Comparative Study on the In-Ladle Treatment Techniques for Nodulizing the Iron’s Graphite

The objectives of this research is to study and understand the nodulizing of ductile iron using in-ladle treatment process. Among the more common nodulizing agents is magnesium (Mg) which is conventionally added to the cast iron by combining suitable alloys of one or both of these elements with molten cast iron. Depending on the characteristics of each master alloy used as nodulizer, different treatment methods and techniques are used, among these, the most widely used being in-ladle, in-mould, and flow-through, the first being the most used. This research deals with the parameters, that affect the quality of ductile iron produced using in-ladle treatment process. The parameters involved are the percentage of magnesium–ferrosilicon (Fe–Si–Mg) used and the nodulizing technique. In-ladle treatment used consists of a deep pocket into the bottom of ladle, in which magnesium–ferrosilicon is placed into it together with a steel scrap barrier (steel sheets) or calcium carbide. This study, take into account, the degree of assimilation of magnesium, which shows the performance of the chosen process, depending on the nodulizer used and the temperature of the treatment.

Experience of thick-walled calcium-containing cored wire application at steel ladle treatment

Metal processing in ladle by calcium-containing cored wires is one of the most spread methods of ladle treatment and modifying. Results of analysis of efficiency induces of existing cored wires application depending on their diameter, wall thickness and filling coefficient presented. It was shown that the basic efficiency index of a cored wire application – recovery coefficient – depending on wire quality (homogeneity of filling by calcium along the wire length), wire grade, conditions of its injection into liquid steel and other parameters can vary within a range from 50 to 95%. Reasons of unsatisfactory calcium recovery at usage of calcium-containing wires of 14–15 mm diameter with steel shell 0.4 mm thick and filling of mechanical mixture of steel shots and metallic calcium in various proportions was considered. Advantages of the modern calcium-containing cored wire with thicker wall were highlighted, including their higher wire rigidity and stability of its supply by a wire feeder into liquid steel. It was established that calcium content in a cored wire at the level of 100 g/m was the most effective composition. It was noted that increase of speed of cored wire feeding into steel will result in an increase of calcium recovery and in a decrease of probability of metal splashing out the steel ladle.

Formation and Evolution of DS-Type Inclusions in 15-5PH Stainless Steel

15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate the formation mechanism of large-size DS-type inclusions, the evolution, growth, and aggregation of inclusions during vacuum oxygen decarburization, ladle refining, and vacuum casting were studied. The results show that the DS-type inclusions with sizes larger than 20 μm were CaO–Al2O3–SiO2–MgO–CaS composite inclusions. After Si–Al additions in vacuum degassing, typical inclusions were spinel or Al2O3. After Ca–Si additions during ladle treatment, typical inclusions were liquid or dual-phase Al2O3–CaO–SiO2–MgO. During the solidification process, due to the segregation of S and the decrease in solubility, the typical inclusions in the final casting became Al2O3–CaO–SiO2–MgO–CaS. For optimal fatigue performance of stainless steel castings, slag and refractory composition control were also necessary because the [Mg] contents mainly come from the slag and lining.

Modelling and optimization of sulfur addition during 70MnVS4 steelmaking: An industrial case study

Štore Steel Ltd. is one of the major flat spring steel producers in Europe. Among several hundred steel grades, 70MnVS4 steel is also produced. In the paper optimization of steelmaking of 70MnVS4 steel is presented. 70MnVS4 is a high-strength microalloyed steel which is used for forging of connecting rods in the automotive industry. During 70MnVS4 ladle treatment, the sulfur addition in the melt should be conducted only once. For several reasons the sulfur is repeatedly added and therefore threatening clogging during continuous casting and as such influencing surface defects occurrence and steel cleanliness. Accordingly, the additional sulfur addition was predicted using linear regression and genetic programming. Following parameters were collected within the period from January 2018 to December 2018 (78 consequently cast batches): sulfur and carbon cored wire addition after chemical analysis after tapping, carbon, manganese and sulfur content after tapping, time between chemical analysis after tapping and starting of the casting, ferromanganese and ferrosilicon addition and additional sulfur cored wire addition. Based on modelling results it was found out that the ferromanganese is the most influential parameter. Accordingly, 12 consequently cast batches (from February 2019 to October 2019) were produced with as lower as possible addition of ferromanganese. The additional sulfur addition in all 12 cases was not needed. Also, the melt processing time, surface quality of rolled material and sulfur cored wire consumption did not change statistically significantly after reduction of ferromanganese addition. The steel cleanliness was statistically significantly better.

Application of microcrystalline complex modifiers for steel ladle treatment. Part 1. The role of nonmetallic inclusions in steel quality forming

Contamination of steel by nonmetallic inclusions (NI) has a negative effect on mechanical characteristics of metal used under no favorable conditions. Conditions of NI forming in the process of steel smelting, ladle treatment and casting considered. It was shown that it is impossible to get rid of many NI. However, the task of forming less “harmful” NI having minimal effect on the decrease of finished products indices is quite practicable. To refine steel of NI it is reasonable to accomplish operations in a melt to modify NI morphology from dangerous acute-angled aluminous to globular oxide-sulphide. This task can be solved by introduction into metal complex modifiers comprising calcium, barium, strontium and rare earth metals. Addition of complex modifiers is a good alternative to complicative and long-time operations to decrease NI general content to lower levels, for example, by long-time metal ladle treatment. Application of the method enables in some situation to avoid expensive operations related to deep metal desulphuri zation and its dehydronization. Clean steel production becomes considerably easier at application of multicomponent alloys, obtained by a technology of accelerated crystallization. Application of such compositions results in forming globular oxide and oxide-sulphide compounds, as well as eutectics with low-melting point, which are comparatively quickly removed out of liquid metal. At that due to decreasing of liquation processes forming in the liquid metal, higher quality of large ingots and work-pieces, obtained from 420 t mass ingots can be reached.

Strategy of automation of electric arc heating of steel melt in ladle-furnaceStrategy of automation of electric arc heating of steel melt in ladle-furnaceStrategy of automation of electric arc heating of steel melt in ladle-furnace

Prices hike for consumable materials and energy carriers, increase of requirements to steel quality stipulate the items of intensification of ladle treatment processes and decrease of their energy- and material capacity. Analysis of energy losses in ladlefurnace accomplished, as well as basic factors effecting the energy costs during treatment analyzed. A methodology elaborated for making thermal balance of ladle-furnace: it was proposed to present the melt treatment process in ladle-furnace as a series of separate operations, each having specific features of the process (heating, desulphurization, alloying) and their combination. Based on analysis of 20 thousand heats passports at ladle-furnace of MMK BOF shop, a mathematical model of energy supply system of ladle-furnace was elaborated. Based on the analysis made, a strategy of heating automation was proposed. In particular, electric losses were emphasized, t. e. total losses of electric arc energy, in which provisionally losses at arc open part radiation were included. Control of those flows creates conditions for heating efficiency increase. Conclusions were made that decrease of electric losses is observed at prolonged (about 8−12 min) heating periods and sufficient amount of slag, as well as at injection of additives after heating. Such a mode provides decrease of thermal losses by 4−5%. A new technology of steel melt treatment in ladle-furnace was proposed, characterized by decreased consumption of electric energy.