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Volume 20, Issue 2
Displaying 1-4 of 4 articles from this issue
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Yoji Awano, Takashi Kimura1973 Volume 20 Issue 2 Pages 37-42
Published: June 25, 1973
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIn order to clarify the effect of impurities contained in sinterforged irons on the mechanical properties, studies were carried out under various conditions using five kinds of iron powder.
With the increase of the amount of nonmetallic inclusions, the tensile strength was little affected, but the elongation and reduction in area were linearly decreased, and the impact strength was more remarkably decreased. The impact strength was also affected by forging temperature and heating atmosphere. A peculiar phenomenon was observed in the sinterforged irons made at 900°C, in which the upper yield strength was higher than the ultimate tensile strength in the stress-strain curve.View full abstractDownload PDF (2901K) -
Hidenori Kuroki, Youichi Tokunaga1973 Volume 20 Issue 2 Pages 43-48
Published: June 25, 1973
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe purpose of present work was to evaluate the effects of molybdenum and nickel additions on impact properties of iron compacts, in relation to the activation of sintering process, to the solution hardening of ferritic matrix, and also to the decrease of ductile-brittle transition temperature.
Samples were prepared by compacting and sintering the reduced-ore iron powders (NC100⋅24) which contained either 1-8% of reduced molybdenum powders of 3μ in mean diameter, or 2-10% of carbonyl nickel powders of the same mean diameter. The pressing was performed under the pressure of 2-9 t/cm2 and the sintering for 1 hr at 1100-1350°C in hydrogen.
Results were summarized as follows:
The addition of molybdenum increased the impact strength above the transition temperature, as the result of a remarkable densification due to the activated sintering in a phase.
The addition of nickel decreased the impact strength above the transition temperature due to the superior effect of solution hardening.
The addition of both elements apparently reduced the ductile-brittle transition temperature. This reduction caused the increase of impact strength at room temperature, when 2% of nickel was added.
The abnormal brittleness, which was often observed in the impact test of high density sintered iron at room temperature, also appeared when 1-10% of nickel was added, but disappeared with the addition of 4-8% of molybdenum.View full abstractDownload PDF (1904K) -
Hidenori Kuroki, Youichi Tokunaga1973 Volume 20 Issue 2 Pages 49-54
Published: June 25, 1973
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSImpact strength of iron compacts, prepared from commercial powders by single compacting under the pressure of 2-9 t/cm2 and by sintering in hydrogen at the temperature range of 1100-1300°C for less than 1 hr, did not simply increase with densification at room temperature, but decreased in the density range around 7 g/cm3.
Three different mechanisms for the observed phenomena of abnormal brittleness were considered.
First, a shear crack could propagate through large flaky pores formed by the removal of pressed powder lubricants between iron particles. This type of brittleness disappeared after the elimination of flaky pores by sintering at higher temperatures for longer periods.
Second, an abnormal growth of ferritic grains could cause an increase of ductile-brittle transition temperature, together with the increase of porosity on grain boundary. This type of brittleness was the same as previously observed by the authors on double pressed materials, and it became remarkable with the progress of sintering.
Third, when the ductile-brittle transition occurred above room temperature, the impact strength of high density (above 7 g/cm3) sintered irons could become lower than that of lower density ones at room temperature, because the transition appeared more evidently with densification.View full abstractDownload PDF (3590K) -
Hisashi Suzuki, Teruyoshi Tanase, Kozi Hayashi1973 Volume 20 Issue 2 Pages 55-61
Published: June 25, 1973
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe structure and the thermal stability of ε' phase formed by the strain-induced transformation of binder phase near the ground surface-layer in WC-Co cemented carbide, have been investigated mainly by optical microscopy. For microscopic studies, two-phase WC-20%Co alloy specimens with high and low carbon contents and with coarse WC grains (-50μ) were sintered in vacuum at 1400°C for 1 hr. For X-ray studies, two-phase WC-45%Co alloy specimens with fine WC grains (-1.6μ) were sintered at low temperature around 1250°C to minimize the grain size of binder phase.
Results obtained were as follows: (1) The depth of layer of the ε' phase formed by grinding was naturally affected with cobalt contents, carbon contents and mean grain size of WC in the alloy. (2) The ε' phase was formed in a plate shape along slip bands in binder phase, suggesting that the habit plane of ε' phase is (111)γ. (3) The rapid growth of the phase due to annealing was observed at relatively high temperatures up. to about 400°C and 600°C in high carbon and low carbon alloys, respectively. The increased amount of the ε' phase seemed to be affected by the amount of ε' phase pre-existed and the grain size of binder phase. The above results were considered to have a close relation with mechanical properties of cemented carbide at these temperatures. (4) The precipitate of Co3W appearing by annealing low carbon alloy at high temperatures was usually observed along the ε' phase pre-existed.View full abstractDownload PDF (7159K)
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