Steel Grades Research Articles

An approach to coupling the gas flow dynamics and thermodynamics of hydrogen solubility in L485ME steel grade for estimation of fracture toughness

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

Residual stresses of MAG-welded ultrahigh-strength steel rectangular hollow sections

Residual stresses are an important factor in the performance and stability of welded structures. This study investigates the characteristics and significance of residual stresses in MAG-welded ultrahigh-strength steel rectangular hollow sections. The research incorporates comprehensive X-ray diffraction residual stress measurements, electron backscatter diffraction analysis, statistical analyses, and finite element method simulations to provide valuable insights into the behaviour of welding residual stresses. The results reveal clear microstructural variations between the cold-formed corner and the flat side of the rectangular hollow section caused by welding heat input, emphasizing the need to consider these variations in residual stress assessments. Furthermore, the study examines the dependence of residual stresses on the steel grade, with higher strength steel exhibiting compressive stresses and lower strength materials experiencing tensile stresses in corner areas. Statistical analysis indicates that welding sequence and direction have negligible effects when applying the employed welding sequence. In any case, higher heat input leads to significantly larger residual stresses. Finally, the study presents a novel analytical model based on validated finite element simulations to predict the maximum variation of residual stresses depending on welding heat input. The findings provide valuable insights into the significance of welding residual stresses and their predictability. The comprehensive measurements, simulations and proposed models contributes to a better understanding of residual stress phenomena, facilitating the development of reliable design guidelines for welded structures in various engineering applications.

Comparative study about the results of HAZ physical simulations on different high-strength steel grades

With continuous improvements, structural steels are available in even higher strength grades above 1000 MPa yield strength. As the great majority of these steels are used in welded structures, their weldability needs to be taken into account. Several factors can cause difficulties during welding of these steels, but in this paper the softening behavior and the toughness characteristics of the heat-affected zone (HAZ) are examined. As the critical parts of the HAZ in a real welded joint are relatively small, their investigating ability is limited. However, the physical simulation provides a way of evaluating specimens made from a given material to produce the specified HAZ areas in a suitable size range for subsequent testing. In this research work, three different strength categories of high-strength structural steels (with yield strength of 960 MPa, 1100 MPa, and 1300 MPa) are investigated by physical simulation. In the case of different technological variants of gas metal arc welding (GMAW) process, the effect of the cooling time t8/5 is investigated in different HAZ subzones considered to be critical. The thermal cycles were determined according to the Rykalin 3D model. The investigated cooling times were t8/5 = 5 s, 15 s, and 30 s. The properties of the selected coarse-grained, intercritical and intercritically reheated coarse-grained zones are analyzed by laser scanning microscope, scanning electron microscope, hardness test, and instrumented Charpy V-notch impact toughness test. Furthermore, additional investigation like JMatPro calculations, electron backscatter diffraction measurements, and prior austenite grain size calculation were carried out. As a result of the tests, the investigated heat-affected subzones indicated higher sensitivity to the welding heat input compared to conventional structural steels. Overall, the results of the tests show that the application of shorter t8/5 cooling time can be beneficial for the investigated high-strength steel grades, since significant toughness reduction and the risk of softening occur in the whole cooling time range.

Numerical Simulation of Macro-Segregation Phenomena in Transition Blooms with Various Carbon Contents

This paper presents a numerical simulation of the steel grade transition from the ladle nozzle to the solidification end of the bloom. The simulation is based on models encompassing fluid flow, solidification, heat transfer, an electromagnetic field, and solute transport. To validate the accuracy of the steel grade transition model, transition blooms of high-carbon steel are sampled. Subsequently, the model is applied to investigating the steel grade transition between medium-carbon steel and low-carbon steel. The findings indicate that the regions exhibiting significant differences between their molten steel flow velocity and bloom casting speed in the strand model are primarily concentrated within 1 m below the meniscus. Additionally, the mushy zone in the strand model possesses a substantial volume. Solute elements continuously permeate the liquid phase from the solid phase through the mushy zone. Consequently, the distribution of solute elements in the transition bloom is primarily influenced by the molten steel flow in the tundish and macro-segregation in the casting process. The segregation degree of each solute element varies among grades with different carbon contents. In the austenite phase, the segregation degree of each element follows the order C > Si > Mo > Mn > Cr > Ni, while in the ferrite phase, the segregation degree is ordered as C > Si = Mn. Considering macro-segregation, the transition bloom partition model proves to be more stringent than the original partition method. This results in longer transition blooms when a significant difference exists between the new and old grades. For example, in Scheme 1, the original plan transition bloom length is 8.88 m, whereas the new plan transition bloom length is 10.88 m. Similarly, in Scheme 2, the original plan transition bloom length is 34.64 m, and the new plan transition bloom length is 35.16 m. Conversely, shorter partition intervals occur when there is an overlap in the composition of the new and old grades. In Scheme 3, the original plan partition interval for the new and old grades is 4.08 m, while the new plan partition interval is reduced to 0.94 m.

Influence of different types of counterbodies on tribotechnical properties of polytetrafluoroethylene

This paper presents the results of a study of different types of counterbodies on the tribological properties of polytetrafluoroethylene (PTFE). The characteristics of the polymer, the roughness and hardness of counterbodies made of the following materials are given: copper, aluminum, brass and steel grade 45. It is shown that the best wear resistance is obtained for a friction pair – polytetrafluoroethylene with steel grade 45 and brass. The friction surfaces of the counterbodies and the polymer were studied by optical, electron microscopy, and IR spectroscopy.

Characterizing steel corrosional features in atomic force microscopy: A Sobel edge detection approach

One of the fundamental characterizations in assessing a material’s surface its surface roughness. Here, we introduce a computational method using measured atomic force microscopy surface roughness data to perform Sobel edge detection of heterogeneity on corroded steel samples. This method enables the spatial mapping of corrosion-induced features and general inconsistencies on a sample’s surface using a freely available algorithm written in the Python computing language. The non-optical method has been tested on three different grades of steel, and results indicate reasonable accuracy when compared to visual observations made from grayscale optical data.

Hardening and improving the corrosion resistance of carbon steel 45 with thermal chemical treatment

The issues of creating a hardening coating by plasma spraying of Ti powder on steel grade 45 with subsequent cementation are considered in order to improve mechanical properties and evaluate corrosion resistance. X-ray phase analysis showed the presence of basic (Fe) and strengthening phases (TiC, Fe3C) in the material under study.

The Structure of Boride Diffusion Coatings Produced on Selected Grades of Structural Steels

In the article the microstructure and phase composition of boride coatings deposited on selected structural steels were investigated. The boride coatings were produced using pack cementation method using commercial EKABOR-2 mixture containing of 50 wt. % of new and 50 wt. % of used powder. Boride coatings were deposited on alloyed structural steels grades (PN/EN 10084 standard): 16MnCr5, 18CrNiMo7-6, 41CrAlMo7 42CrMo4. Cylindrical samples with a diameter of 30 mm and a height of 30 mm were boronized in powder at 1000°C for 2, 4 and 6 hours in an argon atmosphere. The process was carried out in an industrial CVD Bernex BPX 325S device. The microstructure was analyzed using scanning electron microscope Phenom XL equipped with EDS spectrometer. The XRD phase analysis was conducted using XTRa diffractometer (ARL). The thickness as well as phase composition was analyzed on coatings formed on each grades of steels. The most of obtained boride coatings were characterized by single-phase structure (Fe2B). The formation of brittle FeB phase was detected only on 16MnCr5 steel grades steels.

Emerging Behaviour of Alloy Steel Microstructure in Hydrogen Sulphide Environment - A Review

Alloy steel is known to be different from carbon steel due to the presence of the alloying element in varying compositions which is usually done for the purpose of modifying and improving the performance of the steel. However, a major problem with the alloy steel is that it usually exhibits different behavior in terms of the microstructures and the mechanical properties, especially, in sulphide environment. Thus, this study focused on the different microstructure of alloy steel and their performance in different environment with strong emphasis in sulphide environment. It was established in the study that a major problem of alloy steel in hydrogen sulphide environment is the sulphide stress cracking which is attributed to the presence of hydrogen and its absorption by the alloy steel. Hence, this study provides a potential guide and information on the capacity of the grades of alloy steel that can thrive in sulphide environment.

ADJUSTABLE NITROOXIDATION TECHNOLOGY FOR LOW ALLOY STEEL

The article discusses the production of a surface diffusion nitride-oxide layer on low-alloy structural steel with specified structures and properties. To develop a controlled technology for nitro-oxidation of low-alloy carbon steel, the dependences of the composition and structure of the nitrided and oxide layer on the chemical composition of the steel and the technological parameters of the process were studied. Technical iron was used as a model alloy and samples of industrial steel grades 40X, P6M5 and steel 45 were processed. Saturation temperatures were studied in the ranges above and below the eutectoid temperature for the “Fe-N” system and, accordingly, for the “Fe-O” system and it was found that the best structures are at saturation temperatures below the eutectoid.

Superwettable surfaces and factors impacting microbial adherence in microbiologically-influenced corrosion: a review.

Microbiologically-influenced corrosion (MIC) is a common operational hazard to many industrial processes. The focus of this review lies on microbial corrosion in the maritime industry. Microbial metal attachment and colonization are the critical steps in MIC initiation. We have outlined the crucial factors influencing corrosion caused by microorganism sulfate-reducing bacteria (SRB), where its adherence on the metal surface leads to Direct Electron Transfer (DET)-MIC. This review thus aims to summarize the recent progress and the lacunae in mitigation of MIC. We further highlight the susceptibility of stainless steel grades to SRB pitting corrosion and have included recent developments in understanding the quorum sensing mechanisms in SRB, which governs the proliferation process of the microbial community. There is a paucity of literature on the utilization of anti-quorum sensing molecules against SRB, indicating that the area of study is in its nascent stage of development. Furthermore, microbial adherence to metal is significantly impacted by surface chemistry and topography. Thus, we have reviewed the application of super wettable surfaces such as superhydrophobic, superhydrophilic, and slippery liquid-infused porous surfaces as "anti-corrosion coatings" in preventing adhesion of SRB, providing a potential avenue for the development of practical and feasible solutions in the prevention of MIC. The emerging field of super wettable surfaces holds significant potential for advancing efficient and practical MIC prevention techniques.

AUGMENTATION OF DEPTH OF PENETRATION AND PRODUCTIVITY BENEFITS OF ATIG WELDS USING THE AHP

Weldability is an important issue in the fabrication of different grades of stainless steel used in industry. Tungsten inert gas (TIG) welding is widely used in industry for accurate and precision work, but lack of penetration is observed in this process even though current and welding speed can be varied considerably to increase heat input to obtain deeper penetration. Increased heat input adversely affects mechanical properties of the weldment. To overcome this, activated flux TIG welding is often used in industry to achieve higher depth of penetration with relatively less heat input. In this study, activated flux TIG welding is used with input variables such as heat input, welding speed and pulse frequency. The chosen base metal is SS 304L stainless steel, and a hybrid flux mixture containing fluxes of SiO2, MnO2 and MoO3 in a ratio of 1:1:2 is used to obtain the desired depth of penetration. Nine experimental runs are conducted to obtain the optimum depth of penetration. Heat input values are 2.767 kJ/mm, 1.470 kJ/mm and 1.281 kJ/mm and pulse frequency is 160 Hz, 120 Hz and 80 Hz. Welding speed varies from 0.5 mm/s to 1.18 mm/s. A maximum depth of penetration of 4.42 mm is achieved with a heat input of 2.767 kJ/mm, welding speed of 0.5 mm/s and pulse frequency of 160 Hz. The reversed Marangoni effect and arc constriction effect are the mechanisms responsible for the deeper penetration in ATIG welding. In this research, a multi criteria decision making tool, the Analytical Hierarchy Process (AHP), is used to validate the optimum value obtained. The optimal values obtained in the research are in good accordance with those obtained using the AHP. The outcome of the present investigation indicates the applicability of ATIG welding for joining large thickness of stainless steel flats to give enhanced productivity by reducing the number of weld passes.

Oxide Scale Formation on Low-Carbon Steels in Future Reheating Conditions

The mitigation of CO2 emissions is one of the major areas of research in iron ore-based steelmaking. In this study, four simulated current and potential future reheating scenarios with different fuel and oxidizer gases were studied regarding the amount of oxide formation and the adhesion of the steel–oxide interface: (1) methane–air; (2) coke oven gas–air; (3) hydrogen–air; (4) and an oxyfuel scenario with 50:50 methane/hydrogen as fuel gases. Isothermal oxidation tests were conducted at temperatures of 1150, 1230 and 1300 °C. Four low-carbon steel grades were tested in the previously mentioned gas atmospheres. The structure and composition of the formed oxide scales was analyzed with FESEM-EDS microscopy. The amount of oxide formation correlated with the water vapor content of the gas atmosphere for all four steel grades; however, notable differences were found between individual steel grades regarding the degree of oxidation increase. No clear evidence was found of the gas atmospheres affecting the adhesion of oxide scales to the steel substrate. The adhesion of the interface was mainly determined by the content of silicon in the steel grade and the test temperature.

Multi-objective optimization and evolution of dissimilar welding process between Cr-Mo steel and austenitic stainless steel for power plant application

In this study, response surface methodology (RSM) was employed to optimize the welding parameters’ effects on mechanical properties of dissimilar welds between Cr-Mo steel grade (P11) and austenitic stainless steel (AISI 316LN). To determine the best welding parameters, variance analysis (ANOVA), desirability function, and perturbation analysis were used to create regression models and identify the significant parameters influencing tensile strength and hardness gaps in the weld joints. The results indicated that welding speed is the most significant parameter affecting both the austenitic hardness gap and tensile strength, while gas flow has the most significant impact on the hardness gap of Cr-Mo steel. Furthermore, welding speed positively influences the mechanical properties of dissimilar weld, whereas welding current has a slight negative effect on tensile strength. The optimum welding parameters were found to be 130 A for welding current, 70 mm min−1 for welding speed, and 13 l min−1 for welding gas flow, resulting in hardness gap values of 18.10 HV (Stainless steel side), 27.38 HV (Cr-Mo steel side), and a tensile strength of 453.90 MPa. The optimum parameter effect is concentrated at the weld interfaces between the fusion zone and the heat-affected zone. This effect led to limitations in grain coarsening, a reduction in the martensite and delta ferrite phase percentages, a slight increase in the bainite ratio, and a decrease in carbide precipitations. As a result, a homogenization of strain distribution in the optimum weld was achieved, leading to ductile fracture in Cr-Mo steel.

DEVELOPMENT OF OPTIMAL TECHNOLOGICAL PARAMETERS FOR PLASMA COATING DEPOSITION

This paper considers using ion-plasma spraying of mold surfaces. This makes it possible to replace scarce and expensive tungsten-containing steels with other materials. 4Х5МФС and 5ХНМ steel grades were chosen as materials for copper alloy die-casting molds in this work. The choice of these steel grades is due to the fact that these steels do not contain tungsten due to its sharply increased scarcity and limited molybdenum content, and they also meet the requirements for the substrate material on which the titanium nitride coating is applied. Coatings were applied to samples for laboratory tests and die-casting mold parts by the condensation method with ion bombardment. Titanium nitride is applied at different partial nitrogen pressures – from 310-3 to 1 Pa to determine the required nitrogen pressure, which ensures that the working surfaces of mold parts receive coatings with the best performance haracteristics. The coatings obtained at different nitrogen pressures differ in the amount and size of the droplet phase. The largest amount of the droplet phase containing α-Ti is observed in coatings obtained at nitrogen pressures of 310-3, 310-2 Pa. An increase in nitrogen pressure (410-1, 1 Pa) significantly reduces the level of microdistortions of the crystal lattice in the coating, and its plasticity increases. In this regard, the coating's brittleness is reduced at a sufficiently high hardness. The titanium nitride coating obtained at a nitrogen pressure of 1 Pa is the most effective in protecting the working surfaces of mold parts from destruction. Laboratory tests have shown that the titanium nitride coating applied under optimal process parameters increases the corrosion resistance of mold parts to which it is applied by 3 times and the scale resistance by 2–4 times.

Effectiveness of repairing yielding anchor rods in exposed column bases in steel structures

AbstractOne of the features of Japanese structural steel design is an economical design option for yielding exposed column bases before first‐story columns, namely weak‐base/strong‐column design, which is unlike the strict capacity design for column bases. This study aims to develop a repair methodology that identifies damage states of the yielding column bases and anchor rods, and selects appropriate repair/retrofit methods. As a standard repair method for damaged exposed‐type column bases, the applicability and effectiveness of the re‐tightening process of anchor rods need to be examined. This study first reviews the literature on standard retrofit techniques for column bases and required deformation capacity of ductile anchor rods. The threaded anchor rod deformation capacity with different steel grades and screw threads commonly used were tested to clarify the required ductility. To clarify the reparability of exposed column bases, numerical models of four‐ and six‐story steel moment resisting frame buildings were developed and validated by shaking table test results. The results show that this simple repair method was proven to be effective through the test program and numerical analysis and it's not always applicable for standard anchor rods assumed for pin or fixed column bases designed to remain elastic. Finlly, a repair methodology and flow chart that identifies the damage states of anchor rods and selects appropriate repair/retrofit methods for the exposed steel column base was suggested and applied to the simulation results.

High-cycle rotating-bending fatigue performance of S690QL welded joints

In recent decades, high-strength steels have become increasingly popular in the construction industry. Materials like S690QL steel are mainly characterised by their enhanced mechanical properties, including high yield and tensile strength. As a result, this leads to improved performance, durability, and safety of steel components, making such materials commonly used in several offshore applications due to their exceptional strength and cost-efficiency. Within the offshore industry, the most critical connections are usually the welded joints, thus rising significant concerns regarding the characterisation of the material in the area close and affected by the welding process. Furthermore, this material is highly prone to the appearance of cold cracks. To address these issues, rotating-bending fatigue tests were successfully conducted on S690QL steel to evaluate and compare the fatigue life within different regions of the investigated welded joints, specifically the weld material, heat-affected zone and base material. Increasing thickness of the weld plates was found to have a negative impact on the fatigue resistance, which aligns with the lower static strength for the thicker case. Also, variations in fatigue strength across the thickness were observed. The heat-affected zone exhibited a heterogeneous microstructure, leading to increased fatigue variability during testing, but the fatigue resistance observed aligns with the findings in the literature for comparable steel grades. Detailed experimental results are presented, particularly regarding this heat-affected zone, where the majority of fatigue failures occur, which provide bases for the development of new normative material-scale SN curves.

Influence of Chemical Composition on Structure and Mechanical Properties of Vacuum-Carburized Low-Alloy Steels.

This study presents research results concerning the vacuum carburizing of four steel grades, specifically conforming to European standards 1.7243, 1.6587, 1.5920, and 1.3532. The experimental specimens exhibited variations primarily in nickel content, ranging from 0 to approximately 3.8 wt. %. As a comparative reference, gas carburizing was also conducted on the 1.3532 grade, which had the highest nickel content. Comprehensive structural analysis was carried out on the resultant carburized layers using a variety of techniques, such as optical and electron scanning, transmission microscopy, and X-ray diffraction. Additionally, mechanical properties such as hardness and fatigue strength were assessed. Fatigue strength evaluation was performed on un-notched samples having a circular cross-section with a diameter of 12 mm. Testing was executed via a three-point bending setup subjected to sinusoidally varying stresses ranging from 0 to maximum stress levels. The carburized layers produced had effective thicknesses from approximately 0.8 to 1.4 mm, surface hardness levels in the range of 600 to 700 HV, and estimated retained austenite contents from 10 to 20 vol%. The observed fatigue strength values for the layers varied within the range from 1000 to 1350 MPa. It was found that changing the processing method from gas carburizing, which induced internal oxidation phenomena, to vacuum carburizing improved the fatigue properties to a greater extent than increasing the nickel content of the steel.

Behavior of Zn5Al hot-dip galvanized steel members under fire exposure

PurposeBased on the known positive effects of conventional hot-dip galvanizing under fire exposure and indicative results on zinc–aluminum coatings from smallscale tests, a series of tests were conducted on zinc-5% aluminum galvanized test specimens under fire loads to verify the previous positive findings under largescale boundary conditions.Design/methodology/approachThe emissivity of zinc-5% aluminum galvanized surfaces applied to steel specimens was determined experimentally under real fire loads and laboratory thermal loads in accordance with the normative specifications of the standard fire curve. Both large and smallscale specimens were used in this study. The steel grade and surface conditions of the specimens were varied for both test scenarios.FindingsLargescale tests on specimens with typical steel construction dimensions under fire loads showed that the surface emissivity of zinc-5% aluminum galvanized steel was significantly lower than that of the conventionally galvanized steel. Only minor influences from the weathering of the specimens and steel chemistry were observed. These results agree well with those obtained from smallscale tests. The design values of zinc-5% aluminum melt (Zn5Al) required for the structural fire design were proposed based on the obtained results.Originality/valueThe novel tests presented in this study are the first ones to study the behavior of zinc-5% aluminum galvanized largescale steel construction components under the influence of real fire exposure and their positive effect on the emissivity of steel components galvanized by this method. The results provide valuable insights and information on the behavior in the case of fire and the associated savings potential for steel construction.

Intergranular Corrosion Analysis of Austenitic Stainless Steels in Molten Nitrate Salt Using Electrochemical Characterization

This study investigates the influence of molten nitrate salt exposure on the intergranular corrosion (IGC) behavior of three grades of austenitic stainless steel (namely, AISI 304, AISI 304H, and AISI 321H). Two electrochemical techniques, double loop electrochemical potentiokinetic reactivation and potentiodynamic polarization methods, are applied after stainless steel is exposed to 600 °C molten nitrate salt, 60% NaNO3, and 40% KNO3 for varying immersion durations. Corrosion morphology is examined using optical microscopy and scanning electron microscopy images to assess susceptibility to IGC. IGC is prompted by the presence of chromium carbides at grain boundaries, which leads to chromium depletion around these carbides. The findings of the experiments reveal distinct IGC behavior among stainless steel grades. For AISI 304, the degree of sensitization (DOS) increases as exposure time progresses. However, AISI 304H and AISI 321H stainless steel exhibit diminishing DOS after 100 and 10 h of exposure, respectively. This trend is attributed to desensitization or the healing effect when stainless steel is exposed to molten salt for a prolonged time. The depletion and recovery of Cr near grain boundaries are confirmed by the inverse relationship to DOS of pitting potential.