scholarly journals On the Simultaneous Improving of Strength and Elongation in Dual Phase Steels via Cold Rolling

Metals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1676
Author(s):  
Yousef Mazaheri ◽  
Amir Hossein Jahanara ◽  
Mohsen Sheikhi ◽  
Ehsan Ghassemali
Keyword(s):  
Cold Rolling ◽  
Strain Hardening ◽  
Deformation Process ◽  
Volume Fraction ◽  
Thermomechanical Processing ◽  
Dual Phase ◽  
Three Stages ◽  
Dp Steels ◽  
Average Size ◽  
The Given

The ferrite-pearlite microstructure was cold-rolled to form dual phase (DP) steels, the percentage reduction of which varied. To do so, the steels were annealed in two steps and then the workpiece underwent water quenching. Accordingly, a decrease was observed in the average size of the ferrite grains, from above 15 µm to below 2 µm, subsequent to the thermomechanical processing. By an increase in the reduction percentage, the volume fraction of martensite grew. The balance between strength and elongation also improved nearly 3 times, equivalent to approximately 37,297 MPa% in DP in comparison to 11,501 MPa% in the ferrite-pearlite microstructure, even after 50% cold-rolling. Based on Hollomon and differential Crussard-Jaoul (DC–J) analyses, the DP steels under investigation deformed in two and three stages, respectively. The modified C–J (MC–J) analysis, however, revealed that the deformation process took place in four stages. The rate of strain hardening at the onset of the deformation process was rather high in all DP steels. The given rate increased once the size of the ferrite grains reduced; an increase in the volume fraction of martensite due to larger percentage of reduction also contributed to the higher rate of strain hardening. The observation of the fractured surfaces of the tensile specimens indicated ductile fracture of the studied DP steels.

scholarly journals A Dislocation-Based Theory for the Deformation Hardening Behavior of DP Steels: Impact of Martensite Content and Ferrite Grain Size

2010 ◽  
Vol 2010 ◽  
pp. 1-16 ◽  
Author(s):  
Yngve Bergström ◽  
Ylva Granbom ◽  
Dirk Sterkenburg
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Deformation Process ◽  
Volume Fraction ◽  
High Energy ◽  
Martensite Content ◽  
Plastic Deformation Process ◽  
Deformation Hardening ◽  
Dp Steels ◽  
Ferrite Grain Size

A dislocation model, accurately describing the uniaxial plastic stress-strain behavior of dual phase (DP) steels, is proposed and the impact of martensite content and ferrite grain size in four commercially produced DP steels is analyzed. It is assumed that the plastic deformation process is localized to the ferrite. This is taken into account by introducing a nonhomogeneity parameter, f(ε), that specifies the volume fraction of ferrite taking active part in the plastic deformation process. It is found that the larger the martensite content the smaller the initial volume fraction of active ferrite which yields a higher initial deformation hardening rate. This explains the high energy absorbing capacity of DP steels with high volume fractions of martensite. Further, the effect of ferrite grain size strengthening in DP steels is important. The flow stress grain size sensitivity for DP steels is observed to be 7 times larger than that for single phase ferrite.

Effect of Tailoring Martensite Shape and Spatial Distribution on Tensile Deformation Characteristics of Dual Phase Steels

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
B. Ravi Kumar ◽  
Vishal Singh ◽  
Tarun Nanda ◽  
Manashi Adhikary ◽  
Nimai Halder ◽  
...  
Keyword(s):  
Grain Size ◽  
Spatial Distribution ◽  
Volume Fraction ◽  
Tensile Deformation ◽  
Void Formation ◽  
Martensite Phase ◽  
Continuous Annealing ◽  
Dual Phase ◽  
Deformation Characteristics ◽  
Dp Steels

The authors simulated the industrially used continuous annealing conditions to process dual phase (DP) steels by using a custom designed annealing simulator. Sixty-seven percentage of cold rolled steel sheets was subjected to different processing routes, including the conventional continuous annealing line (CAL), intercritical annealing (ICA), and thermal cycling (TC), to investigate the effect of change in volume fraction, shape, and spatial distribution of martensite on tensile deformation characteristics of DP steels. Annealing parameters were derived using commercial software, including thermo-calc, jmat-pro, and dictra. Through selection of appropriate process parameters, the authors found out possibilities of significantly altering the volume fraction, morphology, and grain size distribution of martensite phase. These constituent variations showed a strong influence on tensile properties of DP steels. It was observed that TC route modified the martensite morphology from the typical lath type to in-grain globular/oblong type and significantly reduced the martensite grain size. This route improved the strength–ductility combination from 590 MPa–33% (obtained through CAL route) to 660 MPa–30%. Finally, the underlying mechanisms of crack initiation/void formation, etc., in different DP microstructures were discussed.

Micromechanical Simulation Approach of Dual Phase Steel Artificial Microstructure Using Random Field Model

2021 ◽  
Vol 1016 ◽  
pp. 534-540
Author(s):  
Mohamed Imad Eddine Heddar ◽  
Nadjoua Matougui ◽  
Brahim Mehdi
Keyword(s):  
Grain Size ◽  
Random Field ◽  
Dual Phase Steel ◽  
Field Model ◽  
Volume Fraction ◽  
Gaussian Kernel ◽  
Dual Phase ◽  
Strain Behavior ◽  
Proportional Relationship ◽  
Dp Steels

In this study, a random field (RF) model with a Gaussian kernel was applied to generate an artificial microstructure of dual phase (DP) steels. Micrographs obtained from Scanning Electron Microscopy (SEM) were analyzed using image processing software to extract the grain size and the volume fraction of each phase. Based on watershed (Ws) segmentation and quantitative analysis, the real and artificial microstructures were compared by analyzing grain features related the solidity, grain size and aspect ratio (the proportional relationship between its width and its height). Consequently, this approach allows to simulate the overall stress-strain behavior of the analyzed microstructures. As a result, it was shown that the strain localization starts to develop at the ferrite/martensite interface and that the RF model could replicate the micromechanical behavior of DP steels.

Strain-Hardening Model of Dual-Phase Steel With Geometrically Necessary Dislocations

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Chuang Ren ◽  
Wen Jiao Dan ◽  
Yong Sheng Xu ◽  
Wei Gang Zhang
Keyword(s):  
Strain Hardening ◽  
Dual Phase Steel ◽  
Volume Fraction ◽  
Lattice Mismatch ◽  
Cell Model ◽  
Interpolation Method ◽  
Nonlinear Function ◽  
Dual Phase ◽  
Hardening Model ◽  
Point Interpolation Method

The strain-hardening behavior of metal during the uniaxial tension can be treated as the competing result of generation and annihilation of statistically stored dislocations (SSDs). Geometrically necessary dislocations (GNDs) are generated to accommodate a lattice mismatch and maintain deformation compatibility in dual-phase (DP) steels because of the heterogeneous deformation of the microstructure. In this study, a dislocation-based strain-hardening model that encompasses GNDs was developed to describe the mechanical properties of dual-phase steel. The GNDs were obtained based on a cell model of uniaxial deformation and the SSDs were calculated using a dynamic recovery model. The strain of each phase is a nonlinear function of the overall material strain obtained by the point-interpolation method (PIM). The proposed strain-hardening model was verified by using commercially produced DP600 steel. The calculated results obtained with GNDs are able to predict more precisely the experimental data than that without. The effects of martensite volume fraction and grain size on the strain-hardening behaviors of individual phases and material were studied.

Thermal Stability and Nanocrystallization of Amorphous Ti-Ni Alloys Prepared by Cold Rolling and Post-Deformation Annealing

2007 ◽  
Vol 539-543 ◽  
pp. 1964-1970 ◽  
Author(s):  
Vladimir Brailovski ◽  
Sergey Prokoshkin ◽  
E. Bastarash ◽  
Vincent Demers ◽  
K.E. Inaekyan ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Cold Rolling ◽  
Amorphous Phase ◽  
Volume Fraction ◽  
Thermomechanical Processing ◽  
True Strain ◽  
Cold Work ◽  
Martensitic Transformations ◽  
Ni Alloys ◽  
Equiatomic Alloy

The thermomechanical processing consisting in severe cold rolling (true strain 0.7–1.9) followed by a post-deformation annealing (200-700oC) is applied to Ti-50.0 and 50.7at%Ni alloys. The thermal stability of the amorphous phase as well as the influence of post-deformation annealing on the structure, substructure and temperature range of martensitic transformations are studied using TEM and DSC techniques. For a given level of cold work, the equiatomic alloy has a higher volume fraction of amorphous phase than the nickel-rich one. For both alloys, the higher the volume fraction of the amorphous phase, the higher the thermal stability. For a given post-deformation annealing temperature, the DSC martensitic transformation peaks from the material subjected to amorphization cold work are sharper and the hysteresis between the direct and reverse transformations is narrower than those for a material subjected to strain hardening cold work. This observation confirms the absence of the well-developed dislocation substructure in the severely deformed alloy subjected to nanocrystallization heat treatment, which is consistent with TEM results.

Microstructure and Texture of Cold Rolled and Recrystallized CrNoNi Medium-Entropy Alloy

2018 ◽  
Vol 941 ◽  
pp. 833-838
Author(s):  
Gunasekaran Dan Sathiaraj ◽  
Werner Skrotzki ◽  
R. Jose Immanuel ◽  
Aurimas Pukenas ◽  
Rolf Schaarschuch ◽  
...  
Keyword(s):  
Cold Rolling ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Texture Evolution ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Alloy Plate ◽  
Texture Intensity ◽  
Different Temperatures ◽  
Average Size

An equiatomic CrCoNi medium-entropy alloy plate was heavily deformed by conventional cold rolling and subsequently annealed at different temperatures. Microstructure and texture evolution of the deformed and annealed sheets were investigated by electron backscatter diffraction and X-ray diffraction. Heavy cold rolling induces an alloy type α-fibre texture with major brass component. This type of texture is indicative of low stacking fault energy of the CrCoNi alloy. Annealing at 700 °C leads to a homogeneously recrystallized microstructure with ultrafine grains of about 800 nm average size. The volume fraction of different texture components is almost similar after annealing at different temperatures. However, the overall texture intensity after annealing is very weak. Finally, in order to understand the microstructure and texture evolution of the CrCoNi alloy, it is critically compared with other low stacking fault energy FCC materials.

Multiscale Material Modeling and Simulation of the Mechanical Behavior of Dual Phase Steels Under Different Strain Rates: Parametric Study and Optimization

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Tarek M. Belgasam ◽  
Hussein M. Zbib
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Mechanical Behavior ◽  
Volume Fraction ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Dual Phase ◽  
Strain Rates ◽  
Microstructure Parameters ◽  
Dp Steels

Recent studies on developing dual phase (DP) steels showed that the combination of strength/ductility could be significantly improved when changing the volume fraction and grain size of phases in the microstructure depending on microstructure properties. Consequently, DP steel manufacturers are interested in predicting microstructure properties as well as optimizing microstructure design at different strain rate conditions. In this work, a microstructure-based approach using a multiscale material and structure model was developed. The approach examined the mechanical behavior of DP steels using virtual tensile tests with a full micro-macro multiscale material model to identify specific mechanical properties. Microstructures with varied ferrite grain sizes, martensite volume fractions, and carbon content in DP steels were also studied. The influence of these microscopic parameters at different strain rates on the mechanical properties of DP steels was examined numerically using a full micro-macro multiscale finite element method. An elasto-viscoplastic constitutive model and a response surface methodology (RSM) were used to determine the optimum microstructure parameters for a required combination of strength/ductility at different strain rates. The results from the numerical simulations were compared with experimental results found in the literature. The developed methodology proved to be a powerful tool for studying the effect and interaction of key strain rate sensitivity and microstructure parameters on mechanical behavior and thus can be used to identify optimum microstructural conditions at different strain rates.

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