Papers by Author: Li Xin Wu

Abstract: Increasing attention has been paid on fatigue performance evaluation in the recent years. More efficient fatigue testing methods are imperatively needed to accomplish the test requirement. The modified staircase theory is introduced in this paper. Traditional staircase method and modified staircase method are respectively used to evaluate the fatigue performance of pressure vessel steel Q345R. Results show the fatigue limits are 194MPa and 193MPa respectively, which indicates the modified staircase method can enhance the testing efficiency about 50% and keep the test veracity.

Abstract: The corrosion resistances of a weathering steel SPA-H and a carbon steel Q345 after atmospheric corrosion rests of two cities were measured. The results showed that the corrosion resistance was better for SPA-H than Q345 based on the corrosion rate. The corrosion rates of two steels at Qionghai city were lower than those of Jiangjin city. The characterization of the rusts showed the rust layer on SPA-H was denser and thinner than that of Q345. The rust layers were mainly composed of goethite (α-FeOOH) with a few of lepidocrocite (γ-FeOOH). SPA-H had better weatherability attributed to the alloying elements of copper, chromium and phosphorus enriched in the rust layer. The environment factor such as the sedimentation of SO2 has more effect on the corrosion rates than other factors such as alloy elements.

Abstract: The accelerated wet-dry cyclic corrosion tests at different chloride content have been carried out on 09CuPCrNi. The morphology and composition of the rust products have been investigated. The rust layers were composed of the dense inner layer and the loose outer layer. The rust layers were mainly composed of magnetite (Fe3O4) and maghemite (γ-Fe2O3). The rust phase of -Fe2O3 was detected in higher amounts in the rust layers of 1% wt NaCl which resulted in the rust layers much denser. The alloying elements of copper, chromium and phosphorus enriched in the rust layers are helpful to the formation of γ-Fe2O3. The protective denser rust layers play an important role in corrosion resistance of the steel.

Abstract: The dilatometry curves and the critical phase transformation temperatures of high strength low-alloyed (HSLA) cold rolled sheet steel were determined by thermal simulation test machine. The samples were austenitized at 900°C,deformed at 40% of deformation and cooled at different rates of 0.1°C/s~ 60°C/s. The continuous cooling transformation (CCT) diagram under deformation condition can be drawn. The results showed that the critical phase transformation temperatures are as follows: Ac3=900°C, Ac1=735°C, Ar3=825°C, Ar1=695°C. A few amount of martensite in high strength low-alloyed cold rolled steel can be obtained at the cooling rate of 60°C/s. The experimental data provide the technical references for rolling control, cooling control and heat treatment in real production.

Abstract: The effect of tempering process on the microstructure of ultra low carbon bainitic (ULCB) steel produced by relaxation precipitation controlled phase transformation (RPC) has been investigated by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The results showed that the final microstructure mainly contained lath-like bainitic ferrite, granular bainite and martensite-austenite (MA) constituent in ULCB steels. On tempering at 650°C a slight increase was detected in the effective grain size as the strain-induced precipitates pinned up the dislocation walls and subgrains. After tempering at 700°C, bainitic ferrite laths started to coarsen and polygonal ferrite occurred. The effective grain size of ULCB steels in as-rolled condition was 1.5 μm at the tolerance of 10o~15o measured by EBSD technique.