Papers by Author: Zhi Gang Li

Abstract: The Light weight heat treated C-grade bullet proof steel was developed through composition design and optimization based on multiplex alloying, multiplex micro-alloying design ideas and complex phase structure strengthening theory. The puzzle how to avoid the quenching deformation problem of super high strength thin sheet was solved through heat treatment in die with a suit of cooling system. Such C-grade bullet proof steel plate has fine tempered lath martensite structure and has a higher strength than production which is made by a Inc. in Sweden. The shooting and certification test results show that the shot resistance of C-grade bullet proof steel plate can met the protection demand of the Protection specification for cash carrying vehicles (GA164-2005)standard. Comparison with C-grade bullet proof steel plate made by a Inc. in Sweden, the developed C-grade bullet proof steel plate can degrease 5 to 10% weight under the same shot resistance condition. It will be in favour of lightweight for cash truck and anti-hijacking vehicle and energy conservation and emission reduction.

Abstract: The effect of morphology and distribution of sulfides on tensile, impact and bending fatigue properties of non-quenched and tempered steel 49MnVS3 has been investigated in this paper. Microscopic structure and morphology of sulfides are observed, and impact fracture and fatigue fracture have been analyzed by SEM. The results show that the morphology of sulfides is mostly strip and distributes in ferrite, which affects mechanical properties and fatigue life. The length direction of sulfide strip is parallel to the rolling direction of steel. When the length of sulfide is short relatively and is approximate to the shape of particles. The impact properties and bending fatigue performance of 49MnVS3 are higher. Under those conditions, there are more ductile characteristics in their impact fracture and the fatigue fracture. The reasons for the effect of sulfide morphology on the mechanical and fatigue properties are explained.

Abstract: The FEM was used to analyze the stress distribution of a motorcycle frame on the condition of normal running, starting up, turning and braking, respectively. Having been carrying on the 2000km of running test, the initial design motorcycle frame was found several cracks or fractures in the bending points of the square tube and in the welding seam, whose reasons were analyzed then. The metallographical structures of materials and crack parts of the frame were observed and analyzed and Q235. Based on the results mentioned above, the Q345 steel(Chinese steel mark) was used to replace the Q195 steel in the bending square tube and the prop of the steering column. And the welding and manufacture processes were optimized and improved. Finally, the motorcycle frame whose materials had been optimized could keep running in good condition and satisfy the demands after 16000km of running test.

Abstract: The crankshafts of semi-finished products were manufactured by two processes: as-cast followed by normalizing and iron mould with sand liner as-cast. Then those were machined and nitridized followed by the bending fatigue test. At last mechanical properties and impact properties of sampled crankshafts were tested. The mechanical properties are similar in the crankshafts treated by both of the processes, however, the bending fatigue limits of as-cast spherical graphite iron crankshafts are much higher than that of normalized spherical graphite iron crankshafts, whose crack producing work and extending work is higher as well. The higher extended work is considered to relate to the oeil-de-boeuf ferrite and graphite structure and pearlite in as-cast spherical graphite iron crankshafts, while the normalized ones with lower fatigue limit value are composed of spherical graphite and pearlite. Cracks having initiated in the graphite, the tips of cracks can be blunted and the crack propagation can be impeded efficiently by ferrites surrounding the graphite in this structure.

Abstract: There are three common empirical expressions used for the fatigue curves, which are power function, exponential function and three-parameter power function expression, respectively. The mathematical difference between the former two and the latter is whether there exists the constant term S0 in the equations. The S0 can be calculated to determine whether the two-paprameter expression or three-parameter expression should be used. If the two-parameter expression should be used, the power function and exponential function expressions can be compared to determine which one is the optimum one. Finally, the method has been validated by several groups of fatigue data.