Shipbuilding Steel Research Articles

Micromechanism of Decrease of Impact Toughness in Coarse-Grain Heat-Affected Zone of HSLA Steel with Increasing Welding Heat Input

This paper analyzes the micromechanism of decrease of impact toughness with increasing the welding heat input in coarse-grain heat-affected zone (CGHAZ) of a low-alloy high-strength ship-building steel plate. By comparing the microstructures, measuring the extending length of the fibrous crack, identifying the critical event of cleavage fracture, measuring the critical length, and calculating the local cleavage fracture stress σ f, and then using the basic principles of the micromechanism of cleavage fracture, this work reveals the essential causes of deteriorated toughness in the CGHAZ of high-strength steel welded joints.

Effect of complex inoculation of a high-strength shipbuilding steel on the composition and morphology of nonmetallic inclusions

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.

Maps of structure changes in austenite of low carbon steel 09CrNi2MoCuV during hot deformation and their use to improve industrial technologies

A temperature threshold Tnr of static recrystallization after various prestrains and a threshold strain ɛp of dynamic recrystallization depending on the temperature and strain rate are determined for austenite of low-carbon shipbuilding steel 09CrNi2MoCuV. On the basis of these data obtained with a Gleeble 3800 thermomechanical simulator, the temperature and deformation conditions are mapped allowing one to distinguish between particular ranges of technological parameters of thermomechanical treatment, where certain mechanisms of polycrystal structure evolution predominate in austenite of the considered steel.

Control of Structure Formation During Thermomechanical Treatment of Shipbuilding and Pipe Steels of Unified Chemical Composition

Principles are established for controlling low-alloy steel structure formation during thermomechanical treatment for the possibility of creating steels for different purposes from slabs of a single chemical composition. Technology is developed for manufacturing high-strength shipbuilding steels with a yield strength of 460 MPa and strength category K65 pipe steels of unified chemical composition.

Multi-wire SAW of 640 MPa Arctic shipbuilding steel plates

Extensive industrial use of thick high-strength steel plates in Arctic shipbuilding calls for submerged arc welding (SAW) processes with higher deposition rates. One of the most effective ways of increasing the deposition rate is to increase the number of welding wires. Although SAW processes with up to six wires exist, their use is not widespread and two- or three-wire modifications, which are the focus of this paper, are the most common approaches. This paper presents a case study of the development of a welding procedure for welding of high-strength steel shipbuilding plates using a three-wire SAW process. Welding parameters and conditions were evaluated with the aim of achieving a high-quality weld. Optimal parameters for 12-mm plate thickness were found to be: Св-08ГСМТ wire (similar to Mn4Ni1Mo) of 3.2 mm in diameter, single-pass welding, welding flux 48AF-56, I = 840 A, U = 37 V, Q = 5.4 kJ/mm. Optimal parameters were also found for 16-mm plate for two pass welding. Testing of the weld joint included a static tensile strength test, an impact energy test at different temperatures, a bending test, a low-cycle fatigue strength test, microstructure examination and a hardness test. The tests showed satisfactory results that indicate that the developed welding technique is applicable for Arctic shipbuilding applications. The paper provides improved understanding of the welding technique selection process for Arctic shipbuilding as well as providing industrially valuable information about the developed welding technique.

Experimental Fatigue Analysis of Butt-Welded Joints

Fatigue experiments on butt-welded steel joints in the recently established fatigue laboratory at the Kiel University of Applied Sciences, Germany, are presented in this paper. The tests were carried out on 5 mm thick shipbuilding steel of grade AH36 with a yield stress of ReH = 355 N/mm2, joined by submerged arc welding technique. A new SincoTec MAG 100 resonance frequency pulser was used to carry out the constant amplitude load controlled fatigue tests. The results are compared to the work of different researchers and the recommendations issued by the International Institute of Welding (IIW).

Evaluation of FSW on High Yield Strength Steels for Shipbuilding

FSW process has been evaluated on three shipbuilding steels (DH36, S690QL and 80HLES steels) by fully penetrated butt welds on 8mm thick plates. Non destructive tests were carried out to highlight the presence of intrinsic defects known for the welding process (eg kissing bond). The validated inspection methodology (volume and surface testing) confirm the integrity of welds and the absence of geometrical defects for examinations and mechanical tests as part of a qualification procedure.

Investigations for indications of deliberate blasting on the front bulkhead of the ro-ro ferry MV ESTONIA

The roll-on-roll-off passenger ferry MVESTONIA sank during the night of 28 September 1994 in the Baltic Sea. In October 2000, divers recovered two palm-sized test pieces from the front bulkhead of the wreck. The investigators analysed these specimens to determine whether there were any indications of deliberate blasting. Since the wreck had been submerged for almost six years, it was clear that chemical traces would not be present on the surfaces of the test pieces. Therefore, the investigators performed comparative tests on shipbuilding steel to find a microstructural criterion that exclusively characterises a blast. The shipyard Jos. L. Meyer, Germany, had built the ESTONIA and supplied shipbuilding steel plates similar to that used for building the vessel in 1979/1980. The comparative tests comprised mechanical tests, shot peening tests and blasting tests using different explosives. Testing demonstrated that blasting always formed twinned ferrite grains in the microstructure over the whole cross-section of each of the 8mm thick comparative plates. Although one of the original test pieces of the ESTONIA showed deformation twins, this was only confined up to 0.4mm underneath the surfaces and not spread over the whole cross-section. Comparative shot peening tests produced the very same pattern of subsurface deformation twins. Therefore, the twins detected in the microsection of the test pieces of the ESTONIA wreck traced back to the shot peening process performed by the shipyard in 1979/1980 and not to a deliberate blast.

Effects of different restraints on the weld-induced residual deformations and stresses in a steel plate

Effects of three different plate boundary constraints on the residual stress field and deformation are investigated numerically during butt-joint welding. For the numerical solution of the heat transfer equations, the finite element method is used to predict the temperature profile as well as residual stress field due to three different plate boundary conditions. The distortion of the welded plate is modeled as a nonlinear problem in geometry and material, adopting a finite element solution based upon the thermo–elastic–plastic large deflection theory. High-strength shipbuilding steel AH36 with temperature-depending material properties and nonlinear stress–strain material properties (bilinear isotropic hardening option uses the von Mises yield criteria) are assumed for the numerical analysis. For verifying the results, the temperature profile is compared with the result obtained in a previous research. In the mechanical analysis, three different boundary conditions are applied. Effects of plate thickness, plate width, and mesh model on the residual stress with boundary constraint are studied.

Influence of Inactivation Treatment of Ship's Ballast Water on Corrosion Resistance of Ship Steel Plate

The effect of seawater after ultraviolet inactivation on corrosion of a shipbuilding steel plate was investigated by means of natural corrosion potential experiments and immersion corrosion test. The effects of natural seawater and treated seawater after ultraviolet inactivation on corrosion of the selected steel plate samples were compared with each other. The results showed that there was no obvious change in the chemical composition of treated seawater compared with natural seawater. The corrosion potential slightly increased by 10 mV, whereas the corrosion rate rose significantly by 20%. The experiments verified the naturally formed biofilm in the natural seawater for the inhibition of corrosion on the shipbuilding steel plate. The possible influences of ballast water treatment on biofilm by ultraviolet and electrolysis inactivation under the condition of practical usage were also investigated. And it was found that ballast water treatment methods with no continuous disinfection could protect original tank biofilm structure, reducing the intensity of tank corrosion.

Change of Steel’s Yield Stress Over Ship’s Service Life and its Effect on the First Yield Hull Girder Bending Moment - Technical Note

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 that the total hull girder bending moment will exceed the first yield bending moment) could be substantial.

Effectiveness of barium-bearing ferroalloys in steel smelting

The influence of barium-bearing ferroalloys on the mechanical properties of cast and deformed steel is studied. Such ferroalloys greatly reduce the metal’s content of gases and nonmetallic inclusions, increase the impact strength of steel for railroad castings, and improve the plasticity of high-strength shipbuilding steel.

Study of the quality of ultrathick high-strength shipbuilding steel plate

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.

INFLUENCE OF MICROSTRUCTURE OF AH32 CORROSION RESISTANT STEEL ON CORROSION BEHAVIOR

International martime organization (IMO) has approved and considered corrosion resistant steel as the only alternative for anti-corrosion coating since May 2010. The implementation of the standard will have a profound impact on ship building, steel, shipping and other industries. At present, Japan has a relatively mature technology, South Korea has completed the pre-development work, while China has only carried out some preliminary studies. If the technology is blocked, a large number of steel needs to be imported which would push up the cost of construction of the shipbuilding industry, and has a direct impact on the orders of shipping enterprises. The amount of steel for cargo oil tank in China is more than two million tons each year, and therefore, the localization of research and application of corrosion resistant steel for cargo oil tanks has become an urgent task. The impact of microstructure of the existing shipbuilding steel on corrosion behavior in simulated corrosion environment is studied based on the standard in this paper to develop our own corrosion resistant steel. According to the standard, immersion test was used to measure the corrosion process of AH32 corrosion resistant steel in the bottom simulated environment of cargo oil tanks. Using gravimetric measurement, electrochemical polarization and impedance methods, scanning electron microscopy and electron probe et al, the influence of microstructure of AH32 corrosion resistant steel on its corrosion behav- iors was analysed. The experimental results showed that: during the test simulating the corrosion of the

Microstructural studies and impact toughness of dissimilar weldments between AISI 316 L and AH36 steels by FCAW

In this study, AISI 316 L austenitic stainless steel and AH36 low-alloy ship building steel pair were joined with flux-cored arc welding method by using E309LT1-1/4 filler metal under four different shielding gas compositions containing CO2 at different ratios. Microstructure, impact toughness of welded materials, and their microhardness distribution throughout joining were determined. In macro- and microstructure examinations, stereo optical microscope, scanning electron microscope (SEM), SEM/energy dispersive spectroscopy, and SEM/mapping analysis techniques were used. After notched impact toughness, fracture surfaces were examined using the scanning electron microscope. This study investigated effects of shielding gas composition on microstructure, impact toughness, and microhardness distribution of transition zone between AH36 steel and weld metal of joined material. It is observed that based on an increase in amount of CO2 in shielding gas, impact toughness values of the weldment decreased. Microhardness values change throughout weld metal depended on shielding gas composition. Moreover, an increase in amount of CO2 within shielding gas decreased δ-ferrite amount in weld metal. The increase in amount of CO2 within shielding gas leads to expanded transition zone in interface between AH36 and weld metal and also affects notched impact toughness values negatively due to the inclusion amounts occurring in weld metal and hence caused it to decrease.

Increased crashworthiness due to arctic conditions – The influence of sub-zero temperature

Offshore activities and shipping in arctic regions increased significantly in the past decade due to the expected natural resources and due to the upcoming advantages of the northern sea route. Hence, structural solutions used in arctic conditions need to resist the low temperatures at an adequate safety level. Therefore, this paper analyses the collision resistance of ships exposed to sub-zero temperature (SZT). Further, it assesses the influence of the material properties for 0, −30, −60 and −90 °C of typical shipbuilding steel. Thereby, the theoretical influence of SZT on the collision force will be presented as well as the potential gain from specially selected materials for SZT, arctic materials, compared to standard materials, both with and without the presence of rupture. As a result, the potential increase in crashworthiness of structures under SZT will be presented and thereby a contribution to safe arctic operations and transport.

A Particle Swarm Algorithm-Based Optimization for High-Strength Steel Structures

Crash resistant ship structures with high post accidental residual strength are more and more important as a requirement of Goal Based Standards. A first step in the development of structures, which fulfill these requirements, is the rational identification of crashworthy structural concepts. Therefore, efficient optimization algorithms are needed, besides reliable numerical collision simulations. Particle swarm optimization (PSO) algorithms tend to improve the objective fast, which makes them a good choice for lengthy nonlinear finite element-based collision simulations. As an application of PSO and numerical collision simulations a liquefied natural gas tanker is optimized for crashworthiness. Furthermore, one concept using normal shipbuilding steel only and one concept using a combination of normal and high strength steel is investigated. Hence, it will be shown if the benefits from high strength steel outweigh the increase in cost. Therefore, it will be shown if the combination of normal and higher strength steel can result in increased crashworthiness, even though the high strength steel has a lower failure strain when compared with the normal steel.

Effect of aluminum and calcium on the ductility of thin sheet shipbuilding steel in the Z-direction

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.

The influence of different He-Ar ratios on high power CO<SUB align=right>2 laser welding process and weld formation

Pure He is usually used as a plasma blowing gas in high power laser welding because of its high ionisation energy. Its high price however, drives researchers to put more efforts into finding the suitable alternatives. In this paper, 12 mm e-grade shipbuilding steel plates were welded using a 15 KW CO2 laser machine, with the mixture of He and Ar as the blowing gas. The effects of different He-Ar ratios of the blowing gas on laser welding process and weld formation were studied by using a high-speed camera and spectrum was acquired simultaneously. It is found that plasma profile changes with the addition of Ar into He and the spectrum is mainly Fe spectral line even when there are 60% Ar. Sound joints can be obtained even with 40% He + 60% Ar while no acceptable joint formed when using pure Ar.

ENVIRONMENTAL INFLUENCES ON STRESSED METALLIC SURFACES

This paper presents some aspects regarding the damage of metal surfaces undergoing mechanical stress corrosive environmental interaction. This interaction is investigated on samples made of two types of low-alloy steel, general use steel type OL524Ak and a shipbuilding steel grade E36, subjected to cyclic load in aqueous solution of 3.5% NaCl. Both electrochemical and fractographic aspects reveal the initiation and development of damage processes on the metal surfaces. It is also highlighted that the processes of damage by corrosion fatigue of the steel structures can be monitored based on recordings of the electrochemical parameters.