Papers by Author: Hui Bin Wu

Abstract: A type of X80 grade high strength and toughness pipeline steel was designed and researched. The strengthening mechanism of the steel was analyzed by SEM, TEM and XRD, and the CO₂ corrosion behavior of the steel was simulated by high-temperature and high-pressure autoclave. The result shows that the microstructure of the base metal is mainly acicular ferrite with a small amount of granular bainite. Acicular ferrite consists of laths which occlude and interweave with each other, and there are many dislocation and carbonitrides distributing in acicular ferrite, which made the pipeline steel have good strength and toughness. Under the simulation of the actual working conditions, the activity of reactants is low at 30°C, so the corrosion rate is smaller at this temperature; the maximum of corrosion rate occurs at 60°C; when the temperature increases to 90°C, the corrosion rate is lower than that of 60°C, that is because hindering corrosion effect which take by the acceleration deposit of corrosion product is better than the acceleration corrosion reactions.

Abstract: This paper focus on the development of low-alloy anti-corrosion steel for the upper deck of COT(cargo oil tank), and the corrosion behavior of Cr-containing low-alloy steels in O₂-CO₂-SO₂-H₂S moisture were studied using homemade COT corrosion simulation device. After the corrosion experiment, related corrosion data was measured, and macro morphology and structure of corrosion scale were observed by SEM(Scanning Electron Microscope). The phase and chemical composition of corrosion product film were analyzed by XRD(X-ray diffraction) and EDS(energy dispersive spectroscopy). The effect of misorientation distribution on anti-corrosion property of steel was investigated by EBSD(electron backscattered diffraction). Based on the results, corrosion scale of COT on the upper deck consist of α-FeOOH, γ-FeOOH, FeS₂, S and Fe_1-xS, and the type of corrosion is mainly general corrosion. Cr enrichment was found on the inner corrosion product film, the addition of Cr leads to the increasing of low-angle grain boundaries and sub-grain structure which is conducive to the improvement of corrosion resistance.

Abstract: The samples of 9Ni steel were treated by Quenching + Tempering (QT) and Quenching + larmellarizing + Tempering (QLT). The morphology, thermal stability and mechanical stability of the reversed austenite in 9Ni steel were studied by TEM, XRD, EBSD, subzero treatment, three-point bending, uniaxial tension and uniaxial compression. It turns out that blocky reversed austenite occurs in QT-treated steel, while blocky and filmy reversed austenite occurs in QLT-treated steel, additionally, the filmy reversed austenite distributes in the lath boundaries. Subzero treatment shows that certain amount of reversed austenite in QLT-treated samples transforms after dipping into liquefied nitrogen, but it retains a higher level of more stable austenite in QLT-treated sample than that in QT-treated sample. Both tension and compression facilitate the transformation of reversed austenite into martensite, and the retained austenite mainly locates within grains.

Abstract: Crack initiation, propagation and microfracture processes of B-class shipbuilding steel have been investigated by using an in-situ tensile stage installed inside a scanning electron microscope chamber, meanwhile the secondary crack propagation at low temperature brittle fracture has also been studied. It is revealed that micro cracks always nucleated at the notch of specimens due to the stress concentration and then propagate along the interface of ferrite-pearlite. The plastic deformation of polygonal ferrite occurred in the loading process, the cracks propagated as “Z” morphology in the matrix. In the low temperature brittle fracture zone, the secondary crack propagated through the ferrite matrix in the manner of transgranular crack. When the secondary crack propagated to pearlite region, the intragranular crack and transgranular crack were observed in the pearlite region .

Abstract: Thermal simulation test, TEM(Transmission Electron Microscope) and nanobeam EDS techniques were used to investigate the dissolving and precipitation behavior in Nb-bearing mciroalloyed steel. The experimental results indicate that: there are two families of precipitates in the as forged samples. The larger precipitates of Nb(C,N) disappear after being held for 2h at 1300°C,while the inclusions of MnS formed from the solidification even remain for 48h held at that temperature. After 30% of predeformtion at 850°C and 900°C, the strain-induced precipitation occurs, that is, the other tiny precipitates. Compared with the samples relaxed at 850°C, the ones that are held at 900°C show larger particles by same holding time but demonstrate the same size when the relaxation time reaches 1000s.

Abstract: After bainitic transformation, the dislocations formed in deformed austenite remained to be pinned by the precipitates so that thermostability of the bainitic ferrite was improved. Coarsening of the precipitates accompanied by their distribution density change occurred during reheating. After long reheating, further precipitates nucleated in bainite. Dislocations inside laths getting rid of pinning of precipitates and their polygonization play the precursor to the evolution of microstructures, in which lath boundaries disappeared gradually.

Abstract: Cooled in water after isothermal relaxation of deformed austenite for different time, a Nb-bearing microalloyed steel always exhibited synthetic microstructures of bainitic ferrite, granular bainite and acicular ferrite. When these samples were reheated to and held at 650°C or 700 °C, the non-equilibrious microstructures tended to evolve into equilibrious ones, accompanied by obvious change of hardness. The rate of microstructures evolution was closely related to relaxation time of deformed austenite. The sample relaxed for 60s displayed the highest thermal stability, while microstructure evolution was quickest in the sample relaxed for 1000s even though it was softest before reheating. By hardness measurement, it was found that softening was not only process occurring during reheating, in which hardness fluctuated with time. There were two peaks in hardness-time curve of each sample having undergone relaxation, while single peak occurred in the curve of the sample not being relaxed. These results indicate that thermal stability of microstructures is determined by their history of formation.