Shipbuilding Steel Research Articles

Joining 30 mm Thick Shipbuilding Steel Plates EH36 Using a Process Combination of Hybrid Laser Arc Welding and Submerged Arc Welding

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 B Segregation at Prior Austenite Grain Boundaries on Microstructures and Toughness in the Heat‐Affected Zone of Mg‐Deoxidized Shipbuilding Steel Plates

The effect of B segregation at prior austenite grain boundary (PAGB) on the microstructure and toughness in the heat‐affected zone (HAZ) after high heat input welding at kJ cm−1 for Mg‐deoxidized shipbuilding steel plates is clarified. With 0.0022 wt.% B addition, B segregation occurs at PAGBs in two forms: solute B and fine Fe23(BC)6 precipitates. B segregation with a concentration of about 4 at.% decreases boundary energy by 0.13 J m−2, which reduces the nucleation density of boundary ferrites by increasing the critical activation energy of ferrite nucleation. Thus, coarse grain boundary ferrites (GBFs) and ferrite side plates (FSPs) are suppressed with film‐like allotriomorphic ferrites formed at PAGBs, and ferrite transformation temperature reduces from 712–543 to 679–541 °C. In B‐free steels, (Fe, Mn)3C particles form at PAGBs with the Mn‐depleted zone (MDZ) at around (Fe, Mn)3C, promoting GBFs and FSPs. However, (Fe, Mn)3C precipitates and MDZ are not observed at PAGBs with B addition, because B segregation delays Mn diffusion to PAGBs. Thus, GBFs and FSPs reduce, and intragranular acicular ferrites (IAFs) increase with B addition, making the dislocation density and high‐angle grain boundary density increase, which improve HAZ toughness at −40 °C from 40 to 141 J.

Experimental and Mathematical Studies for Optimality of GTAW Parameters on Similar and Dissimilar Steel Substrates

Argon arc welding is a frequently used process, to assist various manufacturing processes. The paper highlights the postweld experimental results of similar (EN 10025 Steel-Grade S295) and dissimilar (D36 shipbuilding steel) materials, which possess a wide range of applications in manufacturing industries. In this work, experimental studies are carried out for optimality of gas tungsten arc welding (GTAW) parameters on a butt joint with single and double V 45° groove angles using Taguchi orthogonal L9 array design. The welding is carried out using the back hand technique, and the filler rod is taken as ER303L to obtain finer welded joints. After the weld, residual stresses, microhardness, and geometrical properties of weld are studied at varied zones, that is, weld zone, HAZ, and base metal to examine the weld efficiency with specific predefined weld parameters. Furthermore, tensile tests are carried out for the weldments with optimal predefined weld parameters, and subsequently, the welded specimens with better tensile strength are discussed in the results. Genetic algorithm and mathematical modelling are opted for selecting the final optimal welding parameters. As per the obtained results of residual stresses, hardness, and tensile tests, dissimilar double V groove butt joint is projected to have more effective weld joint.

Methods of corrosion testing used for development and commercial exploitation of new shipbuilding steels and alloys. Review. Part II. Corrosion cracking and field marine tests

The review describes methods of stress corrosion cracking (SCС) tests that implement various conditions for samples loading: at a constant static load or deformation, at a constant or increasing load of samples with a previously grown fatigue crack, with a slow strain rate. Such tests shall be carried out to determine the resistance of shipbuilding materials to be used in loaded ship structures in contact with seawater. Brief descriptions of the mechanism of stress corrosion cracking of steels and alloys are given. The necessity to carry out bench tests of steels and their welded joints, as well as models simulating individual units and elements of structures, is indicated. At this stage, conditions are ensured as close to operating conditions as possible due to exposure in various climatic zones of the world’s oceans (variations in temperature, chloride concentration, amount of dissolved oxygen, degree of biofouling, and their simultaneous impact). It is shown that during verification field tests (final stage) new materials promising for operation in marine conditions pass the final evaluation of corrosion resistance in the form of elements of ship structures and systems in the conditions of ship operation.

Methods of Corrosion Testing Used for the Development and Industrial Utilization of Novel Shipbuilding Steels and Alloys. A Review. Part II. Corrosion Cracking and Marine Field Testing

Methods of Corrosion Testing Used for the Development and Industrial Utilization of Novel Shipbuilding Steels and Alloys. A Review. Part II. Corrosion Cracking and Marine Field Testing

Methods of сorrosion testing used for development and commercial exploitation of new shipbuilding steels and alloys. Part I. Laboratory corrosion tests

Shipbuilding steels and alloys may be subjected to various types of corrosion damage when exposed to sea water. For reliable long-term operation of ships and marine structures, despite the use of corrosion protection, materials are chosen that, in addition to the required mechanical properties, have sufficient corrosion resistance to ensure a given service life. Evaluation of corrosion resistance of new materials for use in shipbuilding was made by carrying out mandatory delivery trials using methods that have been repeatedly tested experimentally and whose results have been confirmed in practice. The complex study of corrosion resistance of steels and alloys is based on step-by-step laboratory, bench, and field tests. The review provides a brief description of laboratory corrosion test methods that are part of mandatory delivery trials. Parameters determining the aggressiveness of seawater as a corrosive medium, including salinity, oxygen content are considered. Laboratory test methods include electrochemical studies with determination of potential and rate of corrosion, pitting potential on the basis of polarization curves construction, as well as the generally accepted gravimetric method of corrosion rate determination. Installations for testing in moving (with varying flow rate) seawater are given.

Formation of austenite in ferrite-beinite, beinite-martensite and martensitic shipbuilding steels and its influence on the transformed structure

This article investigates the kinetics of austenite grain growth during heating and the features of phase transformations depending on the austenite grain size in ferrite-bainitic, bainite-martensitic and martensitic shipbuilding steels. The kinetics of dynamic and static recrystallization is studied depending on the holding time at a given temperature. The studies carried out made it possible to determine the effect of the austenite grain size in shipbuilding steels of manganese, manganese-nickel and nickel alloying composition on the transformed structure.

Methods of Corrosion Testing Used for the Development and Industrial Utilization of Novel Shipbuilding Steels and Alloys. Part I. Laboratory-Scale Corrosion Testing

Methods of Corrosion Testing Used for the Development and Industrial Utilization of Novel Shipbuilding Steels and Alloys. Part I. Laboratory-Scale Corrosion Testing

CHANGE OF STEEL’S YIELD STRESS OVER SHIP’S SERVICE LIFE AND ITS EFFECT ON THE FIRST YIELD HULL GIRDER BENDING MOMENT

The publication deals with the decrease of the yield and tensile stress of high tensile shipbuilding steel AH-32 over ship’s service life and its effect on the first yield bending moment as a representative of the hull girder capacity. An example is given for a sample 25K DWT (25 thousand tons deadweight) bulk carrier. The probability of failure is calculated as the probability of the total hull girder bending moment exceeding the first yield bending moment. The probabilistic distributions of yield and tensile stress are obtained from laboratory test of the specimen of AH-32 steel (corroded plates of a 20 year old ship). It is found that although the decrease of yield stress may not be great, the increase of the probability of failure (i.e., the probability yield bending moment) could be substantial.

Structure heterogeneity and mechanical properties studied in thickness up to 100 mm of low-alloyed shipbuilding steel sheets with a yield strength not less than 420 MPa

This paper presents a study of changes in the structure and properties in thickness of rolled sheets up to 100 mm of low-alloyed shipbuilding steel with a yield point not less than 420 MPa. The fracture surface of samples after impact bending tests at low temperatures was investigated. It was found that the combination of the parameters of lath morphology bainite (fraction, areas average size and length) and the size of structural elements at given tolerance angles of 5 and 15° (indicating the presence or absence of a developed subgrain structure of deformation origin) determine the level of impact work at low temperatures testing.

Weld Characteristic Analysis for Weld Process Variables of Tip-Rotating Arc Welding in Butt Joint of Shipbuilding Steels

Weld Characteristic Analysis for Weld Process Variables of Tip-Rotating Arc Welding in Butt Joint of Shipbuilding Steels

Heterogeneous Microstructure-Induced Mechanical Responses in Various Sub-Zones of EH420 Shipbuilding Steel Welded Joint Under High Heat Input Electro-Gas Welding

Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy, electron backscatter diffraction and mechanical testing. Comparing with the coarse-grained heat-affected zone (CGHAZ), the weld metal presents higher toughness (129.3 J vs. 37.3 J) as it contains a large number of acicular ferrites with high-angle grain boundaries (frequency 79.2%) and special grain boundary ∑3 (frequency 55.3%). Moreover, coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation. Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5, which is the main reason for the occurrence of tensile fracture.

Influence of welding HAZ microstructure on low-temperature impact fracture behaviour in C–Mn shipbuilding steel

The influence of microstructure on the low-temperature impact toughness of the heat-affected zones (HAZs) in C–Mn shipbuilding steels was investigated in welding thermal simulations and the Charpy impact test. Within the temperature range −80°C to −40°C, the Charpy impact energy initially increased and thereafter decreased with decreasing peak temperature of welding. The impact energy was maximised at a peak welding temperature of 850°C. The deterioration of low-temperature impact toughness was associated with enlarging effective grain size and numerous low-angle boundaries. The distribution of dual-phase structures and martensite/austenite (M/A) constituents significantly affected the fracture mode. The impact energy fluctuations observed in the analysis are also explained.

Effect of Heat Treatment on Structure and Properties of Martensite Stainless Steel for Ice-Class Ships Obtained by Direct Laser Deposition Method

At present, to increase competitiveness of shipyards for manufacturing of shipbuilding parts new high technologies are used. Additive production methods, including direct laser deposition (DLD) technology, which meets all the requirements of competitiveness, are increasingly being applied. Heavy-duty large-size parts such as propellers, blades, hubs and other critical parts used in shipbuilding have become possible to produce with DLD. In the process of DLD it is possible to produce parts, including shipbuilding steels used in the Arctic conditions, with the required mechanical characteristics not inferior to similar brands of materials obtained by casting or plastic deformation methods. The work is devoted to research of thermal process influence on structure and mechanical properties formation of deposited samples from steel powder 06Cr15Ni4CuMo. Features of formation of microstructure components by means of optical microscopy, X-ray structure analysis (XRD) are investigated, and also CCT diagram is constructed. Tensile and impact toughness tests have been conducted. As a result, it was found that the material obtained by the DLD method in its initial state significantly exceeds the strength characteristics of heat-treated castings of similar chemical composition, but is inferior to it in terms of plasticity and viscosity. The increase of viscosity and plasticity up to the level of cast material in the grown samples is achieved during the subsequent heat treatment, which leads to the formation of the structure of tempered martensite and reduction of its content in the two-stage tempering in the metal structure. The strength of the material is also reduced to cast metal after heat treatment.

Optimization of strength, ductility and wear resistance of low-carbon grade A shipbuilding steel by post-ECAP annealing

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.

Effect of Aging Regimes on the Fracture Mechanism of Low-Alloy Steels with Different Structures

Abstract—Low-alloy shipbuilding and pipeline steels are currently supplied after thermomechanical treatment, in which a ferrite–pearlite or ferrite–bainite structure depending on alloying is formed. During the thermomechanical treatment and then during cooling, a large number of defects are developed and recorded, which makes the crystalline structure nonequilibrium and leads to a nonuniform distribution of carbon and nitrogen atoms. The properties of steel with a nonequilibrium structure may degrade during processing treatments (cold straightening, bending, welding) and during exploitation or long-term storage. The effects of the modes of strain aging on the mechanism of steel fracture are studied and efficient ways to prevent embrittlement caused by aging are sought.

Research of the Quality of High-Strength Shipbuilding Steel with High Concentration of Calcium

The microstructure of the commercial melt of high-strength shipbuilding steel with a calcium concentration in the ladle sample of 0.009% is investigated, the presence and qualitative composition of nonmetallic inclusions are determined, and mechanical tests are carried out. Owing to the fact that high calcium steel is contaminated with many oxide linage inclusions, the mechanical properties of rolled products (impact strength, Z-direction ductility, quality of technological sample fracture) are sharply reduced. To ensure high purity of high-strength shipbuilding steel with respect to nonmetallic inclusions, it is necessary to observe the strictly regulated technology of deoxidation with aluminum and modification with ferrocalcium to obtain the content of these elements in the metal in the previously recommended limits of 0.01–0.02 and 0.002–0.004%, respectively.

Experimental study of the relationship between fracture initiation toughness and brittle crack arrest toughness predicted from small-scale testing

It is vital to prevent brittle cracks in large structures. This is particularly important for a number of industry sectors including offshore wind, Oil & Gas, and shipbuilding where structural failure risks loss of human life and loss of expensive assets. Some modern steels exhibit high Charpy energy – i.e. high initiation fracture toughness, but poor resistance to crack propagation – i.e. low crack arrest toughness. The correlation between initiation and arrest toughness measured through small-scale testing is investigated in five different steels, which include S355 structural steel (with two different thicknesses), X65 pipeline steel, two high strength reactor pressure vessel steels and EH47 shipbuilding steel. Small scale mechanical tests were carried out to characterise the materials’ properties and were compared to the materials’ microstructures. A wide range of tests were carried out, including instrumented Charpy, drop weight Pellini, fracture toughness, tensile testing, and optical microscopy. Nil ductility transition temperature (NDTT) is used to characterise a material’s arrest properties. Initiation fracture toughness correlated with higher upper shelf Charpy energy and smaller average grain sizes, as expected, however none of these correlated well with the arrest toughness measured through NDTT. The NDTT correlated most strongly with the T27J temperature which indicates the start of lower shelf of the Charpy curve. This correlation held for all materials including those where the NDTT lies on the upper shelf of the Charpy curve. While initiation fracture toughness can be predicted through high Charpy toughness and operation temperatures on the upper shelf, crack arrest behaviour should be predicted from characteristics of the ductile to brittle transition temperature, for example by using the T4kN from instrumented Charpy tests or T27J.

The effect of the loss of superhydrophobic surface properties on biofouling and flow around shipbuilding's steel plates

The dependence of the degree of biofouling on the magnitude of the contact angle θ during temporary degradation of the superhydrophobic coating of shipbuilding steel A40S in the process of being under water is examined. The experiment showed that the gas gap between the liquid and the structured surface makes it difficult for the first settlements to appear at θ ≥ 130°. In 35 days of being underwater and losing the hydrophobic properties of the coating, there were discovered the serpules (Serpula vermicularis), bryozoans (Bryozoa) and green algae (Chlorophyta), but there is no balanus (Balanidae - Chthamalus stellatus) and sponges (Porifera), which are observed on the untreated opposite sample side. The results of an in vivo experiment were used to CFD the dependence of water's flow velocity along the plate surface. Numerical calculation was determined the ratio of the initial flow velocity rate to its value at the end of the model plates. The transition from the hydrophilic state to the hydrophobic state reduces the value of the surface resistance by 1.44 times (changes in the velocity ν0/ν ≈ 2.6 are hydrophilic, ν0/ν ≈ 1.8 hydrophobic). An increase in surface roughness due to fouling will further increase the speed ratio by another 1.19–1.22 times.

Research on the evolution mechanism of pinned particles in welding HAZ of Mg treated shipbuilding steel

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 <250 kJ/cm. During welding process, a number of reversible chemical reactions involving [Mg] and MgO generation or consumption occurred in the heat affect zone for Mg treated shipbuilding steel, and the temperature for more MgO formation just meet the thermodynamic conditions that the solid solution behavior of pinned particles TiN started to accelerate. Due to the extremely low disregistry value between MgO and TiN, the newly generated MgO which was determined by the [Mg] content in steel was highly likely to precipitate on the original TiN particles, delayed the solid solution of TiN, and generated more stable pinned particles.