence: 91%

“…Different amounts of carbon were added, namely in a first run a higher content of 0.7% and then 0.08 and 0.3%C (all concentrations given in mass%). The 0.08%C was added to obtain a well sintered material with hardly any oxygen (carbon being required as reducing agent, see [5]) and as low content of carbon as possible after sintering. The higher contents were chosen to check if there are any interactions between carbon and nitrogen in the material.…”

Section: Methodsmentioning

confidence: 99%

“…rapidly cooled after sintering [26,27], and therefore the critical reaction "window" for N pickup is passed very fast. However, it should also be considered that furnaces with rapid cooling facility usually operate at 1120°C while the high temperature sintering furnaces, which are particularly well suited for sintering of such steels [4,5], have much lower cooling rates, resulting in more pronounced N pickup. Furthermore, the Cr-Mo steels are also attractive for use in surface densified gears [28] which must not be sinter hardened to retain their deformability, thus being cooled slowly through the critical T range.…”

Section: Sintering Atmospherementioning

confidence: 99%

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Reaction of Unalloyed and Cr-Mo Alloyed Steels with Nitrogen from the Sintering Atmosphere

Dlapka

Gierl‐Mayer

Calderon

et al. 2016

Powder Metallurgy Progress

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Nitrogen is usually regarded as an inert sintering atmosphere for PM steels; however, this cannot be taken for granted in particular for steels alloyed with nitride forming elements. Among those elements, chromium has become more and more important as an alloying element in sintered low alloy structural steels in the last decade due to the moderate alloying cost and the excellent mechanical properties obtainable, in particular when sinter hardening is applied. The high affinity of Cr to oxygen and the possible ways to overcome related problems have been the subject of numerous studies, while the fact that chromium is also a fairly strong nitride forming element has largely been neglected at least for low alloy steel grades, although frequently used materials like steels from Cr and Cr-Mo prealloyed powders are commonly sintered in atmospheres consisting mainly of nitrogen. In the present study, nitrogen pickup during sintering at different temperatures and for varying times has been studied for Cr-Mo prealloyed steel grades as well as for unalloyed carbon steel. Also the effect of the cooling rate and its influence on the properties, of the microstructure and the composition have been investigated. It showed that the main nitrogen uptake occurs not during isothermal sintering but rather during cooling. It could be demonstrated that a critical temperature range exists within which the investigated CrM-based steel is particularly sensitive to nitrogen pickup.

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Section: Sintering Studiessupporting

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Section: Sintering Atmospherementioning

confidence: 99%

See 1 more Smart Citation

Reaction of Unalloyed and Cr-Mo Alloyed Steels with Nitrogen from the Sintering Atmosphere

Dlapka

Gierl‐Mayer

Calderon

et al. 2016

Powder Metallurgy Progress

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show abstract

“…If such a powder compact is studied by thermoanalytical techniques, and the gaseous species formed during sintering are analysed by MS, characteristic reduction 'windows', temperature intervals, are identified in the heating section of the run, which can be detected by the mass signals of the reduction products, m18 for H 2 O and m28 for CO. In principle, CO might also indicate N 2 since the mass number is the same, but CO and N 2 can be easily distinguished by tracking also m12 and m14, respectively, since it has been shown that if CO is formed, the m12 graph is virtually a copy of that for m28, just with lower signal intensity [18].…”

Section: Compacts From Chemically Homogeneous Metallic Systemsmentioning

confidence: 99%

Chemical reactions during sintering of PM steel compacts as a function of the alloying route

2018

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Due to their large specific surface, powders and powder compacts typically contain significant amounts of oxygen which has to be removed in the early stages of sintering. In the present study, it is shown that the homogeneity/heterogeneity of the oxygen affinity within the compact, which depends on the alloying route chosen, strongly affects the de-oxidation process. For several types of alloy steels, it is shown that systems alloyed through the mixing or master alloy route and containing elements with widely varying oxygen affinity exhibit oxygen transfer reactions through the internal gas phase. For pre-alloyed grades, in which the oxygen affinity is homogeneous, i.e. consistent between the powder particles, transfer reactions occur rather within the metallic particles themselves. In any case, the sintering temperature should be selected such as to grant reduction also of the most stable oxides contained.

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“…[6] Two main problems arise from the presence of surface oxides: 1) oxide layers on the metal powders hamper the progress of neck formation during sintering, because the diffusion of metal atoms through the oxide layers around the metal particles is the rate-determining factor during consolidation progress. [9][10][11] 2) In addition, non-metallic inclusions formed during sintering degrade the material properties of the final product as compared with a bulk material without imperfections. [12,13] The use of pre-alloyed powders is particularly sensitive for surface oxide formation as compared with the sintering of powder mixtures.…”

Section: Introductionmentioning

confidence: 99%

Investigations on Oxide Particles Formed during Sintering of CrMnNi‐Transformation‐Induced Plasticity (TRIP) Steel Powder Metallurgically Materials Using Automatic Feature Analysis

et al. 2020

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The combination of powder metallurgical and ceramics-derived processing enables the manufacturing of innovative metal components. Using high-alloyed transformation-induced plasticity (TRIP) steels facilitates the manufacturing of metal components with outstanding mechanical properties for advanced load applications. The oxygen affinity of some alloying elements promotes the formation of non-metallic particles during sintering, which deteriorate the mechanical properties. Bulk specimens are prepared from a 17Cr7Mn6Ni-TRIP steel powder using a ceramics-derived extrusion process with organic binders at ambient temperature. Processing comprises the thermal binder removal in air and the sintering in pure argon or hydrogen atmospheres. The sintered specimens are analyzed for their amount and composition of non-metallic particles using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The focus of this article is on the automated particle identification and analysis using an automatic SEM-EDS-related device. The automatic feature analysis provides statistical information on the chemistry, size, and morphology. The particles mainly consist of Cr, Mn, Si, and O forming Mn 2 SiO 4 and MnCr 2 O 4. The number of particles mainly depends on the debinding temperature and on the sintering atmosphere. The use of a pure hydrogen sintering atmosphere significantly depresses the formation of MnCr 2 O 4 , whereas silicates remain stable under the applied atmospheric and thermal conditions.

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Studying the Progress of Sintering in Ferrous Powder Compacts by In-Situ Measuring the Thermal Conductivity

Cited by 11 publications

References 18 publications

Reaction of Unalloyed and Cr-Mo Alloyed Steels with Nitrogen from the Sintering Atmosphere

Reaction of Unalloyed and Cr-Mo Alloyed Steels with Nitrogen from the Sintering Atmosphere

Chemical reactions during sintering of PM steel compacts as a function of the alloying route

Investigations on Oxide Particles Formed during Sintering of CrMnNi‐Transformation‐Induced Plasticity (TRIP) Steel Powder Metallurgically Materials Using Automatic Feature Analysis

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