Mariusz Adamczyk

The article presents the results of hot rolling tests on a feedstock composed of S355J2 and NANOS-BA® steel layers into flat bars. The study was carried out to assess the susceptibility of the materials to create S355J2/NANOS-BA clad plates in the hot rolled bonding process. The subject of the article are the phenomena occurring during the connection of well-weldable S355J2 structural steel with ferritic-pearlitic microstructure with nano-structured, non-weldable NANOS-BA® steel with nanobainitic microstructure in the process of hot rolling and heat treatment. The microstructure and selected strength properties of high-strength clad plates are described after hot rolling with integrated inter-operational annealing at 690°C for 4 h and after additional isothermal annealing at 210°C for 120 h. As a result of hot rolled bonding process with two-stage heat treatment process a durable combination of S355J2 and NANOS-BA® steels with high mechanical properties was obtained, including: Rm>1199 MPa and A=14%, without microscopically visible cracks in the joined plane. High-strength laminated flat bars combining the features of the component layers such as high strength, ballistic and abrasive resistance, while maintaining good plasticity, weldability and relatively low production costs may be the answer to the current industry demand.

W artykule przedstawiono wyniki badań wpływu zróżnicowanej szybkości chłodzenia próbek w zakresie temperaturowym przemiany perlitycznej na rodzaj i morfologię struktury oraz na twardość stali szynowej w gatunku R350HT. Parametry temperaturowo-czasowe eksperymentów zaprojektowano w oparciu o kinetykę przemian fazowych austenitu, opracowanej z zastosowaniem badań dylatometrycznych. Warunki przyśpieszonego chłodzenia z szybkością w zakresie 1–10 °C · s–1 po odkształceniu plastycznym próbek na gorąco symulowano z zastosowaniem urządzenia Gleeble 3800. Wyznaczono relację pomiędzy wyjściową mikrostrukturą i zmienną szybkością chłodzenia a odległością między płytkami cementytu w perlicie S0 oraz twardością stali szynowej R350HT. Dokonano identyfikacji krytycznych parametrów chłodzenia, zapewniających uzyskanie odpowiedniej twardości, która jest wymagana dla obszaru przypowierzchniowego główki szyny ze stali R350HT, przy zachowaniu mikrostruktury drobnopłytkowego perlitu.

The article describes to design the parameters of hot rolling and heat treatment technology in a way that would allow for permanent bonding of S355J2 and NANOS-BA® steel into one high-strength clad plates. In the article, guidelines for the hot rolling process of clad plates with two-stage heat treatment were described, which were then verified in a semi-industrial technological line. The materials obtained in this way in different initial states were subjected to metallographic and strength tests. Based on three technological variants of the process, S355J2/ NANOS-BA® clad plates were produced. After additional heat treatment, a nanobainitic microstructure of high strength and ballistic and abrasion resistance was created in the applied layer, which indicates the possibility of using this type of clad plate in the armaments, machine building, or construction industry.

The article presents the results of controlled cooling experiments after austenitising a V36 section made of structural steel S480W. The experiments involved variable cooling intensity affecting the cross-section of the test element. The tests aimed to investigate the possibility of modifying the microstructure and uniformly increasing the mechanical properties of steel sections with varied cross-sectional wall thickness in relation to free-air cooling. The research work involved the determination of section-related cooling characteristics identified using various parameters of compressed air blown from nozzles onto selected surfaces of the section. The accelerated cooling tests led to the formation of a fine ferritic-pearlitic microstructure having ferrite grain size Dα restricted within the range of 6.8 μm to 6.5 μm. In addition, the tests resulted in the obtainment of uniform hardness distribution in cross-section, an increase in yield point Re and tensile strength Rm (restricted within the range of approximately 40 MPa to 60 MPa) while maintaining similar elongation.

The article presents the results of physical experiments consisting in the rolling of layered plates (clad plates). The experiments involved two types of two-layered flat bars, i.e. S235JR and X20Cr13 as well as S235JR and X5CrNi18-10. The experiment resulted in the development of a technology for the fabrication of layered flat bars made of structural steel S235JR, corrosion-resistant steel X20Cr13 and austenitic acid-resistant steel X5CrNi18-10. Microstructural observations were performed using a light microscope (LM) and a scanning electron microscope (SEM). The observations revealed the possibility of obtaining permanent joints through hot rolling and the possibility of applying steel grades S235JR, X20Cr13 and X5CrNi18 in the fabrication of layered plates.

The article presents the technology of drawing thin wires made from selected iron-based alloys for use in additive manufacturing using WAAM method. The final technology of wire production was developed with the use of a drawing bench, depending on the deformed material. Steel wires with a diameter of 1 mm and mechanical properties adapted to the 3D printer were produced.

Part 1 of the article presents the technological path of producing semi-finished products for wires constituting input material in additive technologies. On the basis of the developed chemical compositions of experimental Fe-based alloys, laboratory ingots with a square section of 120×120 mm / 130×130 mm were produced, which were then hot rolled into flat bars. In order to select the physical parameters of the drawing tests, numerical modelling of the process was performed. As a result of the simulations, it was found that the calculated drawing force exceeds the capabilities of the experimental drawing machine and for this reason, hydrostatic extrusion was used to produce bars intended for drawing wires. The hydrostatic extrusion method was used to make bars with a diameter of 5 mm from three tested materials, while three experimental steels showed insufficient susceptibility to extrusion at high pressure and cracked at various strain values. An analysis of possible causes of bar breakage during extrusion was carried out on the basis of the results of microstructure examination.

The article contains results of research and analyses concerning application of nanostructured bainitic steel in the form of plates for manufacturing of armour components. The presented results of examination of microstructure and properties include a wide range of laboratory experiments and industrial tests, which resulted in the achievement of the assumed functional properties. In the period of 2017-2021, a scientific and industrial consortium consisting of Łukasiewicz – Institute of Ferrous Metallurgy (leader); WITPiS, Tarnów Mechanical Works, Alchemia and Heatmasters Poland carried out a project funded by the POIR 04.01.04 programme aimed to develop the design and to manufacture an observation and protective container with a specified resistance to penetration by armour-piercing projectiles and with a lower mass of steel armouring in relation to that currently produced. The aim of the project was achieved by using armour plates made of nanostructured bainitic steel (nanobainitic), which are characterised by high resistance to high-energy impact concentrated in a small area. The technological tests carried out in the project mainly concerned the development of a new container and industrial technology of armour plates production and their application in the armour of this container. Based on the results of investigation of the semi-industrial scale material, the optimum chemical composition for industrial scale melting and casting was determined. An industrial technology for the production of plates of nano-structured bainitic steel was developed, which includes the following processes: smelting and casting, preliminary heat treatment and ingot hot processing, as well as hot rolling, final heat treatment, and surface treatment. A test batch of the material in the form of 1500×2470 mm armoured plates was fabricated under industrial conditions. The final result of the project is a container armoured with bainitic nanostructured steel plates with implementation documentation and a technology for producing armoured plates from this steel under the technical and technological conditions of domestic steel manufacturers.

The article presents the results of studies on the impact of accelerated cooling after the austenitisation of bars with a diameter of 180 mm made of structural steel S355J2 on the microstructure and mechanical properties. The aim of the research was to develop basic parameters of heat treatment technology using the heat remaining in the bars after hot rolling. Tests of heating and cooling of the bars were carried out in devices included in the line for semi-industrial hot rolling simulation, controlled cooling and heat treatment (LPS-B) at Łukasiewicz – IMŻ. The following cooling operations were performed after bar austenitisation: cooling in still air, controlled cooling with air blow, water-air mixture, water spraying and immersion cooling in water. Based on the research and analyses, it was found that the use of optimised variants of accelerated cooling leads to the modification of the microstructure and to grain refinement, without the formation of undesirable phase components. Consequently, the mechanical properties (yield strength and impact toughness) increase above the level obtained as a result of cooling in still air, including standard normalisation. Preliminary tests of accelerated air stream cooling of bars were carried out after austenitising in industrial conditions. The final criterion for selecting and implementing the type of technology for heat treatment of bars using heat after hot rolling in Huta Bankowa’s technical and technological conditions will be the assessment of the economic efficiency of the project.