材料期刊网

Formation and Thermal Stability of Large Precipitates and Oxides in Titanium and Niobium Microalloyed Steel

ZHUO Xiaojun , WOO Daehee , WANG Xinhua , LEE Haegeon

钢铁研究学报(英文版)

Ascast CC slabs of microalloyed steels are prone to surface and subsurface cracking. Precipitation phenomena initiated during solidification reduce ductility at high temperature. The unidirectional solidification unit is employed to simulate the solidification process during continuous casting. Precipitation behavior and thermal stability are systematically investigated. Samples of adding titanium and niobium to steels have been examined using field emission scanning electron microscope (FESEM), electron probe Xray microanalyzer (EPMA), and transmission electron microscope (TEM). It has been found that the addition of titanium and niobium to highstrength lowalloyed (HSLA) steel resulted in undesirable large precipitation in the steels, ie, precipitation of large precipitates with various morphologies. The composition of the large precipitates has been determined. The effect of cooling rate on (Ti,Nb)(C,N) precipitate formation is investigated. With increasing the cooling rate, titaniumrich (Ti,Nb)(C,N) precipitates are transformed to niobiumrich (Ti,Nb)(C,N) precipitates. The thermal stability of these large precipitates and oxides have been assessed by carrying out various heat treatments such as holding and quenching from temperature at 800 and 1 200 ℃. It has been found that titaniumrich (Ti,Nb)(C,N) precipitate is stable at about 1 200 ℃ and niobiumrich (Ti,Nb)(C,N) precipitate is stable at about 800 ℃. After reheating at 1 200 ℃ for 1 h, (Ca,Mn)S and TiN are precipitated from CaAl oxide. However, during reheating at 800 ℃ for 1 h, CaAlTi oxide in specimens was stable. The thermodynamic calculation of simulating the thermal process is employed. The calculation results are in good agreement with the experimental results.

关键词: carbonitride;microsegregation;dendritic region;unidirectional solidification;heat treatment;thermal stability

THERMODYNAMIC PROPERTIES OF ALPHA-HELIX PROTEIN - A SOLITON APPROACH - COMMENT

Physical Review E

We disagree with the deduction of the equations of motion for the Davydov soliton and of the results in the paper by Jia-Xin Xiao et al. [Phys. Rev. A 44, 8375 (1991)]. The weakness and faults of the Davydov theory are also indicated.

关键词: davydov solitons;vibron solitons;molecules;excitation;system