ZHUO Xiaojun
,
WOO Daehee
,
WANG Xinhua
,
LEE Haegeon
钢铁研究学报(英文版)
Ascast CC slabs of microalloyed steels are prone to surface and subsurface 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 (FESEM), electron probe Xray microanalyzer (EPMA), and transmission electron microscope (TEM). It has been found that the addition of titanium and niobium to highstrength lowalloyed (HSLA) steel resulted in undesirable large precipitation in the steels, ie, 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, titaniumrich (Ti,Nb)(C,N) precipitates are transformed to niobiumrich (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 titaniumrich (Ti,Nb)(C,N) precipitate is stable at about 1 200 ℃ and niobiumrich (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 CaAl oxide. However, during reheating at 800 ℃ for 1 h, CaAlTi 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
ZHANG Qiaoying
,
WANG Litao
,
WANG Xinhua
,
LI Hong
,
WANG Wanjun
钢铁研究学报(英文版)
Nonmetallic inclusion distribution in the surface layer of IF steel slabs during unsteady casting was investigated using the original position statistic distribution analysis (OPA) method. It was found that most nonmetallic inclusions larger than 10 μm existed in the subsurface layers of 05-35 mm from the slab surfaces and very few large nonmetallic inclusions were found in the inner regions (≥45 mm from slab surfaces). In addition, it was found that at high casting speed level (14 m/min), even a slight change of casting speed could result in a remarkable increase of the nonmetallic inclusions. Thus, at high casting speed, changing the casting speed should be avoided or considerably lower speed changing rate must be used.
关键词:
IF steel;transient casting;slab surface layer;nonmetallic inclusion
HUANG Fuxiang
,
WANG Xinhua
,
ZHANG Jiongming
,
JI Chenxi
,
FANG Yuan
,
YU Yan
钢铁研究学报(英文版)
The solidification process of AISI 304 stainless steel during cooling at a rate of 005 K/s has been observed in situ using a confocal scanning laser microscope (CSLM). The results show that the δ phase appeared first in liquid steel, as the temperature decreased, the γ phase precipitated prior at δgrain boundary at 1 4522 ℃, the liquid steel disappeared at 1 4313 ℃, and then the γ phase precipitated on the δ ferrite. Based on the ScheilGulliver solidification model, the solidification processes of AISI 304 stainless steel are simulated using the Scheil model in ThermoCalc, and the simulation results agree well with the results observed in the experiment.
关键词:
stainless steel;confocal scanning laser microscope;strip casting;ThermoCalc
LIU Jingang
,
YAN Huicheng
,
LIU Liu
,
WANG Xinhua
钢铁研究学报(英文版)
In the water modeling experiments, three cases were considered, ie, a bare tundish, a tundish equipped with a turbulence inhibitor, and a rectangular tundish equipped with weirs (dams) and a turbulence inhibitor. Comparing the RTD curves, inclusion separation, and the result of the streamline experiment, it can be found that the tundish equipped with weirs (dams) and a turbulence inhibitor has a great effect on the flow field and the inclusion separation when compared with the sole use or no use of the turbulent inhibitor or weirs (dams). In addition, the enlargement of the distance between the weir and dam will result in a better effect when the tundish equipped with weirs (dam) and a turbulence inhibitor was used.
关键词:
tundish;flow field;turbulence inhibitor;weir;dam;water modeling experiment
