Advanced Materials Research Vols. 476-478

Abstract: A thermodynamic model of the microalloy precipitation elements in austenite region for Fe-C-N-Al-Ti-Nb steel has been established. Through calculating the action of the microalloying element in austenite, it can be found that carbon in steel accelerates the precipitation of Nb greatly, Nb in solution decreases quickly and the precipitation of Nb increases quickly with the increase of carbon. When the C in steel is low, the main constituent of the precipitation is TiN in high temperature, and TiN guadually turns to be NbC with the decrease of tempertature. When the carbon in steel is high，the main constituent in the precipitation is NbC even though the temperature is higher. The nitrogen in steel has a slight effect on NbN precipitation.

Abstract: The influence of microstructures with different heat treatments on corrosion properties of X80 pipeline steel was investigated in near-neutral pH soil using electrochemical measurement and surface analysis(SEM, EDS and XRD). The results showed that the microstructure of X80 steel affected the properties of corrosion product layers. Generally, X80 steels with heat treatments had a higher corrosion rate than the as-received steel. The increase of pearlite content enhanced the corrosion of ferrite through a galvanic effect. The appearance of upper bainite and martenite increased further the activity of the steel. The corrosion product layer formed on as-received X80 steel was compact and complete, provided an effective protection to the underneath steel. However, the corrosion product layers on the heat-treated X80 steels were generally inhomogeneous, loose, porous and defective, and provided minor protectiveness. The cathodic/anodic reactions of X80 steel are dominated by the oxygen reduction and formation of iron oxides that deposit on the steel surface which was through a physical block effect to afford the protection.

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: The basic requirement of polymer for chemical flooding was introduced, development progress and performance evaluation of salt-resistant polymers for chemical flooding were discussed, and development direction of polymers for chemical flooding was indicated in this paper.

Abstract: For the re-concentration minerals of RE dressing tailings in Bayan Obo mine, Fe and P compounds were selectively reduced by the methods of coal-based direct reduction in reactionary pot. The metal and slag in sponge iron obtained from reduction was melted and separated. Compared to that in re-concentration minerals, the content of valuable elements oxide in melt-separation slag was enriched to about 2.5 times. Therefore, melt-separation slag can be used as the basic material to extract the valuable elements.

Abstract: The effect of continuous annealing parameters on the microstructure and magnetic property of cold rolled dual phase steel (DP steel) are investigated. Correlations of microstructure, magnetic properties and continuous annealing parameters are revealed. The mechanism of the magnetic property varying with continuous annealing process is also discussed. The results show that recrystallization is almost completed when heating to 740°C. For the DP steel soaked in the range of 770°C-830°C and quenched in different temperature, the TEM results indicate its microstructure mainly consists of the ferrite and martensite phase. The martensite volume fraction increases gradually with increasing the soaking and quenching temperature. It is found that magnetic properties of dual phase steel are very sensitive to continuous annealing process. With rising soaking and quenching temperature, the coercivity and hysteresis loss increase obviously, whereas the maximum permeability and the remanent induction tend to decrease.

Abstract: For reducing the wall-film entering the cylinder in liquid phase, the phenomena of wall-film entering the cylinder in liquid phase should be at minimum lever or be avoided. So the first thing for learning the wall-film is to detect the way of the wall-film entering the cylinder. Therefore, the way of the wall-film enter the cylinder in liquid phase is detected by changing the temperature of the wall-film location and time for wall-film evaporated. At the end the way is validated by experiment test bed and it is improved that the way is feasible.

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: Brine recirculation pumps are essential components used for circulation of brine in multi-stage flashing chambers desalination plants. Failure of these pumps would result in shutdown of the desalination plants. The rotating parts of these pumps (shaft and impeller) are usually made out of stainless steels or Duplex stainless steels. The pressure parts (casings) are usually made out of Ni-resist ductile irons (NDI). In recent years there have been a number of cases in which NDI casing materials failed by stress corrosion cracking (SCC) especially in the Arabian Gulf region. This makes re-evaluation and further studies on the performance of these materials of paramount importance due to process-related economic and reliability considerations. As possible substitutes to NDI casing materials, the authors of this research have recently published material demonstrating the superiority of the SCC resistance of the super DSS, UNS S32750, over the ASS, UNS S31603, in hot brine environment. Economically, the idea of using chemical corrosion inhibitors to enhance the SCC resistance of the ASS, UNS S31603, is appealing, non famous and worth looking at. In this work the effect of corrosion inhibition on the corrosion resistance and SCC of the ASS, UNS S31603, in hot brine environment, is investigated. Brine water was injected with typical treat rate of 350 ppm of passivating type commercially available Molybdate corrosion inhibitor. Theoretically the corrosion inhibitor was proposed to improve the corrosion resistance of ASS, UNS S31603, in brine solution. Electrochemical polarization measurements and SCC tests were used to evaluate the performance of the metal under inhibited and uninhibited environments. Results have shown that treating the brine with this particular type of inhibitor under this particular treat rate and test conditions increased the pitting tendency of the ASS, UNS S31603. Results from both SCC tests and electrochemical measurements are in agreement and both role out the possibility of enhancing corrosion resistance and SCC of ASS UNS S31603 using Molybdate inhibitor.

Abstract: Three groups of 0.04C-16Cr ferritic stainless steels, with boron quality score of 0ppm, 16ppm and 26ppm, were smelted by a vacuum induction furnace. The chemical soak method, the tafel polarization curve method and the anode circular polarization curve method were used to research their general corrosion and intergranular corrosion resistance. The results showed that both general corrosion and intergranular corrosion of the casted 0.04C-16Cr ferritic stainless steels happened in dilute H2SO4 medium. The resuluts of electrochemical and chemical soak indicate that the addition of B improves intergranular corrosion resistance of 0.04C-16Cr stainless steel, moreover, the intergranular corrosion resistance increases with an increasing content of B. The addtion of B makes the general corrosion rate and self-corrosion current density of the 0.04 C-16Cr stainless steel reduced at active dissolution region in dilute sulphuric acid medium, so the general corrosion resistance of the 0.04 C-16Cr stainless steel is improved. The blunt-dimensional current density of the steel with 26ppm B is the lowest and the passivation zone of it is wider, so the stability of passive film and protection capacity of the steel with 26ppm B are the best. The electrochemical characteristics of general corrosion coincided with the results of soak corrosion.