Papers by Keyword: Strain Aging

Abstract: The peculiarities of the microstructure and properties of BrBNT1.7 beryllium bronze tape samples were studied: the samples were subjected to dispersion hardening as a result of quenching in a supersaturated solid solution and aging. Friction deformation in a dry friction mode provides additional effective hardening while maintaining increased plasticity (bending-and-unbending test).

Abstract: In this paper, research on a testing method of indentation test proposed by F M Haggag is discussed first, and the experimental testing research on metallic material properties with strain aging is carried out and discussed using indentation test. The authors proposed to use indentation test to measure the properties of metallic materials with strain aging embrittlement based on experimental verification. And it provides a possibility to measure the properties of metallic materials with strain aging using nondestructive testing method.

Abstract: Tensile and impact toughness test on X100 line pipe with different pre-strain at different aging temperature were conducted to study the effect of pre-strain and aging temperature on properties of X100 line pipe. The result shows that yield strength and tensile strength of X100 line pipe would increase significantly with the introduction of pre-strain, while the impact toughness would decrease significantly. Effect of strain aging on tensile properties of X100 line pipe are more significantly. The yield strength, and tensile strength would increase significantly with the introduction of strain aging both transversal and longitudinal direction.

Abstract: Effect of grain boundary on strain ageing behaviour of Nb-bearing ULC steel sheets has been studied at the aging temperature from 70 to 220°C, using 2% pre-strained specimens with different ferrite grain sizes of 9.5μm and 183μm. Two different hardening stages were exhibited in the fine-grain specimen, whereas only a single hardening stage was shown in the large-grain specimen. The increase in YP of the first hardening stage was around 30MPa; the activation energy of this stage was estimated to be from 83 to 86kJ/mol, which is close to that of body diffusion of carbon atoms in α-Fe. The increase in YP of the second hardening stage reached 90MPa; the activation energy was 135kJ/mol, which is close to that of body diffusion of Fe atoms in grain boundary and precipitation of η-carbide. From TEM observations and nanoindentation analyses, it was inferred that the dominant mechanism could be dislocation pinning by carbon atoms for the first hardening stage, and grain boundary hardening or hardening around it for the second.

Abstract: 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.

Abstract: With the development of new steels and processing techniques, there have been corresponding advances in the fatigue performance of steels. Methods to increase fatigue performance are typically designed to produce gradients in surface properties and are based on heat treating operations, including enhanced carburizing and induction hardening, as well as surface mechanical deformation. In this paper selected examples based on recent work on deep rolling is used to illustrate the importance of the base steel properties on the final performance of surface modified materials. The degree of fatigue improvement by deep rolling, a process to mechanically deform fillet surfaces to improve fatigue resistance in cylindrical components, depends on the deformation response of the substrate to the rolling process. Recent results on the behavior of three medium carbon steel alloys deformed at temperatures up to 360 °C, are discussed. Deep rolling increased fatigue resistance, and the degree of improvement was higher when deep rolling was applied in the dynamic strain aging (DSA) temperature range rather than at room temperature. Observed variations in fatigue performance are interpreted based on fundamental deformation mechanisms and are used to present an overall perspective on approaches to increase the fatigue resistance of conventional and newly developed steels.

Abstract: A new concept is suggested that serves to explain the effects of thermomagnetic treatment. Its validity is proved via measurements of magnetic properties and electron microscopy examination of structure of soft magnetic materials after different treatments. This concept allows one to consciously choose the treatment mode aiming on improvement of magnetic properties of alloys.

Abstract: In this paper, torsion fracture behavior of drawn pearlitic steel wires with different heat treatments was investigated. Samples with different heat treatment conditions were subjected to torsion and tensile tests. The shear strain along the torsion sample after fracture was measured. Fracture surface of wires was examined by Scanning Electron Microscopy. In addition, the method of Differential Scanning Calorimetry was used to characterize the thermodynamic process in the heat treatment. A numerical simulation via finite element method on temperature field evolution for the wire during heat treatment process was performed. The results show that both strain aging and recovery process occur in the material within the temperature range between room temperature and 435 °C. It was shown that the ductility measured by the number of twists drops at short heating times and recovers after further heating in the lead bath of 435 °C. On the other hand, the strength of the wire increases at short heating times and decreases after further heating. The microstructure inhomogeneity due to short period of heat treatment, coupled with the gradient characteristics of shear deformation during torsion, results in localized shear deformation of the wire. In this situation, shear cracks nucleate between lamella and the wire breaks with low number of twists.

Abstract: The strain aging of heavily drawn pearlitic steel wires has been studied by means of electrical resistivity mearsurement. The kinetic of the early stage of strain aging after being drawn to true strain 2.89 is described by a Johnson-Mehl equation. The apparent activation energy ΔH is estimated as 31.7kJ/mol. The results indicate that the mechanism of the early stage of strain aging of heavily drawn pearlitic steel correlates with the formation of interstitial solute atoms-vacancy pairs.

Abstract: In Fe-C-Mn steels, the carbon atoms in solution can be either completely free in the iron matrix or in interaction with manganese atoms. In this context, a methodology based on the combined use of thermoelectric power and internal friction measurements was developed in order to evaluate quantitatively these two populations of carbon atoms. This methodology was used to determine the binding energy of the C-Mn dipoles and to follow the precipitation kinetics of the two populations of carbon atoms and/or their segregation kinetics to the dislocations during an isothermal treatment. Lastly, the influence of each population of carbon atoms on the strain aging of extra-mild steels was discussed.