EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

In November 2015 voestalpine Stahl Linz started up its secondary metallurgy No. 4. This facility consists out of a ladle furnace, a RH vacuum degasser and a trimming stand and is located in the east of the steel plant just opposite to the slab caster CC 7. Already in the early phase of a feasibility study it was decided that this secondary metallurgy will be an investment for the `high end´ quality segment. Beside the secondary metallurgy itself it was also necessary to install auxiliary equipment, like a secondary dedusting unit with 700.000 m3/h, a ladle tilting/preparation stand and three ladle preheaters. Additionally numerous relocations of existing equipment were required in order to get space for these new installations. Strategic focusing on the topmost quality segment requires a consequent fine tuning of the entire process chain. Together with the extension of the secondary steelmaking capacity of voestalpine´s LD 3 steel plant in Linz continuous increasing demands on quality as well as logistics are covered. The `metallurgical link´ of a RH degasser and a ladle furnace using common ladle cars has been proven successfully, based on the experience of two similar existing configurations. Supplementary, the new concept of the secondary metallurgy no. 4 was extended by utilizing an additional trimming stand for desulphurization and wire feeding as well as a third crane lifting position. The ladle furnace is installed with a 25 MVA transformer and thus heating rates up to 5 degrees per minute can be achieved. Moreover the ladle furnace is equipped with a lance injection system for desulphurization which can also be used for rinsing, an automatic coupling system to the ladle bottom rinsing bricks, four lines for wire feeding and in total 20 alloying bins for the numerous Fe-alloys and slag conditioning materials. The ladle furnace cover is cupper plated in order to avoid skull built-up on the lid, coming from a very low ladle free board. The RH degasser is equipped with a four stage steam ejector pump with two parallel ejectors for the high amounts at the beginning of the vacuum process. A pressure of 1 mbar can be achieved within 5 minutes. A combination of burner and oxygen lance is installed for heating and deskulling the refractory of the vessel. The oxygen lance is used for adjusting the correct carbon to oxygen ratio and can also be taken for chemical heating. The alloying system with the 20 alloying bins is used commonly with the ladle furnace. Furthermore there are two micro alloying bins for smaller, but more accurate amounts of additions and two further vacuum bins. The trimming stand is equipped with a centric positioned lance injection system for desulphurization, four lines for wire feeding and again, like on ladle furnace and RH-degasser, with an automatic coupling system – here also with the possibility of soft bubbling for inclusion separation. The treatment on the trimming stand is done under a ladle cover, similar to the ladle furnace, which is also interchangeable between those two facilities. All three installations are equipped with an automatic sample and temperature device, including a vacuum sampler on the trimming stand which meets special demands for analyzing lowest contents of residual elements. Hydrogen measuring systems are available on the ladle furnace and the RH degasser. The whole secondary metallurgy no. 4 is operated from one common control room. All metallurgical operations are done on the level 2 system, the process observation is followed either on the level 1 system or on over 20 different camera positions/screens. The installation was also designed in conformance with the safety regulations of the EN DIN norm 14677. Therefore, amongst many other required safety items, a key transfer system is applied. On one hand this system prevents unauthorized access to plant components and on the other hand provides safety to people working on plant components from unintentionally caused movements. Beside the logistic advantages within the steel plant process flow, the new facility shows excellent metallurgical results. Multiple treatment steps can be operated at three optimized aggregates. For example, the treatment steps of grades for heavy plate and high strength hot strip consist of desulfurization by injection at the trimming stand, alloying and adjustment of temperature at the ladle furnace and fine tuning of the analysis and degassing at the RH degasser. Finally the inclusion modification is done again at the trimming stand. On the other end of the production spectrum ultralow carbon grades are tapped with low tapping temperature in order to relieve the converter from excessive refractory wear. These grades are heated in the unkilled´ status on the ladle furnace and are then vacuum-treated on the RH-degasser. In case of operational necessities it is also possible to run the new secondary metallurgy in asplit´ mode: one steel grade with low heating requirements is prepared for the RH-degasser and finally treated there and sent* to a CC, while the other steel grade is produced as non-vacuum treated steel grade on the ladle furnace for another CC. The full strength of all 4 secondary metallurgical installations in the steel plant LD 3 will come to its final fulfillment in terms of capacity and quality requirements after the commissioning of the new CC 8 in autumn this year. By this time the aimed direct logistic link´ betweenone secondary metallurgy´ to one CC-machine will be given.