The demand for cleaner steels requires reducing the number of macroscopic non‐metallic oxide inclusions. A major problem of “clean steel” is the measurement and evaluation of the rare large ...inclusions which exceed a critical size harmful to the product. To this end, volumetric methods of evaluating macro‐inclusions in the three‐dimensional steel matrix are necessary to qualify steel heats or continuous cast slabs and to check if the refining and casting processes are stable and have been improved. Ultrasonic scans are a powerful tool to assess the quality of the volume. In order to activate macroscopic oxide inclusions for the reflexion of the ultrasound, as‐cast material is deformed by hot rolling. The aim of the present research work was to find out the most effective hot rolling practice with respect to ultrasonic detection of the rare large oxide inclusions. For this purpose, heavily contaminated neighbouring slab samples, corresponding to a severe incidence of ladle slag carryover, were hot rolled in a different manner. The 23‐kg‐samples were either elongated by a ratio λ = 2, 3, 10 or 15, or alternatively cross‐rolled, e.g. spread and stretched by ratios 2 × 5 or 3.2 × 3.2. The best compromise to quantify macroscopic steel cleanliness under consideration of cost and time requirements is based on the pure 10fold elongation or the cross‐rolling by 2fold x 5fold. It likewise became clear that rare large oxides can be detected with good sensitivity, as long as the hot rolling reduction ratio is large enough.
Recycling of ladle slag in cement composites: Environmental impacts Serjun, Vesna Zalar; Ana MladenoviauthorSlovenian National Building and Civil Engineering Institute, Dimieva 12, 1000 Ljubljana, Slovenia; Breda MirtiauthorUniversity of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Geology, Akereva 12, 1000 Ljubljana, Slovenia ...
2015
Journal Article
This is the observation of pin hole defects occurred in cast iron by green sand mold with SEM. All 109 samples (gas hole defects) gathered from 34 foundries are observed. The defects are classified ...in 4 types as follows : In D), there are still more 3 types defects. A) round pin hole, B) thin & long pin hole, C) fissure pin hole, D) slag pin hole (a : ladle slag, b : inoculant, c : manganese sulfide). Typical SEM photo (A～D) is shown the figure. By standardizing these, SEM photos, it will be possible to classify the pin hole defects occurred in foundries and it will help studying of prevention.
In steelmaking process, the refining technology are progressed greatly by the introduction of combined blowing converter and the spread of the process of hot metal pretreatment. At Mizushima Works, ...the top-and-bottom blowing converter (K-BOP) were introduced in April 1980 and the hot metal pretreatment facilities had the capacity of pretreating all hot metal in November 1988. For the purpose of the development of best K-BOP only for decarburization practice, we made the experiments of reducing the bottom oxygen flow rate. As a result, it was able to reduce to 0.25 Nm3/min·t from 0.8 Nm3/min·t (conventional way) with same metallurgical characteristics, when the inert gas is used at final stage of blowing at the rate of 0.35 Nm3/min·t or above using pretreated hot metal. Based on this principle, we changed the K-BOP's tuyeres and obtained the prolongation of converter life and the reduction of process gas cost. Furthermore, by using the pretreated hot metal and controlling the converter slag basicity to more than 5 and the (%MgO) to around 10% and deoxidizing the ladle slag, the quality and cleanliness of ultra low carbon steel for cold-rolled sheet is able to be improved drastically.
The nonmetallic inclusions absorbed by ladle slags during secondary steelmaking operations and in the tundish and mold during casting are crucial to the production of interstitial‐free (IF) steel. ...However, little to no research has been conducted on the separation and dissolution of inclusions along with a focus on IF steel. Herein, a theoretical study of the separation of solid alumina at the steel–slag interface is conducted. The dissolution of alumina particles is observed in situ in different IF steel slags, and the dissolution mechanism is analyzed. The results show that the interfacial tensions and slag viscosity have a large influence on the predicted displacement, but for IF steel production, the dissolution of inclusions in the slags has a greater influence on the removal of inclusions than on inclusion separation. Using ladle slags with a proper CaO wt%/Al2O3 wt% is the most effective way to remove the Al2O3 inclusions compared with the other slags in IF steel production.
The separation of Al2O3 inclusions at the steel–slag interface is calculated, and the single hot thermocouple technique (SHTT) method is proposed to observe in situ the Al2O3 dissolution in various slags in interstitial‐free production. The results show the restrictive link of inclusions absorbed by slags is the dissolution of inclusions in the slag instead of the separation of inclusions.
In the present paper, different trials using BaO as a ladle slag tracer were performed to investigate the role of slags on the formation of non-metallic inclusions. Results of these trials showed ...that the ladle slag may actively contribute to the generation of inclusions. In those heats where the tracer was added it was found that about one-third of the large inclusions detected in the final product had BaO in their composition. These inclusions may be generated by emulsification of the ladle slag during the refining stage at the ladle furnace. Additionally, inclusions containing BaO were also observed in some of the heats processed with the same ladle that previously had been used with traced slags. This fact suggests that the slag layer that remains stuck to the ladle wall after finishing the heat may be a source of inclusions for the next heat.
It is necessary to have information on the thermodynamic behavior of titanium oxide in ladle type slags in order to control the titanium content in several grades of steel. In the present study, the ...thermodynamics was determined from the equilibrium between Fe–Csat–Ti and CaO–SiO2-–30%Al2O3–MgO–TiOx slags in equilibrium with CO and from the equilibrium between Fe–Csat–(1618)%Cr–Si–Ti and CaO–SiO2–20%Al2O3–MgO–TiOx slags in equilibrium with CO. From the experiment with Fe–Csat–Ti alloy, the activity coefficients of TiO1.5 and TiO2 vary with basicity from 0.3 to 1.5 and from 0.5 to 2.3, respectively. And from the experiment with Fe–Csat–(1618)%Cr–Si–Ti alloy, the activity coefficients of TiO1.5 and TiO2 vary with basicity from 0.4 to 1.4 and from 0.6 to 3.5, respectively. The results obtained from the equilibrium between Fe–Csat–(1618)%Cr–Si–Ti and CaO-SiO2–20%Al2O3–MgO–TiOx slags were used to estimate the titaniumcontent of silicon-added stainless steel. Experiments were also conducted using Fe–Al–Ti melts in equilibrium with CaO–SiO2–Al2O3–TiOx slags saturated with MgO. In this case most of the titanium in the slag is present as TiO2(Ti4+). The present results were used to predict the titanium content of aluminum-killed steel in equilibrium with ladle slags containing titanium oxide and the predictions agreed with plant data.
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