Zhaodong Wang

Analysis of rolling pressure in asymmetrical rolling process by slab method

The plane strain asymmetrical rolling was analyzed using slab method. The contact arc was replaced by parabola, and the constant surface friction status was adopted during the analysis. The deformation area was divided into three zones according to the direction of the friction. Then, the three zones were studied, respectively. A rolling force model and a rolling torque model were developed based on the analysis, and they were used to analyze the influence of asymmetrical rolling factors on deformation area and unit pressure if they had good precision which was determined by comparing the calculated results with the measured ones.

Effects of Ultra Fast Cooling on Microstructure and Mechanical Properties of Pipeline Steels

X70 (steel A) and X80 (steel B) pipeline steels were fabricated by ultra fast cooling (UFC). UFC processing improves not only ultimate tensile strength (UTS), yield strength (YS), yield ratio (YS/UTS), and total elongation of both steels, but also their Charpy absorbed energy (AK) as well. The microstructures of both steels were all composed of quasi polygonal, acicular ferrite (AF), and granular bainite. MA islands (the mixtures of brittle martensite and residual austenite) are more finely dispersed in steel B, and the amount of AF in steel B is much more than that in steel A. The strength of steel B is higher than that of steel A. This is mainly attributed to the effect of the ferrite grain refinement which is resulted from UFC processing. The finely dispersed MA islands not only provide dispersion strengthening, but also reduce loss of impact properties to pipeline steels. UFC produces low-temperature transformation microstructures containing larger amounts of AFs. The presence of AF is a crucial factor in achieving desired mechanical properties for both steels. It is suggested that the toughness of the experimental steel increases with increasing the amount of AF.

Microstructure and Abrasive Wear Behavior of Medium Carbon Low Alloy Martensitic Abrasion Resistant Steel

The effect of processing parameters such as hot rolling and heat treatment on microstructure and mechanical properties was investigated for a new 0. 2 7 mass % C and Ni, Mo-free low alloy martensitic abrasion resistant steel. The three-body impact abrasive wear behavior was also analyzed. The results showed that two-step controlled rolling besides quenching at 880 °C and tempering at 170 °C could result in optimal mechanical property: the Brinell hardness, tensile strength, elongation and −40 °C impact toughness were 531, 1530 MPa, 11.8% and 58 J, respectively. The microstructure was of fine lath martensite with little retained austenite. Three-body impact abrasive wear results showed that wear mechanism was mainly of plastic deformation fatigue when the impact energy was 2 J, and the relative wear resistance was 1. 04 times higher than that of the same grade compared steel under the same working condition. The optimal hardness and toughness match was the main reason of higher wear resistance.

Effects of Tempering Temperature and Mo/Ni on Microstructures and Properties of Lath Martensitic Wear-Resistant Steels

The tempering behavior was experimentally studied in lath martensitic wear-resistant steels with various Mo/Ni contents after tempering at different temperatures from 200 to 600 C. It is shown that a good combination of hardness (HV) (420–450) and–20 °C impact toughness (38–70 J) can be obtained after quenching and tempering at 200–250 °C. The microstructure at this temperature is lath structure with rod-like and/or flake-like ε-carbide with about 10 nm in width and 100 nm in length in the matrix, and the fracture mechanism is quasi-cleavage fracture combining with ductile fracture. Tempering at temperature from 300 to 400 °C results in the primary quasi-cleavage fracture due to the carbide transformation from resolved retained austenite and impurity segregation between laths or blocks. However, when the tempering temperature is higher than 500 °C, the hardness (HV) is lower than 330 and the fracture mechanism changes to ductile fracture due to the spheroidization and coarsening of cementite. Additions of Mo and Ni have no significant effects on the carbides morphologies at low tempering temperatures, but improve the resistance to softening and embrittling for steels when tempered at above 350 °C.

Development of New Generation Cooling Control System After Rolling in Hot Rolled Strip Based on UFC

Ultra-fast cooling (UFC) is an advanced technology in hot rolling field. Through this technology, great changes on the run-out table are produced in the strip cooling process. In order to adapt to these changes, a new generation of hot strip cooling control system after rolling was developed based on the UFC basic principle. The system can not only accomplish temperature of UFC delivery side, coiling temperature, cooling rate, etc, and multi-objective accuracy control, but also offer more flexibility and new attractive possibilities in terms of cooling pattern on the runout table, which could be of prime importance for the production of some difficult steels. In addition, through the time-velocity-distance (TVD) profile prediction combined with speed feed-forward control and coiling temperature feedback control, the coiling temperature control precision can be effectively improved during accelerative rolling in the system. At present, the system has been successfully used in the conventional strip production line and CSP short process production line, and its application effect is perfect.

Heat Transfer During Quenching by Plate Roller Quenching Machine

For plate quenching on a roller quenching machine, heat transfer process is investigated. According to the practical online experiment of plate center temperature, average heat transfer coefficient under different conditions and temperature fields are analyzed by numerical simulation. The results show that, at the water temperature of 15 °C, the instantaneous maximum quenching cooling rate is 17.6 °C/s for the plate of 50 mm in thickness in roller quenching process. In the temperature range of 400 — 850 °C, the maximum is 12. 1 °C/s. With the plate surface temperature decreasing, surface heat transfer coefficient increases at first, and reaches the maximum value of about 15 000 W/(m2 • K), and then decreases. The calculated heat transfer coefficients are applied to analyze plate temperature field of different thicknesses, and the difference between the calculated and measured temperature is less than 5%.

Construction and Application of Quenching Critical Cooling Rate Model

Based on exploring quenching mechanism, three types of quenching critical cooling rate models of medium-carbon steel and low-carbon steel and low-alloy construction steel were established, as modified Maynier model, Eldis model and isothermal curve model, respectively. During construction process, regression analysis and Newton interpolation method were used for higher calculated precision. Through comparing and analyzing, the superior one was selected to evaluate the full hardening thickness after quenching. According to hardness analyzing, the deviation between predicted hardness distribution and the experimental value is within 6%.

Textures and Properties of Hot Rolled High Strength Ti-IF Steels

The texture evolution in a high strength Ti-IF steel during the processing of hot rolling, cold rolling, and annealing is studied. For comparison, both ferrite rolling and austenite rolling are employed. It is found that the texture type is the. same after ferrite rolling and austenite rolling, but the texture intensity is much higher in the ferrite rolled sample. Furthermore, texture characteristics at the surface are absolutely different from those at the mid-section in both ferrite rolled and austenite rolled samples, as well as under the cold rolled and annealed conditions. The shear texture {110}<001> disappears and orientation rotates along {110}<001<→{554}<225>→{111}<112>→ {111}<110>→{223}<110> during cold rolling. Compared to the austenite rolled sample, the properties of the cold rolled and annealed sheet which is subjected to ferrite rolling are higher.

Calculation Method of Optimal Speed Profile for Hot Plate During Controlled Cooling Process

The healthy and rapid development of the controlled cooling technology was hampered by the uneven cooling phenomenon. During the process of hot plate production, the homogeneous cooling along the length direction of plate was constrained by lots of factors. And because the speed was a flexible control parameter, the calculation method of optimal speed profile was developed based on the measured start cooling temperature and its matrix equation was solved by the Cholesky decomposition method. The optimal speed profile was used in online control system. As a result, the temperature distribution along the plate length direction was relatively uniform, and 95% of measured final cooling temperature difference from the target temperature; 700 °C was controlled within +20 °C.

Texture Evolution in a Warm-Rolled Ti-IF Steel During Cold Rolling and Annealing

The texture characteristics of a Ti-IF steel in ferritic hot-rolled (warm-rolled), cold-rolled, and annealed status were studied. The hot bands were obtained by finish rolling in ferrite region, coiling at very low temperature, and then directly annealing in industrial trial. It was found that