Processes in PM steel compacts during the initial stages of sintering

Danninger, Herbert; Gierl, Christian

doi:10.1016/s0254-0584(00)00419-3

Cited by 57 publications

(63 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These findings are in excellent agreement with the reduction processes observed by thermal analysis techniques (see Fig. 5a), which show two main reduction stages: the first one at *800°C corresponding with the reduction of the iron oxide layer covering most of the surface of the powder particles and the second one at *1100°C indicating the reduction of more stable oxides, or internal oxides that need higher temperatures to diffuse to the powder surface [1,2].…”

Section: °Csupporting

confidence: 89%

“…As observed in Fig. 3 Oxidation/reduction phenomena on steel powder mixes containing additions of different oxidationsensitive elements Thermal analysis techniques have been proved to be very efficient tools for studying the oxidation/reduction phenomena taking place when sintering steel powders [1,2,9,16,17]. Thermogravimetry curve and m28 (CO) signal-which is in all experiments considerably more intense than m44 (CO 2 )-are shown in Fig.…”

Section: °Cmentioning

confidence: 81%

“…Hydrogen is the most effective reducing agent at low temperatures, taking care of the reduction of iron oxides layers covering most of the surface of the steel powders at temperatures around 400°C. However, the reduction of more stable oxides, or internal oxides that need high temperatures to diffuse to the powder surface, necessarily takes place at higher temperatures at which the dominant mechanism is the carbothermal reduction [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

“…However, it is still not well known how the specific composition of the master alloy affects the oxidation/reduction phenomena and therefore how the processing conditions have to be adapted for these new materials. Thermogravimetry analysis coupled with mass spectrometry has proved to be the most effective method for analyzing the oxidation/reduction reactions at different stages of sintering [1][2][3]. Identification of critical temperature ranges with these techniques has provided the tools for an optimum design of the sintering cycles for conventional steels and even for Cr-prealloyed grades [1,[7][8][9].…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Application of thermal analysis techniques to study the oxidation/reduction phenomena during sintering of steels containing oxygen-sensitive alloying elements

Calderon

Gierl‐Mayer

Danninger

2016

J Therm Anal Calorim

Self Cite

View full text Add to dashboard Cite

For the consolidation of steel parts manufactured by powder metallurgy (PM) techniques, removal of the surface oxides covering metallic powder particles is a necessary prerequisite. In PM steels with conventional compositions, reduction of the oxides is easily achieved in traditional sintering furnaces. However, processing steels containing alloying elements with a high oxygen affinity represents a big challenge that requires a deeper understanding of the chemical processes occurring during sintering. In the present work, thermogravimetry analysis coupled with mass spectrometry is used to describe the oxidation/reduction phenomena that take place when sintering steel powders and how these processes are modified by the addition of admixed particles containing oxygensensitive elements. Carbothermal reduction processes are studied using pure oxides (Fe 2 O 3 , MnO 2 , Cr 2 O 3 and SiO 2 ) as well as water-atomized Fe powders mixed with small amounts-4 mass/%-of Cr, Mn and Si powders or FeMn-Si-(Cr) master alloy powders. The results show that there is an oxygen transfer from the base iron particles to the oxidation-sensitive elements-''internal getter effect''-taking place mostly through the gas phase. Different alloying elements (Cr, Mn, Si) show different temperature ranges of susceptibility to oxidation. Combination of these oxygen-sensitive alloying elements in the form of a master alloy powder reduces their sensitivity to oxidation. Also, the use of master alloys promotes the concentration of the oxides on the surface of the alloying particles and not in the grain boundaries of the surrounding iron particlesas occurs when using Mn carriers-which should have a beneficial impact on the final mechanical performance.

show abstract

Section: °Csupporting

confidence: 89%

Section: °Cmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Application of thermal analysis techniques to study the oxidation/reduction phenomena during sintering of steels containing oxygen-sensitive alloying elements

Calderon

Gierl‐Mayer

Danninger

2016

J Therm Anal Calorim

Self Cite

View full text Add to dashboard Cite

show abstract

“…The densification behaviour of powder particles in the examined alloy is complicated due to the large surface area and associated oxide layers. Formation of transient liquid phase, according to (Danninger & Gierl, 2001), enhances homogenization of the alloying element, mainly magnesium and copper, by accelerating material transport through spreading of the melt in the pore network and the pressing contacts and by increasing the diffusional cross-section. The results presented in Table 6 show values of theoretical density in different processing conditions as well as densification behaviour Ψ.…”

Section: Fig 10 Oxide Layer Covering Aluminium Particlesmentioning

confidence: 99%