Papers by Author: Zhou Hua Jiang

Abstract: The effects of the alloying sequence and refining time on the inclusions in Fe–9Cr alloy reinforced with Y₂O₃ nanoparticles were investigated. The size and number of inclusions in the alloys were determined via optical microscopy, and their morphology and composition were determined via scanning electron microscopy. The Y₂O₃ mainly acted as a nucleating agent in the Si–Mn+Y₂O₃+Ti alloying process, promoting the precipitation of other oxides, which was beneficial for the formation of Y–Ti–O particles. In contrast, no Y–Ti inclusions were formed when the Si–Mn+Ti+Y₂O₃ alloying process was employed. In addition, the inclusions in the alloy tended to stabilize after refinement for 5–10 min. This study offers a general pathway for the manufacture of oxide dispersion strengthened steel via a smelting process.

Abstract: A three-dimensional mathematical model of mold electromagnetic stirring (M-EMS) for round billet was established. Based on Maxwell’s equations, the distribution of electromagnetic field was solved by ANSYS software. Different process parameters’ influence on magnetic flux density and electromagnetic force (EMF) was studied. The results show that the magnetic flux density reaches the maximum at the stirrer center in the axis direction and increases with the increasing distance from the circle center on the cross section of the stirrer center. The tangential EMF is symmetric about the circle center and reaches the maximum at the edge of round billet. Both the magnetic flux density and the tangential EMF increase with the increasing current intensity. With the increasing current frequency, the magnetic flux density decreases, while the tangential EMF increases in the applied range of current frequency for M-EMS.

Abstract: The precipitates and precipitation kinetics of super austenitic stainless steel with high Mo and N (HHSASS) were investigated by optical microscope (OM), scanning electron microscope (SEM) and quantitative metallography method. The results show that the TTP curves are C-shaped, the “nose” temperatures of precipitation are found to be 1000°C with the incubation periods of 120s and 600s, respectively. At 1000°C, some precipitates form as ellipsoidal-shaped and connect along the grain boundaries first. Then a few precipitates start forming as needle-shaped within austenite grains. Until aging for 300min, the field is filled with needle-shaped precipitates. The main precipitates in HHSASS are Sigma phase and Chi phase that are rich in Cr and Mo. The precipitates on the grain boundaries are ellipsoidal-shaped and those in the austenite grains are needle-shaped. About the structures of precipitates need to be further researched.

Abstract: 23Co-Ni is an ultra-high strength steel and it needs ultra low nitrogen content in the steel. The removal of nitrogen for 23Co-Ni steel in a 6t/12t Vacuum Induction Melting Furnace (VIM) with different melting processes was studied. The results show that, the longer of the melting time and the higher of the vacuum level, the lower of the final nitrogen contents is. The denitrogenization rate can reach 70% when the melting time is more than 8 hours. The electromagnetic stirring can increase the denitrogenization speed. When the VIM is vacuumed to 1-3 Pa, it can make the nitrogen content reaches 0.0005%-0.0008%.

Abstract: The kinetics of nitrogen absorption in Fe-Cr-Mn (Mo) alloys under 0.1 MPa nitrogen pressure and 1873K was investigated by top blowing nitrogen gas into the steel melts. A thermodynamic model of nitrogen solubility was established. Also the effect of surface active elements oxygen and sulfur on nitrogen absorption was studied. The results show that Fe-Cr-Mn (Mo) melts achieve nitrogen saturation value within 50 minutes, the nitrogen solubility increases with the content of chromium and manganese, but the experiment values of nitrogen solubility are general lower than theoretical values because of the open nitrogen gas atmosphere and high surface active elements content in the steel melts. The nitrogen absorption can be described well by a second order reaction and the interfacial reaction is restrictive step. The rate of nitrogen absorption decreases by lowering the surface reaction constant due to oxygen and sulfur in the steel melts. The effect of the surface active elements oxygen and sulfur on nitrogen absorption can be described well as .

Abstract: Genetic algorithm-back propagation neural network (GA-BPNN) was used for activity prediction of slag, then activity prediction software of slag was developed by Matrix Laboratory (Matlab) and Microsoft visual C++ (VC++), and activity database of slag was established. The software is simple operation and activity of slag can be predicted accurately, almost activity of slag in the condition of different temperature and composition of slag system can be predicted. The plenty of activity data was collected by the database of software, therefore, more accurate activity data for thermodynamic and dynamics calculation of metallurgist were provided by software. The software lays a good foundation for producing more advanced steel materials.

Abstract: Bimetallic rolls’ interfaces manufactured by liquid-solid bonding method have been studied in the manuscript. Effect of pretreatment method of roll core, pouring temperature and preheating temperature of core to the bonding of interfaces are analyzed. Line scanning to the element chromium is done with SEM, the effect of technology to the organize structure and element diffusion is researched; Shear stress experiment of interface is done to analyze the effect of technology to bond strength.

Abstract: High nitrogen stainless steels with excellent mechanical and corrosion resistance properties is focused on to develop a new class of engineering material. The manufacture process of high nitrogen stainless steels under high nitrogen pressure is complicated. There are some theoretical problems to be solved for large scale melting and cast high nitrogen stainless steels. The thermodynamic calculation models of nitrogen solubility in the liquid phase, δ ferrite phase and γ austenitic phase built can well predict the nitrogen solubility and analyze the effect of temperature, alloy components and nitrogen pressure on the nitrogen solubility. The minimum nitrogen pressure for preventing the nitrogen porosity formation has been calculated by the micro-segregation. By the analysis nitrogen behavior of melting and cast high nitrogen stainless steels, it is possible to produce high nitrogen stainless steels in a large scale in China.

Abstract: The influence of microstructure evolution of a nickel-based superalloy after long-term aging on the tensile properties and deformation behavior was investigated. The results shows that the aging time exhibits an significant effect on the strength of alloy under low strain rate and the elongation decrease with increasing the aging time, but the aging time has no obvious effect on the strength of the alloy and elongation is affected significantly by aging time. During deformation under high strain rate, the dislocation motion is blocked and the dislocation can not release in time, the strengthening phase peak size effect does not appear in the aging time ranging from 0h to 1000h, so the influent of aging time on the strength of the alloy is not obvious. After long-term aging, no precipitation appear in both sides of the grain boundary which leads to the coordination ability of plastic deformation of grain boundaries reducing, so the ductility of the alloy decreases rapidly in a short aging time.

Abstract: The formation reson of the surface defect of 0Cr18Ni10Ti after rolling is analyzed, some improving solutions are performed for avoiding the surface defect and enhancing the production quality. The investigation shows that the surface defect of rolled steel is mainly ascribed to the inclusions containing Ti, and TiO2 and TiN is a primary source of inclusions in the steel. An effective way of reducing the inclusion performed is decreasing the Ti and N content in liquid steel. By appropriately increasing the carbon content of molten steel entering into the AOD, decreasing the carbon content of the end of blasting oxygen, slag skimming in the ladle and slagging in LF furnace, feeding SiCa wire before Ti alloying in LF furnace and optimization of Ti alloying method and protection casting with no oxidation, the yield of Ti is greatly increased, the TiO2 and TiN inclusions is controlled better, the quality of products 0Cr18Ni10Ti all are greatly improved. The number of continuous casting furnace is increased from one to the three furnace, and the production efficiency is obviouly enhanced in TISCO.