Advanced Materials Research Vols. 750-752

Abstract: According to the present situation of production X80 pipeline steel, the performance requirements of X80 pipeline steel, and the effect and control technology of various elements in steel, and the size and shape control technology of inclusions are reviewed. Weakness of X80 pipeline steel and the future developing direction of pipeline steel of our country.

Abstract: Through the metallographic and electron microscopic analysis on the tensile specimens of low-alloy-high-strength-welding HG70C, we can see that the hot rolling process has an effect on mechanical properties of HG70C: the longer the heating time is, the stronger the yield strength and tensile strength will be. The thicker the finishing slabs are,the stronger the yield strength and tensile strength will be. But it has little effect on the elongation rate. The longer the heating time is, the more even these organizations will be. The decrease of rolling pressure will reduce the aggregation of the inclusion and the formation of banded structure which is conducive to improving the yield strength and tensile strength of HG70C. And martensite is a product of high temperature. There is certain relationship between the formation of banded structure and the formation of martensite.

Abstract: Nitrogen-spray water jet quenching is a new kind of quenching, whose cooling velocity can be controlled. Thus different phase can be achieved according requirement, which can improve the characteristic of material. 9SiCr alloy steel was tested during Nitrogen-spray water jet quenching. The continuous cooling curves of 9SiCr under mixture of Nitrogen-spray water quenching for different pressure and mixture ratio of Nitrogen and spray water are obtained. After quenching, the metallographic structures were investigated, in which the uniform martensite was obtained after quenching.

Abstract: In order to reduce the production cost, economic-type X70 pipeline steels with the thickness of 14.6 and 15.9mm were redesigned . The latest alloy system of pipeline steel designed by non-molybdenum C-Mn-Cr-Nb alloy system, which replaces the high-molybdenum C-Mn-Mo-Nb alloy system, was adopted along with acicular ferrite microstructure. The microstructure of X70 strip is homogeneous and ferrite grains are fine, resulting in high strength, excellent low-temperature toughness and weldability.

Abstract: The formation of the microstructure of gray cast iron is a complex process. There remains many unanswered questions about the process. Using annealing method, the first crystallized primary austenite dendrites from the molten iron was displayed. The room temperature microstructures of gray cast iron with and without Cu, Cr addition were studied. The relationship between microstructure and mechanical property was discussed. The results show that the amount of primary austenite dendrites of the multi-alloyed gray cast iron increases significantly and the secondary dendrite arm spacing seems narrow. The microstructure at room temperature is fine and homogeneous. Tensile strength increases significantly, up to 300MPa with adding 0.58%Cu and 0.29%Cr.

Abstract: A heavy section ductile casting (HSDIC) with dimensions of Φ590 mm×800 mm was prepared. Cooling curves at the center, at 85 mm from the center, at 170 mm from the center and at 255 mm from the center of the casting were recorded and analyzed. The results show that the precipitation of initial graphite, nucleation of eutectic cell and mass eutectic reaction at 255 mm from the center were all earlier than the other three locations. Moreover, it takes the longest time of 53 minutes of recalescence at 170 mm from the center with the highest temperature rise of 7 °C, though the cooling rate at this location is not the lowest in the casting, the mechanical properties are the worst. In addition, the largest amount of chunky graphite appears at 170 mm from the center.

Abstract: Dephosphorization is one of key goals for converter to smelt high carbon steel. The chemical equation of dephosphorization reaction and the expression of phosphors distribution between slag and steel were deduced on fundamental of metallurgical thermodynamics and the steelmaking situation of Shougang Shuicheng Iron and Steel (Group) Co. Ltd. The rerults showed that the dephosphorus capcaty of slag increases with the increase of the content of FeO in slag, but decreases with the increase of temperature. Compared with the single slag operation, the total weight of slag met the dephosphorus requirement by the double slag process for high carbon 70 steel in 100t convert can be decreased to 80%.

Abstract: Electrochemical method was employed to investigate galvanic corrosion behaviors of super13Cr and N80 couples in 5% NaCl solution at different temperature. Corrosion morphologies and products of the couples were analyzed by SEM, EDS and XRD. The results show that there existed distinct potential difference between super13Cr and N80 with different degree of corrosion in 5% NaCl solution at different temperature. N80 was accelerated to corrode as anode, however, super 13Cr was protected as cathode when their coupling. In order to avoid galvanic corrosion, the super 13Cr-N80 couples could not be used without any protection of N80 from 25°C to 80°C. Corrosion current density of the super13Cr-N80 couples increased with increasing temperature in 5% NaCl solution, as well as the more serious corrosion of N80, of which corrosion products are Fe₃O₄.

Abstract: Using confocal laser microscope with an infrared heater for 45 steel under different rate of solidification dendrite formation in the process of in situ observation, in the melt solidification phase has different cooling rate the cooling of dendrite formation, analysis of cooling rate on final solidified structure. Results show that with the reduction of temperature in the solidification process dendrite growth continuously, new nuclear has been formed, with the speeding up of the cooling rate, the dendritic structure refinement.

Abstract: The YAG and YIG powders have been prepared by co-precipitation technique in which NH₄HCO₃ or (NH₄)₂CO₃ is used as a precipitant and Y(NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and Fe (NO₃)₃·9H₂O as raw materials. The composition, the phase formation process and the properties of the YAG and YIG powders were investigated by means of XRD, SEM, TEM and EDS. The results indicated that the precipitant effects the preparation of pure-phase powders. The resultant YAG and YIG powders showed good dispersity and excellent sinterability using AHC as precipitant.