Papers by Author: Guo Dong Wang

Abstract: In this work, a novel type of δ-TRIP steel was designed, and the content and stability of retained austenite in δ-TRIP specimens under different annealing processes were detected and studied, respectively. The volume fraction of austenite was determined by X-ray diffraction (XRD). The microstructure and mechanical properties were analyzed systematically. The results show that a complex microstructure composed of three phases (ferrite, bainite and retained austenite) was obtained in the δ-TRIP steel. With the increasing of annealing temperature, both retained austenite and bainite content in the specimen increased, while the carbon content in retained austenite decreased, leading to a poor stability for retained austenite. Both tensile and yield strength improved with the increasing of annealing temperature, while the elongation reduced. The feature of retained austenite led to an excellent combination of ductility and strength, which was better than traditional TRIP steel.

Abstract: Grain-oriented silicon steel was produced by strip casting route. The effect of different annealing temperature on primary annealing and secondary annealing was investigated. The result showed that the average grain diameter increased and the grain uniformity was gradually destroyed with the increasing annealing temperature. Regardless of annealing temperature, the primary texture consisted of strong γ-fiber and weak λ-fiber. With the increase of annealing temperature, the γ-fiber intensity increased. In addition, the Goss component was not shown at 780-880 °C but appeared at 980 °C. After secondary annealing, complete abnormal grain growth occurred in all samples and the average grain diameter increased with the primary annealing temperature. The Goss sharpness of secondary grains firstly increased and then decreased with a peak value obtained at 830 °C. This result was explained in terms of the combination of the inhibiting force, primary grain diameter and primary texture.

Abstract: A 1000MPa grade steel plate for coal mining machinery equipment was studied in this paper. The ultra-high strength steel plate is processed by direct quenching after hot rolling plus tempering (DQ-T) to obtain high toughness and ductility. It has found that the tempering temperature has an important influence on the steel microstructure, precipitation behavior and the plate mechanical properties. At the lower tempering temperatures from 400 °C to 450 °C, the steel plate has a low toughness. When the tempering temperature is higher than 450 °C, the higher mechanical properties can be obtained due to the carbides precipitation, dislocation dissolution and carbide decomposition from residual austenite after quenching. The steel microstructure is comprised of tempered sorbite and bainite, in which sorbite plays an important role in obtaining premium microstructure.

Abstract: Based on ultra fast cooling, effects of cooling paths on microstructure and mechanical properties of vanadium bearing microalloyed steel were investigated by the observation of optical microscope and scanning electron microscope and the testing of mechanical properties, moreover, the work-hardening exponent was determined based on stress-strain curves. The results show that using ultra fast cooling can effectively refine ferrite grain size and the ferrite grain size is decreased as the final temperature of ultra fast cooling is decreased. In addition, the microstructure and mechanical properties can be controlled by cooling paths. The ferrite-perlite microstructure with lower strength and higher n-value of approx. 0.2 and the ferrite-bainite microstructure with higher strength and lower n-value of approx. 0.16 can be gained at the higher and lower final temperature of ultra fast cooling, respectively. And the yield ratio are all lower than 0.85.

Abstract: In this work, the bainite transformation during isothermality of aluminium bearing TRIP steel was studied by dilatometric experiment on a pushrod Formastor-F highspeed dilatometer with radio frequency induction heating. The aluminium bearing TRIP steel consisted of the microstructure of austenite, ferrite and bainite in the form of laths which produced by intercritical annealing and isothermal transformation followed by rapid cooling. The effect of intercritical annealing temperature and isothermal transformation temperature were studied by dilatometric experiment and JEOL JXA-8530F Electron Probe Microscopic Analyzer (EPMA).

Abstract: To implement the new generation thermo mechanical control process (NG-TMCP), the automatic control system of ultra fast cooling (UFC) was developed by combined with the renovation project of controlled cooling system in one plate production line. This system was composed of basic automation subsystem and process automation subsystem. As the main control unit of the basic automatic control system, a S7400 PLC system is used to control the UFC device and to achieve the chain control between the UFC system and the mill system. While the process control system is to realize the automatical setting of the cooling schedule by the developed finite element temperature field model and the temperature homogeneity model. The industry application shows that the NG-TMCP which is based on the UFC can reduce the alloy content effectively and implement the low-cost reduction produce of high-grade products.

Abstract: During the past two decades, progress has been achieved for the plate production in various areas, from the level of equipment to the processing techniques, and from the product size to the quality of the products as well. However, plate camber which may affect the stability of rolling has been one of those thorny problems due to the complexity and variation of plate camber. Analysis of the factors which may lead to plate camber, including slab wedge, temperature uniformity across the plate width, side-guide alignment, stiffness difference at two sides of the mill and the inclination of the roll gap, the features of the plate camber have been studied. Using measurement and quantitative analysis of plate camber, process data analysis of the plate, equipment monitoring and operation adjustment, a systematical diagnostic strategy of plate camber has been carried out. It has shown that the developed diagnostic strategy is satisfactory in one domestic Plate Mill.

Abstract: The plate camber is one of the thorny problems in the plate rolling process. The characteristic variables of plate camber at the delivery and at the entry sides of the mill were illustrated based on the primary concepts of camber. The relationship between the plate characteristic variable and velocity distribution in the deformation area of the plate was also determined. This paper focuses on the features of asymmetry in the transverse direction during rolling, an elastic deformation mathematical model of four-high mill has been developed to optimize the predictive model of plate camber, which ensures the theory of influence factors of plate camber to be applied in plate rolling.

Abstract: Thermo-mechanical Controlled Processing (TMCP) is one of the greatest achievements in steel industry in the 20th century, which, however, depends too much upon low temperature rolling for the refinement of austenite grains, causing great loss in terms of productivity. To overcome this disadvantage, a new processing route with ultra fast cooling as the core has been proposed, and pilot rolling and industrial trials were carried out. As compared to conventional accelerated cooling, the ultra fast cooling can achieve cooling rate up to 300°C/s for 3 mm thick strip and highly homogeneous cooling by the pressurized water spraying. In the present work, the metallurgical backgrounds for ultra fast cooling in thermo-mechanical processing were studied and elucidated. By the pilot hot rolling experiments with a lean composition of a typical 600 MPa grade high strength steel, it has been found that the application of ultra fast cooling (UFC) at the exit of hot rolling mills can improve the strength by as much as 100 MPa as compared to the conventional TMCP. The strengthening mechanism lies in that the ultra fast cooling immediately after hot rolling may further improve the strengthening effects by precipitation, grain refinement, and dislocation hardening. The theoretical calculations and experiments indicate that the grain refinement, dislocation hardening, and precipitation in the TMCP with in-front UFC have caused the strength increments of 36, 34 and 54 MPa over the conventional TMCP with ACC, respectively. The microstructure characterization showed that the density of high angle grain boundaries had been increased, and the average size of precipitates had been reduced from about 34 nm to 10 nm with the cooling pattern changing from ACC to the application of UFC. The theoretical estimation indicates that when the cooling profile is changed from the conventional ACC to UFC+ACC, and to UFC, precipitation strengthening accounts for more and more strength increment in the improved strength of hot rolled micro-alloyed steels.

Abstract: The precipitation of vanadium takes place mainly in ferrite by interphase precipitation or nucleation on dislocation line, which makes sense for the industry production due to the precipitation strengthening. The objective is to analysize the cooling process of V-steels to exert the precipitation strengthening of vanadium. The steels with 0.09%C-0.055%N/0.0107%N/0.0168%N/0.0193%N-0.08%V/0.085V steel are the researched steel grades. Using solid solubility products model and thermodynamic equation, the full solid solution temperature, nucleation rate curve and PTT curve of precipitation process are calculated. The effect of nitrogen on the precipitation behaviour of V(C,N) in γ and the precipitation of V(C,N) in α are simulated. Based on the calculation results the trial process is determined. The laboratorial trials are carried out with ultra fast cooling. The precipitate particles are observed by TEM. The solid solution amount increases monotonously and the size of precipitate particle decreases with the nitrogen content. The solid solution temperature of 0.055%N, 0.0107%N, 0.0168%N and 0.0193%N are 977.0°C, 1028.0°C, 1062.3 and 1078.9°C respectively. The laboratorial trial results shows that the tensile strength is improved about 100 MPa due to the precipitation strengthening. The relationship between the coiling temperature and the strength is parabolic curve downward and the relationship between the coiling temperature and the elongation is parabolic curve upward. This calculation can determine both the proper nitrogen content and the optimal cooling process. The trial results proves this method is feasible and efficiency.