This study is concerned with a correlation between the microstructure and the local brittle zone (LBZ) phenomena in high-strength low-alloy (HSLA) steel welds. The influence of the LBZ on toughness was investigated by means of simulated heat-affected zone (HAZ) tests as well as welded joint tests. Micromechanical processes involved in microvoid and cleavage microcrack formation were also identified using notched round tensile tests and subsequent scanning electron microscopy (SEM) analyses. The LBZ in the HAZ of a mUltipass welded joint is the intercritically reheated coarse-grained HAZ whose properties are strongly influenced by metallurgical factors such as an effective grain size and high-carbon martensitic islands: The experimental results indicated that Charpy energy was found to decrease monotonically with increasing the amount of martensitic islands, confirming that the martensitic island is the major microstructural factor controlling the HAZ toughness. In addition, microvoids and microcracks were found to initiate at the interface between the martensitic island and the ferrite matrix, thereby causing the reduction in toughness. These findings suggest that the LBZ phenomena in the coarse-grained HAZ can be explained by the morphology and the amount of martensitic islands.

Microstructure and Local Brittle Zone Phenomena in High-Strength Low-Alloy Steel Welds

The upstream oil and gas industry has been contending with massive data sets and monolithic files for many years, but “Big Data” is a relatively new concept that has the potential to significantly re-shape the industry. Despite the impressive amount of value that is being realized by Big Data technologies in other parts of the marketplace, however, much of the data collected within the oil and gas sector tends to be discarded, ignored, or analyzed in a very cursory way. This viewpoint examines existing data management practices in the upstream oil and gas industry, and compares them to practices and philosophies that have emerged in organizations that are leading the way in Big Data. The comparison shows that, in companies that are widely considered to be leaders in Big Data analytics, data is regarded as a valuable asset—but this is usually not true within the oil and gas industry insofar as data is frequently regarded there as descriptive information about a physical asset rather than something that is valuable in and of itself. The paper then discusses how the industry could potentially extract more value from data, and concludes with a series of policy-related questions to this end.

Data as an asset: what the oil and gas sector can learn from other industries about “Big Data”

https://iopscience.iop.org/article/10.1088/2053-1591/ab4dd4/pdf

Challenges associated with the wire arc additive manufacturing (WAAM) of aluminum alloys

Wire arc additive manufacturing (WAAM) is arc welding-based additive manufacture which is providing a major opportunity for the aerospace industry to reduce buy-to-fly ratios from 20:1 with forging and machining to 5:1 with WAAM. The WAAM method can build a wide range of near net shapes from a variety of high-grade (metallic) materials at high deposition speeds without the need for costly moulds. However, current WAAM methods and technologies are unable to produce parts reliably and with consistent structural material properties and required dimensional accuracy. This is due to the complexity of the process and the lack of process control strategies. This article makes a brief review on monitoring methods that have been used in WAAM or similar processes. The authors then identify the requirements for a WAAM monitoring system based on the common attributes of the process. Finally, a novel multi-sensor framework is realised which monitors the system voltage/current, part profile and environmental ox...

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Realisation of a multi-sensor framework for process monitoring of the wire arc additive manufacturing in producing Ti-6Al-4V parts

Prediction of impact toughness based on the microstructural characteristics of steel weld metals is complicated due to the innumerous parameters involved. The common practice that associates this property with the microstructure of the last bead of multipass weldments has been proven to be unsatisfactory, because the amount of acicular ferrite, the most desirable constituent, may not always be the main contributor to toughness. Parameters such as the recrystallized fraction, the presence of micro-phases and inclusions may also have a relevant role. Thus, to consider the influence of all these parameters, the method proposed by the International Institute of Welding (IIW) is not sufficiently comprehensive and so complementary techniques are necessary. This situation is more relevant for high strength steel weld metals, where very refined microstructures may not be adequately resolved, resulting in misidentification of the microstructure. The use of scanning electron microscopy as an auxiliary technique to optical microscopy has been successfully used for many decades to study C–Mn and low alloy weld metals, mainly when refined microstructures are to be assessed. Recently, in addition to the previously mentioned techniques, Electron Back Scattering Diffraction (EBSD) has also been used to enable a more effective analytical procedure. This technique, which provides valuable information about grain boundaries, is advantageous for refined microstructures to confirm constituents such as acicular ferrite, bainite, and martensite. This work proposes a contribution to the microstructural characterization of C–Mn and high strength steel weld metals based on the analysis carried out by optical microscopy, scanning electron microscopy and EBSD techniques, involving the influence of recrystallization in multipass welds, microstructural constituents, microphases, and inclusions. The microstructure/toughness relationship analysis of some experimental results obtained over the last decades for weld metals with ultimate tensile strength varying from 400 to 1000 MPa was done using the methodology proposed in this work to check its effectiveness and to explain the impact toughness behavior.

Microstructure characterization and its relationship with impact toughness of C–Mn and high strength low alloy steel weld metals – a review

Control of welding parameters is an important factor in gas metal arc welding (GMAW) because these parameters determine the heat input, cooling conditions, and time during which the microstructure and the geometry of the weld are formed. It is therefore essential that sufficient heat is transferred to highly conductive metals like aluminum and appropriate heat input used with very sensitive metals such as stainless steel and high-strength steels or when welding dissimilar metals. The objective of this study is to identify parameters of current, voltage waveforms, and electrode feeding motion that directly contribute to improvement in metal and heat transfer conditions from the electrode to the base metals. The effects of these parameters on welded joint geometry are determined. The work critically reviews research on the effect on welded joints of control of current waveform, voltage, and the alternating electrode and analyzes the different parameters that promote forces acting during metal transfer. Experiments and case studies based on controlled waveforms are discussed. The analysis shows that in controlled short-circuit gas metal arc welding (CS-GMAW), all identified parameters contribute to control of heat input and reduction in the amount of spatter and fumes generated. Variable polarity gas metal arc welding (VP-GMAW) is found to be particularly effective for aluminum welding because of its good control of mass metal transfer and weld penetration. Mixed waveform approaches (i.e., 20 pulses/controlled short circuit) improve weldability in difficult welding positions.

Review of current waveform control effects on weld geometry in gas metal arc welding process

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.

Multi-wire SAW of 640 MPa Arctic shipbuilding steel plates

Structure and properties of welded joints of low-alloy thermomechanically processed (09G2FB) and quenched and tempered shipbuilding steels (10XN2MD, 08XN3MD, and 12XN3MF), welded with manual metal arc welding (MMA) and submerged arc welding (SAW), were studied. Effects of specific energy input on the microstructure, mechanical properties, and impact energy of the heat-affected zone (HAZ) have been investigated, and probable reasons for crack formation in welded joints have been found. It was found that welding heat input increase leads to a significant increase in grain size near the fusion boundary and the formation of martensite with high hardness. Therefore, the heat input is recommended to be limited to 2.5–3.5 kJ/mm for these specific steel grades. The study indicates that microalloying elements can be used to limit the grain growth when the steel is subjected to high temperatures during welding thermal cycle. Carbon content and alloying level reduction tend to increase the steel ductility and lower the HAZ toughness.

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Study of the sensitivity of high-strength cold-resistant shipbuilding steels to thermal cycle of arc welding

The effect of heat input on the microstructure and mechanical properties of dissimilar S700MC/S960QC high-strength steels (HSS) using undermatched filler material was evaluated. Experiments were performed using the gas metal arc welding process to weld three samples, which had three different heat input values (i.e., 15 kJ/cm, 7 kJ/cm, and 10 kJ/cm). The cooling continuous temperature (CCT) diagrams, macro-hardness values, microstructure formations, alloy element compositions, and tensile test analyses were performed with the aim of providing valuable information for improving the strength of the heat-affected zone (HAZ) of both materials. Micro-hardness measurement was conducted using the Vickers hardness test and microstructural evaluation by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical properties were characterized by tensile testing. Dissimilar welded samples (S700MC/S960QC) with a cooling rate of 10 °C/s (15 kJ/cm) showed a lower than average hardness (210 HV5) in the HAZ of S700MC than S960QC. This hardness was 18% lower compared to the value of the base material (BM). The best microstructure formation was obtained using a heat input of 10 kJ/cm, which led to the formation of bainite (B, 60% volume fraction), ferrite (F, 25% volume fraction), and retained austenite (RA, 10%) in the final microstructure of S700MC, and B (55%), martensite (M, 45%), and RA (10%), which developed at the end of the transformation of S960QC. The results showed the presence of 1.3 Ni, 0.4 Mo, and 1.6 Mn in the fine-grain heat-affected zone of S700MC. The formation of a higher carbide content at a lower cooling rate reduced both the hardness and strength.

Effect of Heat Input and Undermatched Filler Wire on the Microstructure and Mechanical Properties of Dissimilar S700MC/S960QC High-Strength Steels

Experiments were carried out to determine the properties of the welded joints in 8 mm thick high-strength steels produced by quenching and tempering and thermomechanical rolling with accelerated cooling (tensile strength 821–835 MPa). The dependence of the strength, elongation, hardness, impact energy and crack opening displacement on the heat input in the range 1.0–0.7 kJ mm− 1 was determined. The results show that the dependence of the strength of the welded joints decreases and that of the elongation increases. The heat input has only a slight effect on the impact energy and crack opening displacement in the heat-affected zone.

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Pavel Layus

Papers

Review of current waveform control effects on weld geometry in gas metal arc welding process

Multi-wire SAW of 640 MPa Arctic shipbuilding steel plates

Study of the sensitivity of high-strength cold-resistant shipbuilding steels to thermal cycle of arc welding

Effect of Heat Input and Undermatched Filler Wire on the Microstructure and Mechanical Properties of Dissimilar S700MC/S960QC High-Strength Steels

Effect of heat input on the mechanical properties of welded joints in high-strength steels