Investigation on the Microstructure Hardness for the Hot Compressed Duplex Steel

Effect of microstructure size and type on the hardness for the duplex steel were disclosed by using of optical microscope (OM), scanning electron microscope (SEM) and nanoindenter for the samples hot compressed under different temperature with reduction of 10%, 30%, 50% and 70%. OM and SEM were used to measure the average martensite lamellar width, space and indenter morphology. nanoindenter test characterized the microstructure hardness for the samples under different process. Experiment results show that martensite hardness for the sample hot compressed at 950°C has larger diversity than that of sample hot compressed at 1200°C. The martensite hardness fluctuation range for the sample compressed at 950°C is almost from about 7GPa to 12GPa, while, for the sample compressed at 1200°C, the fluctuation range is basically from about 9GPa to 12GPa. However, the average hardness for the samples hot compressed at 950°C is comparably smaller, which is related with lower quench temperature. The larger martensite hardness fluctuation is mainly related with induced ferrite formation and finer martensite lamellar width. For the ferrite phase, the hardness fluctuation range is lower.

Influence of aeration rate and method of process activation on the degree of purification of zinc-containing waste water by ferritization

The aeration rate for the degree of purification of highly concentrated galvanic wastewater from zinc and ferrum ions was investigated using various activation methods. It is shown that the intensity of aeration has a significant effect on the quality of wastewater treatment and the characteristics of water treatment sludge. The efficiency of the use of an energy-saving method for activating the ferritization process with the use of electromagnetic pulses for the extraction of zinc ions from wastewater has been confirmed. It was determined that with an increase in the aeration rate to 3.5 dm3/min per 1 dm3 of the reaction mixture and the use of thermal activation of the process, the residual concentration of zinc ions remains within the range of 0.12÷0.2 mg/dm3. In this case, the concentration of ferrum ions decreases to values of 0.08÷0.14 mg/dm3. It was found that at an aeration rate of 2.5 dm3/min and the use of pulsed electromagnetic (EMP) activation, the residual concentrations of heavy metal ions decrease to values of 0.08÷0.16 mg/dm3. Comparison of the results indicates the advisability of using low rates of aeration of the reaction mixture. This, together with the use of resource-saving EMR process activation, allows to achieve a significant reduction in energy costs. The quantitative phase composition of ferritization precipitates was determined, in which the crystalline phases of zinc ferrite Zn2Fe2O4 and magnetite Fe3O4, as well as ferrum oxyhydroxide FeO (OH) and sodium sulfate Na2SO4, prevail. It is found that with an increase in the volumetric aeration rate, the proportion of the ferrite phase increases. At an aeration rate of 2.0 dm3/min, more than 85 % of the zinc ferrite phase was found in the sediments. Taking into account the qualitative and quantitative composition of precipitates, it is recommended to use them in the production of building materials. The experimental results obtained make it possible to provide a comprehensive processing of liquid galvanic waste.

Microstructure and Oxidation Behavior of Fe-25Mn-9Al-8Ni-1C-xTi Alloy Prepared by Vacuum Arc Melting

In this study, Fe-25Mn-9Al-8Ni-1C-xTi alloy (x = 0, 0.1, 0.2, 0.3, 0.4 wt.%) was prepared by vacuum arc melting, and the corresponding microstructure and oxidation behavior at 600 °C were studied. The results show that Fe-25Mn-9Al-8Ni-1C-xTi alloy mainly contains austenite phase, ferrite phase and TiC phase. With Ti content increasing, the austenite phase content decreases, while the contents of ferrite phase and TiC phase increase. The oxidation performance test results show that the addition of Ti element greatly reduces the oxidation weight gain of the alloys at the initial oxidation stage. With the extension of the oxidation time and the further increase of the Ti content, the alloys oxidation weight gain shows a trend of first increasing and then decreasing. When the Ti content is 0.2 wt.%, the oxidation weight gain of this series of alloy reaches the lowest value during the stable oxidation period. Compared with Fe-25Mn-9Al-8Ni-1C alloy, its weight gain per unit area is reduced by 21.1%. Fe-25Mn-9Al-8Ni-1C-xTi alloy oxide layer exhibits a double-layer structure. The outer oxygen layer is mainly loose iron-oxides, while in the inner oxygen layer, the oxides are mainly composed of manganese-oxides and aluminum-oxides, which are relatively dense.

Understanding Corrosion Morphology of Duplex Stainless Steel Wire in Chloride Electrolyte

The corrosion morphology in grade 2205 duplex stainless steel wire was studied to understand the nature of pitting and the causes of the ferrite phase’s selective corrosion in acidic (pH 3) NaCl solutions at 60 °C. It is shown that the corrosion mechanism is always pitting, which either manifests lacy cover perforation or densely arrayed selective cavities developing selectively on the ferrite phase. Pits with a lacy metal cover form in concentrated chloride solutions, whereas the ferrite phase’s selective corrosion develops in diluted electrolytes, showing dependency on the chloride-ion concentration. The pit perforation is probabilistic and occurs on both austenite and ferrite grains. The lacy metal covers collapse in concentrated solutions but remain intact in diluted electrolytes. The collapse of the lacy metal cover happens due to hydrogen embrittlement. Pit evolution is deterministic and occurs selectively in the ferrite phase in light chloride solutions.