Microstructure And Mechanical Properties Of A Cold-Work Tool Steel Produced Via Electron Beam Melting (EBM)

Electron Beam Melting (EBM) is one of the most promising techniques within Metal Additive Manufacturing (AM) strategies, which presently is for the manufacture of high execution segments for the aviation and clinical businesses, generally. Among the modern applications imagined for the eventual fate of EBM, the creation of high carbon prepares for the tooling business is of extraordinary interest. In this study, martensitic highly alloyed (Cr-Mo-V) cold-work tool steel was produced by EBM. A suitable heat treatment was proposed in order to obtain an optimal microstructure, which was studied by means of optical and scanning-electron microscopy. The performance of the material was evaluated based on the hardness achieved and the abrasive wear resistance of the material processed through EBM when compared with that of the conventionally produced state.

Microstructure And Mechanical Properties Of A Cold-Work Tool Steel Produced Via Electron Beam Melting (EBM)

Electron Beam Melting (EBM) is one of the most promising techniques within Metal Additive Manufacturing (AM) techniques, which currently is for the fabrication of high performance components for the aerospace and medical industries, mostly. Among the industrial applications envisioned for the future of EBM, the fabrication of high carbon steels for the tooling industry is of great interest.In this study, martensitic highly alloyed (Cr-Mo-V) cold-work tool steel was processed by EBM. A suitable heat treatment was proposed in order to obtain an optimal microstructure, which was studied by means of optical and scanning-electron microscopy. The performance of the material was evaluated based on the hardness achieved and the abrasive wear resistance of the material processed through EBM when compared with that of the conventionally produced state.

Influence of Chromium and Niobium on the Press-Hardening Process of Multiphase Low-Alloy TRIP Steels

Press-hardening is an intensively developing forming technology which is mainly used for the production of car body parts. Because it is a hot forming technology, small forming forces can be utilized and, due to the lower spring-back effect, more accurate products are achieved. In car bodies, materials with high energy absorption and a sufficient hardening coefficient are mainly used in impacted parts. One of these materials is TRIP multiphase steels with different chemical composition. In these steels, it is possible to achieve an ultimate strength up to 1000 MPa with the ductility of 20-30%. In order to achieve the desired properties, it is necessary to select a suitable heat treatment that allows to achieve a multiphase structure. Phase transformations and mechanical properties are influenced by the use of suitable alloying elements. Three low-alloy, multiphase TRIP steels with different chemical compositions with a carbon content of 0.2% were chosen for the experimental program. The first steel was alloyed only with manganese and silicon, in the second niobium was added, and in the third the influence of chromium on increase of hardenability and strength was investigated. Press-hardening was performed in a heated forming tool. To describe the effect of the cooling rate, the forming was carried out in a tool at room temperature and after preheating to 425°C. The influence of holding time in the tool at 425°C to support the formation of bainite and retained austenite stabilization was also investigated. Mixed ferritic-bainitic-martensitic structures with some retained austenite content were obtained.

Choosing a Suitable Heat Treatment Regime for Stress-Relief and Microstructure Stabilization of Ti6Al4V Alloy 3D-printed by SLM Method

During the processing of Ti6Al4V alloy by a 3D printing method SLM (selective laser melting), high internal stresses are developed in the material as a result of high temperature gradients between microvolumes of the powder melted at a given time and the already solidified material. Cooling rates thus reach up to the order of 108 °C·s-1. At such rates, a diffusionless martensitic transformation occurs, which also contributes to internal stresses in the material. High internal stresses can be a problem already during production; they can manifest themselves by cracking of products, deformations of thin parts, etc. Even in defectless products, internal stresses negatively affect their properties; in particular, they reduce ductility. Therefore, it is desirable to include a heat treatment after the 3D printing, which would reduce the stresses and transform the metastable martensitic structure into a stable one. As a result of the heat treatment, the ductility increases at the expense of strength. The subject of this paper is to find such heat treatment regime that provides the best combination of mechanical properties.

Investigation of Size Effects Due to Different Cooling Rates of As-Quenched Martensite Microstructures in a Low-Alloy Steel

Martensite transformation is a complex mechanism in materials that is classically initiated by a suitable heat treatment. This heat treatment process can be optimized based on a better understanding of the physical mechanisms on the length scale of several prior austenite grains. It is therefore appropriate to consider individual process steps of heat treatment in isolation. The aim of this study is to characterize the microstructural size changes caused by a variation of the cooling rate applied during the quenching process. For this purpose, individual martensitic microstructures from different heat treatments are analyzed using the electron backscatter diffraction (EBSD) method. With special orientation relationships between the parent austenite and martensite, the structure of the prior austenite grains and the close packet plane packets can then be reconstructed. The influence of the heat treatments on these characteristics as well as on the martensite blocks is thus quantified. No significant influence of the quenching rate on the sizes of martensite blocks and packets could be found.

Determination and Improvement of the Postharvest Storability of Little Mallow (Malva Parviflora L.): A Novel Crop for a Sustainable Diet

Little mallow (Malva parviflora L.) has been traditionally used as an alternative food source. To the authors’ knowledge, there is no available published information about the postharvest storability of little mallow. This study was conducted in three steps. It aimed to determine the postharvest storability of little mallow leaves and to improve its storability using different strategies. First, the effects of four different storage conditions on the storability of little mallow leaves were tested to determine the most favorable conditions for further studies: 5 ± 1 °C and 95% relative humidity (RH); 9 ± 1 °C and 95% RH; 13 ± 1 °C and 95% RH; and 24 ± 1 °C and 55% RH as control. Preliminary experiments suggested that the best temperature and RH combination is 9 ± 1 °C and 95% RH. Hence, the effects of hot water dipping (HWD) were tested at three different temperatures (40, 45, and 50 °C) for two different durations (60 and 120 seconds); the results suggested that the 40 °C treatment is the most suitable heat treatment for improving the storability of mallow. The final experiments were conducted with 15 different treatments, including HWD, eco-friendly edible bio-materials, modified atmosphere packaging, and ultraviolet radiation. Results showed that low-density polyethylene (LDPE) (60 × 60 cm; thickness, 50 μ) and polypropylene (PP) (35 × 50 cm; thickness, 35 μ) packaging provide the highest efficacy for preserving overall quality. The edible quality of little mallow can be extended to 15 days with PP and 12 days with LDPE. However, both materials caused an abnormal odor after that time. Further studies involving additional edible coatings are necessary to determine if the storage duration of little mallow leaves could be extended.

Magneto-Transport Properties in LaMnO3 Thin Films on a-SiO2 Substrates Produced by Metal Organic Decomposition Method

We have studied the magneto-transport properties in LMO thin films on a-SiO2 substrates produced by the metal organic decomposition (MOD) method. LMO thin films have been prepared by the MOD method in the 100 % O2 gas atmosphere on different heat treatment conditions. Although LMO single crystal is an antiferromagnetic insulator, LMO thin films we have produced in the 100 % O2 gas atmosphere by use of the MOD method shows the ferromagnetic metal properties for suitable heat treatment conditions. We consider that the excess of O2- ions in LMO thin films produced in the 100 % O2 gas atmosphere induces the strong hole self-doping into those and changes to ferromagnetic metal. The quantity of excess O2- ions in LMO is sensitive to the heat treatment conditions of the LMO production, especially the temperature, time and atmosphere gas. We have obtained the coercive forces from the magnetic field dependence of magnetoresistance. Based on the temperature dependence of the coercive forces, we have estimated the Curie temperature of LMO thin films.

Influence of Site Conditions and Quality of Birch Wood on Its Properties and Utilization after Heat Treatment. Part II—Surface Properties and Marketing Evaluation of the Effect of the Treatment on Final Usage of Such Wood

This work is a follow-up contribution to the characteristics of Betula pendula (silver birch) wood from different habitats and the impact of the subsequent heat treatment. Specifically, it focuses on the surface properties of birch wood in the form of veneers, namely color, hardness, roughness and wetting, and in particular on the marketing evaluation of the attractiveness of colored birch wood and, thus, its possible use in practice in the Czech Republic. Three heat treatment steps at 170, 190 and 200 °C were used. The resulting values of the properties of the treated birch veneers were compared with the untreated reference veneers and also with beech veneers. These properties were the wood density, the colorimetric parameters, the roughness parameters, the wetting parameters, the hardness and density, and none of the parameters studied showed negative changes due to the temperature adjustment. Overall, both in terms of properties and in terms of marketing appraisal, there is the potential for birch to replace, for example, beech, especially in the furniture industry, by application in the form of heat-treated veneers after suitable heat treatment. The conclusions of the marketing analysis resulting from the questionnaire survey conducted on a sample of respondents show the significant preference for the heat-treated birch wood compared to reference birch samples without heat treatment.

Microstructure of Built Part Obtained by Powder Bed Fusion Process with Metal

The influence of various process parameters on the building of maraging steel powder by the selective laser melting (SLM) processes is investigated. The microstructure in the built part was observed and the influence of the heat treatment was evaluated. As results, the depth of solidified layer was higher than that of deposited metal powder, and its value was influenced with the process parameters. The microstructure in the boundary between the built part and the substrate was quite different from the built part even if the suitable heat treatment was performed.