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连铸板坯可能在板坯厚度的中央有一些裂纹,这些裂纹被称为中心裂纹。本文根据中心裂纹的调查研究和有关操作条件的分析结果,对中心裂纹的形成机理进行了论述,其结果概述如下:(1)中心裂纹是通过钢水凝固过程中被封闭在液态中心最后阶段的附近而形成的缩孔。(2)由模腔数据计算的封闭的钢水的厚度大约是6mm。(3)铸坯的缺陷周期间隔与在矫直点附近的辊子圆周相吻合。(4)当铸坯是在裂纹敏感区铸造时,中心裂纹是易于发 相似文献
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连铸坯裂纹成因及预防 总被引:2,自引:0,他引:2
梁伟红 《金属材料与冶金工程》2002,(1):28-31,42
分析了钢的高温力学性能和作用在连铸坯上的各种应力以及化学成分对铸坯产生裂纹的影响,指出裂纹产生的外因是钢水的静压力,热应力,组织收缩应力和其它外力的作用,当这些应力之和超过了钢的高温临界强度和变形量时,就在凝固前沿或凝固壳中产生裂纹,在二冷区凡是增加共内应力,降低强度和塑性的因素将促进裂纹的发生和扩展,裂纹产生的因是钢的高温力学性能和化学成分,提出了防止连铸坯产生裂纹应从两方面考虑,一是工艺参数和设备运转状态,设法降低连铸坯承受的应变和应变速率,二是钢的化学成分,提高钢水纯净度。 相似文献
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一、前言电磁搅拌技术早在1922年Mcneill就论述了熔融金属的流动对凝固组织、中心偏析和夹杂物分布的影响。1934年Bruchanov利用电转磁场研究了钢水的流动对凝固组织形态的影响,以及对减少钢中气体含量、改善 相似文献
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在大方坯、小方坯铸造中,为了防止中心偏析和中心疏松,在结晶器内和凝固末端,采用电磁搅拌使凝固组织等轴晶化,在凝固末期采用轻压下技术来防止凝固收缩时的钢水流动。但是对偏析晶粒影响很大的等轴晶率和等轴晶粒大小,因钢种、铸坯尺寸、铸造速度、钢水过热度及流动条件等会发生怎样的变化,目前还未建立定量的推定方法。 相似文献
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Electropulse modification (EPM) process, a new physical field method for improving the solidification structure of metals was introduced.Different from other research, EPM is only acting pulse current on melt under liquid state.The solidification structure of Al-Si alloys, A1-Cu alloys,cast iron and steel can be modified obviously with this method: the solidification structure of ZL101 alloy presented the Na and Sr modification and the mechanical properties were enhanced; a large number of primary silicon appeared in the microstructure of ZL109 alloy; the equiaxed grain zone was expanded and the grains were fined in Al-5.0wt% Cu alloy; the graphitization took place in solidification process of molten cast iron; the grain sizes of solidification structure of T8 steel were reduced significantly and the shape of steel pearlites also changed; the equiaxed grain zone increased to 88% from original untreated 19%, the equiaxed grains were fined and the intercrystalline crack was avoided in concasting billet by continuously treating liquid electrical sheet steel in tundish.Effects of rare earths on casting Al-Si alloys were also summarized.The method of modifying the solidification structure of rare earth Al-Si alloys with EPM in producing the alloys was proposed. 相似文献
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The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software.The actual and simulated solidification structures were compared under mold electromagnetic stirring (MEMS)conditions (current of 300 A and frequency of 3 Hz).There-after,the solidification structures of the large round billet were investigated under different superheats,casting speeds,and secondary cooling intensities.Finally,the effect of the MEMS current on the solidification structures was obtained under fixed superheat,casting speed,secondary cooling intensity,and MEMS frequency.The model accurately simulated the actual solidification structures of any steel,regardless of its size and the parameters used in the continuous casting process.The ratio of the central equiaxed grain zone was found to increase with decreasing su-perheat,increasing casting speed,decreasing secondary cooling intensity,and increasing MEMS current.The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity. 相似文献
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为了更为精细化地表达及控制铸坯质量,以H13模具钢电渣重熔铸坯凝固组织为研究对象,引入分形维数对其主体形貌特征进行定量描述。结果表明,基于数盒子法计算得到的分形维数可定量表征凝固组织形貌的自相似复杂程度,其值从柱状晶向中心等轴晶先减小后增大;凝固组织分形维数可作为衡量铸坯偏析程度(偏析率大小)的指标,且分形维数越大,对应区域偏析率越小,偏析越轻;通过凝固组织分形维数、偏析率和偏析点平均面积与二次枝晶间距关系的研究发现,使用二次枝晶间距表征铸坯凝固组织形貌差异并由此反映偏析程度的方法存在局限性。 相似文献
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《钢铁冶炼》2013,40(1):26-30
AbstractBased on the coupled method of cellular automaton (CA) and finite element (FE), the solidification structure of 160×160 mm cast billet of high carbon SWRH77B steel was simulated. The nucleation density, kinetics of the dendrite tip growth, crystallographic orientation and coupling of CA and FE methods are discussed. In the current study, the influence of superheat on the solidification structure of the billet is researched in detail. The results show that for an increase in superheat extent from 20 to 30°C, the density of grain in billet decreased from 4·662×106 to 3·087×106 m?2, and the grain mean radius increased from 295·1 to 346·3 μm. The three-dimensional microstructure of high carbon SWRH77B steel was simulated by the CAFE method, and there was good agreement with the results from industrial billet. 相似文献
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为改善20CrMnTi钢小方坯凝固组织,基于ProCAST软件中的CAFE模型,对其凝固组织进行数值模拟,研究了不同钢水过热度、铸坯拉速、二冷比水量对凝固组织的影响。模拟结果表明,降低钢水过热度、提高铸坯拉速、降低二冷比水量均可达到增大铸坯等轴晶率和细化晶粒的目的,其中过热度对其影响最大。过热度每降低10℃,等轴晶率平均增加3.7%;拉速每增加0.1 m/min,铸坯等轴晶率平均增加1.8%;比水量每降低0.1 L/kg,铸坯等轴晶率平均增加1.65%。生产应用表明,钢水过热度30℃时,当拉速由原2.2 m/min降低至2.1 m/min,二冷比水量由0.6 L/kg提高至0.7 L/kg,铸坯中心疏松明显减少。 相似文献
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Aiming at the process of electromagnetic continuous casting (EMCC), a three dimensional finite element model on electromagnetic field and temperature field was developed through the commercial software ANSYS to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in soft contact mold under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases of exciting current frequency and density make the effects of induction heat on solidification process increased remarkably. Especially, with the increase of exciting current frequency, the early solidification process and shell growth become non-uniform in billet circumferential direction. Morever, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is decreased greatly. 相似文献
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Hua-jie Wu Ning Wei Yan-ping Bao Guo-xin Wang Chao-ping Xiao Jin-jin Liu 《Canadian Metallurgical Quarterly》2011,18(2)
Effects of mold electromagnetic stirring (M-EMS) on the solidification structure of 45# steel billet were investigated by examination of interdendritic corrosion The results show that the primary and secondary dendrite arm spacings increase from the edge of the billet to the center and decrease obviously with increasing electromagnetic torque, which will be beneficial to refine the solidification structure and enlarge the equiaxed crystal zone. The ratio of equiaxed crystal increases by 15.9% with the electromagnetic torque increasing from 230 to to the central area, where the cooling rates are similar at different torques. The closer to the central area, the less the influence of M-EMS on the cooling rate is. The ratio of the primary to secondary dendrite arm spacing is approximately 2.0, namely, λ1 ≈2λ2, and is constant irrespective of the stirring intensity and position of the billet. Original position analysis (OPA) results indicate that the center segregation of the billet is greatly improved, and the more uniform and compact solidification structure will be obtained with the increase of stirring intensity. 相似文献
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为了改善20CrMnTi小方坯的凝固组织,采用移动边界法先对20CrMnTi钢的温度场进行模拟,在此基础上,采用元胞自动机有限元法(CAFE法)对其凝固组织进行了数值模拟。当模拟结果与实际结果基本吻合时,进一步探讨了硅、铬、锰、钛等合金元素对20CrMnTi钢凝固组织的影响规律。模拟结果表明,在该钢号的合金元素规定范围内,适当减少硅元素的质量分数,能够提高铸坯中心等轴晶比例,使晶粒数目增加,晶粒平均半径减小。适当添加铬元素能够扩大铸坯中心等轴晶区,从而减小晶粒平均半径,增加晶粒数量。增加锰元素质量分数可以提高铸坯的中心等轴晶率。最后根据所得模拟结果对该钢种的合金元素进行调整,达到了扩大铸坯中心等轴晶区和细化晶粒的目的。 相似文献