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Properties of coated tools for improved performances
No full textThe degradation of materials, connected to ageing and wear, can be limited by suitable treatments aimed at the increase of surface properties Among the surface modification techniques thermal spraying processes allow a lot of advantages improving the performance and extending the life of materials and components. The convenience for the substitution of nodular cast iron with coated steel for the manufacture of rolls to be employed in a rod mill plant was studied by means of disk on disk wear tests on plain carbon samples coated with the fuse and spray technology, using 7 different type of nickel or cobalt based powders, comparing their wear resistance with the behaviour of nodular cast iron specimens. On the basis of the wear tests, the most promising coating materials were applied to steel rolls and their behaviour and duration on a rod rolling plant were compared with those of nodular cast iron rolls. The rolls coated with nickel based alloy admixed with WC-Co powder reached the best performance, with a duration about 40 % higher than the cast iron ones
Influence of Increasing Notch Radius on Properties of Nitrided Hot Work Tool Steels
No full textTool steels are a very large group of complex alloys which have evolved for many diverse hot and cold forming applications and they constitute a class of strategic materials. Hot work tool steels fall into groups which have either chromium, tungsten, or molibdenum as the major alloying element. The medium carbon and the relatively high alloy content make these steels air hardenable and resistant to impact and softening during repeated exposure to hot working operations.
In this work the impact properties of Charpy U-notch samples with increasing notch radius are presented and discussed. The samples were manufactured with AISI HI3 hot working tool steel and a modified composition, and were tested in the as quenched state and after nitriding. After the impact test, the microhardness properties were evaluated and correlated to the heat treatment. The notch radius strongly affect the impact resistance of the samples, namely at the lowest values. The microstructure details and the fracture morphology were observed by light microscopy and SEM
Study of innovative coatings for hot working tools
No full textThermal spraying processes have many advantages that help improve the performance and extend the life of materials and components. In the present paper the properties and wear behaviour of plain carbon specimenscoated with Ni or Co based alloy powders have been studied for the coating of tools employed in hot working applications, e.g. rolls in a rod mill plant. The morphologies of the different coating layers were very similar, showing the presence of porosity and inclusions, especially at the interface with the coated material, however their influence on the wear behaviour of the specimens was negligible. All the Ni based alloysshowed similar behaviour and satisfactory wear resistance, although small changes in chemical composition induced different hardnesses in the coating layers. The best wear resistance was observed with harder specimens. The Co based powder did not allow the formation of layers with hardnesses high enough to provide good wear resistance. When the Co based powder was mixed with a Ni based powder, the wear behaviour proved disappointing in applications involving rolling and sliding
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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