YU Wei
,
QIAN Ya-jun
,
WU Hui-bin
,
YANG Yue-hui
钢铁研究学报(英文版)
Two types of steel, C-Mn-Cr-Mo-B microalloyed steel and C-Mn-Mo-Nb-Cu-B microalloyed steel, are designed to develop 1000 MPa ultra-high strength steel. Two kinds of processes, thermomechanical controlled process (TMCP) combined with traditional off-line quenching and tempering (QT) process versus controlled rolling process (CR) combined with direct quenching and tempering (DQ+T) process, are applied. The effect of heat treatment processing mode on the microstructure and mechanical properties is studied. The relationship between microstructure and mechanical properties is investigated by SEM and TEM. After tempering at 450 to 550 ℃ for 1 h, the steel produced by TMCP+QT process shows combination of excellent strength and low temperature toughness. The yield strength is above 1000 MPa, elongation above 15% and impact energy at -40 ℃ more than 30 J. After tempering at 450 ℃, a large number of ε-Cu particles precipitated in C-Mn-Mo-Nb-Cu-B steel produced by CR+DQ+T process lead to a significant increase in yield strength. And after tempering at 500 to 600 ℃, the yield strength of the steel is further improved to 1030 MPa because of precipitates, such as nitride or carbide of niobium, carbide of molybedenum and vanadium. When the tempering temperature is increased above 620 ℃, the yield strength is still higher than 1000 MPa and elongation is above 20% and impact energy at -40 ℃ is more than 35 J. After tempering at above 500 ℃, the toughness of the steel treated by TMCP+QT process is superior to that of steel by CR+DQ+T process.
关键词:
Heat treatment, High strength steel, Microtructures, Mechanical properties
CHEN Zhiming
,
LUO Fei
,
XU Yuge
,
YU Wei
钢铁研究学报(英文版)
Roll eccentricity is an important factor causing thickness variations during hot strip rolling and might define the limit of strip thickness control accuracy. An improved multiresolution wavelet transform algorithm was proposed to compensate for the roll eccentricity. The wavelet transform method had good localization characteristics in both the time and frequency domains for signal analysis; however, the wavelet method had a frequencyaliasing problem owing to the less than ideal cutoff frequency characteristics of wavelets. This made its component reconstruction of an inaccurate signal. To eliminate inherent frequency aliases in the wavelet transform, fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) were combined with the Mallat algorithm. This synthesis was described in detail. Then, the roll eccentricity component was extracted from rolling force signal. An automatic gauge control (AGC) system added with a multiresolution wavelet analyzer was designed. Experimental results showed that the antialiasing method could greatly restrain the inverse effect of eccentricity and the thickness control accuracy was improved from ±40 μm to ±15 μm.
关键词:
hot strip rolling;roll eccentricity compensation;wavelet analysis;frequency alias
