High Strength Steel Weld Metals Research Articles

Effect of post-weld heat treatment on mechanical and microstructural properties of high strength steel weld metal

The usage of high strength steel (HSS) is steadily increasing, primarily driven by the pursuit of weight reduction, leading to a subsequent decrease in greenhouse gas emissions. This paper investigates the impact of various post-weld heat treatment (PWHT) temperatures of 525 °C, 550 °C and 575 °C with a holding time of 2 h on both the microstructure and mechanical properties of weld metal produced using a HSS metal cored wire. The investigation reveals that PWHT does not significantly alter strength but has a more pronounced influence on toughness. The as-welded condition exhibited the highest toughness. Among the samples subjected to the PWHT, the one treated at 575 °C showed the highest impact energy, reaching 69 J at −60 °C. This outcome is attributed to the increased presence of acicular ferrite in the microstructure, surpassing that of samples subjected to PWHT at different temperatures.

Correction to: High strength steel weld metal properties: metallurgical criteria and computational tools

Correction to: High strength steel weld metal properties: metallurgical criteria and computational tools

High strength steel weld metal properties: metallurgical criteria and computational tools

High strength steel weld metal properties: metallurgical criteria and computational tools

Corrosion resistance analysis of the weld metal of low-alloy high-strength steel considering different alloy compositions

In order to find the low-alloy high-strength steel welded with the strongest corrosion resistance, the corrosion resistance of HSAL weld metal was studied by considering different alloy compositions. Corrosion resistance of alloy compositions of 460, 690, and 980 MPa was analyzed in an atmospheric environment and simulated seawater environment, respectively. The results of the corrosion weight gain test, weight loss test, and Kelvin probe test showed that the HSAL weld metal with 980 MPa alloy composition has the best corrosion resistance in an atmospheric environment. Through seawater immersion and electrochemical testing, it was found that the HSAL weld metal with 980 MPa alloy composition had good corrosion resistance in a simulated seawater environment, the HSAL with 690 MPa alloy composition had medium corrosion resistance, and the HSAL with 460 MPa alloy composition had the lowest corrosion resistance. The corrosion resistance of the weld zone is the best and that of the heat-affected zone is the worst; these findings may be helpful for research in related fields.

Influence of the interpass temperature on the microstructure and mechanical properties of the weld metal (AWS A5.18 ER70S-6) of a narrow gap welded API 5L X70 pipe joint

To reduce manufacturing costs, manufacturers may perform welding with a high interpass temperature (IT), which can reduce the welding idle time and increase the productivity of welding production. However, an increase in IT can jeopardize the behavior of welded joints. Therefore, the present study investigated the effects of high ITs (295, 345, and 390 °C) on the weld metal (AWS A5.18 ER70S-6) of a narrow groove high-strength low-alloy steel (API 5L X70) pipe welded by a gas metal arc. The increase in IT led to a decrease in the welding idle time. The highest ITs (345 and 390 °C) reduced the thermal gradient, thus increasing the cooling time from 800 to 500 °C (t8/5), which enhanced the formation of low-toughness constituents (sideplate and proeutectoid ferrites) and reduced the acicular ferrite content. This induced a drop in the weld metal Charpy V-notch (CVN) impact energy. Nevertheless, even the IT = 390 °C condition (with the lowest CVN impact energy) satisfied the DNVGL-ST-F101 standard requirements, which indicates that a high IT can be used to increase the effective productivity factor and reduce the welding cost. However, it is necessary to evaluate the risk of this decrease in CVN impact energy for each application.

Metallurgical Design Rules for High-Strength Steel Weld Metals

A review of a dilatometric analysis of selected Fe-C-Mn high-strength steel shielded metal arc weld metals showed that balanced Ti, B, Al, O, and N additions reduced the austenite-to-ferrite transformation-start (TS) temperature. These microalloy additions must match the following aim levels for composition control: Ti at 400 ppm (0.04 wt-%), B at 40 ppm (0.004 wt-%), Al at 200 ppm (0.020 wt-%), O at 400 ppm (0.04 wt-%), and N preferably below 80 ppm (0.008 wt-%) to ensure effective deoxidation, form complex inclusions, and distribute them to enable development of highly fracture-resistant refined weld metal microstructures. It may be wiser to avoid the rich and lean ends for these microalloy additions, except N, which should be held at the lean end, preferably much below 80 ppm (0.008 wt-%). The balanced Ti, B, Al, O, and N additions offered nearly a 100°C shift in lowering the Charpy V-notch (CVN) test temperature for either 28 or 100 J absorbed energy. Dilatometric evaluations of reheated weld metals showed that 1) the balanced Ti, B, Al, O, and N additions lowered the actual TS temperature by about 60°C compared to the calculated austenite-to-ferrite transformation temperature obtained from the constitutional equation; 2) N with more than 100 ppm (0.010 wt-%) effectively nullified the beneficial effects of Ti, B, and Al additions in lowering the transformation temperature; and 3) at N content much below 80 ppm (0.008 wt-%), both a lower TS temperature and a narrow start-to-finish (TS–Tf) temperature range helped in achieving exceptional weld metal CVN impact toughness.

Model description of hydrogen-induced damage evolution in high-strength steel weld metal based on results of a novel test method

In this paper, the development of a novel method for testing welded tensile specimens under two-stage external tensile loading is presented. The test method is intended to investigate the susceptibility of submerged arc welded high-strength steel specimens of type S690QL-S3Ni2.5CrMo to hydrogen-induced damage. Multiple cracking events within one specimen prove that the locally prevailing boundary conditions decisively determine the hydrogen-induced damage sequences.By means of SEM and EBSD analyses on specimens after test completion, interrelationships about the microstructural damage behavior are being examined. The crack tip environments are of particular importance here, since complex stress and strain conditions tend to cause hydrogen accumulation and further propagation of inter- and transgranular cracks here. In the vicinity of crack tips, retained austenite is of special importance. This metastable phase might undergo a deformation-induced transformation into crack-sensitive martensite and simultaneously release high local hydrogen contents as a former hydrogen trap. Finally, a model description including various sections of the stress- and hydrogen-induced damage evolution is derived from the empirical-analytical results.

The Toughness of High-Strength Steel Weld Metals

Low-temperature phase transformation (LTPT) welding consumables are a new class of welding wires developed to mitigate hydrogen-induced cracking in the welding of high-strength steels without preheating or postweld heat treatment. LTPT weld metals have a high strength, but their toughness needs further investigation. LTPT weld metals predominately contain a martensite microstructure, which is necessary to achieve high strength; however, martensitic weld metals containing oxide inclusions have relatively poor toughness. Three welding processes — gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and hot wire GTAW — were investigated. Optical microscopy, scanning electron microscopes, and transmission electron microscopes were employed for characterization. The role of the shielding gas in the formation of oxide inclusions in LTPT weld metals was investigated. The formation of oxide inclusions in the weld metals was related to the CO2 in the shielding gas. When 100% Ar or a pure inert shielding gas mixture was used for all three welding processes, oxide inclusions were greatly reduced, and the weld metal toughness improved considerably, matching the base metal toughness. The mechanism by which inclusions promote fracture propagation in the weld metal was proposed.

Model Description of Hydrogen-Induced Damage Evolution in High-Strength Steel Weld Metal Based on Results of a Novel Test Method

Model Description of Hydrogen-Induced Damage Evolution in High-Strength Steel Weld Metal Based on Results of a Novel Test Method

Effectsof Ti on Microstructure, Mechanical Properties and Corrosion Behavior of High-Strength Steel Weld Metals for Offshore Structures

Effectsof Ti on Microstructure, Mechanical Properties and Corrosion Behavior of High-Strength Steel Weld Metals for Offshore Structures

Microstructure and impact toughness of high strength steel weld metals deposited by MCAW-RE process using different shielding gases

Microstructure and impact toughness of high strength steel weld metals deposited by MCAW-RE process using different shielding gases

Study on toughening mechanism of Ti on weld metal of high strength steel

The effect of Ti element on acicular ferrite microstructure of high strength steel weld was studied by scanning electron microscope(SEM), Transmission electron microscopy(TEM) and EDX spectrum analysis. The results show that Ti element content in a certain range can promote the precipitation of acicular ferrite in high strength steel weld metal. The increase of Ti content in the weld makes the Ti-rich inclusions increase, which is conducive to the formation of acicular ferrite. Charpy impact test results show that with the increase of Ti content, the impact toughness of weld metal increases first and then decreases. The tensile test results show that the tensile strength of weld metal increases and the elongation decreases with the increase of Ti content. There are high density dislocations and M-A components in acicular ferrite. M-A elements hinder the crack growth and improve the impact toughness of weld metal. When the Ti content is 0.253%, the impact energy of the weld metal is 155 J at-60 °C, and the impact toughness is the best.

Microstructural characterization and mechanical properties of high-strength steel weld metals obtained by GMAW process with rotating electrode (GMAW-RE)

The GMAW process with rotating electrode (GMAW-RE) is a variation of the conventional GMAW process, where the electrode is submitted to a rotating movement, with pre-established rotation diameter and frequency. The method improves the lateral fusion along the sidewalls and contributes to the improvement of narrow gap welding, with significant gains in costs and productivity due to the reduced volume of the deposited weld metal. Although there are some studies about operational characteristics of the process, the literature involving mechanical properties of welded joints remains limited, requiring more experimental evidence to confirm the potential of this process for replacement of conventional GMAW process in industry. This work shows comparative analysis of mechanical and microstructural properties of high-strength steel weld metals obtained by the conventional GMAW and GMAW-RE processes. The weld metals obtained by multipass welding performed in steel plates with dimensions of 500 × 300 × 10 mm were submitted to Charpy-V notch, microhardness tests and metallographic examination from samples removed transversally to the weld bead. The residual stresses were analyzed using X-ray diffraction method at the top surface of the welded joints in the longitudinal and transverse directions of the weld bead. The results showed that the GMAW-RE welding procedure attained the approved standard according to the ASME IX Code, despite using materials with different mechanical strengths once the rupture of the test specimen after tension test has occurred on the base metal 7.4 mm far from fusion line. The joints did not show evidence of lack of fusion along the sidewalls, as verified by the bend tests and metallographic examination. In addition, the GMAW-RE process provided a weld metal with slightly superior mechanical properties compared to the GMAW process due to the more refined microstructure observed with higher amount of acicular ferrite, which favors the impact behavior. The association of higher productivity, reduced costs, lower residual stresses and adequate mechanical properties indicates that GMAW-RE process has a potential alternative for replacement of the GMAW in industrial applications.

Microstructure and mechanical properties of ultralow carbon high-strength steel weld metals with or without Cu-Nb addition

Two types of ultralow carbon steel weld metals (with and without added Cu-Nb) were prepared using gas metal arc welding (GMAW) to investigate the correlation between the microstructure and mechanical properties of weld metals. The results of microstructure characterization showed that the weld metal without Cu-Nb was mainly composed of acicular ferrite (AF), lath bainite (LB), and granular bainite (GB). In contrast, adding Cu-Nb to the weld metal caused an evident transformation of martensite and grain coarsening. Both weld metals had a high tensile strength (more than 950 MPa) and more than 17% elongation; however, their values of toughness deviated greatly, with a difference of approximately 40 J at −50°C. Analysis of the morphologies of the fracture surfaces and secondary cracks further revealed the correlation between the microstructure and mechanical properties. The effects of adding Cu and Nb on the microstructure and mechanical properties of the weld metal are discussed; the indication is that adding Cu-Nb increases the hardenability and grain size of the weld metal and thus deteriorates the toughness.

Effect of CeO2 on microstructures and mechanical properties of welded high-strength steel weld metal

The effect of CeO2 on the microstructures and mechanical properties of welded high-strength steel weld metal was investigated by optical microscopy, scanning electron microscopy and mechanical testing. The results demonstrate that the addition of CeO2 can promote the refinement and spheroidization of inclusions, refine the grains, and form acicular ferrites in the weld metals. When the addition of CeO2 increased from 0% to 3%, the content of bainites gradually decreased, and the lath structure disappeared. The formation of the acicular ferrite ductile phase inhibited the formation of bainites and other strengthened phases in the weld metals, and the microstructure of acicular ferrites was excessive. When the CeO2 content was 1%, the tensile strength was 903 MPa, the yield strength was 848 MPa, and the low-temperature impact toughness was 61 J at −40 °C. When the CeO2 content was 3%, the low-temperature impact toughness of the weld metal gradually increased to a maximum value of 71 J. The weld metal had the highest toughness but the lowest strength. The addition of CeO2 changed the pattern of crack generation, and the fracture mode changed from quasi-cleavage fractures to ductile fractures with dimples. To achieve a good matching of strength and toughness, the wire No. 2 with 1% CeO2 had the best comprehensive mechanical properties.

Influence of rotation frequency and rotation diameter on mechanical properties and microstructure of weld metal produced by MCAW-RE

The MCAW process with rotating electrode (MCAW-RE) is a variation of the conventional gas metal arc welding process, which a metal-cored wire is submitted to a rotational movement along a pre-established diameter. This process enhances narrow gap welding, since the rotational motion of the electrode allows the electric arc to reach peripheral regions of the groove, preventing lack of fusion on the sidewall. As a result, reduced costs and superior productivity compared with the conventional GMAW process are obtained. The limited literature about this process is focused on the operational characteristics, and works studying the mechanical properties are not available. Thus, this work evaluates the mechanical and microstructural properties of weld metals obtained by the MCAW-RE process in order to allow a decision about its technical feasibility to replace the GMAW process in industry. Initially, beads on plate weld tests were performed with varying rotation frequency and rotation diameter, in order to determine the parameters to be used in welded joints. High-strength steel weld metals were obtained by welding performed in steel plates with dimensions of 500 × 300 × 10 mm. Mechanical tests and metallographic examination were carried out in samples removed transversally to the weld bead. The results showed that the impact toughness of the weld metals can achieve the requirements for several industrial applications. The results showed that the GMAW process with rotating electrode-cored wire has a high potential for replacement of the GMAW in industrial applications.

Study on Improvement of Welding Technology and Toughening Mechanism of Zr on Weld Metal of Q960 Steel.

Q960 high-strength steel is widely used in pressure vessels, bridges, offshore platforms and other important steel structural components because of its high strength and good plastic toughness, but alloy elements added to this kind of steel have strong hardenability, especially after welding, so the strength and toughness cannot meet the requirements, which limits its application in a wider range. In this paper, from the point of view of the metallurgical treatment of the weld, the goal is to improve the strength and toughness of the Q960 high strength steel weld metal In order to analyze the influence of Zr on the welding process of Q960 steel and the strengthening and toughening effect of weld metal, this paper takes Fe-Mn-Mo-Cr-Ni as the main alloy system, BaF2-CaF2-Al-Mg as the basic slag system, and adopts the method of melting consumable electrode self-shielded for welding, and analyzes the welding process, microstructure, tensile property and impact toughness of the welded joint. The experimental results show that when the weld metal contains 0.0061% Zr, the minimum spatter rate is only 7%, the maximum slag removal rate is 95%, the maximum hardness is 357HV, the maximum elongation is 34%, and the impact toughness is the highest. At this time, the acicular ferrite content in the weld microstructure is the highest, and there is a certain amount of equiaxed fine-grained ferrite, and the content of proeutectoid ferrite is the least, which effectively improves the strength and toughness of the weld metal.

Influence of Chemical Composition on the Mechanical and Microstructural Properties of High Strength Steel Weld Metals Submitted to PWHT

The development of new filler metals for offshore industry is challenging because high strength and toughness levels are required after post-welding heat treatment (PWHT) is applied to reduce residual stresses. The higher chromium contents added to the chemical composition of welding consumables to attain the required ultimate tensile strength are usually associated with reduced toughness. This work presents a comparative analysis of the behavior of two high strength steel weld metals with different Cr–Mo and Mn–Ni additions that were submitted to PWHT. Weld metals obtained by shielded metal arc welding process were evaluated using mechanical tests (Charpy-V notch and Vickers microhardness) and microstructural analysis (scanning electron microscopy and electron backscattered diffraction) conducted in samples removed from the center line of weld deposits, both in the as-welded and heat-treated (600 °C for 1 h) conditions. Although similar results were obtained in the as-welded condition, different behaviors were observed after PWHT. While impact toughness for Cr–Mo additions was reduced by carbide precipitation, as predicted by thermo-calc simulation, weld metal based on Ni–Mn addition exhibited improvements after PWHT because the predominantly martensite microstructure was tempered. This makes the latter more appropriate for weldments submitted to PWHT.

Nucleation Behavior of Acicular Ferrite in 1 GPa Class High Strength Steel Weld Metal

Nucleation Behavior of Acicular Ferrite in 1 GPa Class High Strength Steel Weld Metal

Influence of welding procedure and PWHT on HSLA steel weld metals

The development of consumables for welding of high strength steels represents a continuous challenge taking into account the great variety of alloy systems. In this regard, there are many applications, such as offshore structures, where the welding is still preferably done by the SMAW process. In order to evaluate the properties of weld metals obtained by other processes with higher productivity, the present work presents a comparative analysis between the mechanical properties of high strength steel weld metals obtained by shielded metal arc (SMAW) and gas metal arc (GMAW) welding processes. Multipass welding by SMAW and GMAW processes was performed with preheating of 200°C, in 750×150×19mm plates. After welding, a post weld heat treatment (PWHT) at 600°C for 1h was performed and this condition was compared to the as welded one. Mechanical tests and metallographic examination by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were performed for mechanical and microstructural characterization. Thermodynamic calculations were also performed by using Thermo-Calc software, in order to evaluate the occurrence of carbides as a consequence of the PWHT.Although presenting impact toughness behavior slightly different due to the chemical composition and carbide precipitates, as predicted by computational simulation, both processes showed a good relationship between mechanical strength and impact toughness for all analyzed conditions, even after PWHT.Based on this scenario, it can be inferred that GMAW process can be applied as an interesting alternative for welding of high strength steels, once this process promotes a significant improvement in productivity with good quality.