Due to its superior features compared to plain steel products, stainless steel has been widely used for various applications, since it is commercialized in the beginning of the 1900's. Since ...stainless steel is characterized by high chromium (and nickel) content, stainless steelmaking processes have been developed differently to those of ordinary steelmaking. However, like plain carbon steels, non‐metallic inclusions significantly influence the quality of stainless steel products. In order to gain a better understanding of the impact of inclusions on the characteristics of stainless steel products, information from a large amount of previous research on non‐metallic inclusions in stainless steel is reviewed. As expected, non‐metallic inclusions are a probable cause of pitting corrosion, as well as crack initiation and growth. The formation and origin of inclusions during the steelmaking and continuous casting processes are also discussed based on a number of relevant studies.
In order to gain a better understanding of the impact of non‐metallic inclusions (NMIs) on the characteristics of stainless steel products, information from a large amount of previous research on NMIs in stainless steel is reviewed. NMIs are a probable cause of pitting corrosion, as well as crack initiation and growth. The formation and origin of inclusions during steelmaking and continuous casting processes are also discussed.
•Pit-shaped defects in Cf53 rolled products due to large composite CaS-inclusions.•Large composite CaS-inclusions accumulate on the inner wall to form SEN clogging.•T.O, T.Ca, T.S content, and steel ...temperature affect the formation of CaS-inclusions.•Reducing Ca wire amount fed in Cf53 steel has significant industrial application.
Aiming at the frequent issue of pit-shaped surface defects in S-bearing and Al-killed steel products and the related poor castability due to submerged entry nozzle (SEN) clogging, the melting and casting process of a popular auto steel Cf53 has been studied based on in-situ investigation and experimental analysis. To clarify the generation of the pit-shaped defects, the local surface chemistry, evolution of steel inclusions throughout the melting process, SEN clogging substances, and the internal relationship among them were systematically analyzed. The results show that this type of defect in the Cf53 rolled products is caused by the large-sized composite inclusions rich in CaS, which originate from the molten steel during the refining process, gradually accumulate on the inner wall of the SEN during casting, and finally lead to SEN clogging. The loose structure of clogging inclusions makes them prone to fall off into the mold and get trapped by solidifying steel shell. The formation mechanism of the inclusions was studied through FactSage software calculation. The results show that the increase in total sulfur and total calcium content, and the decrease in total oxygen content and temperature in steel will lead to CaS inclusion formation, which agrees reasonably well with experimental results. An optimized refining process to reduce calcium addition into molten steel is proposed accordingly, which achieves a remarkably alleviation in casting SEN clogging and an elimination of the pit-shaped defects on the final rolled products as well.
Energy consumption is a vital aspect in the production of high quality materials by using electro slag remelting as a refining method. The electrical conductivity and the melting point of the slag, ...determined by the slag composition, as well as the fill ratio, the amount of slag and the melt rate have as significant influence. Several of these factors as well as a new method to measure the slag surface temperature with a two-color pyrometer were investigated in laboratory scale remelting trials. Two different slags with an average and a low electrical conductivity were used. While there is only a small impact of the slag cap height and the melt rate, the slag composition showed a strong effect, both on the slag surface temperature as well as on the specific energy consumption. Additional investigations confirmed that the effect of the slag composition on the amount and compositions of non-metallic inclusions, respectively the cleanliness level of the steel after remelting is rather minor. The results suggest possibilities for easily applicable, improved process parameters, which can combine high product quality with significantly reduced energy consumption.
Energy consumption is a vital aspect in the production of high quality materials by using electro slag remelting as a refining method. The electrical conductivity and the melting point of the slag, ...determined by the slag composition, as well as the fill ratio, the amount of slag and the melt rate have as significant influence. Several of these factors as well as a new method to measure the slag surface temperature with a two-color pyrometer were investigated in laboratory scale remelting trials. Two different slags with an average and a low electrical conductivity were used. While there is only a small impact of the slag cap height and the melt rate, the slag composition showed a strong effect, both on the slag surface temperature as well as on the specific energy consumption. Additional investigations confirmed that the effect of the slag composition on the amount and compositions of non-metallic inclusions, respectively the cleanliness level of the steel after remelting is rather minor. The results suggest possibilities for easily applicable, improved process parameters, which can combine high product quality with significantly reduced energy consumption.
Spring steel wires are extensively utilized in automotive engines valve and suspension applications. Owing to spring often work under high-frequency dynamic loads and periodic alternation stress, ...non-deformable inclusions often act as fatigue fracture origin of spring steel. The control of inclusions in spring steel for automobile are extensively reviewed. On the one hand, the new perspective on the problems left over the past decades, include the new viewpoint on whether FeO is an inherent constituent of inclusions, the new understanding of the origin of CaO-based inclusions, the new perspective of whether the VD treatment progress should be removed but RH retain, have been discussed. On the other hand, the new approaches, via, calcium treatment, alkali oxide treatment, rare earth treatment, new refractory application, have also been summarized. Finally, the unsolved problems, the source of CaO-based inclusions, the mechanism of alkali metals modified inclusions, the based thermodynamic data for reactions between rare earth yttrium (Y) and non-metallic inclusions, the operability of CaO-containing refractory in industry, that should be explored further are also been discussed.
In order to raise the hardness and strength of the surface layer of mechanical components and induce favorable residual compressive stresses, case‐hardening procedures have become established in the ...heat treatment of steel. In this work, a calculation concept for the fatigue strength of components that have been case‐hardened through carburizing heat treatment is being developed. The residual stress and the load stresses in complex‐shaped, carburized materials are determined using a finite element (FE) model. The fatigue limit of the components is derived using probabilistic methods and taking into account hardness gradients, residual stresses, and non‐metallic inclusions. The model is validated with available axial bending fatigue test data and then used to predict the rotating bending fatigue limit of samples with various geometries and heat‐treatment conditions. This work demonstrates the capability of combining probabilistic and FE‐based modeling to represent complex interactions between variables that affect the fatigue of heat‐treated components, such as steel cleanliness, notch shape, case‐hardening depth, or loading conditions.
Highlights
Combined FE‐based and probabilistic methods can predict fatigue strength accurately.
Interplay of heat‐treatment output, geometry, load, and material is considered.
Crack initiation position gets shifted by increased case‐hardness depth.
Fatigue strength reduction due to defects in steel depends on load concentration.
Spring steel wires are extensively utilized in automotive engines valve and suspension applications. Owing to spring often work under high-frequency dynamic loads and periodic alternation stress, ...non-deformable inclusions often act as fatigue fracture origin of spring steel. The control of inclusions in spring steel for automobile are extensively reviewed. On the one hand, the new perspective on the problems left over the past decades, include the new viewpoint on whether FeO is an inherent constituent of inclusions, the new understanding of the origin of CaO-based inclusions, the new perspective of whether the VD treatment progress should be removed but RH retain, have been discussed. On the other hand, the new approaches, via, calcium treatment, alkali oxide treatment, rare earth treatment, new refractory application, have also been summarized. Finally, the unsolved problems, the source of CaO-based inclusions, the mechanism of alkali metals modified inclusions, the based thermodynamic data for reactions between rare earth yttrium (Y) and non-metallic inclusions, the operability of CaO-containing refractory in industry, that should be explored further are also been discussed.
The evolution of inclusions with Ce addition and Ca treatment in Al-killed steel during RH refining process was investigated through experimental observations and thermodynamic calculations. The ...results indicated that the typical inclusions before Ce addition are CaO–Al2O3 inclusions, which were a liquid state during RH refining. After Ce addition, the typical inclusions was transformed from calcium aluminate inclusion to (Ca–Ce–S–O)+(Ce–Al–Ca–O) complex inclusion. After Ca treatment, the types and morphologies of typical inclusions in steel did not change. Experimental observation and thermodynamic calculations shown that a certain amount of Ca addition can’t affect the formation of Ce-containing inclusion, which may indicate that Ca treatment should not be carried out for rare earth treated steel.
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