Advanced Materials Research Vols. 476-478

Abstract: From the viewpoint of oxide metallurgy and the impact of V on Steel organization, the morphology, size, distribution and composition of the inclusions in Steel after V deoxidation were studied by using optical microscopy and SEM, and organization changes of steel after adding V were investigated. The results of the experiment were showed that acicular ferrite was radially appeared at the core of small inclusions after adding V. Carbon, nitrides (VN, V3C4) of V can become nucleation of intragranular ferrite, which were small and dispersed. V could also refine the organization of steel.

Abstract: Optimization of FCD design in a single strand slab tundish producing stainless steel is carried out by physical modelling using a 0.4 scale water model and mathematical modelling study. Reducing the residual metal volume at the end of casting, promoting the near-surface plug flow for inclusions removal and improving the transient slab quality are concerned, the optimized FCD is two dams and an impact pad, among them the dam1 (close to ladle shroud) with two 30 degrees upward inclined drain holes, another dam2 (close to tundish exit) is bottom rectangular-grooved which is beneficial for reducing the residual metal volume. Besides, the height of impact pad and drain holes must be concerned simultaneously, in the present study the height is 20mm and 60mm, respectively. Compared with turbulence inhibitors, impact pad will decrease the melt exposed to air at the steady state of casting. The holes at the higher level of dam may cause slag entrapment during the refilling process of ladle change operation.

Abstract: The basic thermodynamic analysis of silicothermic reduction during direct alloying to smelting vanadium steel with V₂O₅ was discussed in this paper. The high-temperature carbon tube furnace and medium frequency vacuum induction furnace were used to study the phase compositions of the reduction products and the change law of the yield of vanadium when V₂O₅ was reduced by ferrosilicon. The research shows that the main phases of the silicothermic reduction products were VSi₂、FeVO₄ and Ca₂SiO₄ under the condition of using CaO to restrain the volatile of V₂O₅. Yield of vanadium was gradually improved with the increase of ferrosilicon during the direct alloying. The yield of vanadium in the steel is as high as 95.25% when the addition of ferrosilicon is 35%.

Abstract: The amount, size, composition and source of the inclusion in 82B continuous casting billet was studied by means of electrolysis, anode slime separating, sieve grading and X-ray powder diffraction to lower the amount of non-metal inclusion and to increase the quality of steel. The results show that the total amount of inclusions is up to 183.8ppm where the particle sizes of 75.11% inclusions are smaller than 10μm, and the inclusions are mainly composed by the FeO precipitated in the front of steel billet solidification, and the manganese sulfide and the composite oxides such as calcium and/or silicon aluminates developed by desulphurizing and deoxidizing operation.

Abstract: As the development of oil gas transportation project for long distance over the world, the pipeline steel are developed to high grade to reduce the construction cost and increase the efficiency of the gas transportation. But the statistics of the built pipeline engineering in the world showed that most of the steels are below the grade of X70, and the used X80 grade steels are less than 5000km. In 2008, the second west-east pipeline project will startup in China, and the whole line will use X80 grade pipeline steels. So the matched bend pipes should be studied. In this paper, the X80 pipeline steels were reheated under selected condition to simulate the heat history of bending process of it. And the deduced microstructure was observed, also the relationship between microstructure and mechanical properties were discussed. The optimum heat treatment technics were gained. This research will be helpful to the field hot bending in the second west-east gas project.

Abstract: Bend pipes are key points in construction of pipeline. The world well known second west east pipeline project will use X80 pipeline steel in whole line. So the study on X80 grade bend pipe is very important and timely. Here , a series of experiment were done to optimize the microstructure of X80 bend pipes, and corresponding reheating technics were studied. By compare with current standard used in china, the CVN toughness and shearing area and strength were discussed. By this research, the optimum reheating program for X80 grade bend pipes were gained.

Abstract: Clogging of 409 Stainless Steel is serious, and it has difficult in continuous-casting, which have an effect upon the quality of casting blank. By way of calculation and analysis, TiN inclusions form in 409 stainless steel with w[N]•w[Ti] ≥0.00014, but TiN is oxidated to TiO₂ easily. A lot of TiO₂ inclusions which are due to reoxidization increase, which attach to the inner wall of the nozzle and form TiO₂ type clogging. With [Ca]≥0.00032% and [Ti]=0.003%, CaO•TiO₂-MgO•Al₂O₃ dual phase inclusions bring on CaO•TiO₂ type clogging in the nozzle. At the same time, there are some strategies to control the above mentioned clogging.

Abstract: The mechanical properties and decarburization layer depths after heat treatment have been investigated for the experimental steels，which were melted by means of 10Kg vacuum induction furnace in the laboratory . It has been confirmed that additions of silicon and vanadium can improve strength of the steels and, the tensile strength of the steels increases with silicon content from 1.4% up to 2.0%. The reduction of carbon content and the addition of carbide forming elements decrease the decarburization sensitivity of the steels tested. The tensile strengths of the steels with carbon less than 0.5% are between 1016.88 to 1674.64 MPa, and the impact energy between 15.50 to 34.50 J, which are compared with the tensile strength of 1160.89MPa, the impact energy of 19.00 J for 55SiCrV. The steels with optimized compositions, which consists of 0.4~0.5% C, 1.6~2.0% Si, 0.8% Cr, 0.2% V, have a satisfactory property with high strength, high toughness and good anti-decarburization.

Abstract: Keywords: vanadium pentoxide；carbon black；reduction and nitridation；vanadium nitrogen alloy. Abstract. The V₂O₅ extracted from low vanadium shale and carbon black are used as raw materials to prepare briquetting samples through mixing, grinding and pressing. The samples are prereduced, final reduced and nitrated to produce vanadium nitrogen alloy with high nitrogen content. Thermodynamic analysis and experiment results show that：（1）In order to avoid V₂O₅ volatilization loss during reduction, the briquetting samples should be pre-reduced for 4 hours below the melting point 670°C of V₂O₅, which can transform V₂O₅ into low valence vanadium oxide.（2）During V₂O₅ being self-reduction under N₂ atmosphere, if the final reduction temperature is below 1271°C, the VN is preferential formation; if more than 1271°C, the reduced product forms V₄C₃.（3）To make a product with high nitrogen and low carbon content, the final reduction and nitride temperature should be controlled below 1300°C.

Abstract: The cleanness of 30Cr2Ni4MoV steel was researched by chemical analysis, SEM and electrolytic experiment. The results show that the large-sized inclusions in the casting is the direct reason for the product to scrap. It found that there is a increase trend of large-sized inclusions and oxygen content from VD to pouring process with a cleanness detection of smelting process. It have achieved a good effect by adopting some measures to improve steel cleanliness which includes controlling the carbon content of EAF tapping reasonablly, low melting point controlling of inclusions, extending soft blow time and optimizing the flow field of tundish. The quantity of inclusions has reduced from 38.8 per square millimeter to 16.0 per square millimeter. The oxygen content has reduced from 58 × 10-6 to 32 × 10-6, and the nitrogen contents has reduced from 85 × 10-6 to 70 × 10-6 after process improvment.