基于二次枝晶间距变化特征的连铸方坯CET位置判断新方法

从碳钢连铸坯实际凝固组织入手对典型枝晶二次枝晶间距(secondary dendrite arm spacing,SDAS)进行测量分析,并发现了铸坯表面向中心凝固过程中的SDAS突增现象。结合铸坯横断面二维温度场数值模型分析可知,柱状晶向等轴晶转变(columnar to equiaxed transition,CET)的过程会影响铸坯内部的传热过程,这种影响最终以典型枝晶SDAS突增的形式体现出来。基于典型枝晶SDAS突增现象,确立了铸坯内部CET定量判定的新方法,即将典型枝晶SDAS最大增加率的起始位置确定为铸坯内部CET起始位置。计算所得CET位置与铸坯内部温度梯度变化拐点的最大相对误差仅为8.3%,且与生长速率变化区间相对应,同时也与实际凝固组织形貌转变位置吻合,证明了该方法的有效性。     

冷却速度对ZL114A合金二次枝晶臂间距的影响

利用金相显微镜及自动图像分析仪,测定ZL114A合金在同一凝固条件下、铸件不同壁厚部位的二次枝晶臂间距(SDAS),研究ZL114A合金凝固期热参数与SDAS的关系.结果表明,随着铸件壁厚的增加,冷却速度减小,局部凝固时间增长,二次枝晶臂粗化,SDAS增大;在呋喃自硬树脂砂型铸造条件下,SDAS与冷却速度及局部凝固时间之间的关系为SDAS=20.8tf0.3,SDAS=69.34v-0.3.     

铸件模数Mc对A357合金二次枝晶臂间距及致密度的影响

研究试样直径和铸件模数Mc与铸件二次枝晶臂间(SDAS)的关系，通过测试A357合金不同凝固条件下铸件不同部位的SDAS，得出砂型铸造凝固条件下SDAS与铸件模数M之间的关系式。研究了铸件模数等对铸件致密度的影响，确定了获得高致密度铸件的合理的凝固条件。     

火花塞壳体冷挤压成形工艺及模具设计

１成形工艺分析火花塞壳体材料ＭＬ１０，由于其形状较复杂，冷挤成形有一定难度，经分析，决定采用以下工艺方案：整形→预成形→镦挤六方→外圆成形→中径反挤压成形→冲孔，各工位分别叙述如下。（１）整形（图１），将不平整的毛坯两端面镦平。图１整形工艺图（２）预...     

铝—钢双金属复合铸件研制

用钢套铸接表面预电镀纯金属、浸Ａｌ－Ｓｉ基合金后立即浇注的方法制造了“钢套内表面浇注铝金”结构形式铝钢双金属铸件，优化了双金属铸件铸造工艺、热处理工艺；研究了钢套铸接表面金属预镀层和双金属界面附近的合金元素对双金属铸件铸态及热处理后界面过渡层裂纹和抗剪强度的影响。获得的双金属铸件铸态界面过渡层厚度为０．００７－０．０１８ｍｔｎ，界面剪切强度为５０－９４ＭＰａ，热处理后面过渡层增厚，界面剪切强度明显     

铝─钢双金属复合铸件研制

用钢套铸接表面预电镀纯金属、浸Ａｌ－Ｓｉ基合金后立即浇注的方法制造了“钢套内表面浇注铝合金”结构形式的铝钢双金属铸件。优化了双金属铸件铸造工艺、热处理工艺；研究了钢套铸接表面金属预镀层和双金属界面附近的合金元素对双金属铸件铸态及热处理后界面过渡层裂纹和抗剪强度的影响。获得的双金属铸件铸态界面过渡层厚度为０．００７～０．０１８ｍｍ，界面剪切强度为５０～９４ＭＰａ，热处理后界面过渡层增厚，界面剪切强度明显下降。给出了最佳铸造工艺和热处理工艺     

江苏省铸造协会第二届会员代表大会预通知

各相关单位：根据《江苏省铸造协会章程》规定，江苏省铸造协会（以下简称江苏铸协）第一届理事会即将完成使命，将于2014年4月召开江苏铸协第二届会员代表大会，大会将选举产生新一届理事会。现将相关信息预通知如下：     

一种铸态亚共析U-Nb合金晶粒细化的热处理工艺研究

通过对某种铸态和预淬火态亚共析U-Nb合金样品的900℃等温淬火实验，利用金相显微镜(OM)，透射电镜(TEM)和X射线衍射(XRD)等方法研究了单靠热处理工艺细化该种铸态合金晶粒的可行性。实验结果表明，由a y1-2两相组成的铸态样品在a y1-2→y1等温转变过程中没有明显的重结晶行为，y1新相的晶粒特征表现为原y1晶界的平直化迁移，因此淬火后晶粒不能细化；由单一a″相组成的预淬火态样品在a″→y1等温转变过程中则发生完全重结晶，等温0．25h能使晶粒尺寸减小1倍。分析认为，该种铸态合金通过预淬火处理使晶格缺陷增多，以及所生成的单一a″相中存在大量的孪晶结构降低了等温转变时y1新相的形核能导致了a″→y1等温转变发生重结晶。结论认为，采取两次淬火的热处理方法可以细化该种铸态亚共析U-Nb合金晶粒。     

斜坡预结晶M2钢半固态坯料的组织和热塑性

采用斜坡预结晶法制备出M2高速钢半固态铸坯，并对其微观组织和热塑性进行了研究。半固态加工技术解决了M2高速钢铸态坯料中碳化物偏析严重的问题，改善了铸态微观组织和热塑性加工性能，使其晶粒由发达的树枝晶变为细小圆整的等轴晶，共晶碳化物明显比常规铸态中的薄且少，并且其共晶碳化物不同于常规铸态组织中那样发达的网状组织，碳化物网的连续度也大大降低。因此，这也提高了它的热塑性，且锻后半固态坯料的碳化物不均匀度低于常规铸态。然而，其在单向应力下的最佳热塑性温度范围没有改变，仍然是900-1200℃。     

挤压铸造制备半固态AZ61镁合金的组织演变及力学性能(英文)

采用挤压铸造后直接二次重熔的方法制备半固态AZ61镁合金。首先通过挤压铸造预成形铸态AZ61镁合金,以获得细小的枝晶;然后在半固态区间进行二次重熔,细小的枝晶演变成球状晶,完全球化的晶粒被液相均匀包裹。研究结果表明:通过挤压铸造预成形的铸态AZ61镁合金与传统铸造预成形的铸态AZ61镁合金相比,在相同的二次重熔条件下,挤压铸造预成形的铸态AZ61镁合金获得更细小的半固态组织。此外,挤压铸造加上二次重熔触变成形的AZ61镁合金,力学性能优于传统铸造后二次重熔触变成形的AZ61镁合金。     

半连续浇铸AZ61合金中枝晶形貌特性

采用彩色金相与能谱对半连续浇铸的AZ61镁合金进行了组织和成分上的观察,发现冷却速率较快的铸锭边部的二次枝晶间距比冷却速率较慢的铸锭心部的二次枝晶间距大,与普通模铸的显微组织呈现的规律不同,并对这一现象进行了理论上的分析讨论。分析认为边部二次枝晶间距的异常增大与二次枝晶臂表面溶质的微观偏析密切相关,粗枝晶臂表面溶质浓度与细枝晶臂表面溶质浓度差值越大,粗枝晶臂的粗化驱动能越大,枝晶的二次枝晶间距就越大。     

电渣熔铸速度对金属凝固组织的影响

采用移动传热边界法及CAFE法,模拟了在不同熔铸速度下铸锭晶粒的生长过程以及二次枝晶臂间距的分布,进而探讨了熔铸速度对铸件凝固质量的影响。结果发现,电渣熔铸过程中,金属熔池的形状决定了柱状晶的生长方向。随着熔铸速度的增加,生长方向与熔池上升方向之间的夹角也增大,这会造成铸件力学性能的降低。二次枝晶臂间距是决定铸件冶金质量的一个重要因素,其是铸件局部冷却速度的函数。随着熔化率的增加,二次枝晶臂间距减小,这有利于减小铸件中的晶内偏析及显微缩孔的产生,从而有利于提高铸件质量。熔铸速度是电渣熔铸过程的主要控制参数,对铸件凝固质量有很大的影响,太高或太低的熔铸速度均会造成铸件凝固质量的降低。     

冷却速度对铸件二次枝晶臂间距影响的模拟研究

设计了45#钢阶梯凝固试验并进行了有限元分析,研究了不同冷却速度对二次枝晶臂间距尺寸的影响。根据模拟结果拟合了冷却速度与二次枝晶臂间距经验公式,为判断铸件冷却温度、建立高温扩散退火预判机制、降低铸件偏析和避免裂纹的产生提供理论依据。     

Effects of chill casting processes on secondary dendrite arm spacing and densification of Al-Si-Mg alloy

Based on the resin bonded sand casting process, the-effects of chill processes on the secondary dendrite arm spacing（SDAS） and densification of Al-Si-Mg alloy were studied. The influences of the chill thickness and effective distance of chill operating on the SDAS were researched; and the effect of chill＇heat capacity on SDAS was investigated. The result reveals that, SDAS decreases with increasing the thickness of chill but the effect of chill is finite. The effective distance of chill operating for the chill with different thickness were obtained, and the functional relations among modulus, length of castings and thickness of chill were discussed, and the synthetical network chart of the relation among them was plotted. The relationship between local solidification rate and SDAS was defined by means of quadratic polynomial regression.     

Solidification structure simulation and casting process optimization of GCr15 bloom alloy

Based on the solidification heat transfer model and CAFémodel,the solidification structure of GCr15 bloom alloy was studied.Using nail shooting and acid etching experiments,the solidification models were verified.The secondary dendrite arm spacing(SDAS)model of GCr15 was obtained by simulation calculation and metallographic observation.With the increase of casting speed,the SDAS,equiaxed crystal ratio(ECR)and average grain size increase.With the rise of superheat,the SDAS increases in the 20-70 mm of thickness and decreases in the 80-160 mm of thickness.The ECR decreases and the average grain size increases with the increase of superheat.With the increase of specific water flow,both the SDAS and ECR decrease.The minimum average grain size is obtained when the specific water flow is 0.20 L·kg^-1.The central carbon segregation index is reduced from 1.11 to 1.075.     

Heat transfer and solidification analysis in the mould region of a horizontal copper alloy billet continuous caster

Abstract

Mathematical modelling has been widely used as a powerful tool for process design and optimisation of the continuous casting process. A three-dimensional heat transfer model was developed to simulate heat transfer and solidification in a horizontal billet continuous casting system. In this model, the air gap formation and its effect on heat extraction from the billet was also modelled and considered. The developed model was run to simulate the heat transfer and solidification for an industrial billet casting machine. The predicted temperature distribution within the mould and billet was compared with those measured on an industrial caster and good agreement was obtained. Parametric studies were carried out to evaluate the effects of different parameters on the temperature distribution and solidification profile within the cast brass billet. Finally, the secondary dendrite arm spacing (SDAS) was determined experimentally and a semi-empirical correlation between measured SDAS and corresponding calculated cooling rate was proposed for continuously cast brass billet.     

Volume change during the solidification of grey cast iron: its relation with the microstructural variation,comparison between experimental and theoretical analysis

The expansion/contraction during the solidification of grey cast iron was studied using Linear Variable Differential Transformer (LVDT). The experiments were conducted with and without melt treatment. Two types of inoculant used for melt treatment: ASSC (Si, Ca, Sr & Al) and MBZCAS (Si, Ca, Zr, Ba, Mn & Al). Microstructural investigations carried out to quantify the eutectic cells, undercooled graphite, primary austenite and secondary dendritic arm spacing (SDAS). It was found that the casting shows hardly any shrinkage during early solidification but in the eutectic region, the casting expands until the end of solidification. The measured and the calculated volume changes are close to one another, but the former shows more expansion. The addition of MBZCAS promotes more flake graphite, and ASSC does not increase eutectic cells much. In addition to that, it lowers the primary austenite fraction, promotes more eutectic growth, decreases undercooled graphite and SDAS. As a result, the volume expansion changes in the eutectic region.     

A356铝合金显微疏松与二次枝晶臂距的计算机模拟

以商品化软件PROCAST为基础进行二次开发, 对A356铝合金托盘件凝固过程显微疏松缺陷和二次臂距(SDAS)进行了数值分析, 建立了有氢气析出量影响在内的显微疏松判据模型, 预测了显微疏松出现的位置与体积分数. 预测结果得到了X射线无损探伤实验的验证. 开发了温度场测试系统, 测试了铸件凝固过程的冷却曲线, 模拟结果与实际结果符合良好.     

Research on Solidification Structure of Billet for Bearing Steel

Secondary dendrite arm spacing (SDAS), which is an important parameter for solidification structure, has a significant effect on the level of segregation and the time for dispelling micro-segregation. The solidification structure of billets, poured under different drawing speeds for high-carbon chromium continuous casting and etched by saturated water solution of picric acid, was investigated by OLYMPUS BX51 optical microscope; and the indexes of carbon and sulfur segregation were also determined. It is con...