It is demonstrated that during secondary refining at the ladle furnace the carbon content of steel and the residence time of the metal in the
ladle exert a significant impact on the residual content of non-metallic inclusions (NMI) in steel. Mathematical calculations showed that
the dynamic forces have minor effect on the motion of small sized NMI, making it difficult to penetrate deep into the slag.
The modification of the chemical composition of non-metallic inclusions by rare-earth elements in the new-developed microalloyed steels was discussed in the paper. The investigated steels are assigned to production of forged elements by thermomechanical treatment. The steels were melted in a vaccum induction furnace and modification of non-metallic inclusions was carried out by the michmetal in the amount of 2.0 g per 1 kg of steel. It was found that using material charge of high purity and a realization of metallurgical process in vacuous conditions result in a low concentration of sulfur (0.004%), phosphorus (from 0.006 to 0.008%) and oxygen (6 ppm). The high metallurgical purity is confirmed by a small fraction of non-metallic inclusions averaging 0.075%. A large majority of non-metallic inclusions are fine, globular oxide-sulfide or sulfide particles with a mean size 17 µm2 . The chemical composition and morphology of non-metallic inclusions was modified by Ce, La and Nd, what results a small deformability of nonmetallic inclusions during hot-working.
The paper presents the results of research on the impact of impurities in the feed ingots (master heat) on the precipitation of impurities in
the ATD thermal analysis probe castings. This impurities occur mostly inside shrinkage cavities and in interdendritic space. Additionally,
insufficient filtration of liquid alloy during pouring promotes the transfer of impurities into the casting. The technology of melting
superalloys in vacuum furnace prevents the removal of slag from the surface of molten metal. Because of that, the effective method of
quality assessment of feed ingots in order to evaluate the existence of impurities is needed. The effectiveness of ATD analysis in
evaluation of purity of feed ingots was researched. In addition the similarities of non-metallic inclusions in feed ingots and in castings
were observed.
This paper presents the findings of fatigue strength tests of 15CrNi6 steel following low-pressure carburizing and oil quenching, subjected to cycles of one-sided three-point bending. The fatigue fractures were compared with the results of fatigue strength studies of 16MnCr5 steel following low-pressure carburizing and nitrogen quenching. The fatigue tests for 16MnCr5 steel were conducted as part of a high-cycle resonance test, with a pendular bending load. The study also involved an analysis of the effects on non-metallic inclusions in the structure on the mechanism of fatigue destruction. The inclusions were found to initiate fatigue cracks. In both cases, a similar method of a fatigue fissure initiation was observed, independent of the study method or specimen material.
In this work, the authors proposed a modification of the working space one-strand tundish adapted for slab casting process. Numerical simulations of liquid steel flow in the considered flow reactor were performed. The tundish is equipped with a dam with a multi-hole filter. Two variants of the filter hole arrangement were tested and their effect on the liquid steel flow hydrodynamic structure in the tundish was examined. The computer calculations results were verified by performing experiments on the water model. The result of numerical and physical simulations an RTD (Residence Time Distribution) type F curve was generated, which define the transition zone between the cast steel grades during the sequential casting process. The results of the researches showed that the modification of a dam with a multi-hole filter affects on the formation of the liquid steel flow hydrodynamic structure and the transition zone. Furthermore, examinations of the liquid steel refining ability in the considered tundish were carried out. The influence of the filter holes arrangement on the non-metallic inclusions flotation process to the slag phase and liquid steel filtration processes was checked. Numerical simulations were performed in the Ansys-Fluent computer program.
Non-metallic inclusions found in steel can affect its performance characteristics. Their impact depends not only on their quality, but also,
among others, on their size and distribution in the steel volume. The literature mainly describes the results of tests on hard steels,
particularly bearing steels. The amount of non-metallic inclusions found in steel with a medium carbon content melted under industrial
conditions is rarely presented in the literature. The tested steel was melted in an electric arc furnace and then desulfurized and argonrefined.
Seven typical industrial melts were analyzed, in which ca. 75% secondary raw materials were used. The amount of non-metallic
inclusions was determined by optical and extraction methods. The test results are presented using stereometric indices. Inclusions are
characterized by measuring ranges. The chemical composition of steel and contents of inclusions in every melts are presented. The results
are shown in graphical form. The presented analysis of the tests results on the amount and size of non-metallic inclusions can be used to
assess them operational strength and durability of steel melted and refined in the desulfurization and argon refining processes.
The effect of CaSiAl modification (43-49% Ca, 43-48% Si, 2% Al) on the non-metallic inclusions and mechanical properties of cast lowcarbon steel is discussed. Tests were carried out on the cast steel with 0.2% C and micro-additives of V and Nb, used mainly for heavy steel castings (e.g. slag ladles). The modifier in an amount of 1.5 and 3 kg / Mg was introduced to the liquid steel before tapping the metal into a ladle. Test ingots of Y type and a weight of 10 kg were cast and then subjected to a normalizing heat treatment. Using light microscopy and scanning electron microscopy, qualitative and quantitative evaluation of the non-metallic inclusions present in as-cast samples was carried out. Additionally, tests of mechanical strength and impact strength were performed on cast steel with and without the different content of modifier. It was found that increasing the modifier addition affected impact strength but had no significant effect on tensile strength and yield strength. The material with high impact strength had the smallest area fraction of non-metallic inclusions in the microstructure (0.20%). The introduction of modifiers changed the morphology of non-metallic inclusions from dendritic to regular and nodular shapes.