Papers by Author: Ming Tu Ma

Abstract: Hot stamping has been developed into a sophisticated stage with standardized technology and typical product USIBOR1500. Most of the hot stamped components from 22MnB5 blanks possess high strength-ductility with TS⋅El product from 10 to 15 GPa%. To meet the further requirement of automakers on body lightening, energy saving and impact safety, the new HFQPT process is proposed, i.e. Hot Stamping in combination with Quenching-Partitioning-Tempering treatment, for higher strength-ductility auto parts with TS⋅El product 20∼30 GPa%. Based on the key technology of AHSS in retained austenite RA and TRIP effect, the Q-P-T treatment is integrated to hot stamping process to obtain retained austenite on the martensite matrix to improve ductility of hot stamped ultra-high-strength components. A low temperature P-T furnace is added to the hot stamping line followed the hot pressing machine to perform Partitioning-Tempering treatment immediately after Hot Press Forming and Quenching, named as HFQPT process. The blank steels for new hot stamping process HFQPT line can be further developed on the basis of low alloyed TRIP assisted steels, Q-P steels and Q-P-T steels, and produced in traditional hot strip mill HSM or in compact steel production CSP line through thin slab casting & direct rolling to deliver ultra-thin-hot-strip (thickness t = 1.2 ∼2.0 mm).

Abstract: The property and microstructure of rolled non-quenched and tempered steels of Nb-V comprehensive micro alloying have been investigated .The mechanical properties and the load –displacement curves were measured respectively by using electron tension test machine and digital-impact test machine . The microstructure and fracture surface of impact samples were observed with SEM .The results show that micro-alloying Nb and V non-quenched and tempered steel behaves higher tension strength and toughness than that of only V micro-alloying one under the condition of about same plasticity. Improvement of the properties is related with that Nb can effectively make fine pearlite group and inter-lamella spacing at the impact fracture pearlite flakes. Corresponding relationship between various domain of fracture morphology and characteristics points at the curve of digital impact has been discussed.

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: Ultrafine TiO2 powders as rutile and anatase phase were simply precipitated at room temperature for only tens of hours by simply controlling the pH value and Ti4+ concentration via aqueous TiCl4 solution. Under the optimal pH value and Ti4+ concentration, the average particle size of powders with rutile phase was 3.7nm, while that of powders with anatase phase was 3.0nm. The average particle size was calculated from the broadening of corresponding X-ray spectral peaks by Scherrer formula. In addition, 3.0 mol.l-1 are suggested to be used as concentration of stock solutions instead of the current concentration 2.0 mol.l-1.

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.