Advanced Materials Research Vols. 941-944

Abstract: According to the different reaction mode, the combustion synthesis sintering can be divided into two kinds of mode: the self-propagating by heating ignition such as laser (SHS, Self-propagating High-temperature Synthesis) and whole explosion in the vacuum furnace (TE, Thermal Explosion). In this experiment, the Ni-Al powder compact is synthesized completely to nickel aluminides by SHS and TE. The experimental parameters controlling the ignition step such as material parameter and adiabatic temperature were calculated as a function of initial stoichiometry. Al mole ratio in initial powder mixture was varied from Ni: Al=3:1 to Ni: Al=1:1 for controlling adiabatic temperature.

Abstract: In the TC4 titanium alloy subject to high pulsed magnetic field, the phase transformation from α to β occurs. When the magnetic induced intensity increased from 2T, 3T to 4T with constant 30 pulses, the percent of α phase adds up gradually. When the magnetic induced intensity is 4T the volume fraction of α phase amounts up to 59%. It is ascertained that magnetic field has taken a positive influence on the phase transformation because of the variation of inner energy induced by magnetic field.

Abstract: 5083 aluminum alloy was processed with combined process of warm rolling and annealing. Elongation and tensile strength of samples were measured to analyze the influences of annealing temperature and annealing time on its mechanical properties.Results show that low temperature superplasticity is very sensitive to temperature. The maximum elongation for 5083 aluminum alloy reaches 443% at 250°C and a strain rate of 1×10^-3s^-1, which means that 5083 aluminum alloy exhibits excellent low temperature superplasticity. Low temperature annealing before drawing could not effectively improve the elongation.

Abstract: PHACOMP, Equilibrated alloying method and d-electrons alloy design theory have been employed for the prediction of TCP phases in nickel-base superalloys. The prediction of d-electrons alloy design theory was agreement with the samples aged at 900°C/1000h.

Abstract: Ultra-rapid annealing (URA) experiments were carried out to study the effect of heating rate on the recrystallization kinetics, grain size and Bake-hardening (BH) properties of Ultra-low carbon Bake Hardening Steel annealing with different heating rates followed by gas cooling (about 100°C/s) with variation of soaking times. It was shown that the degree of grain refinement is controlled by the parameters of heating rates and soaking time of the Ultra-rapid annealing cycles. For the steels investigated, the final grain size decreases with increasing heating rate and increases with increasing soaking time. The effects of dislocation density, varied by means of non-temper rolling reduction and a temper rolling reduction of 1% on the Bake-hardening properties were investigated within an aging temperature of 170°C for 20 min.

Abstract: According to the requirement of 20CrMnTiH steel, the effects of casting peed, EMS current intensity and secondary cooling system on internal quality of billets are studied. The results show that, it is beneficial to internal quality control of 20CrMnTiH billets when the casting speed is in the range of 1.2~1.4m/min, and when the current intensity of EMS is 380A, the level of center porosity can be controlled in 1.0, the index of carbon segregation can be controlled in 1.08 and equiax crystal ratio reaches 34.9%. Furthermore, it is beneficial to internal quality improvement when weak secondary cooling system is adopted. With the application of the studies, the quality of billet macrostructure and hardenability can meet the requirement of 20CrMnTiH steel.

Abstract: Experimental methods, such as OM, SEM and X-EDS, were used to study the microstructure of X80 pipeline steel. It mainly consists of fine acicular ferrite (AF). X80 pipeline steel possesses high strength and impact energy at-30°C approaches to 400J. Grain refinement and precipitation hardening are the main reasons for high strength, and toughness improvement can be attributed to grain refinement and particular microstructural characteristics of AF.

Abstract: Experimental methods, such as OM, TEM and property testing, were used to study the HAZ microstructure and property of X80 pipeline steel. HAZ can be divided into three regions, such as coarse grain zone, transition zone and fine grain zone. Granular bainite of CGHAZ consists of bainite ferrite (BF) lath and M/A constituents. Charpy impact energy of the HAZ is much lower than that of base metal, for the grain size of CGHAZ is much larger than that of BM, and crack formation and propagation of granular bainite is easy.

Abstract: The effect of peak temperature on austenite grain size was investigated by using thermal simulation and OM, TEM analysis. Grains grow slowly below 1250°C, and dramatically grow up as the temperature exceeds 1350°C. The primary precipitates in X80 pipeline steel are TiN and NbC, TiN particles cannot absolutely dissolve in steel during holding for 2s at 1300°C.Although TiN particles exist in steel, they cannot hinder grain growth of CGHAZ during welding process. The phenomenon can be explained by Ostwald Ripening mechanism.

Abstract: The aging of initial TP304H austenitic stainless steel was simulated at 650°C,700°C and 750°C for 30d,60d and 150d respectively. These samples and the others, the samples aging for 15kh, 78kh and 80kh at the same temperature during the actual operation, were studied through the hardness test and tensile test to analyze the mechanics performance and its changing of TP304H steel. The results showed that for the same aging time, the hardness, yield strength and tensile strength of TP304H steel rise firstly and then turn to decrease with the growth of the aging temperature, while at the same aging temperature, the hardness, yield strength and tensile strength increase with the extension of aging time, which is similar with the increase tendency of mechanics parameters of TP304H aging during actual operation.