Vol 59, No 11-12 (2016)

Results are presented from a computer study of a promising method of high-rate plastic deformation – Multi-ECAP-Conform (M-ECAP-C) – for obtaining long ultrafine-grained semifinished products (wire rods) of aluminum alloy EN-AW 6101 in a single pressing cycle. It is shown that the distribution of cumulative strain in a semifinished product can be controlled by changing the geometry of the tool. The study examined three geometric variants for the outlet section of the pressing channel and used the results to develop an efficient new channel geometry for pressing by the M-ECAP-C method. The new channel shape makes the strain state of semifinished products more uniform during the stage of stable flow of the material, lowers the pressing forces, and reduces the tensile stresses in the deformation zone.

This article examines one of several approaches currently being taken to the recycling of metallurgical slag in the liquid state inside drum-type units. Technological and design features of the units are discussed. The recycling units make it possible to obtain different types of products from slag melts. A new design of an experimental rotor-type unit is also described.

A new method is proposed for monitoring the internal profile of blast furnaces. The method is based on the use of a compact measurement unit comprised of a laser rangefinder and a digital goniometer. Results are reported from the use of the method to evaluate the actual profile of the shaft of a blast furnace while it was banked. The technology is shown to have promise when used in combination with thermographic monitoring of the technical condition of the top of the shaft and monitoring of heat losses in the cooling system.

Cold modeling is performed on transparent models to examine the effect of the configuration of forging ingots on the kinetics of their solidification. Aspects of the changes in the vertical and horizontal solidification rates across the ingots are studied in the investigation.

The effect of microalloying additions of N, V, Ti, Al, and Nb on structure formation and properties of medium-carbon steels alloyed mainly with chromium (30Kh2AF–40Kh2FABT type) is considered. Steel microalloying makes it possible to provide marked austenite structure refinement due to grain growth limitation by (Ti, V)N particles, retardation of austenite recrystallization and grain growth during stamping by Nb(C, N) particles (and Nb in solid solution), which leads to the formation of a fine final steel structure, as a result of which there is improvement of both strength properties and impact strength. Steel of the class in question may be produced by economic controlled stamping technology with cooling from rolling heating and subsequent tempering instead of heat treatment with quenching and separate heating and tempering. As a result, a unique set of properties is achieved: mechanical properties, brittle failure resistance, corrosion resistance, seismic resistance, fire resistance of long rolled product, building structure components, engineering components, oil recovery equipment, etc.

A Thermo-Calc program is used to calculate isothermal and polythermal sections of diagrams and phase composition for alloys of the Fe–Mn–Al, Fe–Mn–Al–Ni, and Fe–Mn–Al–Ni–C systems. Phase diagrams are used to study the effect of nickel, aluminum, manganese, and carbon on the equilibrium structure of alloys of the Fe–Mn–Al–Ni–C system. Concentration ranges are determined for existence of single-phase γ-alloys in the range 1000–1200°C. It is established that achievement of a considerable aluminum content (10%) and existence of increased specific strength for austenitic alloys of the Fe–Mn–Al–Ni–C system containing not less than 5% Ni is possible with a manganese content of not less than 20% and carbon not less than 1.4%.

Redistribution of components forming the structure and properties during hot rolling of microalloyed steels, similar in chemical composition to hardened steels during hot stamping, of an industrial melt containing carbon from 0.098 to 0.219%, is studied in detail. It is established that a key production parameter controlling the intensity of occurrence of these processes is the temperature at the start of rolling in the finishing group of stands, i.e., T₆. An increase in T₆ leads to significant enrichment with respect to carbon content, and a finer structure due to the formation of niobium carbonitride precipitates in surface layers compared with the rolled product axial zone. An increase in carbon content and a reduction in the concentration of niobium and other microalloying components within steel reduces the intensity of development of these processes. It has been shown by experiment that significant metal chemical and structural inhomogeneity forming in the continuous billet casting stage may be avoided or significantly reduced during hot rolling on the basis of controlling excess phase precipitation. This leads to a marked increase in the level of production and service properties of both hot-rolled product and metal objects prepared from it by hot stamping.

The article is devoted to finding new production methods making it possible to prepare rolled product of carbon or low-alloy steels with a fine-grained structure, and this means greater strength with limitation or exclusion of expensive alloying with niobium. The possibility is considered of retarding recrystallization during hot rolling as a result of reprecipitation of manganese sulfide particles previously dissolved on heating for rolling. Laboratory tests are performed with the aim of determining the optimum heating temperature for rolling in order to implement the mechanism described.

The contemporary level of pipe rolling technology makes it possible to manufacture line pipes of strength class K42–K65 in corrosion- and cold-resistant versions. Pipes of this type are intended for building oil and gas pipelines that are used for developing fields, including those in the Far North. Avoidance of the main defects of both steel smelting and pipe rolling origin, revealed during pipe piercing and rolling, is an important problem for metallurgists in both domestic and overseas pipe plants. A reduction in scrap of metallurgical origin is facilitated by the use of advanced steel smelting technology in electric-arc furnaces followed by extra-furnace treatment and continuous billet casting. Steel 06GBA has been developed with the aim of improving pipe outer surface quality as a result of reducing carbon content and adding niobium. Replacement of steel grade 10GFBYu by steel 06GBA makes it possible to improve the output of finished pipes considerably.

A method is proposed for determining the residual ductility of the material of a semifinished product. The method makes it possible to forge bars on a radial forging machine with the use of technically sound regimes for the reduction of semifinished products. The investigation that was performed involved both theoretical and experimental research. The theoretical part included determination of the stress state in the deformation zone in accordance with a new mathematical model, determination of the shear strain and ductility of the metal, and evaluation of its residual ductility in the forging of bars on a radial forging machine. In addition, an experiment was performed which involved the multi-pass forging of bars of different alloys with different reductions in each pass. The adequacy of the model was checked by comparing the calculated data with the experimental results obtained by forging bars made of different alloys.

Work is devoted to studying important efficiency indices of carbon-carbon composite materials of the Uglekon type, i.e., air-tightness and corrosion resistance in different corrosive media. Range characteristics are established for one of the main structural parameters, i.e., pyrocarbon coating thickness based on a slip underlayer of a supporting base of Uglekon material providing air-tightness, and consequently the efficiency of all composites under extreme high temperature and chemical activity conditions of corrosive media. The effect of thermal loads on air-tightness is also studied. Research results are entirely confirmed during approval of the composites developed on full-scale structures under severe conditions of high pressure, high temperature, and corrosive media, and long-term operating capacity is provided for the properties tested.

An expert analysis of industrial safety is presented in the form of a case study. The analysis entailed determination of the following: the degree of agreement between the actual operating parameters of a BN2.8-16 drying drum and its design parameters; the technical condition of the dryer, with corroborating calculations. Recommendations were developed for continued use of the unit (drum).

Results are presented from the use of numerical modeling to perform an empirical assessment of the effect of the initial process parameters in hot die forging (the temperatures to which the deforming tools and semifinished product are heated) on the temperature field in the semifinished product during deformation. A series of numerical experiments is performed on the basis of the finite-elements method, the resulting data are analyzed, and relationships between the parameters are established and explained.

The effect of process parameters in the production of progressive multiphase automobile steels on the assimilation of the elements used for alloying and microalloying is examined in order to develop an efficient steelmaking technology for this purpose, Data from the production and ladle treatment of 96 experimental heats of steels that are similar to these steels in chemical composition is statistically analyzed to improve these elements' assimilation by optimizing the regimes used for the addition of ferroalloys and other materials at different stages of the steels' treatment. It is established that the assimilation coefficients for Mn, Cr, Nb, V, and Si (to a lesser extent) are nearly independent of the timing and volume of the in-treatment additions of materials that contain these elements. On the other hand, the efficiency of the assimilation of Al and Ti depend to an appreciable extent on the type of material used and the treatment stage in which it is added. The results that are obtained are used to formulate a new approach to optimizing the addition of materials during the production of two-phase ferritic/martensitic steels of the HCT980X type. The adequacy of this approach was demonstrated by a trial heat that was made of this type of steel.

Results are given for a study of the effect of heat treatment parameters on supercooled austenite transformation kinetics in steel 20GFL. Specimen microstructure is studied in specimens 10 × 10 mm in cross section with the following regimes: soaking at 860 and 940°C, cooling in an air stream 3–8 m/sec through a channel 100 mm in diameter. The change in microstructure features in the course of high-temperature soaking at 940°C for 30 and 60 min after specimen cooling in salt water is determined. It is established that in cast steel there is chemical composition microliquation inhomogeneity with respect to carbon and manganese, which decreases during soaking (60 min) and is accompanied by austenite grain growth. Critical cooling rates are determined with which a structure forms containing upper and lower bainite. A dependence is obtained for impact strength KCV⁻⁶⁰ on soaking temperature and time in the γ-region. The effect is demonstrated of alloying with vanadium on the possibility of stimulating the formation of globular lower bainite components.

The possibility is considered for preparing bimetallic composite material (BCM) based on low-carbon microalloyed steel clad with corrosion-resistant steel alloyed with nitrogen. BCM mechanical and corrosion roperties are studied. It is shown that the material proposed is no worse than existing bimetals with respect to corrosion resistance, and concerning composite strength properties it surpasses traditional materials by 40–45%.

Results are presented from an investigation of the structure and mechanical properties of tool steels R6M5 and EK-80 after their high-temperature gas extrusion (HTGE). It is shown that this treatment has a significant effect on steels’ phase composition, the structure of the phases that are formed, and, thus, the steels’ mechanical properties (hardness, ultimate strength, and ductility). It was determined that after undergoing HTGE at 1000–1150°C the steels have a hardness of 60–64 HRC and the same ductility as before the treatment. This makes it possible to use them to fabricate small tools by a simplified technology – single or double annealing of extruded semifinished products in the range 500–600°C without additional heating before quenching. Small tools made from such semifinished products last 2–3 times longer than tools made from cold-drawn rolled products.

A multistage process is described as the basis for metallographic studies of intermetallic formation during reaction of molten aluminum with titanium. A mechanism is proposed explaining the complex nature of the change in aluminide formation rate, including aluminide inclusion formation by breakdown. Stages are separated for reaction of titanium with molten aluminum: latent period; continuous intermetallic layer formation at a titanium-aluminum boundary; titanium dissolution in aluminum; band formation and growth within a melt with intermetallic fragments; increase in aluminide content in crystallizing melt. x-Ray structural and energy-dispersion analysis methods are used to demonstrate formation of just a single intermetallic TiAl₃, which confirms thermodynamic calculations performed by Kattner.

The use of plasma-based technologies elevates productivity and product quality in the fabrication of welded structures made of aluminum and its alloys. High-power heat sources must be used to achieve high levels of productivity in the welding of aluminum structures. Also, the presence of an oxide fi lm that impedes the formation of the weld dictates the use of reverse-polarity current in the arc welding of such structures. The use of combination heat sources can resolve the problem of improving quality and productivity in the welding of aluminum alloys. This article presents results from a study of the plasma welding of aluminum alloys with the use of a dual-arc plasmotron that provides for the combustion of two direct arcs on reversepolarity current. It is shown that the plasmotron can operate stably under these conditions. Use of the given technology reduces the thermal load on the plasmotron, enhances its ability to melt through the alloys, improves cathodic cleaning of the metal’s surface in the region of the weld, and ensures the formation of welds that are free of defects.