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

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).

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

MRS Proceedings ◽

10.1557/opl.2013.253 ◽

2012 ◽

Vol 1485 ◽

pp. 83-88 ◽

Cited By ~ 3

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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Continuous Cooling Transformation of Under-Cooled Austenite of SXQ500/550DZ35 Hydropower Steel

Metals ◽

10.3390/met11101562 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1562

Author(s):

Zhenglei Tang ◽

Ran Guo ◽

Yang Zhang ◽

Zhen Liu ◽

Yuezhang Lu ◽

...

Keyword(s):

Cooling Rate ◽

Hardness Measurement ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Continuous Cooling Transformation Diagrams ◽

Transformation Diagrams ◽

Hot Rolled ◽

Vickers Hardness Measurement ◽

Undercooled Austenite

The expansion curves of the continuous cooling transformation of undercooled austenite of SXQ500/550DZ35 hydropower steel at different heating temperatures and cooling rates were measured by use of a DIL805A dilatometer. Combined with metallography and Vickers hardness measurement, the continuous cooling transformation diagrams (CCT) of the studied steel under two different states were determined. The results show that in the first group of tests, after the hot-rolled specimens were austenitized at 920 °C, when the cooling rate was below 1 °C·s−1, the microstructure was composed of ferrite (F), pearlite (P) and bainite (B). With the cooling rates between 1 °C·s−1 and 5 °C·s−1, the microstructure was mainly bainite, and martensite (M) formed as the cooling rate reached 5 °C·s−1. When the cooling rate was up to 10 °C·s−1, the microstructure was completely martensite and the hardness value increased significantly. In the second group of tests, after the hot-rolled specimens were quenched at 920 °C and then heated at an intercritical temperature of 830 °C, in comparison with the first group of tests, and except for additional undissolved ferrites in each cooling rate range, the other microstructure types were basically the same. Due to the existence of undissolved ferrite, the microstructures of the specimens heated at intercritical temperatures were much finer, and the toughness values at low temperatures were better.

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Phase Transformation Behaviors of Nb-V-Ti Microalloyed Pipeline Steel X70

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.750-752.380 ◽

2013 ◽

Vol 750-752 ◽

pp. 380-384

Author(s):

Yu Hui Wang ◽

Ya Nan Zheng ◽

Tian Sheng Wang ◽

Bo Liao ◽

Li Gang Liu

Keyword(s):

Phase Transformation ◽

Pipeline Steel ◽

Polygonal Ferrite ◽

Granular Bainite ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Continuous Cooling Transformation Diagrams ◽

Transformation Diagrams

The CCT (continuous cooling transformation) diagrams of the Nb-V-Ti without Mo containing microalloyed pipeline steel X70 were investigated. The microstructures observed in continuous cooled specimens are composed of P (pearlite), PF (polygonal ferrite), QF (quasi-polygonal ferrite), and GF (granular bainite ferrite). At low cooling rates between 0.1°C/s and 1°C/s, the microstructure of the steel consisted of banded ferrite and pearlite but higher cooling rates suppressed its formation.

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

Metallurgical and Materials Transactions B ◽

10.1007/s11663-021-02130-9 ◽

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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NUMERICAL MODELING OF PHASE TRANSFORMATION DURING GRINDING PROCESS

Jurnal Teknologi ◽

10.11113/jt.v79.10573 ◽

2017 ◽

Vol 79 (5) ◽

Author(s):

Syed Mushtaq Ahmed Shah ◽

M. A. Khattak ◽

Muhammad Asad ◽

Javed Iqbal ◽

Saeed Badshah ◽

...

Keyword(s):

Phase Transformation ◽

Phase Transformations ◽

Thermal Stresses ◽

Heating Temperature ◽

Temperature History ◽

Grinding Process ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Heating And Cooling

The rapid heating and cooling in a grinding process may cause phase transformations. This will introduce thermal strains and plastic strains simultaneously in a workpiece with substantial residual stresses. The properties of the workpiece material will change when phase transformation occurs. The extent of such change depends on the temperature history experienced and the instantaneous thermal stresses developed. To carry out a reliable residual stress analysis, a comprehensive modelling technique and a sophisticated computational procedure that can accommodate the property change with the metallurgical change of material need to be developed. The objective of this work is to propose a simplified model to predict phase evolution during given temperature history for heating and cooling as encountered during grinding process. The numerical implementation of the proposed model is carried out through the developed FORTRAN subroutine called PHASE using the FEM commercial software Abaqus®/standard. Micro-structural constituents are defined as state variables. They are computed and updated inside the subroutine PHASE. The heating temperature is assumed to be uniform while the cooling characteristics in relation to phase transformations are obtained from the continuous cooling transformation (CCT) diagram of the given material (here AISI 52100 steel). Four metallurgical phases are assumed for the simulations: austenite, pearlite, bainite, and martensite. It was shown that at low cooling rates high percentage of pearlite phase is obtained when the material is heated and cooled to ambient temperature. Bainite is formed usually at medium cooling rates. Similarly at high cooling rates maximum content of martensite may be observed. It is also shown that the continuous cooling transformation kinetics may be described by plotting the transformation temperature, directly against the cooling rate as an alternative to the continuous cooling transformation diagram. The simulated results are also compared with experimental results of Wever [20] and Hunkle [21] and are found to be in a very good agreement. The model may be used for further thermo-mechanical analysis coupled with phase transformation during grinding process.

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Effects of Vanadium on the Continuous Cooling Transformation of 0.7 %C Steel for Railway Wheels

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.367.60 ◽

2016 ◽

Vol 367 ◽

pp. 60-67 ◽

Cited By ~ 4

Author(s):

Solange T. Fonseca ◽

Amilton Sinatora ◽

Antonio J. Ramirez ◽

Domingos J. Minicucci ◽

Conrado R. Afonso ◽

...

Keyword(s):

Room Temperature ◽

Initial Temperature ◽

Volume Fraction ◽

Martensite Formation ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Xrd Techniques ◽

Railway Wheels ◽

Cct Diagrams

To understand the effect of vanadium on the austenite decomposition of a 0.7 %C steel used in railway wheels the Continuous Cooling Transformation (CCT) diagrams were obtained and the microstructures analyzed with optical, SEM, TEM and XRD techniques. Vanadium refined the austenitic grain (12 and 6 μm for 7C and 7V, respectively), what can be explain by the presence of fine (10 nm in diameter) V4C3 precipitates, which restricts the austenitic grain growth. In addition, vanadium, in solid solution, reduced the pearlite interlamelar spacing (0.13 and 0.11 μm for 7C and 7V, respectively) by depressing the initial temperature pearlite formation (644 and 639 °C for 7C and 7V, respectively). He increased the ferrite volume fraction from 1 to 3 % at cooling rate of 1 oC/s, due the fact that vanadium is a ferrite stabilizer. Vanadium addition did not affect the initial temperature for martensite formation, but increased the hardenability with martensite formation at slower cooling rates (10 and 5 oC/s for 7C and 7V, respectively). For higher cooling rates (20 to 100 oC/s), the austenite transformation to martensite at room temperature was incomplete and all steels presented martensite and retained austenite, which volumetric fraction was near the same for both steels varying from 20 to 40 %.

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Phase transformations in Ti3Al and Ti3Al + Mo aluminides

Journal of Materials Research ◽

10.1557/jmr.1991.0969 ◽

1991 ◽

Vol 6 (5) ◽

pp. 969-986 ◽

Cited By ~ 29

Author(s):

S. Djanarthany ◽

C. Servant ◽

R. Penelle

Keyword(s):

Phase Transformations ◽

Cooling Rate ◽

Titanium Aluminides ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Continuous Cooling Transformation Diagrams ◽

Transformation Diagrams ◽

Phase Relationships

We have analyzed the phase relationships in two titanium aluminides containing 3.4 at. % Mo with different aluminum compositions. The alloys were first homogenized in the β field, then cooled continuously at different cooling rates from 80 °C/s to 0.1 °C/s. The continuous cooling transformation diagrams (CCT) show that phase transformations and resulting microstructures are highly dependent on cooling rate. The microstructure consists of ordered α2 (DO19), ordered β0 (B2), and athermal ω (hexagonal) phases. The “tweed microstructure” is observed. The evolution of microhardness was determined as well as the relative partitioning of Al and Mo in (α2', α2) and β0 phases as a function of cooling rate.

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Comparison of Measured Phase Volumes with Calculated ones Created by TTT-CCT Diagram Transformation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.537-538.497 ◽

2007 ◽

Vol 537-538 ◽

pp. 497-504

Author(s):

Zoltán Dudás

Keyword(s):

Phase Transformation ◽

Experimental Work ◽

Experimental Results ◽

Mechanical Processing ◽

Continuous Cooling Transformation ◽

Temperature Transformation ◽

Continuous Cooling Transformation Diagrams ◽

Transformation Diagrams ◽

Cct Diagrams ◽

Measured Phase

Knowledge of the TTT (Time-Temperature-Transformation) or CCT (Continuous- Cooling-Transformation) diagrams of steels is an important factor in the thermo-mechanical processing of steels. Much experimental work has been undertaken to determine such diagrams. Significant works have been written which can calculate TTT and CCT diagrams for steels. The aim of the present work is to show the developed model that can provide accurate enough TTT and CCT diagrams for steel 42 CrMo4 (where the austenitisation temperature was 1050°C). The calculated results are compared by the experimental results. The developed TTT phase transformation diagrams based on FEM-based phase elements and the star-like cooling simulation make it possible to create virtual CCT diagram data.

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

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4051004 ◽

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.

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Continuous Cooling Transformation Behavior of a Ti Addition Steel

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.556-562.480 ◽

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.

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