Advanced Materials Research Vols. 194-196

Abstract: The effect of nitrogen on the mechanical properties of 20MnSi steel at high temperature was investigated. Mechanical tensile test was conducted using a Gleeble-1500D. Microstructure and fractograms were analyzed using SEM and TEM. The results indicate that nitrogen in concentration of 0.4 ~ 0.6% improves the grain boundaries and grain refinement, and thus the strength and section shrinkage and plasticity of the steel. Further increase in concentration of nitrogen has little effect on section shrinkage.

Abstract: In present research, the structure evolution of the pearlite steel wire during cold drawing is systematically investigated, and the relationship between structure evolution and strength increase during wire drawing is analyzed. During cold drawing, the wire strength increases; inter-lamellar spaces of the pearlites decrease, which has an important effect on properties of cold drawn wires; accumulation of high density dislocation in ferrite phase can be thought to be one of the reasons for strengthening the wire, meanwhile, the amorphous phase forming in cemetites also make the wire strengthen; especially, the wire strength is effected seriously by the intensity of the fiber texture <110>, and as drawing, the wire strength increases.

Abstract: Electrical parameters and low-frequency noise test were measured for N80 steel casing drilling, through extracting low-frequency parameters and combining with conventional fatigue crack growth characterization methods and analyzing their morphology. After fatigue crack growth, the results showed that: (1) Electrical parameters of N80 increase, and power spectral density of 1/f noise increases two orders of magnitude. (2) Values of γ and B are significantly increased, indicating that the process of fatigue produced more cracks, defects, and combination centers, from the mechanism of fatigue crack growth of N80, defects and cracks resulting from fatigue are the numbers of kind of fluctuations. In essence, low-frequency noise is a type of fluctuations, which show that low-frequency noise as the characterization of non-destructive., which can serve as a viable tool to study the defects and the characterization of defects.

Abstract: Study researches durable factors of the grain size in 18CrNiMo7-6 by heating and cooling method. Results show that alloying elements Nb and Al have a strong pining effect on the grain boundaries, Al/N ratio between 2.0-2.5 can promote the grain not to grow up for a long time, and refine grains significantly with furnace heating and after carburizing-quenching once, and can inhibit the abnormal growth of individual grains.

Abstract: In order to improve the corrosion resistance of pipeline steel X80 and maintain its good mechanical properties simultaneously, a low-temperature pack aluminizing process was carried out at 723 K on pipeline steel X80 after a surface mechanical attrition treatment (SMAT). The phase composition, microstructure and element distribution of the as-aluminized pipeline steel X80 were characterized by XRD, SEM and EDS, respectively.The results show that the as-received aluminide layer consists of Fe2Al5, which exhibits a good cohesion with SMATed pipeline steel X80 substrate with the thickness of around 90 μm. The element concentrations of Al and Fe atoms show a gradual change in the range of aluminide layer. After corrosion test processed in 3.5% NaCl solution, there is no obvious corrosion crack or uphills piled up by corrosion products on the surface of as-aluminized SMATed pipeline steel, which can conclude that pack aluminizing assisting by SMAT at low-temperature is an effective way for protecting pipeline steel X80 against corrosion.

Abstract: Clean heavy rail steel was prepared by the process of vacuum induction furnace smelting, forge work and rolling. Effects of Rare earths (RE) on phase transformation and microstructure of heavy rail steel were investigated by thermal simulation machine, metallographic microscope and scanning electronic microscope. Thermal simulate tests indicate that, RE can move the C curve of pearlite transformation to lower right, prolong the incubation period of pearlite and improve the stability of undercooled austenite. The minimum incubation period of pearlite transformation is increased from 24s to 30s by RE. Furthermore, RE can decrease the critical cooling rate of pearlite transformation from 1°C•s^-1 to 0.5°C•s^-1 and the critical cooling rate of quenching from 15°C•s^-1 to 13°C•s^-1. Additionally, RE can fine the annealing and anormalizing pearlite notably. The pearlite laminae distance of heavy rail steel added RE is decreased by 12.9% (annealing) and 13.3% (normalizing), respectively.

Abstract: The development of texture and grain boundary character are researched for a boron bearing IF steel after recrystallization annealing for different times at 810°C. The results show that the main texture components are {111}<110> and {111}<112> after the cold rolling samples annealing different times. The maximal volume fraction of <111>//ND texture is about 78% for the sample annealing for 120sec. The main CSL boundaries are ∑3，∑5，∑7，∑9，∑11，∑13b and ∑17b. And the ∑3 grain boundary increase with increasing the annealing times from 60sec to 180sec.

Abstract: The burden calculation of ferromanganese alloy was calculated based on the slag composition and designed product. The calculation results showed the total error rate of this method was 1.53% and the error rate of ore, coke and silicon was 4.66%, 1.71%, and 5.66% respectively, which was much better than using the traditional elements recovery method with the total error rate was 8.00% and the silicon error rate reached to 18.55%. This new method is more accurate than the traditional method and much closer to the actual production data. And it can apply to different ferroalloy factories because it is based on phase diagram and the mass conservation law. At the same time, the calculation result can reflect the gap between enterprise production craft level and ideal production level. This method has certain reference value to improve production technology, product quality and economic profit of enterprise.

Abstract: The coarse grain heat affected zone(CGHAZ) at different parameters t8/5 of high-strength bridge steel Q460q were simulated with thermal simulation machine. the microstructure of CGHAZ and the effect of granular bainite on the toughness were analyzed in this paper.The results show that: When t8/5<60s, lath bainite and granular bainite intertwine, and the quantity of strip M-A constituents in granular bainite decreased, so toughness is higher.When t8/5>60s, the quantity of eutectoid ferrite and granular bainite increased, coarse M-A constituent resulting in the grain size of effective crack propagation becoming coarser and toughness decreased significantly.

Abstract: In this paper,Q345E steel as the object of study,analysis of several typical internal defects of UST to explore the reasons for failure caused by UST testing.The results show that: the center segregation of Mn/S is likely to induce center segregation structure of P+B with a whole cleaning micro-cracks,large size spherical oxide of Si/Ca is an important incentive for causing micro-cracks;Billet board defect detection defect likely to cause an important reason;crack at the alloying elements sharply higher than the matrix composition.Billet defects is an important reason to cause steel surface defects；the alloying elements in place nearing the crack sharply higher than the matrix composition.