By adding Mn into SAE8620 gear steel, the effect of Mn on the microstructure and hardness of steel treated by quenching and partitioning process is investigated in this research. Microstructure is observed. Hardness is measured, after that it is converted into tensile strength. And the content of austenite is determined by X-ray diffraction analysis. It is found that higher content of Mn increases the content of martensite and reduces that of blocky ferrite and also leads to higher hardness of steel. In addition, XRD pattern shows obvious existence and enhancement of retained austenite.

Technology and defect in the low-pressure semi-solid die casting of aluminum wheel hub under different process has been studied. The simulation software ADSTEFAN 2012 is used to analyze the solidification in different die temperature. Stereomicroscope, digital camera and optical microscope (OM) are used to study defect in the casting. The result shows that the low slurry temperature (606°C) will result in higher viscosity, and the low preheated die temperature will increase the cooling rate so that shrinkage is formed in the isolate solidification area. In the technology of casting wheels, the optimum temperature of the slurry is 614°C, preheated temperature of die is 400°C.

Austenitic continuous heating transformation dynamics, microstructural evolution and quenching properties of 22MnB5 steel during resistance heating were investigated. Steel sheets with thickness of 1.6 mm were heated to various temperatures (800~1200 °C) either by resistance heating at two heating rates of 100 and 300 °C/s or furnace heating. The increment of superheat degree was parabolic relationship with increasing heating rate. Samples heated above Ac3 of respective heating rates exhibited a full martensite microstructure and a hardness of above 490 HV. Austenitic coarsening rate of resistance heating samples was much lower than those by furnace heating. Austenite grain size by resistance heating was smaller than 38 μm while these by furnace heating reached 74 μm at 1200 °C. Samples heated by resistance heating at 300 °C/s had a good performance of 1800 MPa tensile strength and 5.6 % elongation, and product of strength and elongation reaches 10080 MPa%. The good combination of tensile strength and elongation by resistance heating might result from the finer austenite grain size and smaller martensite plate.

To aid the optimizing design of filling system, computer simulation technique is introduced to predict injection-forming process and to protect defects during trial manufacture of automotive parts by using semi-solid die cast process. By comparing formed appearance of parts in experiments and that in simulations, and observing the relationship between internal defects inspected by X-ray and flow field obtained in simulation, it is indicated that there are quite good agreements between simulation and experiment, right predictions for cast defects resulting from filling process can be made and improving direction is proposed. The realization of numerical visualization for filling process of high speed during semi-solid die cast process will play an important role in optimizing technology plan and process.Introduction Semi-solid die cast process with many features [1], [2] is a forming technology developed on the base of general molten metal die cast, and is gradually becoming maturity as near-net-shape processing of material. Comparing with traditional die cast, there are a lot of unsolved technology problems in Semi-solid die cast process. For example, because mature data are absent from the design of gating system, design experiences in die cast of molten metal are used. To optimize forming process, to aid the die design and to forecast cast defects, the introduction of computer simulation will play an important promoting role in enhancing technique level of semi-solid formation and product quality. As one of the steps in which automotive parts are systematically developed, using simulation technique during trial manufacture of Al alloy parts aims at optimizing forming technology and improving quality of product.

In this study, a improved mathematical model was developed for Nb-Ti microalloyed steel during hot rolling simulation. Using the compression test, the dynamic and static recrystallization characteristics of Nb-Ti microalloyed steel were studied. Though multi-pass hot rolling simulation, it is found that the recrystallization during hot rolling can play an important role, it can make the mean flow stress lower and refine the grains. And respective comparison between calculated and measured data of microstructure showed some of the validation of the built model. Meanwhile, the evolution characteristic of average austenite grain size during hot rolling can be achieved by theoretical model and experiment.