共查询到18条相似文献,搜索用时 140 毫秒
1.
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
2.
连铸方坯是棒线类钢铁产品的主要母材,其宏观/半宏观偏析等缺陷,一定程度反映了铸坯成分分布和组织性能的不均匀,是影响高端钢材质量提升的重要因素。从二维横断面入手对铸坯内部低倍组织进行表征、分析与优化是目前铸坯内部偏析缺陷调控的主要手段;然而,铸坯内部凝固枝晶和中心偏析均具有三维空间形貌和分布特征,导致仅通过二维横断面进行研究可能会存在一定误差;同时,连铸拉坯方向(垂直于横断面)上凝固枝晶与偏析的波动特征能够更直观地反映连铸坯内部组织性能和质量沿长度方向的波动,这也是影响高品质钢连铸坯及后续产品质量稳定性的关键之一。从凝固行为特点、组织波动变化规律、中心偏析控制等3个方面总结讨论近年来连铸方坯拉坯方向的凝固行为与偏析控制研究进展。CET转变是铸坯凝固组织调控的重点,其判定依据及其与偏析相关性的研究表明,拉坯方向上CET位置存在波动性且与中心偏析形貌特征相关。液相穴内非对称流场及温度变化会造成拉坯方向凝固枝晶的波动特征以及凝固终点的周期性波动;同时,实际铸坯以及相关定性定量模型也表明了拉坯方向偏析元素的分布具有波动特征,并可以利用时间序列技术等方法展开解析。中心偏析控制技术的发展明显提升了连... 相似文献
3.
4.
凝固组织形貌对铸坯宏观偏析的形成有非常重要的影响,并在一定程度上决定了铸坯后续的加工使用性能。基于高通量试验原理,引入分形维数和无量纲周长对82B帘线钢连铸坯凝固组织形貌特征展开分析。结果表明,对于连铸坯两侧中间区,窄宽度长区域取样方法得到的凝固组织面积率可近似等效为固相率;同时凝固组织整体形貌的分形维数随着固相率的增加而增加,但其无量纲周长呈现相反的趋势,故两者对凝固组织渗透率大小存在相反的影响作用;计算表明,实际铸坯组织的渗透率最小值对应的固相率为0.667。提出了一种基于实际铸坯分析凝固组织形貌特征变化规律的新方法,同时能为连铸末端电磁搅拌与轻压下等偏析控制技术的最佳作用固相率提供参考。 相似文献
5.
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
6.
7.
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
8.
9.
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
10.
11.
ABSTRACTAn experimental apparatus for simulation of continuous casting process of GCr15 bearing steel billet is established. With the apparatus, the billets of diameter 140?mm are casted in various superheats and cooling conditions. The solidification macrostructure, dendrite morphology, segregation and carbide are investigated. It is shown that melting superheats and cooling conditions remarkably influence the microstructure and solute segregation. It is found that the secondary dendrite arm spacing of the steel increases with the increase of the superheat temperature, and with decrease of the cooling rate. Lower superheat with higher cooling rate promotes the refining of the microstructure. Refining equiaxed grains structure in the centre of the billet leads to lower segregation of carbon. Furthermore, with increasing cooling rates, the spacing of the pearlite laminar is refined and the precipitation of proeutectic carbides is suppressed. 相似文献
12.
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
13.
14.
15.
A. M. Glenn S. P. Russo P. J. K. Paterson 《Metallurgical and Materials Transactions A》2003,34(7):1513-1523
The effect of titanium and titanium diboride inoculation on the spatial variation of local solidification time for direct
chill (DC) cast ingots of aluminum alloy 5182 (AA5182) was studied. The results have been compared to those of an ingot cast
without grain refining. To accomplish this, the effect of grain refining on a number of ingot characteristics such as grain
size, macrosegregation, spatial variation of dendrite arm spacing, and thermal conductivity was investigated. Furthermore,
the effect of grain refining on the well-known relationship between dendrite arm spacing and local solidification time had
to be established for AA5182. The results indicated that the spatial variation of dendrite arm spacing in the industrial ingots
was independent of grain refining, although the nonrefined ingot produced significantly finer dendrite arm spacings in its
center. This was attributed to the influence of showering crystals in the nonrefined ingot. The relationship between dendrite
arm spacing and local solidification time was also found to be independent of grain refining. 相似文献
16.
利用分形几何中的分形维数定量表征了铝熔体经低过热度浇注和电磁搅拌作用下半固态合金浆料中初生相的尺寸细化和球化程度.通过OM、Matlab软件平台编制计盒维数法计算程序,研究半固态初生相α-Al形貌的分形特征和电磁搅拌方式对其形貌分形维数变化规律的影响.结果表明,合金的凝固组织具有分形特征,可通过分形维数对初生相尺寸细化和球化程度进行定量表征.初生相的形貌分形维数随搅拌方式由无搅拌、单向连续搅拌过渡到双向连续搅拌时,呈逐渐减小的变化规律,是一个降维的过程.在双向连续搅拌作用下初生相的分形维数最小,晶粒细化球化程度达到最佳 相似文献
17.
采用化学侵蚀、彩色金相和电子探针(EPMA)等方法对AISI304奥氏体不锈钢连铸方坯凝固组织及其残留铁素体的形貌、化学组成等特征进行了分析,并采用DICTRA软件对铁素体向奥氏体的扩散转变进行了模拟研究,结果表明AISI304不锈钢铸坯表层树枝晶区的二次枝晶间距为12~20μm,富Cr贫Ni的残留铁素体呈骨骼状分布;铸坯中心等轴晶区的残留铁素体为蠕虫状分布,中心等轴晶区的残留铁素体富Cr贫Ni的同时富Si贫Mn,且其富Cr贫Ni的程度比柱状晶区的残留铁素体轻。钢液成分和先析铁素体向奥氏体扩散转变时间、距离是影响残留铁素体化学组成的主要因素。 相似文献
18.
A study of solidification phenomena performed under industrial conditions is presented. The solidification structure of high carbon, medium carbon and microalloyed steel grades was observed and correlated to casting parameters such as superheat and secondary cooling. Experimental data of dendrite morphology are related to calculated solidification variables. The calculation is based on the solution of the enthalpy balance equation. An expression for the dependence of secondary dendrite arm spacing on solidification variables is proposed for columnar growth. The results are compared to the findings of other authors. The effect of chemical composition on secondary dendrite arm spacing was observed. Therefore the developed relationships are extended to carbon content on the basis of the presented experimental data. 相似文献