The aim of experiment was to analyse the structural transformations and changes in mechanical properties of K720 steel during heat treatment (quenching). Three types of cooling medium were selected. The heating parameters and subsequent delays at the recrystallisation temperature were the same for all samples and were observed in a laboratory furnace. Water with the highest cooling capacity was selected as the benchmark cooling medium. Subsequently, the hardening oil TK – 46 was used. Sunflower oil was selected as the last quenching medium, which can be considered an ecological replacement of quenching oil with possibility of biological disposal. The microstructure and microhardness of individual samples were subjected to a metallographic evaluation and evaluated according to ČSN EN ISO 6507, respectively. The impact toughness analysis was performed according to the ČSN EN ISO 148-1 and a three-point bending test was performed according to ČSN EN ISO 7438. This test specifies a method for determining the ability of metallic materials to undergo plastic deformation in bending. The bend test includes subjection of round, square, rectangular or polygonal cross-section to plastic deformation by bending, without changing the direction of loading, until the specified angle of bend is reached.

The goal of this paper is an evaluation of research aimed at corrosion and mechanical resistance of the so-called duplex system applied to a steel sheet. This system consists of a metal coating applied by hot-dip galvanising, to which an acrylic, water-soluble paint is commonly applied (commonly available on the Czech market) using standard technology in an air stream. For the purposes of the corrosion resistance comparison, one set of test specimens is provided only with a hot-dip galvanised coating. The mechanical resistance of applied anti-corrosion protection was determined by means of a pull-off adhesion test (according to the ČSN EN ISO 4624 standard), as well as an indentation test (according to the ČSN EN ISO 1520 standard). The corrosion resistance tests were then conducted in a salt spray environment (according to the ČSN EN ISO 9227 standard) for the samples not damaged by mechanical tests. Based on the obtained results, in general, waterborne paints with high dry matter content, low specific gravity and high zinc phosphate content, which are applied in several thinner layers, can be recommended.

The paper content is focused on the various evaluation methods of mechanical pre-treatment of hot-dip galvanized surface performed in order to increase the organic paint adhesion (both synthetic and waterborne). Emphasis was placed on low volatile organic compounds (VOC) values in coating systems. Corrosion degradation of the tested coatings was also monitored. The mechanical surface pre-treatment was performed using a standard technology, so-called sweeping, with synthetic corundum with F40 grain size (these samples served as a standard). Alternative methods that can be used in operations without blasting equipment were also investigated. These included regrinding with two different grain sandpapers (P40 and P100) and regrinding with a corrosion resistant steel brush (wire diameter 0.3 mm). The surface texture was evaluated in accordance with the ČSN EN ISO 4287 standard. Corrosion-mechanical resistance was evaluated by a pull-off adhesion test (according to the ČSN EN ISO 4624 standard) and in a salt spray environment (according to the ČSN EN ISO 9227 standard). Based on the obtained results, mechanical pre-treatment with a corrosion resistant steel brush and possibly P100 grit sandpaper can be recommended, as pre-treatment with these tools showed statistically the best corrosion-mechanical properties.

The paper is focused on analysing the pearlitic steel phase transformations and their influence on the mechanical properties. The intention is to perform a detailed analysis of the heat treatment process using the exact heating temperature and chemical composition to achieve the optimal mechanical properties of the tool. The key area is monitoring and regulating the heat treatment. This technology is constantly undergoing an optimisation process and is an effort to introduce new trends in monitoring phase transformations and processes. The use of non-destructive methods is an adequate tool. The principle is to determine the exact structural phase at a given moment, which can be very difficult when a complex shaped part is heat treated. Which precludes the use of some other methods of phase transformation analysis. Specifically, the determination of the exact moment of finish of the austenitisation process is eminent. The monitoring of these processes will be ensured by both a non-contact pyrometer and also by the AE method with an adequate sensor and waveguide. The resulting structural phases formed after the heat treatment will be evaluated by electron microscopy, followed by the analysis of the mechanical properties of selected steels.