Bartłomiej Walnik

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.