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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.

Non-metallic inclusions are one of the common defects in stainless steel castings and have received widespread attention. In this paper, the morphology and composition of non-metallic inclusions in stainless steel investment casting were studied by metallography. The experimental results suggest that there are numerous non-metallic inclusions in this stainless steel casting. Due to the different formation mechanisms, these non-metallic inclusions vary greatly in morphology and chemical composition. The main inclusions are circular or spindle-shaped endogenous composite inclusions composed of a variety of oxides, whose substrate is manganese silicate (MnO-SiO2), rich in Al2O3, CaO, Cr2O3 and TiO2. A small number of inclusions are sickle-shaped exogenous inclusions produced by the furnace lining repair materials SiC-Al2O3 involved in the melt. The endogenous inclusions appeared as black granules with clear internal structure under optical microscopy (OM), with equivalent diameter distribution from 2 to 8 µm, and a few circular inclusions with sizes up to 80 µm. The endogenous inclusions are encapsulated in a niobium carbide shell, which was quite different from the exogenous inclusions. The exogenous inclusions are larger in size and aspect ratio and have multiple endogenous inclusions attached to the surface. The amount and size of coarse inclusions in stainless steel castings can be reduced by measures such as promptly keeping the furnace lining clean and sufficiently removing the steel slag from the melt.

This paper presents practical experience in studying the causes of corrosion damage on the inner surface of gas pipelines made of 09Mn2Si steel after their use in gas fields. The influence of the features of the microstructure of samples of this pipe steel on the development of local defects on their surface is studied. According to metallographic studies, an uneven distribution of phases inside the steel and the presence of nonmetallic inclusions are recorded, which leads to the occurrence of heterogeneity on the inner surface of the pipe. The tests carried out under conditions of moisture condensation and alternating wetting of the steel surface with water in the presence of CO2 showed that the pronounced banding of steel and the presence of corrosion-active nonmetallic inclusions are the main causes of corrosion initiation and can lead to the development of deep local damage on the surface of gas pipelines made of 09Mn2Si steel.

A comprehensive model is developed for the assimilation of calcium from a cored wire; it takes into account heat transfer, sheath melting, the release and possible evaporation of calcium, and its subsequent reaction with nonmetallic inclusions in steel. The developed mathematical model is used to perform numerical calculations of the injection of a cored wire into steel for various operating regimes.

An electrogas weld metal deposited with an approximately 20 kJ/mm heat input was examined to investigate the chemical and microstructural characteristics of nonmetallic inclusions related to the weld microstructure. The inclusions in this weld were found to be very active for ferrite nucleation, and the larger inclusions tended to be more effective for multiple-nucleation. Experimental evidence demonstrated that the high nucleation potency of inclusions was attributable to the TiO layer formed on the inclusion surface and that the multiple-nucleation was due to the polycrystalline nature of the TiO layer. In addition, small patches of the TiN phase were present on the outer surface of inclusions. From the morphological and chemical composition, this phase was believed to be formed from the steel matrix by the precipitation reaction upon cooling.

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.