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Microstructure evolution in warm forged sintered ultrahigh carbon steel

Szczepanik S., Nikiel P., Mitchell S. C., Kawalla R.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 2

301--307

EN

Fe–1.4C–0.65Si–0.85Mo ultrahigh carbon steel was liquid phase sintered in 10%H2–90%N2 at 1300 °C from Höganas Astaloy 85 Mo HP base iron, fine graphite and silicon carbide powders mixed with polypropylene glycol. The microstructure then comprised fine pearlite and grain boundary cementite networks and the density increased from ∼6.8 g cm−3 to ∼7.7 g cm−3. A group of specimens then underwent austenitisation, isothermal quenching/autotempering at M(10%) temperature, followed by cooling to room temperature. This produced a crack-free martensitic microstructure, which transformed to ferrite plus fine spheroidised carbides by annealing for 3 h at 750 °C. To attain full density and well-distributed submicron carbides, these specimens were warm forged at 700–750 °C. To ascertain if some processing steps can be discarded, as-sintered and quenched samples were similarly thermo-mechanically processed. The required stresses and resultant microstructures depended on temperature and strain rate, with optimum microstructure, for Bähr processing at 775 °C of quenched material, fully comparable with that of prior spheroidised specimens. Microstructures and hardness values are presented for all processing routes.

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Development of sintered Mn-(Mo)-(Cr)-C steels.

Mitchell S.C., Wronski A.S., Cias A.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

633-646

EN

The potential of manganese and chromium as alloying elements, reflected in their widespread use in wrought medium-to-high strength steels, is still to be realised in Powder Metallurgy alloys. The attempts to sinter Mn [+ Cr] alloys have largely ended in failure, due to either poor mechanical properties or lack of reproducibility. The authors have analysed previously published results and identified the principal reason as lack of process control: both in powder preparation and during sintering. This leads to large-scale oxidation, in the form of brittle networks, and also to lack of diffusion, due to the oxide film barriers. Reviewed now are the necessary processing conditions established for the successful processing of manganese steels. The development of additional chromium and molybdenum alloying is also considered and results are presented which additionally incorporate current areas of research, involving warm compaction, high temperature (including liquid phase) sintering and sinter and air hardening.

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Dimensional changes during sintering of manganese-carbon steel compacts.

Pieczonka T., Mitchell S.C., Ciaś A., Sułowski M., Wronski A.S.

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

1171-1174

EN

Sintering behaviour in high purity hydrogen of Hoganas NC 100.24 iron powder with carbon and two different types of ferromanganese additions was investigated. The influence of different manganese contents (3.0 and 4.0 wt.-%), type of ferromanganese used (low and high carbon) and isothermal sintering temperature (1120, 1240 and 1300 degrees centigrade) on dimensional changes was investigated by dilatometry. It is shown that the dimensional changes occuring during heating and isothermal sintering and the final density of sintered compacts are influenced by manganese and carbon through their interactions with base iron. The results assist in the choice of industrial sintering conditions when the requirement is very small dimensional changes of compacts for a range of manganese and carbon contents.