Search

Vertical rolling is an important technique used to control the width of continuous casting slabs in the hot-rolling field. Accurate prediction of vertical rolling force is a core point maintaining rolling-mill equipment. Owing to the limitation of the algorithm in use, the prediction accuracy of most vertical rolling force models based on the energy method can only reach more than 10%. Therefore, it is challenging to optimize the rolling-force model to improve prediction accuracy. An innovative approach for optimizing the calculation of vertical rolling force with a unified yield criterion is presented in this paper. First, the maximal width of a dog-bone region is determined by the slip-line method, and the dog-bone shape is described using a sine-function model. Second, the velocity and corresponding strain-rate fields satisfying kinematically admissible conditions are proposed to calculate the total power of the vertical rolling process. Finally, the analytical solution of the rolling force and the dog-bone-shape model is obtained by repeatedly optimizing the weighted coefficient b of intermediate principal shear stress on the yield criterion. Moreover, the effectiveness of the proposed mechanical model is verified by measured data in the strip hot-rolling field and other models’ results. Results show that the prediction accuracy of the vertical rolling force model can be improved by optimizing the value of b. Then, the impacts of reduction rate, initial thickness, and friction factor on dog-bone shape size and vertical rolling force are discussed.

As an important optical component in laser system, silicon mirror surface is required to have micron-level flatness and subnanometer-level roughness. The research concentrates on how to improve roughness as far as possible while maintaining flatness of silicon mirror surface during chemical mechanical polishing (CMP) process. A polishing edge effect model is established to explain the reason of flatness deterioration, and a roughness theoretical model is set up to get the limit of perfect surface roughness. Based on the models above, a polishing device is designed to maintain the surface flatness, and the optimized polishing process parameters are obtained by orthogonal tests to get a near-perfect surface roughness. Finally the maintenance of flatness and the improvement of roughness can be achieved at the same time in one step of CMP process. This work can be a guide for silicon mirror manufacture to improve optical reflection performance significantly.

Marangoni drying induced by organic vapor is an important process in integrated circuit manufacturing to obtain an ultra-clean surface, but its application is limited by the utilization of flammable vapor. Thermal Marangoni drying induced by a temperature gradient is a safe and environmentally friendly technology. However, the regulation of thermal Marangoni-driven flow is complicated, and current understanding of the thermal Marangoni drying mechanism is inadequate. In this work, we present a coupled model of thermal Marangoni drying that combines the two-phase flow, heat transfer, and water vapor transfer in air. The evolution of entrained water film thickness, dynamics of Marangoni-driven flow, and evaporative cooling are numerically simulated. The results show that the achieved minimum residual thickness of the entrained water film is thinned more than tenfold compared with that of the wafer withdrawn without the thermal Marangoni effect. The temperature rise and Marangoni stress grow dramatically in the film and meniscus at the initial time, and then they remain as almost invariant after achieving the dynamic equilibrium between the heating and evaporative cooling. The convective water vapor transfer in air and the reduction of entrained water film thickness improve the evaporative flux, which in turn suppresses the increase in the thermal Marangoni effect until the dynamic equilibrium is attained. Furthermore, the higher heat source, lower wafer thermal conductivity and smaller wafer thickness can enhance drying performance. The investigation of drying dynamics will contribute to a comprehensive understanding of the thermal Marangoni drying process and provide guidance to its industrial applications.

With the rapid development of high-energy laser system, thick silicon mirror, as an important optical component to reflect laser, is required to have a surface with micron-level flatness, which poses significant challenges to silicon mirror manufacture process. Fine rotation grinding (FRG) is a typical efficient method for silicon mirror manufacture. A geometric model is developed in this paper to research silicon mirror surface figure control mechanism in FRG process. The model demonstrates the relationship between the grinding spindle obliquity and the mirror surface figure. From an application perspective, the relationship between the spindle obliquity and the spindle dial gauge indication is further presented. Based on this model, a MATLAB program is designed to give a series of simulation results for researching spindle adjustment regularity and getting the most ideal spindle obliquity. Besides, several grinding experiments are carried out. The simulation and experiment results are in good agreement, and a silicon mirror surface with the flatness of less than 2 μm is achieved. The proposed grinding geometric model can provide an actual guide for grinding spindle adjustment to control the surface figure of silicon mirror.

Accurate determination of a chemical mechanical planarization (CMP) process reaching the end point is an important problem in the CMP process. In present work, the variation of the motor power signal of the polishing platen in the CMP process has been investigated, and the moving average method with 121-points moving window was used to smooth the original signal curve. Experiment results showed that the processed signal could facilitate the extraction of end-point feature for the in-situ end-point detection (EPD) system and it was relatively steady before and after the layer transition stage, which made it more reliable to detect the end point in situ. Comparing with other EPD methods, the system was less complicated, and it was easier to code for algorithm development. Finally, further analysis was performed and series of experiments provided a planarized via-revealed surface with low via dishing.

The rolling force model was the core factor for the control system of the cold rolled sheet, the prediction accuracy affect the final flatness and the strip thickness directly. A novel approach for the rolling force prediction of cold rolled sheet was first proposed based on the plastic mechanics, in which the cylindrical velocity field was used to analyze the metal flow in the deformation region by the upper bound analysis in this paper. The analysis solution of rolling torque, rolling force and stress state coefficient are obtained by minimizing the total power which contain the internal plastic power, frictional power, shear power and tense power. Moreover, the effects of frictional factor, reduction ratio and the tense on the location of neutral point and stress state coefficient are discussed, respectively, and the validity of the proposed model was verified by comparing with the traditional models. The calculation process was programed and applied in the control system of one 1450 mm cold tandem mill successfully, the prediction results was in good agreement with the actual measured ones, and deviation proportion in the range of ±10.0% reached 97.3%, it can meet the requirements of the control system in cold rolling process.

In this study, a specially designed carrier with a one-zone pneumatic loading system that uses a thick copper disk as the workpiece was developed. Comparative studies of the fluid pressure and workpiece orientation between the disk and wafer carriers during chemical mechanical polishing were conducted. The results reveal that the copper disk leans down toward the leading edge and produces a negative-dominated (approximately 70%) fluid pressure, which differs from the multi-zone carrier but agrees with other studies in which the fluid pressure is measured from the disk side. Different balancing statuses and wedged gaps are formed in these two structures.

A parabolic velocity field is proposed to get the minimum required rolling force in hot rolling process, the equal area yield criterion is used to calculate the plastic deformation power, the collinear vector inner product method is used to get friction power, the analytical equation of strip rolling power functional is obtained, and the required rolling force was calculated by minimizing the power functional. Meanwhile, the location of neutral point, shape factor, and stress state coefficient are discussed. The accuracy of the proposed theoretical model is examined through comparing with the experimental measured ones and online measured ones, it shows good agreement, the relative error of rolling force is less than 9.1%, and the proposed model is considered to be effective in hot tandem rolling process.

In this paper, three-dimensional velocity field is proposed by means of stream function method with bisecting yield criterion in chamfer edge rolling of ultra-heavy plate. Parabolic dog-bone shape function is derived so as to obtain velocity field with fixed angle of chamfer edge by stream function method, dog-bone shape coefficient η can be derived from volume invariant condition, and then the plastic deformation power, shear power as well as friction power are obtained respectively with the bisecting yield criterion. Summing up the power contributions, total power functional is presented, from which minimum value can be obtained by searching method, and vertical rolling force and torque are also finally obtained. The predictions of roll force and torque are compared with different angles of chamfer edge as well as different plate thicknesses. The results are shown to be in a very good agreement with the analytical and experimental results.

There is an increasing requirement for improved accuracy of the rolling models which are widely used in rolling plant in order to produce high-quality products, because this accuracy is important for rolling schedule setup and automatic control. A three-dimensional mathematical model for cold rolling using tangential velocity field and energy method is firstly proposed to investigate the deformation of the strip at the roll gap based on elastic and plastic mechanics. The field and geometrical approximation yield criterion are used to integrate the internal plastic deformation power. The friction power is analyzed using the co-line vector inner product method. Finally, the analytical expressions of roll separating force and roll torque are obtained quickly considering the effect of roll flattening on the roll separating force. The predicted roll separating forces are consistent with other researchers’ models, especially for on-line measured roll separating forces in a tandem cold rolling plant. The accurate predicted results provide valuable guidelines for optimization of rolling process.

This work described the manufacture of hot rolled X100 pipeline steels at the laboratory based on thermomechanically controlled processing (TMCP) and high-temperature processing (HTP) concepts. Continuous cooling phase transformation was assessed by dilatometric tests for both steels. Microstructures were characterized using optical and electron microscopes to elaborate the evolution of mechanical properties with process parameters. The main microstructures for both steels were changed from granular bainite to lath bainite/martensite or acicular ferrite with increasing cooling rate. However, the TMCP steel always had lower transformation critical temperatures than the HTP steel. After hot rolling, the TMCP steel with predominantly acicular ferrite showed more excellent mechanical properties than the HTP steel with mainly granular bainite. In this sense, the combined addition of Mo and low Nb is superior to high Nb content for the alloy design of X100 pipeline steel. The optimum performance of TMCP steel can be obtained using the following process parameters: 820 °C finish rolling temperature, 460 °C final accelerated cooling temperature, and 25 °C/s cooling rate. The statistical analysis of precipitates showed that their type, morphology, and size distribution were similar for both steels, implying that the effect of high Nb content seems not to be exploited completely in as-rolled HTP steel.

The thickness of the plate in temperature gradient rolling is first divided into 2 m elements, and m is an undetermined parameter which can be limited. Based on these thickness elements with different temperatures, the rolling force of this advanced process is first analyzed with slab method. Also the predictions of thickness ratio with different temperatures and reductions of each thickness elements are proposed in this paper. The results measured after rolling experiments are used to compare with these calculated by this model in order to verify its accuracy. In the experiment, a multi-metals riveting plate in the same temperature is designed to simulate a single metal one in gradient temperatures based on the thickness elements. Since the model is based on an analytical method which is strongly supported by the rolling theories, it can be applied in real gradient temperature rolling for ultra-heavy plate.

An analytical model, in which unequal radii are replaced with an equivalent radius, is creatively proposed to predict the rolling force and roll torque in general case of snake rolling. With the model, the effects of roll radius ratio, roll speed ratio, offset distance between rolls, reduction and friction coefficient on rolling forces in hot snake rolling of aluminum alloy are obtained. Also, the thicknesses of slab are investigated in different zones, which firstly propose the changes of thickness during snake rolling. Owing to the good agreement with the results measured in experiments and calculated by finite element method and other traditional models, those calculated by the proposed model are verified. The proposed model can be used to predict more accurate theoretical results for snake rolling force and torque.

Edge rolling plays a vital role in width control of strip rolling, where plastic deformation concentrates in the edge of the slab. Then, the center of the slab remains its initial shape. The local deformation is different from overall one which obtained in horizontal rolling. In this paper, dog-bone shape is creatively described by a continuous symmetric parabola used to describe, and based on the complex mathematical function, a kinematically admissible continuous velocity field for edge rolling is established. Finally, the upper deformation power function is yielded. Based on minimum of the power, the results in edge rolling force and torque are obtained. Some vertical rolling forces for copper and aluminum experiments are calculated by the function, and then, also the results are verified by the traditional models. Anyway, the maximum error is less than 18 %. This is a crossover study on both mathematical curve and mechanical analysis which can be seen as a combination of the theory and engineering.

When the thicknesses of the outer layers are different in sandwich rolling, based on the different kinds of arrangements with the hard and soft materials the thickness ratio of two outer layers is changed differently during the rolling process. After the first analysis of the different outer thicknesses sandwich rolling, the rules for final thickness ratio of the two outer layers are proposed. In soft–hard–soft sheets (s–h–s) the thickness ratio of outer layers is remained in the final bonded sandwich sheet however in hard–soft–hard sheets (h–s–h) the thickness ratio is alleviated by sandwich rolling itself. A model based on slab method is proposed to analyze this phenomenon and 4 groups of experiments with Al and Cu as well as steel are conducted. The results calculated by the model well agree with those measured in the experiments. Then the accuracy and worthy of the model are verified.

The automatic width control of the strip that is used in vertical rolling is a key issue in the hot strip rolling process. It is the first time that the internal deformation power and the friction power are obtained by using angular bisector yield criterion and Pavlov projection principle in the vertical rolling. At the same time, the shear power is determined by use of the integral mean value theorem. Then the vertical rolling force and shape parameters are obtained by minimizing the total power functional. The relative error of rolling forces is less than 8.29 % compared with those measured on-line in a hot strip rolling plant. Moreover, the formula forms of the three powers mentioned above are greatly simplified and improved.

Multi-pass submerged arc welding was performed on the HSLA steels using multi-microalloyed electrodes in the present work, and three different heat input processes were employed to investigate the microstructure evolution and corresponding mechanical properties of weldments. The emphasis was placed on studying the influence of microstructure aspects on impact toughness of weld metal and HAZ with different heat inputs to reveal fracture micromechanism and to optimize the welding system. According to the experimental results, the acceptable welding parameters were ascertained for the studied steel to obtain a good balance of high strength and toughness welded joint. The optimal range of size distribution of non-metallic inclusion formed in the weld metal was determined and the essential causes of deteriorated HAZ toughness were revealed. Keywords: HSLA steel, Submerged arc welding, Impact toughness, Acicular ferrite

In this paper, sandwich rolling with symmetrical thickness and materials is intensively studied. The inner metal is out of touch with both upper and lower rolls in the sandwich sheets, and all the forces are delivered from upper and lower sheets. This special character makes the relative slip distance and elongation distance appear. Then, the defected length is formed during the sandwich rolling. It verifies that the point where both inner and outer metals have the same velocity is also the point where the two metals are both deformed. Slab method is first applied in predicting the defected length of the sandwich sheets. Sandwich rolling experiments with aluminum and copper are conducted. The results obtained in this paper are also compared with those measured in experiments and calculated by stream function model recorded in references. So the model can be used in the real work conditions. It is helpful to find the best shearing position in the head of the sandwich sheets. The cost of materials is reduced based on the present model. When sheets are rolled in continual rolling passes, the defected length can be more important and serious. Specifically, if the sheets are wide, expensive and multilayer, the shearing position can be more significant to the industrial application.

A new sine velocity field is proposed to analyze total power in the roll gap for rolling in hot strip finishing mill. The field and linear geometric midline yield criteria are used to calculate the plastic deformation power, and the collinear vector inner product method is used to get friction power. Then analytical equation of strip rolling power functional is obtained. Finally, the roll force and torque can be calculated by minimizing the power functional. In the model, average deformation resistance is determined by the thermo-mechanical coupled analysis. The prediction accuracy of the proposed model is examined through comparing with the on-line measured results in a hot strip finishing mill. It shows that the predicted roll forces are in good agreement with the measured ones, and the maximum error is less than 12 %. Moreover, the effects of various rolling conditions, such as thickness reduction, friction factor, and shape factor, on roll force, location of neutral angle, and stress-state coefficient are discussed systematically.

To analyze plate rolling force, a simple available velocity field is first proposed in this article. Based on the velocity field, the internal deformation energy rate and the friction energy rate are analyzed by the equal perimeter yield criterion and the method of the collinear vector inner product, respectively. Finally, the rolling force accounting for the elastic flattening of the roller and the temperature rise of the rolled piece are ultimately obtained through the minimization of the total energy rate. The theoretical rolling forces are compared with actual measured data, and a good consistency is found since the maximum error between them is less than 4.7%. In addition, the discussion of different rolling conditions, such as friction factor, thickness reduction, and shape factor, upon rolling force, location of neutral angle, and stress state coefficient is also carried out.

A novel in-situ wafer bending/orientation measurement system, cooperated with our previous developed fluid pressure mapping system, was developed for 12-inch chemical mechanical polishing (CMP) equipment. Wafer bending and wafer orientation are studied for copper wafer sliding against the IC1000 pad. The results reveal a micron level wafer bending, and a slight wafer pitch angle of 10−5 degree. Both the wafer pitch angle and interfacial fluid pressure increase with the speed till a critical speed and then decrease. The convergent-dominated wedged gap caused by the convexly bended, trailing edge pitched wafer gives a reasonable explanation to the positive-dominated fluid pressure.

The effect of reheat temperature on continuous cooling bainite transformation in a low carbon microalloyed steel was investigated using a dilatometer based on welding thermal simulation process. The variation of microstructure was analyzed in detail by means of optical microscope and transmission electron microscope (TEM). The results showed that the morphology of the main microstructure changes from polygonal ferrite to granular bainite with increasing reheat temperature at a given lower cooling rate. For the higher cooling rate, the microstructure is predominantly lath bainite irrespective of the reheat temperature. The specimens with the relatively fine austenite grain size have the lowest bainite start and finish temperatures among the simulated sub-zones of heat affected zone, which is consistent with the result of the bainite lath width size observed using the TEM. Meanwhile, although the prevailing type of impingement mode of transformation is anisotropic growth impingement for all heat treatment processes, the reheat temperature has some influence on the maximum transformation rate and effective activation energy of bainite transformation.

In this paper, the effect of slurry injection position on removal rate and nonuniformity was experimentally investigated on a 300-mm polisher developed by the authors, and the effect of slurry injection position on slurry fluid pressure distribution during polishing was also measured by a novel in situ fluid pressure measurement system integrated in the polisher. In situ pad conditioning was employed in all experiments. The results showed that removal rate, nonuniformity, and fluid pressure distribution were influenced dramatically by the slurry injection position. The slurry injection position determines the slurry distribution, and therefore, the removal rate profile and fluid pressure distribution were affected.

Microstructural variation in high strength low carbon bainitic steel weldment was investigated in detail by means of optical microscope, transmission electron microscope and scanning electron microscope equipped with electron backscattered diffraction. The results showed that the welded joint has various microstructures such as acicular ferrite, coarse granular ferrite and fine polygonal ferrite. The martensite–austenite (MA) constituent has a variable structure in each sub-zone, which includes fully martensite and fully retained austenite. Meanwhile, the fine grained heat affected zone has higher content of retained austenite than the welded metal (WM) and coarse grained heat affected zone (CGHAZ). The orientation relationship between retained austenite and product phases in the WM and CGHAZ is close to Kurdjumov–Sachs relationship. However, the polygonal ferrite in the fine grained HAZ has no specific orientation relationship with the neighboring retained austenite. The toughness of the coarse grained region is much lower than that of the WM because the coarse bainite contains many large MA constituents to assist the nucleation of microcracks and coarse cleavage facet lowers the ability to inhibit the crack propagation.

An analytical solution based on slab method is first proposed to calculate the rolling force and rolling torque in asymmetrical sheet rolling where the work rolls radii, their speeds, and the interfacial frictions may be different. In the solution, the shear stress acting along the vertical sides of each slab is taken into account. To verify the validity of the proposed analytical solution, the analytical rolling force and torque were compared with experimental and analytical results of other investigators. Very good agreements are found. By this proposed analytical solution, it is noted that the calculation time and computer expense are saved, and the characteristics of asymmetrical cold and hot sheet rolling are obtained easily and rapidly.

A two-dimensional velocity field for broadside rolling is proposed by reducing the dual-stream function velocity field. By using the field and the strain vector inner product, an analytical solution of roll torque and separating force for broadside rolling is first obtained. The theoretical predictions of roll torque and separating force are compared with actual measured data. The result reveals that the proposed solution is appropriate for solving broadside rolling, and the roll torque and separating force are in good agreement with the actual measured ones since the maximum errors are less than 15%. Moreover, the effects of various rolling conditions such as thickness reduction, friction factor and shape factor, upon separating force, location of neutral angle, and stress state coefficient are discussed systematically.

Martensite–austenite (M–A) constituent formed during welding is generally recognized as an important factor to decrease the toughness of welded joint. In this article, the morphology and chemical composition of M–A constituent in the low carbon bainitic steel welded joint was analysed in detail by means of optical microscope, transmission electron microscope and scanning electron microscope with electron probe microanalysis. The experimental results show that the M–A constituent formed in the different sub-zones presents different morphologies and different amounts. The maximum amount of M–A constituent occurs in the coarse grained heat affected zone (HAZ). It is evident that the carbon atoms segregate on the M–A constituent and carbon concentration on the slender M–A constituent is higher than that on the massive M–A constituent. Meanwhile, the distribution profile of silicon on the M–A constituent shows an obvious inhomogeneity. Most of M–A constituents have a twinned structure and/or a high dislocation density. According to impact testing results, the crack initiation energy in the HAZ specimens deteriorates significantly because the large M–A constituent can assist the formation of cleavage crack. On the other hand, the coarse prior austenite grain in the HAZ lowers the crack propagation energy.

Thermo-mechanical process followed by accelerated cooling and high temperature tempering was applied to investigate the microstructure evolution and mechanical properties of a high strength crack-free steel. Optical microscopy, transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) technique were employed to analyze the complex microstructural characteristics of the steel. The results indicated that the precipitation strengthening effect played an important role in optimizing the tempered strength. According to EBSD results, the average grain size of as-rolled specimens was about 3.2 μm, and it increased slightly with the tempering temperature. Therefore, the grain refinement wasthe major reason for the good mechanical properties of the crack-free steel.

The correlation of microstructural characteristics and toughness of the simulated coarse grained heat affected zone (CGHAZ) of low carbon bainitic steel was investigated in this study. The toughness of simulated specimens was examined by using an instrumented Charpy impact tester after the simulation welding test was conducted with different cooling times. Microstructure observation and crystallographic feature analysis were conducted by means of optical microscope and scanning electron microscope equipped with electron back scattered diffraction (EBSD) system, respectively. The main microstructure of simulated specimen changes from lath martensite to coarse bainite with the increase in cooling time. The deterioration of its toughness occurs when the cooling time ranges from 10 to 50 s compared with base metal toughness, and the toughness becomes even worse when the cooling time increases to 90 s or more. The MA (martensite–austenite) constituent is primary responsible for the low toughness of simulated CGHAZ with high values of cooling time because the large MA constituent reduces the crack initiation energy significantly. For crack propagation energy, the small effective grain size of lath martensite plays an important role in improving the crack propagation energy. By contrast, high misorientation packet boundary in coarse bainite seems to have few contributions to the improvement of the toughness because cleavage fracture micromechanism of coarse bainite is mainly controlled by crack initiation.

The effect of austenite grain size on isothermal bainite transformation in a low carbon microalloyed steel was studied by means of optical microscopy, SEM and TEM. Two widely varying austenite grain sizes, a fine average grain size (∼20 μm) and a coarse average grain size (∼260 μm), were obtained by different maximum heating temperatures. The results showed that the morphology of isothermal microstructure changes from bainite without carbide precipitation to bainitic ferrite with a decrease in holding temperature. Coarse austenite grain can retard the kinetics of bainite transformation and increase the incubation time of bainite transformation by reducing the number of nucleation site, but it does not influence the nose temperature of the C curve of bainite start transformation, which is ∼534°C.

The relationship between martensite–austenite (MA) constituent and cleavage crack initiation in the heat affected zone of a low carbon bainitic steel was investigated according to welding simulation and instrumental Charpy impact testings. The results showed that with increasing heat input, the toughness of the specimen deteriorates and the MA constituent size increases gradually. The MA constituent can assist the formation of microcrack by interface debonding mechanism. According to the classical Griffith theory, the calculation size of Griffith crack is consistent with the width size of the MA constituent under most circumstances, indicating that the decrease in the crack initiation absorbed energy is mainly attributed to coarse MA constituent.

In this study, two API X80 pipeline steels were fabricated by varying Ti additions, and their microstructures and fracture characteristics were analyzed to investigate the effects of Ti-enriched carbonitride on the tensile properties and Charpy impact properties. Lathy bainite, a mass of matensite/austenite (M/A), coarse cubic Ti-enriched inclusions, chain-typed Ti-enriched precipitations, weak toughness and high tensile strength were found as consequences of higher amount of Ti content. Those large scale and chain-typed Ti-enriched car-bonitrides are one kind of crack sources during fracture. The negative effect of higher amount of Ti on the impact properties is increased with decreased temperature.

For several decades, chemical mechanical polishing (CMP) has been the most widely used planarization method in integrated circuits manufacturing. The final polishing results are affected by many factors related to the carrier structure, the polishing pad, the slurry, and the process parameters. As both chemical and mechanical actions affect the effectiveness of CMP, and these actions are themselves affected by many factors, the CMP mechanism is complex and has been a hot research area for many years. This review provides a basic description of the development, challenges, and key technologies associated with CMP. We summarize theoretical CMP models from the perspectives of kinematics, empirical, its mechanism (from the viewpoint of the atomic scale, particle scale, and wafer scale), and its chemical-mechanical synergy. Experimental approaches to the CMP mechanism of material removal and planarization are further discussed from the viewpoint of the particle wear effect, chemical-mechanical synergy, and wafer-pad interfacial interaction.