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Chen B.-Z.,Northeastern University China | Chen Y.-L.,Northeastern University China | Chen Y.-L.,Tianjin Iron and Steel Co. | Zhu F.-X.,Northeastern University China | Gong W.-X.,Tianjin Iron and Steel Co.
Dongbei Daxue Xuebao/Journal of Northeastern University | Year: 2010

The 07MnNiMoVDR steel for low-temperature pressure vessel was investigated via thermal expansion testing in combination with TEM detection for the transformation of microstructure between different temperature intervals and change of carbide precipitation in the tempering process. The results showed that when the specimens are tempered at 300°C the residual austenite is decomposed and the lamellar θ-carbides are found between α-phase laths which are still of relatively high dislocation density. When tempered at 650°C, the α-phase laths are recovered with part of them recrystallized. Moreover, the precipitates are distributed between the recovered α-phase laths and on the recrystallized grain boundaries.

Wang Z.-Y.,Northeastern University China | Wang Z.-Y.,Tianjin Iron and Steel Co. | Ji C.,Northeastern University China | Gong W.-X.,Tianjin Iron and Steel Co. | Zhu M.-Y.,Northeastern University China
Kang T'ieh/Iron and Steel | Year: 2012

The optical microscope and SEM were applied to analyze the formation mechanism of transverse corner cracks of boron micro-alloyed steel slab. It is found that the cracks occur at relatively low corner temperatures of slab in straightening section that is in No.3 brittle zone of boron steel firs. The corner temperature of slab is relatively low due to the relatively low casting speed, irrational distribution of secondary cooling water and sprayers. Increasing casting speed and decreasing the cooling water flux at slab corners in the straightening section for mild cooling were performed first to control corner temperature above the upper limit in No.3 brittle zone of boron steel. Combined with the adjustment of dynamic, as a result, the corner temperature of slab was increased apparently, transverse corner cracking and internal quality of slab was greatly improved.

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