副溶血弧菌特异性卵黄抗体(AHPND-VpIgY)对凡纳滨对虾幼体被动免疫和育苗成活率的影响

将抗高致病性副溶血弧菌(Vibrioparahaemolyticus)特异性卵黄抗体(AHPND-VpIgY)应用于育苗生产,通过测定氨氮、亚硝酸盐、细菌总数、弧菌总数、相对保护率和育苗成活率,评价了AHPND-VpIgY在育苗期对凡纳滨对虾(Litopenaeusvannamei)幼体的保护效果。结果表明,0.1g/m3和0.2g/m3AHPND-VpIgY组的相对保护率为35.7%和57.2%,两者均显著高于非特异性卵黄抗体组(P<0.05);两组的育苗成活率为50.8%和57.2%,比对照组分别提高19.1%和25.6%。各实验组氨氮、亚硝酸盐、细菌总数及弧菌总数与对照组无显著差异,对水质无影响。综上,特异性的AHPND-VpIgY能在不改变水质的前提下,有效提高凡纳滨对虾幼体的存活率、相对保护率和育苗成活率,从而提高凡纳滨对虾苗种产量和质量。

压下对重轨钢大方坯内裂纹敏感性的影响

为研究压下对连铸坯内部裂纹产生的影响,利用ABAQUS有限元软件建立了230 mm×280 mm断面大方坯压下数学模型.通过压下模型对重轨钢连铸坯压下过程进行热力耦合模拟计算,对压下过程中产生的内部裂纹进行了预测.首先,对连铸坯不同中心固相率为0.3~0.7的温度场进行计算;然后,利用压下模型计算了连铸坯中心固相率0.3~0.7时凝固前沿的等效塑性应变.研究结果表明,在连铸坯中心固相率为0.3~0.7的位置处分别施加7 mm压下量进行压下,连铸坯凝固前沿等效塑性应变未超过临界等效塑性应变(0.4%),连铸坯未出现内裂纹;同时,对连铸坯在中心固相率为0.6位置处进行了不同压下量的研究,研究结果表明,当连铸坯压下量超过7 mm时,凝固前沿的等效塑性应变超过临界塑性应变(0.4%),连铸坯出现内裂纹,并且压下量越大,连铸坯内裂纹越严重.同时,工业试验结果与模型计算结果基本吻合,验证了模型计算的准确性.

连铸板坯三维二冷动态配水与精准压下研究与应用

在现有工艺条件下,校验和完善二冷区铸坯凝固传热计算数学模型,开发三维二冷配水模型,解决目前设备状况下冷却水分布不均匀对铸坯温度的影响,从而控制铸坯表面质量,特别是铸坯的角部裂纹,同时对板坯连铸二冷配水制度进行改进和优化,使之满足高效连铸生产条件和改善铸坯质量的需要.提出压下参数计算公式,结合所开发三维二冷配水模型,优化现有压下工艺,提出并应用精准可控单段压下、非稳态压下控制,集中解决连铸板坯中心偏析、中心疏松和缩孔等内部质量问题.同时优化模型数据库,使之数据更加完备,模型计算更加准确,同时模型具备异钢种混浇过程二冷及压下控制功能,能够进行凝固终点W形预测与控制,可进一步提高模型适用性和准确性.模型开发并成功在多家钢厂现场应用,有效改善了铸坯裂纹和偏析等铸坯表面和内部的质量问题.

IF钢连铸开浇工艺对头坯洁净度影响的研究

IF钢连铸开浇过程头坯洁净度水平较低,目前各企业一般将开浇坯作判废或降级处理,这导致了产品质量不稳定,成材率低等问题.为研究IF钢非稳态开浇阶段连铸坯的洁净度水平及优化措施,采用现场取样、检测分析及数值模拟计算相结合的方法,分析了IF钢开浇阶段不同拉速变化曲线条件下连铸坯沿拉坯方向的洁净度变化规律.通过实验检测发现沿拉坯方向头坯T[O]、[N]及显微夹杂物含量呈现明显下降趋势,距离头坯头部6 m处T[O]含量为13×10^(-6),接近正常坯水平,距离头坯头部7 m处[N]含量约为19×10^(-6),接近正常坯水平,开浇工艺对于连铸坯T[O]、[N]及显微夹杂物含量影响不大.匀速、前快后慢和前慢后快三种拉速工艺条件下,大型夹杂物在距离头坯头部2 m处的质量分数约为0.2 mg·kg^(-1),但之后均存在不同程度的大型夹杂物数量波动现象,而前快后慢工艺影响范围最小,在5.5 m后均达到正常水平.通过数值计算同样发现,前快后慢的提拉速工艺条件下产生的头坯洁净度更快地接近正常坯洁净度水平(约开浇430 s后,对应拉坯5 m).基于本文研究,提出了一种优化的IF钢连铸开浇过程提拉速的工艺方法.

Simulation of solidification microstructure of Fe-6.5%Si alloy using cellular automaton-finite element method

3D microstructures of Fe–6.5%Si(mass fraction) alloys prepared under different cooling conditions were simulated via finite element-cellular automaton(CAFE) method. The simulated results were compared to experimental results and found to be in accordance. Variations in the temperature field and solid-liquid region, which plays important roles in determining solidification structures, were also examined under various cooling conditions. The proposed model was utilized to determine the effects of Gaussian distribution parameters to find that the lower the mean undercooling, the higher the equiaxed crystal zone ratio; also, the larger the maximum nucleation density, the smaller the grain size. The influence of superheat on solidification structure and columnar to equiaxed transition(CET) in the cast ingot was also investigated to find that decrease in superheat from 52 K to 20 K causes the equiaxed crystal zone ratio to increase from 58.13% to 65.6%, the mean gain radius to decrease from 2.102 mm to 1.871 mm, and the CET to occur ahead of schedule. To this effect, low superheat casting is beneficial to obtain finer equiaxed gains and higher equiaxed dendrite zone ratio in Fe–6.5%Si alloy cast ingots.

MTA废气分析在VOD脱碳过程中的应用

为了实现对VOD脱碳终点碳含量进行动态控制,以某钢厂120tVOD炉冶炼不锈钢的脱碳过程为研究对象,通过MTA（multi task analyzer）废气分析系统分析VOD精炼中CO、CO_2等废气成分随时间变化的规律。同时以物质碳平衡为基础,建立了基于废气分析的VOD冶炼碳终点控制的模型,对精炼过程中钢水碳变化情况进行分析。通过对实际值和预测值之间的偏差进行考察,说明了模型能够较好地预测碳含量的总体发展趋势。模型计算VOD脱碳终点碳质量分数误差都在±0.03%之内,模型计算值与实际测量值具有一定的吻合性。

Control of Macrosegregation Behavior by Applying Final Electromagnetic Stirring for Continuously Cast High Carbon Steel Billet

Solidification behavior of continuously cast high carbon steel billets was investigated with an objective of producing high quality billets by determining the optimum final electromagnetic stirring （F-EMS） parameters. Char- acteristics of centerline segregation were analyzed for lots of billet samples collected from the plant through obtaining the carbon concentrations of drill chips, which were correlated with the operating parameters of the caster and stir- rers, but a problem occurred that segregation control results of trial billets with the same casting and stirring param- eters often have drastic fluctuations. An attempt was made to find out the induced reasons of this problem by meas uring the electromagnetic torque, analyzing the secondary dendrite arm spacing （SDAS） and the corresponding cool- ing rate of the typical specimens, and observing the longitudinal profile of etched billet samples. Then a simple dy- namic secondary cooling model was developed based on the solidified shell thickness control mode, by which the maximum carbon segregation index was reduced effectively, and thus the segregation fluctuation problem was basi- cally solved. Finally, the most favourable stirring parameters were determined as the casting speed of 1.65 m/rain, the liquid core thickness of 40 mm, stirring current of 360 A and frequency of 12 Hz.

In Situ Observation of Solidification Process of AISI 304 Austenitic Stainless Steel

The solidification process of AISI 304 stainless steel during cooling at a rate of 0.05 K/s has been observed in situ using a confocal scanning laser microscope （CSLM）. The results show that the 8 phase appeared first in liquid steel, as the temperature decreased, the γ phase precipitated prior at δ-grain boundary at 1452. 2 ℃, the liquid steel disappeared at 1 431.3 ℃, and then the γ phase precipitated on the δ ferrite. Based on the Scheil-Gulliver solidification model, the solidification processes of AISI 304 stainless steel are simulated using the Scheil model in Thermo Calc, and the simulation results agree well with the results observed in the experiment.

Q235B板坯夹杂物研究

为提高某厂Q235B连铸板坯质量,采用金相法、无水溶液电解法及夹杂物自动扫描分析系统得出试样中夹杂物尺寸大多小于20μm,大于20μm数量少,其形貌多为不规则块状,小于20μm夹杂物为脱氧过程中产生的脱氧产物,成分为Al2O3-SiO2或纯的Al2O3;大于20μm夹杂物是浇注过程中卷入的保护渣和钢水冲刷落入钢液的耐火材料,成分为CaO-Na2O-Al2O3-SiO2等硅酸盐及钙的铝酸盐。