Papers by Author: Li Hui Wang

Abstract: The surface of hot-dip galvanized high strength low alloy (HSLA) steel easily occurs orange peel in the deformation process. On the other hand, the defects possess a specific directivity and sits at approximately a 45-degree angle to the sheet steel rolling direction. The microstructures and properties of steel specimens with the orange peel defects and the normal were analyzed, which results showed that their microstructures consist of ferrite and few granular pearlite. The yield point elongation of the HSLA steel resulted in the orange peel defects on the surface of sheet stamping and it is associated with skin rolling and stretch rolling process. Further studied on the fine microstructures by means of SEM and electron back scatter diffraction (EBSD) techniques, which was apparent for the defect steel that the orange peel defects were resulted from weak favorable {111} texture might be the key factors aggravating the formation of orange peel defects. It can be concluded that the formation of Cottrell atmospheres caused the yield point elongation by the interaction between dislocation and diffusive solute atoms as basic reason and the directivity of the orange peel defects was related with the LUDERS slip forming. The yield point elongation can be eliminated to avoid the orange peel defects beyond to 1.8% skin-rolling and stretch rolling method with an appropriate annealing technology.

Abstract: Effects of continuous annealing process on microstructure and properties of Si based cold-rolled TRIP Steel were studied. The results show that the TRIP effect is more obvious on the condition of 800°C with 120s annealing process and 400°C with 520s aging treatment than others progress. The yield strength of the tested steel is 405MPa, tensile strength is 670MPa, elongation is 32% and strain hardening exponent is 0.230. The microstructures are ferrite, bainite and retained austenite and the volume fraction of retained austenite for the tested steel is 9.20%.

Abstract: By analysis of TWIP Steels with different manganese content, the results showed that the microstructures and properties had been changed with different Mn content. The elongation of the tested steel with 22.5% Mn was high for 55.5 % and n value of that reached to 0.360. When Mn content of the tested steel was 17.9%, the yield and tensile strength were higher and its elongation was lower for the tested steel than that of the tested steel with 22.5% Mn. The microstructures of the tested steel with high Mn content were austenite before and after being stretched at room temperature. Mn content was decreased and the microstructure of the tested steel after being stretched had a small amount of martensite transformation at room temperature. That is to say, double effect with TWIP and TRIP had occurred, but TWIP effect was dominant. TWIP effect increased plasticity and strain hardening capacity to improve formability. TRIP effect was mainly to improve strength so as to further attain the strength of the tested steel.