Quantitative analysis of Ni effect on CCT diagrams of novel air-cooled bainite steels using artificial neural network models

The quantitative effect of Ni content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels was analyzed using artificial neural network models. The results showed that Ni may retard the high- and medium-temperature transformation and martensite transformation. The results conform to the materials science theories.

Effect of Chromium on CCT Diagrams of Novel Air-Cooled Bainite Steels Analyzed by Neural Network

The quantitative effects of chromium content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.

Establishment of continuous cooling transformation diagrams of aluminum alloys using in situ voltage measurement

An effective method was proposed to establish the continuous cooling transformation（CCT） diagrams of aluminum alloys using in situ voltage measurement.The voltage change of samples with predefined dimension was recorded under the constant current state during continuous cooling.Solutionizing time,together with starting and finishing temperatures of phase transformation of the alloy can be obtained from relationships of voltage vs time and temperature.A critical cooling rate without detectable phase transition during continuous cooling can be determined.Continuous cooling transformation diagrams of tested samples can be established conveniently based on these results.Microstructure observation and differential scanning calorimetry（DSC） testing were applied to verify the reliability of continuous cooling transformation diagram.

Effect of Si,C and Mn on the formation of bainite in ferrite-bainite steel

High-strength steels have been widely applied to automotive chassis parts.In order to form complex shapes,high hole expansion rates and high formability are required.Dual phase (DP) steel has a good formability,but a poor hole expansion rate.In this circumstance,another kind of steel which has a microstructure of ferrite-bainite,rather than ferrite-martensite,has been found to be an alternative solution.It is called FB steel.This steel with Si,C and Mn additions are applied in this study.A two-step cooling process is used to get the desired F+ B microstructures.Continuous cooling transformation (CCT) diagrams are made with deformation and without deformation,and starting times and temperatures of the phase transformations of interest are obtained.It is shown that Si,C and Mn contents in the steel strongly affect the shapes and positions of the CCT diagrams,as well as the final microstructures of FB steel.An increase of the Si content can promote the formation of ferrite and move the CCT diagram toward the left.However,when Si content is too high,when comparing to carbon and manganese contents,the formation of bainite will be retarded because of the formation of more ferrite.It increases the amount of C in a solid solution in the untransformed austenite and promotes the formation of pearlite.C and Mn can inhibit the formation of ferrite and retard the accumulation of C in austenite.Therefore,the appropriate balance of C,Si and Mn contents in steels will be able to help in obtaining the desired microstructure.

C-Curves of Tool Steels for Annealing and Their Application

TTT diagrams,CCT diagrams and critical points of steels H13,S7,S5 for annealing were measured and investigated by means of Formastor-Digital full-automatic phase transformation dilatometer in order to make their annealing technology reasonable and scientific.The basis is provided for making a new annealing technology scientifically.The new technology improves the quality of annealed materials,saves energy and increases productivity.

ALLOYING BEHAVIOUR OF Ca IN STEEL 58CrV

Effect of Ca on hardenability and CCT diagram of steel 58CrV has been investigated by means of end-quenching and thermal expansion.An addition of 0.006 wt-%Ca to the steel may improve the hardenability,reduce the critical cooling rate of transformation of pearlite or bainite under continuous cooling and increase the M_s.AES analysis showed that Ca segre- gates markedly along austenitie grain boundaries,and accelecrates the segregation of C,Cr and Si.It is believed that besides towards deoxidizing and desulphurizing as well as improving sulphide morphology,a trace of Ca in steel 58CrV behaves towards microalloying.

Effect of Hot Deformation on Pearlite Transformation of 86CrMoV7 Steel

The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The results showed that hot deformation accelerated pearlite transformation and fine pearlite microstructure. Moreover, the undissolved carbides became the nucleating sites of pearlite, accelerated pearlite formation and fine pearlite if the steel had been deformed at high temperature. In contrast, undissolved carbides did not make any influence on pearlite transformation if the steel had not been deformed at high temperature.

Continuous Cooling Transformation Behavior and Microstructure Control of Nb Microalloyed Reinforcing Bars

In this paper,CCT(continuous cooling transformation)diagrams are determined for Nb-containing reinforcing bars with different Nb,Mn additions,and initial austenite grain sizes by simulating industrial conditions via dilatometry tests.It was found that coarse austenite grain size,high Mn content and Nb remaining in solution all increase hardenability of Nb-containing rebars,namely lower Ar3 for acicular phase transformation products,which leads to continuous yielding during tensile deformation when the volume fraction of acicular ferrite or bainite microstructure reaches a certain volume fraction.By coupling with actual cooling rates for different size rebars,it can be explained why bainitic structure is prone to form in the center of rebars,especially for small size rebars.In order to achieve required ferrite-pearlite microstructure,cooling strategy is optimized for industrial production.

Effect of Cooling Rate and Deformation on Microstructures and Critical Phase-Transformation Temperature of Boron-Nickel Added HSLA H-Beams

Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy （HSLA） H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation （CCT） diagram of this new type of steel was obtained by using Gleeble 1500 ther- momechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were in- vestigated by optical microscopy （OM）, scanning electron microscope （SEM）, Rockwell and Vickers hardness tests. Phase analysis was also studied by X^ray diffraction （XRD）. The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cool- ing was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46℃, due to deformation induced ferrite transfor- mation during continuous cooling, but Rockwell hardness has little change.