Influence Of Strain Aging Research Articles

The influence of strain aging on characteristics of austenite formed during heat treatment of spring wire

The influence of strain aging on characteristics of austenite formed during heat treatment of spring wire

The Influence of Strain Aging at Different Temperatures on the Mechanical Properties of Cold-Drawn 10B21 Steel Combined with an Electron Microscope Study of the Structures.

The effect of aging treatments at various temperatures on the mechanical properties and microstructure of 10B21 cold heading steel with a 20% reduction in area (ε = 0.1) was investigated. The mechanical properties were evaluated based on tensile tests and hardness tests, while the evolution of microstructure was observed by using an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results reveal that aging treatment enhance the strength and hardness of 10B21 cold heading steel after drawing, and the highest values of strength and hardness are attained at an aging temperature of 300 °C. Specifically, the yield and ultrahigh tensile strength after aging at 300 °C are measured at 620 MPa and 685 MPa, respectively, which are 30 MPa and 50 MPa higher than the cold-drawn sample. Moreover, the hardness after aging at 300 °C reaches 293 HV, which has an increase of 30 HV compared to the cold-drawn state. The improvement in mechanical properties may be related to the strain-aging mechanism and the increased density of dislocations. In addition, the analysis of the TEM results reveal that the presence of the second-phase Ti(C,N) contributes to pinning the dislocations, whereas the dislocations are pinned between the cementite (Fe3C) lamellar and stacked at the grain boundaries, leading to strain hardening of the material.

Effect of Strain Aging on Stages of Plastic Strain and Tensile Fracture of Specimens of Steel 08G2B. Part II. Stage of Concentrated Strain

Periods of the stage of concentrated strain of specimens of low-carbon steel 08G2B with ultrafine structure are studied by joint analysis of stress–strain curves and fields of digital image correlation (DIC). The DIC data and detection of a through crack on the surface of a tensile specimen are used to justify the use of the parameters of the second period of the stage of concentrated strain as criteria of crack resistance. Experimental data are used to determine the main factors representing the influence of strain aging on the level of mechanical properties of the steel.

Further Analysis of Dynamic Strain Aging in Context of an Internal State Variable Constitutive Formalism

Observations and analyses of dynamic strain aging in several metals are revisited. Common experimental trends are reviewed. A model of transport of solutes to a dislocation core is presented and predictions of the model are compared to experimental observations. A key element of the analysis is the influence of strain aging on the rate of structure evolution. The evidence presented here, based on strain-rate change measurements performed by Mulford and Kocks in Inconel 600, is that indeed the predominant effect of strain aging is to influence the rate of structure evolution. Estimates are presented for the rate of structure evolution and the extent of transport of solutes to the dislocation core in Inconel 600. While intriguing trends in hardening are observed, no fundamental insight is presented for the mechanism that contributes to the increased rate of structure evolution during strain aging.

Influence of Strain Aging on Fatigue Behavior and Structural Evolution of P91 Steel

Research on fatigue behavior and microstructural evolution of P91 steel under pre-dynamic strain aging conditions (pre-DSA), and strain aging (SA) conditions at 550 °C has been carried out, and the experimental results were compared with the pure fatigue (PF) results, also at 550 °C. The comparison indicated that, under various strain amplitudes, the fatigue life of P91 at 550 °C decreased after pre-DSA or SA treatments relative to PF, and that the effect of the pre-DSA treatment was more significant. The SA treatment induced the localization of plastic deformation, creating obvious stress concentrations on the surface that led to the initiation of multiple cracks which decreased the fatigue life of P91. Transmission electron microscopy analysis of P91 indicated that pre-DSA promoted higher dislocation density and increased the mechanical strength, while SA decreased the dislocation density and the mechanical strength. During fatigue tests, the martensite laths in pre-DSA and SA specimens recovered more completely relative to those under PF, and the recovery extent was directly related with the decrease of fatigue life.

Influence of strain aging on the ductility of 05Γ2ΦБ steel in controlled rolling and accelerated cooling

Influence of strain aging on the ductility of 05Γ2ΦБ steel in controlled rolling and accelerated cooling

Influence of Strain Aging on the Microstructure-Property of an X100 Pipeline Steel

The influence of strain aging on the microstructure-property characterization of an X100 pipeline steel was investigated by means of a thermal simulation technique, microscopic analysis method and mechanical properties testing. The experimental steel was prestrained in the tension at 6 pct and then was baked at 150oC, 200oC, 250oC and 300oC for 60 minutes, respectively. The results indicated that the strength and hardeness of test steel X100 increase and the plasticity and toughness decrease with the increasing of strain aging temperature, and it can get a higher ratio of yield to tensile and a lower strain-hardening coefficient which result in lower hardening capacity of X100 pipeline steel. There are two reasons for this strain aging phenomenon. One is the solute atoms of C, N in the α-Fe which Aggregated at the dislocation zones; the other is the compounds precipitation of C, N induced by the dislocations.

Factors Affecting Non-Propagation of Fatigue Crack in a Low-Carbon Steel. Effect of Oxide-Induced Crack Closure.

Rotating bending fatigue tests were carried out in air and in pure argon to clarify the effect of oxide-induced crack closure on crack non-propagation. The materials used were Ti added extra-low-carbon steel with no strain ageing, 0.02% carbon steel with a single ferrite phase, and annealed 0.19% carbon steel. The results obtained are as follows. (1) Threshold stress for fatigue crack growth is lower for Ti added extra-low-carbon steel in argon than for that in air, though the fatigue crack has a tendency to propagate more slowly in argon than the air. The above result shows that oxide-induced crack closure plays a significant role in crack non-propagation. (2) It seems that the influence of oxide-induced crack closure on crack non-propagation is smaller than the influence of strain ageing and microstructure. (3) A non-propagating crack is observed in the steel with a single ferrite phase even when strain ageing and oxide-induced crack closure do not occur.

The influence of prolonged exposure to operating temperatures and strain aging on the material properties of nuclear power plant reactor vessels and pipings

This report presents information regarding the variation under the effect of operating temperatures of the mechanical properties of steels and their welded joints, in the production of NPP apparatus and pipings used in the types VVER and RBMK reactors. Together with the properties characteristic of the types 20, 22 K, 08X18H12T, 15X2MFA steels after exposure to the temperature range of 250–400°C for 10 4 h, the values of the mechanical properties of these materials and their weldments (cut from the real components of operating NPP) after the exposure for 10 5 h at material operating temperatures are given. This work has shown that variation in properties after such prolonged operation periods is negligible and moreover the values of UTS, YS, A and Z are not inferior to those required by the USSR ‘Norms of strength calculation’. The estimation of structural strength (low cycle fatigue resistance, static and cyclic crack resistance) has been carried out as related to the pipings manufactured from the 08X18H12T steel after their operation period of 10 5 h. No visible variations of these characteristics have been observed. The influence of strain aging in the operating temperature range of 150–400°C on low cycle fatigue resistance of the types 15X2MFA, 15X2HMFA, 22 K steels and their welded joints, produced by various welding processes (manual, automatic under flux, electroslag weldings) has also been studied. It has been found that with the application of specific temperatures and strain rates, the aging effect may predetermine the material long-term lifetime related to a decrease at the stage of fatigue crack initiation. The strain aging effect is most evident with low carbon weld metal after manual arc welding without preheating which is the welding process that may be applied during assembly.

The influence of strain aging on the fatigue crack propagation threshold

While the influence of strain-aging on the endurance limit and on the dislocation behaviour during cyclic deformation has received some attention in the literature, almost no attention appears to have been paid to the influence of strain aging on fatigue crack propagation. An influence of strain aging on fatigue propagation can be expected to manifest itself most clearly at the very small propagation rates near ..delta..K /SUB th/ , the fatigue crack propagation threshold. The present study was therefore performed to determine whether an influence attributable to strain aging could be detected near ..delta..K /SUB th/ during tests carried out on two mild steels having different sensitivities to strain aging.

Effects of hardening and localization of strain in strain aging of technical purity iron

1. The hardening effect in strain aging of technical purity iron increases with an increase in the degree of preliminary strain by tension (by increasing the density of introduced dislocations) regardless of the character of strain distribution in the sample if the aging time is sufficient for occurrence of hardening according to the “stopper” mechanism. 2. With nonuniform strain distribution in the sample (completion of preliminary strain within the limits of the yield plateau or with the formation of a neck) there is observed the phenomenon of “geometric loss of strength,” which is presumably related to an increase in the effective value of the stress concentration factor in aging and is especially marked in short aging (comparatively weak blocking of dislocations). 3. Intensification of strain hardening in strain aging is accompanied by strengthening of the tendency of strain aged technical purity iron toward localization of strain, which does not contradict the classical equations of Konsider and Hart. 4. Equations were obtained making it possible to describe the influence of strain aging on localization of strain in uniaxial tension.

Influence of strain aging on the strain-rate sensitivity of the flow stress

Previously published studies on the deformation kinetics of several fcc alloys, i.e. single crystals of Al-0.7% Mg, polycrystals of AlMg, Inconel 600, Inconel X750, NiCo, AuCu, and FeC, are cited, and two models are proposed to explain the reported observations. The calculations suggest that excess vacancies play an important role in the dynamic strain aging of the alloys and that an intermediate thermal annealing process should remove the vacancies. (BLM)

Strain ageing effects and stress relaxation in iron during shock loading

The influence of prestraining and ageing upon the stress relaxation, which follows the elastic precursor wave during shock loading of iron, has been determined experimentally. Prestraining through the Lüders strain is observed to eliminate this stress relaxation under shock loading. Suitable time-temperature ageing treatments after prestraining cause a reappearance of the shock stress relaxation. Thus the influence of prestraining and ageing upon the stress relaxation in iron is qualitatively the same as the influence of these treatments upon the upper to lower yield point drop in conventional low strain rate tensile tests. Quantitative differences between the influence of strain ageing upon the shock stress relaxation and the conventional yield drop are observed. The return of the shock stress relaxation by ageing of prestrained iron (containing both nitrogen and carbon) appears to be governed by the diffusion of carbon while the return of the conventional yield drop appears to be governed by the diffusion of nitrogen. Further, for a given ageing temperature, the critical ageing time for the return of shock stress relaxation is from one to two orders of magnitude longer than the critical ageing time for return of the conventional yield drop. The relationship of these results to the current theories of dislocation behavior in iron containing small amounts of carbon and nitrogen is discussed.