Advanced Materials Research Vols. 557-559

Abstract: The mechanical performance, workability, weldability and corrosion resistance of structural high strength low alloy (HSLA) steels used in offshore engineering have been generally required. The effect of grain size on the corrosion resistant performance of a C-Mn structural steel has been investigated with stress on hunting a appropriate grain size to balance mechanical properties and corrosion resistant performance. The results showed that the C-Mn steel with grain size in 10～25μm scope provided expected mechanical properties and corrosion resistance.

Abstract: The microstructure of the TWIP steel before and after tenslie test was investigated by metallographic microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the plastic growth of TWIP steel was mainly due to the TWIP effect induced by twining crystal. Some austenite grains had two or more twining system in the TWIP steel. Both the boundaries of twins and original austenite grain hindered the growth of twins. Its main textures included Goss{110} , Brass{110}, Copper{112} and CuT{552} and evoluted under the effect of twins and dislocation mechanism.

Abstract: Combining with the production experience in steel making and rolling plant, the oxide inclusions of IF steel were investigated. In the operation process, the inclusions of IF steel are main Al₂O₃-TiN. They are granular and dispersed in the steel, and most of sizes are 1~5μm. In the inclusion center, the Al₂O₃ plays the role of TiN heterogeneous nucleation center. So reducing the Al₂O₃ inclusion is essential to stabilize the Ti content and strengthen the fixtation to C and N in steel. The quantity of Al₂O₃ inclusion was closely relation to the operation process. The Al₂O₃ inclusions can be significantly reduced by taking some measure.

Abstract: Short cracks play the dominant role in material fatigue damage process, from the physical point of view, the solid containing cracks is actually a non-linear dissipation system, so it can be described by fractal theory. The evolution of short fatigue crack is a fractal curve, the irregular process can be described by fractal dimension. The material 20 steel in high temperature low fatigue is experimentally studied, the evolution of short cracks are observed. By analyzing experiment results, the fractal dimensions evolving with the evolution process are as follows, with the development of the damage degree, the fractal dimension is increased, and the dimension of the crack implicates many physical parameters, it can provide a reference for understanding the damage degree of material, it also provide reference for the life of short crack stage of material.

Abstract: According to the working condition of the wear-resistant and heat-resistant parts, it designed the composition of the wear-resistant and heat-resistant steel. Different amount of Ti were added to wear-resistant and heat-resistant steel. The effects of Ti on microstructure, hardness and wear resistance of wear-resistant and heat-resistant steel were researched by microstructure observation, x-ray diffraction，hardness and wear resistance test. The results show that proper amount Ti combines with C to form a certain number particle TiC in the wear-resistant and heat-resistant steel. TiC is dispersively distributed in austenite matrix and improves the hardness and wear resistance of wear-resistant and heat-resistant steel greatly. It has a certain economic benefit.

Abstract: In this study, double-slag method is used to melt low-phosphorous steel by semi-steel. The results show that, the average phosphorous content of the aimed molten iron of BOF is 0.0052% and after the first slag pure-out, the dephosphorization rate is 56.2%, while the total dephosphorization rate of BOF melting is 92.46%, rang from 91% to 93.4%. Low phosphorous content alloy and slag-stopping tapping technology is adopted and rephosphorization of molten iron is controlled in 0.002%. Finally the average phosphorous of the finished product is 0.0064%, range form 0.0055% to 0.0071%, which means that Pangang Group can produce the steel with phosphorous content is less than 0.008%.

Abstract: The oxidation resistance of FeCrNi heat-resisting steel at 1150°C and 1200°C is analyzed and studied using XRD, SEM and EDS techniques. The results show that the oxidation resistance of the heat-resisting steel is improved remarkably after adding yttrium. The value of oxidation rate of experimental Sample 1 (without adding Y) is 3.25 times and 1.56 times higher than Sample 2, respectively at 1150°C and 1200°C after oxidizeing for totally 144h. On the surface of the heat-resisting steel containing Y, the dense and adherent Cr₂O₃ scale and FeCr₂O₄ scale are formed and played the protection role. In the internal oxidation layer, the pinning effect of silicon dioxide is strengthened by Y, and Y has a pining effect directly.

Abstract: The phase transformation of high Cr ferritic heat-resistant steel has been investigated by using differential scanning calorimeter and predicted by Thermo-calc calculation. The steel specimens were hot rolled and followed by air cooling, and then heated from room temperature up to different austenitization temperature as 800°C, 900°C, 1000°C and 1100°C. The DSC curves during heating process showed that the magnetic transition temperature and the Ac1 temperature are 744.9°C and 850.9°C, respectively. The austenitization range was about 58°C. The onset and offset temperature of martensite transformation both increase with the increase of austenitization temperature. The experimental results and the Thermo-calc calculated results both displayed that M23C6 carbides precipitated at around 950°C, and δ-ferrite started to form at about 1020°C.

Abstract: This paper mainly researches the volatile phenomenon of V₂O₅ at high-temperature and the appropriate additions to depress volatilization of V₂O₅ effectively during direct alloying with V₂O₅ to smelting vanadium steel. It shows that the volatilization loss of V₂O₅ is 4.34% when V₂O₅ is heated to 1600°C for 10 minutes. The reductant ferrosilicon and additives CaO can depress the volatilization of V₂O₅ effectively. The volatilization loss of V₂O₅ decreases to 1.55% at 1600°C when the mass ratio of ferrosilicon to V₂O₅ is 1:1. CaO can react with V₂O₅ to form calcium vanadate to decrease the activity of V₂O₅. The volatilization loss of V₂O₅ decreases to 1.82% with adding 48.0% CaO in the V₂O₅–CaO system at 1600°C. The volatilization loss of V₂O₅ with adding more than 30% CaO can decrease to 0.48% when keeping the mass ratio of ferrosilicon to V₂O₅ is 1:1.

Abstract: The failure analysis was performed for T91 finishing superheater bursting tube. It is concluded that improper initial microstructure resulted from non-standard heat treatment contributes to poor creep properties at high temperature and subsequent tube bursting. In addition, life evaluation was carried out on the basis of creep-rupture test result of experimental steel with similar improper microstructure. It is in accordance with the practical condition and provides significant guidance for safety and operation supervision.