Evolution Of Non-metallic Inclusions Research Articles

Evolution of nonmetallic inclusions in 80-t 9CrMoCoB large-scale ingots during electroslag remelting process

Evolution of nonmetallic inclusions in 80-t 9CrMoCoB large-scale ingots during electroslag remelting process

Effect of ladle-lining materials on inclusion evolution in Al-killed steel during LF refining

Abstract The effect of lining materials (Al2O3 and Al2O3–MgO·Al2O3) of ladle on evolution of non-metallic inclusions in aluminum-killed (Al-killed) steel during ladle furnace refining without Ca treatment was investigated through industrial experiments. The results showed that non-metallic inclusions experienced the changes from Al2O3 → MgO–Al2O3 → CaO–Al2O3. During the refining process using either of the two ladle lining materials, for all non-metallic inclusions, the vast majority are distributed in the high Al2O3 area of the CaO–Al2O3–MgO phase diagram, with very little or none in the low melting point zone. Non-metallic inclusions are mainly smaller than 3 μm, while those larger than 3 μm consisted primarily of MgO·Al2O3 and CaO–Al2O3 inclusions. The use of an Al2O3–MgO·Al2O3-lining ladle is more effective in reducing the number density of inclusions in the steel. However, during the refining process, the Al2O3-lining ladle does not have a significant impact on the presence of MgO–Al2O3 and CaO–Al2O3 inclusions in the molten steel. The Al2O3–MgO·Al2O3-lining ladle does not have a significant effect on MgO–Al2O3 inclusions, but it does promote the formation of CaO–Al2O3 and CaS inclusions in the molten steel.

Evolution of Non-metallic Inclusions in a 303-ton Calcium-Treated Heavy Ingot

Evolution of Non-metallic Inclusions in a 303-ton Calcium-Treated Heavy Ingot

Effect of Beam Oscillation on Microstructure and Mechanical Properties of Electron Beam Welded EN25 Steel.

EN25 steels have been found to be applicable in shafts, gears, etc., but welding of EN25 steel was performed using electron beam welding with different oscillation beam diameters varying from 2 mm to 0.5 mm. The present study reports the effect of beam oscillation on the evolution of nonmetallic inclusions, microstructures, and mechanical properties of EN25 steel. Heat input calculations showed that the application of beam oscillations resulted in significantly lower heat inputs compared to their non-oscillating counterparts. The highest fraction of the retained austenite (9.35%) was observed in a weld prepared with beam oscillation at a 2-mm oscillation diameter, and it decreased to 3.27% at an oscillating diameter of 0.5 mm, and it further reduced to 0.36% for non-oscillating beam cases. Residual stresses were compressive in the fusion zone, irrespective of beam oscillation. Beam oscillation resulted in equiaxed grain in the recenter region of the fusion zone, attributed to heat mixing and the evolution of random texture. The application of beam oscillations resulted in a significant decrease in the size of the nonmetallic inclusions to 0.1-0.5 compared to 5-20 mm in base metal. All tensile samples failed in the base metal, indicating good strength of the weld. Fusion zone hardness (250-670 HNV) and wear properties (COF 0.7 to COF 0.45) improved irrespective of with and without beam oscillation.

Simulating the Evolution of Non-Metallic Inclusions During the Forging Process

Abstract Radial forging of metallic materials requires both high temperatures and large plastic deformation. During this process, non-metallic inclusions (NMIs) can debond from the metallic matrix and break apart, resulting in a linear array of smaller inclusions, known as stringers. The evolution of NMIs into stringers can result in matrix load shedding, localized plasticity, and stress concentrations near the matrix–NMI interface. Due to these factors, stringers can be detrimental to the fatigue life of the final forged component, especially when present near a free surface. By performing a finite element model of the forging process with cohesive zones to simulate material debonding, we contribute to the understanding of processing-induced deformation and damage sequences on the onset of stringer formation for both Type 1 and Type 2 alumina NMIs in a Ni–200 matrix. Through a parametric study, the interactions of forging temperature, strain rate, strain per pass, and interfacial decohesion on the NMI damage evolution metrics are studied, specifically NMI particle separation, rotation, and cavity formation. For Type 2 alumina NMIs, embedded in a Ni–200 matrix, the simulations indicate that at temperatures below 800 °C, particle separation dominates the NMI damage sequences, whereas at temperatures between 900 °C and 1000 °C, below an interfacial bond strength of 178 MPa, cavity formation is the dominate damage evolution mechanism, resulting in matrix load shedding and stress concentrations around the NMI.

Evolution of Nonmetallic Inclusions in Ti‐Bearing Al‐Killed Steel during Heat Treatment at 1200 °C

To understand the evolution behaviors of the inclusions in Ti‐bearing Al‐killed steel, steel samples taken from a 20CrMnTi casting billet are heated at 1200 °C for different times, and the changes in composition, size, and numbers of the inclusions are investigated. Some modeling experiments are also designed to reveal the interaction between solid steel and inclusions using premelted slags. It is found that oxysulfide, sulfide, and nitride inclusions are detected in the casting billet before heating. During heating, small changes are observed in the types of inclusions, while the size of these inclusions increases with time. The Mn and S in steel transfer to the sulfide phase of these inclusions and further generate a (Ca, Mn)S solution. The Ti in steel replaces some of the Al element in the oxide part of the inclusions, resulting in the increase of TiOx content and the drop of Al2O3 content in the inclusions. When the TiOx content is sufficient, a thin layer of TiN is predicated at the edges of the oxide part. The reaction between the TiOx in inclusions and the N in steel plays a role in this evolution.

Effect of Deoxidizing and Alloying Routes on the Evolution of Non-Metallic Inclusions in 55SiCr Spring Steel

Compared to the conventional deoxidation process with Al or Si-Mn for 55SiCr spring steel production, the possibility of using a Si-Ca-Ba compounded deoxidizer to control the behavior of non-metallic inclusions in spring steel was explored in this study. The effect of the addition sequence of deoxidizer and alloys into molten steel on the morphology, size, and composition of the inclusions was emphatically studied at 1873 K (1600 °C) using a high-temperature electric resistance furnace. The results indicate that adding alloy first can form less harmful inclusions in steel, which are roughly spherical and smaller than 3 μm in diameter, and its inclusion evolution path is MnO-SiO2-Al2O3→CaO-SiO2-Al2O3 and CaO-Al2O3-MgO. While adding deoxidizer first, the inclusions in steel are harmful due to its mostly irregular geometry and relatively large size over 5 μm. The inclusion evolution path is Fe-O→CaO-Al2O3(-SiO2) and CaO-Al2O3-MgO. The formation and evolution mechanism of inclusions under different addition sequences were discussed. In addition, the solubility limits of MgO from refractory into steel were studied to inhibit its corrosion by molten steel.

Role of Interfacial Properties in the Evolution of Non-metallic Inclusions in Liquid Steel

Role of Interfacial Properties in the Evolution of Non-metallic Inclusions in Liquid Steel

Formation and evolution of non-metallic inclusions in X70MS pipeline steel during LF-RH-CC process

The formation and evolution of non-metallic inclusions in X70MS pipeline steel during LF-RH-CC process were investigated by industrial trials, and the evolution mechanism of non-metallic inclusions was analyzed and discussed with thermodynamic calculations. The results show that after RH vacuum refining, the inclusions in molten steel are mainly spherical CaO-MgO-Al2O3 and CaO-Al2O3. After calcium treatment, the inclusions are transformed into spherical CaS-CaO-Al2O3 and CaO-CaS with finer size. During calcium treatment, it is difficult for [Ca] and [S] in the molten steel to react directly to form CaS, and CaS is mainly generated at the edge of liquid calcium aluminate. When w[Al] in molten steel is 0.032%, w[Ca] is controlled above 0.0035%, which is more favorable to avoid the generation of liquid calcium aluminate. Calcium treatment to the tundish reaches the casting liquid level, the molten steel occurred a continuous reoxidation, reoxidation of inclusions composition transformation is mainly determined by the [Ca] and T[O] contents of the molten steel, this process inclusions are transformed from CaO-CaS to liquid CaO-MgO-Al2O3. During cooling and solidification of the molten steel, the CaS content in inclusions increases sharply, the CaO content decreases sharply, and the changes in inclusions are mainly affected by the reaction between the molten steel and the inclusions and the precipitation of new phases.

Patterns of formation and evolution of non-metallic inclusions during the production of IF, IF-HS-steels to reduce the rejection of rolled products by steelmaking defects

Patterns of formation and evolution of non-metallic inclusions during the production of IF, IF-HS-steels to reduce the rejection of rolled products by steelmaking defects

Effect of Tundish Flux on Compositional Changes in Non-metallic Inclusions in Stainless Steel Melts

The effect of the tundish flux on the evolution of non-metallic inclusions in Si-killed 304 (18%Cr-8%Ni) stainless steel has been investigated at 1773 K. The interfacial reaction between molten steel and the CaO–Al2O3–MgO flux causes the aluminum pick-up from the liquid slag into the steel melt, resulting in a decrease in the oxygen content in the steel. The aluminum originating from the slag modifies the pre-existing Mn-silicate inclusions into alumina-rich inclusions in the steel. Because the oxygen content in the steel decreases as it reacts with the CaO–Al2O3–MgO flux, the degree of supersaturation for alumina formation is too low to precipitate new-born alumina particles in the steel. By analyzing the population density function (PDF) results for inclusions, it can be observed that the growth of spinel-type inclusions occurs by the diffusion of aluminum and magnesium in the steel. On the other hand, the composition of the steel, as well as the evolution of inclusions, is negligibly changed when the CaO–SiO2–MgO flux is added to the molten steel. Furthermore, the computational simulation for predicting the evolution of inclusions in molten steel during a continuous casting tundish process was carried out based on a refractory-slag-metal-inclusion (ReSMI) multiphase reaction model.

Effect of Sulfur Content on Evolution of Nonmetallic Inclusions in Low Sulfur Al‐Killed Steels during Heat Treatment

Herein, the effect of total sulfur (T.S) on the transformation of inclusions in Al‐killed steels is investigated through lab experiments and kinetic calculations. During the heating process, CaS content in inclusions obviously rises up, while the CaO content reduces. The CaO content in inclusions with 11 ppm S in steel is higher than 15%, while it is less 5% for the steel with 25 ppm S. The initial CaO–Al2O3 inclusions before heating change to CaS–MgO–Al2O3 at 1200 °C. The higher T.S promotes the transformation of inclusions in low sulfur Al‐killed steels, leading to the higher CaS content in inclusions after the heat treatment. A kinetic model is developed to predict the transformation of inclusions in low sulfur Al‐killed steels during the heat treatment. The transformation fraction of inclusions decreases with the larger size of inclusions and increases with the higher T.S content in steel at the heating temperature.

Evolution of Nonmetallic Inclusions in GCr15 Bearing Steels During Continuous Casting Process

Industrial trials and thermodynamic calculation are carried out to systematically investigate the variation of steel cleanliness and inclusions during the reoxidation of molten steel, steady and unsteady continuous casting process of GCr15 bearing steels. Comparing with inclusions in molten steel, the content of Al2O3, CaO, CaS, and MgO of inclusions in the steady bloom is increased by 2.17%, −18.47%, 14.01%, and 2.27%, respectively, due to the reoxidation of molten steel will inhibit the transformation of inclusions. As the casting length in the first bloom increases from 2 to 9 m, the total oxygen (T.O) content reduced from 12.9 to 7.2 ppm and the number density of inclusions decreases from 15.65 to 10.97 # mm−2 with a gradual decrease in Al2O3 content. Based on thermodynamic consideration, in molten steel, the lower content of T.O, the lower Al2O3 content of inclusions. For solid steel, with the increase in content of T.O, mainly the Al2O3 content of inclusions gradually increases and the CaS content gradually decreases when the T.O content is between 4 and 8 ppm. However, the Al2O3 and CaO content of inclusions gradually increases, then the MgO and CaS contents gradually decreases when the T.O content is between 8 and 25 ppm.

Evolution of Non-Metallic Inclusions in Al-Killed Stainless Steelmaking

The evolution of non-metallic inclusions (> 10 µm) for the Al-killed steel in the stainless steelmaking is described. The effects of the slag basicity at the AOD/VOD process, Ca treatment, raw materials (dolomite and spent refractory), reoxidation and vacuum condition on the evolution of the non-metallic inclusion were investigated using the thermo-chemical program (FactSageTM) and the SEM-EDS analysis of the non-metallic inclusions sampled at each process (AOD/VOD-ladle treatment-tundish-continuous casting) and discussed for the beneficial modification of the non-metallic inclusions to obtain better surface quality of the steel in the secondary refining process. The phase stability diagram of the inclusion newly developed from the analysis results and the mechanism for the evolution of non-metallic inclusion in Al-killed stainless steel was suggested.

Evolution of Nonmetallic Inclusions during the Electroslag Remelting Process

The evolution of inclusions during the electroslag remelting (ESR) process, especially the inclusions in droplets is investigated by an industrial trial which remelts a plain carbon steel billet in the slag of CaF2–Al2O3–CaO–MgO. Results show that oxide inclusions change from SiO2–MnO to Al2O3–MnO during the ESR process. The transfer of aluminum from the slag to the steel increases the aluminum content in the steel and causes the reaction between (MnO), (SiO2) in inclusions with the [Al] in the steel to generate (Al2O3) inclusions. Thermodynamic results show that inclusion evolution is mainly influenced by the temperature and the total Al content in the steel. With the increase in temperature at the electrode tip, the MnO content in inclusions increases rapidly. Meanwhile, as the aluminum transfers from the slag to the steel, the Al2O3 inclusion increases clearly with the corresponding decrease in MnO and SiO2 inclusions. In addition, from the electrode to the ingot, the number density of inclusions decreases from 208.82 to 33.49 # mm−2, whereas the average size increases from 3.79 to 5.76 μm. Both the chemical modification and the physical absorption of slag mainly occur at the liquid film and droplet stage.

Evolution of Non-metallic Inclusions in Si-Killed Stainless Steelmaking

Evolution of Non-metallic Inclusions in Si-Killed Stainless Steelmaking

Evolution of non-metallic inclusions with cold drawing in progressively cold drawn eutectoid pearlitic steel wires

This article focuses on the analysis of the evolution of inclusions present in eutectoid pearlitic steel subjected to a real cold drawing process. To this end, wires belonging to different stages of the manufacture chain were studied, starting from an initial hot rolled bar (not cold drawn at all). In addition to the information obtained through visual inspection, a quantitative analysis of the micro-defects generated by these inclusions has been carried out. The analysis has been performed using materialographic techniques, scanning electron microscopy (SEM) and the image analysis program (AnaliSYS 3.1®)..

Evolution of Non-metallic Inclusions Through Processing in Ti-V Microalloyed 316L and Al-V Microalloyed 17-4PH Stainless Steels for Hipping Applications

Powders produced by air-melted gas atomization (AMGA) and vacuum induction gas atomization (VIGA) from Ti-V microalloyed 316L and Al-V microalloyed 17-4PH stainless steels along with their feedstock material and Hot Isostatically Pressed (HIP’d) products have been examined. Inclusion characteristics and development through process along with changes in grain size have been characterized. The main findings are that a thin oxide film forms on the powder surface, thicker for the 316L powder than the 17-4PH powder as indicated by XPS analysis of selected powder precursors, and large inclusions (predominantly oxides) are also observed on the 316L powder. This results in a high number of inclusions, including more complex two-phase inclusions, on the prior particle boundaries in the HIP’d material. Grain growth occurs during HIPping of the 316L powders with some evidence of inclusions locally pinning boundaries. In the vacuum-melted powder, smaller Ti-rich inclusions are present which give more grain boundary pinning than in the air-melted powder where Ti was lost from the material during melting. Consideration has also been made to determine the variation of Ti and V microalloying elements and residual Cu through processing. It was found that Ti was lost during air melting but partly retained after vacuum melting leading to the presence of fine and complex Ti-containing precipitates which provided grain boundary pinning during HIPping and heat treatment. V was retained in the melt by the use of both AMGA and VIGA processes, and therefore available for precipitation during HIPping. Residual Cu was retained during both air and vacuum melting and was associated with Mn S and Mn O S inclusions overwhelmingly outweighing that of Mn O inclusions in the two HIP’d 316L samples.

Evolution of Nonmetallic Inclusions with Varied Argon Stirring Condition during Vacuum Degassing Refining of a Bearing Steel

In the current study, industrial trials are performed to investigate the effect of argon stirring conditions on nonmetallic inclusions of a bearing steel during vacuum degassing (VD). Three argon stirring modes, including strong stirring, moderate stirring, and weak stirring during the last 10 min of the high‐vacuum period, are compared. The removal fraction of >1 μm inclusions and >5 μm inclusions is the highest with the moderate stirring mode, reaching 15.7% and 42.2%, respectively. Inclusions of MgO·Al2O3 are easier to remove than CaO–Al2O3 and entrained CaO–Al2O3–SiO2 ones as MgO·Al2O3 inclusions have a higher coagulation coefficient, a higher contact angle, and a lower adhesion work between the inclusion and the molten steel. Meanwhile, the removal efficiency of inclusions in the bearing steel is in the order of Al2O3 > MgO·Al2O3 > solid CaO–Al2O3 > liquid CaO–Al2O3 and entrained CaO–Al2O3–SiO2. Liquid CaO–Al2O3 inclusions with >5 μm size originate from slag entrainment and can be efficiently removed from the molten steel by the moderate stirring mode.

Evolution of nonmetallic inclusions in pipeline steel during LF and VD refining process

AbstractThe formation and evolution of nonmetallic inclusions in pipeline steel were investigated by SEM, EDS and INCA Feature Analysis System, with the industrial process of electric arc furnace → ladle furnace (LF) refining → vacuum degassing → continuous casting. The composition, size and amount of inclusions during refining process were discussed systematically. The results show that inclusions at each refining step are mainly small-particle inclusions (below 5 µm), and the total number of inclusions has been reduced significantly due to the refining effect of slag during LF refining. The calcium (Ca) treatment increases the amount of small inclusions. The types of inclusion are mainly Al2O3 and MnO–SiO2–Al2O3 before LF, and they are transformed into CaO–Al2O3, MgO–Al2O3 and CaO–MgO–Al2O3 during LF process. After Ca treatment, inclusions are changed to CaO–Al2O3–(CaS) and CaO–MgO–Al2O3–(CaS). Typical inclusions are still mainly CaO–Al2O3 and CaO–MgO–Al2O3 in tundish, but the composition of those inclusions has been changed and located to the low melting point region in ternary phase diagram. Such inclusions will further be removed as continuous casting approaches.