Reasons for banding formation in steels of K60 strength category

2020 ◽  
pp. 55-60
Author(s):  
A. N. Zavalishchin ◽  
◽  
O. N. Tulupov ◽  
M. I. Rumyantsev ◽  
E. V. Kozhevnikova ◽  
...  
Keyword(s):  
Structural Heterogeneity ◽  
Cast Billet ◽  
Chemical Inhomogeneity ◽  
Dendritic Segregation ◽  
Rolled Sheet ◽  
Working Pressure ◽  
Sheet Plane ◽  
Subsequent Formation ◽  
Continuously Cast

Active development of pipeline transport of gas and oil with increasing working pressure to 120 atm. increases the need for pipes with large wall thickness that correspond the requirements of the DNV OS-F101 standard. Quality of continuously cast billets is decisive for improving quality of sheet metal for main pipelines. Inheritance of cast structure imperfections by a hot-rolled sheet leads to structural heterogeneity of the strip and the layered nature of the fracture surface and adversely affects the mechanical properties and corrosion resistance. Structural heterogeneity of rolled products is appeared in the form of axial ferrite-martensitic metal banding and metal banding in the main section of the sheet consisting of a mixture of ferritic and pearlitic grains — pearlitic metal banding. The flatness in the axial zone of the rolled products is due to axial chemical heterogeneity which is objectively formed during crystallization of the continuously cast billet and further phase transformations. The axial chemical inhomogeneity does not resolve despite the recrystallization of the structure and deformation and the high content of alloying elements contributes to the formation of the martensite phase and large carbonitride precipitates. The cause of pearlite bands is considered usually to be the presence of dendritic segregation. According to us the reason of this metal banding is the shift of the temperature front of γ → α transformation parallel to the sheet surface in depth as a result of which before the next volume of formed ferrite the concentration of carbon dissolved in austenite increases with the subsequent formation of pearlite. The enrichment of austenite proceeds along the boundaries preserved from the δ → γ transformation during cooling the slab and the formed pearlite structure repeats the shape of the boundaries of these grains in the section parallel to the sheet plane.

scholarly journals Study of surface defects in tubes made from nondeformed continuously cast billets

2021 ◽  
Vol 98 (2) ◽  
pp. 54-62
Author(s):  
L.V. Opryshko ◽  
◽  
T.V. Golovnyak ◽  
Keyword(s):  
Outer Surface ◽  
Surface Defects ◽  
Gas Bubbles ◽  
Chemical Inhomogeneity ◽  
Tube Surface ◽  
Steel Smelting ◽  
Study Results ◽  
Inner Surface ◽  
Continuously Cast

Defects of outer and inner surfaces of hot-rolled tubes of various steel grades and sizes manufactured on tube-rolling unit with a continuous mill (TPA 30-102) at Interpipe Nikotube LLC from a nondeformed continuously cast billets produced by MZ Dniprostal LLC have been studied. Characteristic genetic and morphological signs of defects were revealed which makes it possible to reliably classify them, identify cause of defect formation and recommend measures to eliminate them. Defects on the outer and inner surfaces of tubes are of metallurgical origin and associated with quality of initial continuously cast billets (a consequence of violation of the smelting and continuous casting technology). Defects on the inner surface of tubes were caused on defects in the axial zone of original billets (unacceptable porosity, looseness, chemical inhomogeneity, liquation stripes and cracks, etc.) and are classified as steel-smelting films and bulges. It was found that displacement of the thermal center of crystallization (a feature of the machines for continuous steel casting of curvilinear type) had an additional negative effect on quality of the inner surface of the studied tubes. Defects on the outer surface of tubes are tears of burning in places of accumulation of low-melting inclusions and their eutectics, as well as steel-smelting scabs on rolled dirt and gas bubbles. Likelihood of formation of scabs on outer surface of the studied tubes over rolled crust introversions is not excluded. The study results will allow manufacturers to reliably classify defects, promptly reject tubes with unacceptable defects of metallurgical origin and minimize supply of low-quality products to consumers. These results will later be included in the classifier of defects in tubes manufactured on the TPA 30-102 unit from nondeformed continuously cast billets. The results of the study of natural signs of defects of metallurgical origin in the tube surface will be useful for elaboration of measures aimed at improvement of the technology of manufacturing initial tube billets. Keywords: tube surface defects, continuously cast billets, microstructure, rolled contamination, low-melting inclusions, eutectic, gas bubbles, decarburization, liquation.

scholarly journals The cooling rate effect during a continuously cast billet solidification on the dendritic structure features of carbon steel

2021 ◽  
Vol 97 (1) ◽  
pp. 9-19
Author(s):  
O.I. Babachenko ◽  
◽  
K.G. Domina ◽  
G.A. Kononenko ◽  
O.L. Safronov ◽  
...  
Keyword(s):  
Carbon Steel ◽  
Cooling Rate ◽  
Volume Fraction ◽  
Dendritic Structure ◽  
Heat Removal ◽  
Cast Billet ◽  
Dendritic Segregation ◽  
Wide Range ◽  
Continuously Cast Billet ◽  
Continuously Cast

The analysis of the formation process of the cast structure of carbon steel grade ОС (ДСТУ ГОСТ 4728:2014) after the completion of its crystallization with a change in a wide range of metal cooling rate during solidification of a continuously cast billet (ССB) with a diameter of 450 mm has been carried out. The effect of the cooling rate during the solidification of ССB Ø 450 mm on the parameters of the chemical heterogeneity of the distribution of silicon and manganese in the microstructure of carbon steel has been shown. It has been determined that the effect of the metal cooling rate during the solidification of the investigated CCB on the size of dendritic crystals is described by the inversely proportional relationship: у = 423.75 х-0,161. With a change in the cooling rate of the metal during solidification from 106 до 1 °C/min, the size of the dendrites in the direction from the surface to the central layers of the CCB Ø 450 mm increased by ~ 8 times, and the density of the dendritic structure of carbon steel ОС decreases by 65 times. In this case, the nature of its dependence on the intensity of heat removal is the opposite nature of the change in the size of dendrites. It has been established that by varying the cooling rate in the range 1 – 106 °C/min, one can achieve a significant change in the average size and density of dendritic crystals while maintaining the constancy of the volume fraction of segregation areas of silicon and manganese ~ 24% in carbon steel (0.42 – 0.50 % wt. C). It has been determined that in the entire investigated range of cooling rates 1 – 106 °C/min, the coefficients of dendritic segregation КдI and КдII of silicon and manganese change insignificantly and amount to 1.8-1.9 and 1.5 for КдI and КдII, respectively. In this case, the values of the coefficients КдI and КдII for both elements are practically constant in both pearlite and ferrite. It has been proven that both silicon and manganese have high diffusion mobility only at sufficiently high temperatures, when steel is in a solid-liquid state. Based on the results of X-ray microanalysis, it has been established that the heterogeneity of the distribution of chemical elements, which is formed as a result of dendritic segregation of silicon and manganese, is the primary and constant component of the microstructure of carbon steel. Keywords: carbon steel, continuously cast billet, solidification, cooling rate, dendritic structure.

scholarly journals Research of the effect of the cooling rate during solidification of a continuously cast billet on the features of the dendritic structure of carbon steel

2020 ◽  
pp. 229-246
Author(s):  
A.I. Babachenko ◽  
K.G. Domina ◽  
G.A. Kononenko ◽  
Zh.A Dement`eva ◽  
Е.А. Safronova
Keyword(s):  
Carbon Steel ◽  
Cooling Rate ◽  
Dendritic Structure ◽  
Steel Grade ◽  
Cast Billet ◽  
Dendritic Segregation ◽  
X Ray ◽  
Continuously Cast Billet ◽  
Continuously Cast ◽  
Dendritic Branches

The analysis of the formation process of the cast structure of carbon steel grade EA1N (EN 13261: 2009 + A1: 2010 (Е)) after the completion of its crystallization with a change in a wide range of metal cooling rate during solidification of a continuously cast billet (ССB) with a diameter of 470 mm has been carried out. The effect of the cooling rate during the solidification of ССB Ø 470 mm on the parameters of the chemical heterogeneity of the distribution of silicon and manganese in the microstructure of carbon steel has been shown. It has been determined that the effect of the metal cooling rate during the solidification of the investigated CCB on the size of dendritic crystals is described by the inversely proportional relationship: у = 510,85 х-0,156. With a change in the cooling rate of the metal during solidification from 106 до 1 ℃ / min, the size of the dendrites in the direction from the surface to the central layers of the CCB Ø 470 mm increased by ~ 8 times, and the density of the dendritic structure of carbon steel EA1N decreases by 64 times. In this case, the nature of its dependence on the intensity of heat removal is the opposite nature of the change in the size of dendrites. It has been established that by varying the cooling rate in the range 1 – 106 ℃ / min, one can achieve a significant change in the average size and density of dendritic crystals while maintaining the constancy of the volume fraction of segregation areas of silicon and manganese ~ 23% in carbon steel (~ 0.4 % wt. C). The results of X-ray spectral analysis of samples of ССB Ø 470 mm made of carbon steel grade EA1N showed that the maximum content of silicon and manganese is characteristic of the former spaces between the first-order dendritic branches, their minimum content is for the former dendritic branches. At the same time, the amount of these elements in steel microvolumes, which are the former spaces between the second-order dendritic branches, is on average 50 % more than in the former dendritic branches. It has been determined that in the entire investigated range of cooling rates 1 – 106 ℃ / min, the coefficients of dendritic segregation КдI and КдII of silicon and manganese change insignificantly and amount to 1.8-1.9 and 1.5 for КдI and КдII, respectively. In this case, the values of the coefficients КдI and КдII for both elements are practically constant in both pearlite and ferrite. It has been proven that both silicon and manganese have high diffusion mobility only at sufficiently high temperatures, when steel is in a solid-liquid state. Based on the results of X-ray microanalysis, it has been established that the heterogeneity of the distribution of chemical elements, which is formed as a result of dendritic segregation of silicon and manganese, is the primary and constant component of the microstructure of carbon steel.

scholarly journals 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”

2021 ◽  
pp. 35-39
Author(s):  
A. V. Tereshchenko ◽  
I. A. Kovaleva
Keyword(s):  
Surface Defects ◽  
Mechanical Damage ◽  
Steel Grade ◽  
Cast Billet ◽  
Hot Metal ◽  
Continuously Cast Billet ◽  
Continuously Cast ◽  
Metal Products ◽  
Hot Rolled

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.

scholarly journals On the Quality of Steel from Continuously Cast Billet

1967 ◽  
Vol 7 (6) ◽  
pp. 288-295
Author(s):  
Shinkichi Koike ◽  
Akira Kimura ◽  
Tooru Hikage ◽  
Toshio Watanabe
Keyword(s):  
Cast Billet ◽  
Continuously Cast Billet ◽  
Continuously Cast

Influence of technology parameters of free-cutting steel continuous casting on the billet internal structure

2020 ◽  
Vol 76 (2) ◽  
pp. 139-142
Author(s):  
A. T. Kunakbaeva ◽  
A. M. Stolyarov ◽  
M. V. Potapova
Keyword(s):  
Regression Analysis ◽  
Continuous Casting ◽  
Internal Structure ◽  
Sulfur Content ◽  
Manganese Content ◽  
High Quality ◽  
Correlation And Regression Analysis ◽  
Cutting Steel ◽  
Continuously Cast

Free-cutting steel gains specific working properties thanks to the high content of sulfur and phosphorus. These elements, especially sulfur, have a rather high tendency to segregation. Therefore, segregation defects in free-cutting steel continuously cast billets can be significantly developed. The aim of the work was to study the influence of the chemical composition of freecutting steel and casting technological parameters on the quality of the macrostructure of continuously cast billets. A metallographic assessment of the internal structure of cast metal made of free-cutting steel and data processing by application of correlation and regression analysis were the research methods. The array of production data of 43 heats of free-cutting steel of grade A12 was studied. Steel casting on a five-strand radial type continuous casting machine was carried out by various methods of metal pouring from tundish into the molds. Metal of 19 heats was poured with an open stream, and 24 heats – by a closed stream through submerged nozzles with a vertical hole. High-quality billets had a cross-sectional size of 150×150 mm. The macrostructure of high-quality square billets made of free-cutting steel of A12 grade is characterized by the presence of central porosity, axial segregation and peripheral point contamination, the degree of development of which was in the range from 1.5 to 2.0 points, segregation cracks and strips – about 1.0 points. In the course of casting with an open stream, almost all of these defects are more developed comparing with the casting by a closed stream. As a result of correlation and regression analysis, linear dependences of the development degree of segregation cracks and strips both axial and angular on the sulfur content in steel and on the ratio of manganese content to sulfur content were established. The degree of these defects development increases with growing of sulfur content in steel of A12 grade. These defects had especially strong development when sulfur content in steel was of more than 0.10%. To improve the quality of cast metal, it is necessary to have the ratio of the manganese content to the sulfur content in the metal more than eight.

Production of High-Quality Wheel Steel. Part 1. Production Aspects of Continuously-Cast Billet Quality for Railway Wheel Manufacture

Metallurgist ◽  
2021 ◽  
Author(s):  
D. A. Pumpyanskiy ◽  
S. V. Tyutyunik ◽  
E. A. Kolokolov ◽  
A. A. Mescheryachenko ◽  
I. S. Murzin ◽  
...  
Keyword(s):  
Steel Part ◽  
Wheel Steel ◽  
Cast Billet ◽  
High Quality ◽  
Railway Wheel ◽  
Billet Quality ◽  
Continuously Cast Billet ◽  
Continuously Cast

Effect on Position of Electromagnetic Stirring on Inclusion Behaviors in Billet

2013 ◽  
Vol 805-806 ◽  
pp. 1716-1719 ◽  
Author(s):  
Gui Fang Zhang ◽  
Yue Hua Ding ◽  
Zhe Shi
Keyword(s):  
Liquid Steel ◽  
Electrical Current ◽  
Medium Carbon Steel ◽  
Electromagnetic Stirring ◽  
Cast Billet ◽  
Inclusion Removal ◽  
Optimum Position ◽  
Steel Cleanliness ◽  
Plant Trials

A considerable number of research works have been carried out to study the effects of electric current and frequency of Electromagnetic Stirring (EMS) on the quality of cast steels, but there are only a few studies available addressing the effects of EMS location on inclusion removal and steel cleanliness An ideal position of EMS will improve inclusion floatation and separation from liquid steel. However, inappropriate installation will lead to the entrapment of the slag into liquid steel, and impact the quality of cast billet. The current applied for these plant trials was 300A at a frequency of 3Hz,positions form axial centers of EMS to the top of the mold were 450mm, 510mm and 690mm respectively . 130 billets of medium carbon steel were produced and samples were taken for spectral analysis to study the effects of installation location of EMS on steel cleanliness. The experimental results show that the optimum position of EMS should be placed 510mm from the top end of the copper mold when the electrical current is 300A at frequency of 3 Hz. The three parameters of placement of EMS in paper were obtained from the simulation results, and this paper focused mainly on the effect EMS position on inclusion behaviors in billet.

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