Relationship between secondary dendrite arm spacing and local solidification time of 30Cr2Ni4MoV alloy at slow cooling rates

Solidification process of 231 t 30Cr2Ni4MoV ingot manufactured by slow cooling process was studied using experimental and numerical simulations, which tackled the problems of high cost and long period in large ingot studying. Based on the numerical results of large ingot, five characteristic locations under different temperature gradients and cooling rates chosen from the large ingot were simulated. The experiments were performed under the same temperature conditions as in numerical simulations with specialized instrument. The influences of temperature gradient in the solid-liquid interface and solidification rate on the size and morphology of solidification structure were analyzed at cooling rate ranging from 10-3 to 10 2℃ s-1. Solidification macrostructure and microstructure showed that no columnar dendrite was found in any specimen. The grain size and secondary dendrite arm spacing decreased at larger cooling rate, and the relationship between secondary dendrite arm spacing and local solidification time or cooling rate was determined.

FEM Simulation of the Hydrogen Diffusion in X80 Pipeline Steel During Stacking for Slow Cooling

The influence of temperature on the hydrogen diffusion behavior in X80 pipeline steel during stacking for slow cooling was studied using electrochemical penetration method, the temperature field and the hydrogen diffusion in this pipeline steel during stacking for slow cooling were simulated by ABAQUS finite element method （FEM） software. The results show that in this process there is a reciprocal relationship between the natural logarithm of hydrogen diffusion coefficient and temperature. The cooling rate decreases gradually with the increase of steel plate thickness. The hydrogen content is higher at high temperature （500-400 ℃） than that in low temperature region （300-100 ℃）. The FEM simulation results are consistent with the experimental ones, and the model can be used to predict the hydrogen diffusion behavior in industrial production of X80 pipeline steel.

Mineral phase reconstruction behavior of direct reduction and smelting titanium slag at high temperature and slow cooling

Titanium slag in this study was produced by subjecting titanomagnetite concentrate to direct reductionelectric furnace smelting. Processing mineralogy and mineral phase reconstruction behavior at high temperature and slow cooling treatment were examined by chemical analysis, X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM）, and energydispersive spectroscopy （EDS）. Anosovite solid solution is the main titanium product by the direct reduction and smelting process. Results of slow-cooling experiments show that crystal volume and size increase as cooling rate decreases. Anosovite and gangue mineral crystals develop fully with large crystal volume and size at a cooling rate of 2 K.min-1. Moreover, the growth of anosovite crystal was characterized by crystal nucleation and growth theory. These results provide further insights into the separation of anosovite from gangue by mineral processing.

Comparison of conventional and directional freezing for the cryopreservation of human umbilical vein endothelial cells

AIM:To compare conventional slow equilibrium cooling and directional freezing(DF) by gauze package for cryopreservation of human umbilical vein endothelial cells(HUVECs).METHODS:HUVECs were randomly assigned to conventional freezing(CF) and DF by gauze package group. The two groups of HUVECs were incubated with a freezing liquid consisting of 10% dimethylsulfoxide(DMSO), 60% fetal bovine serum(FBS) and 30%Dulbecco’s modified Eagle’s medium(DMEM) and then put into cryopreserved tubes. CF group, slow equilibrium cooling was performed with the following program:precool in 4℃ for 30 min,-20℃ for 1h, and then immersion in-80℃ refrigerator. DF group, the tubes were packaged with gauze and then directional freezing in-80℃ refrigerator straightly. One month later, the vitality of HUVECs were calculated between two groups.RESULTS:There was no significant difference in the survival rate and growth curve between CF and DF groups. The DF group was significantly better than CFgroup in adherent rates, morphological changes and proliferative ability.CONCLUSION:In the conventional cryopreserved method, cells are slow equilibrium cooling by steps(4℃,-20℃ and finally-80℃), which is a complicated and time-consuming process. But the improved DF by gauze package method is better than conventional method, for which is convenient and easy to operate.

Morphological evolution ofγ'precipitate under various rejuvenation heat treatment cycles in a damaged nickel-based superalloy

The morphological evolution ofγ’precipitates for a damaged nickel-based superalloy GTD-111 under different rejuvenation heat treatments(RHTs)was investigated.The degeneratedγ’precipitates can be completely dissolved into the y matrix under the full solution condition of 1200℃/2 h,and only fineγ’precipitates re-precipitated during the cooling stage of the full solution can be observed,but these fineγ’precipitates cannot grow continuously to be similar as those in virgin alloy during the subsequent long-term aging.It is found that the newly developed RHT schedule,including the full solution,the partial solution,and the aging treatments,can effectively recover the degeneratedγ’precipitates in the GTD-111superalloy to their original state.Moreover,the effects of different RHT cycles on theγ’evolution were investigated.The experimental results show that the degeneratedγ’precipitates can be restored to be analogous with those in virgin alloy by slow cooling after the full solution and an appropriate partial solution followed by the long-term aging.Compared with the different microhardness under various RHT schedules,the microhardness after full solution and partial solution followed by aging is more close to that of the initial alloy.

Microstructural Evolution and Properties of a High Strength Steel with Different Direct Quenching Processes

A high strength low alloy steel with low carbon equivalent was selected for simulating online direct quench- ing and coiling （DQ-C） process. The influence of stop quenching temperature on mechanical properties and micro- structures was studied and compared with normal direct quenching and tempering （DQ-T） process. The study con- firmed that required mechanical properties were obtained for both the processes. Properties of the experimental steel with DQ-C process could reach the same level as that of DQ-T process in general. In the DQ-C process, strength de- creased with increase in stop quenching temperature. Martensite was obtained and experienced an aging process at stop quenching temperature below Mi. On fast cooling below Mi, martensite was partially transformed and carbon partitioning occurred during slow cooling. The reduction in solid solution carbon and increased amount of retained austenite led to lower strength compared with the DQ-T process. DQ-C process was more favorable for microalloy carbide precipitation. However, impact toughness under different cooling conditions was adequate because of low car- bon equivalent and refined microstructure.

High-temperature solution growth of large size chalcogenide FeTxSe(T:Fe,Co)superconducting single crystals

We report the growth of high quality Fe excess and Co doped,FeTxSe single crystals in nominal ratio via slow cooling method of high temperature solution growth technique and,their structural and physical properties through the X‐ray diffraction,Raman spectroscopy,magnetic and transports measurements.Selective area electron diffraction(SAED)patterns and X‐ray diffraction of cleavage piece confirm the growth of single crystals in(h0l)orientations.Observations of phonon vibration modes(A_(1g) and B_(1g))in Raman spectroscopy measurements mark the qualitative analysis of these single crystals.Low temperature magnetic and electrical transport studies manifest the superconducting nature of both single crystals.