To optimize CaF2 content in highly basic CaO-18%Al2O3-SiO2-10%MgO-CaF2 (%CaO/%SiO2=6, denoted as C/S=6) refining slags used for the production of Al-killed duplex stainless steel with high ...cleanliness demand, the effect of CaF2 content on the viscosity and refining ability of the slags were studied and compared with typical CaF2-free highly basic CaO-30%Al2O3-SiO2-10%MgO (C/S=6) slag. The effect of CaF2 addition in decreasing slag viscosity becomes less obvious with increasing temperature and CaF2 content. When CaF2 content exceeds 10%, slag viscosity only marginally decreases with further increasing CaF2 content. Both monoxide-CaO and monoxide-MgO phases are precipitated in all the CaF2-bearing slags. CaF2 addition slightly increases monoxide-MgO precipitation, but dramatically decreases monoxide-CaO precipitation. Viscosities of the CaF2-bearing slags were also theoretically calculated and good agreement with the measured values was observed. Moreover, the 6% CaF2-bearing slag has very close viscosities above 1833 K but much lower viscosities below 1833 K, compared with the CaF2-free highly basic slag. Further evaluation of the 6% CaF2-bearing slag on steel cleanliness confirms that 6% CaF2 addition is sufficient for the highly basic CaO-18%Al2O3-SiO2-10%MgO-CaF2 (C/S=6) slag. The mechanism of CaF2 in decreasing the viscosity of CaF2-bearing slags was discussed from the viewpoints that CaF2 behaves as a network breaker and that CaF2 suppresses the precipitation of solid phases. The first aspect was identified to play a much greater role in decreasing slag viscosity.
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•Complex calcium aluminate NMI decomposes at 900°C, with delayed transformation kinetics (120+150min).•Void formation at 900°C with CaS and MnS NMIs possibly due to phase ...transformation and atmospheric reaction.•Steel matrix flowing onto spinel-CaS and MnS NMIs at 900°C is attributed to steel softening during heat treatments.•Void formation and crack initiation around NMIs may be due to hydrogen embrittlement under extreme conditions.•HT-ESEM is suitable for in-situ high-temp NMI imaging but limited by steel matrix flow and partial NMI coverage.
The kinetics of solid-state reactions involving non-metallic inclusions (NMIs) in steel is a topic of growing interest due to the need to understand the effects of heat treatments on NMI composition and stability. In this study, a High Temperature Environmental Scanning Electron Microscope (HT-ESEM) is utilized to conduct in-situ observations of various types of NMIs, including calcium aluminate complex, CaS, MgAl2O4-CaS, MnS, and TiN, in steels at temperatures of 800 °C and 900 °C for different holding times. The observed morphological variations in the NMIs indicate a decrease in the fractions of CaS and MnS, promoting void formation and ferrite–austenite phase transformation. To estimate the NMI reactions with the residual atmosphere in the sample chamber during experiments, HT-ESEM-driven thermodynamic calculations have been performed using FactSage 8.2 software. These calculations provide valuable insights into the interpretation of the experimental data, facilitating a better understanding of the complex NMI reactions in steel.
•A fatigue strength assessment procedure for steels with inclusions is proposed.•Such a procedure implements a defect content analysis and the area-parameter model.•The multiaxial critical ...plane-based criterion by Carpinteri at al. is also implemented.•A return period optimisation, in terms of fatigue strength estimations, is performed.•An experimental campaign is analysed to evaluate the accuracy of the above procedure.
In the present paper, a procedure for fatigue strength assessment of high strength steel (AISI 4140) containing non-metallic inclusions (NMIs) is proposed. Such a procedure implements: (i) a defect content analysis, (ii) the area-parameter model, and (iii) the multiaxial critical plane-based criterion by Carpinteri at al. According to the defect content analysis, the distribution of NMIs is determined in two cross-sections perpendicular to the maximum principal stress directions under normal and shear uniaxial cyclic loadings. The return periods, obtained optimising the accuracy of the procedure in terms of fatigue strength estimation, are determined by taking into account five different prediction volumes. The results achieved through the proposed procedure are compared with both the experimental data and the results obtained employing the Carpinteri et al. criterion without optimisation.
Still existing scientific, technical and technological developments to improve the quality of welded joints of metal pipe structures contain contradictions and uncertainty about the effects of ...alloying elements, such as molybdenum, mechanical and visco-plastic properties, as well as metallographic component joints. All this indicates the need for a systematic study of these problems for the development of rational metallurgical and technological measures to significantly improve the technological and corrosion-mechanical properties of weld metal. Metallographic studies, using laboratory equipment with high identifying ability, found that the doping of weld metal with molybdenum in the amount of 0.2-0.4% causes fragmentation of ferrite-pearlite structure, including carbides Mn and Fe, and also reduces the number and size of non-metallic inclusions – sulfides, oxides and silicates. Moreover, non-metallic inclusions have a dispersed appearance, which promotes plasticization of the structure, which directly increases the viscous-plastic characteristics and resistance of the metal joints to crack formation. Based on the results of metallographic research, the optimum content in the weld metal of the alloyed element – molybdenum, which is 0.2-0.4%, is determined.
•TiN inclusions accelerate the oxidation process of steel.•TiN inclusions act as the nucleation site for the internal oxides.•TiN inclusion stringers induce the spall fracture of oxide scales.
The ...effects of TiN inclusions on the oxidation behavior of modified stainless steels have been investigated systematically in this study. It was found that the oxidation rate of steel with TiN stringers is almost seven times faster than the clean one during the homogenized treatment. In the oxidation layers, the TiN stringers induce the spall fracture and facilitate the air permeation. At the oxidation interface, the TiN inclusions act as the nucleation sites for the oxides and promote the internal oxidation. The air permeation and internal oxidation causes the severe oxidation of modified austenitic stainless steels.
The aluminum oxide-coating on cemented carbide tools used for metal cutting have been regarded as inert during cutting of steels. Because diffusional dissolution is not possible. Chemical degradation ...of aluminum oxide coatings is often overlooked, especially in the presence of ambient oxygen and non-metallic inclusions. High-pressure diffusion couples, advanced microscopy, and thermodynamics are used to investigate and predict the chemical degradation of aluminum oxide-coated tools. During interactions with steel and different combinations of inclusions with and without ambient oxygen. The results show that alumina is resistant to chemical degradation by steel in the absence of oxygen. However, this is not the case when oxygen and non-metallic inclusions are present. These experiments and microscopy together with the thermodynamic calculations allow for the creation of a method and guidelines for chemical wear modeling and steel inclusion engineering when machining with aluminum oxide-coated tools.
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•Ex-situ experiment shedding light on previous contradicting in-operando results.•Overestimated inertness of alumina (Al2O3) coated tools exemplified.•Chemical degradation of alumina coated cutting tools explained.•Method of understanding and predicting interactions between alumina coated tools, steels, incisions, and air proposed.
The evolution of non-metallic inclusions in liquid steel involves a series of processes, including nucleation, growth by diffusion and Ostwald ripening, growth by collisions, floating up and removal ...of relatively large inclusions, as well as pushing and engulfment of remaining inclusions during solidification. All the evolution processes occur uniquely at the interface between inclusions and liquid steel. Therefore, interfacial properties between inclusions and liquid steel, such as interfacial energy and contact angle, play a crucial role in the evolution of inclusions, thus determining the inclusion characteristics. To effectively control the inclusion characteristics, the role of interfacial properties in the evolution processes of non-metallic inclusions is systematically reviewed in this work, based on theoretical analysis and published experimental results. In the early and middle stages of deoxidation, inclusions should have as high interfacial energy or contact angle as possible to enhance inclusion removal. In the later stage, however, the interfacial energy should be decreased as much as possible to weaken the clustering and pushing of inclusions, favoring the formation of small-sized and uniformly-distributed inclusions. To optimize the characteristics of Al2O3 inclusions, which are the most common in steel, several control strategies are proposed.
Open-cell ceramic foams are widely used as filters for the purification of molten metals due to their high permeability and high efficiency for capturing non-metallic inclusions. With the ...consideration of manufacture and filtration behaviour, most filters are produced by replica methods. The intrinsic multiscale porous structure requires the ceramic foams to have sufficient strength. As a consequence, different processing approaches, material compositions and characterizations are investigated. Meanwhile, to further enhance the filtration performance, the functionalization of ceramic foam filters is often conducted with surface coating. This review summarizes the processing and characteristics of ceramic foam filters (CFFs), the nature and formation of non-metallic inclusions (NMIs), the filtration mechanism and applications of CFFs. The characterization of mechanical and filtration performance, as well as the corresponding strengthening and functionalization methods are also presented.
•A criterion for fatigue assessment of high strength steels is proposed.•The influence of non-metallic inclusions on fatigue life is taken into account.•The Carpinteri et al. criterion is used in ...conjunction with the area-parameter model.•An experimental campaign is analysed to evaluate the criterion accuracy.
In the present paper, a criterion for fatigue assessment of high strength steels is proposed, where the influence of non-metallic inclusions on fatigue life is taken into account. To such an aim, the Carpinteri et al. criterion is used in conjunction with the area-parameter model by Murakami and Yanase. An experimental campaign available in the literature is analysed to evaluate the criterion accuracy.
This research focuses on providing a detailed characteristic of non-metallic inclusions (NMIs) in 316L stainless steels with and without Ca treatment after machining using different cutting speeds. ...The electrolytic extraction (EE) technique was used for three-dimensional determinations of the inclusion characteristics. Quantitative data from the fragile non-metallic inclusions (such as size, surface area, number) in chips obtained from different cutting speeds and materials were determined. The morphologies of NMIs in the chip samples were quite different compared to the original inclusions in the stainless steel samples before machining. It was proved that the deformation degree of soft inclusions such as MnS and CaO–SiO2–Al2O3–MgO–TiOx is dependent on the cutting speed as well as the temperatures and deformation degrees of the metal matrix during machining. The total surface areas of MnS inclusions increase from 2.8 to 3.8 times compared to the original total areas with an increased cutting speed. The total surface areas of soft oxide inclusions also increase from 1.1 to 3.5 times compared to the original total areas. In addition, the tool-chip contact lengths were also measured on the rake face of the tool, and the results were compared to the determined characteristics of the observed inclusions. It was found that the modification of NMIs by Ca treatment in 316L stainless steels is preferred for high cutting speeds.
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