Papers by Keyword: Precipitation Hardening

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Authors: S.S. Campos, E. Valencia Morales, H.J. Kestenbach
Authors: Yong Qing Ma, Xiao Jing Zhang, Yu Fen Liang, Guo Fang Liu
Abstract: The processing of austenite catalytic cryogenic treatment of two components of Cr-W-Mo-V high alloy medium-upper carbon steels and the effect on the retained austenite transformation and tempering hardness were studied in this paper. The results show that, the effect of austenite catalytic cryogenic treatment of Cr-W-Mo-V high alloy medium-upper carbon steel is better than that of direct cryogenic treatment after quenching, and the content of residual austenite reduced to below 5%, and the hardness improved by 1.5HRC than that of conventional quenching and tempering. The retained austenite catalytic temperature of Cr-W-Mo-V high alloy medium-upper carbon steel merely is higher than 10°C~20°C of the temperature for the highest tempering hardness. Catalytic temperature Tc can be determined by experimental method of conventional quenching and tempering of the steel, in which the microstructure feature is precipitation of M3C carbide particle of 0.01μm~0.03μm in martensite matrix, and the content of retained austenite decreases evidently. By cryogenic treatment after the austenite catalyzed the retained austenite of quenching are transformed into more martensite, and in the subsequent tempering processing the original quenching martensite and the martensite from retained austenite transformation almost will form synchronous precipitation hardening. Thus the tempering hardness improves evidently as well.
Authors: Marion Merklein, Hung Nguyen
Abstract: Aluminum alloys have great potential for lightweight construction. In order to achieve an optimized properties distribution for the forming operation and to enhance the formability of aluminum alloys, so called Tailored Heat Treated Blanks (THTB) are developed. In this context, this paper is about the local precipitation hardening of sheet metals for the application of THTB. By using a specific, short-term heat treatment via conductive heating plates the thermal induced hardening of the fast hardenable alloy AA6181PX is quantified and qualified. Considering the processibility of the local precipitation hardening for THTB, a process window for the heat treatment parameters is presented allowing a precise setting of the mechanical material properties.
Authors: Katarzyna Kubok, Lidia Litynska-Dobrzyńska, Anna Wierzbica-Miernik, Joanna Wojewoda-Budka
Abstract: Alloys of nominal composition Mg-3Zn-xCa (x = 0, 0.5, 1.0) wt.% were prepared by resistance melting and casting under a protective argon atmosphere. All specimens were examined by hardness tests during ageing at 175 °C. It was shown that calcium addition causes the increase in hardness. A detailed characterisation of microstructure of metastable phases has been carried out using transmission electron microscopy (TEM). Calcium addition resulted in much refined and more homogeneous distribution of the precipitates when compared with the binary Mg-3%Zn alloy. The age-hardening of the ternary alloy is attributed to the fine disc-shape plates lying on the basal plane of the matrix.
Authors: Z. Horita
Abstract: The process of severe plastic deformation (SPD) makes it possible to reduce the grain size to the submicrometer or nanometer range in many metallic materials. When the SPD process is applied to age hardenable alloys, it may also be possible to control aging behavior. In this study, a technique of equal-channel angular pressing (ECAP) is used as an SPD process and aging behavior is examined on the three selected Al alloy systems such as Al-Ag, Al-Mg-Si and Al-Si-Ge. The microstructures are observed using transmission electron microscopy and the mechanical properties including hardness are measured. It is shown that the SPD process introduces unusual phenomena in the precipitation process and there should be a potential for enhancement of strength over the conventional age-hardening process or for improvement of ductility while keeping the high strength.
Authors: Piotr Osuch, Tadeusz Knych, Beata Smyrak, Andrzej Mamala
Abstract: Precipitation hardening AlMgSi alloys are widely used not only as constructional material, but also a very attractive material for the manufacturing of conductors for overhead power lines. These alloys, with a mass density typical of aluminum and with relatively low resistivity, reach twice the level of mechanical properties, compared to aluminum. Semi-finished product in the manufacturing of overhead conductors is wire rod produced by the technology of the continuous casting and rolling (CCR), for example Continuus-Properzi. The entire complex of wire rod required properties (electrical, tensile, rheological, fatigue) are obtained through proper selection of the quantities of alloying elements (Si, Mg) and structure modifier (Fe, Ti) as well as the right combination of type and sequence of thermo-mechanical treatments and technological process parameters. The article discusses the physical background of opportunities to controlling the wire rod properties, taking into consideration all elements of technology for continuous casting and rolling and also thermo-mechanical treatments. In particular, article contains the presentation and analysis of investigations results identifying the structure, electrical properties and hardness of materials from particular stages of the process, refer to physical phenomena affecting the properties of the material during CCR process including the final product intended for the manufacture of wires.
Authors: S. Saha, Kanykumari Datta, Manoj Kumar Mitra, L.E. Lindgren, J. Post
Abstract: The strain induced martensite formation is known to be sensitive to the stress state [1]. The amount of martensite formed varies if the same amount of load is applied in different states of stress. For example, martensite formed is maximum in tension, minimum in compression and somewhere in between, in shear. Martensite could also originate due to elastic stress, or in absence of any mechanical energy, solely, by change in temperature (thermal martensite). Thus, it is the aim of this project to understand the different kinds of martensite that originate due to different processing paths and then, to understand how the precipitation behaviour is affected by the process of arriving at the martensite. Basically, it is to understand how the dislocation substructure varies under various stress states and thermal states, and how it affects the kinetics and type of precipitation in metastable austenitic stainless steels. This work is carried out with a high alloy, metastable and precipitation hardenable stainless steel called Sandvik NanoflexTM. Formation of strain induced martensite in semi austenitic metastable stainless steels is strongly a function of strain rate. It is also a function of stress state: in this study a planer planar shear state and an axial tensile state of stress are compared. The morphology of martensite formed in tension is different from that in shear. Predominantly sheared samples show rippled structures with ridges and valleys where as predominantly tensile deformation creates samples with planer planar laths separated by crevasse-like boundaries. The morphological difference in the martensite formed under different stress-states, creates different shape of precipitates in semi austenitic metatstable stainless steels. The predominantly sheared samples show roundish precipitates where as predominantly tensile deformed samples show precipitates with a core. Difference in the dislocation substructure is thought to be the root cause of such morphological differences in the martensite and precipitates formed through different stress states.
Authors: Yang Yang, Pi Zhi Zhao, Li Ying Zou, Rong Hui Fan
Abstract: By means of Vickers hardness tester, optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and high resolution transmitted electron microscope (HRTEM), the bake softening and precipitation behaviors of AA5182 H19 sheet for can end stock at 205°C and 249°C were investigated. All specimens at both temperatures showed recovery and bake softening phenomenon, which meaning the dislocation density and HV decreased. However, the specimens baked at 205°C showed higher recovery impediment, because the bake softening curve departed from the dynamic laws when it had less amount of recovery than the specimens baked at 249°C. The hardness was higher for the specimen baked at 205°C compared with the specimen baked at 249°C, even both specimens had the same dislocation density measured by XRD. Further observations revealed that the precipitated particles in the specimens baked at 205°C distributed along the shear bands. The precipitates were needle shape with the length of 5-15 nm and the width of 5-10 atom layers, which occurred mostly in the area with higher dislocation density. These precipitates were guessed to be Al-Mg binary phases, which could contribute to the higher hardness of the specimens baked at 205°C.
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