An Atlas of Continuous Cooling Transformation (CCT) Diagrams Applicable to Low Carbon Low Alloy Weld Metals

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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Experimental Determination of Continuous Cooling Transformation (CCT) Diagrams for Dual-Phase Steels from the Intercritical Temperature Range

Metals ◽

10.3390/met8090674 ◽

2018 ◽

Vol 8 (9) ◽

pp. 674 ◽

Cited By ~ 5

Author(s):

Krishna Bräutigam–Matus ◽

Gerardo Altamirano ◽

Armando Salinas ◽

Alfredo Flores ◽

Frank Goodwin

Keyword(s):

Low Carbon Steel ◽

Dual Phase ◽

Low Carbon ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Hardness Tests ◽

Wide Range ◽

Two Phases ◽

C Partitioning ◽

Cct Diagrams

The phase transformation kinetics under continuous cooling conditions for intercritical austenite in a cold rolled low carbon steel were investigated over a wide range of cooling rates (0.1–200 ∘ C/s). The start and finish temperatures of the intercritical austenite transformation were determined by quenching dilatometry and a continuous cooling transformation (CCT) diagram was constructed. The resulting experimental CCT diagram was compared with that calculated via JMatPro software, and verified using electron microscopy and hardness tests. In general, the results reveal that the experimental CCT diagram can be helpful in the design of thermal cycles for the production of different grades of dual-phase–advanced high-strengh steels (DP-AHSS) in continuous processing lines. The results suggest that C enrichment of intercritical austenite as a result of heating in the two phases (ferrite–austenite) region and C partitioning during the formation of pro-eutectoid ferrite on cooling significantly alters the character of subsequent austenite phase transformations.

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The Continuous Cooling Transformation Diagrams of Synthetic Weld Metals (SW-CCT Diagrams)

JOURNAL OF THE JAPAN WELDING SOCIETY ◽

10.2207/qjjws1943.33.101 ◽

1964 ◽

Vol 33 (2) ◽

pp. 101-110

Author(s):

Hiroshi Kihara ◽

Haruyoshi Suzuki ◽

Michio Inagaki ◽

Otomaro Takaki ◽

Shigeru Nishi ◽

...

Keyword(s):

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Weld Metals ◽

Continuous Cooling Transformation Diagrams ◽

Transformation Diagrams ◽

Cct Diagrams

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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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Continuous Cooling Transformation Diagrams of 2.25Cr-1Mo-0.25V Submerged-Arc Weld Metal and Base Metal

Metals ◽

10.3390/met10081055 ◽

2020 ◽

Vol 10 (8) ◽

pp. 1055

Author(s):

Hannah Schönmaier ◽

Bernd Loder ◽

Thomas Fischer ◽

Fred Grimm ◽

Ronny Krein ◽

...

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Weld Metal ◽

Base Metal ◽

Lower Bainite ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Upper Bainite ◽

Cct Diagrams ◽

Scanning Electron

The transformation behavior and microstructural evolution during continuous cooling within the heat affected zone between the weld beads of a 2.25Cr-1Mo-0.25V all-weld metal and the corresponding 2.25Cr-1Mo-0.25V base metal were investigated by means of dilatometer measurements, optical and scanning electron microscopy. Furthermore, macro-hardness measurements were conducted and the ferrite phase fraction was analyzed from optical microscopic images using an imaging processing program. Thereupon a continuous cooling transformation (CCT) diagram for the 2.25Cr-1Mo-0.25V base metal and three welding CCT diagrams with different peak temperatures were constructed to realistically simulate the temperature profile of the different regions within the heat affected zones between the weld beads of the multi-layer weld metal. The microstructural constituents which were observed depending on the peak temperature and cooling parameters are low quantities of martensite, high quantities of bainite and in particular lower bainite, coalesced bainite and upper bainite as well as ferrite for the welding CCT diagrams. Regarding the base metal CCT diagram, all dilatometer specimens exhibited a fully bainitic microstructure consisting of lower bainite, coalesced bainite and upper bainite. Only the slowest cooling rate with a cooling parameter of 50 s caused a ferritic transformation. Nevertheless, it has to be emphasized that the distinction between martensite and bainite and the various kinds of bainite was only possible at higher magnification using scanning electron microscopy.

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Containerless solidification of undercooled SrO–Al2O3 binary melts

Physical Chemistry Chemical Physics ◽

10.1039/c4cp05861e ◽

2015 ◽

Vol 17 (9) ◽

pp. 6495-6500 ◽

Cited By ~ 8

Author(s):

Katsuyoshi Kato ◽

Atsunobu Masuno ◽

Hiroyuki Inoue

Keyword(s):

Binary System ◽

Glass Forming Ability ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Glass Forming ◽

Aerodynamic Levitation ◽

Cct Diagrams ◽

Containerless Solidification

The continuous cooling transformation (CCT) diagrams of the SrO–Al2O3 binary system under containerless conditions using an aerodynamic levitation furnace provide a slight difference in glass-forming ability at the edge of the glass-forming region.

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Influence of Chromium Content and Prior Deformation on the Continuous Cooling Transformation Diagram of Low-Carbon Bainitic Steels

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.835.58 ◽

2020 ◽

Vol 835 ◽

pp. 58-67

Author(s):

Mohammed Ali ◽

Antti J. Kaijalainen ◽

Jaakko Hannula ◽

David Porter ◽

Jukka I. Kömi

Keyword(s):

Cooling Rate ◽

Hot Deformation ◽

Laser Scanning ◽

Chromium Content ◽

Bainitic Ferrite ◽

Granular Bainite ◽

Low Carbon ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling

The effect of chromium content and prior hot deformation of the austenite on the continuous cooling transformation (CCT) diagram of a newly developed low-carbon bainitic steel has been studied using dilatometer measurements conducted on a Gleeble 3800 simulator with cooling rates ranging from 2-80 °C/s. After austenitization at 1100 °C, specimens were either cooled without strain or given 0.6 strain at 880 °C prior to dilatometer measurements. The resultant microstructures have been studied using laser scanning confocal microscopy, scanning electron microscopy and macrohardness measurements. CCT and deformation continuous cooling transformation (DCCT) diagrams were constructed based on the dilatation curves, final microstructures and hardness values. Depending on the cooling rate, the microstructures of the investigated steels after cooling from the austenite region consist of one or more of the following microstructural components: lath-like upper bainite, i.e. bainitic ferrite (BF), granular bainite (GB), polygonal ferrite (PF) and pearlite (P). The proportion of BF to GB as well as the hardness of the transformation products decreased with decreasing cooling rate. The cooling rate at which PF starts to appear depends on the steel composition. With both undeformed and deformed austenite, increasing the chromium content led to higher hardenability and refinement of the microstructure, promoting the formation of BF and shifting the ferrite start curve to lower cooling rates. Prior hot deformation shifted the transformation curves to shorter times and higher temperatures and led to a reduction in hardness at the low cooling rates through the promotion of ferrite formation.

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