脉冲电流处理方式对45钢凝固组织的影响

45钢(0.43%C)在10kg中频感应炉出钢前(凝固前)经2600V、0.862Hz、电容器电容量200μF脉冲电流处理60s和钢水在铸模凝固过程用相同参数的脉冲电流处理3.5min后发现,两种脉冲电流处理方法均能改善钢的凝固组织:增加等轴晶和减少柱状晶数量,并减少魏氏组织,使珠光体片层间距减小;同时改善了钢的成分偏析,碳、硫、磷的偏析指数分别由未经脉冲电流处理的1.257、1.502和1.384降低至脉冲电流处理的1.125～1.194、1.067～1.300、1.227～1.092。     

脉冲电流对钢凝固组织的影响

 研究了高频脉冲电流对钢水凝固过程中组织的影响,实验室试验结果表明：在钢水中外加一个高频脉冲电场,能有效地控制钢的凝固组织,减少柱状晶,增大等轴晶区。进行了连铸工业试验,效果明显：铸坯中心缩孔和中心裂纹被消除,中心偏析和中间裂纹也得到降低。     

脉冲电流在改善金属凝固组织中的作用

综述了脉冲电流在改善金属凝固组织方面的研究现状。从理论上归纳和分析了脉冲电流在金属凝固过程中产生作用的主要机制。     

Solidification Microstructure of Aluminum AA 6016-T4 Resistance Spot Welds Using a Short-Pulse Technique

The influence of the duration of the current pulse on the solidification microstructure of resistance spot welded (RSW) samples of aluminum alloy 6016-T4 with the short-pulse technique was investigated through experiments and numerical modeling. Microstructure was analyzed in terms of morphology and size, and primary and secondary dendrite arm spacing were measured on experimental samples. A reduction in pulse width resulted in a fine, columnar-dendritic microstructure in the outer regions of the fusion zone as well as a larger equiaxed-dendritic zone in the fusion zone center. A two-dimensional, axisymmetric finite element model of the spot welding process with new methods for calculation of the solidification parameters G (thermal gradient in the solid behind the solid–liquid interface) and R (velocity of the solid–liquid interface) was used for investigation of influence of pulse time on solidification microstructure and comparison to experimental results. Morphological trends in the solidification structure showed good agreement between experiments and simulations, and the influence of the pulse duration on the solidification parameters evolved because of changing heat transfer conditions. Simulated solidification data suggest that the solidification of aluminum during RSW falls in the regime of rapid solidification.

     

电流处理细化纯铝凝固组织的研究

介绍了一种改善金属凝固组织的外场处理新方法一电流处理方法。研究了液态下施加直流电流和脉冲电流对工业纯铝凝固组织的影响。结果表明，该方法可以细化纯铝的凝固组织，使粗大的柱状晶变为细小的等轴晶；处理参数不同，对铝锭的宏观组织细化程度不同。     

脉冲电流对7075铝合金铸态组织的影响

研究了脉冲电流及Al-5Ti-B变质剂对7075铝合金铸态组织的改善和机理。结果表明,通入电脉冲及添加变质剂能抑制二次枝晶的生长,改善铸造组织的形貌,基体主要是均匀的等轴晶和近球形晶粒,同时,与直接浇铸的试样对比,合金中铜和铁元素的偏析现象得到一定程度缓解。     

电脉冲脉宽对高硼中碳合金钢凝固组织的影响

 为改变高硼中碳合金钢中硬质相的形态和分布,在高硼中碳合金钢凝固过程中施加电压1600V、频率30Hz、脉宽不同的电脉冲,并研究了电脉冲脉宽对其凝固组织的影响规律。结果表明,经过电脉冲处理,高硼中碳合金钢凝固组织中马氏体片层间距变小,基体中W、Cr、Mo、V等合金元素含量升高,基体硬度提高;硬质相体积分数降低,片层状硬质相消失,网状硬质相产生断网现象,硬质相形态和分布也变得均匀。随着电脉冲脉宽的增加,断网现象先变得明显,后又减弱。在该试验条件下,脉宽为30μs时,断网现象最明显,硬质相的分布和形状也最均匀。     

Effect of electric current pulse on solidification of silicon steel pertinent to twin roll casting

Abstract

An experimental study with respect to the influence of electric current pulse (ECP) on the solidification structure of molten silicon steel was investigated with a copper mould designed to simulate the twin roll casting process. The experimental results showed that the application of ECP can increase the proportion of equiaxed grains up to 67·5%. The mechanism of exerting ECP is also discussed. It can be confirmed that the application of ECP on twin roll casting could effectively improve the solidification structure of silicon steel strip.     

脉冲电流对钢液凝固过程中夹杂物迁移行为的影响

在钢液凝固过程中施加脉冲电流,通过观察和分析凝固试样中夹杂物的形貌、数量、尺寸和分布状态等,以研究施加脉冲电流对钢中夹杂物迁移行为的影响。结果表明,在脉冲电流的影响下,钢液凝固初期形成的晶核会发生脱落而形成结晶雨;在晶核下落过程中,钢中夹杂物也会随之向下部迁移。随着脉冲电流强度的逐渐增加,钢锭上、中部夹杂物逐渐减少,晶粒尺寸变小。在本试验条件下,当电流强度为56.6 A/cm2 时,钢锭上、中部夹杂物的总面积和总数量分别比未施加脉冲电流时的降低46.9% 和35.6%。对于夹杂物含量要求较高的钢种而言,在钢锭凝固过程中施加脉冲电流,控制结晶雨的形成和迁移过程不失为一种有效去除钢中夹杂物、提高钢锭质量的技术手段。     

脉冲电流对钢液凝固过程中夹杂物迁移行为的影响

在钢液凝固过程中施加脉冲电流,通过观察和分析凝固试样中夹杂物的形貌、数量、尺寸和分布状态等,以研究施加脉冲电流对钢中夹杂物迁移行为的影响。结果表明,在脉冲电流的影响下,钢液凝固初期形成的晶核会发生脱落而形成结晶雨;在晶核下落过程中,钢中夹杂物也会随之向下部迁移。随着脉冲电流强度的逐渐增加,钢锭上、中部夹杂物逐渐减少,晶粒尺寸变小。在本试验条件下,当电流强度为56.6 A/cm2 时,钢锭上、中部夹杂物的总面积和总数量分别比未施加脉冲电流时的降低46.9% 和35.6%。对于夹杂物含量要求较高的钢种而言,在钢锭凝固过程中施加脉冲电流,控制结晶雨的形成和迁移过程不失为一种有效去除钢中夹杂物、提高钢锭质量的技术手段。     

Analysis of Graphite Morphology of Gray Cast Iron in Pulse Magnetic Field

Theelectromagneticrefinementofmetalsolidi ficationstructureisanewlydevelopedtechnique. Themagneticfieldcanrefinethesolidificationstruc turebyactingupontheliquidmetal,suchasvibra tionandstirring.Atpresent,suchtechniquesare mainlyappliedtoalloyswithlower…     

How Suspended Particles Affect Surface Morphology in Powder Mixed Electrical Discharge Machining (PMEDM)

The effect of SiC powder mixing into the dielectric liquid on surface topology and structure of interstitial free (IF) steel has been studied. Four process parameters, namely pulse duration, pulse current, concentration of powder, and type of dielectric liquid material, have been selected as varying parameters. Surface modifications due to suspended SiC particles were identified by using optical, scanning electron microscopy, and X-ray diffraction analysis. It was observed that suspended particles around discharge column accelerated and gained sufficient velocity to penetrate to the molten pool before solidification by means of electrophoresis and negative pressure induced after cessation of a discharge, which leads a surface embedded with added fine particles under that prevent formation of penetrating cracks during machining. However, surface cracks that formed due to high transformational stresses developed during solidification were found to be unaffected by means of mechanical action of the particles.     

Study on Improving Solidification Structure of Rare Earth Al-Si Alloys with Electropulse Acting on Liquid Alloy

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.     

脉冲电流参数对过共晶高铬铸铁近液相线熔化后凝固组织的影响

对过共晶高铬铸铁近液相线溶化后的凝固过程进行脉冲电流处理,研究了脉冲电流参数（脉冲电压和频率）对凝固组织的影响.发现脉冲频率和电压的增大都有助于过共晶高铬铸铁凝固组织中碳化物的细化和粒化.脉冲频率的增大促进大量细小颗粒状初生碳化物的析出,离异共晶现象变得更加明显,层片状共晶碳化物减少.脉冲电压的增加促进初生碳化物细化和粒化,片状共晶碳化物变短.过高的电压也促进离异共晶,导致更多的初生碳化物的形成.      

脉冲电磁场凝固组织细化和均质化技术研究与应用进展

由于金属凝固过程中选分结晶的作用,不可避免地会出现成分不均匀现象。连铸过程中由于强制冷却,这种成分不均匀现象更为严重。这不仅影响了铸坯和铸锭后续加工性能,并影响了最终产品质量和性能的均匀性和稳定性。研究和生产实践表明,细化凝固组织是解决成分不均匀性的有效手段。脉冲电磁场因能耗低、施加方便、细晶效果显著,近年来得到了广泛关注,有望成为冶金界广泛应用的凝固组织细化和均质化技术。分别介绍脉冲电流、脉冲磁场和脉冲磁致振荡3种脉冲电磁场凝固组织细化和均质化技术的研究现状和应用进展。     

Structure Evolution and Solidification Behavior of Austenitic Stainless Steel in Pulsed Magnetic Field

 To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.     

Electrofusion of zona-free mouse embryonic cells in electrolytes and their development in vitro

The influence of increasing the physical electrofusion parameters, direct current (DC) pulse strength, pulse duration, pulse number, alternating current (AC) voltage and alignment time, in electrolytes on the rates of fusion, degeneration and development of zona-free mouse 2-cell embryos were examined. Furthermore, the effects of physiological saline and mannitol as fusion media and various mouse strains were also evaluated. Dulbecco's phosphate-buffered saline (PBS) supplemented with 10% fetal calf serum was used as the main fusion solution. A significant increase in the rate of fusion (P < 0.05) was obtained by increasing pulse strength from 30 to 300 V/mm. The embryos fused at the pulse strengths of 30 to 70 V/mm had significantly higher development rates to blastocysts compared with those fused at 100 to 300 V/mm (P < 0.05). There were no significant differences in the rates of fusion, degeneration and development to blastocysts when the pulse duration was increased from 30 to 90 microseconds. Although fusion rates were increased (P < 0.05) by increasing the pulse number up to 4, a significant decrease (P < 0.05) in development to blastocysts was observed when the pulse number was 5. Application of AC voltage prior to the DC pulse tended to increase the fusion rate (89.2-93.8%), compared with fusion with the DC pulse only (75.0%). Prolongation of alignment time from 5 to 15 sec had no effect on the fusion rate. Under the optimum conditions (2 pulses of DC of 70 V/mm, 70 microseconds pulse duration and AC of 5 V/mm for 5 sec), no significant difference was obtained in the fusion and development rates in different mouse strains, nor were fusion and development rates significantly different among PBS, physiological saline and mannitol solutions (P > 0.05).     

Columnar to Equiaxed Transition During Solidification of Small Ingot by Using Electric Current Pulse

A new approach to applying the electric current pulse (ECP)with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduced. The ECP was applied to different stages of the solidification. The results showed that the application of the ECP in both the initial stage (the thickness of solidified shell reached 2 mm approximately)and the late stage (the thickness of solidified shell reached 14 mm approximately)of solidification can promote the columnar to equiaxed transition (CET). The analysis showed that during solidification, a large number of nuclei around the upper surface fell off due to ECP, which subsequently showered on the melt and impinged the growth front of the columnar crystal. There-fore, the CET occurred. In addition, this method was also employed to influence the solidification process of bearing steel, and the results showed that the structure was changed from columnar crystal to equiaxed crystal, indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.     

Excimer laser surface processing of Ti-6Al-4V

We have examined the effect of surface processing in air, using excimer laser light at 248 nm wavelength, on the oxygen content, microstructure, and surface hardness of Ti-6Al-4V. Processing with a single pulse results in the transformation of theα +β material toα′ martensite. Multiple pulse processing results in rapid incorporation of oxygen in the material. Oxygen initially dissolves in the material in the liquid phase. As the concentration exceeds the solid solubility limit during solidification, TiO particles precipitate. In contrast to equilibrium oxidation processes in Ti, only TiO is observed as an oxidation product; further processing results in increased oxygen incorporation and an increased volume fraction of TiO but no other oxides of Ti. The TiO particle size is a function of the oxygen concentration and the number of pulses, with some grain growth occurring after many pulses. The effects of solution hardening by dissolved oxygen and precipitation hardening by the TiO are identifiable as functions of oxygen concentration and mean free path between particles, respectively. A maximum surface hardness almost twice that of electropolished Ti-6Al-4V is observed.     

Ti和Si对铁液黏度和凝固性质的影响

通过振荡杯高温熔体黏度仪对含Ti铁液的黏度进行测定,研究在冷却过程中Ti、Si对铁液黏度、黏流活化能、凝固温度以及凝固速度的影响.发现含Ti铁液在发生凝固以前,其黏度差别不大,黏流活化能为37.07~44.03 kJ·mol-1.Ti含量对铁液的凝固温度和凝固速度影响较大,Ti含量高的铁液开始凝固温度较高,而且凝固速度更快.硅含量低是钒钛铁液凝固温度低的主要原因.