Inclusion variations and calcium treatment optimization in pipeline steel production

SiCa line and SiCaBaFe alloy were injected into liquid pipeline steel at the end of LF refining as calcium treatment,and samples were taken from the ladles,mould,and slabs.Analysis of Ca content and inclusions shows that Ca content in steel decreases obviously in the following process after calcium treatment;the compositions,morphology,and sizes of inclusions also vary much in the production;primary inclusions in the ladles prior to calcium treatment are mainly Al2O3 inclusions,but they turn to fine irregular CaS-CaO-Al2O3 compound inclusions after the treatment,then become fine globular CaO-Al2O3 inclusions in the mould,and finally change to a few larger irregular CaS-CaO-Al2O3 complex inclusions in the slabs.Thermodynamic study reveals that inclusion variations are related with the preferential reactions among Ca,Al2O3,and S and the precipitation of S in CaO-Al2O3 inclusions with high sulfur capacity.New evaluation standards for calcium treatment in high-grade pipeline steel were put forward according to the inclusion variations and requirements of pipeline steel on inclusion controlling,and the calcium process was studied and optimized.

Purifying Fe-based amorphous alloys to enhance glass-forming ability by designing a novel refining slag

Designing low melting point and low basicity refining slag suitable for Fe-based amorphous alloys and understanding the inclusions’formation,removal,influencing mechanisms are quite vital in the fields of metallurgy and materials.In this study,a novel 13%SiO_(2)-32%CaO-30%Al_(2)O_(3)-25%B_(2)O_(3)(wt.%)refining slag was designed after careful calculations of the liquid phase region,slag-metal equilibrium,surface tension,viscosity,deoxidation capability and sulfur distribution ratio.After refining with our designed slag,the content of impurities and the number density of inclusions in a representative Fe_(83)Si_(2)B_(15)(at.%)amor-phous alloy were significantly reduced.Moreover,the glass-forming ability(GFA)of the alloy was also enhanced,enabling the preparation of amorphous ribbons with a lower cooling rate.Based on the impu-rities in Fe-based amorphous alloys as well as the calculated oxide and sulfide free energy diagrams,CaO,SiO_(2),Al_(2)O_(3) oxides and CaS,TiS,MnS sulfides will form in the master alloy.The high melting point in-clusions in the melt are generally removed via a floatation-separation-absorption process and the Mn,Ti,S impurities are removed via slag-metal interface reactions during refining.As for the detrimental effect of inclusions on glass formation,the small lattice disregistry between Ti,Mn-containing inclusions and primaryα-Fe gains reveal that these inclusions are effective in promoting the heterogeneous nucleation,and therefore greatly deteriorate the GFA.These findings are important and provide an ideal solution to purifying the Fe-based amorphous alloys by refining and enhancing the GFA for industrial production.

Inclusion evolution in 50CrVA spring steel by optimization of refining slag

In order to control the CaO-Al;O;-SiO;-MgO system inclusions in 50 CrVA spring steel in a lower melting temperature region,high temperature equilibrium experiments between steel and slag were performed in the laboratory,under the conditions of the initial slag basicity within 3-7and the content of Al;O;between 18-35mass%,to investigate the formation and evolution of this type of inclusion.The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al;O;content in slags,and CaO-Al;O;-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al;O;content in slags.The most favorable composition for the refining slag is composed of 51-56mass% CaO,9-13mass% SiO;,20-25mass% Al;O;and 6mass% MgO.In this case,the inclusions in 50 CrVA spring steel are mostly in the low melting point regions,in which their plasticities are expected to improve during steel rolling.The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed.It is also found that adding around 11mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion.Further work should be carried out focusing on the evolution rates of MgO-based inclusions.

A Refined Theory of Axisymmetric Poroelastic Circular Cylinder

A refined theory of axisymmetric deformation of an isotropic poroelastic circular cylinder in a steady-state is presented directly by utilizing the general solutions and Lur＇e method without any advance hypothesis.The refined equations are derived under non-homogenous boundary conditions,and the approximate solutions are obtained by omitting higher-order terms.The all-inclusive refined equations and approximate solutions constitute the refined theory of circular cylinders.Correlative examples are brought up to analyze influences of liquid-solid coupling properties on the mechanical behavior of poroelastic materials.Moreover,the present results are converted into those of homologous pure elastic problem directly.