Novel Concept of Cleansing the Liquid Steel by the Fine In-Situ Phase Due to the Composite Ball Explosion Reaction in RH Ladle

The production of high purity steel is a major task for the iron and steel enterprises in the 21st century. To improve the quality of steel products and produce the cleanness steel, the key technique is to control inclusions in the molten steel. In the present investigation, a novel fine inclusion removal technology due to the dispersed in-situ phase induced by the composite ball explosion reaction was put forward. A composite ball with this function has been designed and the industrial experimental investigation was also carried out. The results indicate that feeding composite ball in RH ladle is a novel technology and the inclusion in the molten steel can be removed effectively. Compared with conventional inclusion removal technology, the number of the oxide inclusion can be decreased to a lower level and the inclusion size becomes much finer. Using this novel technology, the total oxygen in the as-cast slab can approach to 6ppm and the steel production cost for per ton can be reduced by 5 -12 RMB. This novel technology can be achieved without special facility and be realized in most steelmaking plant.     

In-Situ Analysis of Bulk Solidifying the Hyper-Monotectic Alloy Under a Compound Electric-Magnetic Field by Physical Simulation

A physical simulation was carried out to investigate the realistic experiment of bulk solidifying the Zn-Bi hyper-monotectic alloy under various compound electric-magnetic fields(CEMF).For this experiment,two crucial parameters determinate the cast microstructure,the one is electric-magnetic force(EMF)and the other is the frequency of AC current.Results show that the minor phase could be mixed in the other phase from the initial layered structure when the EMF above a specific value under fixed frequency,and the average diameter of minor phase droplet decreases with increasing EMF.The evolution of the liquid phases structure is reasonable agree with the realistic experiment of Zn-Bi hyper-monotectic alloy,which suggests that the mechanism revealed by the physical simulation could represent the one in the realistic experiment.     

Table-like magnetocaloric effect and large refrigerant capacity of composite magnetic refrigerants based on LaFe11.6Si1.4Hy alloys

Composite magnetic refrigerants were prepared by physical mixing LaFe_(11.6)Si_(1.4)H_y alloys with different Curie temperatures(Tc). The phase structures of these LaFe_(11.6)Si_(1.4)H_y alloys were analyzed by X-ray diffraction(XRD) and the magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The results indicate the experimental magnetic entropy change(-△S_M)-Tcurve corresponds reasonably with the(-△S_M)-Tcurve calculated by the linear combination of(-△S_M)-T curves of the single material. An optimal mixing ratio can make the composite magnetic refrigerant possess a table-like(-△S_M)-Tcurve which is beneficial to magnetic Ericsson cycle. When three LaFe_(11.6)Si_(1.4)H_y alloys with different T_c are mixed, the full width at half maximum(△T_(FWHM)) of(-△S_M)-T curves is about 48.7 K and the RC is about 177.76 J/kg under a magnetic field change of 2 T. The composite magnetic refrigerants based on LaFe_(11.6)Si_(1.4)H_y alloys can be promising candidates for near room temperature magnetic refrigeration and the work will be helpful to develop novel composite magnetic refrigerants with table-like MCE and large RC.     

Co-Al基三元系中B2相的溶解度间隙与稳定性

Information on phase equilibria in the Co-Al based systems which are related to some magnetic and heat resistance materials is important for their microstructural control. Recently, it was proposed with a theoretical calculation on electronic band structure that some Heusler-type alloys Co2 XAl (X: Cr and Mn) should be a new type of spinelectronic materials so-called half-metallic ferromagnet. In the case of the Co2CrAl, however, magnetic properties expected from the theoretical work can not been experimentally obtained and the reason has been still unknown. On the other hand, a tunne- ling magnetoresistance (TMR) effect due to the half-metallic properties was reported in Co2 (Cr0.6 Fe0.4 ) Al alloy, but not the Co2CrAl alloy. In the present paper, it is reported that this discrepancy with the theoretical work in the Co2CrAl alloy is bought about by phase separation between A2 and B2 phases, and that the substitution of Fe for Cr can suppress the precipitation of A2 phase in the B2 phase. Such a phase separation is originally due to the miscibility gap between CoAl and Cr formed in the Co-Al-Cr ternary system as well as that reported by Hao et al. in the Ni-Co-Al-Fe system.     

Principle and Practice on High Nitrogen Steel Melting by Blowing Ammonia Gas

 Abstract: During the HNS melting process, the absorption reaction of Nitrogen in the liquid steel by blowing NH3 and N2 was investigated respectively. In order to obtain higher content of nitrogen in steel, the liquid steel should be deoxidized and desulfurized because the [O] and [S] as surface activity element is not favorable to absorb nitrogen in melting process. Based on the metallurgical thermodynamics, the coupling reaction of NH3 with [O] can improve the generation of activity nitrogen atom in liquid steel. Nitrogen atom is easier to be absorbed than nitrogen molecule. At the same time, blowing ammonia gas can remove the oxygen from liquid steel and decreased the inclusion in the steel. Experiments of HNS melting in ten-kilogram inductive furnace indicated that, for liquid steel with same content of alloys and blowing the same mole of nitrogen , the absorption effect of nitrogen by blowing NH3 increase 18~75% than that of blowing N2.The technical process of melting HNS by blowing NH3 under normal pressure is feasible in industry production.h     

Solidification Structure of Cu-Fe Alloy under a Rotary Electromagnetic Stirrer

The effect of rotary electromagnetic stirring(EMS)on the Cu grain size and Fe dendrites is investigated in this paper,in order to get a Cu-Fe alloy ingot with good quality.The macro-and micro-structures are observed by Leica-DMR optical microscope.The solidification structures of Cu-2 and 8wt.%Fe consist with finer equiaxed grains.The Cu grain size is most sensitive to the Fe content.EMS can’t effectively improve the grain size for the Cu-Fe alloy.For ingot cooled without EMS,there are also many large Fe-rich particles distribute in the Cu-matrix,beside the Fe dendrites,because of the existence of metastable miscibility gap in the undercooled liquid state.And the Fe-rich phases are not found in the ingots with EMS,indicating the EMS can affect the undercooling of the liquid and further restrain the liquid phase separation.Under the EMS,the Fe dendrites break up into many smaller Fe fragments.And the size of Fe fragments decreases with the increasing stirring current.     

Isothermal and athermal type martensitic transformations in yttria doped zirconia

The phase transformation from the high temperature tetragonal phase to the low temperature monoclinic phase of zirconia had been long considered to be a typical athermal martensitic transformation until it was recently identified to be a fast isothermal transformation. The isothermal nature becomes more apparent when a stabilizing oxide, such as yttria, is doped, by which the transformation temperature is reduced and accordingly the transformation rate becomes low.Thus it becomes easy to experimentally establish a C-curve nature in a TTT (Time-Temperature-Transformation) diagram. The C-curve approaches that of well known isothermal transformation of Y-TZP (Yttria Doped Tetragonal Zirconia Polycrystals), which typically contains 3mol% of Y2O3. In principle, an isothermal transformation can be suppressed by a rapid cooling so that the cooling curve avoids intersecting the C-curve in TTT diagram. Y-TZP is the case, where the stability of the metastable tetragonal phase is relatively high and thus the tetragonal phase persists even at the liquid nitrogen temperature. On the other hand, the high temperature tetragonal phase of pure zirconia can never be quenched-in at room temperature by a rapid cooling; instead it always turns into monoclinic phase at room temperature. This suggests the occurrence of an athermal transformation after escaping the isothermal transformation, provided the cooling rate was fast enough to suppress the isothermal transformation. Thus, with an intermediate yttria composition, it would be possible to obtain the tetragonal phase which is not only metastable at room temperature but athermally transforms into the monoclinic phase by subzero cooling. The objective of the present work is to show that, with a certain range of yttria content, the tetragonal phase can be quenched in at room temperature and undergoes isothermal transformation and athermal transformation depending on being heated at a moderate temperature or under-cooied below room temperature. Because both of the product phases are essentially the same monoclinic phase, both transformations are regarded as martensitic transformation, i. e. isothermal and athermal martensite. In some steels such as Fe-Mn-Ni and Fe-Ni-C, the occurrence of both isothermal and alhermal martensitic transformations has been reported. However, in these cases, the isothermal transformation occurs at temperatures slightly above the Ms (Martensite start) temperatures, and thus these transformations are considered to conform the same C-curve. On the other hand, the Ms temperature of the present material is well below the C-curve, which suggests that completely different mechanisms are controlling the kinetics of these two modes of transformations. Other aspects on these transformations are also to be reported..     

Corrosion Behavior of Fe-based Bulk Metallic Glass and In-situ Dendrite-reinforced Metallic Glass Matrix Composites in Acid Solution

The corrosion behavior study was conducted on a novel Fe_(77)Mo_5P_9C_(7.5)B_(1.5)in-situ metallic glass matrix composite(MGMC).This composite sample was developed by introduction of bccα-Fe dendrites as reinforcing phase.The corrosion behavior of this composite was compared to its monolithic counterpart and other Fe-based alloys such as 304 Land 2304Lstainless steels.The corrosion resistance of MGMCs in H_2SO_4 solution shows inferior to that of other Fe-based alloys.Experiments suggest that Fe-BMGs samples possess better corrosion resistance property than that of Fe-MGMCs.The possible underlying reasons can be the inhomogeneity induced by the precipitation ofα-Fe dendrites in the MGMCs.     

Modification Mechanism of Rare Earth Elements in ZA27 Casting Alloys

The model of the liquid-phase ZA27 alloys was set up by molecular dynamics theory. The atomic structure of phase, RE-compounds, and the phase-liquid interface in ZA27 alloys were constructed by computer programming. Electronic structures of phase with rare earth elements dissolved and of phase-liquid interfaces with rare earth elements enrichment in ZA27 casting alloys were investigated by using the Recursion method. The ESE energy of RE elements and the structure energy of RE-compounds, phase, and the liquid-phase ZA27 alloys were calculated. The results show that rare earth elements are more stable to be in the phase interface than in phase, which explains the fact of very small solid solubility of rare earth elements in phase, and the enrichment in the solid-liquid growth front. This makes dendrite melt and break down, dissociate and propagate. RE-compounds can act as heterogeneous nuclei for phase, leading to phase refinement. All above elucidates the modification mechanism of rare earth elements in zinc-aluminum casting alloys, at electronic level.     

Formation of core-type macroscopic morphologies in Cu-Fe base alloys with liquid miscibility gap

The effects of alloying elements on the macroscopic morphologies in Cu-Fe base alloys were experimentally investigated. It was found that macroscopic homogeneity can be achieved by the addition of Mn, Ni, Al, or Co in the Cu-Fe base alloys, while the core-type macroscopic morphologies with Cu-rich or Fe-rich cores, which are radially separated as two layers in the inner and outer parts of the ingot solidified in the cast-iron mold, were formed by the addition of C, Cr, Mo, Nb, Si, or V. It is shown that the formation of the core-type macroscopic morphology is strongly connected with the existence of a stable miscibility gap of the liquid phase in the Cu-Fe base alloy due to the addition of alloying elements. The liquid phase with less volume fraction always forms the center part. This result can be explained by a mechanism that the minor droplets as the second phase are forced to move into the thermal center due to Marangoni motion, which is caused by the temperature dependence of interfacial energy between two liquid phases.     

基于相图和组织控制的先进材料开发

Recent progress on research activities of phase diagrams in our laboratory has been presented. Experimental studies and thermodynamic calculations based on CALPHAD (Calculation of Phase Diagrams) method have been conducted in the following alloy systems. 1. Database on microalloying steels including carbide, nitride and sulfide is now being constructed. 2. ADAMIS (Alloy Database for Micro-Solders) containing 8 elements of Ag, Bi, Cu, In, Sb, Sn, Zn and Pb hasbeen constructed, which can handle all combinations of these elements and all composition ranges. 3. A thermodynamic database of Cu-base alloys including Cu-X binary system and Cu-Fe, Cu-Ni, Cu-Cr base ternarysystems has been constructed. 4. Experimental and thermodynamic calculations on Fe, Ni, Co and Ti aluminides have been conducted. 5. Experimental and thermodynamic calculations on Co base magnetic recording media have been conducted. 6. Thermodynamic analysis of interaction between magnetic and chemical orderings has been performed. By utilizing the information on phase diagrams, the following advanced materials have been developed. (A) New type of high speed steel with high hardness about Hv≈1000 by carbide dispersion carburizing method, (B) New Pb-free machinable stainless steel using titanium carbosulphide. (C) New Pb-free solder for Die-attaching use. (D) Shape memory alloys; Cu-base, Ferromagnetic Ni-base and Fe-base. (E) Invar alloys. (F) Egg-type powder. Typical examples of phase diagrams, phase stability, database and its application for the development of advanced materials will be presented.     

Solidification of the Cu-35wt pct Fe Alloys with Liquid Separation

The microstructures of the Cu-35wt pct Fe alloys were investigated by melt-fluxing in combination with cyclic superheating and melt-spinning technique, respectively. Using the melt-fluxing with cyclic superheating technique, it was found that a complicated sub-microstructure formed in the separated minor phase, when the undercooling was 120 K (120 °C). The processes of the phase transformation from a liquid state to room temperature for undercooled Cu-35wt pct Fe alloys were discussed, in order to understand the solidification with metastable liquid separation. By means of melt-spinning technique, it was indicated that the microstructure of solidification for Cu-35wt pct Fe alloys could be refined due to the high cooling rate.     

Particle rearrangement during liquid phase sintering of Cu–20Zn and Cu–10Sn–10Pb prepared from prealloyed powder

Abstract

It would be useful to be able to produce brass and bronze components made from prealloyed powders by supersolidus liquid phase sintering. The microstructures obtained in such alloys are sensitive to constituent alloying elements and small change in sintering temperature. Although the formation of liquid during sintering is potentially attractive for densification, the effects of gravity on the liquid phase can result in graded densification. Evaporation of alloying elements and their solubility in the base metal also affect the extent to which heterogeneous cross-sections are obtained. The aim of the present study was to examine the effect of alloying and sintering temperature on the mode of particle rearrangement, and consequently on graded densification, by microstructural and fractographic analysis. Comparing the fracture morphology from top to bottom of the fracture surface is also helpful in developing a model to describe the phenomena during sintering of similar alloys.     

Application of Molecular Interaction Volume Model for Phase Equilibrium of Sn-Based Binary System in Vacuum Distillation

Based on the molecular interaction volume model (MIVM), the activities of components of Sn-Sb, Sb-Bi, Sn-Zn, Sn-Cu, and Sn-Ag alloys were predicted. The predicted values are in good agreement with the experimental data, which indicate that the MIVM is of better stability and reliability due to its good physical basis. A significant advantage of the MIVM lies in its ability to predict the thermodynamic properties of liquid alloys using only two parameters. The phase equilibria of Sn-Sb and Sn-Bi alloys were calculated based on the properties of pure components and the activity coefficients, which indicates that Sn-Sb and Sn-Bi alloys can be separated thoroughly by vacuum distillation. This study extends previous investigations and provides an effective and convenient model on which to base refining simulations for Sn-based alloys.     

Wear Protection by Fe‐B‐C Hard Phases

Four as‐cast iron alloys with (mass%) 1B + 3C, 2B + 2C, 3B + 1C and 4B + 1C were investigated in respect to their microstructure by optical and scanning electron microscopy with EDX and ESBD and by microprobe analysis. The microhardness of eutectic Fe₃(C,B) increased with the B/C ratio and raised the resistance to scratching by Flint particles. The low melting range of the castings was used for the powder metallurgical production of a metal matrix composite by liquid phase sintering of admixed hard particles in an Fe‐B‐C base material. Abrasive wear tests showed that the eutectic carborides in the base material raised the wear resistance even more than the admixed particles.     

稀土钼合金组织结构的研究

在TZM钼合金的基础上，通过复合添加稀土Y、Ce的试验，生产出了高温性能优异且工艺易于控制的钼合金。对不同配方稀土钼合金的组织结构进行了深入分析，指出弥散颗粒不仅存在晶界，也可存在于晶内，因此可同时强化晶界和晶粒，但粗大的弥散颗粒和Mo-Ti固溶体对合金性能不利。用化学法富集了合金中的弥散相，通过X射线衍射和能谱综合分析，确定了弥散相的相结构，证实了在合金中稀土元素Y、Ce与Ti、Zr形成Y2O3结构的复合氧化物。Ti在合金中则有三种可能的存在形态：一是形成复合氧化物，二是形成Ti(C,N),三是形成Mo-Ti固溶体。     

波纹状Ti—Mn复合阳极工业实验

电解二氧化锰（ＥＭＤ）用波纹状Ｔｉ－Ｍｎ复合阳极由波纹状Ｔｉ基Ｔｉ－Ｍｎ合金复合阳极大板、Ｔｉ加强筋及铝横担组成。该阳极的特点是ＥＭＤ质量高，产量大，槽电压低，电流效率高，使用寿命长。工业实验表明这种复合阳极优于纯钛和其他传统阳极。     

微量添加晶界合金对烧结Nd-Fe-B力学性能及微观结构的影响

采用双合金法制备系列烧结Nd—Fe—B磁体(保持其主合金成分不变：Ndl4．1Dy0．5Fe79.0B6.4(原子分数)，所添加的晶界合金中的B含量从0．95％(原子分数)逐步增加到6．95％(原子分数))，研究了微量添加晶界合金对烧结Nd—Fe—B力学性能及微观结构的影响。研究结果表明：微量添加晶界合金所制备的磁体，其抗弯强度值普遍高于单合金法制得的磁体；前者的抗弯强度最高可达397MPa，高于铸造，热压磁体的抗弯值，而后者的抗弯强度仅为309MPa。由相结构分析可知，当添加的晶界合金中的B含量为O．95(原子分数)，主相晶格的四方度减小，这时磁体具有最高的抗弯强度。另外，微量添加晶界合金，可使磁体中晶界相的分布更加均匀，从而基本上消除了主相晶粒直接接触的现象，使晶粒的不规则长大得到抑制。这也是微量添加晶界合金后磁体具有较高抗弯强度的原因之一。对磁性能的研究结果表明，微量添加晶界合金几乎不影响烧结Nd—Fe—B磁体的磁性能。