Nonmetallic Inclusion Control of 350 km/h High Speed Rail Steel

Inclusion has an important effect on quality of high speed rail steel. In consideration of the lower acceptance percentage of the inclusion and its constraint against the requirement for large scale production of 350 km/h high speed rail steel in Panzhihua Iron and Steel (Group) Co, the technology of nonmetallic inclusion control for 350 km/h high speed rail steel was studied. An optimized model of the argon-blowing in ladle furnace (LF), the control of the components of the ladle slag, and the technique of calcium treatment for the molten steel was brought forward. Using the researched technology, the removal ratio of the inclusion was increased and the components, distribution, and shape of the inclusion in the rail steel were changed, which resulted in a reduction in the average total oxygen content to 10. 17 × 10⁻⁶ and an increase in the comprehensive acceptance percentage of the nonmetallic inclusion from 48. 21% to 98. 1%. Test has shown that this metallurgical technology can meet the requirement for large scale production of 350 km/h high speed steel in Panzhihua Iron and Steel (Group) Co.     

Eliminating corrosive nonmetallic inclusions from pipe steel

Measures to optimize the production of corrosion-resistant steel have been introduced at OAO Severskii Trubnyi Zavod. They ensure that the steel’s content of corrosive nonmetallic inclusions of the first and second type is no more than 2 mm^?2. The measures were developed on the basis of research on the morphology and composition of nonmetallic inclusions and their formation and also current concepts regarding the formation and removal of corrosive nonmetallic inclusions.     

Nonmetallic inclusions in electric furnace steel ShKh15SG-V bars

The mechanisms of formation and the methods of controlling nonmetallic inclusions (NIs) in bearing steel are considered. The number and composition of NIs in electric furnace ShKh15SG-V steel bars made using various versions of heat and out-of-furnace treatment are studied by fractional gas analysis and number estimation according to State Standard GOST 801-79. A high calcium content is found to result in large globular NI numbers in the bars. Fractional gas analysis is shown to correctly determine the oxide inclusion content in steel.     

The Role of Nonmetallic Inclusions in Accelerating the Local Corrosion of Metal Products Made of Plain-Carbon and Low-Alloy Steels

Using the principles of physicochemical modeling to describe the deoxidation and desulfurization of steel in the ladle and interactions between the metallic and slag phases with allowance for features of the equipment in use at specific plants, the paper shows that it is possible to quickly optimize the parameters of out-of-furnace treatments of the steel without losing productivity. The optimum parameters make it possible to fully realize all of the main advantages of such treatments: further refining of the steel, modification of the nonmetallic inclusions, guaranteeing that the steel will be clean in terms of the presence of corrosion-active nonmetallic inclusions, and, thus, ensuring that the steel will be resistant to local corrosion.__________Translated from Metallurg, No. 4, pp. 58–61, April, 2005.     

Development of Recommendations on Making Tube Steels Produced at the Severstal’ Combine Cleaner with Respect to Corrosion-Active Nonmetallic Inclusions

Recommendations are given on out-of-furnace treatments which will allow the production of steel that is clean in terms of its content of corrosion-active nonmetallic inclusions.__________Translated from Metallurg, No. 4, pp. 62–66, April, 2005.     

Study of the Effect of Process Parameters in Steel Production on the Content of Corrosion-Active Nonmetallic Inclusions in Corrosion-Resistant Pipes

The main reason for the accelerated local corrosion of tubes is contamination of the steel by corrosion-active nonmetallic inclusions (CANI), which determine the metallurgical properties of tube steel in terms of their corrosion resistance. Studies have shown that there are two main types of corrosion-active nonmetallic inclusions: CANI₁ — inclusions based on calcium aluminates; CANI₂ — complex inclusions that contain calcium sulfide. In order to master to production of tubes of steel 20-PKS at the Volga Pipe Plant (VTZ), a study was made of the effect of the parameters of out-of-furnace treatments on the contamination of steel by CANI. 1. The mechanisms and main sources of formation of CANI in tube steels made by the VTZ were determined. The main reasons for the formation of CANI₁ in furnace slag containing thermodynamically active CaO are mixing of the metallic and slag phases during the argon blow and the simultaneous introduction of additions to correct the chemical composition of the steel. Inclusions of the CANI₂ type may be formed by deoxidation operations carried out with suboptimal proportions of added aluminum and calcium (lime). 2. The following measures are recommended to ensure that steel 20-PKS made by the VTZ is clean with respect to both types of CANI: • optimize the composition of the ladle slag (increase the average content of Al₂O₃, increase the average content of SiO₂ as much as possible, and in any case decrease the average concentration of CaO); • keep the mass ratio of added CaO to added Al within the range 1.5–2; • continue the argon blow done after addition of the last batch of ferroalloys for at least 15–20 min; • ensure that the intensity of the blow is at least 0.5–1.5 m³/min. 3. Vacuum-degassing steel in the ladle after treatment on a ladle-furnace unit makes it possible to distribute the CANI more uniformly over the volume of the steel. __________ Translated from Metallurg, No. 7, pp. 38–42, July, 2005.     

Nonmetallic inclusions in vacuum-treated austenitic stainless steel

The nonmetallic phase in 08X18H10T and 03X18H10 vacuum-treated austenitic stainless steel is investigated by means of a scanning electron microscope. The composition of the nonmetallic inclusions in cast samples of metal from the casting ladle, the vacuum unit, and the continuous-casting machine and samples of cold-rolled sheet (thickness 1.2 mm) is studied. In 08X18H10T steel samples from the tundish of the continuous-casting machine, the nonmetallic phase consists mainly of titanium-nitride aggregations, the crystals of which contain oxides of aluminum and titanium; a few of the nonmetallic inclusions are small globules with a titanium-oxide shell. In cold-rolled sheet, the nonmetallic inclusions are distributed over the whole cross section and consist of small (5–6 μm) crystals of titanium nitrides. Cast samples of 03X18H10 austenitic titanium-free steel are relatively free of nonmetallic inclusions. The nonmetallic phase consists mainly of small inclusions of alumocalcium silicate. In cold-rolled sheet (thickness 1.2 mm), the nonmetallic phase consists of a few very small globules (2–3 μm). The results are compared with the composition of the nonmetallic phase in analogous steel with no vacuum treatment.     

Method of manufacture of high-speed steel from swarf and its properties

Conclusions The feasibility is demonstrated of direct processing of fine high-speed steel swarf by a powder metallurgy technique including prepressing, extrusion, and heat treatment operations The process developed enables sintered steel to be produced possessing properties similar to those of standard steel. The true mechanical properties of standard (cast) and sintered (extruded) steels were determined, with the aid of the theory of plasticity of porous materials, by plotting their deformation diagrams. It is shown that the above theory is applicable to materials possessing coarse structural porosity. Quantitative discrepancy was found between compression and tensile curves, resulting from the presence in such materials of isolated nonmetallic inclusions and from the discontinuity of their microstructure, which may be regarded as initial porosity.Translated from Poroshkovaya Metallurgiya, No. 4(208), pp. 35–40, April, 1980.     

Refining Steel in the Tundish

Making the steel of continuous-cast ingots cleaner with respect to nonmetallic inclusions is one of the most important problems in ferrous metallurgy and is difficult to solve simply by means of a single out-of-furnace treatment. This article discusses steps being taken by the Magnitogorsk Metallurgical Combine to improve the refining of nonmetallic inclusions from steel, these measures involving the use of filtration diaphragms in the tundish. The diaphragms are designed so that an inert gas can be injected into a prescribed region of the tundish through a reinforcing layer located inside the concrete diaphragm. The gas forms a bubble screen on the path travelled by the nonmetallic inclusions, forcing them to rise to the surface. Test results showed the following: the quality of the steel is improved — the average rating for point segregation on metallographic sections was 1.58 with the use of a standard diaphragm and 1.36 with use of the diaphragm supplied with argon; the use of argon reduces the content of sulfides in steel cast through the experimental diaphragm by 14% and reduces the content of oxides by 17–19%. __________ Translated from Metallurg, No. 7, pp. 36–37, July, 2005.     

Effect of a pipe-steel killing technology on the composition and number of nonmetallic inclusions

Pipes made from steels 19G, 17GS, 17G1S, 10G2FBYu, 13G1S-U, and 20KT of various manufacturers and technologies are studied. Electron microprobe and fractional gas analyses are used to determine the main types and number of nonmetallic inclusions (NIs). The effect of a modification procedure on the oxidic cleanness of steel 20KT (produced at JSC “Volzhskii Pipe Works”) is studied. The use of a silicocalcium-filled wire is shown to increase the total contamination of the steel by nonmetallic, in particular, calcium aluminate and magnesium spinel inclusions, which are conditionally related to corrosion-active nonmetallic inclusions (CANIs). Fractional gas analysis is shown to allow the number of oxide inclusions of various types to be accurately determined in pipe steels. No correlation is found between the volume fraction of oxide inclusions determined by fractional gas analysis and the number of CANIs determined by a metallo-graphic method.     

Fracture toughness of calcium-modified ultrahigh-strength 4340 steel

Commercial and low-sulfur 4340 steels have been studied to determine the effect of calcium treatment on modifying the morphology of nonmetallic inclusions and plane-strain fracture toughness (K _IC ) of the ultrahigh-strength, low-alloy steels at commercial heat level. The significant conclusions are as follows: (1) for the low-sulfur 4340 steel, the addition of calcium in the molten steel gave rise to the formation of finely distributed, spherical, calcium-sulfide (CaS) inclusions with a mean diameter of 1.3 μm; (2) in comparing the calcium-modified 4340 steel with commercial 4340 steel, the calcium-modified steel not only had an improvedK _IC by about 25 MPa•m^1/2 in the longitudinal (L) orientation and by about 30 MPa • m^1/2 in the transverse (T) orientation, but also had increased fracture ductility and Charpy impact energy at similar strength levels; and (3) for the commercial 4340 steel, the calcium treatment was not very effective in modifying the morphology of the inclusions on improving the mechanical properties of the steel. The beneficial effect of calcium modification coupled with low sulfur content on theK _Ic is briefly discussed in terms of a crack extension model involving the formation of voids at the inclusion sites and their growth and eventual linking-up through the rupture of the intervening ligaments by localized shear.     

Removal of Inclusions from Aluminum Through Filtration

Filtration experiments were carried out using both an AlF₃ slurry-coated and an uncoated Al₂O₃ ceramic foam filter to study the removal of nonmetallic inclusions and impurity elements. The results showed that the 30-ppi ceramic foam filter removed up to 85 pct inclusions from aluminum. Several pictures of two- and three-dimensional morphologies of both nonmetallic and intermetallics inclusions also have been presented. The following contributing mechanisms for the removal of nonmetallic inclusions in the deep-bed filtration mode are proposed: (1) collision with walls and interception effect and (2) the formation of both intermetallic and nonmetallic inclusion bridges during filtration. Fluid dynamics modeling of inclusion attachment to the filter walls showed that most inclusions, especially those with larger sizes, are entrapped at the upper part of the filter, whereas smaller inclusions are dispersed well throughout the filter. The calculated inclusions removal fractions for the 30-ppi filter showed that almost all inclusions >125 μm are removed, and inclusions ~5 μm in size are removed up to 85 pct. The interfacial energy between two collided same-size inclusions was calculated, indicating that a strong clustering of inclusions may result within the filter window. Magnesium impurities were removed up to 86 pct by the AlF₃ slurry-coated filter. The filter acted in active filtration mode in addition to the contribution of the air oxidation of dissolved [Mg], which was calculated to be 13 pct. The total mass transfer coefficient of dissolved [Mg] to the reaction interface was calculated to be 1.15 × 10⁻⁶ m/s.     

Effects of test temperature on internal fatigue crack generation associated with nonmetallic particles in austenitic steels

Internal crack generation associated with nonmetallic inclusions or precipitates has been investigated on high-cycle fatigue at 4 K, 77 K, and 293 k of 25Mn-5Cr high-manganese austenitic steel and nitrogen-strengthened 25Cr-13Ni austenitic stainless steel. In both steels, the internal crack initiation typically occurred at 4 K or in long-life range over 10⁶ cycles at 77 K. Particles such as inclusions and precipitates were responsible for the internal crack-generation behavior, and the origins were identified as mainly Al₂O₃ inclusions in 25Mn-5Cr steel and AIN precipitates in 25Cr-13Ni steel, respectively. We discuss the crack-generation stage I mechanism and the relationship between stress range and size of crack-initiation site. The generation of fatigue cracks associated with the nonmetallic particles in the specimen interior involved a stage I crack. A threshold condition assumption was proposed, that the crack propagation occurred at any stress level when the local stress intensity factor range reached over a constant at or around the initiation crack associated with defects.     

Flexural Strengthening of RC Beams with Prestressed CFRP Sheets: Using Nonmetallic Anchor Systems

This paper presents the flexural behavior of reinforced concrete beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) sheets using nonmetallic anchor systems. The developed nonmetallic anchor systems replace the permanent steel anchorage. Nine doubly reinforced concrete beams are tested with various types of nonmetallic anchor systems such as nonanchored U-wraps, mechanically anchored U-wraps, and CFRP sheet-anchored U-wraps. The flexural behavior of the tested beams, including detailed failure modes of each nonmetallic anchor system, is investigated. The study shows that the developed nonmetallic anchors are more effective in resisting peeling-off cracks compared to the permanent steel anchors and the beams strengthened with the nonmetallic anchors provide comparable load-carrying capacity with respect to the steel anchored control beam.     

Evaluating Pipes from the Sinarskii Pipe Plant Based on their Content of Corrosion-Active Nonmetallic Inclusions

To refine existing standards on the content of corrosion-active nonmetallic inclusions (CANI) in semifinished products, the Sinarskii Pipe Plant has made a study of the change in the density and shape of CANI from the semifinished product to the finished pipe. The study was performed on three heats having a CANI density within the established norm (no more than 2 inclusions/mm²) and on six specimens with a CANI density greater than 2 inclusions/mm². Researchers followed the change in inclusion density in relation to the degree of deformation of semifinished products of steel 20-PKS made by the Volga Pipe Plant. The semi-finished products were 120 and 156 mm in diameter and were used in pipe production. An analysis of the study results showed that CANI density in the finished pipe is no greater than 2 inclusions/mm² if the CANI in the semifinished product are uniformly distributed, their average density is no greater than 2 inclusions/mm², and their maximum density is no greater than 4 inclusions/mm². It was determined that CANI density is not affected by the degree of deformation of the semifinished product. __________ Translated from Metallurg, No. 7, pp. 43–44, July, 2005.     

Analysis of various versions of the deoxidation of rail steel at OAO NTMK

The deoxidation of steel melted using various types of deoxidizers during out-of-furnace treatment is studied. The total oxygen and nitrogen content and the oxygen contents in the main types of oxide nonmetallic inclusions are determined by fractional gas analysis of steel samples taken from heats performed by various schedules. The main types of nonmetallic inclusions and their size distributions are found with qualitative and quantitative metallography. The oxygen content in the rail steel is minimal (5 ppm) when calcium carbide CaC₂ is introduced into the metal in tapping of a converter. When the metal is deoxidized using a steel wire filled with calcium or a steel wire filled with silicocalcium, the oxygen content in rail steel is ≈8 and ≈11 ppm, respectively. A comparison of various processes of rail steel deoxidation under the OAO NTMK conditions shows that the limitation of the aluminum content (no more than 30 ppm) or the use of a wire with a calcium or calcium carbide filler is more effective than the use of a wire filled with silicocalcium.     

Investigation of the process of joining of constructional carbon steels

Conclusions In joining of carbon steels in the zone of former contact there occurs a white band which is tentatively identified as ferrite, which has a significant influence on the mechanical properties of the joint. The strength characteristics of the zone of joining of low- and medium-carbon steels reach the level of properties corresponding to a monolithic material with a deformation temperature of not less than 950°C and a degree of deformation of not less than 30%. The relative reduction is within limits of 2–15%. Fractographic analysis showed that fracture occurs in the ferritic band.The reason for formation of the ferritic band must be assumed to be preferential precipitation of excess ferrite in this area in cooling as the result of occurrence of micropores and and nonmetallic inclusions, which are embryos of the new phase. It was established that the ferritic band is distinguished by higher microhardness than the ferrite of the matrix of the steel.Translated from Poroshkovaya Metallurgiya, No. 4(328), pp. 69–72, April, 1990.     

Production of Boron-Bearing Grades of Steel with a Regulated Sulfur Content at the Chelyabinsk Metallurgical Plant

The rate of growth of ferrous metallurgy depends not only on improvements in the equipment and processes that are used, but also on the industry’s ability to meet the continually rising standards on the quality of metal while simultaneously minimizing the consumption of alloying materials. The use of boron opens up new possibilities in the production of economically alloyed grades of steel. The service properties of these steels are equal and, in many cases, even superior to those of steels obtained with the use of traditional methods of alloying. The Chelyabink Metallurgical Combine has developed a technology for the furnace refining and out-of-furnace treatment of boron-bearing steels with a controlled mass content of sulfur. The new technology is now being used to make all grades of steel that must meet certain requirements on hardenability, sulfur content, and the level of contamination by nonmetallic inclusions.Translated from Metallurg, No. 1, pp. 34–35, January, 2005.