Continuous Cooling Transformation (CCT) Diagram of Aluminium Alloy Al-4.5Zn-1Mg

2006 ◽  
Vol 519-521 ◽  
pp. 1467-1472 ◽  
Author(s):  
O. Kessler ◽  
R. von Bargen ◽  
Fabian Hoffmann ◽  
H.W. Zoch
Keyword(s):  
Heat Treatment ◽  
Aluminium Alloy ◽  
Aluminium Alloys ◽  
Age Hardening ◽  
Solution Annealing ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Precipitation Behaviour ◽  
Cct Diagrams

Age hardening is one of the most important processes to strengthen aluminium alloys. It usually consists of the steps solution annealing, quenching and aging. For heat treatment simulations as well as for the appropriate choice of quenching processes in heat treatment shops, knowledge of the temperature- and time-dependent precipitation behaviour during continuous cooling is required. Quenching should happen as fast as necessary to reach high strengths, but also as slow as possible, to reduce residual stresses and distortion. This optimal quenching rate of an aluminium component depends on its chemical composition, initial microstructure and solution annealing parameters as well as on its dimensions. Unfortunately continuous cooling transformation (CCT) diagrams of aluminium alloys do almost not exist. Instead isothermal transformation (IT) diagrams or given average quenching rates are used to estimate quenching processes, but they are not satisfying neither for heat treatment simulations nor for heat treatment shops. Thermal analysis, especially Differential Scanning Calorimetry (DSC) provides an approach for CCT-diagrams of aluminium alloys, if the relevant quenching rates can be realized in the DSCequipment. The aluminium alloy Al-4.5Zn-1Mg (7020) is known for its relatively low quenching sensitivity as well as for its technical importance. The complete CCT-diagram of 7020 with cooling rates from a few K/min to some 100 K/min has been recorded. Samples have been solution annealed and quenched with different cooling rates in a high speed DSC. The resulting precipitation heat peaks during cooling have been evaluated for temperature and time of precipitation start, as well as their areas as a measure for the precipitate amount. Quenched samples have been further investigated regarding their microstructure by light and electron microscopy, hardness after aging and precipitation behaviour during re-heating in DSC. The CCT-diagram correlated very well with the microstructure, hardness and re-heating results. A critical cooling rate with no detectable precipitation during continuous cooling 155 K/min could be determined for 7020. A model to integrate the CCT-diagram in heat treatment simulation of aluminium alloys is under development.

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.

scholarly journals Correlations and Scalability of Mechanical Properties on the Micro, Meso and Macro Scale of Precipitation-Hardenable Aluminium Alloy EN AW-6082

Metals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 608
Author(s):  
Anastasiya Toenjes ◽  
Heike Sonnenberg ◽  
Axel von Hehl
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Tensile Strength ◽  
Aluminium Alloy ◽  
Aluminium Alloys ◽  
Volume Fraction ◽  
Solution Annealing ◽  
Macro Scale ◽  
Testing Cost ◽  
Physical Correlations

The mechanical properties of heat-treatable aluminium alloys are improved and adjusted by three different heat treatment steps, which include solution annealing, quenching, and aging. Due to metal-physical correlations, variations in heat treatment temperatures and times lead to different microstructural conditions with differences in the size and number of phases and their volume fraction in the microstructure. In this work, the investigations of the correlation between microhardness measurements on micro samples and the conventional mechanical properties (hardness, yield strength and tensile strength) of macro samples and the comparability of the different heat treatment states of micro and macro samples made of a hardenable aluminium alloy EN AW-6082 will be discussed. Using the correlations between the mechanical properties of micro samples and macro samples, the size of the samples and, thus, the testing cost and effort can be reduced.

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

2016 ◽  
Vol 367 ◽  
pp. 60-67 ◽  
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 %.

Aluminium Alloys Measurement in Quenching Dilatometer and Application of the Data

2015 ◽  
Vol 1127 ◽  
pp. 73-77 ◽  
Author(s):  
Michal Kövér ◽  
Peter Sláma
Keyword(s):  
Heat Treatment ◽  
Magnetic Properties ◽  
Thermal Expansion ◽  
Phase Transformations ◽  
Aluminium Alloy ◽  
Aluminium Alloys ◽  
Annealing Temperature ◽  
Material Structure ◽  
Solution Annealing ◽  
Transformation Diagrams

Thermal expansion is an important material property. From change of this quantity phase transformations can be evaluated. Therefore dilatometry is a common tool for construction of transformation diagrams in steel and prediction of material structure according to the performed heat treatment. However there are some restrictions for quenching dilatometers, such as magnetic properties of the material or weldability of the controlling and measuring thermocouple. In this article the quenching dilatometry is proposed for evaluation of precipitation during continuous cooling from solution annealing temperature. Aluminium alloy EN AW 6082 was chosen as the experimental material. Due to poor weldability of the experimental material new sample geometry was introduced.

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).

Simulation of Gas and Spray Quenching during Extrusion of Aluminium Alloys

2009 ◽  
Vol 424 ◽  
pp. 57-64 ◽  
Author(s):  
Michael Reich ◽  
S. Schöne ◽  
O. Kessler ◽  
M. Nowak ◽  
O. Grydin ◽  
...  
Keyword(s):  
Aluminium Alloy ◽  
Aluminium Alloys ◽  
Spray Cooling ◽  
Extrusion Process ◽  
Age Hardening ◽  
Solution Annealing ◽  
Transfer Coefficients ◽  
Extrusion Press ◽  
State Process ◽  
Gas Nozzle

After the extrusion process most aluminium alloy profiles don´t satisfy the necessary strength requirements. An increase of strength can be obtained by age hardening of hardenable aluminium alloys. Age hardening includes the three steps of solution annealing, quenching and aging and is usually carried out in a separate process after extrusion. The integration of the sub-steps solution annealing and quenching in the extrusion process results in a marked reduction of the complete process chain. The applicability of this integration depends primarily on the quenching power of the cooling module and on the quench sensitivity of the aluminium alloy. Using the finite element method the non-steady-state process of quenching the profiles after leaving the extrusion press has been simulated. The boundary conditions for quenching are varied for a gas nozzle field and a spray cooling using heat transfer coefficients based on experiments. The simulation results support the design of gas nozzle fields or spray cooling for the extrusion process of different aluminium alloys.

Influence on the Microstructure of Pinion Steel with Different Cooling Rates after Normalizing

2014 ◽  
Vol 513-517 ◽  
pp. 12-15
Author(s):  
Zhi Jun He ◽  
Jing Li ◽  
Jin Xin Liu
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Transformation Curve ◽  
Steel Heat ◽  
Continuous Cooling Transformation Curve

According to continuous cooling transformation curve of pinion steel, heat treatment simulation tests of 8 series were developed. The results show that the microstructure of pinion steel depends on the cooling rate after normalizing. Furnace cooling according to 30°C/h after normalizing can get the typical F+P organizations; Converter cooling after normalizing mixed with some bainite organizations; Furnace cooling with the break after normalizing can get clear stripped bainite organizations.

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.

Microstructure Characteristics in Continuous Cooling Transformation of an Nb Microalloyed Steel

2011 ◽  
Vol 228-229 ◽  
pp. 72-76
Author(s):  
J. H. Yang ◽  
Q. Y. Liu
Keyword(s):  
Microalloyed Steel ◽  
Controlled Rolling ◽  
Controlled Cooling ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Microstructure Characteristics ◽  
Continuous Cooling ◽  
Nb Content ◽  
Nb Microalloyed Steel ◽  
Two Stages

Deformation dilatometry has been used to simulate controlled hot rolling followed by controlled cooling of a Nb microalloyed pipeline steels, the microstructure and transformation characteristics in the steel and the effect of deformation on transformation are studied. According to the results of both dilatometry measurements and microstructure observations, the continuous cooling transformation curves (CCT) of the tested steels are constructed. The results show that Nb content and deformation enhance the formation of acicular ferrite; the microstructure of the steel range from PF, QF to AF with increasing of cooling rates from 0.5 to 50°C /s in a two stages controlled rolling and the microstructure revolution is sensitive to cooling rates when it is lower than 5°C /s, however, when the cooling rate increasing further, the microstructure didn’t change very much but M/A constituents in matrix is refined and dispersed.

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