PSI - Issue 43

Róbert Cíger et al. / Procedia Structural Integrity 43 (2023) 312–317 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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of strength, resistance to elevated temperatures, wear, and chemical corrosion. Depending on the injection technology used and the injected medium, the individual criteria for tool steels may differ. High-alloy powder steels are used for a given application, due to the high content of carbide-forming elements ensuring high hardness and wear resistance as published by Cao et al. 2022. The production of tool steels using powder metallurgy is currently considered to be an ever-evolving progressive method of tool steel production. The process of steel production by powder metallurgy involves melting of the base materials, atomization (powder production) and subsequent sintering as published by Danninger et al. 2017, and Dunkley et al. 2019. The development of new processes and technologies such as MICROCLEAN technology enables the production of steels with a very fine microstructure containing evenly dispersed carbides, despite the high content of alloying elements. The disadvantage of powder metallurgy is the high energy consumption, but powder metallurgy is a suitable way to produce high quality tool steels that could not be produced using conventional foundry methods. The size of the carbides directly affects the abrasive resistance of the steel, as published by the author Egorova et al. 2020. The disadvantage of the presence of large carbides is the deterioration of the polish-ability of the material, which is one of the important properties of steel intended to produce parts for injection molding machines that come into direct contact with the injected medium. In addition to the size of the carbides, the hardness of the steel influences the abrasion resistance of the steel. We assume that the resistance to abrasive wear increases with increasing hardness. The dependence of hardness and wear resistance has been demonstrated as published by Zhang et al. 2022. However, an increase in the strength of steels can lead to a decrease in notch toughness as published by Moses et al. 2022. This can lead to cracks and subsequent failure of the screw by brittle fracture. A suitable method for determining the energy required for fracture initiation is to test the notch toughness with the Charpy hammer. By suitable heat treatment, it is possible to achieve microstructural changes of the material to achieve the required mechanical properties of tool steel, which will ensure trouble-free operation of injection equipment during operation. The effect of tempering temperatures on the strength and plasticity of M390 steel has clearly demonstrated the dependence of carbide growth with increasing tempering temperature as published by Wang et al. 2020. Heat treatment of tool steels such as M398 steel and M390 steel may involve cryogenic freezing to reduce residual austenite after hardening, which is considered undesirable, except for TRIP steels as published by Xu et al. 2021, and Barriobero et al. 2021. In recent years, several research teams have focused on the study of methods of h eat treatment of specific tool steels. and tempered at 200 °C, had the best resistance to chemical corrosion with the potential to disintegrate as published by Farayibi et al. 2021. They further found that the matrix around M 7 C 3 carbides and MX carbonitrides showed a high susceptibility to corrosion. 2. Experimental material and methods The sample materials used in this experiment was two special tool steels manufactured by BÖHLER, namely M390 and M398. This type of investigated steel is one of the high-alloy tool martensitic chromium steels with a high content of carbide particles. Steels are produced using powder metallurgy using the MICROCLEAN technology. The product is a special tool steel, the resulting microstructure of which has very fine carbides evenly distributed throughout the volume of the material. Due to the production method and chemical composition, the steel provides extremely high resistance to mechanical wear as well as corrosion resistance. The main concept for increasing macro-hardness is the high content of MC and M 7 C 3 carbides. These steels have their use in the plastics industry, specifically to produce screw injection molding machines. It is gradually heated and melted to the injection temperature depending on the type of plastic polymer in the temperature range from 160 °C to 250 °C, depending on the selected type of injected material. The injection of plastic takes place by means of a straight movement of the screw to the front position, the back flow cylinder prevents the backflow of the molten plastic granulate. The investigated material M398 is a newly developed material, the task of which will be to replace the material M390. Other properties that predetermine M398 steel for the production of screws include, high dimensional stability during heat treatment, good resistance to chemical corrosion, the possibility of polishing to a mirror finish. Table 1 shows and compares the values of the prescribed chemical composition from BÖHLER, and the chemical composition measured by the authors using a Spectrolab Jr. chemical analyser. The device works on the principle of the optical method, it is suitable for conductive samples. The chemical composition is determined based on the analysis