Cooling process optimization during hardening steel in water polyalkylene glycol solutions

Objects of investigations are water solutions of polyalkylene glycol (PAG) which are used as the quenchants in the heat-treating industry. They are tested by standard cylindrical probe made of Inconel 600 material. The main and not solved yet is the problem of transition from data achieved for standard probe to data suitable for any form and size of real steel part. It opens possibility to make predictable calculations. Taken this into account, it has been investigated water solutions of PAG of different concentration. It is underlined that cooling intensity of quenchant can be evaluated by Kondratiev number Kn. The mentioned number Kn varies within 0≤Kn≤1 when generalized Biot Biv number varies within 0≤Biv≤∞. As a main achievement of investigation is established correlation between standard Kn number and Kn number of real steel part. In many cases, when film boiling is absent, the established correlation is a linear function. It allows optimizing quenching processes: obtain high surface compressive residual stresses, save alloy elements and improve environment condition. All of this is achieved by tolerating chemical composition of steel with size and form of quenched object as it is proposed by UA Patent No. 114174. Also, the number Kn allows interruption of quench process when surface compressive residual stresses are at their maximum value that essentially improves the quality of steel components. Moreover, interrupted cooling prevents quench crack formation, decreases distortion of quenched steel parts. The results of investigations can be used by engineers in the heat-treating industry and scientists for further research.

Corrosion Fatigue Damages of Rebars under Loading in Time

Nowadays, a relatively small number of studies concern the study of corrosion processes in reinforced concrete structures under load. Additionally, rather little research has been carried out concerning changes in the stress–strain state parameters of structures under the simultaneous action of aggressive environment and load. This issue requires additional experimental and theoretical investigation. Determination of mechanical properties, fatigue characteristics and susceptibility to corrosion cracking was performed on samples of reinforcing St3GPF steel. The chemical composition of steel was determined by structural analysis. The spectral method for the determination of alloying elements and impurities in steels is based on the excitation of iron atoms and admixtures by electric discharge, decomposition of radiation into a spectrum, followed by its registration on photoplate with the use of electrograph. Experimental tests of samples in an aggressive environment under the action of statically applied tensile force showed that corrosion damage has little effect on the strength characteristics. At the same time, the decrease in area reduction and the decrease in strain were recorded. Additionally, the action of cyclic loads in an aggressive environment leads to a significant reduction in the fatigue limit to values from 20 to 24% of the yield strength of the original samples, which is 2–3 times lower than the fatigue limit of undamaged samples.

Peritectoid carbide transformation based on ε-carbide Fe2C in Fe-C system alloys. Part 2. Metallographic studies

Original metallographic studies of annealed medium carbon steel (steel 45, steel 40X and steel 35XGA) are carried out in order to reveal leakages in pearlite of these steels of low-temperature carbide transformation of peritectoid type, in which solid solutions of ferrite and cement form a solid solution of wide area of homogeneity based on ε-carbide Fe2C. Most of the inclusions of pearlite cement 45 steel are almost entirely covered with a light grey “foam” shell of nanoglobular crystals ε-сarbide Fe2C. In the process of crystallization of ε-сarbide Fe2C on the cement plates of pearlite steel 45 three morphological types of structure of ε-сarbide Fe2C can be distinguished: “foam” globular shell, granular “outgrowths” and wrapping of particles of decomposed and partially dissolved cement plates. Chromium, which is a part of steel 40X, abruptly inhibits peritectoid transformation. On many cement plates pearlite surface is smooth. In areas where the concentration of chromium is low, the process of formation of ε-сarbide Fe2C is active, with the formation of individual sites with light gray “foam” shell of nanoglobular crystals ε-сarbide Fe2C. It can be expected that in high-alloy chrome steels, the peritectic transformation can be completely blocked through the stabilization of chrome cement or its transformation into thermodynamically stable high chrome carbides. In 30ХГСA steel a sharp intensification of the process of peritectoid transformation of solid solutions of ferrite and cement which are part of pearlite is fixed. The reason for acceleration of the disintegration process of pearlite cement into individual fragments and intensification of release of ε-сarbide Fe2C in the form of column-shaped crystals between the plates of pearlite cement is silicon and manganese, which are part of steel 30ХГСА. As a result of the acceleration of martensite decomposition, the morphology of the released crystals of ε-сarbide Fe2C has changed from “foam” nanocrystals of ε-сarbide Fe2C, typical for steel 45 and steel 40X, to granular. There was also intensive fragmentation or disintegration of cement plates with the appearance of plane-parallel boundaries between the fragments and the formation of large longitudinal flat inclusions of ε-сarbide Fe2C above 100 nm, whose axis is mainly perpendicular to the axis of the cement plate. On the basis of the performed experiments it is possible to consider as proved the presence of low-temperature carbide peritectoid phase transformation in the Fe-C alloy system as a result of interaction of solid solutions of ferrite and cement at 3820C with formation of solid solution on the basis of ε-сarbide Fe2C with wide area of homogeneity. The influence of the chemical composition of steel on the peritectoid transformation between ferrite and cement slurries opens up additional possibilities for regulating the microstructure of pearlite, such as the degree of dispersion of pearlite, which has a determining influence on a number of performance characteristics of steel, such as wear resistance, yield strength and others.

Increase of resistance of piercing mill mandrels at seamless pipes production of 13Cr grade martensite class stainless steel at line ТПА 159‒426 of JSC VTZ

At production of pipes of type 13Cr grade steel used at development of oil and gas deposits in areas with aggressive environment, intensive wear of instrument takes place, first of all, piercing mill mandrels. Factors, influencing the resistivity of the piercing mandrels considered, including chemical composition of the material, the mandrel is made of and its design. Based on industrial experience it was shown, that chrome content in the mandrel material practically does not affect on the increase of its resistivity, since the formed thin protective oxides having high melting temperature, are quickly failed and practically are not restored in the process of piercing. To increase the resistivity of piercing mandrels at production of casing tubes of type 13Cr grade steel, a work was accomplished to select a new material for their manufacturing. The chemical composition of steel presented, which was traditionally used for piercing mandrels manufacturing, as well as a steel grade proposed to increase their resistivity. First, molybdenum content was increased, which increases the characteristics of steel strength and ductility at high temperatures and results in grain refining. Second, tungsten content was also increased, which forms carbides in the steel resulting in an increase of its hardness and “red resistivity”, as well as in preventing grains growth during heating. Third, cobalt content was also increased, which increases heat resistivity and shock loads resistivity. The three elements increase enabled to increase the mandrels resistivity by two times. Results of mandrel test of steel 20ХН2МВ3КБ presented, the mandrel having corrugation on the working cone surface, which enabled to reach the resistivity growth to 12 passes without significant change of instrument cost. Microstructure of mandrels made of steels 20Х2Н4МФА and 20ХН2МВ3КБ shown. Application of the centering pin of special design was tested, which provided forming of a rounding edge on the front billet ends, eliminated undercut of mandrel external surface in the process of secondary billet grip and increase the service life of the piercing mill mandrels. At production of seamless pipes of martensite class type 13Cr stainless steels having L80 group of strength, an increase of piercing mandrel resistivity was reached by more than four times, which together with other technical solutions enabled to increase the hourly productivity of the hot rolling section of Volzhsky pipe plant ТПА 159-426 line by more than two times.

Nitrogen-containing steels and methods of their production

The systems of alloying Fe – Cr – N, Fe – Cr – Mn – N, Fe – Cr – Ni – Mn – N, Fe – Cr – Ni – N are considered and attention is paid to the compositions of developed or already used steels. Mechanical, operational and other properties of a number of modern nitrogenalloyed steels with an equilibrium and super-equilibrium concentration of nitrogen are considered. The optimal intervals of their doping with nitrogen are given and the contribution of nitrogen to formation of the structural-phase state and the complex of their properties is estimated. For example, in the Fe – Cr – N system of practical interest are the austenitic steels Fe – (21 – 22) Cr – (1.1 – 1.3) N, solid solution hardened, technologically plastic, with a yield strength of 800 MPa and high corrosion resistance. Corrosion-resistant high-strength austenitic steels are in demand of the Fe – Cr – Mn – N system, such as Fe – (18 – 21) Mn – (14 – 22) Cr – (0.4 – >0.6) N, in which nickel as austenite-forming element is completely or partially replaced by manganese and nitrogen. Examples of steels of the Fe – Cr – Mn – Ni – N system with high service properties are given. Since alloying steels with nitrogen requires an assessment of the maximum possible level of its content (solubility) in the metal and the creation of conditions for the introduction of nitrogen into the liquid metal and its preservation in the solid metal, attention is paid to: calculations of nitrogen solubility, taking into account the effect on it of the chemical composition of steel, temperature and pressure at which alloying occurs; the concept of compositionally stable nitrogen content and the coefficient of compositional stability. The main methods of production of nitrided steels are considered. The quality of metal in open smelting and after refining electro-slag remelting (ESR) is compared. The latter makes it possible to preserve nitrogen during the remelting of nitrided steels, to ensure its uniform distribution along the height and cross-section of the ingot, to obtain ingots with a good surface and a dense structure with a radialaxial orientation and without shrinkage defects. The advantages of the method of electroslag remelting under pressure (PESR) are noted – the ability to obtain high-quality metal with a nitrogen content above its equilibrium concentration (under standard conditions) and to provide an almost ideal ecology of production.

Optimization of chemical composition of steel for gearweels of agricultural industry engineering

Development of new steels in mechanical engineering to create alloys with predetermined properties that can minimize material and labor costs during their processing. Optimization of the chemical composition of the alloy based on the analysis of the impact of complex alloying on the structure and consequently on the manufacturability of steel. This will reduce the level of internal intensities in the heat treatment process. Based on the analysis of existing trends in mechanical engineering, it is established that the complexity of modern parts of gearweels imposes on the material increasing technological requirements for stamping, machinability, weldability, hardenability, cementation and gouging in the hardening process which explains the need for alloying steel via a certain group of chemical elements. The influence of different compositions of steels for gearweels on the level of internal intensities occurring in parts during heat treatment is studied. The optimal composition of complex-alloyed cementing steel is established.

Effect of Raw Materials Formula on Performance of Steel Slag Cement

At present, the commonly used cement has low tensile strength and low flexural strength, which is a fatal defect of cement materials. It is extremely urgent to conduct research on this shortcoming of cement. In addition, the steel industry steel mill produces a large amount of waste steel slag. The chemical composition of steel slag is similar to that of cement. This experiment makes full use of waste steel slag as raw material to prepare cement to improve the performance of cement materials. Using limestone, sandstone, shale, steel slag and river sand as the main raw materials, through the powder preparation, mixing, calcination, grinding, molding process and performance analysis of raw materials. After the calcination, the cement clinker in the form of a block becomes higher in hardness as the steel slag is incorporated. The higher the calcination temperature, the smaller the steel slag incorporation maximum. When the calcined at 1150 °C is mixed with 17.5% steel slag, a cement with better performance can be obtained.

Effect of Temperature and Time on Decomposition of δ-ferrite in Austenitic Stainless Steel

Microstructure of austenitic stainless steel is primarily monophasic, i.e. austenitic. However, precipitation of the δ-ferrite in the austenite matrix is possible depending on the chemical composition of steel. δ-Ferrite is stable on room temperature but it transforms into σ-phase, carbides and austenite during heat treatment. In this work, the results of analysis of influence of temperature and time on decomposition of δ-ferrite are presented. Magnetic induction method, microstructure and hardness analyses were used for testing the degree of decomposition of the δ-ferrite. Analysis of results showed that increase in temperature and time increases the degree of decomposition of δ-ferrite.