The continuous cast round bloom of DZ2 high-speed axle steel is remelted by electroslag with argon protective atmosphere and rolled into axle billets. The composition, hydrogen and oxygen content and the number, size and morphology of inclusions in the axle billets are analyzed and detected, and the corresponding results are compared with that in the axle billet rolled directly by continuous cast slab. The results show that after electroslag remelting, the C content of the axle billet is more uniform at longitudinal and transverse direction(0.25%-0.27%C),but average Al and Si content respectively decreased from 0.25% and 0.018% in ingot head to0.23% and0.015% in ingot tail, hydrogen and oxygen content respectively increased from0.85×10-6and9×10-6in cast bloom to1.52×10-6and  10×10-6in ESR ingot. The inclusions in the ESR axle billets are mainly small-size spherical calcium aluminate, the size of inclusions above 10 μm is few and the number density between 5- 10 μm is 0.068/mm²and1-5 μmis0.04/mm², which indicates that electroslag remelting in protective atmosphere can not only remove large inclusions, but also significantly reduce the number of small-size inclusions in steel.

The effect of oxygen content T [O] on distribution, size and morphology of sulfide inclusions in 160 mm × 160 mm cast billet of Y1215 free cutting steel and the deformation status of sulfide inclusions in hot rolling to φ8.0 mm coil are studied. The results show that with the increase of oxygen content, the size and distribution of sulfide inclusions in cast billets have no obvious difference; but the complex inclusions increase including MnS as core covered or adhered by MnO-SiO ₂ and MnO-SiO ₂-Al ₂O ₃ as core adhered by MnS. In the φ8.0 mm rolled coil rod, rod as T [O]0.0074%, the sulfide deformation in the wire rod is obvious, part of the sulfide is broken because of serious tensile deformation, the length-width ratio of sulfide is 23.2, as T[O] 0.0145%, the sulfide deformation along the rolling direction is small mainly in the spindle shape with length-width ratio3.4.For Y1215 free cutting steel, in order to obtain spherical or spindle sulfide inclusions, the T [0] in smelting steel can be controlled between 0 0095% and 0 0145%

Niobium-containing phase precipitating in liquid steel during solidification in (220 mm×260 mm) continuous casting bloom of Nb microalloying F40MnVS steel (adding 0.029% Nb) is studied in the paper. The results show that there are many micro-sized large particles of NbC(/%:80-94Nb,1.2-7. 1V,1.6- 17. 1Ti) in bloom. The large NbC is distributed between the dendrites its morphologies can be block shape, long strip shape, or eutectic shape with steel matrix, part attached to sulfide. NbC at the edge position in bloom is mostly less than 5 μm,the morphology is mostly dotted while that at middle and center position is large and mostly long with size even up to tens of microns. The large NbC still exists in hot- rolled bar. According to calculated results by Thermo-Calc software, the NbC precipitates in liquid steel during solidification process when solid fraction reaches 0.961, and the existence of element Ti may be the mutual dissolution result of NbC and TiN. By increased the heating temperature of bloom before rolling to1200 ℃, the size of large NbC could be obviously decreased.

In accordance with the current in electroslag remelting(ESR)GCr15 bearing steel D inclusions exceeding the standard problem,the different slag systems are designed,and respectively with the help of Factsage software and empirical formulae to calculate the melting characteristics of the slag system,viscosity,electrical conductivity and other physical parameters,using laboratory slag metal balance experiments and field 2.5 t electroslag remelting experiments,the results show that, the optimal ESR slag system is 55CaF ₂-25Al ₂O ₃- 15CaO-5MgO.With use of the optimal slag system the average total oxygen content in steel is 41.98% lower than that with the traditional slag system,and can reduce the change in the total oxygen content of steel in different locations of electroslag ingot; as compared to the original slag system the number of 1-5  μm inclusions  decreases by 31.25%.Through the slag system on inclusions control,it can improve class D inclusion in GCr15 bearing steel,rating level reaches 0.5,and can better“clean”electric slag ingot.

In order to study the effect of tellurium on sulfide morphology of non-quenched and tempered steel 38MnVS6 for automobile crankshaft,0.012% Te is added by feeding 70 m Mn-Te wire in the smelting process to achieve the purpose of tellurium treatment. The nonmetallic inclusions in Φ380 mm continuous casting round bloom and Φ105 mm hot rolling round bar are studied by metallographic microscope and scanning electron microscope. Through the research, it is found that the morphology of sulfide is the same in the transverse and longitudinal direction of continuous casting bloom. MnS and MnTe form eutectic compounds, and the existence of MnTe changes the precipitation morphology of MnS,which can make the sulfide morphology change to short rod or even ellipsoid, and the overall length and size become smaller performance to reduce average  length from 45 μm to 15 μm.Affer adding0.012%Te,MnTe and MnS inclusions occur solid solution, and the morphology of inclusions is very similar in both size and morphology in bloom and rolled bar, while the sulfide in rolled bar without Te treatment is obviously elongated with the rolling direction.

In order to study the control of 90 t BOF-RH-LF-CC flowsheet produced ultra-low carbon steel AISI 1006 inclusions, the sample was taken at different sampling point at cross section of 200 mm×200 mm cast bloom to analyze inclusions, the analysis results show that the ratio of inclusions of small particles in the steel are relatively large, and the inclusions with size of5- 10 μm accounted for90. 1%,3.6% of the 10- 13 μm,and5.4% above 13 μm,and the larger size inclusions are mainly distributed in the center of the casting bloom. The largest distribution of inclusions is at the length of side 1/4 of the cast billet, followed by the near center, and the least inclusions near the surface of the cast bloom. The inclusions in the casting bloom are mainly Al ₂O ₃,Al ₂O ₃ ·CaO · (CaS ·MnS),Al ₂O ₃ ·CaO ·MgO · (CaS ·MnS),MgO · Al ₂O ₃ · (CaS ·MnS)composite inclusions, which are endogenous inclusions. The process optimization is carried out, RH high vacuum holding time is controlled for more than 15 minutes, Deoxygenation slagging and desulfurization be controlled well during LF refining, the refining time is controlled for within 90 minutes, the alkalinity of the refining final slag is 6 to 7, the silicon calcium line is fed before leaving the station for modification treatment, the soft blowing time is controlled for more than 25 minutes, the continuous casting is well protected, the tundish large argon flow is purged for more than 10 minutes to avoid the secondary oxidation, the inclusions are controlled in the direction of calcium aluminate, and the T.O content of molten steel is reduced, after process optimization, T.O content of mloren steel ≤20×10 ^-6,rate of B 、D 、Ds inclusion≤1.0.

The effects of adding Ce(0-0. 32% ) -Mg(0-0. 04% ) alloy on the as-cast inclusions and solidification organization of GCr15 bearing steel are investigated. The results show that the addition of Ce-Mg alloy can lead to the modification of inclusions and the generation of a large number of Ce-and Mg inclusions with regular shape, fine size and disperssed distribution ；and the inclusions are more fine and diffuse as 0.016% [ Ce] and 0.002% [ Mg]. With the increase of the mass fraction of Ce-Mg alloy, the distribution of carbides in the as-cast structure of steel becomes more uniform and the reticular carbide network structure becomes thinner, and as 0.016% [ Ce] and 0. 002% [ Mg], the pearlite lamellae is the thinner and the lamellae spacing is the minimized. The addition of Ce-Mg alloy can significantly reduce the segregation of C and Cr elements between dendrites and dendrite stem, and reduce the dendrite spacing to hinder the coarsening of dendrites.

17-7PH precipitation hardening stainless steel consumable electrode is prepared by 35 t electric arc furnace- AOD decarbonization- LF refining- ingot casting process, and 2 t electroslag ingot is obtained by gas shielded electroslag furnace. The change law of inclusion number, size and composition in 17-7PH steel before and after electroslag remelting are analyzed by ASPEX scanning electron microscope, and the morphology and type of inclusions in steel is further observed by SEM-EDS. The experimental results show that, after electroslag remelting, the oxygen content decreases from 6.6 x 10 ^-6 to 5.7 x 10 ^-6 and the nitrogen content decreases from 200 x 10 ^-6 to 180 x 10 ^-6. The types of inclusions don't change before and after remelting, but the total number of inclusions decreases significantly, especially the number and size of large particle inclusions decrease significantly. The total inclusions in electroslag ingot are mainly AIN inclusions, which are large in size and most in quantity. In order to improve the cleanliness of 17-7PH steel electroslag ingot , it is necessary to reduce the nitrogen content of consumable electrode as much as possible, so as to reduce the formation of AIN inclusions formed during electroslag remelting.

The GCr15 steel production flow steel is 120 t BOF-LF-RH-CC process. As adding 200 kg aluminum block at BOF tapping for strong deoxidation and controlling the aluminum content 0.030% ~ 0.045% in steel in LF process, at end LF the main inclusions in steel are MgO ·Al ₂O ₃ and the MgO.Al ₂O ₃ inclusions are removed during RH degassing and the calcium aluminate inclusions are main inclusions in steel after RH. However, but MgO·Al ₂O ₃inclusions are formed again in the tundish steel. Due to the existence of Al-MgO and C-MgO reactions in LF refining process, the MgO ·Al ₂O ₃ inclusions could be formed again after LF refining in high carbon aluminum deoxidized GCr15 bearing steel. However, when just adding 40 kg aluminum block for preliminary deoxidation in the BOF tapping process, the amount of MgO·Al ₂O ₃ inclusions in steel significantly decrease after LF refining, and the regeneration of MgO.Al ₂O ₃ inclusions in tundish steel could be prevented. In addition, adding low titanium and low aluminum ferrosilicon in the LF refining process instead of adding in tapping process effectively control the amount of MgO · Al ₂O ₃ inclusions in steel.

The evolution of inclusions in the refining process of EH36 steel produced by the route of "120 t BOF-LF- RH-260 mm slab CC” has been researched. Through sampling and testing of each working procedure in situ, in combination with inclusions thermodynamic calculation, the variations of inclusion types and size are analyzed. It is found that the number density of inclusions in steel gradually decreases , but the number density of >5 μm large particle inclusions gradually increases during the refining process of MLF—>RH—>tundish". The main types of large particle inclusions are MnO- SiO ₂ series oxide and CaO Al ₂O ₃ series calcium aluminate, such as 3 CaO·Al ₂O ₃, 12CaO ·Al ₂O ₃ and CaO・Al ₂O ₃. During the refining process, CaO · 6Al ₂O ₃ and CaO ·2Al ₂O ₃ are formed first when the Ca content in steel is low, and the main inclusions of 12CaO , 7Al ₂O ₃, 3CaO , Al ₂O ₃ are formed with Ca content increasing in steel.

By established a model of inclusions dynamic at the steel-slag interface the refining slag absorbing inclusions phenomenon is studied. Results show that certain parameters, i. e. particle size, interfacial tension and slag viscosity ,determine the inclusions transfer behavior. Paiticle size and interfacial tension determine definitely large size inclusions transfer behavior, while interfacial tension only determines definitely micro size inclusions rating ≤20 ㎛ transfer behavior. Macro-sizes affects the inclusions displacement more than the Micro-sizes. For the removal of Micro-inclusions, by inclusions mathematical dynamic model coupled by steel and slag surface tension models, the effect of interfacial tension on obsorbing process has been studied. It is obvious that the particles blow 122.9 ㎛  size could be rebounded into steel when they are flowed to steel-slag interface layer. It is obtained that there is no way by re-designing refining slags to effectively remove ≤ 122. 9 ㎛ micro-inclusions from steel to slag layer and further to get the aim to decrease the oxygen content in steel.

The types and quantity density of non-metallic inclusions, and the change of total oxygen in steel ML08Al produced by the two processes BOF-RH-CC and BOF-LF-CC are analyzed. The results show that the main non-metallic inclusions in steel after BOF deoxidizing alloying of two process are Al ₂O ₃, in the process of "BOF-LF-CC" , the partial non- metallic inclusions in steel at the end of LF refining are changed from Al ₂O ₃ to Al ₂O ₃ ・ CaO and Al ₂O ₃ • MgO, but in the process of "BOF-RH-CC" , after RH vacuum the non-metallic inclusions Al ₂O ₃ are still dominated. After deoxidizing alloying, the total oxygen content in BOF molten steel is 27. 8 x 10 ^-6 ~31. 5 x 10 ^-6 , the total oxygen content in steel at LF end is 20. 2 x 10 ^-6 ~22. 5 x 10 ^-6 , but the total oxygen content in steel at RH end is 14. 7 X 10 ^-6~ 15. 3 x 10 ^-6. The removal rates of inclusions by LF refining and RH vacuum treatment are 49. 6% and 80. 9% respectively. Therefore, the cleanness of the cold heading steel ML08Al produced by the process of "BOF-RH-CC" is better than that produced by the process of “BOF-LF-CC”.

The cord steel 82A is melt by 80 t LD-LF-CC process. It is found that ladle refractories have obvious influence on Al content in steel. Two kinds of ladle refractories ( magnesia carbon brick and magnesia alumina carbon brick) are used for industrial production. The test results show that when 82 A cord steel is produced by using magnesia carbon brick ladle with refining slag basicity 0.9, the content of Al in steel can be controlled below 0.001% , and the inclusions can be controlled in the low melting point zone, which is beneficial to improve the quality of 82A cord steel and the wire breaking rate decreases from original 1% to 0.42%.

The types, sizes, distributions and morphological changes of inclusions in magnesium treated ( 0. 0006% Mg ) and calcium treated (0. 0010% Ca) 0.45% C steel are compared and analyzed by optical microscopy, scanning electron microscopy and in-situ electrolysis in non-aqueous solution. The results show that compared with the traditional calcium treatment process, after adding a certain amount of magnesium to 0.45% C steel, the Al ₂O ₃ in steel is transformed into fine and dispersed MgO • Al ₂ O ₃ , and MnS takes MgO • Al ₂ O ₃ as nucleation particles at the end of solidification to form MnS- MgO • Al ₂O ₃ composite inclusions with soft outside and hard inside. The inclusions with this structure are not easy to deform ,and can still keep spherical or spindle shape during rolling, which can improve the ratings of A-type sulfide and B-type alumina; The inclusions in steel are more dispersed and distributed, the proportion of small-sized inclusions in steel with 0 ~ 4μm2 increases, and the morphology of inclusions in steel is improved which is more conducive to improving the properties of steel.

As compared with no-adding Te( 0Te ) steel, in contening 0.005 9% Te(Te/S = 0.098 )Φ38 mm bar of 46MnVS steel rolled from 0480 mm cast bloom the average equivalent diameter and average area of MnS inclusions are increased by 27% and 72% , respectively ， the number of spherical or ellipsoidal inclusions with length-width ratio of 1～3 is increased by 21% ,and the fine sulfide rating decreases from 3.0 to 2.0. Te will be dissolved in MnS to form ( Mn,Te )S, which coarsens and spheroidizes sulfides in steel, to increase ellipsoidal and spindle sulfides in rolled products. The HV10 microhardness value of MnS inclusions increased from 142. 2 to 152.1 by Te modification, to improve the ability of MnS to resist rolling deformation.

Through 3 heats IF steel of 210 t RH refining process test, the effect of titanium-adjusted time on cleanliness of IF steel in RH refining process is studied by scanning electron microscopy. The results indicate that titanium adjustment after adding aluminum for 2,4 and 6 min, the average N content in molten steel at RH end is 26. 7 x 10 ^-6, 23. 6 x 10 ^-6 and 27. 4 x 10 ^-6 , respectively. When the oxygen blowing amount for heating,the oxygen consumption is 30 〜40 m ³ and the average initial oxygen content in liquid of RH is 579 x 10 ^-6, the T[O] is 70. 3 x 10 ^-6 at the RH end； When the oxygen blowing amount for heating, the oxygen consumption is 75 ~ 90 m ³ and the average arrival oxygen of RH is 669 x 10 ^-6, the T[O] is 109. 2 x 10 ^-6 at the RH end. The T[O] at the RH end shows an increase trend with the increase of oxygen activity before adding aluminum. The quantity density of inclusions with 5μm equivalent diameter in steel is 9. 32 /mm ² when adjusted Ti alloy after adding aluminum 6 min, it is lowest.

The formation mechanism of CaO-MgO-Al ₂O ₃ inclusions in GCr15 bearing steel at LF refining end point is studied by ASPEX automatic scanning electron microscope combined with thermodynamic theory analysis. The results show that Al ₂O ₃ is the main type inclusion in molten steel when the LF refining started to reach stability, and then evolves into an approximately spherical Al-Mg-Ca-( S) type composite inclusion at LF refining end. The stable phase diagram of MgO • Al ₂O ₃/CaO • A1 ₂O ₃/A1 ₂O ₃ shows that MgO •Al ₂O ₃ can be transformed into CaO-MgO-Al ₂O ₃ inclusions when [ Ca] is greater than 1.2 x 10 ^-6 in molten steel. The MgO • A1 ₂O ₃ inclusion would be formed firstly in the refining process, afterwards ,the Ca would react with MgO • A1 ₂O ₃ inclusion to form CaO-MgO-A1 ₂O ₃ composite inclusion. As a result of the precipitation of CaS inclusion in the solidification, therefor the CaO-MgO-Al ₂O ₃ -(CaS) composite oxide inclusion is detected in the final steel sample.

The Q195 steel is produced by M120 t BOF→LF→Ca addition→160 mm x 160 mm CC” process. It was found by tracing test that the number of ≥27μm large size inclusions at test area 50 x 400 mm ² in the billet is 31 and generated by LF top slag entrapped during gas stirring, calcium treatment formed CaS, submerged entry nozzle material stripped and formed endogenous large size calcium-aluminate inclusion in steel as the flow rate of argon is in the range of 300～600 L/min. The proportion of LF top slag entrapped is about 29. 1% in all the large size inclusions. As the flow rate of argon decreases from 300～600 L/min to 100 L/min, it is found that the LF top slag entrapped could be significantly decreased ,at some test area the ≥27μm inclusions number decreases to 19.

The measures as applying the process of Si-Ca deoxidation, controlling the total content of oxygen in the EAF molten steel and the content of Al ₂O ₃ in LF slag,Control refining time ≥40 min,vacuum degassing(VD),control soft blow time ≥20 min, and protecting cast to prevent secondary oxidation of the molten steel and promote the floating o£ inclusions in the steel are adopted at Hengsteel. The number and size of Grade B inclusion Al ₂O ₃ in the molten steel are reduced to improve the cleanliness of steel. Production practice shows that controlling steel [Al]s≤0.004% ,T[O] ≤0.0020% , refined final slag (FeO) ≤0.8% and alkalinity (R) between 2.0 and 3.2 in liquid of hydraulic cylinder steel are available to control Grade B inclusion. Grade B inclusions not exceeding class 1.0 is beneficial to control the production of " white spots" in the SRB process.

Cleanliness in GCrl5 bearing steel produced by 120 t BOF-LF-RH-CC process investigated results show that the inclusions dominated in steel are Al ₂ 0 ₃ . MgO spinel and Al ₂ 0 ₃ -MgO-CaO type after LF refining and the Al ₂ O ₃ • MgO spinel is almost disappeared and the inclusions in steel are mainly liquid calcium aluminate after RH treatment. T. 0 content decreases to 5. 3 X 10 ^-6 after RH treatment and Al ₂O ₃ • MgO spinel regenerates in tundish liquid during casting, and the ≥20um calcium aluminate inclusions are not found in liquid at end RH and tundish, and in casting bloom.