Establishing the true causes of defects to ensure the quality of continuously cast billets and hot‑rolled products at all stages of the process chain at OJSC “BSW – Management Company of the Holding “BMC”

Establishing the true causes of defects is one of the main prerequisites for improving the quality of metal products. One of the undesirable phenomena in the production of continuously cast billets, hot‑rolled products is the oxidation of hot metal in the environment with the formation of scale on its surface. Defects, which are violations of the continuity of the metal and deviations from the normal specified macro‑and microstructure, signifi antly reduce the technological plasticity of the metal in the conditions of its processing and operational stability.After hot rolling of a circle of 95 mm steel grade 30MpV4, surface defects were found in the finishing line. To study and establish the nature of surface defects from hot‑rolled blanks, as well as continuously cast blanks, samples were taken.Analyzing metallographic studies of defects and the production technology of the studied steel grade 30MnB4, it was found that the defects were formed as a result of mechanical damage to the continuously cast billet in the area of the pulling‑correct unit. The reason for the formation of the defect is the ingress of scale on the guide rollers.

Improvement of the technological process of manufacturing bearing grades of steel at the 370/150 mill.

The actual problem of obtaining long products from bearing steel grades with specified microstructure characteristics is considered. The analysis of the capabilities of the existing equipment – a heating furnace and a rolling mill 370/150 of OJSC “BSW – Management Company of the Holding “BMC” was carried out in order to introduce technical measures aimed at reducing carbide heterogeneity in products made of bearing steel grades on the example of steel grade 100Cr6.The influence of different modes of preliminary thermal preparation of continuously cast billets from bearing steel grades on the carbide inhomogeneity in the finished rolling is studied. According to the results of the research, the optimal mode of heat treatment of a continuously cast billet was determined, which allows to produce rolled products that meet the highest requirements of consumers.

EVALUATION OF THE EFFICIENCY OF USING SK30 WIRE IN STEEL PROCESSING AT THE LADLE FURNACE PLANT

The paper presents studies showing the effectiveness of the use of wire with SiCa filler in the out-of-furnace processing of steels. The efficiency of use was evaluated by calculating the contamination with non-metallic inclusions, as well as by determining the phase composition of non-metallic inclusions at the stages of out-of-furnace processing and casting. (installation bucket furnace→vacuum cleaner→continuous casting). The study found that the adjustment of the content of aluminum before casting leads to the formation of refractory inclusions of corundum - (AlO), spinels - (AlO·MgO), which are deposited on the walls of the steel filling path and worsen the spillability of steel. The use of SK30prov with SiCa filler at the final stages of extra-furnace processing (after the introduction of aluminum), leads to the modification of refractory inclusions in low-melting calcium aluminates of the type (CaO·AlO). The presence of low-melting inclusions is more preferable, since this type of inclusions is not deposited on the walls of the filling cup and does not have a negative effect on the contamination of the continuously cast billet and products obtained from them with inclusions.

Influence of the hydraulic pump unit on the quality of the rolled surface

To ensure the competitiveness of rolled metal in the modern market, the decisive factor is the quality of the rolled surface (defects with a depth of no more than 0.2 mm are allowed without stripping). Rolling processing is a source of formation of small surface defects, most of which are obtained in the process of deformation of a continuously cast billet (hereinafter referred to as CCB, billet) at hot rolling mills in the presence of areas with non-removed furnace scale. This is the main reason for the formation of such types of surface defects as rolled scale, ripple, scale shells, which reduces the quality of the rolled surface and increases the sorting of metal with surface defects. In addition, the scale not removed from the surface of the CCB has a negative impact not only on the quality of metal products, but also on the operation of rolling equipment.One of the directions that allows to achieve high quality of the surface of long products in production conditions is the effective removal of scale from the surface of the initial billet before hot deformation. Scale removal from the surface of the workpiece is carried out on the installation of a hydraulic descaling unit, but not always a satisfactory (complete) scale removal occurs.To determine the cause of poor – quality scale removal before hot deformation, the efficiency of the hydraulic descaling unit and the state of the metal – scale interface surface were investigated.

Homogenization of the interfacial bonding of compound-cast AA7075/6060 bilayer billets by co-extrusion

A process chain of compound casting and co-extrusion of AA7075/6060 bilayer billets is introduced to manufacture hybrid components with strength in the core and good corrosion-resistance in the shell. Using optimized compound casting parameter, metallurgical bonding between the shell AA6060 and the core AA7075 can be achieved through remelting and recrystallization of the substrate AA7075. The locally unequal thermal conditions at the interface induces partially weak bonding. The bonding strength in greater distance from the casting gate is generally lower. Hot extrusion is applied to improve the interfacial bonding. Comparisons of the microstructure and the shear strength between as-cast billet and extrudate present the homogenization of the interfacial bonding through the process chain.

Estimating the Stress-Strain State of Roll by Temperature Gradient in the Course of its Heat Treatment

The paper considers the issue of mathematical simulating the stress-strain state of a roll in the course of its heat treatment. It is shown that a sound heat treatment schedule affects significantly the economic efficiency of a metallurgical enterprise. The mathematical apparatus is provided to estimate the thermal interaction in the casting-furnace system, based on which a program for calculating the thermal state of a roll during heat treatment has been developed. Using this program allows evaluating the thermal stresses occurring in a roll during the heat treatment cycle and reducing the risk of discontinuity in the roll cast billet. Also, using the program developed, allows significant reducing the engineer-technologist man-hours for the design of the process cycle of the casting heat treatment. An example of calculating the thermal state of a roll with a diameter of 930 mm in casting is given. The change in the dynamics of the maximum temperature gradient along the product radius is shown, while correlating it with the furnace setting.

Yield of good steel at metallurgical plants of the world depending on large-dispersed precipitation

The moisture in the environment influences the formation of defects in steel and the yield of suitable metal products. However, no numerical dependence of the yield at a metallurgical enterprise on climatic and weather conditions, in particular, on coarse precipitation, has yet been proposed. A significant difference in the yield of steel grades suitable for various groups is shown on days without atmospheric precipitation, with precipitation and during the day after rain. For low-alloy steels, the yield of a suitable continuously cast billet during periods with precipitation is 11.3% lower than on days without precipitation; for high-alloy grades, this difference reaches 16.5%. Based on the annual reports of metallurgical companies, a database has been formed on the average annual output of suitable metal products at various plants around the world. The quantitative dependence of the yield at the enterprise on the number of days in a year with coarse precipitation (rain, snow) and the uneven distribution of these precipitation over the year has been obtained. Coarse precipitation significantly affects the level of yield of suitable metal products at a metallurgical enterprise. With an increase in the number of days with precipitation per year by one day, the level of waste and sorting at the enterprise increases by 0.087%. The increase in the unevenness of atmospheric precipitation per unit leads to an increase in waste and sorting by 0.822%. If the climatic factor is taken into account when forming a strategy for the development of metallurgy in the country, then it is possible to achieve a greater effect for the development of the economy in comparison with other states that do not take this factor into account.