Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： Coupons of the grounding material Q235 steel were buried in an artificial soil of diatomite with different pH values for 20 d, and then the corrosion behavior of the steel was examined. The results indicated that the pH value of the artificial soil had a great effect on the corrosion behavior of Q235 steel. With the increasing of pH value, the corrosion rate of the steel in the artificial soil decreased, which accorded fairly well with that in the actual soil, correspondingly the corrosion type of the coupons turned from rather serious uniform corrosion to slight local corrosion. The corrosion products formed in acidic artificial soil are consistent with those in an alkaline artificial soil, they all composed mainly of α-FeOOH, Fe3O4, γ-FeOOH and Fe2O3, however the products in the late case contained higher Fe3O4 and less α-FeOOH.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： Corrosion behavior of weathering steels with different nickel content was studied by wet/dry cyclic test. The mass loss method was used to evaluate the weatherability of weathering steel, while the rust layers formed on weathering steel were characterized by using SEM, XRD and electrochemical measurements. The result indicates that the higher Ni content，the better corrosion resistance the steel is. The corrosion resistance of the steels with Ni content above 3%(mass fraction) are about twice of the counterpart steel without Ni. The addition of Ni enhances the free corrosion potential of the steel and promotes the formation of α-FeOOH, so as to improve the protectiveness of the formed rust. The EIS results indicate that with the increasing Ni content of the steels, the impedance of the rust layer becomes bigger.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： The corrosion behavior of two low alloy steels, as candidate materials for grounding net, was investigated by indoor corrosion test in a simulated acid soil by means of mass loss method， scanning electron microscopy, electrochemical measurement and Raman spectra. The results showed that the corrosion rate of the two steels went up in the initial stage and then slow down; the corrosion mass loss of Q235 steel was larger than that of A steel; and correspondingly they suffered from local corrosion and then turned to general corrosion. The two steels formed bi-layered corrosion products, of which the outer portions all consisted of α-FeOOH, Fe3O4, Fe2O3 and γ-FeOOH, how ever the inner portions were large different, the concentration of α-FeOOH in the inner protective layer of the A steel was higher than that of the Q235 steel. Tafel polarization curves indicated that the A steel possessed much positive corrosion potential with smaller corrosion current density in contrast with the Q235 steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： The corrosion behavior of a commercial carbon steel Q235, and two new steels A1 and A2 in an artificial soil, which consisted of diatomite and appropriate acid solution to simulate a typical acidic soil at Southern China was studied by mean of corrosion weight loss measurement, and then the corrosion morphology and products were characterized by SEM and XRD. The results showed that the corrosion rate of Q235, A1 and A2 steel in the simulated acidic soil was 0.48, 0.14 and 0.097 mm/a respectively after 300 h corrosion; the tendency to micro-cell corrosion of a steel can be lowered as the carbon content of the steel has been reduced; an appropriate addition of Cr can shift positively the corrosion potential of the matrix; the enrichment of Cr in the inner portion of the rust scale can improve its compactness, and change the propagation mode of corrosion pits; the corrosion products of Q235, A1 and A2 steel were mainly consisted of α-FeOOH, γ-FeOOH and Fe3O4, however, the corrosion products of A1 and A2 steels possess a ratio of α-FeOOH to γ-FeOOH ca 10 times higher than that of Q235 steel, which implying a better protectiveness of the rust layers for the two new steels.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： Welding thermal cycle process of test steels containing different Nb was investigated under different heat inputs with a Gleeble-3800 thermo-mechanical simulator. The microstructural characteristics of the coarse- grained heat- affected zone (CGHAZ) were observed by using optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD), while their impact toughness was tested. The results indicate that with the increasing heat input, lath bainite transformed gradually into granular bainite, and the size and proportion of M/A islands increased, while the average grain size also increased. Under the same heat input, austenite in high Nb steel was refined obviously, with more dispersive and refined M/A islands distributed in the microstructure of high Nb steel, and the proportion of high angle boundaries was high. With the increasing heat input, the impact toughness of steels decreased sharply. The critical heat input value for a sharp decrease in impact toughness were approximately 35 kJ/cm for high Nb steel and 25 kJ/cm for low Nb steel. However, the impact toughness of the high Nb steel was significantly higher than that of the lower Nb steel in the range of experimental parameters.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： The effect of V and Si on the microstructure and mechanical properties of medium-carbon pearlitic steels for wheel was studied by means of OM、SEM and TEM, as well as tensile and impact tests. The results showed that the austenite grain size, the pearlite colony size and interlamellar spacing were significantly refined by increasing V content, which also led to an increase in the volume fraction of proeutectoid ferrite of the steels. With the increasing of V content, the yield strength at room temperature and the impact toughness at - 20℃ were enhanced due to precipitation strengthening and grain refinement effects of VC. However, the tensile strength at room temperature was decreased due to the increasing of the soft phase, i.e., proeutectoid ferrite. The increase of Si content resulted in the great decrease of proeutectoid ferrite and the significant refinement of pearlite interlamellar spacing but the slight refine-ment of austenite grain size. Si addition also promoted the VC precipitation but had only a little influence. The yield- and tensile-strength were enhanced mainly by the effect of solid solution strengthening and the refinement of pearlite interlamellar spacing due to Si addition. The balance of strength and toughness in medium-carbon pearlite steels could be effectively optimized by microalloying with the combination of medium 0.07%-0.08%V(mass fraction) and relatively high 0.8%-0.9%Si (mass fraction).
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： As an important carbide forming element, Nb plays an important role in steel. Precipitated Nb can restrain the austenite grain growth during soaking process and provide precipitation strengthening after g /a phase transformation. Precipitated or dissolved Nb can inhibit recrystallizaton of deformed austenite. Recently, both Nb and Mo are added in steel to enhance the role of Nb. However, these kinds of researches mostly focused on continual cooling process of g /a transformation or isothermal process during tempering, and precipitation behavior of MCtype carbide in steel containing Nb and Mo during reheating process and the effect of Mo on precipitation of NbC in ferrite were rarely reported. Therefore, in this work, precipitation behaviors of MC-type carbide and the synergistic effect of Nb and Mo in steel containing Nb or Nb-Mo during reheating process at the heat rate 20 ℃/min were investigated by means of Vickers hardness test, SEM, HRTEM and DSC. The results show that both Nb and Nb-Mo steels have hardness peaks at 300 and 700 ℃, which are attributed to the precipitation of e-carbide and MCtype carbide, respectively. The MC-type carbide precipitates at about 650 ℃ during reheating process, which is in a good agreement with the nose temperature of MC-type carbide calculated by Avrami equation. (Nb, Mo)C particle forming in Nb-Mo steel during precipitation has a small mismatch with ferrite matrix compared with NbC, leading to the decrease of interfacial energy. Thus, the precipitation kinetic of MC-type carbide in Nb-Mo steel is faster than that in Nb steel, which results in the denser and finer MC-type carbide and higher precipitation strengthening effect.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： With the development of Ti microalloying technology, the application and theory research of Ti in microalloyed steels are becoming more deeply and widely. However, the effect of tempering time on the microstructure and mechanical properties of high Ti microalloyed quenched martensitic steel has been rarely touched upon, meanwhile, it has long been inconclusive whether precipitated phases coarsening or the recovery and softening of martensitic matrix is the dominant role resulting in the decrease of hardness along with long time tempering of microalloyed steel. In this work, the effect of tempering time on the microstructure and mechanical properties of high Ti microalloyed quenched steel was systemactically investigated by TEM, XRD and Vickers-hardness test, and the interaction between precipitation hardening and microstructural softening of the high Ti microalloyed steel was also studied. The results indicate that the hardness increases for Ti microalloyed steel with tempering time 10~300 s, which is attributed to the fact that the precipitation hardening by nano-sized TiC particles is greater than the recovery and softening of matrix. With the tempering time from 300 s to 10 h, nano-sized TiC particles precipitate more and more and the mass fraction of TiC with the size less than 5 nm increases, owning to the precipitation hardening produced by tiny TiC which offsets the hardness decrease due to the gradual softening with recovery of matrix, and therefore, the hardness can keep a long platform; in addition, with the tempering time 10~20 h, the hardness decreases significantly and the deacreasing rate of hardening for steel with Ti microalloying is higher than that for steel without Ti microalloying. The average particle size of TiC increases from 2.76 nm at 10 h to 3.15 nm at 20 h. Calculation results show that the decrease of hardness caused by coarsening of TiC is 11.94 HV, while caused by recovery of matrix is 24.56 HV. It is shown that the recovery of matrix is the dominating factor for reduction in hardness, but coarsening of tiny TiC speeds the decrease of hardness and is also an important factor resulting in the decrease of hardness.
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