Understanding the complexities of bake hardening

Das, Sourav; Singh, Shiv Brat; Mohanty, O. N.; Bhadeshia, H. K. D. H.

doi:10.1179/174367507x247511

Cited by 32 publications

(25 citation statements)

References 32 publications

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“…There were some efforts in the literature to model the BH response [1,[9][10][11][12][13][14]. Out of these previous works, the models developed by Zhao et al [10] and Soenen et al [11] and Das et al [12,13] are essentially statistical in nature and beyond the scope of the current work. There are two models, namely the models developed by Elsen and Hougardy [1] and by Berbenni et al [9] which need some discussion in brief here in order to appreciate the current understanding.…”

Section: Introductionmentioning

confidence: 92%

“…The 'best fit value' of the empirical constant S was found by fitting Equations (12) and (15) to experimental data collected from published literature as mentioned above. The best fit value of S was found to be 7 Â 10 5 ; with this value of S, the predicted value of the BH response (Dr BH ) was within ±10 MPa of the experimental value for most of the cases considered here (279 out of 282 data points) and the correlation co-efficient (R 2 ) value was also quite satisfactory (0.795).…”

Section: Analysis Of the Modelmentioning

confidence: 99%

“…It is well established in literatures that ageing temperature and time, both play a very crucial role in determining the final BH response [1,12,13,17]. Higher the ageing temperature and/or the ageing time, larger will be the strength increment due to BH effect for a given concentration of free carbon atoms in ultra low carbon bake hardenable steel.…”

Section: Effect Of Ageing Time and Temperature On Final Bhmentioning

confidence: 99%

“…Several studies on strain ageing have been carried out during the subsequent 60 years [5][6][7][8]. These as well as the later studies on the subject suggest that strength increment after the BH treatment occurs first due to the formation of Cottrell atmosphere around the mobile dislocations and secondly due to the precipitation of fine carbides [1,2,[9][10][11][12][13][14][15][16][17][18][19]. However, our understanding of the BH phenomena is not complete.…”

Section: Introductionmentioning

confidence: 99%

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A phenomenological model for bake hardening in minimal carbon steels

Das

Mohanty²,

Singh

2014

Philosophical Magazine

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The essence of bake hardening is to exploit the classical strain ageing in a positive way to increase the strength of the formed steel sheets used in outer body panel of a passenger car during the paint-baking operation. A new model that takes into account the strengthening contributions from Cottrell atmosphere and precipitate formation has been developed in the present work. The model predicts the increase in strength as a function of the amount of free solute C (calculated as a function of the annealing temperature), the amount of deformation, ageing temperature and time. The model predictions have been found to agree quite well with the experimental results; the individual contributions of Cottrell atmosphere and precipitation strengthening have been quantified. IntroductionBake hardening (BH) steels are low carbon ferritic steels that are processed in such a way that the ferrite contains an extremely small amount (approximately 15-20 ppm by weight) of carbon in solution in the final strip material [1]. The main use of this grade of steel is in the automobile sector where the autobody parts made of this steel are painted to give them an aesthetic look. When the paint is baked at an elevated temperature (typically 150-200°C), the dissolved free C atoms migrate to pin the dislocations introduced during the forming operations and the resultant increase in the strength of the material is known as the bake hardening response, Δσ BH . The BH response is measured by first prestraining the sample to 2% strain in tension at room temperature. The samples are then unloaded, aged at the required temperature (usually at 170°C) for a fixed time (usually 20 min) and then tensile tested again at room temperature. The difference between the lower yield stress (YS) after aging and the flow stress at unloading is known as the BH response [1] or Δσ BH . The test procedure is schematically shown in Figure 1; the prestrain represents the forming operation during the actual production of the component, the ageing treatment represents the paint-baking operation and the

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Section: Introductionmentioning

confidence: 92%

Section: Analysis Of the Modelmentioning

confidence: 99%

Section: Effect Of Ageing Time and Temperature On Final Bhmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A phenomenological model for bake hardening in minimal carbon steels

Das

Mohanty²,

Singh

2014

Philosophical Magazine

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“…In order to avoid the possibility of overfitting data, the experimental data are randomly divided into two groups respectively called the training set and the test set. The model has been implemented considering the only training data set constituted by 75 pct of the experimental data and it has been tested considering the test data set constitute by 25 pct of the experimental data (De Cooman [10], Cetinel et al [11], Dobrzanski and Trzaska [12], Garcia et al [13], Das et al [14]). …”

Section: The Ann Techniquementioning

confidence: 99%

ANN Model to predict the bake hardenability of Transformation-Induced Plasticity steels

Palmeri

Riccobono

2009

Computational Methods and Experiments in Materials Characterisation IV

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Neural networks are useful tools for optimizing material properties, considering the material's microstructure and therefore the thermal treatments it has undergone. In this research an artificial neural network (ANN) with a Bayesian framework able to predict the bake hardening and the mechanical properties of the Transformation-Induced-Plasticity (TRIP) steels was designed. The forecast ability of the ANN model is achieved taking into account the operating parameters involved in the Intercritical Annealing (IA), in the Isothermal Bainite Treatment (IBT) and also considering the different prestrain values and the volume fraction of the retained austenite before the Bake Hardening (BH) treatment. This approach allowed one to overcome the need to know the metallurgical rules that describe all the active phenomena in multiphase steels. The neural network approach allowed one to overcome the lack of prediction capability in the existing numerical models.

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Effect of Fine Grained Dual Phase Steel on Bake Hardening Properties

Ormsuptave

Uthaisangsuk

2016

steel research int.

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High strength dual phase (DP) steels have been increasingly used in car body structure for reducing weight and increasing safety performance. Bake hardening process is widely applied for improving final mechanical properties of formed components by means of carbide precipitation and occurred Cottrell cloud. In this work, effects of bake hardening on mechanical behavior of coarse and fine grain DP steels are investigated. Initially, fine grain ferritic-pearlitic structure is produced from a low carbon steel by constrained groove pressing (CGP) based on severe plastic deformation. Ferrite grains with a submicro size of 470 nm can be hereby achieved. DP microstructures are generated afterward by intercritical annealing. Finally, bake hardening at the temperature of 160 8C for 20 min is performed under consideration of various pre-strains between 0 and 10%. It is found that bake hardenability of the DP steels can be significantly increased due to the fine grain structure induced by the CGP, which provide enhanced heterogeneous nucleation sites for precipitates and accelerated carbon diffusion.[ Ã ] Prof.

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Understanding the complexities of bake hardening

Cited by 32 publications

References 32 publications

A phenomenological model for bake hardening in minimal carbon steels

A phenomenological model for bake hardening in minimal carbon steels

ANN Model to predict the bake hardenability of Transformation-Induced Plasticity steels

Effect of Fine Grained Dual Phase Steel on Bake Hardening Properties

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