Papers by Author: Chun Lin Qiu

Abstract: Thermo-mechanical process followed by accelerated cooling and high temperature tempering was applied to investigate the microstructure evolution and mechanical properties of a high strength crack-free steel. Optical microscopy, transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) technique were employed to analyze the complex microstructural characteristics of the steel. The results indicated that the precipitation strengthening effect played an important role in optimizing the tempered strength. According to EBSD results, the average grain size of as-rolled specimens was about 3.2 μm, and it increased slightly with the tempering temperature. Therefore, the grain refinement wasthe major reason for the good mechanical properties of the crack-free steel.

Abstract: The low cost Q460 and Q550 steel plates were produced in the 4200mm wide and heavy plate mill using Normal Hot Rolling and High Rate Cooling (NHR+HRC) process. The effect of both rolling processes on microstructure and mechanical property was studied. The results indicate that new type process can realize the good match between microstructure and mechanical properties. Meanwhile the new technology can short rolling time, reduce alloying addition, and improve the output of mill, it is also promote iron and steel industry developing continuously.

Abstract: High strength hull structural steel plate FH40 has been successfully developed by a 3500mm plate production line. Low-carbon micro-alloying niobium elements and TMCP (thermo-mechanical controlled processing) were employed to refine the grains and improve mechanical properties. This paper investigated the effects of TMCP process on the microstructure and mechanical properties of the rolled FH40 plate. Results indicate that the treatment could significantly improve the mechanical strength and impact toughness of the steel and the impact ductility was further enhanced after strain aging. The properties of plates remarkably satisfied with the requirements of the national standard of china and rules requirements by shipping classification associations.

Abstract: The prediction of the hardenability of gear steel has been carried using stepwise polynomial regression and artificial neural networks (ANN). The software was programmed to quantitatively predict the hardenability of gear steel by its chemical composition using two calculating models respectively. The prediction results using artificial neural networks have more precise than the stepwise polynomial regression model. The predicted values of the ANN coincide well with the actual data. So an important foundation has been laid for prediction and controlling the production of gear steel.

Abstract: Based on mean yield criterion, an analytical solution for the mode I crack tip plastic zone (CTPZ) under small scale yielding was derived. The results reveal that the size of CTPZ determined by MY criterion is between those by Mises’ yield criterion the smallest, and by Tresca’s criterion the largest; while the zone is almost coincide with that by Mises’ one. The size of CTPZ is related to the ratio of fracture toughness to yield strength; with increasing of the ratio, the size of the zone increases, meaning the better of fracture toughness.