Behavior of Non-metallic Inclusions in Centrifugal Induction Electroslag Castings

In order to know the behavior of non-metallic inclusions in centrifugal induction electroslag castings (CIESC), non-metallic inclusions in 5CrMnMo and 4Cr5MoSiV1 were qualitatively and quantitatively analyzed. The largest size of inclusions in the casting and the thermodynamic possibility of TiN precipitation in steel were also calculated. The results show that sulfide inclusions are evenly distributed and the content is low. The amount of oxide inclusions in CIESC 4Cr5MoSiV1 steel is close to the ESR steel and lower than that in the EAF steel, and there are some differences along radial direction. Nitride inclusions are fine and the diameter of the largest one is 3-4 μm. With the increase of the centrifugal machine’s rotational speed, the ratio of round inclusions increases and the ratio of sharp inclusions decreases. According to the experiment and the calculation results, it is pointed out that the largest diameter of non-metallic inclusions in the CIESC 4Cr5MoSiV1 casting is only 6.6 μm, and [N%][Ti%] in 4Cr5MoSiV1 steel should be controlled less than 4.4× 10-5 in order to further reduce the amount and size of TiN inclusions.

Study on non-metallic inclusions in Al killed high strength alloy steel refined by high basicity and high Al_2O_3 content slag

Laboratory and industrial studies were carried out to investigate non-metallic inclusions in high strength alloy steel refined by high basicity and high Al2O3 slag.It was found that the steel/slag reaction time largely affected non-metallic inclusions.With the reaction time increased from 30 min to 90 min in laboratory study,MgO-Al2O3 spinels were gradually changed into CaO-MgO-Al2O3 system inclusions surrounded by softer CaO-Al2O3 surface layers.By using high basicity slag which contained as much as 41%Al2O3 in the laboratory study,ratio of low melting temperature CaO-MgO-Al2O3 system inclusions was remarkably increased to above 80%.In the industrial experiment,during the secondary refining,the inclusions changed in order of 'Al2O3→MgO-Al2O3→CaO-MgO-Al2O3'.Through the LF and RH refining,most inclusions could be transferred to lower melting temperature CaO-Al2O3 and CaO-MgO-Al2O3 system inclusions.

Effect of continuous casting speed on mold surface flow and the related near-surface distribution of non-metallic inclusions

For the control of surface defects in interstitial-free(IF) steel, quantitative metallographic analyses of near-surface inclusions and surface liquid flow detection via the nail-board tipping method were conducted. The results show that, at casting speeds of 0.8 and 1.0 m/min, a thin liquid mold flux layer forms and non-uniform floating of argon bubbles occurs, inducing the entrainment and subsequent entrapment of the liquid flux; fine inclusion particles of Al_2O_3 can also aggregate at the solidification front. At higher casting speeds of 1.4 and 1.6 m/min, the liquid mold flux can be entrained and carried deeper into the liquid steel pool because of strong level fluctuations of the liquid steel and the flux. The optimal casting speed is approximately 1.2 m/min, with the most favorable surface flow status and, correspondingly, the lowest number of inclusions near the slab surface.

Study on the separation process of non-metallic inclusions at the steel-slag interface using water modeling

The separation process of non-metallic inclusions at the steel–slag interface was simulated by physical modeling. Three different kinds of particles(octahedral, plate-like, and spherical) and three different oils(kerosene, bean oil, and pump oil) were used to model inclusions and slags, respectively. The effects of inclusion geometry(shape and size) and slag properties(viscosity and interfacial tension) on the separation process were investigated. The results revealed that the variation of surface free energy and the viscosity of the slag are two significant factors affecting the separation process of inclusions at the steel–slag interface. The variation of surface free energy helped inclusions enter the slag phase, whereas the decrease of slag viscosity shortened the separation time. The deformation of the steel–slag interface could give rise to the resistance force, which would resist inclusions passing through the interface. A liquid film formed on the inclusion as it passed through the steel–slag interface, which might be related to the inclusion's shape.

Non-metallic Inclusions in Continuously Cast Aluminum Killed Steels

In aluminum killed steels, the size, shape, quantity and formation of non-metallic inclusions in ladle steel (before and after RH vacuum treatment) and in tundish as well as in slabs were studied by EPMA (Electron Probe Microanalysis) and by analyzing the total oxygen. The results showed that in the slabs the total oxygen was quite low and the inclusions discovered were mainly small-sized angular alumina inclusions. This indicates that most inclusions have been removed by floating out during the continuous casting process. In addition, the countermeasures were discussed to decrease the alumina inclusions in the slabs further.

Evaluation of Characteristics of Non-Metallic Inclusions in P/M Ni-Base Superalloy by Automatic Image Analysis

Non-metallic inclusions,especially the large ones,within P/M Ni-base superalloy have a major influence on fatigue characteristics,but are not directly measurable by routine inspection.In this paper,a method,automatic image analysis,is proposed for estimation of the content,size and amount of non-metallic inclusions in superalloy.The methodology for the practical application of this method is described and the factors affecting the precision of the estimation are discussed.In the experiment,the characteristics of the non-metallic inclusions in Ni-base P/M superalloy are analyzed.

Effects of calcium treatment on non-metallic inclusions and magnetic properties of non-oriented silicon steel sheets

Based on the industrial production of non-oriented silicon steel,calcium treatment by CaSi wire feeding during the RH refining process was studied.The thermodynamics of CaS inclusion formation was analyzed,and the morphology and the size distribution were observed.Furthermore,the change in inclusion characteristics after calcium treatment and the effect of calcium treatment on magnetic properties were discussed.The results show that the formation of MnS and AlN inclusions were restrained,and the aggregating,floating and removing of microinclusions after calcium treatment were effectively promoted.The cleanliness of liquid steel was obviously increased.The main type of inclusions was single phase of CaO,with some complex inclusions composed of CaO,SiO2 and MgO.No CaS inclusion was observed after an appropriate calcium treatment.The size of all inclusions was distributed in the range of 2-20 μm,and the number was about 1.8×105 /mm3.In addition,as an increasing amount of calcium was added,the core loss gradually decreased to a stable level,and the magnetic induction decreased quickly after a slow increase.The optimal calcium treatment mode depends on the chemical composition of steel.

Characterization and analysis of non-metallic inclusions in Ni42-Fe expansive alloy

Cracks and ruptures always occur during wire drawing process of 42% nickel-iron expansive alloy. In order to study the reasons of these phenomena,a method of metallographic observation in combination with sample electrolysis was used to characterize the non-metallic inclusions in the alloy wire. The results indicate that the inclusions in the alloy are oxidation products during the process of melting. There are single or complex phase inclusions composed of elements such as Al,Si,Ca,Ti,Fe,and O2. Among them,the macro-inclusions are TiO2 compound inclusions formed by the adhesion of Al and Si oxides on them. These inclusions are fragile ones with a low strain rate,as well as a rather high hardness,so that they are the main reason that leads to the surface cracks and ruptures in the alloy wires. The analysis has educed that the key point to enhance the product quality is to promote the cleanliness of the melt,control the types and quantity of non-metal inclusions in the alloy.

Effect of cerium addition on non-metallic inclusions in a high-carbon chromium bearing steel

Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min and ingot)were studied using laboratory experiments.An automatic scanning electron microscope system with energy-dispersive spectroscopy was used to analyze the amount,composition,size and morphology of inclusions in the steel at different stages.When the cerium content in the molten steel increased from 0 to 150×10^(-6),the evolution sequence of inclusions was as follows:Al_(2)O_(3)→CeAl11O18→CeAlO_(3)→Ce_(2)O_(2)S.After 28×10^(-6) cerium was added,Al_(2)O_(3) inclusions were modified into CeAl_(11)O_(18) inclusions in the molten steel and then were further transformed into Al2O3 and CeAlO3 inclusions in the solid steel during cooling.With the addition of 65×10^(-6) cerium,inclusions in the molten steel were modified into CeAlO_(3) and a small number of Ce2O2S inclusions.When the addition amount of cerium increased to 150×10^(-6),inclusions were transformed to Ce_(2)O_(2)S.The size of inclusions in the molten steel decreased obviously with cerium addition.On the other hand,the size of inclusions increased during the cooling process in solid steels of No.1 steel(with 28×10^(-6) cerium)and No.2 steel(with 65×10^(-6) cerium).During the cooling process,unmodified MnS inclusions were precipitated in the solid steel of No.1 steel and wrapped outside the Al2O3 and CeAlO_(3) inclusions to form large complex inclusions.During the cooling process of No.2 steel,the inclusion size of CeAlO_(3) increased due to the collision and polymerization.In the No.3 steel(with 150×10^(-6) cerium),the average size of inclusions decreased rapidly and remained at a lower size during the cooling process,which was beneficial to improving the fatigue life of the steel.

Shock-induced energy localization and reaction growth considering chemical-inclusions effects for crystalline explosives

Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear.Herein shock-induced energy localization,overall physical responses,and reactions in a-1,3,5-trinitro-1,3,5-triazinane(a-RDX)crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method.Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions,i.e.,phase states,chemical compositions,and concentrations.The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume,which includes homogeneous intermolecular compression,interfacial impact and shear,and void collapse and jet.As introducing various chemical inclusions,the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions.Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting.Under the shockwave velocity of 9 km/s,the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void,and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions.The lessdense shocking system denotes the greater increases in local temperature and stress,the faster energy liberation,and the earlier final reaction into equilibrium,revealing more pronounced responses to the present intense shockwave.The quantitative models associated with the relative system density(RD_(sys))were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive.RD_(sys)is defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions.When RD_(sys)is below 0.9,local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact.This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.

Surface Defects of Cold-Rolled Ti-IF Steel Sheets due to Non-Metallic Inclusions

Surface defects of the cold-rolled sheets of Ti-IF steel were studied and analyzed. After analyzing surface defects of cold-rolled sheets, such as shelling defects, holes and sliver defects by SEM/EDS, a variety of inclusions were found. In addition, the distribution of macro-inclusions in slabs was analyzed by MIDAS method. The results show the macroscopic inclusion bands of head slabs and normal slabs are in 1/8 slab thickness regions of both inner arc side and outer arc side. The formation process of the defects in the cold-rolled sheets was simulated with an experimental cold-rolling machine for comparison. The results show that there were three kinds of inclusions underneath the surface defects: Al2O3, SiO2 and particles from slag entrainment, which were the main reason for defect formation during cold rolling.

Non-metallic inclusions in electroslag remelting:a review

Non-metallic inclusion in electroslag remelting is a constant topic that has been studied for decades.Different results and conclusions are obtained on some of the subjects from these previous investigations.These differences originate in part from different experimental conditions,including original inclusion chemistries in consumable electrode,slag composition,oxygen level,liquid metal compositions,deoxidation schemes,and melting rates of electroslag remelting.The advances in the operating practices of inclusion control in electroslag remelting production are reviewed.Inclusion evolution during the electroslag remelting and related processing parameters are also reviewed and assessed.The role of the reoxidation of liquid steel during electroslag remelting on oxide inclusion composition is discussed.The generation of inclusions in remelted ingot is critically assessed.Perspective and remaining issues are noted.

Variation of Non-Metallic Inclusions Composition in X80 Pipeline Steel Refined by High Basicity Slag

The transformation of inclusions was studied when control technology of refining top slag in ladle furnace was used in X80 pipeline steelmaking.Sufficient amount of aluminum was added to experimental heats for final deoxidation during BOF tapping,and then the refining top slag with high basicity and strong reducibility was adopted to transform Al 2 O 3 to inclusions with low melting point.The results show that the composition of inclusions changes in order of "Al 2 O 3 → MgO-Al 2 O 3 system→ CaO-MgO-Al 2 O 3 system→ CaO-Al 2 O 3 system".And the inclusions after LF refining are liquid or semi-liquid state at the temperature of steelmaking,which are easily removable to obtain high cleanliness steel by collision,agglomeration and flotation.

Chemical Composition Control of Non-Metallic Inclusions in High Alloy Steel Production Process

There is a close relation between the characteristics of products and the chemical composition control of inclusions in steelmaking process. Therefore, it is very important for a warranty of product’s characteristics to improve inclusion quality resulting in defective products. In the present work, the control technique of inclusions’ chemical composition is discussed thermodynamically based on the Redlich-Kister type polynomial to metallic solution and regular solution model to molten oxide solution. It is very effective for the precise chemical composition control of oxides to determine the concentration of deoxidizers based on the thermodynamic relation among dissolved deoxidizers and oxygen, because it is known that oxide inclusions are equilibrated with them in molten steel in the steel making process. High alloy steel production process was focused in the present work.

Investigation on Dissolution Behavior of Non-metallic Inclusions in Tundish Fluxes for Bearing Steel Continous Casting

With the development of steelmaking technology, tundish has become an important device that can clean steel and remove non-metallic inclusions. Tundish flux plays a more and more important role in tundish metallurgy, furthermore different types of steel and metallurgy technology of tundish must be cooperated with the suitable tundish flux. The tundish metallurgy properties of magnesia and calcium fluxes for bearing steel production were investigated and compared by high temperature simulation experiment and industrial experiment, respectively. Results show that the melting temperature of magnesia tundish flux is higher than that of calcium tundish flux. The calcium flux has the better kinetic condition of dissolution non-metallic inclusions than the magnesia flux. Main crystal phases of magnesia tundish flux change from 12CaO·7Al2O3, 2CaO·SiO2 and MgO to 12CaO·7Al2O3, MgO, 2CaO·SiO2, CaO·Al2O3·3SiO2 and 3CaO·MgO·2SiO2 after absorbing Al2O3 inclusions. The slab samples of bearing steel ware analyzed by the big sample electrolysis method. Results show that the content and size of Al2O3 system inclusions in slab samples using calcium tundish flux are lower than using the magnesia tundish flux. Therefore, the calcium flux should be used to tundish metallurgy in bearing steel production.

Non-Metallic Inclusions in HSLA Steel-Origin,Detection and Refractory Systems to Improve Cleanness

HSLA steels need extremely low levels of tramp elements like P,S,H and O t.During tapping the steel is deoxidized with aluminum and in the secondary metallurgy sulphur (< 10 ppm) and hydrogen (< 1 ppm) are extracted.After tank degassing the steel is strongly Ca-treated by wire feeding to form CaS instead of MnS.Non-metallic inclusions in the steel and centre segregation with MnS are sinks for hydrogen which result in HIC (Hydrogen Induced Cracking).Therefore these steels ask for excellent oxide cleanness and S-contents of < 10 ppm.Macro inclusions of > 50 μm are harmful for the product.These large inclusions are seldom and difficult to be detected.Small inclusions of < 15 μm do no harm to the product.The origin of non-metallic inclusions is,roughly spoken,one third each of de-oxidation-/reoxidation products,refractory and casting powder.Slag carry-over is mainly avoided by sensitive electronic devices.Slag covers and shrouding systems of the steel stream during the transfer of metal between ladle,tundish and mold are effective to avoid reoxidation.Systems to control the flow of steel in tundish and mold favor the floatation of inclusions and their even distribution in the strand.

Composition evolution and deformation of different non-metallic inclusions in a bearing steel during hot rolling

The composition evolution and deformation of different non-metallic inclusions in a bearing steel during hot rolling were investigated by the automatic detection and the improved non-aqueous electrolysis method.Manganese sulfide,MnS–TiN,and liquid CaO–Al_(2)O_(3) inclusions were elongated while TiN and MgO-Al_(2)O_(3) were fractured during hot rolling.The CaS–MnS phase in the MgO–Al_(2)O_(3)–CaS–MnS inclusion was separated from the inclusion,leading to the formation of CaS–MnS type clusters.Meanwhile,the CaS and MnS contents in oxide-containing inclusions decreased while the MgO and Al_(2)O_(3) contents increased after hot rolling.The deformability of different inclusions in the bearing steel was quantitatively compared and discussed.

Effect of Calcium Treatment on Non-Metallic Inclusions in Ultra-Low Oxygen Steel Refined by High Basicity High Al_2O_3 Slag

The influence of calcium treatment on non-metallic inclusions had been studied when control technology of refining top slag in ladle furnace was used in ultra-low oxygen steelmaking.A sufficient amount aluminium was added to experimental heats for final deoxidizing during BOF tapping,and the refining top slag with strong reducibility,high basicity and high Al2O3 in ladle furnace was used to produce ultra-low oxygen steel and the transformation of non-metallic inclusions in molten steel was compared by calcium treatment and no calcium treatment.The results show that the transformation of Al2O3→MgO·Al2O3 spinel→CaO-MgO-Al2O3 complex inclusions has been completed for aluminum deoxidation products and calcium treatment to molten steel is unnecessary when using the control technology of ladle furnace refining top slag to produce ultra-low oxygen steel,and the complex inclusions are liquid at the temperature of steelmaking and easily removable to obtain very high cleanliness steel by flotation.Furthermore,the problems of nozzle clogging in casting operations do not happen and the remaining oxide inclusions in steel are the relatively lower melting point complex inclusions.

Study on formation of non-metallic inclusions with lower melting temperatures in extra low oxygen special steels

Investigations were made both in laboratorial and industrial scales on formation of non-metallic inclusions with relatively lower melting temperatures to improve the fatigue property of the special steels which contained extra low oxygen.It was found in laboratory studies that steel/slag reaction time largely affected non-metallic inclusions in steel.With the slag/steel reaction time increasing from 30 to 90 min,inclusions of MgO-Al2O3 spinel were gradually changed into CaO-MgO-Al2O3 system inclusions which were surrounded by lower melting temperature softer CaO-Al2O3 surface layers.By using high basicity and as much as 41 mass% Al2O3 refining slag,the ratio of the lower melting temperature CaO-MgO-Al2O3 system inclusions was remarkably increased to above 80%.In the industrial experiments,it was found that the inclusions changed in the order of "Al2O3 →MgO-Al2O3 system→CaO-MgO-Al2O3 system" in the secondary refining,and the change from MgO-Al2O3 system to CaO-MgO-Al2O3 system took place from the outside to the inside.The diffusion of CaO and MgO inside the layer of CaO-MgO-Al2O3 was considered as the controlling step of the inclusion transfer.Through LF and RH refining,most inclusions could be transferred to lower melting temperature CaO-Al2O3 and CaO-MgO-Al2O3 system inclusions.

Investigation on Non-Metallic Inclusions in LCAK Steel Produced by BOF-LF-FTSC Production Route

The behavior of non-metallic inclusions in LCAK(low carbon aluminum killed)steel produced by BOF(basic oxygen furnace)-LF(ladle furnace)refining-FTSC(flexible thin slab continuous caster)production route was investigated.The results showed that,LF refining for LCAK steel could decrease the wT[O] significantly,and the inclusions were modified by Ca treatment,which prevented nozzle clogging efficiently.However,owing to the unstable casting condition in the earlier stage of casting,a severe reoxidation occurred,accompanied with mold slag entrapment.The transformation of non-metallic inclusions during the steelmaking process was Al2O3→MgO-Al2O3 type inclusion→MgO-Al2O3-CaO type inclusion with a CaS ring,and the mechanism of the transformation was proposed and discussed via thermodynamic and kinetic analysis.Besides,to avoid CaS precipitation,the product of w2[Al]×w3[S] in steel should be less than 2.0×10-10 at 1873 K,which remands higher desulfurization ratio during LF refining.