A new general methodology to create continuous cooling transformation diagrams for materials fabricated by additive manufacturing

2021 ◽  
pp. 1-27
Author(s):  
Chun-Yu Ou ◽  
C. Richard Liu
Keyword(s):  
Phase Transformation ◽  
Additive Manufacturing ◽  
Critical Temperature ◽  
Cooling Rate ◽  
Thermal Model ◽  
Continuous Cooling Transformation ◽  
Temperature Range ◽  
Continuous Cooling ◽  
General Methodology ◽  
Cct Diagrams

Abstract Additive manufacturing (AM) is a manufacturing method that can build high-strength materials layer-by-layer to form complex geometries. Previous studies have reported large variations in the mechanical properties of materials made by this process. One of the key factors that may contribute to variations within and among parts made by this process is a difference in the material's microstructural phase and composition. A continuous cooling transformation (CCT) diagram is a useful tool that can be used with a thermal model for microstructure design and manufacturing process control. However, traditional CCT diagrams are developed based on slow and monotonic cooling processes such as furnace cooling and air cooling, which are greatly different from the repetitive heating and cooling processes in AM. In this study, a new general methodology is presented to create CCT diagrams for materials fabricated by AM. We showed that the effect of the segmented duration within the critical temperature range, which induced precipitate formation, could be cumulative. As multiple cooling processes occurred in a short time, and the temperature drops at a high cooling rate, a constant average cooling rate was assumed when constructing the CCT diagram. Inconel 718 parts fabricated by selective laser melting were analyzed. The key factor contributing to phase transformation was identified as the accumulated duration within the critical temperature range. The presented methodology demonstrated the capability of combining a thermal model and experimental observation to quantitatively predict phase transformation and could be used to design microstructures and control AM processes.

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.

Continuous Cooling Transformation Behavior and the Phase Transformation Model in Low Carbon High Strength Sheet Steel

2014 ◽  
Vol 1035 ◽  
pp. 27-35
Author(s):  
Yu Pei ◽  
Zhe Gao ◽  
Yi Liu ◽  
Shi Qian Zhao ◽  
Chang Yu Xu ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Sheet Steel ◽  
High Strength ◽  
Transformation Model ◽  
Phase Variable ◽  
Low Carbon ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Mathematical Equations

Phase transformation of austenite continuous cooling process in low carbon high strength sheet steel has been researched by DIL805 thermal mechanical simulate. The Austenite continuous cooling transformation (CCT) diagram of steel has been determined by dilatometry and metallography. With the increase of cooling rate, ferritic transformation, perlitic transformation, bainite transformation and martensitic transformation have produced in the organization. Mathematical equations of phase transformation point-cooling rate and phase variable-cooling rate have been established and phase transformation model of high fit degree has been gained by regression calculation. The results show that calculated value and experimental value are nearly similar, so the phase transformation model is feasible.

Continuous Cooling Transformation Behavior of a Ti Addition Steel

2014 ◽  
Vol 556-562 ◽  
pp. 480-483
Author(s):  
Chen Zhang ◽  
Guang Xu ◽  
Zhang Wei Hu ◽  
Hai Lin Yang
Keyword(s):  
Phase Transformation ◽  
Solid State ◽  
Cooling Rate ◽  
Transformation Behavior ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Cct Curve ◽  
Solid State Phase Transformation ◽  
Ti Addition

The continuous cooling transformation (CCT) behavior of a Ti attached steel was studied through thermal simulation tests, and the influences of different cooling rates on the microstructure and transformation were investigated. The results show that the microstructure changes with the cooling rate, and the CCT curve of studied steel is plotted, which indicates that the solid-state phase transformation mainly consists of four regions. The CCT diagram made it possible to predict the microstructures of studied steel with different cooling rates.

Experimental Determination of Continuous Cooling Transformation Diagrams of Hot-Rolled Heat Treatable Steel Plates Using Quenching Dilatometry

2016 ◽  
Vol 1812 ◽  
pp. 129-134 ◽  
Author(s):  
Gerardo Altamirano-Guerrero ◽  
Emmanuel J. Gutiérrez-Castañeda ◽  
Omar García-Rincón ◽  
Armando Salinas-Rodríguez
Keyword(s):  
Phase Transformation ◽  
Solid Phase ◽  
Microstructural Characterization ◽  
Steel Plates ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Transformation Diagrams ◽  
Hot Rolled ◽  
Cct Diagrams

ABSTRACTThis article outlines the use of quenching dilatometry in phase transformation kinetics research in steels under continuous cooling conditions. For this purpose, the phase transformation behavior of a hot-rolled heat treatable steel was investigated over the cooling rate range of 0.1 to 200 °C/s. The start and finish points of the austenite transformation were identified from the dilatometric curves and then the continuous cooling transformation (CCT) diagrams were constructed. The experimental CCT diagrams were verified by microstructural characterization using scanning electron microscopy (SEM) and Vickers micro-hardness. In general, results revealed that the quenching dilatometry technique is a powerful tool for the characterization and study of solid-solid phase transformations in steels. For cooling rates between 200 and 25 °C/s the final microstructure consists on plate-like martensite with the highest hardness values. By contrast, a mixture of phases of ferrite, bainite and pearlite predominated for slower cooling rates (10-0.1 °C/s).

Hardenability of Medium Carbon Cr-Mn-Mo Alloyed Steels

2019 ◽  
Vol 946 ◽  
pp. 341-345
Author(s):  
Mikhail V. Maisuradze ◽  
Maksim A. Ryzhkov
Keyword(s):  
Cooling Rate ◽  
Structural Steels ◽  
Alloying Elements ◽  
Metallographic Analysis ◽  
Medium Carbon ◽  
Austenite Transformation ◽  
Continuous Cooling ◽  
Different Content ◽  
Cct Diagrams

Three medium carbon Cr-Mn-Mo structural steels with different content of alloying elements were studied. The austenite transformation during continuous cooling was investigated using dilatometer and metallographic analysis. The CCT diagrams were plotted showing the effect of the increased alloying elements content and B and Nb micro-alloying on the hardenability of the studied steels. The hardness dependences on the cooling rate were obtained.

Continuous Cooling Transformation Behavior of High Carbon Pearlitic Steel

2022 ◽  
Vol 905 ◽  
pp. 83-87
Author(s):  
Lu Lu Feng ◽  
Wei Wen Qiao ◽  
Jian Sun ◽  
De Fa Li ◽  
Ping Ping Li ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Vickers Hardness ◽  
Hardness Test ◽  
Pearlitic Steel ◽  
Transformation Behavior ◽  
High Carbon ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Test Steel ◽  
Lamellar Pearlite

The continuous cooling transformation behavior of high-carbon pearlitic steel was studied by employing optical microscopy, scanning electron microscopy, and the Vickers hardness test. The results show that the microstructure of the test steel is composed of proeutectoid cementite and lamellar pearlite in the cooling rate range of 0.05–2 °C/s and lamellar pearlite in the range of 2–5 °C/s. Further, martensite appears at 10 °C/s. With the increase in the cooling rate, the Vickers hardness of the test steel first decreases and then increases. In the industrial production of high-carbon pearlite steel, the formation of proeutectoid cementite at a low cooling rate needs to be avoided, and at the same time, the formation of martensite and other brittle-phase at a high cooling rate needs to be avoided.

Effect of boron on the continuous cooling transformation kinetics in a low carbon advanced ultra-high strength steel (A-UHSS)

2012 ◽  
Vol 1485 ◽  
pp. 83-88 ◽  
Author(s):  
G. Altamirano ◽  
I. Mejía ◽  
A. Hernández-Expósito ◽  
J. M. Cabrera
Keyword(s):  
Research Work ◽  
High Strength Steels ◽  
High Strength ◽  
Microstructural Characterization ◽  
Low Carbon ◽  
Transformation Kinetics ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Cct Diagrams

ABSTRACTThe aim of the present research work is to investigate the influence of B addition on the phase transformation kinetics under continuous cooling conditions. In order to perform this study, the behavior of two low carbon advanced ultra-high strength steels (A-UHSS) is analyzed during dilatometry tests over the cooling rate range of 0.1-200°C/s. The start and finish points of the austenite transformation are identified from the dilatation curves and then the continuous cooling transformation (CCT) diagrams are constructed. These diagrams are verified by microstructural characterization and Vickers micro-hardness. In general, results revealed that for slower cooling rates (0.1-0.5 °C/s) the present phases are mainly ferritic-pearlitic (F+P) structures. By contrast, a mixture of bainitic-martensitic structures predominates at higher cooling rates (50-200°C/s). On the other hand, CCT diagrams show that B addition delays the decomposition kinetics of austenite to ferrite, thereby promoting the formation of bainitic-martensitic structures. In the case of B microalloyed steel, the CCT curve is displaced to the right, increasing the hardenability. These results are associated with the ability of B atoms to segregate towards austenitic grain boundaries, which reduce the preferential sites for nucleation and development of F+P structures.

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