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枝晶形貌是影响铸坯元素分布、缩孔缩松及性能的重要因素,细化枝晶能够有效提高铸坯质量。研究了PMO处理对42CrMoA钢?300 mm连铸圆坯枝晶形貌的影响。研究发现,PMO处理坯的柱状枝晶生长方向发生偏转,枝晶臂间距明显减小,其中一次枝晶臂间距减小率为10%~35%,二次枝晶臂间距减小率为25%~35%。分析认为,PMO造成凝固前沿热流方向及溶质场变化,导致枝晶重新竞争生长,因此一次枝晶生长方向发生改变,且一次枝晶臂间距减小。另外,PMO在铸坯凝固前沿形成感生电流,固液相电导率差异造成枝晶尖端电流聚集,进而导致曲率半径增大,降低了细枝晶的溶解速率,抑制了二次枝晶的熟化过程,因此二次枝晶臂间距减小。研究结果为今后利用PMO改善铸坯枝晶组织提供了指导。 相似文献
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铸坯高中心等轴晶率及小的二次枝晶臂间距有利于降低高碳钢M+E-EMS连铸坯中心偏析。通过建立GCr15钢220 mm×260 mm连铸坯耦合有限元-元胞自动机模型(CAFE)及二次枝晶臂间距(SDAS)模型,研究结晶器电磁搅拌、过热度和拉速对中心等轴晶率及二次枝晶臂间距的影响。结果表明,相比于拉速,过热度和结晶器电磁搅拌对其影响明显。随着过热度降低及结晶器电磁搅拌强度增加,铸坯中心等轴晶率增加而二次枝晶臂间距减小,而拉速对凝固终点和中心固相率影响大。工业试验结果表明,采用结晶器与凝固末端电磁搅拌,相比于过热度35℃和拉速0.75 m/min,控制过热度小于25℃且拉速调整为0.8 m/min时,轴承钢GCr15铸坯中心等轴晶率由原27%增加至38%且二次枝晶臂间距细化,中心碳偏析指数由原1.06~1.39降至0.93~1.13。 相似文献
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为了研究铝合金定向凝固组织的变化规律,采用有限元软件ProCAST对Al Si Cu合金定向凝固过程进行模拟,分析了不同浇注温度和抽拉速率对铸件定向凝固过程中的温度梯度、固液界面前沿、糊状区宽度、枝晶生长速率和二次枝晶臂间距的影响。结果表明,当浇注温度越高时,温度梯度越大,而固液界面前沿下凹越小,糊状区宽度也越窄,从而越有利于顺序凝固的发生;随着抽拉速率的增大,枝晶生长速率先增大后减小,当抽拉速率为200 μm/s时,最大生长速度达到0.093 mm/s,铸件凝固组织最佳;当抽拉速率大于300或小于200 μm/s时,都会导致枝晶生长速率缓慢,枝晶生长不平稳,二次枝晶臂粗大。对模拟得到较优的工艺参数进行试验验证,可以制备出具有较好力学性能的铸件。 相似文献
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针对某钢厂GCr15钢连铸坯质量问题,利用实验室试验和Pro CAST模拟软件对连铸坯二次枝晶臂间距进行研究,分析过热度、拉速和二冷水量对二次枝晶臂间距的影响,并进一步探究碳偏析与二次枝晶臂间距的关系。结果表明,铸坯二次枝晶臂间距从铸坯表面到中心呈先增大后减小的趋势,与Pro CAST模拟结果基本一致。降低过热度和拉速、增大二冷水量均有助于减小二次枝晶臂间距;为了提高连铸坯质量,建议将过热度、拉速和二冷水量分别控制在20℃、0.45 m/min、0.32 L/kg左右。铸坯碳偏析最大值位于柱状晶向等轴晶转变区域(CET)。 相似文献
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分析了55SiMnVB弹簧钢铸坯的凝固组织,测定了树枝晶二次枝晶臂间距,同时对铸坯中的非金属夹杂物了金相形貌的观察与复写,结果表明,55SiMnVB弹簧钢铸坯的凝固组织较疏轻,二次枝晶臂间距较一般合金结构钢小(100~250μm);激冷层较薄(6~8mm);中心等轴晶率低(20%~26%),铸坯夹杂物含量偏高(0.71%~1.28%),降低钢液过热度和提高凝固末端电磁搅拌强度,对减轻偏析,提高中心 相似文献
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《河南冶金》2017,(6)
采用定向凝固技术结合光学显微镜对Fe-Mn-C-Al系TWIP钢的枝晶生长行为进行了研究,通过建立不同的数学模型对生长速率为25μm/s、50μm/s、100μm/s定向凝固TWIP钢试样中的一次和二次枝晶臂间距进行了预测,并与实验结果进行了比较,结果发现,在实验速度范围内,实验用钢的凝固组织都为枝晶组织,并且随着抽拉速度的增加,枝晶被明显细化。3种一次枝晶臂间距模型的计算值与实验值的综合误差率分别是22.45%、35.64%、78.49%,其中Hunt模型预测效果最好。3种二次枝晶臂间距模型的计算值与实验值的综合误差率分别是8.27%、19.70%、41.94%,其中Masana Imagumbai模型可以准确的预测SDAS值。 相似文献
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通过对焦炭在高炉内的历程及其变化规律的剖析,阐述焦炭热性能指标的意义,形象地把焦炭在高炉内的损耗分为三部分(M1,M2,M3)。指出M2对焦比及焦炭价格有一定的指导作用。 相似文献
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K Ohta M Nishi M Ueda S Ohyama T Matsubara T Takahashi T Nakajima 《Canadian Metallurgical Quarterly》1998,99(9):589-594
Cancer of the cardia is traditionally discussed with cardiac cancer of the lower portion of the esophagus and upper gastric cancer invading the esophagus, and the specific characteristics of cancer of the cardia have never been clearly defined. We reviewed the outcome of 172 patients with adenocarcinoma of the cardia who had undergone radical surgery between 1949 and 1994 in the Division of Gastrointestinal Surgery of the Cancer Institute Hospital. The centers of the tumors were located within 2 cm above and below the boundary between the esophagus and the stomach, and their longitudinal diameter was less than 8 cm. We divided the patients into an early period (1949-1979; n = 79) and a late period (1980-1994; n = 93), and focused on the historical transition. There were no differences in patient gender or histology between the two periods. However, the late period was associated with fewer cases of esophageal invasion and shorter longitudinal diameter, as the age of the population advanced. The number of advanced cancers such as the localized and infiltrative type had decreased, and early cancer and early clinical stage had become more common, but despite the fact that the number of early cancers had increased, extended dissection, such as thoracic and paraaortic lymph node dissection, was performed more frequently. By clinical stage, the long-term outcome markedly improved in Stage I patient in the late period, and tended to improve in Stage II and III patients. This appears to have been attributable to the prevention of micrometastasis by extended dissection, although the number of early cancers is another major potential cause. There were no differences in the outcome of Stage IV patients between the two periods, and further advances in multimodality therapy must be awaited. The range of resection is basically proximal gastrectomy, and if there are adequate indications, the prognosis is favorable. In view of the status of lymphatic flow and lymph node metastasis, and long-term results, lateroaortic lymph node dissection is important. Since the number of early cancer patients has been increasing, if intraabdominal recurrence is prevented, intrathoracic lymph node dissection will contribute greatly to the outcome of such patients. 相似文献
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Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed. 相似文献
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TA Solokhina LS Shevchenko IuV Se?ku EG Rytik LV Besedina TS Veshchugina 《Canadian Metallurgical Quarterly》1998,98(6):42-46
Usage of quality of life of psychiatric patients' relatives as the parameter of estimation of the quality of psychiatric care is considered. By means of standard questionnaire elaborated by the authors as well as by means of both individual and group conversations the quality of life was analyzed in 40 relatives which lived together with psychiatric patients. Different spheres of their life and difficulties (financial, social-psychologic, production) were examined in families with such patients. The defects of psychiatric care that had direct influence on the quality of life of the psychiatric patients' relatives are outlined. 相似文献
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