Influence of Strain History and Cooling Rate on the Austenite Decomposition Behavior and Phase Transformation Products in a Microalloyed Steel

2014 ◽  
Vol 45 (8) ◽  
pp. 3619-3630 ◽  
Author(s):  
L. Sun ◽  
K. Muszka ◽  
B. P. Wynne ◽  
E. J. Palmiere
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Microalloyed Steel ◽  
Transformation Products ◽  
Strain History ◽  
Austenite Decomposition ◽  
Decomposition Behavior

The Effect of Strain Path Reversal during Austenite Deformation on Phase Transformation in a Microalloyed Steel Subjected to Accelerated Cooling

2012 ◽  
Vol 715-716 ◽  
pp. 667-672 ◽  
Author(s):  
Lin Sun ◽  
K. Muszka ◽  
Bradley P. Wynne ◽  
Eric J. Palmiere
Keyword(s):  
Phase Transformation ◽  
Strain Path ◽  
Microalloyed Steel ◽  
Transformation Products ◽  
Electron Back Scatter Diffraction ◽  
Accelerated Cooling ◽  
Reversal Effect ◽  
Cumulative Strain ◽  
Temperature Transformation ◽  
Lower Temperature

In the present study, monotonic and cyclical torsional deformations of an X-70 microalloyed steel were conducted at austenite temperatures below the recrystallisation-stop temperature (T5%). The austenite deformation is followed by accelerated continuous cooling to allow the investigation of the strain reversal effect on the subsequent phase transformation mechanisms. The transformation behaviours were studied by a dilatometry method, and the microstructures of the transformed products have been analysed using electron back scatter diffraction (EBSD). The results of this study shows that although subjected to the same total cumulative strain and the same cooling rate, strain path reversal by cyclical torsion produces lower temperature transformation products involving mainly a displacive mechanism, comparing to simple strain path deformation which leads to higher temperature transformation by a reconstructive mechanism.

Phase Transformation Law of Nb Microalloyed Steel at Different Cooling Rates

2021 ◽  
Vol 1035 ◽  
pp. 396-403
Author(s):  
Ping Yu ◽  
Ren Bo Song ◽  
Wen Ming Xiong ◽  
Wei Feng Huo ◽  
Chen Wei ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transformation ◽  
Cooling Rate ◽  
Microalloyed Steel ◽  
Transition Diagram ◽  
Diffusion Type ◽  
Continuous Cooling ◽  
Type Phase ◽  
Test Steel ◽  
Nb Microalloyed Steel

Through the Gleeble3500 thermal simulation test machine, the phase transformation law of Nb microalloyed steel was studied and tested. After the compression deformation, it was cooled to room temperature at different speeds. Obtain the dynamic continuous cooling transformation diagram and the scanning structure diagram of the test steel, and then analyze the phase composition under different cooling speeds through JMatPro material performance simulation. The results show that: at a lower cooling speed (0.1°C/s), austenite decomposition is a diffusion-type phase change that takes place in a high-temperature region, and carbon atoms can diffuse sufficiently. At a moderate cooling rate (1°C/s), the bainite phase transition is a semi-diffusion phase transition in which carbon atoms are displaced in a non-cooperative thermally activated transition mode. When the cooling rate is high (15°C/s), the martensitic transformation is a non-diffusion-type transformation carried out in the low temperature region, and the atoms are directly transferred from the austenite lattice to the martensite lattice. With the increase of the cooling rate and the decrease of the transition temperature, from low-speed cooling→medium-speed cooling→high-speed cooling, respectively, the diffusion type phase transition→semi-diffusion type phase transition→the non-diffusion type phase transition. At different cooling rates, the continuous cooling transition diagram simulated by JMatPro is basically the same as the phase transition in the dynamic continuous cooling transition diagram of the test steel, which proves that the simulation prediction of the dynamic continuous cooling transition of the test steel by the JMatPro software has high accuracy and applicability.

Phase Transformation Behavior of Niobium Containing Microalloyed Steel with Predeformation and Continuous Cooling

2014 ◽  
Vol 804 ◽  
pp. 281-284
Author(s):  
Yuan She ◽  
Zhao Hui Zhang ◽  
Jian Tao Ju ◽  
Bo Jin
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Microalloyed Steel ◽  
Stored Energy ◽  
Transformation Behavior ◽  
Phase Transformation Behavior ◽  
Continuous Cooling ◽  
Cooling Phase ◽  
Niobium Microalloyed Steel ◽  
Change Of Microstructure

The continuous cooling phase transformation behavior of niobium microalloyed steel was studied by Thermecmastor-Z thermomechanical simulator; the continuous cooling transformation curves (CCT) were established. The change of microstructure under different cooling rates was observed, and the influence of deformation in austenite non-recrystallization region on transformation was discussed. Based on these work, it was possible to know that the phase transformation is retarded and the ferritic grain is refined dramatically as the cooling rate increasing. The deformation in austenite non-recrystallization region caused deformation stored-energy, which improved the grain refinement of transformation to some extent, but not significant.

Influence of Cooling Rate and Chemical Composition on Phase Transformation and Hardness of C70S6 Steel

2017 ◽  
Vol 898 ◽  
pp. 1202-1207 ◽  
Author(s):  
Yan Ji ◽  
Ning Bo Zhou ◽  
Xiao Hang Sun ◽  
Bo Jiang ◽  
Lei Lei Xiao ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Chemical Composition ◽  
Cooling Rate ◽  
Transformation Temperature ◽  
Testing Machine ◽  
Transformation Products ◽  
Carbon Equivalent ◽  
Phase Transformation Temperature ◽  
Pearlite Content ◽  
Simulation Testing

The influence of cooling rate and chemical composition on phase transformation and hardness of C70S6 steel were studied by Gleeble-3800 thermal simulation testing machine and box type electric furnace. The results showed that when the cooling rate was between 0.3 and 5 °C/s, the transformation products of two experimental steels were mainly composed of ferrites, pearlite and sorbite. The pearlite content gradually decreased with the cooling rate increasing, while the sorbite content increased and the ferrite content changed little. Both the ferrite and pearlite transformation starting temperature and ending temperature decreased with the cooling rate increasing. Besides, the hardness increased with the cooling rate. At the same cooling rate, the phase transformation temperature increased slightly with the carbon equivalent decreasing, and the pearlite content increased, while the hardness decreased. The hardness of C70S6 steel was reduced by cooling rate decreasing. However, it was difficult to realize the method of decreasing the hardness by adjusting the cooling rate in the case of higher carbon equivalent. Therefore, in order to obtain an appropriate hardness, the Ceq must be controlled. And a Ceq=0.83% was recommended.

Transformation Behavior During Continuous Cooling of Mn-Mo-Nb-B Microalloyed Steel

2010 ◽  
Vol 139-141 ◽  
pp. 260-263
Author(s):  
Shao Qiang Yuan ◽  
Guo Li Liang
Keyword(s):  
Cooling Rate ◽  
Microalloyed Steel ◽  
Transformation Products ◽  
Hardness Measurement ◽  
Granular Bainite ◽  
Transformation Behavior ◽  
Simulation Test ◽  
Tem Analysis ◽  
Cooling Rates ◽  
Component Design

The microstructure of Mn-Mo-Nb-B microalloyed steel was investigated under different cooling rates after austenitic deformation by using thermo-simulation test, hardness measurement, metallographic and TEM analysis. The experimental results show that most constituents are mixed bainite ferrite and granular bainite at the cooling rate of 10 oC-50 oC /s. From the CCT curves, only polygonal ferrite and martensite could be obtained through the very slow and rapid cooling, respectively. The hardness of specimens keeps almost unchanged when cooling rate reaches above 10 oC /s (the utmost cooling rate is 50 oC /s in this simulation). Hence, the microstructure uniformity is attained, that is to say, the transformation products are insensitive to the cooling rates, which attributes to the appropriate component design and optimized hot simulation. Another experimental phenomenon is that the fine scale (<5 nm) carbonitride precipitates were observed in the relatively lower cooling specimens.

scholarly journals Effect of Cooling Rate on Phase Transformation and Microstructure of Nb–Ti Microalloyed Steel

2014 ◽  
Vol 55 (8) ◽  
pp. 1274-1279 ◽  
Author(s):  
Su Zhao ◽  
Donglai Wei ◽  
Rongbin Li ◽  
Li Zhang
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Microalloyed Steel

Microstructure Transformation of Nb-V Microalloyed Steel during Continuous Cooling Process

2012 ◽  
Vol 590 ◽  
pp. 23-27
Author(s):  
Xin Li ◽  
Jie Zhao ◽  
Jun Cheng Bao ◽  
Bao Qun Ning ◽  
Jian Ping Li
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Microalloyed Steel ◽  
Lower Bainite ◽  
Optical Microscope ◽  
Transformation Process ◽  
The Novel ◽  
Cooling Rates ◽  
Continuous Cooling ◽  
Thermal Simulation Experiment

To achieve reasonable rolling technology of the novel Nb-V composite microalloyed steel, the continuous cooling transformation (CCT) curve was established by thermal simulation experiment. Microstructure and microhardness at different cooling rates were characterized using an optical microscope (OM) and microhardness tester. The results indicate that the critical quenching speed of Nb-V microalloyed steel is about 23 °C/s. The start and finishing temperatures of phase transformation decreased with the rise of cooling rate. Widmannstatten (W) structure appears at lower cooling rate interval. Microstructure transfers into martensite (M) and bainite (B) with obviously refined grains in higher cooling rate interval. Microhardness improves with the increase of cooling rates. Microhardness value is greatly improved to 298.6 HV at the cooling rate of 11 °C/s, which could be related to the formation of lower bainite during phase transformation process. When the cooling rate is above 29 °C/s, microhardness values remain unchanged basically. This illustrates that the microstructure of Nb-V microalloyed steel consists of martensite and lower bainite.

Phase Transformation of ER70-Ti for Gas Shielded Wire

2021 ◽  
Vol 1035 ◽  
pp. 388-395
Author(s):  
Xing Han Chen ◽  
Ren Bo Song ◽  
Zhong Zheng Pei ◽  
Kun Peng Che
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
High Strength ◽  
Transformation Products ◽  
Added Value ◽  
Granular Bainite ◽  
High Tech ◽  
Welding Wire ◽  
Transformation Curve ◽  
Wire Steel

ER70-Ti is a high strength gas shielded welding wire steel, which is suitable for ships, bridges and other structures, and can be used for thick plate welding with high current. In the welding wire industry, ER70-Ti is a high-tech deep-processing product with high added value. In this study, the thermal expansion experiment of ER70-Ti wire rod was carried out. The critical temperature of ER70-Ti phase transformation was measured and the continuous cooling transformation curve (CCT curve) of undercooled austenite was drawn. The microstructure and hardness of the samples under different cooling rates were observed. The results show that Ac1 temperature of ER70-Ti sample was 690 °C, Ac3 temperature was 877°C, and Bs temperature was 575°C. When the cooling rate was low (0.1°C/s~2.5°C/s), the phase transformation products of ER70-Ti were equiaxed polygonal ferrite and granular bainite. With the increase of cooling rate, the grain size of ER70-Ti sample was refined and the bainite content increased from 53% to 85%. When the cooling rate was higher than 5°C/s, all the phase transformation products were bainite. The Vickers microhardness also increased with the increase of cooling rate, from 185HV to 325HV.

scholarly journals Optimization of the CCT Curves for Steels Containing Al, Cu and B

2021 ◽  
Author(s):  
Jyrki Miettinen ◽  
Sami Koskenniska ◽  
Mahesh Somani ◽  
Seppo Louhenkilpi ◽  
Aarne Pohjonen ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Austenite Decomposition ◽  
Final Phase ◽  
Cast Irons ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Final Optimization ◽  
Cct Diagrams

AbstractNew continuous cooling transformation (CCT) equations have been optimized to calculate the start temperatures and critical cooling rates of phase formations during austenite decomposition in low-alloyed steels. Experimental CCT data from the literature were used for applying the recently developed method of calculating the grain boundary soluble compositions of the steels for optimization. These compositions, which are influenced by solute microsegregation and precipitation depending on the heating/cooling/holding process, are expected to control the start of the austenite decomposition, if initiated at the grain boundaries. The current optimization was carried out rigorously for an extended set of steels than used previously, besides including three new solute elements, Al, Cu and B, in the CCT-equations. The validity of the equations was, therefore, boosted not only due to the inclusion of new elements, but also due to the addition of more low-alloyed steels in the optimization. The final optimization was made with a mini-tab tool, which discarded statistically insignificant parameters from the equations and made them prudently safer to use. Using a thermodynamic-kinetic software, IDS, the new equations were further validated using new experimental CCT data measured in this study. The agreement is good both for the phase transformation start temperatures as well as the final phase fractions. In addition, IDS simulations were carried out to construct the CCT diagrams and the final phase fraction diagrams for 17 steels and two cast irons, in order to outline the influence of solute elements on the calculations and their relationship with literature recommendations.

Continuous Cooling Transformation of Overcooling Austenite and Structure Evolution of Si Steel

2013 ◽  
Vol 652-654 ◽  
pp. 947-951
Author(s):  
Hui Li ◽  
Yun Li Feng ◽  
Da Qiang Cang ◽  
Meng Song
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Optical Microscope ◽  
Structure Evolution ◽  
Upward Trend ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Hardness Tester ◽  
Gleeble 3500 ◽  
Evolution Of Microstructure

The static continuous cooling transformation (CCT)curves of 3.15 Si-0.036 C-0.21 Mn-0.008 S-0.008 N-0.022 Al are measured on Gleeble-3500 thermal mechanical simulator, the evolution of microstructure and the tendency of hardness are investigated by optical microscope (OM) and hardness tester. The results show that there is no evident change in microstructure which mainly are ferrite and little pearlite under different cooling rates, but the transition temperature of ferrite is gradually reduced with the increase of cooling rate. When the cooling rate is increased from 0.5°C/s to 20°C/s, the ending temperatures of phase transformation are decreased by 118°C, when cooling rate reaches to 10, Widmanstatten ferrite appears. The hardness of the steel turns out gradual upward trend with the increase of cooling rate.

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