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The gear tooth of a high speed shaft cracked after servicing for two years. In this paper, the chemical composition, metallographic structure and fracture morphology of gear shaft materials were analyzed, and the fracture cause of gear teeth was determined. The result showed that there was large size nonmetallic inclusion in the gear teeth, which was result in the fatigue crack of the gear teeth.

In combination with theoretical calculations, experiments were conducted to investigate the evolution behavior of nonmetallic inclusions (NMIs) during the manufacture of large-scale heat-resistant steel ingots using 9CrMoCoB heat-resistant steel and CaF 2 –CaO–Al 2 O 3 –SiO 2 –B 2 O 3 electroslag remelting (ESR)-type slag in an 80-t industrial ESR furnace. The main types of NMI in the consumable electrode comprised pure alumina, a multiphase oxide consisting of an Al 2 O 3 core and liquid CaO–Al 2 O 3 –SiO 2 –MnO shell, and M 23 C 6 carbides with an MnS core. The Al 2 O 3 and MnS inclusions had higher precipitation temperatures than the M 23 C 6 -type carbide under equilibrium and nonequilibrium solidification processes. Therefore, inclusions can act as nucleation sites for carbide layer precipitation. The ESR process completely removed the liquid CaO–Al 2 O 3 –SiO 2 –MnO oxide and MnS inclusion with a carbide shell, and only the Al 2 O 3 inclusions and Al 2 O 3 core with a carbide shell occupied the remelted ingot. The M 23 C 6 -type carbides in steel were determined as Cr 23 C 6 based on the analysis of transmission electron microscopy results. The substitution of Cr with W, Fe, or/and Mo in the Cr 23 C 6 lattice caused slight changes in the lattice parameter of the Cr 23 C 6 carbide. Therefore, Cr 21.34 Fe 1.66 C 6 , (Cr 19 W 4 )C 6 , Cr 18.4 Mo 4.6 C 6 , and Cr 16 Fe 5 Mo 2 C 6 can match the fraction pattern of Cr 23 C 6 carbide. The Al 2 O 3 inclusions in the remelted ingot formed due to the reduction of CaO, SiO 2 , and MnO components in the liquid inclusion. The increased Al content in liquid steel or the higher supersaturation degree of Al 2 O 3 precipitation in the remelted ingot than that in the electrode can be attributed to the evaporation of CaF 2 and the increase in CaO content in the ESR-type slag.

The potential of the application of an X-ray excited optical luminescence (XEOL) analyzer and portable analyzers, composed of a cathodoluminescence (CL) spectrometer and electron probe microanalyzer (EPMA), to the on-line and on-site analysis of nonmetallic inclusions in steel is investigated as the first step leading to their practical use. MgAl2O4 spinel and Al2O3 particles were identified by capturing the luminescence as a result of irradiating X-rays in air on a model sample containing MgAl2O4 spinel and Al2O3 particles in the size range from 20 to 50 μm. We were able to identify the MgAl2O4 spinel and Al2O3 particles in the same sample using the portable CL spectrometer. In both cases, not all of the particles in the sample were identified because the luminescence intensities of the smaller Al2O3 in particular were too low to detect. These problems could be solved by using an X-ray tube with a higher power and increasing the beam current of the portable CL spectrometer. The portable EPMA distinguished between the MgAl2O4 spinel and Al2O3 particles whose luminescent colors were detected using the portable CL spectrometer. Therefore, XEOL analysis has potential for the on-line analysis of nonmetallic inclusions in steel if we have information on the luminescence colors of the nonmetallic inclusions. In addition, a portable EPMA–CL analyzer would be able to perform on-site analysis of nonmetallic inclusions in steel.

Interaction of Pr/Dy with oxygen in nickel melts at PAr = 0.1 MPa and constant temperature was studied using the EMF instantaneous fixing method using a Mo[Cr/Cr2O3//ZrO2(MgO)//O(Nil)]Mo cell and certified sensors. Dependences a[O] = f[Pr/Dy, %] expressed in the form of logarithmic equations made it possible to compare them with each other in the concentration range of 0.001–0.2 wt % of each deoxidizer and determine that the deoxidizing ability of Pr is 1.7 times higher compared to Dy. The activity of oxygen a[O] in Ni–O–Al–(Pr/Dy) melts was calculated in comparison with Al at a concentration of 0.05 wt % of elements and its sevenfold decrease was shown for the first deoxidizer and elevenfold for the second. The morphology of nonmetallic inclusions in metallographic sections of Ni–O–Pr/Dy alloys has been studied, indicating that the inclusions are located along grain boundaries and have different configurations and a complex heterophase composition. Analysis of nonmetallic inclusions with the maximum content of deoxidizing element proved the existence of Pr/Dy oxygen compounds, which confirmed the data of thermodynamic and mass spectrometric studies. The average content of Zr in nonmetallic inclusions during the deoxidation of Pr is two times higher than in experiments during the deoxidation of Dy, which indicates the interaction of Pr/Dy with the EMF ZrO2 sensor and the preferential interaction of Pr compared to Dy and correlates with the data on the determination of a[O].

Nonmetallic inclusion (NMI) populations in superelastic (SE) Nitinol fine wires (<140 μm in diameter) were investigated by combining plasma focused ion beam (PFIB) serial sectioning with scanning electron microscopy (SEM). High purity (HP)—lower oxygen content and standard purity (SP)—higher oxygen content Nitinol wires were sectioned and imaged. The three-dimensional (3D) reconstructions provided more complete connectivity of NMIs and pores as well as information about the distribution of the features within the wire volume that is not possible with traditional two-dimensional (2D) imaging techniques. NMIs were present alone and with pores in the leading and/or trailing edges of the inclusions, in addition to stringers (i.e., fractured, elongated NMI, and intermixed with pores adjacent to each other), all of which were parallel to the wire drawing axis. The area percentages for the NMIs were 0.01% (HP Nitinol) and 0.04% (SP Nitinol), while the volume percentages measured 0.09% (HP Nitinol) and 0.47% (SP Nitinol). The combined PFIB-SEM serial sectioning approach provided the requisite resolution necessary to distinguish between NMIs and pores at micron and submicron sizes. Information gathered from this technique can be used to better inform models and predictions for fatigue lifetimes based on statistical analyses of these feature populations.

Tinplate is widely used in food packaging and chemical packaging. Industrial production continues to reduce the thickness of tinplate steel, which puts higher requirements on the control of inclusions. In this study, compared with traditional detection methods, the Ultrasonic Detection method can analyze the distribution of nonmetallic inclusions in larger size samples, which is closer to the actual production process. The numerical simulation model is established to analyze the flow, heat transfer and solidification behavior of molten steel. The results show: There are two nonmetallic inclusion bands in the sample at the edge of the slab, one is the inner and outer arc side of the sample, and the other is the 1/8 to 1/4 slab thickness region of the inner arc side in the sample. The inclusions in the thickness direction of the slab edge within the range of 1/8 to 1/4 are captured in areas 800 mm to 1400 mm below the meniscus. The solidification of the inner and outer arcs is not symmetrical, which leads to the asymmetrical distribution of inclusions in the inner and outer arcs. This study can provide a reference for improving the tinplate production process.

The properties of MnO-Al 2 O 3 -SiO 2 -based plasticized inclusion are likely to change during soaking process due to its low melting point. In this study, the evolution of the MnO-Al 2 O 3 -SiO 2 -based inclusion of 18wt%Cr-8wt%Ni stainless steel under isothermal soaking process at 1250°C for different times was investigated by laboratory-scale experiments and thermodynamic analysis. The results showed that the inclusion population density increased at the first stage and then decreased while their average size first decreased and then increased. In addition, almost no Cr 2 O 3 -concentrated regions existed within the inclusion before soaking, but more and more Cr 2 O 3 precipitates were formed during soaking. Furthermore, the plasticity of the inclusion deteriorated due to a decrease in the amount of liquid phase and an increase in the high-melting-point-phase MnO-Cr 2 O 3 spinel after the soaking process. In-situ observations by high-temperature confocal laser scanning microscopy (CLSM) confirmed that liquid phases were produced in the inclusions and the inclusions grew rather quickly during the soaking process. Both the experimental results and thermodynamic analysis conclude that there are three routes for inclusion evolution during the soaking process. In particular, Ostwald ripening plays an important role in the inclusion evolution, i.e., MnO-Al 2 O 3 -SiO 2 -based inclusions grow by absorbing the newly precipitated smaller-size MnO-Cr 2 O 3 inclusions.

Inclusions have a great influence on the quality of FeSiB amorphous ribbon. The evolution behavior of inclusions was analyzed. The results show that the spherical and elliptical inclusions, consisting of Al 2 O 3 and SiO 2 , mainly come from industrial pure iron. Ellipsoidal inclusions of 20–30 μm in pure iron were removed by floatation during the smelting process, and spherical inclusions of 1–3 μm combined with deoxidized products in FeSiB melt form Al 2 O 3 ·SiO 2 and CaO·Al 2 O 3 ·SiO 2 inclusions. Some inclusions accumulated on the inner wall of the nozzle during the spraying process, and others flowed out of the nozzle and remained in FeSiB amorphous ribbon. By controlling the total oxygen content in industrial pure iron to 31 × 10 −6 , clogging on the inner wall of the nozzle can be reduced and the free surface smoothness of the amorphous ribbon can be improved.

Up to now, the Fe content of nonmetallic particles has often been neglected in chemical evaluations due to the challenging analysis of matrix elements in nonmetallic inclusions (NMI) in steel by scanning electron microscope and energy dispersive spectroscopy analysis (SEM/EDS). Neglecting matrix elements as possible bonding partners of forming particles may lead to inaccurate results. In the present study, a referencing method for the iron content in nonmetallic inclusions in the submicrometer region is described focusing on the system Fe-Mn-O. Thermodynamic and kinetic calculations are applied to predict the inclusion population for different Fe/Mn ratios. Reference samples containing (Fe,Mn)-oxide inclusions with varying Fe ratios are produced by manganese deoxidation in a high-frequency induction furnace. Subsequent SEM/EDS measurements are performed on metallographic specimens and electrolytically extracted nonmetallic inclusions down to 0.3 µm. The limits of iron detection in these particles, especially for those in the submicrometric regime, as well as the possible influence of electrolytic extraction on Fe-containing oxide particles are examined. The measured inclusion compositions correlate well with the calculated results regarding segregation and kinetics. The examinations performed are reliable proof for the application of SEM/EDS measurements to evaluate the Fe content in nonmetallic inclusions, within the physical limits of polished cross-section samples. Only electrolytic extraction ensures the determination of accurate compositions of dissolved or bonded matrix elements at smallest particles enabling quantitative particle descriptions for submicrometric (particles ≤ 1 µm) steel cleanness evaluations.

Seamless steel pipes are widely used in industrial and civil applications, but are prone to cracking failures. This paper investigates the failure of a 20# seamless steel pipe by analyzing its composition, mechanical properties, and macro-and microstructural features. The results indicate that the cracking originated from non-metallic inclusions near the outer surface, which acted as defect sources. The material and service environment were not responsible for the failure. Once the crack propagated to half of the pipe wall thickness, the remaining section could no longer sustain operational stress, leading to a burst from the inside outward. Preventive measures are proposed to provide theoretical guidance for similar cases.