Boron-containing Steel Research Articles

EVALUATION OF TECHNOLOGICAL PLASTICITY OF HIGH BORON CORROSION-RESISTANT STEEL DURING HOT DEFORMATION OF PIPES USED FOR SPENT NUCLEAR FUEL STORAGE

Statement of the problem. The sustainable development of the global nuclear power industry in the future depends on how effectively the problems of radiation safety and nuclear proliferation are addressed. Such problems occur, among other things, at the final stage of the nuclear fuel cycle – spent fuel management. This task is currently on the agenda of both the international community and national governments of countries that develop or intend to develop nuclear energy [1−3]. Today, in connection with ensuring the safety of nuclear energy, boron-containing steels are widely used in the world practice as a material for biological protection and for the manufacture of special equipment parts. This is due to the fact that the B10 isotope in steels provides neutron capture [4]. Hexagonal pipes made of high-boron steel were needed to shield the support cover of the compacted spent fuel storage facility at nuclear power plants. Corrosion-resistant steels alloyed with boron are widely used in the nuclear power industry due to their special nuclear properties. During the operation of nuclear power plants, fuel assemblies that have served their useful life must be stored in special storage facilities using containers – hexagonal tubes made of 04Сr14Ti3B2V steel. To reduce costs during in the construction and operation of NPPs, part of the spent nuclear fuel management should be performed at Ukrainian enterprises. This will provide a significant import substitution effect. To manufacture hexagonal tubes from 04Сr14Ti3B2V steel according to the ingot-hot deformation-profiling-heat treatment scheme, it is necessary to develop the parameters of hot deformation and subsequent technological operations. The use of these pipes in compacted spent fuel storage facilities of NPPs will allow to increase the storage capacity by 2 times, which will give a significant national economic effect Material and methods of research. Material used for the study was steel 04Сr14Ti3B2V (CS-82), smelted using two variants (vacuum-induction – “VI” and vacuum-induction followed by vacuum-arc remelting – (“VD”). Steel grade 04Сr14Ti3B2V belongs to high-alloy, corrosion-resistant ferritic steels with a high boron content of up to 2 %. The method of differential thermal analysis was used to study the phase transformation temperatures in the steel. X-ray diffraction and micro-X-ray spectral analysis were used to assess the phase state. The steel samples were tested for weldability After cooling, the welded samples were subjected to X-ray transmission [5]. Hot twisting tests and mechanical tests at high temperatures were also performed. The macro- and microstructure of the metal was studied. Results. The macro- and microstructure of steel was evaluated depending on the smelting method. The phase composition of the steel was studied. The study of the plastic properties of steel ChS-82 by means of penetration and hot twisting tests showed that the temperature range of maximum plasticity is in a wide range (from 1 025 to 1 150 0C) with a rather low resistance to deformation. During hot deformation in the temperature range of 1 175 0C and above, metal fracture was observed along the grain boundaries at the melting points of the Cr−Fe−B boride phase. The optimal temperature range for hot deformation of steel ChS-82 is 1 000−1 050 ⁰С. Scientific novelty. For corrosion-resistant high boron steel used for spent nuclear fuel storage, the temperature range of hot deformation was selected and the structural and phase composition was estimated, which will allow deforming the metal on the piercing mill and manufacturing pipes.

Optimizing LPBF-parameters by Box-Behnken design for printing crack-free and dense high-boron alloyed stainless steel parts

Boron has almost null solubility in iron, and its addition to stainless steels leads to the formation of hard borides, beneficial for increasing the wear resistance. However, these boron-containing steels have poor printability, with the occurrence of pronounced cracking, high porosity and risk of delamination. In this work, Box-Behnken design coupled with analysis of variance (ANOVA) was used to optimize the LPBF (Laser Powder Bed Fusion) processing parameters of a highly boron-alloyed stainless steel reinforced with a boride network. The proposed models demonstrated to be accurate in determine the porosity percentage for the studied alloys, in which the laser power and scanning speed play the main role in the alloys’ densification, and absence of extensive defects. These results indicate that the use of design of experiments tools is essential to produce defect-free boron-modified stainless steel specimens with a relatively low number of experiments, identifying a narrow optimized processing window to build bulk composite materials.

Effect of Boron on the Formation of the Naturally Deposited Film and Its Corresponding Interfacial Heat Transfer Behavior in Strip Casting of Boron-Containing Steel

Effect of Boron on the Formation of the Naturally Deposited Film and Its Corresponding Interfacial Heat Transfer Behavior in Strip Casting of Boron-Containing Steel

INVESTIGATING THE EFFECT OF HEAT TREATMENT ON THE COLD FORGING OF 27MNB4 STEEL VIA CALPHAD METHODOLOGY AND FEM

As a material forming method, cold forging is preferred due to the reasons like absence of a heating step and high surface quality. Recently, the finite element method (FEM) has received growing attention for controlling and predicting final material properties for cold forging applications. FEM combines microstructure evolution models with failure criteria, thus providing solutions to complicated problems in the modern cold forging industry. The fastener industry extensively utilizes cold forging, in which manganese and boron-containing steels like 27MnB4 can be formed to obtain high mechanical properties. The current study investigates the effect of two different heat treatments, namely softening and spheroidizing annealing, on the formability of 27MnB4 bolts. Softwares such as Thermo-Calc 2022a and Forge NxT 3.2 were used to predict the microstructure of the wire rod and evaluate the cold forming process of the same rod under two different heat treatment conditions. Therefore, the current study also provides a relationship between microstructural features and the cold formability of 27MnB4 steel. The microstructure of 27MnB4 is predicted by CCT diagrams. The predicted microstructure corresponds to the microstructure of 27MnB4 samples taken from the production line. In addition, temperature, von Mises stress, and equivalent strain distributions for 27MnB4 steel in the hot rolled state were calculated higher than in annealed states due to the differences in the microstructure. These results demonstrate that computational material engineering methods and simulation techniques could be practical tools for cold forming processes.

The Hot Ductility, Microstructures, Mechanical Properties and Corrosion Resistance in an Advanced Boron-Containing Complex Phase Steel Heat-Treated Using the Quenching and Partitioning (Q&P) Process

The objective of this research work is to obtain the hot ductility behavior, and the structural, microstructural and mechanical characteristics of one of the latest generation of AHSS steels, a complex phase (CP) steel microalloyed with boron (0.006 wt.%), processed by hot and cold rolling operations and heat-treated using two different quenching and partitioning (Q&P) treatments, a one-step partitioning (quenching to 420 °C) and the other a two-step partitioning (quenching to 420 °C and reheated to 600 °C). The results show that boron has a marked effect on the solidification process of the CP steel, refining the austenitic grain size. Due to its refinement, the boron-containing steel had better ductility throughout the temperature range examined (700–900 °C), i.e., the hot ductility trough. Thus, the minimum percentage of reduction in area (%RA) value occurring at 800 °C was 43% for the boron-free steel, compared with 58% for the boron-containing steel. Hence, cracking would not be a problem when straightening the strand on continuous casting. The benefit of boron addition on the room temperature properties was found to be very marked for the higher temperature two-step partitioning treatment, giving a yield stress of 1200 MPa, a UTS (ultimate tensile strength) of 1590 MPa and a total elongation above 11%. The final Q&P microstructure, in both one- and two-step partitioning conditions, consisted of retained austenite (RA-γ), martensite and ferrite islands in a bainitic matrix. Furthermore, the boron treated steel on quenching produced a greater amount of RA-γ, which accounted for its better room temperature ductility and produced a martensitic matrix rather than a bainitic one, giving it greater strength. The addition of boron improved the corrosion resistance of this type of third generation AHSS steel.

Деякі аспекти використання сталей під час позареакторного зберігання та транспортування відпрацьованого ядерного палива. (Огляд)

In the world, the nuclear industry is considered an ideal option for an environmentally friendly source of energy generation, based on the separation of the radioactive nuclide of the chemical element 235U. When generating electricity from nuclear power plants, the main disadvantage is the generation of radioactive waste. After spent fuel is removed from a nuclear reactor, it is placed in special containers containing absorption and retention elements. It is obvious that the storage and transportation of spent nuclear fuel plays an important role in the development and overall safety of the nuclear industry, and high-quality neutron-absorbing materials are the basis for the successful manufacture of reliable structures and containers. The development of modern neutron absorption materials ensures reliability, safety, storage duration, as well as reducing the cost of logistics operations associated with the transportation of radioactive waste. Based on the results of the analysis of scientific and technical sources, modern ideas about materials for the manufacture of containers, which are used for storage and transportation of nuclear fuel waste, are summarized. The advantages and disadvantages of the main materials used in the disposal of spent nuclear fuel are considered. It has been established that, from an economic point of view, the most rational material for storing and transporting radioactive waste is ferritic stainless steel with a high boron content, which, in addition to absorption abilities, is characterized by other properties required for this type of product. Since boron has a low ability to dissolve in both austenite and ferrite, this leads to the formation of borides of various types, which contribute to the embrittlement of the structural material. At the same time, the distribution of borides over the volume of a metal product is determined not only by a set of properties, but also by the protective properties of the material, as well as the manufacturability of the final product from it. Despite the fact that boron-containing steels of the ferritic class have been known for a long time, issues related to the processes of structure formation, increasing technological and operational properties still remain insufficiently studied and controversial. There is also no information on the influence of heat treatment on the formation of the structure and mechanical properties of finished products made of ferritic stainless steels. Successful solution of these scientific and technical problems will ensure the production of modern high-quality neutron-absorbing containers for off-reactor storage and transportation of spent nuclear fuel.

Corrosion Properties of Boron- and Manganese-Alloyed Stainless Steels as a Material for the Bipolar Plates of PEM Fuel Cells.

Stainless steels are materials that could be used for constructing not only the bearing parts of fuel cells but also the functional ones, particularly the bipolar plates. The advantage of stainless steel is its valuable electrical and thermal conductivity, reasonably low cost, excellent mechanical properties, and good formability. Paradoxically, the self-protection effect resulting from passivation turns into the main disadvantage, which is unacceptable interfacial contact resistance. The aim of this study was to test a number of possible stainless steels in a simulated fuel cell environment, especially those alloyed with boron and manganese, which were found to improve the contact resistance properties of stainless steels. The primary focus of the study is to determine the corrosion resistance of the individual materials tested. Electrochemical tests and contact resistance measurements were performed following the DOE requirements. Manganese-alloyed LDX stainless steel achieved the best results in the electrochemical tests; the worst were achieved by boron-containing steels. Boron-containing stainless steels suffered from localized corrosion resulting from chromium-rich boride formation. All steels tested exceeded the DOE limit in the contact resistance measurement, with 316L reaching the lowest values.

Stress Development During Cooling of Continuously Cast Boron-Containing Steel Slabs

Stress Development During Cooling of Continuously Cast Boron-Containing Steel Slabs

Fundamental studies of physicochemical properties of environmentally friendly fluorine-free slags and their use in ladle steel industry

The article describes theoretical and experimental studies of dependence of viscosity, coefficients of sulfur and boron distribution between slag and metal, and wear degree of periclase-carbon refractories on basicity and boron oxide content in slag. It is shown that formed slags have basicity of 2.0 – 5.0 and rather high liquid mobility. These slags are characterized by an equilibrium interfacial distribution coefficient of sulfur increased to 5 – 20, which provides equilibrium sulfur content in the metal reduced to 0.001 – 0.005 %. The results of fundamental studies of the physicochemical properties of refining slags of СаО – SiO2 – В2O3 – Al2O3 – MgO system formed the basis for development of the composition of environmentally friendly fluorine-free ladle slags and technological methods for their formation in ladle-furnace unit. The recommended composition of such slags of low viscosity, which allows deep metal desulfurization, direct steel microalloying with boron and low aggressive effect on periclase-carbon refractories, provides formation of slags with a basicity of 3.0 – 4.0, containing 1 – 4 % B2O3 , 15 % Al2O3 and 8 % MgO. The formation of environmentally friendly ladle slags of the recommended composition was carried out in a ladle-furnace by loading lime, boron-containing material – colemanite (Turkey) containing 39 – 41 % B2O3 , 26 – 28 % CaO, not more than 5 % SiO2 and 3 % MgO, and pyramidal aluminum into the steel-teeming ladle for slag deoxidation and boron recovery. Introduction of the developed technology for the formation of ladle slags of recommended composition ensured the production of economically alloyed low-carbon structural boron-containing steels with a low sulfur content, incl. for large diameter pipes with high strength properties.

Effect of Alloying Additives and Microadditives on Hardenability Increase Caused by Action of Boron

The presented work was aimed at evaluating influence of boron on hardenability of steel quantitatively and evaluating this effect during complex use of boron with other alloying additives like chromium, vanadium and titanium. For this purpose, eight melts with variable chemical compositions were prepared. From the ingots, cylindrical specimens with normalized dimensions according to EN ISO 642:1999 were cut out and subjected to full annealing at 1200 °C and to normalizing at 900 °C. Such specimens were subjected to the hardenability Jominy test. In order to distinguish the influence of boron on hardenability of a given melt and thus to eliminate the differences resulting from its chemical composition, grain size and austenitizing temperature, the obtained ideal critical diameter was corrected and the boron effectiveness factor was determined. The performed examinations and analyses showed that inadequate quantities of microadditives result in losing the benefits coming from introduction of boron as the hardenability-improving element and can even result in a reduction of hardenability of the boron-containing steel.

Identification of reasons for non-compliance of mechanical properties in boron-containing steel parts

Fasteners are widely used as machine parts, structures and mechanisms. Medium-carbon alloy steels and boron-containing alloy steels are used as materials in production. Boron-containing steels have a good combination of strength and plastic properties, as well as a high level of hardenability. This article describes the research work carried out in the laboratory, and considers the reasons for obtaining low values of physical and mechanical parameters of parts manufactured at competitive enterprises. The qualitative characteristics of the metal are determined. The results of chemical, physical-mechanical and metallographic tests, as well as the results of the chemical composition of non-metallic inclusions are presented. The reasons for the discrepancy of mechanical properties in boron-containing steels are considered. The dependence of the introduction of chemical elements into steel: nitrogen, titanium, aluminum is determined. The possibility of evaluating the content of “effective boron” at OJSC “BSW” – the Management Company of the Holding “BMC” is described. The mathematical model used at OJSC “Oskol electrometallurgical combine”, which allows to carry out a theoretical calculation of the value of “effective” boron, is described. Recommendations for improving the technological process of smelting boron-containing steels are given.

Experimental studies of heat treatment influence on the welded connections properties in working mechanisms of road building

Introduction. The experimental studies of the heat treatment effect on the properties of welded joints in working mechanisms of road-building machines are carried out in the work. Studying the structures of the metal itself, as well as welded joints and considering their heterogeneity, the author analyzes the strength characteristics of these objects.Materials and methods. By means of metallographic analysis, as well as using boron-containing steel 30MnB5, which is used for the manufacture of structures for construction machines, as a research material, the author examined its microstructure, which took place in certain zones of welded joints. In particular, welded jointss, fusion zones with an overheating area, a complete recrystallization area and the base metal were studied. We also studied the features of cold plastic deformation of the specified steel sample.Results. It was determined that the mechanical inhomogeneity of the steel at these joints is the cause of the structural inhomogeneity of the welded joints. As a result of this process, some dangerous zones of acting voltages concentration are formed. These conclusions predetermine the need to identify some certain zones that concentrate stresses in themselves, while it is mandatory to strengthen the metal in such zones to standard indicators. An increase in the strength properties of the steel under study is possible by applying cold plastic deformation and subsequent thermal cycling (STC). This is achieved by obtaining a fine-grained metal structure with higher strength. The author defines the welded joints and the zone of its fusion with the base metal and the overheating area as the most dangerous areas subject to loading. To control this process, it is recommended to use the passive fluxgate method in the work, while the fusion zone with the overheating section should be inspected first, and then the weld.Discussion and conclusion. The author comes to the conclusion that the experimental studies carried out can contribute to an increase in the efficiency of the process of reducing the stress concentration (SC) in the elements of construction machines made of steel and subjected to intensive operation by reducing the structural and mechanical inhomogeneity of welded joints.

Effect of Deoxidizing Element on the Hot Ductility of Boron-Containing Steel

Effect of Deoxidizing Element on the Hot Ductility of Boron-Containing Steel

Structure, Phase Composition, and Mechanical Properties of a Boron-Containing High-Nitrogen Austenitic Steel Made by Induction Melting

The structure and the mechanical properties of a cast high-nitrogen austenitic steel are studied after hot and cold deformation. The as-cast steel contains the FeCrB and BN phases. During hot deformation, the B13N13C74 phase forms. This phase has a layered structure and is easily deformed during hot or cold rolling. The existence of the B13N13C74 phase only slightly changes the strength and the ductility, but it substantially decreases the impact toughness of the steel as compared to that of similar boron-free Cr–Mn–Ni high-nitrogen austenitic steels.

Influence of boron on microstructure and mechanical properties of Gleeble simulated heat-affected zone in P91 steel

In the present endeavor, a Gleeble thermo-mechanical simulator has been used to simulate subzones of the heat-affected zone (HAZ) of boron-free P91 and boron-modified P91B steels to investigate the influence of boron on microstructure and mechanical properties. The prior austenite grain (PAG) size remained similar to that of parent metal in the fine-grained heat-affected zone (FGHAZ) and inter-critical heat-affected zone (ICHAZ) of P91B steel. The microhardness value of simulated specimens, including parent metals was observed to be similar. But impression creep resistance of boron-containing steel was significantly higher than that of the boron-free steel. The presence of boron decreased precipitates size and increased fraction of low energy Σ3 coincident-site lattice (CSL) boundaries that attributed to improvement of creep resistance. However, there was a slight reduction in solid solution hardening due to increased area fraction of precipitates in parent metal and simulated specimens of boron-containing steel. Hindering of alloy element partitioning during impression creep of P91B-ICHAZ was observed, which was possibly due to the presence of boron in soluble form in the iron matrix and the segregated form on grain and sub-grain boundaries (SGBs). Further, the addition of boron was observed to retard M23C6 precipitate coarsening in the P91B-ICHAZ in comparison to its P91 version.

Experience of JSC “BelZAN” during Production of Boron-Containing Steel Fasteners

The use of boron for microalloying structural steels allowed increasing the strength characteristics of fasteners produced under the JSC BelZAN conditions. Boron-containing steels serve as an effective replacement for medium-carbon and alloy steels 35, 45, 40Kh, 40KhN, and 38KhGNM.

Effect of Direct Microalloying of Boron-Containing Structural Steels on Their Structure and Mechanical Properties

Under conditions of converter shop of JSC “ArcelorMittal Temirtau”, the authors have developed and implemented the direct microalloying technology of structural steels with boron. Microalloying was carried out due to boron recovery from the slags of the CaO–SiO2–B2O3–MgO–Al2O3 system formed in ladle furnaces. The use of the developed technology was provided in steels 08KP, 3SP, 3PS and 09G2S boron content of 0.0016–0.0050%, with a sufficiently high degree of metal desulfurization 36.8–51.7% and reduction in manganese ferroalloys consumption by 0.3–0.6 kg/t of steel, which improved the environmental situation by eliminating the use of fluorspar. For 09G2S steel, the yield σy and tensile σt strengths are higher for the experimental metal then for the steel without boron by an average 27 and 24 MPa, respectively. The elongation percentage of the metal with boron increased by an average 0.2%. The grain-size index of rolled metal of 08KP steel with a thickness of 2.0–2.5 mm, containing 0.001% of boron and a manganese concentration lowered to 0.18%, reaches 10.0 in contrast to 9.0 for the heats of the current production. The yield σy and tensile σt strengths are on average by 6.0 and 5.0 MPa higher for an experimental metal than for a comparative one. The percentage of elongation δ reaches 36.3% for the experimental metal unlike 33.3% for the heats of the current production. Experimental rolled metal of 3PС steel with lower concentration of manganese lowered by 0.02%, as well as with an average boron content of 0.001%, is characterized by an increased yield strength σy, tensile strength σt (on average by 2.0 and 9.0 MPa) and percentage of elongation δ reaching an average of 21.0% with fine-grained structure. The rolled metal of 3SP steel, microalloyed with boron and with a 4-mm thickness that contains manganese content reduced to 0.43%, is characterized by improved strength properties with preservation of plastic characteristics. The absolute value of the yield σy and tensile σt strengths of steel are by 4.0 and 2.0 MPa higher than the strength characteristics of steel without boron.

Borocarbide coarsening and the effect of borocarbide particle size on Charpy V-notch impact properties of medium-carbon boron-containing steel

Abstract Boron-added steel has been used in several automotive components in which the energy absorbed in impact testing is an important requirement. Previous thermodynamic studies have shown that boron addition promotes significant change in equilibrium phases, increasing the volume fraction of precipitated phases, mostly due to increased carbide stability and formation of borocarbides. As volume fraction, size and distribution of precipitates influence the absorbed energy in impact testing of steels, it is important to study M23(B,C)6 borocarbide precipitation and coarsening kinetics and its effects on Charpy V-notch absorbed energy of boron steels. In the present work, borocarbide coarsening kinetics were evaluated using optical microscopy in samples heat-treated at 880 0C for different times. The borocarbide coarsening kinetics data suggest that growth is controlled by an interfacial reaction mechanism. The Charpy V-notch absorbed energy decreases with increasing borocarbide section size and the embrittlement was successfully described by an empirical equation.

Borocarbide coarsening and the effect of borocarbide particle size on Charpy V-notch impact properties of medium-carbon boron-containing steel

Abstract Boron-added steel has been used in several automotive components in which the energy absorbed in impact testing is an important requirement. Previous thermodynamic studies have shown that boron addition promotes significant change in equilibrium phases, increasing the volume fraction of precipitated phases, mostly due to increased carbide stability and formation of borocarbides. As volume fraction, size and distribution of precipitates influence the absorbed energy in impact testing of steels, it is important to study M23(B,C)6 borocarbide precipitation and coarsening kinetics and its effects on Charpy V-notch absorbed energy of boron steels. In the present work, borocarbide coarsening kinetics were evaluated using optical microscopy in samples heat-treated at 880 0C for different times. The borocarbide coarsening kinetics data suggest that growth is controlled by an interfacial reaction mechanism. The Charpy V-notch absorbed energy decreases with increasing borocarbide section size and the embrittlement was successfully described by an empirical equation.

Study of Microstructure and Mechanical Properties of Boron-Containing Hot-Rolled Steel Reinforcement

Stiffened specifications for quality of reinforcement product are dictated by the contemporary market that is expressed in the introduction of new TU and GOST for manufactured products. When switching to the new GOST 34028–2016 enterprises are forced to abandon the use of traditional steel grades and switch to sparingly alloyed steel with expensive alloying elements (such as vanadium, niobium, molybdenum) with a lower carbon content. However, transition to new steel grades does not always provide the required level of properties and is often associated with an increase in production costs. Results are provided for a study of the structure and properties of A400C-class steel reinforcement made from a test melt in PAO Chelyabinsk Metallurgical Combine. During steel melting it was aimed at minimizing the number of expensive alloying elements and their partial replacement with boron. Results of the study show that microalloying steel with boron and using the standard manufacturing technology for hotrolled steel does not give unfavorable results for finished product properties and structure.