Steel Base Research Articles

Microstructure and Mechanical Properties for the Dissimilar Joining of Inconel 718 Alloy to High-Strength Steel by TIG Welding

The dissimilar lap joint was investigated among Inconel 718 and high-strength steel using tungsten inert gas welding. The weld zone has an austenitic microstructure with the existence of secondary phases. The distribution of secondary phases is observed in the weld zone and the fusion line of the Inconel 718. The elemental mapping from the electron probe microanalyzer has analyzed the development of secondary phases along the grain boundaries and interdendritic regions. The hardness of the weld zone varies due to the presence of secondary phases. The hardness mapping-confirms secondary phases causing the higher hardness in the weld zone. The selected filler metal has good compatibility with the Inconel 718 and the high-strength steel base metal to obtain a high-quality weld. The X-ray diffraction analysis confirms the presence of secondary phases in the weld zone.

Weld Overlay Technique using Different Filler Rod Size to Overcome Internal Corrosion of Low Carbon Steel Base Metal

Overlay welding is commonly used to repair and replace the affected corroded surface of the base metal of a component. In other words, it is used to restore the original dimensions of the component. Weld overlay usually applies a corrosion resistant or hard facing layer onto the base metal. This experiment is to determine the suitable filler rod size in repairing corroded low carbon steel (LCS) base metal, respectively to the affected area and to identify the type of distortion occurring on the weldment. It is also to examine the microstructure of the joint between the overlay weld and corroded low carbon steel base metal using SEM/EDX. The overlay welding process was conducted on the corroded samples using SMAW process at defined attacked corroded areas. Filler electrode E-7018 with two diameter sizes of 3.2mm and 2.6mm were selected. It was found that the bigger electrode size produced higher degree of distortion angle compared to smaller electrode size. Resulting from the metallographic and SEM/EDX analysis, the joint between weld overlay and corroded LCS were fused well without any sign of oxides or other impurities present. Overlay welding also remove the sign of chloride ions that cause the LCS base metal to corrode. Thus, the repairing technique using overlay welding was found successful in repairing corroded LCS base metal. Therefore, the most suitable electrode size to do overlay welding on corroded low carbon steel base metal is 2.6 mm diameter electrode.

Development of Technological Bases for Manufacturing Blanks of Friction Disks with Molybdenum Gas-Thermal Coating for Working in Oil in Units of Transport Machines

This article is dedicated to the questions of development of technological bases for the manufacturing blanks of friction disks with molybdenum gas-thermal coating applied by plasma spraying, for working in oil in the transmission units of transport machines. For ensure high performance indicators, there is has been offered a technological scheme for manufacturing friction disk blanks: short blasting preparation of the surface of the disk’s steel base, applying a molybdenum coating, that characterized by high adhesion to the ferrous metals, mechanical processing of the coating by grinding, monitoring the coating’s quality. The developed technological bases for manufacturing blanks of friction disks with molybdenum gas-thermal coating, applied by plasma spraying, for working in oil in transmission units of transport machines are contributed to the creation of efficient products with enhanced performance indicators for friction coefficient, wear resistance, reliability in modern conditions at the enterprises.

Investigation of the Influence of Kinematic and Geometric Parameters of the Thermo- Sprayer Location on the Adhesion Strength of Anti-Friction Coating

The article presents the results of the influence of the kinematic and geometric parameters of the thermos-sprayer location on the adhesion strength of the anti-friction coating. A mathematical apparatus for calculating the inertia forces acting on an anti-friction coating particle is proposed. The results of a number of experimental studies confirming the convergence of theoretical positions are presented. As a result, dependencies have been revealed that make it possible to predict the bond strength of the anti-friction coating with the steel base during gas-flame spraying.

Влияние времени выдержки в расплаве на морфологию цинкового покрытия на сталях с различным содержанием кремния

The formation of zinc coating on steels in the process of hot galvanizing is determined by such factors as the process temperature, holding time, the chemical composition of steel, and particularly, silicon content. In the 1940s of the XX century, R.W. Sandelin described the process of the significant acceleration of the reaction between ferrum and zinc at the silicon content in steel equal to 0.06–0.10 %. There are different methods of control of silicon reactance; however, the simplest method of control of coating thickness is the proper choice of time of product holding in the melt. The paper aims at the identifying the influence of time of holding in the melt on thickness and microstructure of the coating formed on steels with different content of silicon: S235 (Si=0.02 %), S235J0 (Si=0.04 %), S235JR (Si=0.17 %), 9MnSi5 (Si=0.6 %). To quantify silicon, the authors analyzed the chemical composition of steels using the spark spectrometry technique. The study identified that the coating thickens on steel with the course of time of holding in the melt according to the parabolic law. The most intensive growth of coating thickness with the course of time is observed on reactive steels with silicon content of 0.04 % and high-silicon steels with silicon content of 0.6 %. The reactive steel showed the significant growth of variations in thickness. The authors carried out the analysis of microstructure using the TESCAN Vega SB scanning electron microscope; the analysis showed that the growth of a coating is determined by the peculiarities of ζ-phase structure. The analysis of the Fe-Zn-Si triple diagram allowed concluding that with the silicon content of 0.04 % and 0.6 % in steel, the eutectic decomposition of fluid into ζ+η+FeSi phases’ mixture progresses in the system. This process leads to the direct contact of the melt and steel base and intensifies the interdiffusion of ferrum and zinc. As a result, the ζ-phase actively produces that leads to the rapid growth of the coating thickness.

A new form of steel base isolation system for seismic high-rise building

The higher story of a building then it will be more vulnerable to its earthquake or seismic responses. The use of seismic devices will reduce earthquake force. In this study, the steel base isolation material has been proposed. This paper aims to design a new steel base isolation system that have good resistance in both of seismic vibration and axial pull out. The building data are 3D mini three-story, six-story, nine-story steel frame structures. The shaking table is used to test with two types of vibration, medium and maximum. FEM analysis was implemented to find the seismic responses. From the calculation results, a reduced response was obtained in conditions of moderate damage to a three-story frame with an average acceleration of 88% reduction, a maximum acceleration of 22% reduction and a six-story frame in heavy damage with an average acceleration of 73%, the maximum acceleration is reduced into 43%.

Uticaj neusklađenosti na granične krive širenja zamornih prslina osnovnih materijala tipa S690KL, S960KL i S960TM i njihovih, elektrolučno u zaštiti gasa, zavarenih spojeva

Nowadays, one of the basic trends in the industry is the environmental impact reduction, in other words the weight decreasing of structural elements and structures, which can be approached by applying different high strength steels. In case of different steel structures, the main manufacturing and joining technology is the welding, the conventional and advanced methods of fusion and pressure welding processes. Beside the weight decreasing, the reliability and safety requirements according to steel structures have significant grown. During the welding process, the welded parts are affected with heat-effect and mechanical loads, which result in inhomogeneous welded joint. The inhomogeneity of the welded joints appears both in microstructural (local) and in geometrical (both local and global) aspects. The changes in microstructure and geometry appear in deflections (basically acceptable), or rather in failures (basically unacceptable); and these influence both the behaviour and the loadability of welded joints. Discontinuities in base materials and their welded joints have especially high danger in case of cyclic loading conditions, which are typical for different structures and structural elements (e.g. bridges, vehicles). There are different standards and prescriptions containing fatigue crack propagation limit curves and rules for the prediction of the crack growth; simple and two-stage crack growth relationships can be found in the literature, most frequently based on the Paris-Erdogan law. The paper summarizes and presents the results according to our fatigue crack growth investigations on Weldox 700E and Weldox 960E quenched and tempered (Q+T) and on Alform 960M thermomechanically treated (TM) high strength steel base materials and their gas metal arc welded joints. The mismatch effect has also been studied; matched, overmatched, undermatched and matched/overmatched (mixed-matched) welded joints were investigated. 15 mm thick plates were used for the investigations, statistical aspects were applied both for presenting the possible crack locations in the real plates, as well as for processing the measured data. Furthermore, the results will be compared with each other, and fatigue crack propagation limit curves will be derived using simple crack growth relationship.

ТЕОРЕТИЧЕСКИЕ ОСНОВЫ РАСЧЕТА СИЛ ИНЕРЦИИ ПРИ НАНЕСЕНИИ ПОКРЫТИЯ НА ВНЕШНЮЮ ПОВЕРХНОСТЬ ТЕЛ ВРАЩЕНИЯ

The article presents the results of a study of the influence of inertia forces on the adhesion of a coating to the outer surface of bodies of revolution during thermal spraying. A mathematical apparatus is proposed for calculating the inertia forces acting on a coating particle when rotation bodies are applied to the outer surface. As a result, dependences are revealed that make it possible to predict the adhesion strength of the coating to the steel base during thermal spraying.

Ballistic behavior of multilayer wire mesh application armor

In this paper, an attempt was made to increase the ballistic protection of the armor system by combining non-homogenous spaced armor in form of multilayer wire mesh with rolled homogenous armor steel base plate. Different angles of incidence were tested: 0, 20, 25 and 35o, by using 12.7 mm armor piercing incendiary ammunition from 100 m. It was found that the inclination of the armor system has a negative effect on ballistic resistance due to variations in wire body-to-body distance, some of which can increase, causing a decreased contact with the projectile and an insufficient yaw. The yaw causes a sideways impact on the base plate. However, the non-penetrating hits in vertical armor cause a more severe damage on the base plate compared to the inclined armor system. This effect is due to the inclination itself, which is a common behavior of increasing effectiveness of sloped armor.

Pryout capacity of headed stud anchor groups with stiff base plate: 3D finite element analysis

AbstractConcrete pryout failure mode of a group of relatively shallow embedded anchors welded to a steel base plate has not been extensively investigated in the past. Therefore, the failure mechanism and resistance of such anchor groups needs to be clarified. In this paper a three‐dimensional (3D) finite element parametric study for quadruple (2 × 2) anchor groups loaded in shear with no influence of edges is carried out. In the study, embedment depth of anchors and anchor spacing in both directions are varied. The results show that the increase of anchor spacing perpendicular to the shear load direction has no major influence on the concrete pryout capacity, whereas the increase in anchor spacing parallel to the loading direction significantly increases the pryout capacity. For anchor spacing greater than a particular threshold value, the pryout resistance of a group of anchors is approximately equal to the resistance of a single anchor multiplied by the number of anchors. Based on the results of the study, a design formula for anchor group failing in pryout is proposed and compared with the current design code recommendations.

Study of plates with a combined “steel base – (titanium, oxide) coating” structure and preliminary tests of its wear resistance

This paper presents the results of the study of plates with a combined “steel base – titanium, oxide coating” structure, which was obtained by resistive welding and strengthening induction heat treatment. The data of measurements of hardness and preliminary test for wear resistance were given. The possibility of finishing turning on structural chromium steel X40Cr13 was shown.

Mechanical Properties of Aluminium Bracket Strengthening

AbstractThe aim of the research is laboratory investigation of aluminium brackets employed to fasten lightweight curtain walls to building facilities. Tensile loads perpendicular to end plates (vertical) were applied here. The author focused on the solutions intended to increase the load-carrying capacity of aluminium brackets applying the plain washer form A (DIN 125; ISO 7089), plain washer with an outer diameter about 3d (DIN 9021; ISO 7093) and additional cover plates (straps) in the location of bolt anchoring on the base plate. The aluminium brackets were tested on a steel base and concrete substrate. The flexibility of anchoring strongly affects the increase of the end plate middle point displacement and movable crosshead displacement.

Effect of cathodic potential on stress corrosion cracking behavior of different heat-affected zone microstructures of E690 steel in artificial seawater

In this work, the stress corrosion cracking (SCC) behavior of E690 steel base metal (BM) and different heat-affected zone (HAZ) microstructures, i.e., coarse grain HAZ (CGHAZ), fine grain HAZ (FGHAZ), and intercritical HAZ (ICHAZ), was investigated at different cathodic potentials in artificial seawater by slow strain rate tensile tests, scanning electron microscopy and electron back-scattered diffraction measurements. The results show that the HAZ microstructures and BM exhibit different SCC susceptibilities: FGHAZ < ICHAZ < BM < CGHAZ, which are controlled by anodic dissolution (AD) at the open circuit potential. With the cathodic potential equaling to −750 mV, the SCC susceptibility of the four microstructures increases because of the synergistic effect of AD and weak hydrogen embrittlement (HE). At -850 mV, AD is inhibited, and the SCC susceptibility of BM decreases, while the SCC susceptibility of the HAZ microstructures increases. At a potential below -850 mV, the SCC susceptibility of the four microstructures gradually increases because of the augment of HE, and the SCC susceptibility of the HAZ microstructures is higher than that of BM. The distinction reveals that the HAZ microstructures have the greater HE susceptibility than BM.

Isothermal and thermomechanical fatigue behaviour of type 316LN austenitic stainless steel base metal and weld joint

Thermomechanical fatigue (TMF) studies were carried out on type 316 LN austenitic stainless steel (SS) base metal (BM) and its weld joint (WJ) with a temperature interval of 623–873 K under in-phase (IP) and out-of-phase (OP) combinations of mechanical strain and temperature. Tests were performed under mechanical strain control mode using the strain amplitudes in the range, ±0.25% to ±0.6%. Besides, isothermal low cycle fatigue (IF) tests were also conducted on the weld joint at 873 K. TMF cycling resulted in a slightly higher cyclic stress response (CSR) compared to IF loading for the weld joint. The IP TMF cycling yielded a higher plastic strain amplitude in comparison to OP TMF for both the base metal and the weld joint. Cyclic life of the weld joint is found to be inferior to that of the base metal. The fatigue lives exhibited by the base metal and the weld joint varied in the following sequence: IP TMF < IF < OP TMF. Preferential crack initiation in the weld region owing to embrittlement of transformed δ-ferrite was noticed with an increase in the mechanical strain amplitude under both TMF and IF cycling conditions. Crack initiation and propagation generally occurred in transgranular mode under IF and OP TMF and mixed (trans-plus intergranular) mode under IP TMF cycling. Electron back scattered diffraction (EBSD) measurements were employed to investigate the substructural development in terms of local misorientation distribution, inverse pole figure (IPF) maps and boundary dislocation density (ρ) in the weld metal region, under IF and IP TMF cycling. The dislocation density was found to decrease for both IF and IP TMF cycling compared to the as-welded condition, with the decrease being higher for IF cycling. The TMF data generated for the type 316LN SS base metal and weld joint at different strain ranges in the present study clearly demonstrated a lack of conservatism associated with the current design practice which is based on the IF data at the maximum temperature (Tmax) of the service cycle.

Evaluation of fracture resistance of AISI type 316LN stainless steel base and welded pipes with circumferential through-wall crack

Fracture resistance of 316LN SS base and welded straight pipes with circumferential through-wall cracks has been evaluated. The pipe J-R curves have been determined using existing experimental methods and analytical expressions available in literature. The J-R curves of 88.9 mm OD pipe and pipe welds have been compared with the J-R curves obtained from C(T) specimen tests. The results indicate that the C(T) specimen data is not suitable for fracture assessment of pipes due to difference in constraint level and the fracture resistance of the base pipe is inferior to welded pipe. Further, the limit load analyses based on expressions available in literature reveals that the initiation and crack propagation are observed prior to the maximum bending moment.

Metallurgical characterization and corrosion behavior of laser-cladded 310 s + WC alloy coating

Metal parts in alkali recovery boilers such as water-cooled wall tubes and primary air nozzles are easily damaged by high temperature alkali corrosion. In this investigation, 310 s steel base alloy powders mixed with WC was applied on the surface of 1020 steel by laser cladding technology to improve surface quality and extend service life. The content of WC in the alloy powder has a pronounced influence on the microstructure and properties of the obtained cladding layer and it was considered as a variable. The microstructures and elements of the cladding layer was investigated by OM, SEM and XRD. In addition, hardness, friction properties, thermal diffusion properties and alkali corrosion resistance of the cladding layer were further investigated. Finally, research results showed that the microstructure of the laser cladding layer has an organization gradient which is subdivided into planar crystal, cellular crystal, columnar crystal and dendrites orderly from the weld junction. The 310 s + 10%WC cladding layer has the highest hardness of 880 HV, and also has the best friction characteristics, wear resistance, thermal diffusion properties and alkali corrosion resistance.

Microstructure and mechanical properties of hot-rolled low-carbon steel containing Ti–Ca oxide particles: a comparison between base metal and HAZ

The effect of inclusion-induced nucleation on hot-rolled steel base metal was evaluated in comparison with welding heat-affected zone (HAZ). Microstructure and mechanical properties of hot-rolled low-carbon steel containing Ti–Ca oxide particles were studied. The results showed that inclusions in Ti–Ca deoxidized steel distributed dispersely and were effective for intragranular acicular ferrite nucleation. Under hot rolling and controlled cooling conditions, microstructure in steel base metal was significantly refined and mainly consisted of acicular ferrite and intragranular bainite, which exhibited higher strength and excellent toughness. The microstructural evolution behavior followed the process that acicular ferrite plates divided the austenite grain, intragranular bainite packets formed between interlocking acicular ferrite plates, and the remaining austenite decomposed into fine polygonal ferrite grains. The resultant complex microstructure improved the impact toughness significantly. By comparison, in HAZ microstructure, laminar grain boundary ferrite having similar crystallography orientation showed adverse effect on toughness.

Удосконалення технічних рішень теплоутилізаційного устаткування котелень

Наведено результати досліджень щодо застосування в конденсаційних водогрійних теплоутилізаторах систем глибокої утилізації теплоти відхідних газів котельних установок пучків оребрених біметалевих труб певної конфігурації, а саме: з інтенсифікаторами (турбулізаторами) теплообміну всередині сталевих труб та з зовнішнім алюмінієвим оребренням. При цьому димові гази омивають оребрену поверхню, а рух нагріваної води здійснюється усередині труб. Використання таких труб дає змогу посилити теплообмін на внутрішній частині труб, що особливо важливо для конденсаційної зони теплоутилізатора, де відбувається інтенсифікація теплообміну, і з боку димових газів в разі їх охолодження нижче температури точки роси водяної пари та її конденсації. Для конденсаційної зони трубного пучка визначали раціональні геометричні параметри сталевих труб і турбулізаторів потоку на їхній внутрішній поверхні за умови рівності термічних опорів з боку димових газів і води. За результатами виконаних досліджень визначено оптимальні співвідношення параметрів сталевої труби і турбулізаторів потоку, що забезпечують значну інтенсифікацію теплообміну за відносно помірного росту аеродинамічного опору. Показано, що застосування пропонованих труб поліпшує також теплообмін і шляхом уповільнення процесу накипоутворення за рахунок турбулізації пристінного шару нагріваної води. Так відносне зменшення товщини відкладень для труб з турбулізаторами потоку порівняно з гладкими трубами зростає з часом і в деяких режимах перевищує значення 2.

Highly durable nano-oxide dispersed ferritic stainless steel interconnects for intermediate temperature solid oxide fuel cells

Herein, ferritic stainless steel alloys are developed with the dispersion of nano-oxides of reactive elements to improve their oxidation characteristics for solid oxide fuel cell (SOFC) interconnects. Nano-oxides of yttrium, cerium, and lanthanum chromite are homogeneously dispersed in a ferritic stainless steel base powder and specimen pellets are prepared by pressing the powder and sintering it in hydrogen at 1400 °C. The nano-oxide dispersed alloys are tested for oxidation characteristics and electrical properties at 800 °C for 1000 h in air. The results show that the ferritic stainless steel with 3 wt% nano-ceria exhibits significantly improved area-specific resistance (ASR) characteristics. The increase in the ASR for this alloy is found to be only 15 mΩ cm2/kh and is ascribed to the thin dense oxide layer (~0.4 μm), the presence of spinel (MnCrO4) at the outer side of the oxide layer, and the improved oxide layer adherence to the metal substrate. The addition of reactive element oxides altered the oxidation kinetics of the Fe-Cr alloys, thus making nano-oxide dispersed ferritic stainless steel highly durable and most suitable for SOFC interconnects. The oxidation kinetics of the nano-oxide dispersed steel was also discussed as related to cation diffusion.

Application of the Master Curve concept on the choice of duplex stainless steel to avoid brittle fracture

ABSTRACTDuplex stainless steel gets more and more common in structural applications even in steel bridges. For these cases, the choice of duplex stainless steel material to avoid brittle fracture is of great importance as e.g. steel bridges are exposed to low temperatures, generally down to −30 °C or even lower, and fatigue loads. EN 1993‐1‐4 also covers duplex stainless steel, but the given toughness requirements for duplex stainless steel are insufficient. Due to this fact, first investigations have been carried out on various duplex stainless steel base materials and welded specimens based on the fracture mechanic based concept of EN 1993‐1‐10 including the Wallin Master Curve concept. The objective was to achieve a first insight in the applicability of EN 1993‐1‐10 for structural applications with different types of duplex stainless steels in principle. In this frame, Charpy and fracture mechanics tests have been evaluated for 1.4462, 1.4362 and 1.4162 duplex stainless steels of 30 mm and 50 mm thick base materials and weldments. The results have been transformed into the general approach used in EN 1993‐1‐10 originally developed for ferritic structural steel considering the structural detail of a welded longitudinal attachment with a semi elliptical surface crack at the weld toe. The results demonstrate that the investigated duplex stainless steels and their weldments show a very good toughness behaviour and that the EN 1993‐1‐10 model can be transformed for application of duplex stainless steel. The paper presents these first results.