INFLUENCE OF PRE-OXIDATION ON THE NITRIDING PROCESS OF IRON ALLOYS

The article presents the results of studying the kinetics of oxidation of Fe-Cr, Fe-Al and iron alloys at temperatures of 450–550 °C. The influence of preliminary oxidation of these alloys on the nitriding process has been studied. It has been established that alloying of Fe-Cr, Fe-Al alloys increases the amount of absorbed nitrogen, but decreases the overall depth of the nitrided layer. The duration of nitriding required to develop high hardness (over HV 1,000) depends on the composition of the solid solution. At a nitriding temperature of 520 °C, exposure is 10–15 minutes for steels of the first group, at least 3–4 h for steels of the second and third groups, and 5–6 h for steels of the fourth group. Studies have shown that the hardness of the layer is determined mainly by the composition of the solid solution; the amount and dispersion of the carbide phase have less effect. The hardness increases as a result of an increase in the hardening temperature and a decrease in the tempering temperature, which reduce the amount of the carbide phase, but increase the alloying of the solid solution. The hardness of the nitrided layer of high-speed steels P9, P18, having the same composition of the solid solution, is the same (HV 1,340) even despite the significant difference in the amount of the carbide phase. The hardness of the layer of steel 4Х5В2ФС (4Kh5V2FS), which contains more chromium in the solution, is HV 50–90 higher than the hardness of the layer on the steel 3Х2В8Ф (3Kh2V8F), which has 1.5–2 times more of the carbide phase. The behavior of steels with the same high chromium content (12 %), but different carbon content is characteristic. The hardness of the layer in steel 1Х13 (1Kh13), which has few carbides, is HV 100–180 higher than the hardness of the layer in steel Х12М (Kh12M), in which a significant portion of chromium is bound into carbides.

Martensitic transformation in the systems based on Fe-Ni compositions in strong pulsed magnetic fields

Purpose of work. To ascertain the causes of the abnormally large displacement of the martensitic point in steels and iron alloys in strong pulsed magnetic fields at low temperatures. Research methods. Generalization of experimental and theoretical investigations of the strong magnetic field influence on the martensitic transformation in steels and iron alloys, taking into account the magnetic state of austenite. The obtained results. The distributions of the martensitic point displacement ΔMS from the content of the main component - iron and the temperature of the martensitic γ → α- transformation beginning (martensitic point MS) in different experiments are obtained. It is shown that the obtained temperature dependence ΔMS(MS) in a strong magnetic field at low temperatures decomposes into two components, one of which correlates with the generalized Clapeyron-Clausius equations, and the other is opposite to it. In addition, it was found that steels and alloys with intense γ → α- transformation in a magnetic field contain at least 72.5% iron (wt), which at low temperatures in the fcc structure is antiferromagnetic. Scientific novelty. The anomalous temperature dependence of the distribution ΔMS(MS) in a strong magnetic field is explained on the basis of quantum representations of the magnetic interaction of atoms in the Fe-Ni system. This effect is associated with a number of other invar effects, in particular, with an abnormally large spontaneous and forced magnetostriction, a strong dependence of the resulting exchange integral on the interatomic distance. The point of view according to which in these alloys in a magnetic field γ → α- transformation occurs by the type of “magnetic first kind phase transformation” is substantiated. It is assumed that the nucleation of the martensitic phase in a magnetic field occurs in (at) local regions of γ- phase with disoriented atomic magnetic moments (with high compression and increased forced magnetostriction). Practical value. The information obtained in this work provides grounds for explaining the kinetic features of the transformation of austenite into martensite in steels and iron alloys.

Electroplating of iron and its alloys

Analytical review of information on electrodeposition of iron and its alloys from aqueous solutions is carried out. Processes of electroplating of iron and its alloys from aqueous solutions and the principal fields of application of these galvanic coatings are discussed. The principal technological advantages of using iron coatings in the reconditioning of steel parts are considered. Compositions of electrolytes and conditions for plating of iron coatings are provided. Technological parameters of electroplating of iron from industrial electrolytes are considered. Data are presented on the effect of some organic additives on the iron plating process. The effect of the concentration of Fe3+ ions in iron plating electrolytes on electroplating of iron coatings and their physic-mechanical properties is discussed. The data are presented on physic-mechanical properties of iron coatings obtained in different electrolysis modes. Nonsteady-state electrolysis modes are discussed that are used in industry for application of iron coatings. The effect of coating plating conditions on their mechanical properties is studied. Technological parameters of electroplating of iron alloys are considered. Co-deposition of iron with nickel, chromium, titanium, phosphorus, molybdenum, vanadium and tungsten is described. Data are provided on compositions of electrolytes and conditions of electroplating of these alloys. Main fields of application of electroplated iron alloys are discussed. Information is provided.

Effect of Pouring Temperature and Heating of Ceramic Shells Mould on Projection of Thin Wall Castings

One of the research directions of this study is to determine the possibility of making precise, thin-walled castings from selected iron alloys. The scope of research work is aimed at determining the applicability of the casting process of selected iron alloys with the technology of wax pattern, for making precise castings with a wall thickness of less than 3 mm. The article presents the results of tests carried out for experimental castings with the shape of steps, characterized by different wall thicknesses: 1 mm, 5 mm, 10 mm, 25 mm. The castings were made of LH14, Gs42crMo4, L35H7MP2, LH26N9, 316L cast steel, and a new alloy marked “0”. The metal was smelted in an induction furnace with a capacity of 150 kg. The technology of ceramic shell mould used in the plant was used to make the experimental castings. Ceramic shell moulds were heated in a chamber furnace at a fixed temperature. The time of annealing the ceramic mould was constant in a ceramic form. The following parameters were variable during the tests: iron alloy, pouring temperature, and annealing temperature of the ceramic shell mould.

Features of the behavior of the strength properties of iron alloys in the temperature range of magnetic transitions based on the phenomenological theory of phase transitions

Образование магнитного порядка в металлах и сплавах рассматривается как проявление в основной кристаллической решётке металлов и сплавов сопряжённой с ней магнитной структуры, обладающей достаточной жёсткостью и энергией. Изучение их взаимосвязи представляет большой интерес для использования промышленных металлов и сплавов. В результате проведённого исследования можно утверждать, что магнитное упорядочение искажает кристаллическую решётку: при температуре перехода она становится менее стабильной, что приводит к значительно более высокой пластичности вновь образующейся магнитоупорядоченной фазы. B температурных областях магнитных превращений пластичность антиферромагнитной или ферромагнитной фазы больше пластичности парамагнитной фазы и ведёт себя немонотонно. Ключевые слова и словосочетания: фазовые магнитные переходы, прочностные свойства при магнитных перестройках ферромагнетизм→парамагнетизм, антиферромагнетизм→парамагнетизм.