A view at the present and future of express control of steel production

spectrometer together with set of equipment that provide the excitation of characteristic radiation of analyzed liquid steel and transferring it to the spectrometer.

metal in various areas of metallurgical process, for several decades, the structure of the organization of control and the arrangement of the measuring instruments themselves have remained unchangeable fundamentally. Instead of operators performing manual measurements with probes in the form of fishing rods, on which measuring sensors or samplers are pulled on, manipulators are increasingly being used [7]. However, the basic design of the sensors themselves in most cases remains unchanged: a protective cardboard sleeve plus a measuring element or the head of sampler. Measurements are made periodically, lasting from several to tens of seconds, after which the sensor (sampler), having performed disposable measurement (in the case of the sampler, having obtained a metal sample), and then thrown away. For the next measurement, another probe is put on the probe, etc. [8][9][10][11][12][13][14][15][16][17][18].
Typical implementation scheme of monitoring of liquid steel parameters in basic oxygen furnace (BOF) convertor is shown in Fig. 2. Here, a probe system is used for measurements, which allows one to determine several M odern steelmaking is focused on the intensification of all technological processes in order to increase its productivity. The growing competition in the global metal product markets places increasing demands on the quality of steel, while forcing metallurgists to identify reserves to reduce its cost [1].
One of the important tools in the production of quality steel is its analytical control. The metallurgist is faced with the problem of how to control the smelted steel and what means to spend on this to achieve the required quality criteria. Sensor types used at different stages of steelmaking are listed in Fig. 1 [2].
World experience attests that the most successful metallurgical enterprises invest many times more in control tools than, for example, Ukrainian metallurgists, resulting in high-quality metal, the price of which, as well as a significant reduction in rejects, many times covers the costs of controlling its parameters [3][4][5][6].
It should be noted that despite of continuous improvement of the equipment used to perform analytical control of taken sample is immediately fed to the Quik-Lab II automatic optical spectrometer, which is adapted to work on the steelmaking site under the difficult conditions of of its parameters when deepening into a metal: a thermocouple, oxygen activity, carbon content, and take a steel sample. In order to speed up receipt of the analysis results by eliminating the delivery of the sample to the express laboratory, the so-called container laboratory is often installed on the work site -"in field". However, experience has shown that the complexity of container laboratories and high requirements to their maintenance, as a rule, lead to their rapid decommissioning, and resumption of functioning through the express laboratory. Fig. 3 presents the most modern Heraeus Electro-Nite solution to measure in BOF without its tilting and making interruption of the process [19].
In this case, a Sublance-type immersion probe takes a steel sample in an inert gas stream, which ensures that its surface is not oxidized, as a result of which the time-consuming sample preparation for analysis procedure is excluded from the analytical cycle. Thus, the just Sensors for liquid steel control ТЕПЛОФІЗИЧНІ ТА ФІЗИКО-ХІМІЧНІ ПРОЦЕСИ ТВЕРДІННЯ МЕТАЛІВ ТА СПЛАВІВ the steelmaking workshop with very simple usage and minimum maintenance.
As for temperature measurement of liquid steel, the metallurgists worldwide use mainly disposable platinumrhodium thermocouples at the different stages of the technological process. However, for a relatively long time in modern steelmaking -in tundish of continuous casting machines, sensors are used to monitor continuously temperature of steel during casting process. The most successful one is the CasTemp (Heraeus Electro-Nite) (see Fig. 4), which does not require cooling, stays and measures in liquid steel during whole series of casting, replaced together with refractory layer of tundish. This device has been successfully used for two years in Ukraine at the PJSC Dneprovsky Integrated Iron & Steel Works, has passed the trials and planned for use in the PJSC "ArcelorMittal Kryvyi Rih".
When melting the charge of an electric arc furnace, in order to control a moment of the metal scrap melting point reaching, to save energy and time, a new method of continuous contact temperature measurement installation has recently been implemented by feeding fiberoptic into metal. This device is called CoreTemp and is shown in Fig. 5.
However, all these devices are related to the steel temperature measurement accelerating and improvement by direct measurements during steelmaking, but not to its chemical composition. The multicomponent express analysis of smelted steel, despite of visible successes in this matter, still cannot be done without an archaic sampling procedure, introducing distortions and significant delays in the production process. Work is underway to improve the status in this matter, for example, the author used to conduct research more than three decades ago on the possibility to analyze hot samples using the atomic emission method, exploring the possibility of eliminating the operation of cooling the sample before spectral analysis [6,13]. It was proved that it is possible to analyze a steel sample at its temperature below 200 °C. Recent studies have confirmed this possibility, but also showed that considering the temperature of the sample during its "sparking" increases the accuracy of the analysis of the sample on modern optical spectrometers [19]. Along with improving quality of the analysis itself, the problem of representativeness of the sample, i. e. the need to exclude sampling from the analytical cycle is obvious, but there is still no possibility to do this. Attempts are being made to monitor alternative methods, for example, to control "off gases". But this method is completely inaccurate, especially for multicomponent analysis. That is why, in order to obtain objective information about the composition of the steel, you need to get to its representative depth, and, preferably, take measurements in several spots of the melt.
Using probe measurements in liquid steel, it is possible today to obtain several its important parameters, such as temperature, carbon content, active oxygen, aluminum, hydrogen content, from a few seconds to a minute [7,8]. However, today only the sample analysis gives a complete picture of the chemical composition of steel. Sampling is the most archaic element of analytical control of steel, deliver to steelmakers whole series of problems, which necessitate to take them into consideration and minimize. These problems are listed below.
•The chemical composition of a melt is determined not directly, but indirectly (through analysis of the sample), which introduces an inaccuracy/error depending on the "representativeness" of the sample.
•The quality of the "body" of the sample must meet requirements to perform spectral analysis on it.
•Sample preparation introduces an error in the analysis, requires expenses for special equipment.
•The most important drawback of modern multicomponent chemical analysis of steel is the long fulfillment time. This time consists of the time taken to complete the sampling operation, to get it out the sampler, to deliver it to the laboratory (in cases of using the container laboratory or Quik-Lab II, it is excluded), preparation for spectral analysis (with Quik-Lab II -excluded), analysis itself, and transferring the results to the metallurgical unit operator. This procedure takes up to 10 minutes, during which the manufacturing process is waiting for the required corrective action, which is a net loss of productivity. On large volumes of metal, losses are calculated in colossal values. Metallurgists must either accept such losses in productivity or continue metallurgical process without waiting for the analysis results, what negatively affects the monitoring of the process and, as a result, adversely affects quality of smelted metal.  upright to the representative depth. It immerses only the head, which is protected by a Refractory sleeve throughout the depth of immersion, whose edge protrudes forward relative to the front of the Lance head. Thus, the sleeve, in addition to the protective function, serves as an inverted cup in the nose of the Lance head, in which the melt forms a cavity filled with compressed inert gas, which protects the front of the head and the Plasma burner from direct contact with the high-temperature melt. In the cavity, the compressed inert gas is pressurized corresponding to the pressure of the column of the liquid metal at the depth of immersion. Due to this, the liquid metal does not touch the inner part of Lance head, protecting it from destruction and creates favorable conditions for formation of Plasma torch in the cavity. Upon reaching a given depth of immersion in the melt in an inert gas environ, measurements of the melt temperature are performed on the radiation spectrum of the melt surface, which is transmitted to the Pyrometer through Light guide. Then Switch stops the supply of inert gas to the front of Lance head. Inert gas is supplied only to the Plasma burner, with the gas pressure determined by the operator. Then, to the stream of compressed gas, a double-conductor cable located inside the lance is supplied with Current generator, and in a zone limited by the inner walls of the protective sleeve, Plasma torch is generated that excite the characteristic radiation at the melt surface. The intensity of Plasma torch is regulated by the generator and by the inert gas supply. The radiation flux over the optical fiber is transmitted to the atomic emission Spectrometer, which decomposes into a spectrum and registered. By the values of the intensity of the •All activities mentioned above require significant capital investment and ongoing technological costs for consumables.
No one complicated and expensive equipment that will allow metallurgists to abandon sampling will override benefits that can occur, if chemical analysis of liquid steel is significantly accelerated. The Sublance systems for measuring and sampling in BOFs without their tilting, container laboratories in the "field" and other measures, worth millions of dollars, are paid off due to the acceleration of the metallurgical process. This obvious need to solve this problem pushes the search for to find the opportunity to perform direct multicomponent chemical analysis directly in liquid steel.
A lot of research and development has been devoted to finding solutions to this problem. Below is a description of possible implementation of this "super-task" -usage of optical spectrometer as part of set of tools that provide the excitation of characteristic radiation in depth of analyzed steel and transferring it to the spectrometer [20].
This device provides simultaneous temperature measurement and chemical analysis directly in a controlled liquid metal environment (Fig. 6). The main points of its functioning are as follows.
Express-analysis of the chemical composition of hightemperature metallic melt is carried out in the following way. By operator's command or automatic control system of the device, the supply of an inert gas, in particular argon, initiated, which is fed to the Switch and then through Ar channels to the front of the Lance head and/ or through the channel on the Plasma burner of the Immersion lance. The lance immerses into the Metal melt Scheme of spectral analysis of liquid steel characteristic lines of the spectrum, the content of the controlled elements in the melt is determined.
In case of the implementation of the described analysis method, the following results will be achieved: • The duration of the analytical control of the state of the melted metal (steel) during its production is significantly reduced due to the combination of measuring its temperature and chemical analysis, and, most important, the sampling excluding.
• Increases the accuracy and representativeness of the analysis, due to conducting directly on the controlled metal, but not on its sample.
• There is an opportunity to assess the homogeneity of molten metal when moving the immersion probe and performing a series of measurements in various places of the "bath" of the metal. This broadens the vision of the process, makes control "integral".
• The implementation of such project could significantly reduce the costs of monitoring metallurgical processes, reduce the load (costs) on factory laboratories.
Direct measurement of chemical composition of liquid metal may open revolutionary new way of steel production control and technological process organizing. Practical implementation of direct measurement method can be realized with using of manipulators to immerse the measuring probe into the melt in steelmaking units (an oxygen converter, a ladle furnace, an electric arc furnace, a vacuum vessel, a steel refining unit, a steel pouring ladle), or manually, for small volumes of metal, for example, in induction furnaces.
Thus, the great prospect for the activities of engineers and scientists in practical implementation of future analysis of metals in the liquid phase is obvious.