Kinetic Model of TiN Particle Dissolution and Coarsening during Welding Thermal Cycle

With carbon extraction replica technique, electron diffraction and EDAX analysis, second particle size distribution in two Ti microalloyed steels and their heat-affected zones were investigated. The results show that the particles in the Ti microalloyed steels are TiN particles, and the TiN particles in the steel with lower Ti/N ratio exhibit smaller size and lower dissolution and coarsening rate and extent. Based on the investigation results, kinetic models for TiN particle dissolution and coarsening during welding thermal cycle were developed. The predicted values calculated by using the models are in good agreement with the experimental ones.

Effect of TiN Particles and Grain Size on the Charpy Impact Transition Temperature in Steels

The toughness of ferritic steels is influenced by the grain size distribution, second phase, precipitates and coarse inclusions. In this work an examination of the effect of coarse TiN particles （〉0.5 μm） and ferrite grain size on the Charpy impact transition temperature in high strength low alloyed steels has been carried out. Steels with high Ti content （up to 0.045 wt%）, have been heat-treated and furnace cooled to obtain a ferrite-pearlite microstructure with different ferrite grain sizes. Coarse TiN particle size and ferrite grain size distributions have been measured and Charpy impact testing has been carried out. Scanning electron microscopy （SEM） analysis has been used to measure the grain boundary carbide thickness and to determine if the coarse TiN particles are acting as cleavage initiation sites by fractographic analysis. The Charpy ductile-brittle transition temperatures （DBTT） have been predicted using standard literature equations, and compared to the measured values. The relationship between the ferrite grain size and coarse TiN particle size and number density in terms of whether the coarse TiN particles act as effective cleavage initiation sites is discussed in this paper.

Microstructure and mechanical performances of CGHAZ for oil tank steel during high heat input welding

Microstructure and mechanical performances of the coarse grain heat-affected-zone （CGHAZ） for oil tank steel with different Ti content were investigated through Gleeble-3500, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometer. The results show that the strength and low- temperature toughness of base material are significantly improved for the high titanium content steel, but the impact toughness of CGHAZ is seriously deteriorated after the high heat input welding and declined sharply with the heat input increasing, while the effects of heat input on impact toughness are very weak for the low titanium content steel, impact toughness of which is gradually larger than that of high titanium content steel with the welding heat input increasing because of the granular bainite increasing, TiN particle coarsening, and （Ti, Nb） N composition evolution during the high input welding for high titanium content steel.

Synthesis and Gas-sensing Performance of Nanosized SnO_2

Nanosized tin dioxide particles were prepared by sol-gel dialytic processes with tin(Ⅳ) chloride and alcohol as start materials. The nanoparticles of tin dioxide were charactered by thermogravimetry and differential thermal analysis(TG-DTA), X-ray diffraction(XRD), transmission electron microscopy (TEM) and BET. The results show that the average diameter of tin dioxide particles dried at 353 K was about 2 nm. Even if the tin dioxide particles were calcined at 873 K, the average diameter of particles was less than 10 nm. The removal of Cl- was solved by using this kind of method. The mechanism of the formation of tin dioxide nanosized particles was proposed and analyzed in this paper. We also measured the sensitivity of the sensor based on the tin oxide powder calcined at 673 K to NH 3, alcohol, acetone, hexane and CO. The gas-sensing performance results indicate that this sensor has a higher sensitivity to alcohol and acetone, and selectivity for NH 3, hexane and CO at an operating temperature of 343 K.

In situ TiN-reinforced CoCr2FeNiTi(0.5) high-entropy alloy composite coating fabricated by laser cladding

The fcc structural CoCr2 FeNiTi(0.5) high-entropy alloy(HEA) composite coating with TiN particles reinforced was acquired by laser cladding on the commercial904 L stainless steels.The results show that phase structure is mainly composed of fcc solid solution and TiN phases.The coating exhibits excellent structural stability below850℃.The microstructure consists of irregular dendrite and TiN particles.Transmission electron microscopy(TEM) results reveal that the close-packed plane of fcc phase is(111) with interplanar spacing of ~ 0.208 nm.The interface between TiN and fcc matrix is semi-coherent.And the angle of boundary between dendrite and matrix is ~ 65°.The hardness and corrosion resistance of coating have much improvement compared with those of substrate.