Stahlschlussel Key To Steel 2007: Decode and Decipher Steel Designations with Ease

The production of new steel by recycling old steel requires up to 10 times less energy than the primary production of steel from iron ore [5]. As foreseen in the steel industry, electric arc furnace (EAF) steelmaking, either scrap-based or based on hydrogen-direct-reduced iron, will contribute substantially to the reduction of CO2 emissions [4]. However, there will still be a need to introduce carbon into the EAF process, either to carburize the steel or to create foaming slag to improve the energy efficiency of the steelmaking process. To develop a fully green steel using EAF, it will be necessary to use alternative carbon sources that are either renewable or circular (e.g., biomass, plastic, rubber wastes, etc.) [4].

Stahlschlussel Key To Steel 2007

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Production starts with scrap remelting in EAF followed by secondary metallurgy [5]. For a wide variety of steel grades, intensive scrap-steel recycling in an EAF is already common practice [6,7,8,9,10,11,12]. Scrap is usually well sorted already by suppliers and typically has a low impurity content. On the other hand, when end-of-life (EOL) steel scrap is recycled, the different steel grades are generally separated according to main alloying elements (Cr, Ni, Mo). Some nonferrous and nonmetallic contaminants (copper wires, aluminium, plastic from the shredding of cars, concrete residuals from demolition of buildings, etc.) are generally mixed in small quantities with the steel because of the imperfect separation of different materials prior to melting. Some impurities are removed as slag when the mixture is melted or during subsequent refining steps, and some elements evaporate, but some metallic elements cannot be simply removed (copper, lead). Consequently, the exploitation of steel scrap can lead to an overall increase in the impurity concentrations in steels that cannot be removed by metallurgical processes. Many problems are related to excessive levels of impurities that are prone to precipitation, segregation, and/or the formation of various complex nonmetallic inclusions [5,6,7,8,9,10,11,12]. Accordingly, studies that address open issues in scrap recycling are of great importance.

Initially, the role of the titanium added to steel as ferrotitanium was mainly to reduce the grain size and to act as a deoxidizer [25]. Titanium dissolved in steel is characterized by a high affinity for oxygen. Titanium lowers the activity of the oxygen in iron [22]. Since surface defects can occur on final steel products, control of the formation of oxide inclusions in Ti-bearing stainless steels is necessary. In addition, the deoxidation products can potentially form deposits within a submerged entry nozzle and thus clog the nozzle [26].

In steels, titanium is also highly reactive with carbon, nitrogen, and sulphur [27]. Nitrogen is an element that causes a great deal of concern. Since titanium nitride forms in preference to titanium carbide, based on thermodynamic considerations, it is essential (i) to add sufficient titanium to chemically bind the nitrogen first and then the carbon or (ii) to reduce the nitrogen as much as possible using other steelmaking techniques [27].

Titanium alloying can be made in the form of metal scrap, sponge, or as a ferrotitanium alloy. Ferrotitanium addition for binding interstitial elements is usually performed after the steel is refined in a ladle furnace (LF) [26]. For the cored wire, FeTi alloying is made as deep and late into the ladle as possible. Prior to the alloying, the liquid steel should be thoroughly deoxidized to reduce the oxidation of, and thus maximize the recovery of, the titanium [27]. In the case of titanium-stabilized stainless steels, the LF refining process involves deoxidation by Al followed by the addition of the Ti-alloy [26,28,29].

The aim of this study was to evaluate the influence of impurities on nonmetallic inclusion formation and the quality of hot-rolled plates manufactured from titanium-stabilized, austenitic stainless steels of AISI316Ti grade, i.e., from Cr-Ni-Mo steels produced by secondary metallurgy. In particular, the influence of the impurities present in a recycled ferrotitanium and the detected oxygen contents in the steel were highlighted. The metallographic results were compared and discussed with reference to the results obtained using mathematical modelling. NMI features obtained by automated metallographic analyses were employed to numerically estimate the quality of the hot-rolled plates. In the relevant scientific literature, NMIs are classified according to their type (carbides, nitrides, sulphides, oxides, etc.), and other, more complex inclusion types is a well-covered topic [6,7,9,10,11,13,14,15,16,17,18]. However, the use of NMI features for the detection of production abnormalities in terms of two-class classification has not been reported.

For the metallographic analyses, the representative steel samples were selected using sampling in the longitudinal (i.e., rolling) direction. Steel samples taken from the hot-rolled plates are designated as Sample A, Sample B, and a reference Sample R.

In representative microstructures of the analysed hot-rolled steel plates A, B, and R, large accumulations of impurities and oxygen were observed. Moreover, it is obvious that not only Ti but large amounts of additional impurities were introduced into the steel by alloying using a recycled FeTi (see Ti, O, S, Mo, Bi and Pb maps in Figure 2). In addition, a considerable proportion of the volume was also represented by segregations of the impurity elements Mo, S, Pb, and Bi cosegregations (Figure 10 and Figure 11).

The presence of low-melting-point eutectic phases can initiate liquation cracking [38]. The hot cracking of steels is dependent on the levels of impurity elements. The impurities S, P, Pb, Bi, Sn, and Sb affect the hot workability of stainless steels. S and Pb segregate to the phase and solidification grain boundaries where cracks appear during hot deformation [39]. Particularly in Ti-stabilized, fully austenitic stainless steels, various carbosulphides and eutectics in conjunction with S, N, and C are deleterious [40].

Although many material properties exhibit a continuous span, the standards for specific steel grades determine the limit values and can thus also be considered as binary (normal vs. abnormal). On the other hand, many properties such as surface defects, cracks, etc. are inherently binary (normal vs. abnormal). The remaining production without detected defects or within the specified tolerances can be considered as the normal production class. Using thresholding of the MDs, we could use the MD as a predictive classification model, although with some precautions and limited predictive accuracy [35]. Nevertheless, the MD has found various applications [34]. MD is used to construct a continuous measurement scale to discriminate observations and measure the level of abnormality of abnormal observations that are compared to a group of normal observations [34].

The MD, as a measure of the difference between only two classes, offers some possibilities for the automatic detection of anomalies in steel measured indirectly using data obtained with the automatic detection of nonmetallic inclusions. Since the MD is by nature a comparative method, the data obtained (automatic detection of nonmetallic inclusions) on charges without any, or with noticeable, anomalies could be used for the normal or reference class.

Macrofractographic evaluation was performed using a stereomicroscope. Chemical analysis for steel grade identification was conducted using optical emission spectrometry. Hardness testing was performed using a universal hardness tester employing standard Rockwell C technique according to ASTM E-18 and Vickers hardness technique under 5 kg-force applied load according BS EN ISO 6507-1 standard. In addition, high-magnification fractographic observations were conducted on ultrasonically cleaned specimens, using a scanning electron microscope with a secondary electron detector for topographic evaluation and an energy dispersive x-ray spectrometer for elemental analysis.

The chemical composition of the shaft sample, analyzed by optical emission spectrometry, is presented in Table 1. The material composition matches to the special high-alloy stainless steel grade, which is almost equivalent to AISI XM-19/UNS S20910 standard steel grade (austenitic steel), see Ref. [1]. This high-alloy stainless steel offers exceptional corrosion resistance in combination to high strength and toughness.

Compared to untreated stainless steel bracket material, the antibacterial effect of the PIIID silver-modified surface was just as significant with regard to reducing the biofilm volume and the surface coverage as the galvanically applied silver layer and the PVD silver coating. Regarding the live/dead distribution, however, the PIIID modification was the only surface that showed a significant increase in the proportion of dead cells compared to untreated bracket material and the galvanic coating.

Orthodontic stainless steel with a silver-modified surface by PIIID procedure showed an effective reduction in the intraoral biofilm formation compared to untreated bracket material, in a similar manner to PVD and galvanic silver coatings applied to the surface. Additionally, the PIIID silver-modified surface has an increased bactericidal effect.

The biofilm growth was analyzed by live/dead fluorescent staining and subsequent CLSM. This well-established method for quantifying initial biofilms enables biofilm morphology to be recorded in an almost native manner [28, 35, 51, 61]. In addition to bacterial cells, in the microscopic image of the stained biofilm, human cells, potentially gingival epithelial cells, can be detected on the samples surfaces. It has already been demonstrated that oral bacteria are able to colonize human gingival epithelial cells and thereby integrate them into the biofilm formation [63]. The quantification of the biofilms showed a significant reduction in plaque accumulation with regard to biofilm volume and surface coverage on all silver-modified surfaces compared to untreated bracket material. Silver has an antibacterial effect due to silver particles inducing destruction of the respiratory chain by inhibiting important enzymes [53]. In addition, they inhibit the DNA replication of the microorganisms [26]. No significant differences between the individual silver surface modifications were observed. In contrast to this, with regard to the live/dead distribution, the PIIID procedure was the only examined surface modification that showed a significant increase in dead bacteria compared to untreated bracket steel and the galvanic coating. This indicates that the implanted silver ions in stainless steel bracket material lead to an improved antimicrobial effect. Therefore, despite the low implantation depth of a few nm, the PIIID procedure presented a significant antibacterial effect. 2ff7e9595c