共查询到16条相似文献,搜索用时 149 毫秒
1.
通过分析不同成分球铁磨球零件性能和金相组织,对金属型磨球的非平衡凝固特性进行了较深入的研究.试验结果发现,过共晶球铁凝固时出现非平衡奥氏体;亚共晶球铁出现非平衡渗碳体相和晕圈铁素体;在柱状晶与等轴晶过渡区中存在着夹杂和偏聚物.为改善球铁磨球的显微组织及性能,球铁成分应控制在共晶或稍过共晶范围. 相似文献
2.
利用彩色金相对过共晶和亚共晶球铁磨球五组试样进行了试验对比。对金属型球铁磨球高温凝固的动态过程及其结晶组织的形态进行了深入分析,讨论了平衡结晶组织与非平衡结晶组织的差异,探讨了金属型球铁磨球非平衡凝固的特性。 相似文献
3.
金属型亚共晶球铁凝固特点的研究 总被引:2,自引:0,他引:2
对金属型浇注亚共晶球铁磨球的凝固特点进行了研究,在型壁激冷及高Si成分作用下,亚共晶球铁结晶时形成的晕圈铁素体较肥大,或成团块分布在球墨四周,或多个晕圈连成一片,造成基体碳量局部降低和波动。非平衡凝固时,亚共晶成分析出非平衡渗碳体,造成结晶组织异常分布;非平衡溶质稀土镧形成的碳化镧在晶界的编聚,引起晶内基体碳含量的降低,对球铁零件的结晶组织和力学性能产生不良影响。 相似文献
4.
过共晶球铁凝固过程中奥氏体的生长方式与形貌特征 总被引:1,自引:0,他引:1
采用着色腐蚀技术显示出过共晶球铁中的高温凝固组织,观察分析过共晶球铁凝固过程中奥氏体的生长方式与形持征。结果表明:在非平衡凝固条件下,过共晶球铁凝固时通常会析出初生枝晶和晕圈枝晶,其形成条件主要与冷却速率和熔体的过冷有关。随铸件模数Mc增大,枝晶数量减少,二次臂间距显著增大,形态趋于不发达,由初生枝晶向晕圈枝晶过渡。当Mc≤0.3cm时,二次臂间距的实测值与理论预测值基本吻合。初生石墨球周围往往形成环状封闭奥氏体壳;共晶前期石墨球周围形成封闭或不封闭的框架奥氏体壳;共晶后期石墨球往往被周边生长着的共晶奥氏体所包覆,最终成为共晶奥氏体的一部分。 相似文献
5.
对球磨机中磨球的工作情况、受力情况及失效形式进行了分析研究。为克服磨球在使用过程中性脆、耐磨性不好的缺陷,根据金属型球铁磨球非平衡凝固特性.提出了金属型球铁磨球的工艺设计方案。 相似文献
6.
朱煜明 《特种铸造及有色合金》1999,(3):58-60
细化共晶团是提高球铁综合力学性能的有效途径。加快铁水凝固的冷却速度就可以实现共晶团的细化。金属型铸造可以加快冷却速度,但是由于冷速过快,容易使球铁铸件出现白口;同时也由于金属型直接与铁水接触,影响金属型的使用寿命,造成铸件生产成本增加。金属型覆砂工艺... 相似文献
7.
金属型球铁磨球凝固时偏聚物和夹杂定位的研究 总被引:5,自引:0,他引:5
金属型球铁磨球凝固时存在非平衡异晶相。它不参与柱状晶成形,以自身晶相形态结晶,一部分被柱状晶偏聚到最后凝固区(LTF)的夹杂团块上。非平衡溶质La偏析在局部晶界上,而多数La汇集成夹杂团块。偏聚物和夹杂团块最后分布在柱状晶-等轴晶间的过渡区上。 相似文献
8.
9.
10.
考察了Cu-1.7%Cr过共晶合金的定向凝固组织,对过共晶组织中出现亚共晶合金的初生α相的生长进行了探讨.研究表明:Cu-1.7%Cr过共晶合金定向凝固组织由初生β相、α相和(α-β)共晶组成;α相和(α+β)共晶的成分较大偏离平衡相图中的各相成分;初生β相分布在α相基体上.Cu-1.7%Cr凝固组织中α相的形成是非平衡凝固过程中枝晶α相和共晶相之间竞争生长的结果.α相是一种非平衡凝固组织,(α+β)共晶是偏离了平衡共晶成分的伪共晶组织.随着冷却速率的增加,α相的形貌尺寸减小,而数量有所增加. 相似文献
11.
Most lost-foam casting processes involve non-equilibrium solidification dominated by kinetic factors, while construction of a common dynamic solidification curve is based on pure thermodynamics, not applicable for analyses and research of non-equilibrium macro-solidification processes, and the construction mode can not be applied to nonequilibrium solidification process. In this study, the construction of the dynamic solidification curve (DSC) for the nonequilibrium macro-solidification process included: a modified method to determine the start temperature of primary austenite precipitation (TAL) and the start temperature of eutectic solidification (TES); double curves method to determine the temperature of the dendrite coherency point of primary austenite (TAC) and the temperature of eutectic cells collision point (TEC); the "technical solidus" method to determine the end temperature of eutectic reaction (TEN). For this purpose,a comparative testing of the non-equilibrium solidification temperature fields in lost-foam casting and green sand mold casting hypoeutectic gray iron was carried out. The thermal analysis results were used to construct the DSCs of both these casting methods under non-equilibrium solidification conditions. The results show that the transformation rate of non-equilibrium solidification in hypoeutectic gray cast iron is greater than that of equilibrium solidification. The eutectic solidification region presents a typical mushy solidification mode. The results also indicate that the primary austenite precipitation zone of lost-foam casting is slightly larger than that of green sand casting. At the same time, the solid fraction (fs) of the dendrite coherency points in lost-foam casting is greater than that in the green sand casting.Therefore, from these two points, lost-foam casting is more preferable for reduction of shrinkage and mechanical burntin sand tendency of the hypoeutectic gray cast iron. Due to the fact that the solidification process (from the surface to center) at primary austenite growth area in the lost-foam cylinder sample lags behind that in the green sand casting,the mushy solidification tendency of lost-foam casting is greater and the solidification time is longer. 相似文献
12.
HAN Qiyong YANG Ping SONG Weixi University of Science Technolonology Beijing Beijing China Division of Metallography Dept.of Materials University of Science Technology Beijing Beijing China 《金属学报(英文版)》1989,2(10):230-234
The distribution of subversive element sulfur in high temperature phases during solidificationof cast iron was investigated by means of liquid quenching method and autoradiography.Theresults show that in grey cast iron,sulfur is concentrated in the liquid,flake graphite and in theperipherial area of D-type supercooled graphite eutectic cells,but less sulfur is in austenite.Besides,the content of sulfur in A-type graphite is higher than that in D-type graphite,andsulfur content in eutectic austenite is a little higher than that in primary austenite.While,innodular graphite cast iron less sulfur is in liquid and austenite,but more in nodular graphite.The blackness of the spots on the emulsion film corresponds to the atomic percentage ofradioactive substances located on the surface of the specimen. 相似文献
13.
14.
影响铸铁凝固组织的隐形因素(Ⅰ) 总被引:1,自引:3,他引:1
铁液在高于某一温度时,有利于Fe3C生成;在低于某一温度时,Fe3C不稳定,有自发分解为Fe和C的倾向。其临界温度受化学成分及其它因素的影响。铸铁的遗传性包含结构信息保留、成分遗传效应和物性特征保存。更换炉料、多种炉料搭配使用、进行针对性处理、熔液过热等是改善不良遗传性的途径。在同一温度条件下,石墨在熔液、奥氏体和铁素体中的溶解度都比渗碳体的溶解度低;奥氏体-石墨共晶和共析反应温度也都高于奥氏体-渗碳体的共晶和共析反应温度。硅有利于石墨的析出,使Fe—Fe3C介稳定系向Fe—C稳定系转变。所有石墨化元素均降低介稳定共晶温度,而提高稳定共晶温度,并使两者间距扩大。凝固相图反映铸铁在实际条件下的温度-成分-组织关系,其特征界限可依熔化工艺、熔液处理、冷却速度的改变而移动。商业铸铁实际上都在非平衡冷却条件下按共生区概念依凝固相图进行凝固。在过冷条件下,即使是共晶或过共晶成分铸铁,其组织中也可能存在亚共晶枝晶(奥氏体)。 相似文献
15.