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Six thin sections of spheroidal graphites in cast iron have been investigated by TEM and SEM.Thespheroidal graphites consist of two or three layers and have nuclei which are composed of Ce_2O_2S and Ce_2O_3.Cerium is existed ont only in nuclei,but also in central layer and middle layer of graphite. 相似文献
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Jon Sertucha Jacques Lacaze Susana Armendariz Peio Larrañaga 《Metallurgical and Materials Transactions A》2013,44(3):1159-1162
To study the formation of chunky graphite (CHG) in heavy section castings, 68 nodular cast irons of both pearlitic and ferritic grades were cast in cubic blocks 30 cm in edge. The volume fraction of the blocks affected by this degenerate graphite was quantified and related to the chemical analysis of the materials by means of a multivariate analysis. For the composition domain investigated, the effects of Ce, Cu, La, P, Sb, and Sn were statistically established with a high R 2 correlation coefficient. 相似文献
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K. Theuwissen J. Lacaze L. Laffont J. Zollinger D. Daloz 《Transactions of the Indian Institute of Metals》2012,65(6):707-712
It is well-known that if certain trace elements are present in cast iron melts the morphology of the graphite precipitates can be altered. In order to understand the effect of doping elements on primary growth of graphite, pure Fe?CSb alloys were prepared by induction melting. They were then placed in graphite crucibles and heated to a temperature above the Fe?CC eutectic so that the charge became saturated in carbon and melted. To obtain Fe?CCe alloys, metallic Ce was added at the bottom of a graphite crucible and covered with iron, and then heated as for the Fe?CSb charge. In both cases, the melt was then cooled and held slightly above the eutectic temperature so that primary graphite crystals, which had nucleated on the crucible walls and then detached from it, could grow freely in the melt. The influence of the added elements on graphite growth was revealed by the change in the shape and distribution of the crystals compared to those obtained in similar experiments carried out with pure Fe. The experiments were made in air and vacuum so as to point out possible interactions between the elements present in the melt and oxygen. 相似文献
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The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively
studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation
behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different
cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels
corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects
of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent
decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared
to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast
irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents
relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite
phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able
to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron. 相似文献
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The high temperature properties of steels depend on the solidification parameters and the formation parameters of manganese sulphide precipitates. Therefore, the occurrence of MnS precipitations in relation to primary and secondary microstructures was studied for different steel grades with a primary delta‐ferritic solidification or a primary austenitic solidification. The liquidus and solidus temperatures as well as the δ‐γ‐transformation temperature were calculated thermodynamically and measured by a DTA analysis in order to describe the solidification and transformation temperature range. The MnS formation temperature was calculated thermodynamically and compared to the results of SEM/EDX investigations on fracture surfaces of hot tensile specimens torn at different temperatures after in situ melting and controlled solidification. A special focus of these investigations was the location of MnS precipitates in relation to the primary and secondary grain boundaries. To explain the results, calculations were carried out taking into account the supersaturation of manganese and sulphur during the solidification in residual melt on the primary grain boundaries. 相似文献
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球墨铸铁轧辊的补缩,一般是采用砂型明冒口和浇注后每隔20-25分钟用过热铁水点冒口1-2次的办法解决,这样的工艺使冒口金属消耗量占轧辊毛重的15%左右。为了节约金属和提高轧辊上辊颈质量,本研究工作是采用铝型膨胀发热剂单独使用或与绝热套组合成的保温冒口,以取代原工艺以稻草灰覆盖的干砂型冒口。经过实验室及现场对此实验表明:采用保温冒口以后,球墨铸铁共晶凝固时间延长了33-62%,缩孔形状由倒锥形变为盆形,轧辊冒口的致密段高度增加,省去了用过热铁水点冒口的工序。冒口高度可以降低25~50%,节约冒口金属量20~50%。研究工作表明:采用保温冒口是解决球铁轧辊补缩的最合理、经济而简便的措施。 相似文献
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RoleofREandMgonGraphitizationofSpheroidalGraphiteMalleableCastIron¥LiuJin-Hai(HebeiInstituteofTechnotogy,Mianjin300130,China)... 相似文献
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W. J. Boettinger L. A. Bendersky R. J. Schaefer F. S. Biancaniello 《Metallurgical and Materials Transactions A》1988,19(4):1101-1107
Examination of the effect of rapid solidification velocity on the microstructure of Al-3.7 wt pct Ni-1.5 wt pct Fe has revealed
a new mechanism for the formation of discrete second phase particles in rapidly solidified alloys. Cellular growth of α-Al
occurs with the intercellular phase, Al9(Fe, Ni2 in two distinct morphologies. At low velocity (<50 cm/sec) the phase is continuous in the growth direction while at higher
velocity discrete rounded particles are observed. Analysis of the orientation relationship and the number of variants which
exists between phases leads to the proposal of a mechanism where liquid droplets are deposited by the grooves of a moving
cellular interface. These droplets solidify subsequently to form the rounded second phase particles. 相似文献
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试验研究了0.000 5%~0.001 2%Mg对60 kg真空感应炉熔炼的430铁素体不锈钢(/%:0.04C、0.25~0.32Si、0.28~0.38Mn、16.5~16.9Cr)夹杂物形成和凝固组织的影响。结果表明,430钢液中添加镁合金后,钢中形成平均粒径更小,数量密度更大的含MgO复合夹杂物;镁合金的加入可以改善430钢的凝固组织,且浇铸温度越低,改善效果越明显,在1 580℃浇铸时,等轴晶率由常规钢的30.8%提高至镁处理钢的88.5%,相应等轴晶尺寸由1 741.6μm降至945.3μm。含MgO夹杂物与δ相二维错配度极小,可作为430钢有效异质形核剂,促进等轴晶的形成,抑制柱状晶的生长,细化凝固组织。 相似文献
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For demanding applications high steel cleanliness and strictly controlled inclusions are required. Primary inclusions are formed during steel treatments in the ladle. Most of these are removed to the ladle slag or on the lining. However, the rest of the inclusions still remain through the successive process stages, and additionally new inclusions are formed during casting and solidification due to decreasing thermodynamic solubility of oxygen in the steel at lower temperatures, reactions with surrounding slag, refractory materials and eventual contact with air. Inclusions formation and transformation are simulated by thermodynamic calculations in the steel/inclusions/slag system taking into account the solidification phenomena. In this paper inclusions in Si/Mn‐deoxidised steel and Al‐deoxidised Ca‐treated steels are contributed. Calculations are compared with experimental results from steel plants. 相似文献
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A mechanism by which La modifies the Fe-bearing intermetallics in a 6xxx series Al alloy is examined using calorimetry. Thermal events accompanying the formation of various phases are identified by establishing a correspondence between them and microstructures of as-cast alloys. It is concluded that a previously suggested surface adsorption mechanism is unlikely to be operative. During solidification, the addition of lanthanum results in the formation of the La(Al,Si)2 phase and the depletion of the remaining melt of Si. It is hypothesized that the decreased Si/Fe ratio in the melt caused by the presence of La favors the formation of the α-AlFeSi phase, which is less detrimental to the formability of the alloy than the β-AlFeSi phase. 相似文献
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Andriollo Tito Lacaze Jacques Tiedje Niels 《Metallurgical and Materials Transactions A》2020,51(6):2685-2688
Thermal cycling of a high-silicon spheroidal graphite cast iron within the ferritic domain leads to coalescence of graphite particles with dendritic protuberances on the largest ones. This phenomenon occurs if there is some dissolution of graphite at the maximum temperature of the thermal cycle. Upon cooling, carbon redeposits in preferred locations, leading to the protuberances. This communication demonstrates that the ferritic matrix around the overgrowths can creep and remain in close contact with graphite.
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