Dynamic strain aging in DP steels at forming relevant strain rates and temperatures

The dynamic strain aging (DSA) behavior of SA508-III steel was evaluated through tensile tests with different strain rates from 10-4 to 10-1s-1 at 350°C. The OM, SEM and TEM were carried out to observe the microstructures and fracture morphologies of the steel. The results show that the serrated flows appear in the stress-strain curves when the strain rate is between 10-3~10-2s-1, indicating that DSA occurs. Under the strain rate range, the tensile strength increases and the elongation and the reduction of area decrease. However, the fracture surface of the steel after tensile tests is still ductile. DSA in SA508-III steel at the strain rates from10-3 to 10-2s-1 is mainly caused by the interaction between the internal solute atoms and dislocations, which leads to the dislocations multiplication and the formation of sub-grain boundaries and dislocation cell structure.

Download Full-text

Dynamic Strain Aging and the Charpy Specimen Behavior of Annealed 4340 Steel

Journal of Basic Engineering ◽

10.1115/1.3605056 ◽

1968 ◽

Vol 90 (1) ◽

pp. 13-20 ◽

Cited By ~ 8

Author(s):

W. R. Clough ◽

L. A. Jackman ◽

Y. G. Andreev

Keyword(s):

Dynamic Strain Aging ◽

Cleavage Fracture ◽

Strain Aging ◽

Room Temperature ◽

Carbon Steels ◽

Dynamic Strain ◽

Charpy Specimen ◽

Strain Rates ◽

Aging Effects ◽

Lower Carbon

V-notch Charpy bars were ruptured at seven deflection rates at test temperatures from the ambient through the blue-brittle range, while unnotched tensile specimens were equivalently tested at four strain rates. Objectives were to interpret and relate dynamic strain aging manifestations of annealed 4340 shown by the two types of tests. Comparisons are made with elastic-plastic formulations and experimental results for initial yielding and fracture of notched bars at or near room temperature. Quasi-cleavage fracture was observed in excess of 500 deg F. Dynamic strain aging effects are compared with those found with less alloyed lower carbon steels. Arrhenius type relations are developed and discussed, and from these other interrelations are derived, and mechanisms are discussed.

Download Full-text

Dynamic Strain Aging during the Plastic Flow of Metals

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.340-341.823 ◽

2007 ◽

Vol 340-341 ◽

pp. 823-828 ◽

Cited By ~ 8

Author(s):

Wei Guo Guo

Keyword(s):

Experimental Data ◽

Flow Stress ◽

Plastic Flow ◽

Dynamic Strain Aging ◽

Strain Aging ◽

Testing Machine ◽

Strain Curve ◽

Dynamic Strain ◽

Polycrystalline Materials ◽

Strain Rates

In the present paper, in order to better understand the third type “dynamic strain aging” occurring during the plastic flow of metals, the uniaxial compressive experimental data ever obtained in University of California, San Diego using an Instron servo-hydraulic testing machine and the Hopkinson technique are systematically analysed. These experimental data cover the plastic flow stress of several fcc, hcp, bcc polycrystalline materials and several alloys at a broad range of temperatures (77K – 1,100K) and strain rates (0.001/s – 10,000/s). In analysis, the appearing region of the “dynamic strain aging ” under different temperatures and strain rates are respectively plotted by the curves of stress vs temperature, and stress vs strain for fcc, hcp and bcc metals. The results show that: (1) this third type “dynamic strain aging ” occurs in all hcp, bcc and fcc polycrystalline or alloy materials, and there are different profiles of stress-strain curve; (2) the “dynamic strain aging ”occurs in a matching coincidence of the temperature and strain rate, its temperature region will shift to higher region with increasing strain rates; (3) bcc materials do not have an initial pre-straining strain as the onset of work-hardness rate change for the “dynamic strain aging ”; and (4) based on the explanations of dynamic strain aging with serration curves (Portevin-Lechatelier effect) and other explaining mechanisms of references, The mechanism of third DSA is thought as the rapid/continuous formation of the solute atmospheres at the mobile dislocation core by the pipe diffusion along vast collective forest dislocations to result in a continuous rise curve of flow stress. Finally, several conclusions are also presented.

Download Full-text

Effects of microstructure on the dynamic strain aging of ferriticpearlitic steels at high strain rates

EPJ Web of Conferences ◽

10.1051/epjconf/201818303009 ◽

2018 ◽

Vol 183 ◽

pp. 03009

Author(s):

Ahmad Mardoukhi ◽

Jari Rämö ◽

Taina Vuoristo ◽

Amandine Roth ◽

Mikko Hokka ◽

...

Keyword(s):

Dynamic Strain Aging ◽

Strain Aging ◽

Split Hopkinson Pressure Bar ◽

Dynamic Compression ◽

Aging Effect ◽

Grain Structure ◽

Dynamic Strain ◽

Maximum Effect ◽

Strain Rates ◽

Hopkinson Pressure Bar

This paper presents an experimental study of the effects of dynamic strain aging on the mechanical behavior of selected high carbon and chromium-manganese steels in dynamic loading condition. In ferritic-pearlitic steels, the dynamic strain aging is typically caused by carbon, nitrogen, and possibly some other small solute atoms. Therefore, the thermomechanical treatments affect strongly how strong the dynamic strain aging effect is and at what temperature and strain rate regions the maximum effect is observed. In this work, we present results of the high temperature dynamic compression tests carried out for two different ferritic-pearlitic steels, 16MnCr5 and C60, that were heat treated to produce different microstructure variants of these standard alloys. The microstructures were analyzed using electron microscopy, and the materials were tested with the Split Hopkinson Pressure Bar device at three different strain rates at temperatures ranging from room temperature up to 680 °C to study the effect of the heat treatments and the resulting microstructures on the dynamic behavior of the steels and the dynamic strain aging effect. The results indicate that for both steels, a coarse grain structure has the strongest dynamic strain aging sensitivity at small plastic strains. However, at higher strains, all microstructures show similar strain aging sensitivities.

Download Full-text

Dynamic Strain Aging Behavior of a Mg-Ce Alloy and its Implications for Extrusion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.1193 ◽

2012 ◽

Vol 706-709 ◽

pp. 1193-1198 ◽

Cited By ~ 1

Author(s):

Lan Jiang ◽

John J. Jonas ◽

Raja K. Mishra

Keyword(s):

Dynamic Strain Aging ◽

Rate Equation ◽

Texture Component ◽

Strain Aging ◽

Experimental Results ◽

Dynamic Strain ◽

Strain Rates ◽

Compression Tests ◽

Aging Behavior

Compression tests were employed to characterize the DSA behaviour of Mg-Ce alloys. Samples were taken from cast billets and extruded bars of Mg-0.5 wt.% Ce. The DSA behavior was examined at temperatures from 150°C to 400°C at strain rates of 0.001/s to 1.5/s. A rate equation was fitted to the experimental results, which is employed to predict whether or not DSA will occur at the strain rates and temperatures involved in the formation of the RE texture component during extrusion.

Download Full-text

A Modified Johnson-Cook Model for Ferritic-Pearlitic Steel in Dynamic Strain Aging Regime

Metals ◽

10.3390/met9050528 ◽

2019 ◽

Vol 9 (5) ◽

pp. 528 ◽

Cited By ~ 2

Author(s):

Ashwin Moris Devotta ◽

P. V. Sivaprasad ◽

Tomas Beno ◽

Mahdi Eynian ◽

Kjell Hjertig ◽

...

Keyword(s):

Flow Stress ◽

Strain Rate ◽

Dynamic Strain Aging ◽

Strain Aging ◽

Experimental Testing ◽

Flow Behavior ◽

Pearlitic Steel ◽

Dynamic Strain ◽

Model Parameters ◽

Strain Rates

In this study, the flow stress behavior of ferritic-pearlitic steel (C45E steel) is investigated through isothermal compression testing at different strain rates (1 s−1, 5 s−1, and 60 s−1) and temperatures ranging from 200 to 700 °C. The stress-strain curves obtained from experimental testing were post-processed to obtain true stress-true plastic strain curves. To fit the experimental data to well-known material models, Johnson-Cook (J-C) model was investigated and found to have a poor fit. Analysis of the flow stress as a function of temperature and strain rate showed that among other deformation mechanisms dynamic strain aging mechanism was active between the temperature range 200 and 400 °C for varying strain rates and J-C model is unable to capture this phenomenon. This lead to the need to modify the J-C model for the material under investigation. Therefore, the original J-C model parameters A, B and n are modified using the polynomial equation to capture its dependence on temperature and strain rate. The results show the ability of the modified J-C model to describe the flow behavior satisfactorily while dynamic strain aging was operative.

Download Full-text

A New Explanation for the Effect of Dynamic Strain Aging on Negative Strain Rate Sensitivity in Fe–30Mn–9Al–1C Steel

Materials ◽

10.3390/ma12203426 ◽

2019 ◽

Vol 12 (20) ◽

pp. 3426 ◽

Cited By ~ 1

Author(s):

Jia Xing ◽

Lifeng Hou ◽

Huayun Du ◽

Baosheng Liu ◽

Yinghui Wei

Keyword(s):

Strain Rate ◽

Strain Rate Sensitivity ◽

Dynamic Strain Aging ◽

Strain Aging ◽

Rate Sensitivity ◽

Tensile Tests ◽

Dynamic Strain ◽

Strain Rates ◽

Dislocation Arrangement ◽

Hall Plot

In this study, the evolution of the mechanical properties of Fe–30Mn–9Al–1C steel has been determined in tensile tests at strain rates of 10−4 to 102 s−1. The results show that the strain rate sensitivity becomes a negative value when the strain rate exceeds 100 s−1 and this abnormal evolution is attributed to the occurrence of dynamic strain aging. Due to the presence of intergranular κ-carbides, the fracture modes of steel include ductile fracture and intergranular fracture. The values of dislocation arrangement parameter M were obtained using a modified Williamson–Hall plot. It has been found that once the strain rate sensitivity becomes negative, the interaction of dislocations in the steel is weakened and the free movement of dislocation is enhanced. Adiabatic heating promotes the dynamic recovery of steel at a high strain rate.

Download Full-text

Numerical modeling of the dynamic strain aging in steels at high strain rates and high temperatures

EPJ Web of Conferences ◽

10.1051/epjconf/202125002023 ◽

2021 ◽

Vol 250 ◽

pp. 02023

Author(s):

R. A. Rubio ◽

M. Hokka

Keyword(s):

Flow Stress ◽

High Temperatures ◽

Dynamic Strain Aging ◽

Strain Aging ◽

High Strain ◽

Dynamic Strain ◽

Support Vector ◽

Strain Rates ◽

High Strain Rates ◽

Thermomechanical Behaviour

Carbon steels can be heat treated to produce different microstructural variations and mechanical properties. At high temperatures the material plasticity and strength can be influenced by diffusional effects like the Portevin-Le Chatelier effect, leading to a commonly observed increased strength at elevated temperatures. The diffusional effects are influenced by the chemical composition, but also the heat treatment history that affects the local composition and especially the concentrations of free solute atoms. In this work, a numerical approach was implemented to reproduce the thermomechanical behaviour of two different microstructural variants of steel grade C45. The experimental data used to calibrate the model includes information of the plastic behaviour of material subjected to dynamic compression loading at a wide range of temperatures. Special emphasis was focused to describe the effects of the dynamic strain aging (DSA) on the flow stress. A strategy based on machine learning was implemented to obtain a model that reproduces the strengthening of the material due to diffusional effects. Cubic Support Vector Machine models were trained for both microstructure variants of the steel and different surfaces were obtained to describe the topology of the flow stress as function of temperature and strain rate. The model predictions were compared to the behaviour described by the Johnson-Cook model to estimate the influence of the DSA effect on the strength of the material at high strain rates and temperatures. Furthermore, the model quantifies how the microstructure affects the strength of the material and the strength of the DSA-hardening.

Download Full-text

Study on Dynamic Strain Aging Phenomenon of AZ91D Magnesium Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.472-475.2962 ◽

2012 ◽

Vol 472-475 ◽

pp. 2962-2965 ◽

Cited By ~ 1

Author(s):

Na Lin ◽

Kai Huai Yang ◽

Shao Feng Zeng ◽

Wen Zhe Chen

Keyword(s):

Activation Energy ◽

Solid Solution ◽

Magnesium Alloy ◽

Dynamic Strain Aging ◽

Strain Aging ◽

Solution Treatment ◽

Dynamic Strain ◽

Strain Rates ◽

Az91d Magnesium Alloy ◽

Solute Atoms

Tensile experiment of AZ91D magnesium alloy was carried out and serrated flow was apparent throughout the deformation history. Dynamic strain aging (DSA) occurs when the AZ91D magnesium alloy treated by solid solution treatment has been deformed at a set range of strain rates (1.11×10-4 s-1 to1.67×10-3 s-1) and a certain range temperatures (248 K to 423 K). The critical plastic strain εc was observed to increase with increasing strain rates but decrease with increasing temperature. The diffusing activation energy of solute atoms during the DSA occurring in AZ91D magnesium alloy is 140.8 kJ/mol by calculating, which is correspondence match with the diffusing activation energy of Al solute atoms in Mg matrix. Therefore, the micro-mechanism of DSA in the alloy is believed that the Al atoms in solid solution gather around dislocations to form Cottrell solute atmospheres by vacant diffusion and then pin the moving dislocations.

Download Full-text