Bai Bingzhe

Three Dimensional FEM Simulation of Titanium Hollow Blade Forming Process

With the introduction of high by-pass turbofan engines into both commercial and military aircraft industries, the fabrication of large size fan blade through superplastic forming/diffusion bonding (SPF/DB) has become a pivotal technique of turbine fan engine. There are three key steps to form a hollow blade: twisting, hot forming and SPF. In this study, a three dimensional finite element method (FEM) model is established to simulate the forming process of titanium fan blade, in which the mechanical behavior of TC4 obeys Backofens equation. Based on the numerical modeling, the influences of key factors such as the twisting rate, descending velocity, frictional coefficient, strain rate, the sheet thickness ratio of core sheet to face sheet on the forming force were studied. The results show that with increasing of the twisting rate, descending velocity, strain rate, the sheet thickness ratio of core sheet to face sheet, the forming forces increase; however the frictional coefficient has little influence on the forming force.

Effect of Chromium on CCT Diagrams of Novel Air-Cooled Bainite Steels Analyzed by Neural Network

The quantitative effects of chromium content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.Abstract The quantitative effects of chromium content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.

EFFECT OF TEMPERING TEMPERATURE ON LOW TEMPERATURE IMPACT TOUGHNESS OF A LOW CARBON Mn-SERIES BAINITIC STEEL

In order to reduce the cost of alloying elements,low carbon Mn series bainitic steels have been developed.The effect of tempering temperature on the microstructure and low temperature impact toughness of a low carbon Mn-series steel has been investigated in the present study.The as rolled steel plate samples with 30 mm thickness were tempered from 280℃to 600℃for 2 h. Metallographic microstructure show that the microstructure of the as-rolled steel is mostly bainite laths.Bainite laths start to merge and broaden after tempering at 460℃,and quasi-polygonal ferrite structures could be revealed after tempering at 600℃.Compared with the as-rolled steel,after tempering at 460℃,the yield strength of the steel changes slightly,remaining 725MPa,while the Charpy absorbed energy at-40℃increases from 38 J to 146 J,and the ductile-brittle transition temperature(DBTT)decreases from-18℃to-48℃.The EBSD and TEM results indicate that the improvement of low temperature impact toughness after tempering at 460℃is caused by the increase of fraction of high angle boundaries and the decrease of effective grain size during the recovery process of bainite laths.

EFFECT OF FINISH COOLING TEMPERATURE ON MICROSTRUCTURE AND LOW TEMPERATURE TOUGHNESS OF Mn-SERIES ULTRA-LOW CARBON HIGH STRENGTH LOW ALLOYED STEEL

Recently, the steel plates used in the ship, pipeline and bridge generally required not only high strength but also excellent low temperature toughness. As a competitive candidate, the ultra- low carbon high strength low alloyed(HSLA) steel has been developed widely. The low temperature toughness depends on the microstructure of the steels. Therefore, the relationship of low temperature toughness and microstructure should be studied in detail. In the present work, the steel plates with 25 mm thickness after hot rolling were immediately water quenched to 550, 450 and 350 ℃(finish cooling temperature), respectively, and subsequently air cooled to room temperature. The effect of finish cooling temperature on the microstructure and low temperature toughness ofMn-series ultra-low carbon HSLA steel was investigated by SEM, TEM and crystallographic analysis. The results show that the granular bainite, lath bainite and martensite were obtained with finish cooling temperatures decreasing. There are three blocks with different orientations in a single packet for lath bainite microstructure in the sample with finish cooling temperature of 450 ℃, leading to the refinement of effective grain size and large amount of highangle grain boundaries. Electron backscattered diffraction analyses of the cleavage crack path show that the bainite block boundaries can strongly hinder fracture propagation, and thus the refinement of bainite blocks can improve the low temperature toughness of Mn- series ultra- low carbon HSLA steel. Finally, the yield strength of 775 MPa and ductile-brittle transition temperature of-55 ℃can be achieved when the finish cooling temperature is 450 ℃.