Structural Carbon Steel Research Articles

Lifetime Assessment for Multiaxial High-Cycle Fatigue Using Twin-Shear Unified Yield Criteria

In this paper, a life prediction model associated with maximum principal stress and equivalent shear amplitude based on twin-shear unified yield criterion for multiaxial high-cycle fatigue is proposed. The equivalent shear amplitude is the normalized format of the equivalent shear amplitude based on clusters of yield criteria embodying Tresca and the linearization of Huber-von Mises, extending the application to metallic materials. Simultaneously, the effect of mean stress on multiaxial high-cycle fatigue is considered in the proposed model. As an assessment of the new prediction model, the criterion is compared with experimental data of aluminum alloy LY12CZ and carbon structural steel SM45C published in the relevant literature, which shows that most of the data are located within an error range of less than two times the data and are in good agreement with the experiment. Moreover, the proposed model is also compared with other models, such as McDiarmid, Liu, and Freitas, to validate its competitiveness.

Experimental and Computational Method for Determining Temperature Stresses in the Welding of Structures Made of Carbon and High-Alloy Structural Steels

A method for determining temperature stresses in a welded joint of a thin-walled pipe with a base is described. The method is based on experimental data of temperature measurement at reference points of the structure. The features of the elements of the welded joint made of carbon and high-alloy structural steels and the modes of electric arc welding were taken into account. The efficiency of using spline approximation of experimental data to obtain analytical dependences of the distribution of temperature fields and stresses, as well as to obtain a solution of the heat equation by numerical differentiation and integration for this case, is shown. Formulas for calculating temperature stresses for the case of an asymmetric temperature distribution in a cylinder under the action of a moving high-intensity heat source are obtained.

Influence of the electromagnetic field on the corrosion of low-carbon steel in aqueous mineralized media and on the crystallization of calcium carbonate in the presence of iron(II) ions

The influence of the electromagnetic field (EMF) on the corrosion of structural carbon steel in a 3% aqueous solution of sodium chloride in the presence of CO2 was studied. It is shown that the EMF increases the corrosion rate of steel by 1.13 times in a 3% aqueous solution of NaCl in the presence of CO2. When Ca2+ ions are added to the solution, the corrosion rate of steel decreases under the influence of an electromagnetic field. It is assumed that the formation of CaCO3 in the near-surface layer of the solution and its adsorption on the metal surface prevents the development of corrosion. The influence of the electromagnetic field generated in the frequency range from 100 to 200 kHz on the crystallization of CaCO3 from supersaturated aqueous solutions on the model system CaCl2 – NaHCO3 – FeSO4 is studied. It was found that Fe2+, rather than EMF, has a more significant effect on salt deposition. The efficiency of the effect of Fe2+ on the inhibition of salt deposition in the model of mineralized water CaCl2-NaHCO3 is 11.5% higher than when exposed to EMF. During the crystallization of CaCO3, the predominant formation of aragonite is observed. In the presence of iron ions and under the influence of EMF, there was a decrease in the formation of aragonite and an increase in the formation of calcite and vaterite. Keywords: electromagnetic field; corrosion; carbon steel; iron ions; scale deposition; crystallization; calcium carbonate.

ANALYSIS OF THE REASONS FOR CRACKING PIPES OF THE BOILER OF THE RECOVERY

8-381X 
 Abstract. Formulation of the problem. One of the main tasks of production is reliable and trouble-free operation of equipment. In the oxygen-envelope process, when cast iron is purged, a large amount of carbon monoxide CO is emitted in the converter, which has a high temperature of more than 1 700 °С of the outgoing gases. The envelope gases in the waste heat boiler are cooled. Converter gas output is characterized by cyclic unevenness In this case, uneven heating of the walls of the boiler pipes occurs. By circulation pumps, chemically purified water is supplied for forced cooling of the boiler walls. When raising the outgoing gases, the cooling water is converted to pars by its subsequent supply to the consumer. The study is dedicated to solving the scientific and applied problem for the reasons for the formation of defects and the identification of cracks in the pipes of the recovery boiler.The purpose of the work. To investigate the causes of the development of transverse cracks in the pipelines of the recovery boiler by various methods of non-destructive testing, to use the methods of scanning microscopy to analyze the microstructure, mechanical tests, and the magnetic properties of structural carbon steel. Conclusions. One of the main reasons for the appearance of massive cracks in the pipes of cylindrical caissons is thermal fatigue caused by high thermal loads. Transverse cracks have the character of thermal fatigue failure, which is confirmed by changes in the ferrite-pearlite structure of the metal, resulting from uneven local cooling of the walls of the caisson. The reasons for the violation of the water circulation in the boiler are the pressure drop in the boiler and a sharp discharge, the load is the release of water from the boiler.

Modeling of Ductile Fracture for SS275 Structural Steel Sheets

A series of earthquake events give impetus to research on the ductile fracture behavior of steel materials. In the last decades, many fracture models have been developed and utilized in the mechanical or aerospace engineering. Nevertheless, very little application to structural members used in the construction industry has been made due to the lack of a suitable model for the fracture behavior of constructional steel. This paper presents the experimental and finite element (FE) technique to predict ductile fracture in mild carbon structural steel (SS275) sheets, which has been widely used in building structures. The post-necking true stress–strain responses were successfully estimated using the weighted-average method. The Bao and Wierzbicki (BW) model, which requires only two model parameters, was selected for the identification of fracture locus. Each model parameter was calibrated from uniaxial tension and in-plane shear specimens with the aid of digital image correlation (DIC) and finite element analysis. Fracture simulation was then performed and validated based on the experimental results of the specimens under combined tension and shear stress state.

Influence of power density and frequency of the process of laser marking of steel products

The study is about the process of laser marking by melting products made of carbon structural steel 15Cr2 with wide application in industry. A fibre laser operating in the near-infrared region was used to perform the experiments. A raster marking method was used by varying the power density of the laser radiation and the frequency of pulses repetition. For each marked area, the contrast is determined by measuring the saturation of the marked area and the background by the greyscale. Graphs of the dependence of the contrast on the power density for three marking speeds and on the contrast on the frequency for two marking speeds are analysed. The work intervals for the power density and frequency for this steel and fibre laser, are determined.

Research on concrete-filled stainless steel tubular composite columns

Concrete-filled stainless steel tubular composite columns are used in the structures. It is important to define the structural behaviour of this type of columns. This paper presents experimental and theoretical studies of eccentrically loaded concrete-filled stainless steel tubular composite columns. The column specimens were manufactured with high strength outer stainless steel tube, in-filled concrete and inner carbon structural steel. The tubular composite column specimens were designed with plain concrete and steel fiber reinforced concrete. The column specimens were tested and the experimental load–deflection curves of columns were presented in the study. In addition, the tested plain and steel fiber concrete-filled stainless steel tube composite columns were analysed based on a theoretical method for the prediction of strength and load–deflection behaviour. It was observed that the tested tubular column specimens behaved in a ductile manner. A good degree of agreement was obtained between the experimental and theoretical load–deflection curves of concrete-filled stainless steel tubular composite columns. In addition, a parametric study was carried out to examine the influences of loading eccentricity, slenderness, plate slenderness and the concrete compressive strength on concrete-filled stainless steel tubular composite column behaviour. It was concluded from the parametric study that the strength of columns increased by increasing stainless steel wall thickness and concrete compressive strength. However, column strength decreased when the eccentricity and column length were increased.

Investigation of Low-Cycle Fatigue on Structural Carbon Steel

It is possible to explain the phenomenon of fatigue destruction and the patterns that are observed only in the deep study of the processes taking place in the material under conditions of repeated-variable loading, i.e. in the development of the physical theory of metal fatigue. Despite the large number of work on this issue, there is currently no single interpretation of the process of fatigue destruction of metals, which is primarily due to the exceptional complexity of the problem. The purpose of the study is to study low-cycle corrosion fatigue of steel using the example of A 414 Grade A steel. The work solved problems, such as research of kinetics of crack development in conditions of low-cycle loading of metal structure made of carbon structural steel A 414 Grade A. Regression analysis has also been applied to predict a change in the thermodynamic stability of the metal during cyclic loading. Analysis of fatigue crack development at alternating loading cycle was carried out. The results of calculations based on the proposed model of elastoplastic deformation near the top of the crack at the sign-alternating loading cycle can be described by non-linear dependence. The regression analysis revealed that the correlation coefficient of the selected model is-0.93, which indicates a relatively strong relationship between the variables. In experimental way it has been proved that reduction of thermodynamic stability of metal in corrosive medium is connected with increase of number of loading cycles, which leads to accumulation of fatigue damages.

Establishing the Relationship between Cutting Speed and Output Parameters in Belt Grinding on Steels, Aluminum and Nickel Alloys: Development of Recommendations.

This paper presents the research results of one of the main technological parameters of belt grinding, i.e., the cutting speed while machining corrosion- and heat-resistant, structural carbon and structural alloy steels, aluminum, and heat-resistant nickel alloys. Experimental and analytical methods are used to establish the dependence of the output parameters of surface belt grinding on the cutting speed and tool characteristics. An analytical model, considering the physical and mechanical properties of the grinding belt (strength depending on the base and bond; the thermal conductivity; the type of grinding operation) and the machined material, is created to determine the belt grinding speed. The output parameters, such as the arithmetic mean of the surface roughness (Ra) and the material removal rate (MRR) during the belt grinding of steels, heat-resistant and light alloys, have been studied. Based on the empirical dependencies of the belt grinding parameters, the model was developed for the selection and setting of the cutting speed of belt grinding for the aforementioned alloys, taking into account the type of operation, the type of the machined material, and the main characteristics of the sanding belt.

Вплив швидкості охолодження при затвердінні безперервнолитої заготовки на характеристики дендритної структури сталі марки ОС

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.

Control of properties and structure of steel vessels by cooling in various media at the outlet of rolling and pressing lines

When controlling the mechanical properties and structure of vessels made of carbon structural steels manufactured by hot deformation on rolling and pressing lines (PPL) of machine-building enterprises of Russia, such cooling media as water, I20 industrial mineral oil, air are used. The applied cooling media are able to provide the workpieces with a given structure with a wide range of mechanical properties. However, the cooling media have a number of technological limitations and conditions of the use, non-compliance with which leads to reject. When cooled in oil, the probability of ignition is high; when cooled in water, hardening cracks may form, and air is not always able to provide the required rate and uniformity of heat transfer to the environment. The efficiency of control of physical and mechanical properties and structure of deformed vessels made of 50 steel by cooling in TERMAT polymer aqueous solutions in different concentrations on PPL of the plant of JSC NPO Pribor was studied. The effect of varying the concentration from 2 to 9% of TERMAT polymer on the formation of metal structure, as well as physical and mechanical properties of hot-deformed vessels was studied. The results of testing the strength and plastic characteristics of vessels by destructive and non-destructive control methods are presented. According to the results of physical and mechanical properties, regression equations were obtained with at least 95% reliability of R2, which establish the relationship between the controlled plastic and strength parameters of the vessel metal`s properties. The conducted researches allowed to compare the indicators of the main physical and mechanical properties of steel vessels at the PPL outlet and to propose methods of inhomogeneity control that reduce time and material costs by 5–10% during the tests.

Experimental and numerical study of hot-rolled duplex stainless steel CHS columns

Stainless steel circular hollow section (CHS) members have been widely used in building structures because of their comparable strength to structural carbon steels, attractive appearance and excellent corrosion resistance. However, research on stainless steel CHS members has been limited to cold-formed members, whereas hot-rolled CHS columns have received less attention. To this end, the flexural buckling performance of hot-rolled duplex stainless steel CHS columns was investigated by a comprehensive experimental and numerical programme. A total of seven hot-rolled duplex stainless steel CHS columns covering two cross-sectional sizes with varying lengths have been tested under compression. Based on the test results, finite element (FE) models were developed and used in parametric studies to generate data points with a wider range of geometric dimensions. Comparing the test and FE results with current design guidance, it was found that the Chinese standard, CECS 410, and North American design guidance, AISC DG 27, underestimate significantly the flexural buckling resistance of such columns, while the design method in Eurocode 3: Part 1–4 might be unsafe in predicting the resistances for low slenderness values. New column buckling curves based on the Eurocode 3 and AISC DG 27 design formulae with improved accuracy and reduced scatters were also proposed and validated through careful reliability analysis.

Post-fire mechanical properties of carbon steel and safety factors for the reinstatement of steel structures

This paper provides guidance on the post-fire material properties and associated safety factors for structural carbon steel which are required for the assessment and retrofitting of existing steel buildings which have suffered and survived a fire. Nowadays, there is a discrepancy between the methodology which is used in the design stage of a building (mostly based on the partial factor method) and the verification methods used after a fire. In the past decade, a number of researchers have published test data and there is more information available on the mechanical properties of steel following a fire. Nevertheless, a statistical evaluation of these results has yet to be conducted although design codes generally adopt a reliability-based approach for the analysis and assessment of buildings. To fill this gap of knowledge, the current article includes a statistical evaluation of the mechanical data from 718 tests collected from 19 peer-reviewed articles and doctoral theses. The study is done for hot-rolled steel, cold-formed steel as well as wrought or cast iron. By focusing on the effect of a fire on the mechanical properties after cooling, which is mostly related to how the coefficient of variation of their distribution increases, adjusted safety factors are proposed together with a reduced reliability index based on economic and social considerations. It is contended that by following this method, possible misunderstandings can be avoided and decisions on the salvage and rehabilitation of structures can be based on performance data and technical analysis, thus reducing the need for individual judgement.

A105 Work-Material Turning Experimentation using L9 Orthogonal Array Runs with Dry, MQL and Nano-Al2O3 Assisted MQL Machining Conditions

A105 carbon structural steel material exhibits high strength and hence pose machining difficulties such as excessive tool wear due to high cutting temperatures. Abrupt cutting actions due to improper selection of feed rates have posed to bad surface finish of work-pieces. These materials find best applications in flanges and pipe fittings and generally turning operations are conventional methods to change its dimensions and attaining accuracy levels. An attempt is made to experiment on A105 work material using lubricant vegetable coconut oil under minimum quantity lubrication ( MQL) assisted by nano-particles such as Al2O3 in order to find suitable combinations of working environments, to compare with dry cutting, and also to decide suitable feed rates and cutting speeds combinations.

System-based reliability analysis of stainless steel frames under gravity loads

Current structural codes for steel and stainless steel structures such as AISC360-16, AISC370-21, AS/NZS4100 and Eurocode3 are based on the traditional two-step member-based design approach, in which internal actions are first obtained from a structural analysis, usually elastic, and the strength of each member and connection is subsequently checked using a structural design standard. However, the most recent versions of these standards already incorporate preliminary versions of the direct, or one-step, system-based design alternative, which is based on the design-by-analysis concept and allows evaluating the strength of structures directly from numerical simulations, although the standards in their current form do not provide reliability requirements for structural systems. Therefore, it is necessary to build a rigorous structural reliability framework to investigate acceptable target reliability indices for structural systems and to provide adequate system safety factors and system resistance factors. While this framework has been developed based on advanced Finite Element analysis for hot-rolled and cold-formed carbon steel structures in recent years in the form of the Direct Design Method (DDM), the framework does not exist for stainless steel structures. This paper presents an extension of the DDM to the analysis of stainless steel structures, in which system reliability calibrations are presented for six stainless steel portal frames under gravity loads covering the three most common stainless steel families and different failure modes using advanced numerical simulations. From the derived reliability calibrations, suitable system safety factors γM,s and system resistance factors ϕs are proposed for the direct design of stainless steel frames in the European, US and Australian design frameworks under gravity loads.

Studying the Impact of Blast Treatment on the Structure and Mechanical Properties of Carbon Steel

The study has covered the effects of blast treatment on the microstructure parameters and mechanical performance of carbon steel. The calculation results of examining the structure and properties of carbon steel in its initial state and after explosive hardening in various sections of cylindrical carbon steel workpieces have been verified with the finite-element analysis using the ANSYS Workbench software environment. Blast treatment has been demonstrated to lead to a perceptible change in the structural state of carbon (cementite) in steel.

Experimental Study of the Distribution of Temperature Fields in the Butt Contour of a Welded Joint Made of Carbon and High-Alloy Structural Steels

A graphic-analytical method for determining temperature fields in the butt contour of a welded joint of a thin-walled tube with a base is presented. The method is based on the experimental data of temperature measurement at the reference points of the structure. The features of the elements of the welded joint made of carbon and high-alloy structural steels and the modes of electric arc welding were taken into account. A graphic-analytical method for determining temperature fields is proposed, which, on the basis of the theory of welding strains and stresses, makes it possible to determine temperature stresses and strains, both in the elements of the joint and in the contour of the weld.

Damage accumulation in cyclically stable steel under low-cycle loading and elevated temperature

Based on the strain-kinetic fatigue fracture criterion, the kinetics of accumulated damages in structural carbon steel under low-cycle loading at an elevated temperature (150°C), at which the material begins to develop stress aging processes, is estimated. It is shown that stress aging, strengthening the material, narrows the durability area in which there is quasistatic destruction, the limiting case of which is the buckling failure of plastic strain, like single static destruction. This increases the fatigue fracture range, the limiting case of which is the formation of the primary fracture. The recoverable plastic strain causes the main damaging effect. Stress aging contributes to an increase in damage from elastic strain, although in the area of low-cycle failure, the share of damage from elastic strain remains small, growing with increased durability, and in the area of multi-cycle fatigue, this share becomes prevalent. Hardening from stress aging inhibits the development of damage from the one-way accumulated strain. The author confirms the validity of applying the strain-kinetic criterion of fatigue fracture to describe the damage kinetics and limit states during the cyclic elastic-plastic strain of carbon steel in the presence of weak stress aging.

Effect of initial treatment on the structure and mechanical properties of medium carbon steel subjected to ECAP

Effect of initial treatment on the structure and mechanical properties of medium carbon steel subjected to ECAP

INFLUENCE OF CUTTING MODES ON WEAR RESISTANCE OF CUTTERS AND ACCURACY OF FINE BORING OF STEELS

This paper is devoted to experimental study of fine boring of steels, which improves performance and parameters of processing accuracy. The conditions that ensure high wear resistance of cutting blades and improvement of accuracy parameters and processing quality were determined by changing cutting conditions and special geometry of carbide cutters with chip-curving chamfers. In the experiments, single-cutter boring was used, as well as double-cutter according to the feed division method. On the basis of the method of planning an experiment in the presence of a large number of variable input parameters, rational values of speed, feed, depth of cut, as well as parameters of roughness, taper and deviations from the roundness of the machined holes are established. The effect of fine boring modes on wear and tool life of cutting edges has been clarified. The influence of the compliance of cantilever boring bars on the level of oscillation of the cutter was also studied. It was found that intense vibrations occur for boring bars of small diameter <10 mm at a depth of cut >0.1 mm, resulting in intensive wear of the cutters. In preliminary experiments, it was found that boring of soft parts (type 20X and steel 30) is significantly different from machining harder steels and requires the use of other cutting conditions. Although the groups of structural carbon, high-quality and alloy steels may differ insignificantly in terms of processing conditions and the results achieved in the process of fine boring, however, for processing steels with special properties, a distinctive feature arises, namely increase in the level of vibrations with increasing cutting speed within the range usually used for other steels. This paper shows results of an experimental study of the process of thin boring of 35L steel with cutters made of TЗ0K4 hard alloy and chip-curving chamfers along the cutting blades.