Papers by Keyword: Dynamic Strain Aging (DSA)

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Authors: Santosh Kumar Sahoo, V.N. Gaffney, A. Chatterjee, Korukonda L. Murty
Abstract: Annealing behaviour of ferritic HT-9 stainless steel plates was investigated through evolution of microstructural, textural and mechanical properties. Microstructural observations showed two important findings: (a) abnormal grain growth occurs at higher annealing temperatures, (b) drop in in-grain misorientation with increasing annealing temperature. However, textural results showed an increase in texturing till 500oC annealing and a clear drop in texturing beyond 500oC annealing. The strength (both yield and tensile) decreased with increase in testing temperature and the micro-hardness values decreased with increase in annealing temperature. Dynamic strain ageing was observed at certain strain rates and testing temperatures. The onset of the serrated yielding at low temperature limit estimated from the strain rate-temperature plot was found out to be ~ 94kJ/mol identifiable with that for migration of C and N.
Authors: Jin Kyung Kim, Yuri Estrin, Hossein Beladi, Sung Kyu Kim, Kwang Geun Chin, Bruno C. De Cooman
Abstract: High Mn steels demonstrate an exceptional combination of high strength and ductility due to their high work hardening rate during deformation. The microstructure evolution and work hardening behavior of Fe18Mn0.6C1.5Al TWIP steel in uni-axial tension were examined. The purpose of this study was to determine the contribution of all the relevant deformation mechanism : slip, twinning and dynamic strain aging. Constitutive modeling was carried out based on the Kubin-Estrin model, in which the densities of mobile and forest dislocations are coupled in order to account for the continuous immobilization of mobile dislocations during straining. These coupled dislocation densities were also used for simulating the contribution of dynamic strain aging on the flow stress. The model was modified to include the effect of twinning.
Authors: M. Smaga, F. Hahnenberger, A. Sorich, Dietmar Eifler
Abstract: In this investigation specimens of the austenitic steels AISI 304, AISI 321 and AISI 348 were investigated in fatigue tests in the temperature range -60°C ≤ T ≤ 550°C. A detailed microstructure-based characterization of the cyclic deformation behavior of austenitic steels was performed by means of stress-strain hysteresis, electrical resistance and magnetic measurements. Up to ambient temperature the occurring deformation induced martensite formation was measured in-situ with a ferritescope during cyclic loading. The temperature range for dynamic strain aging was reliably identified by means of a temperature increase fatigue test with one single specimen.
Authors: Mattias Calmunger, Guo Cai Chai, Sten Johansson, Johan Moverare
Abstract: Biomass power plants with high efficiency are desired as a renewable energy resource. High efficiency can be obtained by increasing temperature and pressure. An upgrade of the material performance to high temperature material is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. In this study, the materials high-temperature behaviours of AISI 304 and Alloy617 under slow deformation rate are evaluated using high-temperature long-term aged specimens subjected to slow strain rate tensile testing (SSRT) with strain rates down to 10-6/s at 700°C. Both materials show decreasing stress levels and elongation to fracture when tensile deformed using low strain rate and elevated temperature. At high-temperature and low strain rates cracking in grain boundaries due to larger precipitates formed during deformation is the most common fracture mechanism.
Authors: C. Gupta, J.K. Chakravartty, R.N. Singh
Abstract: The deformation and fracture behaviour of AISI 403, a tempered martensitic stainless steel for end fitting application of Pressurised heavy water reactor is being reported. The deformation behaviour studies entailed characterisation of tensile behaviour in the temperature range 77 - 873 K for the as recieved and the fine grained Nb modified variant of AISI 403. the study of elevated tensile behaviour in the two steels has been undertaken with the purpose of characterising the strain rate - temperature domain of the occurrence of dynamic strain aging (DSA) phenomenon. In both steels, while the temperature range for the manifestations of characteristic anomalies in the tensile curve due to DSA was observed within 523 - 673K, the strain domain for the fine grained Nb modfied variety was significantly higher as comapred with the as recievied variety. The low temperature tensile tests for the as recieved AISI 403 revealed the presence of Pseudo=alloy softening in the temperature range 273 - 193 K. The effect of high DBTT of the AISI 403 steel was shown by the fracture toughness tests in the J-integral format at room temperature that displayed significant scatter in smaples with high in-plane and out of plane constraint. Smaples with lower constraint showing stable crack growth were further tested at high temperature to obtain the temperature dependence of initiation fracture toughness and propagation touhgness. Within the DSA tempertaures a sharp decline in the fracture properties were observed. A mechanistic interpretation for the manifestations of the various observed phenomena is presented.
Authors: R.W. Armstrong, G.P. Chambers, M.A. Erickson-Natishan, H.W. Sandusky, M. Wagenhofer, F.J. Zerilli
Authors: M.A. Lebyodkin, Yves Bréchet, Yuri Estrin, Ladislas P. Kubin
Authors: Jiang Ying Meng, Li He Qian, Peng Cheng Guo, Fu Cheng Zhang
Abstract: This work was to clarify the characteristics of serrated flow in an austenitic FeMnC twin-induced plasticity (TWIP) steel at room temperature (RT) using both strain- and crosshead displacement-controlled tensile tests. Three types of serrations were observed in strain-controlled but not in displacement-controlled tests, indicating that strain-controlled tensile tests provide more deformation details. The occurrence of the different types of serrations depends on both strain rate and strain level. Type C serrations were observed in TWIP steels at RT for the first time. The critical strain for the onset of serrations exhibits a positive strain rate dependence at higher strain rates, whereas an “inverse” critical strain behavior was observed in the lower strain rate region.
Authors: Lan Jiang, John J. Jonas, Raja K. Mishra
Abstract: 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.
Authors: Seong Gu Hong, Soon Bok Lee
Abstract: Low cycle fatigue (LCF) tests were carried out in a wide temperature range (20°C-650°C)at strain rates of 1×10-4/s-1×10-2/s for 17% cold worked (CW) 316L stainless steel to investigate the conditions for the occurrence of dynamic strain aging (DSA) and its effects on material properties during LCF deformation. DSA introduced anomalous changes of LCF properties, and the DSA regime under LCF loading condition coincided with that in tensile loading condition. During LCF deformation, dynamic stain aging can be manifested in the forms of the occurrence of the plateau or the peak in the variation of cyclic peak stress with temperature, the negative temperature dependence of plastic strain amplitude or softening ratio, the negative strain rate sensitivity, and the negative strain rate dependence of plastic strain amplitude or softening ratio.
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