Advanced Materials Research Vols. 652-654

Abstract: The static continuous cooling transformation (CCT)curves of 3.15 Si-0.036 C-0.21 Mn-0.008 S-0.008 N-0.022 Al are measured on Gleeble-3500 thermal mechanical simulator, the evolution of microstructure and the tendency of hardness are investigated by optical microscope (OM) and hardness tester. The results show that there is no evident change in microstructure which mainly are ferrite and little pearlite under different cooling rates, but the transition temperature of ferrite is gradually reduced with the increase of cooling rate. When the cooling rate is increased from 0.5°C/s to 20°C/s, the ending temperatures of phase transformation are decreased by 118°C, when cooling rate reaches to 10, Widmanstatten ferrite appears. The hardness of the steel turns out gradual upward trend with the increase of cooling rate.

Abstract: The amount, size and structure of M/A in ultra low carbon bainitic steels，which are mainly affect by the transformation process, the cooling rate and the tempering treatments, have been investigated. The different cooling rate induce the variation of distribution of amount and size of M/A. There are bigger M/A mass with harder phase at low cooling rate while smaller M/A with less hard phase at high cooling rate. A series tempering tests have been carried out, which indicating that the tempering treatment has significant effect on the evolution of M/A.

Abstract: The morphology of sulfide and abrasive resistance of a high sulfur alloy steel cast at different cooling rate were investigated in this paper. The size, volume fraction and distribution of sulfides was decreased as the solidification rate was increased. After heat treatment, many spherical sulfide were found. Most of sulfides within grains were Cr2MnS4, while sulfides at grain boundaries were mainly FeS. High sulfur alloy steel had strong abrasive resistance.

Abstract: This study investigated carbon steel corrosion in three types of soil media (laterite, yellow soil and kaolin). The Frumkin isotherm was used to study the mechanism of the corrosion process. A good linear correlation (y = 3.4x + 3.3) in terms of soil concentration vs. surface coverage was obtained with the value of R2 = 0.996 for carbon steel corrosion in laterite solution at 30oC. A standard weight loss method was used to determine the degree of surface coverage. Investigation on corrosion rate was also carried out on the basis of immersion time and temperature effects. The results showed that yellow soil solution yielded the highest corrosion rate on carbon steel coupon for 5 consecutive days and at various temperatures (30 – 90oC). The thermodynamic properties in terms of heat of reaction and entropy were also investigated in this corrosion study. The results showed that carbon steel coupon was least corroded in the environment of kaolin solution as indicated by its highest endothermic value and lowest entropy. The study showed that the findings are consistent in relation to thermodynamic properties. This work is beneficial for the corrosion study of carbon steel in soil media corresponding to lifetime of buried pipelines and cost safety.

Abstract: The transformation behavior of Nb-Ti micro-alloyed low carbon steel during continuous cooling was studied trough thermomechanical simulator and metallographic analysis. The results show that the dynamic CCT diagrams shift to the left and upper compared with the static ones, the begin temperature of γ→α transformation is gradually lower with the increase of cooling rate. The high temperature deformation improves Ferrite and Pearlite transformation, also improves Bainite transformation and decreases ferrite transformation zone. The rapid cooling can obtain better obdurability mixed microstructure of Martensite and Bainite within a certain cooling rate after deformation.

Abstract: Influence of ultrasonic inoculation treatment on distribution of sulphur in Fe-S alloy was mainly studied. Results showed that Ultrasonic treatment could reduce the segregation degree of sulfur in Fe-S alloy and make the distribution more uniform. When the ultrasonic treatment time was 60s, sulfur segregation was in the lowest of 0.3799, and homogeneity was in the maximum of 0.5470.While treated with ultrasonic power of 150W, sulfur segregation was 0.5068, and sulfur segregation was improved, but homogeneity of sulfur decreased to 0.3411, overall homogeneity distribution of sulfur decreased.

Abstract: The temperature range of high-temperature homogenization was determined by phase diagram calculation and the critical overburning temperature of chromium hypereatectoid steel was measured by DSC. The Comparison of microstructures and element segregation before and after homogenized treatment were investigated for chromium steel ingot by means of optical microscope, scanning electron microscopy and EDS. The results show that the liquation carbides and composition segregation are improved after the chromium steel was treated by high-temperature homogenization. According to the results of EDS analysis and segregation ratio calculation for the samples homogenized at different temperature, the optimum homogenization process for Cr steel is 1210°C for 6h.

Abstract: Based on the thermodynamic calculation, the reductants to reduce V₂O₅ were selected, 0.1% V were added into steels by reducing V₂O₅ during the smelting process. The yielding rate of vanadium was calculated by chemical analysis data. The yielding rate is 98.17% when using Si+20%C as reductant and is about 94.94% when using Al+Mg as the reductant. By comparing the inclusion morphology and composition, contrasts the Brinell hardness and tensile strength of steels using different reductants, it was found that when using Si+20%C reductant, the inclusions in the steel is larger in amount, smaller in size and higher in Brinell hardness and tensile strength.

Abstract: Uniformity of microstructure and mechanical properties is required for the heavy section steel. In the present work, a heavy section wind tower flange was manufactured by controlled ring-rolling. Post-rolling heat treatment was employed to optimize the microstructure and mechanical properties. The chemical composition, microstructure and mechanical properties in different zones of the flange were investigated. The results showed that the chemical composition and microstructure were uniformly distributed in the flange. The tensile strength showed similar values in different sampling locations. The strain and impact energies of specimens prepared along the longitudinal direction were higher than that prepared along both the radius and thickness directions. Notch direction did not have noticeable effect on the impact energy. It is demonstrated that the designed process is effective for producing heavy section steel with improved quality.

Abstract: The classification, properties of the domestic prehardened plastic mould steel are reviewed, the composition design and heat treatment process improvement in the chinese prehardened plastic mould steel are commented, its development direction is pointed out. Quenched and tempered prehardened steel has been developed and upgraded based on foreign steels, while non-quenched and tempered prehardened was invented by ourselves, and has been researching and developing because of its good cost performance ratio.