Papers by Author: Guo Dong Wang

Abstract: The new generation thermo-mechanical controlled processing (TMCP) technology based on advanced cooling technique and equipment is introduced here in the context of 960MPa grade high strength structural steel plates. This new technology accurately controls the cooling rate and temperature, with strong influence on phase transformation and precipitation including microstructure and mechanical properties of the steel. The application of the newly developed technology applied to the production of 960MPa grade high strength structural steel demonstrated its effectiveness, especially in improving low temperature impact toughness. The yield strength was 980~1000 MPa and tensile strength 1080~1200 MPa, with impact toughness approaching 150J at-40°C.Keywords: New generation TMCP technology; Ultra fast cooling process; high strength steels; mechanical properties

Abstract: With the development of auto industry, the F/B dual phase steels were widely used in wheel and underpan due to their lower cost and higher hole expansion property. In the present investigation, the effects of the finishing rolling temperature and initial cooling temperature of ultra fast cooling (UFC) on microstructure and hole expansion property of a low carbon C-Mn steel were investigated using optical microscope (OM) and scanning electron microscope (SEM). It has been found that lowering the finishing rolling temperature can refine the microstructure and the volume fraction of ferrite is increased as the initial cooling temperature of UFC is lowered. Furthermore, both lowering the finishing rolling temperature and the initial cooling temperature of UFC can improve hole expansion property.

Abstract: The low silicon transformation-induced plasticity (TRIP) steel with phosphorus addition is consisted of the microstructure of retained austenite, ferrite and bainite which produced by intercritical annealing and isothermal bainite transformation followed by rapid cooling. In this study, isothermal bainite transformation of different experimental parameters in low silicon TRIP steel with phosphorus addition was investigated in laboratory. The addition of cheap element phosphorus, which has the same effect of silicon in retard the kinetics of carbide formation during isothermal bainite transformation, can reduce the silicon content, improve surface quality, solve galvanizing problem and reduce costs. The effect of bainite isothermal temperature, intercritical annealing temperature and heating rates were investigated by dilatometric experiment on a push-rod Formastor-FII high-speed dilatometer with radio frequency induction heating. The high resolution observations, composition analysis and elements distribution of microstructure were carried out using the electron scanning microscopy of a field emission electron probe microanalyzer (JEOL JXA-8530F) operating at 20KV accelerating voltage.

Abstract: By the analysis of the conventional PID controller characteristics and the equipment hysteretic nature, one design method of multivariable composite controller based on fuzzy switching was introduced in this paper. The controller solved the problem of local optimal value using fuzzy self-tuning PID controller. As a result of introducing parameter of ultra fast cooling flow setting, response speed of frequency converter was reduced. In order to avoid chattering generated when system switching, fuzzy switching scheme was designed. The simulation results show that response characteristic of the controller is better than conventional PID controller and chattering is smaller during the system switching. Applying the controller into constant pressure water supply system, the control effect is improved obviously.

Abstract: The chemical composition of a 960 Mpa grade high strength steel with low carbon equivalent was designed. Effect of direct quenching and tempering process on the microstructure and mechanical properties of the experimental steel was studied. Results showed that fine lath martensite was obtained after controlled rolling and direct quenching. With tempering temperature increasing, the mechanical properties showed different trends for different tempering stages. And this had a direct relationship with the microstructure evolution. The matrix recovery softening, carbon desolution and precipitation of nanomicroalloy carbides influenced the strength change. With increase of tempering time, the strength decreased and toughness improved. Experimental steel tempered at 450 °C for 40min could obtain the best mechanical properties, which meet the requirement with a large impact energy margin.

Abstract: Effect of coil temperature on the texture and microstructure evolution during cold rolling and annealing were investigated by OM, ODF and EBSD. The results indicate that the {223}<110> and {114}<110> textures appeared after cold rolling are inherited followed by annealing, whose intensities would be higher as the coil temperature decreased. Lower coil temperature could improve the uniformity of grain size and increase the fraction of low-angel grain boundaries as well as coincidence site lattice boundaries. And the {111}//ND texture is improved in the lower coil temperature cold and annealing steel sheet, which is beneficial for the deep-drawability.

Abstract: The effects of annealing routes (batch annealing and continuous annealing) on the development of microstructure and texture in a cold-rolled Nb-IF high strength steel sheet were studied by means of optical microscopy(OM), electron backscattered diffraction(EBSD) and ODF analysis. The results show that the finer and more homogenous recrystallization grain can be observed in the CA steel. The CA process leads to an increase in the intensity of the γ-fibers, and the very sharp and uniform γ-fibers are found in this case, which is beneficial to the deep-drawability.

Abstract: Based on the actual production data of ASP (Angang Strip Production) hot strip rolling line, mechanical properties of thin gauge X70 pipeline steel were simulated by BP neural network method. Recursive functions were used to verify the mechanical properties which calculated by BP neural network. Based on predicted mechanical properties with high precision, BP neural network and Genetic Algorithm (GA) were combined to establish the temperature schedule of X70 pipeline steel during ASP hot strip rolling. It is shown that there are four important temperatures during ASP hot strip rolling, such as rough rolling temperature, refine start rolling temperature, refine finish rolling temperature and coiling temperature. Temperature difference of adjacent stages and temperature of former stage is a linear function relationship. For a given mechanical properties, deviations between simulated temperature and actual temperature are within ±10°C. This method can be used to produce different strips with the same compositions but different strengths by regulating suitable temperature schedule, so it is effective to resolve conflicts during hot strip rolling.

Abstract: A successful ultra fast cooling (UFC) technology has been applied to the plate rolling production line in Shouqin Metal Materials Co.Ltd.. Industrial trials are reported for the production of X70 pipeline steels (about 70000 t) under UFC conditions. Pipeline steels with reasonably good properties have been produced on an industrial scale. UFC improves the temperature uniformity, the mechanical properties and the plate profile of X70 pipeline steel. The impact values of X70 pipeline steel at UFC mode exceed the standard requirements of X80 pipeline steel. The productivity is enhanced because cutting quantity of head and tail of the plate is reduced. The enhancement of control accuracy of the red back temperatures is favorable for industrial production of X70 pipeline steel. The reduced production of the steel-making has been industrialized achieved, since a new composition was designed by reducing the vanadium content to less than 0.045wt.%.

Abstract: A Q550 high strength steel was selected at two different cooling rates through ultra-fast cooling process, and its microstructures and strengthening mechanisms were analyzed. The results show the bainite transformation temperature of the steel decreased with the increasing of cooling rate.The ultra-fast cooling process can improve the performance of Q550 compared with the conventional cooling process, and the yield strength, tensile strength and elongation are 600MPa, 755MPa and 19%, and - 20 °Cimpact energy is 253J, and good strength and toughness are obtained under ultra-fast cooling process. The microstructure of this steel is bainite and good strength and toughness are caused by the refinement of bainite and fine precipitates. Ultra-fast cooling technology improves the strength and toughness of this steel effectively.