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In order to clarify the evolution mechanism of inclusions in 95CrMo, the industrial experiments were conducted. The composition, morphology and size of inclusions during refining and solidifying processes were analyzed by SEM-EDS detection and thermodynamic calculations. The inclusion evolution during refining process in molten 95CrMo steel can be concluded as: Al2O3 → Al2O3-MgO-CaO/CaS → Al2O3-MgO-SiO2-CaO-CaS, which is affected by slag-metal reaction and corrosion of refractory. The change of inclusion size during refining was analyzed based on their collision and floatation behavior. The composition of inclusions in billets indicate that there were mainly five types of inclusions, including spinel with sharp angle, spherical oxide inclusion composed of Al2O3, MgO, SiO2 and CaO, oxide-sulfide inclusion with single phase, inclusion with duplex phase, and MnS inclusion. The type of inclusions affects their size. The thermodynamic results indicate that most complex oxides formed in molten steel and no spinel generated during cooling process. CaS formed in the molten steel after tundish metallurgy and there were still some CaS precipitated in solid steel. MnS precipitated after steel solidification. The calculated results based on FACTSAGE 7.1 are in agreement with experimental results on the whole. [ABSTRACT FROM AUTHOR]

In today's steel automotive industry, press hardened steels meet requirements of a lower CO2 consumption and of a better safety of drivers. These steels contain titanium nitrides which can downgrade the in-use properties. From this laboratory study, with a wide range of N (20–120 ppm) combined with high Ti variations (20–110.10−3 wt.%), clear conclusions can be highlighted. Titanium content is the key parameter to drive inclusions content, more than N, as there is a high segregation of Ti in the last liquid, due to a low partition coefficient combined with a low back-diffusion coefficient. Due to this supersaturation in Ti, TiC can be formed. It does not mean that N has no effect. It has to be noticed that the density of inclusions coarser than two microns is highly dependent of the product [Ti] × [N]. Carbon is a very important factor too to take into account as the surpersaturation in Ti in presence of austenite is higher than in presence of delta-ferrite. This gives a few guidelines in the design of inclusions controlled new grades. [ABSTRACT FROM AUTHOR]

In order to find a method to characterize the inclusion distribution of high-cleanliness materials, complementary techniques were tested, such as high-frequency (80 MHz) ultrasonic testing, X-ray tomography or Extreme Value Analysis (EVA). The micro-cleanliness was also characterized by standard methods based on observations of polished surfaces by light optical or scanning electronic microscopy. The combination of all these techniques, enhanced by metiS software, allows us to determine the complete 3D distribution of oxides or to estimate the probability of largest inclusion size by modelling virtual samples. At the end, fatigue testing was performed in order to try to link fatigue results to previous characterization outcomes. [ABSTRACT FROM AUTHOR]

We present an experimental study concerned with investigations of the two-phase flow in a mock-up of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing liquid metal two-phase flows in the mold and the submerged entry nozzle (SEN) by means of X-ray radioscopy. This setup operates with the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results will be presented here revealing complex flow structures in the SEN widely differing from a homogeneously dispersed bubbly flow. The patterns are mainly dominated by large bubbles and large-area detachments of the liquid metal flow from the inner nozzle wall. Various flow regimes can be distinguished depending on the ratio between the liquid and the gas flow rate. Smaller gas bubbles are produced by strong shear flows near the nozzle ports. The small bubbles are entrained by the submerged jet and mainly entrapped by the lower circulation roll in the mold. Larger bubbles develop by coalescence and ascend toward the free surface. [ABSTRACT FROM AUTHOR]