scholarly journals Influence of Deformation Temperature on γ-α Phase Transformation in Nb–Ti Microalloyed Steel during Continuous Cooling

2013 ◽  
Vol 53 (6) ◽  
pp. 1070-1075 ◽  
Author(s):  
Jun Chen ◽  
Fan Li ◽  
Zhen Yu Liu ◽  
Shuai Tang ◽  
Guo Dong Wang
Keyword(s):  
Phase Transformation ◽  
Deformation Temperature ◽  
Microalloyed Steel ◽  
Continuous Cooling ◽  
Α Phase

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.

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.

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.

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