A study on controlled cooling process for making bainitic ductile iron

In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same time. It can be concluded that the bainitic zone of TTT curve is separated from the pearlitic zone. As compared to the water-quenching condition, more even cooling rate and temperature distribution can be achieved in the controlled cooling process. The controlled cooling can keep away from pearlitic zone in the high temperature cooling stage and produce similar results to the process of traditional isothermal cooling with a low cooling rate in the low temperature cooling stage.

GRAIN REFINEMENT OF MICROALLYED STEEL THROUGH HEAVY HOT DEFORMATION AND CONTROLLED COOLING

Heavy deformation and controlled cooling is one of the most effective effective ways for grain refinement in HSIA steels. In this paper, experimental specimens are prepared with a commercial linepipe steel grade X65, and the chemical compositions are (wt% ): Fe-0.094C-1.42Mn-0. 29Si-0. 045Nb-0. 008Ti. After heavy deformation with 80% reduction in non-recrystallization range of austenite, and at controlled cooling rates from 2K/s to 64K/s, the grain sizes vary from 9.55μm to 1.06μm.It is shown by the results that a linear relationship still remains between the yield strength and reciprocal of square root of ferrite grain size as grain size is refined to 1m.The ultra-fine grains might be dynam- ically formed through the deformation-induced transformation when reduction is large enough.The grain sizes decrease when the cooling rates increase.When the cooling rates increase over 10K/s, the grain sizes are rarely changed. The particles distribute on grain boundaries, sub-grain boundaries, deformed bands and within the ferrite grains.

Mathematical model for the thermal process of controlled cooling of wires and its numerical simulation

The mathematical model for the thermal process of billets rolling has beenestablished, including transporting in air and temperature-holding cover, descaling withhigh-pressure water, and the process of rolling and cooling in water box. The calculated data by themodel have been compared with the measured data and the results show that the model is right andcreditable. Based on the model, the main thermal characters of rolling line have been simulated andthe influence of all the parameters on the temperature of rolling has been analyzed.

EFFECT OF THE CONTROLLED ROLLING CONTROLLED COOLING ON STRENGTH AND DUCTILITY OF THE BAINITE MICRO ALLOYED ENGINEERING STEEL

The continuous cooling transformation of hot deformation austenite austenite of test steel and the effect of different processing schedules of controlled rolling and controlled cooling on the strength and ductility have been studied. The theory and the experiment base are presented for controlled rolling and controlled cooling of the SBL micro alloyed engineering steel.

Computer simulation on the controlled cooling of 82B high-speed rod

A modified temperature-phase transformation field coupled nonlinear mathematical model was made and used in computer simulation on the controlled cooling of 82B high-speed rods. The surface temperature history and volume fraction of pearlite as well as the phase transformation history were simulated by using the finite element software Marc/Mentat. The simulated results were compared with the actual measurement and the agreement is good which can validate the presented computational models.

Soft-Sensing Method of Water Temperature Measurement for Controlled Cooling System

Aiming at the water temperature measuring problem for controlled cooling system of rolling plant,a new water temperature measuring method based on soft-sensing method with a water temperature model of on-line self correction parameter was built.A water temperature compensation factor model was also built to improve coiling temperature control precision.It was proved that the model meets production requirements.The soft-sensing technique has extensive applications in the field of metal forming.

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 ℃ was controlled within ±20 ℃.

Effect of Controlled Cooling on Microstructure and Mechanical Properties of H-Beam

Based on ANSYS, an analytical model was established for H beam during controlled cooling. The tempera-ture fields during controlled cooling and air cooling were analyzed and the microstructure and mechanical properties for different parts of H-beam were discussed in detail. After the H-beam was controlled cooled for 4.5 s, its mean surface temperature decreased from 850 to 460 ℃, and the lowest and the highest temperatures were measured at edge of flange and at R corner, respectively. Whereas, for the H-beam air cooled for 30 s, the mean temperature at R corner and web was 700 and 540 ℃, respectively. The microstructures for different parts of H-beam consisted of ferrite and pearlite, and the grain size at R corner was coarser than those at flange and web. The difference of yield and tensile strengths of web, flange and R corner was within 30 MPa, and the elongation was similar. The changes of microstructure were in good agreement with that of temperature field. In addition, the results show that the uni formity of microstructure and mechanical properties can be improved by increasing water flow rate at R corner.

Grain Growth of Deformation Induced Ferrite in V Microalloyed Low Carbon Steel During Controlled Cooling Process

The effect of vanadium on the DIFT (Deformation Induced Ferrite Transformation) microstructure coarsening in low carbon steel during the continuous cooling processes and isothermal processes at different temperatures were investigated using thermo-simulator.The results showed that the steel containing a small amount of vanadium had the similar velocity of grain growth with the vanadium free steel during the continuous cooling process,but a lower velocity of grain growth than that of vanadium free steel during isothermal processes at high temperatures.On the other hand,the vanadium remarkably inhibited grain growth in the steel containing a high amount of vanadium during both the continuous cooling and isothermal processes.Vanadium dissolved in matrix is indicated as an important factor on restraining grain growth through estimating the driving force of normal grain growth and the resistance of precipitation particles of vanadium on grain growth.The influencing mechanism of vanadium dissolved in matrix on the grain growth during the controlled cooling process is discussed.

Effect of controlled rolling/controlled cooling parameters on microstructure and mechanical properties of the novel pipeline steel

The study of controlled rolling/controlled cooling process parameters which affect the microstructure and mechanical properties of a novel pipeline steel has been optimized by the orthogonal experiment with four factors and three levels in this paper. However, the parameters of thermo-mechanical control process （TMCP） optimized by the Gleeble-3500 hot simulator could not satisfy performance requirements of the X100 pipeline steel. In order to improve the performance of this steel, the influence of finish cooling temperature （FCT） on the microstructure and property is studied in detail. It is found that, as this steel is thermo-mechanically treated by this set of parameters （the start heating temperature, finish rolling temperature （FRT）, FCT and cooling rate of 1,180 ℃, 810 ℃, 350 ℃ and 35 ℃/s, respectively）, the micro- structures are mainly composed of granular bainite （GB） and acicular ferrite （AF）. The effective grain sizes are below 20 μm; the steel reaches the optimal balance between the strength and the toughness; the yield strength is 695 MPa; the tensile strength is 768 MPa; the elongation is 16.6 %; the impact energy is 262 J at room temperature. All indexes could meet the requirements of X100 pipeline steel.

The Study on the Microstructure and Mechanical Properties of 400MPa Grade Bar Prepared by Controlled Cooling After Finish Rolling

The production process of bars in Baosteel Nantong Co.Ltd.was adjusted by both decreasing heating temperature and adding controlling cooling procedure after finish rolling for upgrade of bars.A set of water cooling system was also installed behind the finishing mill.On-line tests were conducted,and then the microstructure and mechanical properties of the bars with HRB335 composition and φ22mm diameter were studied.The results showed that the microstructures of the bar cooled by water were ferrite and pearlite with grain sizes of 8.5 to 12 grades,which were finer than that of the bar without water cooling.While the thin outer layer microstructures of the bar cooled by water were mainly tempered sorbite with small amount of tempered troosite.The average yield strength R eL and tensile strength R m of the bars with water cooling increased 105MPa and 73MPa respectively compared with those of the bars without water cooling.The reason of this strengthening was attributed to the synthetic role of fine grains and phase transformation and precipitation mechanism.In addition,The ration of R m /R eL could be higher than 1.25,which is the request of earthquake-proof performance for HRB400E,only when the self-tempering temperatures of the bars were higher than 640℃.

Controlled Rolling and Cooling Process for Low Carbon Cold Forging Steel

Effect of controlled rolling and cooling process on the mechanical properties of low carbon cold forging steel was investigated for different processing parameters of a laboratory hot rolling mill. The results show that the specimens with fast cooling after hot rolling exhibit very good mechanical properties, and the improvement of the mechanical properties can be attributed mainly to the ferrite-grain refinement. The mechanical properties increase with decreasing final cooling temperature within the range from 670 ℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony. The specimen with fast cooling after low temperature rolling shows the highest values of the mechanical properties. The effect of the ferrite grain size on the mechanical properties was greater than that of pearlite morphology in the present study. The mechanical properties of specimens by controlled rolling and cooling process without thermal treatment were greatly superior to that of the same specimens by the conventional rolling, and their tensile strength reached 490 MPa grade even in the case of low temperature rolling without controlled rolling. It might be expected to realize the substitution medium-carbon by low-carbon for 490 MPa grade cold forging steel with controlled rolling and cooling process.

Development of integrated reheating,rolling and cooling models for stelmor production line

Production characteristics of high speed rod are fast speed,complex section and internal microstructure evolution,which bring great problems to analyze and solve the quality disputes.Therefore,a serial process models have been developed based on the characteristics of high speed rod:due to rod stock to be square section,a two dimension model has been developed to predict the evolution of internal temperature and grain coarsening.As for the rod rolling process,an automatic section design system has been written, which can show section filling condition and process parameters such as temperature,pressure and recrystallization etc per pass.As for rod cooling stage,an integrated model which coupled phase transformation,temperature and final properties was developed and applied in real production with good results.

The development and application of ultra fast cooling in hot-rolled

Ultra fast cooling is a new technology which used to control the hot-rolling strip cooling in recent years on the international developed.If suitably cooperated with a number of other new controlled rolling technologies,can achieve fast and accurate temperature control in the hot-rolled strip production process to obtain corresponding transformation microstructure and ideal mechanical properties.This article describes the technical principle and layout of ultra fast cooling in hot-rolled as well as application profiles in the major iron and steel enterprise in China and abroad.Carried out the layout of ultra fast cooling analysis on the adaptability of steel that install between the finishing mill and laminar cooling,on this basis,proposed the use of ultra fast cooling technology proposals.

Forming condition and control strategy of ferrite decarburization in 60Si2MnA spring steel wires for automotive suspensions

The ferrite decarburization behavior of 60Si2MnA spring steel wires for automotive suspensions, including the forming condition and the influence of heating time and cooling rate after hot rolling, was investigated comprehensively. Also, a control strategy during the reheating process and cooling process after rolling was put forward to protect against ferrite decarburization. The results show that ferrite decarburization, which has the strong temperature dependence due to phase transformation, is produced between 675 and 875°C. The maximum depth is found at 750°C. Heating time and cooling rate after rolling have an important influence on decarburization. Reasonable preheating temperature in the billet reheating process and austenitizing temperature in the heat-treatment process are suggested to protect against ferrite decarburization.

Application of Feedforward and Feedback Control Strategy for Wire Rod Hot Rolling Line

The feedforward and feedback control strategy of water flowrate based on the analysis of thermal process in water cooling box was proposed, and the control strategy was applied to wire rod hot rolling at Baosteel Co. The operation has proved that the strategy can control water flowrate in the cooling water box reasonably to ensure the temperature requirement of the wire discharged from the cooling water box.

Influence of Controlled Rolling and Cooling Process on the Mechanical Properties of Low Carbon Cold Forging Steel

In the present paper,controlled rolling and cooling processing was conducted by using a laboratory hot rolling mill.The influence of different processing parameters on the mechanical properties of low carbon cold forging steel was investigated.The results show that the faster cooling after the deformation (especially in low temperature rolling conditions) leads to the refinement of the ferrite grain.The specimen exhibits very good mechanical properties owing to the finer ferrite grains.The pearlite morphologies can also affect the mechanical properties of low carbon cold forging steel.The mechanical properties increase with decreasing final cooling temperature within the range from 650℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony.The mechanical properties of the specimens with fast cooling after the conventional rolling are not only better than those of the specimens with slow cooling after low temperature rolling,but also almost similar to those of the specimens with fast cooling after low temperature rolling.It is suggested that fast cooling after high temperature rolling (the conventional rolling) process would be of important industrial value.

Preparation and nucleation of spherical metallic droplet

The preparation and solidification of metallic droplets attract more and more attention for their signiifcance in both engineering and scientiifc ifelds. In this paper, the preparation and characterization of Sn-based al oy droplets using different methods such as atomization and consumable electrode direct current arc （CDCA） technique are reviewed. The morphology and structure of these droplets were determined by optical microscopy, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The solidiifcation behavior of single droplet was systematical y studied by means of scanning calorimetry （DSC）, and the nucleation kinetics was also calculated. In particular, the development of fast scanning calorimetry （FSC） made it possible to investigate the evolution of undercooling under ultrafast but control able heating and cooling conditions. The combination of CDCA technique and FSC measurements opens up a new door for quantitative studies on droplet solidiifcation, which is accessible to demonstrate some theories by experiments.

An ANN-Based Short-Term Temperature Forecast Model for Mass Concrete Cooling Control

Concrete temperature control during dam construction(e.g.,concrete placement and curing)is important for cracking prevention.In this study,a short-term temperature forecast model for mass concrete cooling control is developed using artificial neural networks(ANN).The development workflow for the forecast model consists of data integration,data preprocessing,model construction,and model application.More than 80000 monitoring samples are collected by the developed intelligent cooling control system in the Baihetan Arch Dam,which is the largest hydropower project in the world under construction.Machine learning algorithms,including ANN,support vector machines,long short-term memory networks,and decision tree structures,are compared in temperature prediction,and the ANN is determined to be the best for the forecast model.Furthermore,an ANN framework with two hidden layers is determined to forecast concrete temperature at intervals of one day.The root mean square error of the forecast precision is 0.15∘C on average.The application on concrete blocks verifies that the developed ANN-based forecast model can be used for intelligent cooling control during mass concrete construction.