Search

This article analyses the effects of deformation on the structure of CMnSi steel at various deformation levels. After hot forging, the structure of CMnSi steel comprises coarse-sized alpha and pearlite particles. The average grain size of steel after forging was 100 μm. After hot rolling, the grain size gradually decreases, with the average size of the ferrite and pearlite grains measured as 60 μm. After that, CMnSi steel was subjected to cold deformation at levels of 40%, 60%, and 80%. The grain size of the CMnSi steel sample after 80% cold deformation reached level 7, corresponding to about 25 μm. For a deformation level of 40%, the grain size was level 5, corresponding to 40 μm, while a deformation level of 60% produced a grain size of 35 μm, corresponding to level 6. In addition, scanning electron microscopy showed that after 80% deformation, smaller particles with a size of about 5 μm appear inside the parent particles. Moreover, energy-dispersive X-ray spectroscopy analysis revealed the carbide appearance in the form M23C6, with M being a mixture of Fe and Mn. These carbides have a fine size of about 1–2 μm and contribute to the prevention of particle growth during subsequent heat treatments.

Naval vessels face multiple risks that can damage their hulls during navigation, leading to on-site repairs through the shield metal arc welding (SMAW) process and underwater wet welding (UWW). This paper presents a weldability study to identify the optimal heat input parameters to improve ASTM A131 DH36 welded joints quality, development, and sustainability. This study analyzes the influence of heat input on the microstructure and mechanical properties of underwater wet welding fillet joints welded with shield metal arc welding at 4 m water depth in a real-life environment located at the bay of Cartagena (Colombia). The methodology involves nondestructive and destructive tests, including visual inspection, fillet weld break, scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers hardness, and shear strength tests. The welds microstructure is composed of ferrite, pearlite, retained austenite, bainite, and martensite; the hardness values range from 170 HV1 to 443 HV1, and the shear strength values range from 339 MPa to 504 MPa. This indicates that high thermal inputs improve the weld quality produced by the underwater wet welding technique and can comply with the technical acceptance criteria of AWS D3.6, making them more sustainable, with less welding resources wastage and less impact on marine ecosystems. [ABSTRACT FROM AUTHOR]

In the study, laser-MIG hybrid welding of high-strength shipbuilding steel was conducted. The microstructure and impact toughness were studied. The microstructure of the Filling and capping weld metal (FCWM) is widmanstatten and acicular ferrite. The microstructure of the backing WM (BWM) and the heat-affected zone (HAZ) are bainite. The impact energy of the joints is greater than 110 J at different charpy impact test positions. The reason for the different toughness is related to the proportion and distribution of the microstructure at the V-notch of the impact specimen. Through the observation of the section, it is also found that the section corresponding to the microstructure of the different HAZ will show significant differences in fracture morphology. [ABSTRACT FROM AUTHOR]

Mechanical properties of constructional steel are negatively affected by a corrosive environment which is of special importance for marine structures. This study deals with the change of mechanical properties of butt-welded specimens made of shipbuilding steel when they are exposed to the real marine environment (fresh water, sea water, sea tide) for prolonged periods (6, 12, 24 and 36 months). Results of the study include engineering stress–strain diagrams obtained using uniaxial tensile tests, and give insight into the change of material strength due to the length of exposure and the type of environment. The values of measured Charpy impact energy illustrate the change in material toughness. It can be concluded that the sea tide has the most negative impact on the mechanical properties of the considered steel, while most of the deterioration of properties happens during the first six months in a corrosive environment. [ABSTRACT FROM AUTHOR]

EH36 shipbuilding steel has been submerged arc welded under 6 kJ mm−1 heat input employing CaF2–TiO2 fluxes. Ensuing weld metals have been examined with an emphasis on inclusion characteristics. Compositional-wise, the inclusion ensemble is largely categorised as a complex Ti-containing type. It is demonstrated that, as a function of TiO2 content, the average Ti content in the inclusions is gradually enhanced, which is compensated by the simultaneous reduction of Al and Mn. Meanwhile, inclusion size distribution curves show log-normal patterns with the frequency peaks ranging from 0.3 to 0.4 μm. Furthermore, inclusion number density and volume fraction show a definitive increasing trend, which are concurrent to the O uptake from 110 to 210 ppm enabled by TiO2 decomposition. [ABSTRACT FROM AUTHOR]

Microstructure evolution roadmap and pertinent mechanical responses in weld metals subjected to various heat inputs have been profiled in EH420 shipbuilding steel by scanning electron microscopy, energy dispersive spectrometry, electron backscatter diffraction and mechanical testing. As the heat input increases from 11.5 to 20 kJ mm–1, relative percentage of acicular ferrites decreases from 62.2 to 41.3%, while that of grain boundary ferrites increases from 10.4 to 30.2%, which are enabled by the diminished number of potent nuclei at lower cooling rate, and largely responsible for the reduced hardness and toughness. [ABSTRACT FROM AUTHOR]

This article presents a cost-effective and reliable method for welding 30 mm thick sheets of shipbuilding steel EH36. The method proposes to perform butt welding in a two-run technique using hybrid laser arc welding (HLAW) and submerged arc welding (SAW). The HLAW is performed as a partial penetration weld with a penetration depth of approximately 25 mm. The SAW is carried out as a second run on the opposite side. With a SAW penetration depth of 8 mm, the weld cross-section is closed with the reliable intersection of both passes. The advantages of the proposed welding method are: no need for forming of the HLAW root; the SAW pass can effectively eliminate pores in the HLAW root; the high stability of the welding process regarding the preparation quality of the weld edges. Plasma cut edges can be welded without lack of fusion defects. The weld quality achieved is confirmed by destructive tests. [ABSTRACT FROM AUTHOR]

Improving the strength values of low–medium-strength shipbuilding steels without changing the chemical properties will be very useful to meet the high-strength requirement in ships. Heat treatments and severe plastic deformation methods are the main methods used to increase the strength values of steel without changing the chemical structure. Considering the high improvement effect in strength values, quenching process and equal channel angular pressing (ECAP) method stand out among heat treatments and severe plastic deformation methods, respectively. In the current study, quenching and ECAP were applied to low–medium-strength shipbuilding steel and the changes in microstructure and mechanical properties of steel after these methods were comparatively investigated. While martensite was formed in the microstructure after quenching, the average grain size decreased compared to the base material without a phase change with ECAP. Hardness values increased by 100% after quenching and increased by 80% after ECAP. Yield and tensile strength values increased by 3.3 and 2.5 times, respectively, after quenching. On the other hand, yield and tensile strength values after ECAP raised less than after quenching and increased 1.5 and 1.7 times, respectively, compared to the base material. Impact toughness values decreased by 80% after quenching and 10% after ECAP compared to the base material. Also, corrosion resistance of the base material decreased by 13% after quenching and increased by 10% after ECAP. Changes in the mechanical properties of the material after these processes were reflected the middle section of a ship using finite element-based programs and approximately 3.3 times higher than that of the base material for all dimension load–ultimate strength values under uniaxial compression were reached in the model reflecting the mechanical properties of the quenched samples. [ABSTRACT FROM AUTHOR]

Results of studying the effect of a calcium modifier of 10KhSND low-alloy steel on its physicomechanical characteristics are presented. The rolled sheets of commercially produced shipbuilding steel, wherein before teeming during melting a ferroalumocalcium alloy was added, were used for investigation. The corrosion rate of examined steel in a model aggressive medium, as well as its fatigue resistance in salt water in torsion, axial loading, and bending tests against the calcium concentration, was elucidated. The effect of calcium concentrations on the austenite grain sizes and dispersity of nonmetallic inclusions, as well as the fracture toughness characteristics (critical stress intensity factor and crack opening) at different temperatures was examined. The microstructure of fracture facets of shipbuilding steel specimens of long-term service on brittle fracture along pearlite grains and ductile fracture along ferrite ones for as-received steel was revealed. Nonmetallic inclusions in specimen fractures of shipbuilding steel at different calcium concentrations were studied. Their quantity grows considerably with its service terms, which exerts negative influence on the corrosion and mechanical properties of the metal. The calcium alloying of steel is shown to contribute to its corrosion resistance and fracture toughness on long-term service in seawater. The recommendations are given as regards optimal modifier concentrations in the shipbuilding metal, which is consistent with minimum austenite grain sizes and dispersity of nonmetallic inclusions. [ABSTRACT FROM AUTHOR]

This article presents a cost-effective and reliable method for welding 30 mm thick sheets of shipbuilding steel EH36. The method proposes to perform butt welding in a two-run technique using hybrid laser arc welding (HLAW) and submerged arc welding (SAW). The HLAW is performed as a partial penetration weld with a penetration depth of approximately 25 mm. The SAW is carried out as a second run on the opposite side. With a SAW penetration depth of 8 mm, the weld cross-section is closed with the reliable intersection of both passes. The advantages of the proposed welding method are: no need for forming of the HLAW root; the SAW pass can effectively eliminate pores in the HLAW root; the high stability of the welding process regarding the preparation quality of the weld edges. Plasma cut edges can be welded without lack of fusion defects. The weld quality achieved is confirmed by destructive tests.

Effect of equal channel angular pressing (ECAP) and subsequent annealing on the microstructure, mechanical properties and tribological behavior of grade A shipbuilding steel was investigated. Coarse-grained microstructure of initial sample is eliminated during the ECAP at 375 °C and more refined microstructure is achieved. Post-ECAP annealing at 575 °C results in some grain growth, and also the cementite lamellae in the pearlite colonies is broken and got spheroidised during the annealing treatment. ECAP increases strength and hardness of steel significantly while it decreases the ductility. On the other hand, post-ECAP annealing treatment brings about an increase in ductility and diminishes the hardness, as expected. Strain hardening capacity, ductility, hardness and oxidation rate were found to be the main factors affecting wear resistance of the grade A steel. It was found that high hardness and strength, good wear resistance with sufficiently high ductility can be achieved in the grade A steel by applying ECAP + annealing processes. [ABSTRACT FROM AUTHOR]

The large heat input welding performance of shipbuilding steel could be improved effectively by Mg treated in steelmaking process, but the mechanism of Mg on the nano-scale pinned particles had not been figured out yet, and this is also the bottleneck for Mg oxide metallurgy developing. In this research, with Mg-treated shipbuilding steel produced by industrial trials, the systematic experiments and theoretical analysis of thermodynamics and crystallography had been done. The results showed that, with increased welding energy, as the core pinned particles, the quantity of particles between 40 nm and 120 nm was stable when the welding energy was

This article analyzes the mechanical properties of rolled plates made of shipbuilding steel of grade A32 with strength gradient across thickness. The microstructure of sheet across thickness varies from ferrite–bainite to ferrite–pearlite pattern. This leads to formation of a steel strength gradient. It has been demonstrated that the ratio of the strength gradient directions influences the applied force upon static bending and bullet resistance. [ABSTRACT FROM AUTHOR]

A comparison is made of the ductility limits of one mild (normal) and two high-tensile strength shipbuilding steels with an emphasis on stress state and loading path dependency. To describe the ductile fracture behavior of the considered steels accurately, an alternative form of ductile fracture prediction model is presented and calibrated. The present fracture model combines the normalized Cockcroft–Latham and maximum shear stress criterion, and is dependent on both stress triaxiality and Lode angle parameter. The calibrations indicate that, depending on the hardening characteristics of the steels, ductile fracture behavior differs considerably with stress state. It is demonstrated that the adopted fracture model is able to predict the ductile fracture initiation in various test specimens with good accuracy and is flexible in addressing the observed differences in the ductile fracture behavior of the considered steel grades. [ABSTRACT FROM AUTHOR]

• A new scaled-down dovetail crack arrest specimen with a temperature gradient has been proposed. • The crack arrest toughness of the dovetail crack arrest specimen has good consistency with the standard wide-plate tensile specimen and compact crack arrest specimens after size effect correction. • A prediction model based on master curve method was proposed to predict the crack arrest toughness in the whole testing temperature range. A new scaled-down dovetail crack arrest (DCA) specimen (thickness = 20 mm, width = 200 mm) with a temperature gradient along the crack propagation direction was designed to evaluate the crack arrest toughness of EH47 shipbuilding steel at different temperatures. The results showed that the scaled-down DCA specimen can be used to evaluate the crack arrest toughness at a wider temperature range and with lower test loads (≤250 kN). Besides, after specimen size effect correction, the test results of the DCA specimen were compared with wide-plate tensile specimen with the thickness of 80 mm. In addition, the results of the 80 mm thick DCA specimen were also compared with those of the wide-plate tensile specimen. It was found that the evaluation results of the DCA specimen and other type specimens have good consistency in the testing temperature range. Moreover, combined with the energy balance theory, the arrest mechanism of the temperature gradient DCA specimens was analyzed. Finally, a probability prediction model was proposed to predict the crack arrest toughness in the whole testing temperature range based on the testing results and the master curve approach. [ABSTRACT FROM AUTHOR]

The welded stiffened plate is widely used in naval architecture and offshore engineering as a basic structural member. The aim of this study is to investigate the effect of welding residual stress and steel grade on the ultimate strength of stiffened plates under uniaxial compressive load by non-linear finite element analysis. Nineteen stiffened plates built with three types of stiffeners with various column slenderness ratios provided in the ISSC'2000 VI.2 benchmark calculations are employed in the present study. The commercial finite element code ABAQUS is applied to simulate the collapse behavior of the stiffened plates and verified against the benchmark calculations. Fabrication-related imperfections, such as initial deflections and residual stresses, are accounted for in the simulations. The ultimate strength of stiffened plates built in common shipbuilding steels, namely S235, S315, S355 and S390, are investigated by varying the yield strength of materials in the simulation. Analysis of the numerical results shows that the welding residual stress reduces the ultimate strength of stiffened plates, and increase in yield strength of the material can effectively improve the ultimate strength of common ship stiffened plates; and quantitative analyses of their influences have also been performed. [ABSTRACT FROM AUTHOR]

A comparison is made of the ductility limits of one mild (normal) and two high-tensile strength shipbuilding steels with an emphasis on stress state and loading path dependency. To describe the ductile fracture behavior of the considered steels accurately, an alternative form of ductile fracture prediction model is presented and calibrated. The present fracture model combines the normalized Cockcroft–Latham and maximum shear stress criterion, and is dependent on both stress triaxiality and Lode angle parameter. The calibrations indicate that, depending on the hardening characteristics of the steels, ductile fracture behavior differs considerably with stress state. It is demonstrated that the adopted fracture model is able to predict the ductile fracture initiation in various test specimens with good accuracy and is flexible in addressing the observed differences in the ductile fracture behavior of the considered steel grades.

Shipbuilding is going through a period of revitalization, growth and technological advancement. One component of these innovations is to improve welding techniques and materials for optimizing processing time, reducing costs and to improve properties and ship performance. The aim of the present work is to evaluate the welding of microalloyed shipbuilding steel, AH36, using the submerged arc welding (SAW) process with one and two wires. The mechanical properties of the welded joint will be presented using microhardness and Charpy V-notch testing. For metallographic characterization, the base metal and welded joint were etched with 2% Nital and Klemm's I reagent. Scanning electron microscopy, X-ray diffraction and colored etching were used to quantify and verify the presence of martensite and retained austenite, the MA microconstituent. The results obtained from Charpy impact tests and another mechanical test can be correlated with the associated microstructure.

Brittle crack arrestability of the heavy gauge steel plates for shipbuilding is now an important issue for the recent mega container ships. In the present work, the brittle crack arrestability of the steel plate with different toughness distributions in thickness is examined in ultra-wide duplex ESSO tests. It is examined whether a running long brittle crack arrests or not in flat temperature condition in ultra-wide duplex ESSO test that are harder mechanical conditions similar to an actual ship hull condition. Test temperatures are selected at which arrest toughness, Kca, evaluated by temperature gradient type standard ESSO test is the same for two test plates. The steel plate with higher toughness in mid-thickness (t/2) than that in quarter thickness (t/4) could arrest a running long brittle crack although the plate with lower toughness in mid-thickness than that in quarter thickness could not arrest it. The typical split-nail shape appeared at the arrested crack front in the plate with higher toughness in mid-thickness than that in quarter thickness. The numerical analyses also demonstrate that the local stress intensity factor at the arrested crack tip is changing sensitively to the crack front shape. It suggests that the higher brittle crack arrestability appears due to the split-nail shape of the arrested crack front enhanced by the inhomogeneous toughness in thickness. [ABSTRACT FROM AUTHOR]

The welded stiffened plate is widely used in naval architecture and offshore engineering as a basic structural member. The aim of this study is to investigate the effect of welding residual stress and steel grade on the ultimate strength of stiffened plates under uniaxial compressive load by non-linear finite element analysis. Nineteen stiffened plates built with three types of stiffeners with various column slenderness ratios provided in the ISSC’2000 VI.2 benchmark calculations are employed in the present study. The commercial finite element code ABAQUS is applied to simulate the collapse behavior of the stiffened plates and verified against the benchmark calculations. Fabrication-related imperfections, such as initial deflections and residual stresses, are accounted for in the simulations. The ultimate strength of stiffened plates built in common shipbuilding steels, namely S235, S315, S355 and S390, are investigated by varying the yield strength of materials in the simulation. Analysis of the numerical results shows that the welding residual stress reduces the ultimate strength of stiffened plates, and increase in yield strength of the material can effectively improve the ultimate strength of common ship stiffened plates; and quantitative analyses of their influences have also been performed.

The purpose of the present study was to fulfil the knowledge gap concerning residual stresses evaluation of friction stir welded GL E36 shipbuilding steel. Plates of 6 mm thickness were welded using two different welding speeds (1 and 3 mm s−1) at a constant rotational speed of 500 rev min−1. This led to different thermal cycles and the objective is to analyse the resulting microstructures and residual stress states. Therefore, in this work, residual stresses were evaluated by X-ray diffraction; metallography and microhardness testing were performed to support these measurements. Results showed that welds produced with different heat inputs have distinguishable residual stress distributions. Increases in the welding speed led to higher residual stress and microhardness in the stir zone. [ABSTRACT FROM AUTHOR]

Laser welding of thick plates in production environments is one of the main applications of high power lasers; however, the process has certain limitations. The small spot size of the focused beam produces welds with high depth-to-width aspect ratio but at times fails to provide sufficient reinforcement in certain applications because of poor gap bridging ability. The results of welding shipbuilding steel AH36 with thickness of 8 mm as a single-sided T-joint using a 10 kW fiber laser are presented and discussed in this research paper. Three optical setups with process fibers of 200 μm, 300 μm and 600 μm core diameters were used to study the possibilities and limitations set by the beam delivery system. The main parameters studied were beam inclination angle, beam offset from the joint plane and focal point position. Full penetration joints were produced and the geometry of the welds was examined. It was found that process fibers with smaller core diameter produce deeper penetration but suffer from sensitivity to beam positioning deviation. Larger fibers are less sensitive and produce wider welds but have, in turn, lower penetration at equivalent power levels. [ABSTRACT FROM AUTHOR]

This work studied the effect of the amount of additives and the composition of refining slags on the metallurgical of steel grades of the S355G10, S420G2, and S460G2 types. The objects of study were samples of industrial melts after out-of furnace refining of steel with different amounts and nature of additives. Based on the results obtained, the recommended amounts of additives and the composition of the refining slag have been developed, which makes it possible to reduce the metal contamination with non-metallic inclusions.

Arc welding process is a significant source of by-products such as metal particulates and noxious gases. It is vital to characterize aerosols and define particle composition and size in order to make an assessment for a welder's exposure to welding fume since welding has been associated not only with many respiratory problems such as cough, chronic bronchitis, and asthma but also lung cancer. In this study, manual metal arc (MMA) welding of shipbuilding steel were realized with rutile, basic and cellulosic covered electrodes using variety of parameters. The most and the least fume generating covered electrodes and parameter combinations were analyzed in terms of fume particle composition and morphology. Results were evaluated with regard to occupational health and safety as well as environmental effects. [ABSTRACT FROM AUTHOR]

Laser welding of thick plates in production environments is one of the main applications of high power lasers; however, the process has certain limitations. The small spot size of the focused beam produces welds with high depth-to-width aspect ratio but at times fails to provide sufficient reinforcement in certain applications because of poor gap bridging ability. The results of welding shipbuilding steel AH36 with thickness of 8 mm as a single-sided T-joint using a 10 kW fiber laser are presented and discussed in this research paper. Three optical setups with process fibers of 200 µm, 300 µm and 600 µm core diameters were used to study the possibilities and limitations set by the beam delivery system. The main parameters studied were beam inclination angle, beam offset from the joint plane and focal point position. Full penetration joints were produced and the geometry of the welds was examined. It was found that process fibers with smaller core diameter produce deeper penetration but suffer from sensitivity to beam positioning deviation. Larger fibers are less sensitive and produce wider welds but have, in turn, lower penetration at equivalent power levels.

The effects of laser ablation coating removal (LACR), from high strength shipbuilding steel, on fatigue performance have been investigated relative to abrasive blasted specimens. It was shown that the fatigue behavior of the steel subjected to LACR is statistically unchanged from those of the baseline material. Residual stress, surface roughness and fractographic analyses were employed to rationalize the fatigue performance. X-ray measurements revealed that tensile residual stress was induced in the surface by LACR. However, depth-resolved residual stress measurement showed that the tensile residual stress is limited to a shallow depth below which there is a deep case of balancing compressive residual stress. Finally, scanning electron microscopic (SEM) analysis of fracture surfaces showed that cracks initiated from valleys in the roughness profile. Thus, the observed fatigue performance is attributed to the combined effects of residual stress and surface roughness. [ABSTRACT FROM AUTHOR]

We recommend to use SSAB Domex steel microalloyed with boron and characterized by elevated resistances to corrosion-erosion fracture and low-cycle fatigue instead of the widespread 18Mn2 steel in the water transport and elements of hydroengineering structures subjected to the action of strong water flows including, in particular, the Kort nozzles, rudder drives, and parts of the river-ship hulls especially sensitive to erosion. [ABSTRACT FROM AUTHOR]

The effect of inoculating a high-strength shipbuilding steel with flux-cored wires containing FeCa and FeCa in a complex with rare-earth metals (REMs) on the distribution, composition, and morphology of nonmetallic inclusions is investigated. It is shown that inoculation with both FeCa and FeCa in combination with REMs with the calcium and cerium content of the metal within 0.002-0.003% for each of them allows obtaining a high-strength shipbuilding steel with a low level of contamination by nonmetallic inclusions. [ABSTRACT FROM AUTHOR]

The effect of top and bottom pouring of large forging ingots on the quality of high-strength shipbuilding steel plate 150 mm thick is studied. It is shown that technology developed for forging billet top pouring in argon at atmospheric pressure and bottom pouring under a slag-forming mix with protection of the metal stream by argon provides a high level of quality for ultrathick shipbuilding steel plate. [ABSTRACT FROM AUTHOR]

Features of extra-furnace refining technology are considered for high-strength shipbuilding steel sheet, with which high metal purity is provided with respect to non-metallic inclusions. It is demonstrated that the maximum ductility of sheet in the Z-direction is achieved due to optimizing the aluminum and calcium content in the steel. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the fatigue strength of S355NL steel, of a common use within the shipbuilding industry, under uniaxial constant and variable loading. Indeed, ship structures are subjected to variable loading due to various sea states, wind and waves. As a consequence, a better knowledge of fatigue behavior under real loading conditions is needed. This study aims at analyzing the influence of loading conditions (load ratio and variable amplitude loading) on the short crack behavior and last, with a proposed model to assess the fatigue crack life. The tools used to prepare inspections in critical areas only take into account the long crack behavior. The results from the proposed model were compared to the assessments these tools are providing with. [Copyright &y& Elsevier]