Papers by Keyword: Oxide Inclusion

Abstract: In the present investigation a batch of impellers made of 319S aluminum alloy with about 300 pieces and produced by semi-solid thixocasting process were subjected the ultrasonic testing (UT). The experimental results revealed that the equivalent size of the defects in the impellers was not more than φ0.4mm FBH+12dB. And there were two main types of defects in 12 mm depth area from the machined surface, where defect was apt to form. One type was single defect and the other was intensive defect. Moreover, other nondestructive testing (NDT) was used to test some impellers containing typical defect, and the result suggests that UT was more sensitive than x-ray testing. The defects existed in the impellers were investigated by Optical Microscope (OM) and Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectrometer (EDS). The observation showed that the both types of defects existed in eutectic zone. The single defect derived from billet and the intensive defect came from die casting process.

Abstract: The influence of Ti oxide on the toughness of heat affected zone for low carbon bainitic steels has been investigated. The optical microscope, SEM and TEM were used to analyze the composition, size and distribution of the inclusions, and the microstructure and mechanical properties after welding thermal simulation were also investigated. The effect of Ti oxide inclusion on the transformation of acicular ferrite has also been studied. The results show that after the melting with Ti dioxide technique the inclusion is complex, in the core is Ti oxides about 1-3 micron and around it is MnS. It has been found the acicular ferrite can nucleate at the inclusions and the Ti oxide inclusion will promote the nucleation of acicular ferrite, and the acicular ferrite will block the growth of bainite. Therefore by introducing the Ti oxide in the steels the microstructure of HAZ could be refined markedly therefore the toughness of HAZ can be improved evidently.

Abstract: The medium carbon steel (C: 0.26%, mass percentage) was deoxidized by Ti alloys, and its features of inclusion and microstructure were systemically studied through the scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS). The results show that the element of titanium in inclusions coexists with manganese, and no single-phase oxides of titanium are observed. Through the statistical analysis, it can be seen that the average size of Ti-contained inclusions is similar to the inclusions without the Ti, and the percentage of large inclusions (>5μm) is smaller in Ti-contained inclusions, which may reduce the harmful effect of inclusions. After etching in 3Vol% Nital solution, it’s found that the Ti-contained inclusions can act as nucleation sits for the intragranular acicular ferrite.

Abstract: The contents of oxygen and nitrogen were important effect on the high speed wire in smelting high carbon steel. Sampled from the process of producing wire rod in Xuanhua iron and steel company and analyzed the contents of oxygen and nitrogen. The quality and size of oxide and nitride were numerical statement in differernt terms. The results were shown that the size of micro inclusion was less than 15 μm, and the inclusion size was not big, but the quantity was large. The quantity of micro inclusions in wire rod was about 10 /mm2 (equivalent diameter of 5 μm). Through the practice analysis and research, we put forward the measures of inclusion control for 65 steel including raw material requirement, improving of the converter, LF refining and continuous casting operations.

Abstract: Combining with the production experience in steel making and rolling plant, the oxide inclusions of IF steel were investigated. In the operation process, the inclusions of IF steel are main Al₂O₃-TiN. They are granular and dispersed in the steel, and most of sizes are 1~5μm. In the inclusion center, the Al₂O₃ plays the role of TiN heterogeneous nucleation center. So reducing the Al₂O₃ inclusion is essential to stabilize the Ti content and strengthen the fixtation to C and N in steel. The quantity of Al₂O₃ inclusion was closely relation to the operation process. The Al₂O₃ inclusions can be significantly reduced by taking some measure.

Abstract: The low carbon steels were smelted with special oxide introduction technique and the HAZ properties has been studied with thermal simulation. The optical microscope, SEM and TEM were used to analyze the composition, size and distribution of the inclusions, and the mechanical properties after thermal simulation were also investigated. The influence of oxide inclusions on the austenite grain size was also studied. The results show that after the smelting the inclusion is complex, in the core is Ti oxides about 1-3 micron and around it is MnS. When the reheat temperature is below 1000, the size of austenite grain is the same for experimental steel and base steel. However, when the reheat temperature is over than 1100, the size of austenite grains in experimental steel is one third of that in base steels. After thermal simulation, with the t_8/5 increasing the toughness of HAZ decreased. The austnite grain size also increased. The microstructure is composed of intergranular ferrite and intragranular acicular ferrite. Therefore by introducing the fine oxide inclusion to the steel the austenite grain was refined and during the phase transformation the acicular ferrite formed at inclusions at first. These two factors are the main causes to improve the toughness of heat affected zone for steels produced by oxide metallurgy technique.

Abstract: The low carbon high manganese steel (C: 0.07, Mn: 2.0, mass percentage) was deoxidized by Ti and Mg alloys, and its features of inclusion and microstructure were systemically studied. Through the scanning electron microscope (SEM) and Energy Dispersive X-ray Detector (EDX), it can be seen that in inclusions, the element of magnesium always coexists with titanium, and no single-phase oxides of magnesium are observed. After etching in 3Vol% natal solution, it’s found that the Mg-contained and Ti-contained inclusions can act as nucleation sits for the intragranular acicular ferrite. These results imply that besides the pinning effect, the oxide of magnesium can also participate in the nucleation for intragranular acicular ferrite. Thus, it may be used in the oxide metallurgy to refine the ferrite microstructure.

Abstract: The influence of the oxide inclusions on the microstucture, properties and the Heat-affected-zone (HAZ) toughness of low alloy steels has been investigated. The low alloying steels were smelted with special oxide introduction technique and the properties of HAZ have been studied with thermo-simulation. The type, size and distribution of the non-metal inclusions in steels has been studied by optical microscope and scanning electronic microscope (SEM). The microstructure and mechanical properties of base metal and samples undergoing welding thermo-simulation were also analyzed. The results show that the inclusions in experimental steel are mainly complex inclusions composed of oxide containing Ti and MnS, these complex inclusions are distributed homogenously and their size is between 1 and 3 micron. The microstructure of HAZ consists of intragranular acicular ferrite (IAF), intergranular ferrite and small amount of lath bainite while the cooling time during the phase transformation between 800°C and 500°C (t_8/5) is short. After the thermo simulation with t_8/5 increasing the toughness of HAZ decreased and the size of prior austenite grain increased. If the size of the austenite grain decreased the amount of IAF also decreases.

Abstract: Reducing oxide inclusions’ number and size by aluminum deoxidization is an effective way for improving working life of high strength steel. For this purpose, during inert gas protection electro–slag remelting (P–ESR) process and H13 steel as electrodes, the deoxidizer being made of aluminum grains, iron powder and calcium fluoride powder mixture was added into slag pool with different addition rates. Results of experiment indicated that, by P–ESR remelting, oxygen content reduced from 0.0045 to 0.0010 with different aluminum addition rates. Based on the SEM and EDS analysis, inclusions transformed from CaO–MnO–SiO2–Al2O3 particles in electrode to pure Al2O3 particles, and number and size of particles modified obviously. Finally, action mechanism of the deoxidizer during P–ESR process was discussed by analysis results and thermodynamic calculation.

Abstract: Nucleating mechanism and controlling methods of Al₂O₃-TiO₂ inclusion formed during steel cooling process is analyzed in this paper. According to the theory of nucleation, only TiO₂ could satisfy the critical requirement of homogeneous nucleation to solidify stably when the temperature declines to less than 1863K. Furthermore, the generation of Al₂O₃ adhering on the surface of solid TiO₂ is going to take place through heterogeneous nucleation, and then Al₂O₃ interacts with TiO₂ to form Al₂O₃-TiO₂ complex oxide. There would be no Al₂O₃-TiO₂ complex oxide or much less Al₂O₃ on condition that the w_Ti·w_O2 is less than 3.96×10^-8. Both deeply deoxygenating treatments and controlling the mass of Ti-Fe alloy added into steel are effective means for improving steel quality.