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.
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.
During the continuous casting of Ti‐stabilized ULC/IF steel grades clogging of the submerged entry nozzle (SEN) is frequently observed. A new statistical evaluation indicates that increasing ...Ti/Al‐ratios in these steels lead to an increase in the occurrence of clogging and its intensity. Investigations of samples of two TiULC heats, taken at the RH‐degasser, show a remarkable increase of inclusions due to FeTi‐addition. The presence of Ti‐bearing alumina particles contrary to the thermodynamical expectations, indicate that their formation takes place as a consequence of FeTi‐addition. Laboratory‐scale experiments confirm the formation of alumina inclusions containing traces of Ti. Their size is found to be significantly smaller compared to pure alumina inclusions. Rising numbers of small inclusions within the steel are suspected to accelerate the buildup of clogging deposits. Two mechanisms are proposed to explain the formation of these particles. On the one hand ferrotitanium acts as a source of oxygen, resulting in the formation of new inclusions during dissolution. On the other hand, the modification of preexisting deoxidation products in regions with high Ti‐contents may play a role.
Titanium is commonly used as a stabilizer for IF steel grades. The FeTi‐addition is known to cause clogging problems in the continuous casting process, which is also shown in a statistical evaluation of the clogging tendency of 3326 melts. Examinations of samples from RH‐processing and laboratory scale‐experiments indicate that FeTi‐addition leads to the formation of small inclusions which are prone to clogging.
The article presents the test results of complex microcrystalline modifiers containing calcium, barium, strontium, rare earth metals. Complex modifiers were used in the processing of steel for ...17G1S-U pipes in order to reduce its contamination with non-metallic inclusions, including corrosive ones. The use of modifiers allowed to reduce metal contamination by non-metallic inclusions of all kinds. The most experimental non-metallic inclusions were obtained during metal processing with INSTEEL®5.1 and INSTEEL®9.4 modifiers. In addition, the use of experienced modifiers ensured the production of complex oxysulfides of calcium, cerium and lanthanum with low oxygen content and thermal expansion coefficients, which increases the corrosion resistance of steel.
This second part of the review on defects as root cause of fatigue failure comprises the origin, the nature and the effects of non-metallic inclusions. Topics addressed are the different kinds of ...inclusions formed during the manufacturing process, various types of mis-match causing local stresses and, as a consequence, fatigue crack initiation, and effects of characteristics such as size, morphology, localization, spatial distribution and orientation of the defects on the fatigue behavior. Methods for inclusion counting and sizing are discussed along with statistical aspects necessary to be considered when evaluating structural components.
•Part of a comprehensive review on material and geometrical defects as root cause in failure analysis.•Discussion of the background as well as of practical effects of non-metallic inclusions in fatigue.•Discussion of the various parameters which affect the influence of inclusions on short and long crack propagation.
Crack initiation at inclusions is a dominant, unavoidable and life-limiting failure mechanism of important structural materials. Fatigue progresses in a complex manner to find the ‘weakest link’ in ...the microstructure, leading to crack nucleation. In this study, fully 3-D characterization methods using high energy synchrotron x-rays are combined with in-situ mechanical testing to study the crack initiation mechanism in a Ni-based superalloy specimen. The specimen was produced via powder metallurgy and seeded with a non-metallic inclusion. Two x-ray techniques were employed: absorption contrast computed micro-tomography (μ-CT) to determine the morphology of the inclusion and its location in the gauge section of the specimen; and far-field high energy diffraction microscopy (FF-HEDM) to resolve the centroids, average orientations, and lattice strains of the individual grains comprising the microstructure surrounding the inclusion. Sequential μ-CT and FF-HEDM scans were carried out at both peak and zero applied stress following schedules of cyclic deformation. The μ-CT data showed the onset and location of crack initiation, and the FF-HEDM data provided temporal and spatial evolution of the intergranular strains. Strain partitioning and the associated stress heterogeneities that develop are shown to stabilize within a few loading cycles. Elasto-viscoplastic fast Fourier transform simulations were utilized to supplement interpretation of the experimental stress distributions and compared with the experimental stress distributions. Appropriate conditions for crack nucleation in the form of stress gradients were demonstrated and created by virtue of the inclusion, specifically the residual stress state and local bonding state at the inclusion-matrix interface.
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Non-metallic inclusions (NMIs) occur typically in low or very low volume fractions (from 10−2 in a high oxygen weld deposit to 10−5 in very clean bearing steels) but play an important role in many ...properties of steel. NMIs play a decisive role in processes involving ductile fracture, fatigue and corrosion, for instance. These are some of the properties more relevant to the performance of steel in structural and mechanical applications. Furthermore, NMIs may influence nucleation during phase transformations of steel. In this work, the relation of these properties to NMIs is reviewed, highlighting progress and difficulties in each area. Perhaps because of their very low volume fraction, NMIs are sometimes overlooked in the basic physical metallurgy education and their study is left to the realm of those interested in steelmaking. In the last decades a dramatic evolution in the understanding of their relationship to properties, however, has led to significant improvements in many steel products: the outstanding increase of fatigue life in automotive springs and in bearings is one of many such examples. It is concluded that steel improvement in many cases requires “inclusion engineering” and this can only be achieved through close collaboration between physical metallurgy, process metallurgy and steelmaking. Those who realized this have made significant progress in steel development in recent decades as highlighted in this short review.
The accurate identification of non-metallic inclusions (NMIs) within steel matrices is critical for high-quality steel production. This study employs synchrotron radiation-based X-ray absorption ...photoemission electron microscopy (X-PEEM) to investigate NMIs in ultra-high-strength steels. Ca-L2,3-edge X-ray absorption spectra were acquired for six NMIs at both room temperature and 400 °C, allowing a comprehensive exploration of structural changes, chemical compositions, and phases. Complex X-PEEM images were analyzed using advanced chemometric techniques, including Principal Component Analysis (PCA), K-means clustering, Fuzzy-means clustering (FMC), and Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS). These methods allowed for the segmentation of X-PEEM images into distinct compositional zones. K-means clustering effectively identified regions of interest (ROIs) within NMIs, while PCA facilitated the microstructure variances of NMIs. Additionally, K-means and FMC revealed detailed compositional variations at the nanoscale. MCR-ALS proved particularly useful in uncovering changes in NMIs after annealing. This study pioneers the integration of X-PEEM with advanced chemometric methodologies, providing qualitative and quantitative spectromicroscopic insights. It significantly enhances our understanding of NMIs formation and alteration processes in ultra-high-strength steels, contributing to the advancement of materials science and steel production optimization. Furthermore, the methodologies and findings presented here serve as a guide for analyzing similar data sets of steel samples, offering valuable insights for future research and industrial applications in steel engineering.
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•Unraveling the Secrets of Steel: Chemometric Insights into Non-Metallic Inclusions Using Advanced X-PEEM.•Chemometric Exploration of NMIs in Ultra-High-Strength Steels: An X-PEEM Spectromicroscopic Approach.•From Synchrotron Radiation to Chemometric Excellence: Probing Non-Metallic Inclusions in Steel Matrices.•Breaking New Ground: X-PEEM and Chemometrics Uncover the Complexity of NMIs in Ultra-High-Strength Steels.•Innovative Chemometric Strategies Transforming X-PEEM Imaging for Enhanced Steel Material Analysis.
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