High Strength Steel Welds Research Articles

Role of Heat Input and Ti Addition on Microstructure Evolution, Mechanical Property, and Corrosion Behavior of Welded Joint Produced by Hybrid Laser-Arc Welding of High-Strength Low Alloy Steel

Role of Heat Input and Ti Addition on Microstructure Evolution, Mechanical Property, and Corrosion Behavior of Welded Joint Produced by Hybrid Laser-Arc Welding of High-Strength Low Alloy Steel

Effect of holding time on strain relaxation in high-strength low-alloy steel welds: An in-situ neutron diffraction approach

In-situ neutron diffraction was employed in the present investigation to study the effects of holding time on the relaxation of residual strains during Post-Weld Heat Treatment (PWHT) for multi-pass High-Strength Low-Alloy (HSLA) steel welds. Different holding time intervals (0.5, 1 and 3 h) were utilized to evaluate and monitor the residual strain relaxation during PWHT. It was found that the holding time has little effects on the strain relaxations as strain relaxations occurs predominantly during the reheating stage of the heat treatment (~80% of strain relaxation). A similar trend is observed for all three holding time arrangements with the high strain relaxation during the reheating stage followed by linear strain relief may confirm the hypothesis that creep (primary and secondary) is responsible for strain relaxation during PWHT. It further confirms the selected soaking temperature of 600 °C has a significant effect on the stress relaxation.This finding is in line with the microstructural characterization studies indicating the formation of sub-grains through polygonization in the Heat Affected Zone (HAZ) and Weld Metal (WM) of the heat treated joints. Ex-situ neutron diffraction which was conducted after PWHT confirmed the in-situ neutron diffraction results and showed slightly higher level of residual stresses for the heat-treated specimen with 1/2 hour holding time (~32% of yield strength of the WM). Furthermore, the tensile, hardness and Charpy impact test results support the notion that a shorter holding time is more beneficial, not only for the cost issues but also for the microstructural and mechanical properties of the welded joints. The findings of this study can be used to optimize the current PWHT codes and standards. It can also be used for the validation studies of the finite element modeling of this process.

Mechanisms of an innovative hybrid arc welding process in enhancing joint penetration and weld property control through resistive and induction heat

Low costs (material, energy and time), high joint properties are the eternal pursuit of modern welding. In this paper, mechanisms of an innovative high frequency electric cooperated arc welding (HFAW) in enhancing welding productivity (joint penetration) and weld property control were comprehensively investigated. The process properties and weld mechanisms of this method were systematically compared with that of the traditional GMAW welding under typical process parameters. The results showed that 4.8 mm joint with an large aspect ratio of 4 was achieved by single pass HFAW at a high welding speed (15 mm/s) and a low welding heat input (reduced 1/3 than the traditional GMAW). The research on weld property control shows that the microstructure of weld zone and heat affected zone (HAZ) in the HFAW joint was much smaller than that in the GMAW joint under optimal parameters. The width of each zone in the HAZ, thermal cycle parameters such as elevated temperature holding time and cooling rate can be regulated independently by the high frequency electric heat input ratio. Such regulation is of great significance for high strength steel welding, which needs to control the welding thermal cycle process accurately. Combined with three-dimensional solid reconstruction of liquid filler metal, the mechanism of the HFAW in enhancing joint penetration was demonstrated. An interesting “self-tracking heating” of the high frequency current was found. The cutting-edge of the liquid metal was violently heated and more than half of the weld in thickness direction was achieved by a novel ultra-speed “interfacial tension driving penetrating” weld forming mechanism, which promises the HFAW high welding speed and large aspect ratio on the premise of satisfactory welding quality.

Laser welding of 4330V steel with a micro-additive of vanadium

This article presents the results of a test of laser welding of high-strength low-alloy steel with a micro-additive of vanadium. Steel 4330V is a delivery material after heat treatment. Welded joint was made by laser welding using a TruDisk 12002 disc laser. As a result of welding, a joint was formed which was subjected to visual and penetration tests from the face side, as well as macro and microscopic tests. Impact tests were carried out at reduced temperature in the weld and in the heat affected zone (HAZ). The resulting joint was also subjected to the Vickers hardness test, bend test and the tensile strength test. This research show how the low-alloy high-strength material behaves during welding without processing before and after welding. In results after welding show incomplete penetration from the root side. No cracks on the weld face. In HAZ hardness was of 520HV0.5 and tensile strength of joint was on level1077MPa.

Investigation of Process Stability and Weld Quality of Underwater Wet Flux-Cored Arc Welding of Low-Alloy High-Strength Steel with Oxy-Rutile Wire

Abstract The paper described the experimental findings of underwater wet welding of E40 steel using self-shielded flux-cored wire with a TiO2-FeO-MnO slag system. The arc stability, weld quality and corrosion resistance with different heat inputs were studied. The results showed that the wet welding process of the designed wire displayed good operability in the range of investigated parameters. The microstructure and mechanical properties of the weld metal depended on the heat input. Due to the high fraction of acicular ferrite in the weld metal, the mechanical properties of the weld metal under low heat input had better tensile strength and impact toughness. Fracture morphologies at low heat input had uniform and small dimples, which exhibited a ductile characteristic. The diffusible hydrogen content in the deposited metal obtained at a heat input of 26 kJ/cm significantly reduced to 14.6 ml/100g due to the combined effects of Fe2O3 addition and the slow solidification rate of molten metal. The microstructure also had a significant effect on the corrosion resistance of the weld metal. The weld metal with high proportions of acicular ferrite at low heat input exhibited the lowest corrosion rate, while the base metal possessed a reduced corrosion resistance. These results were helpful to promote the application of low alloy high strength steel in the marine fields.

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

AHSS welding using undermatching filler wires and process advantages with P-GMAW

The major challenge during welding of advanced high strength steels (AHSS) is finding an appropriate low cost filler wire which minimizes the softening in the heat affected zone (HAZ). The fabricators always prefer undermatching wires to join the thinner sections. This study reports the differences in the microstructure and mechanical properties of Ti-Nb microalloyed steel prior welded using pulse gas metal arc welding (P-GMAW) and standard gas metal arc welding (GMAW). The results indicate that the microalloyed steel welded using P-GMAW has inherent advantage over the standard GMAW. The pulses intensified the vibration perturbation in the weld puddle which cause microstructural refining and increased formation of the acicular ferrite (AF) constituent. The higher percentage of AF present in the weldment resisted propagation of the crack during static tensile test. Microhardness, ultimate tensile strength and joint efficiency during P-GMAW are much higher than the samples welded by standard GMAW.

Acquisition of HSLA steel weld joints with excellent mechanical performance through flash butt welding physical simulation

Flash butt welding (FBW) of high-strength low-alloy steel was physically simulated by the thermomechanical simulator and the influence of upset allowance (δu) on the microstructural and mechanical evolution of the welds was revealed. A moderate increase in δu from 3.5 to 6.5 mm will increase the amount of acicular ferrite and bainite ferrite with finer size in the weld zone, and also provide sufficient plastic deformation and proper dynamic recrystallization, paving the way to obtain excellent strength and plasticity being compatible with that of base metal. The findings will provide valuable references for the practical FBW process.

Thermal induced residual stress and microstructural constituents of dissimilar S690QT high-strength steels and 316L austenitic stainless steel weld joints

The effect of thermal cycle on the residual stress, microstructural constituents, and alloying elements composition of dissimilar S690QT and 316L austenite stainless steel was studied. Finite element model (FEM) using ANSYS 19.1 software and an experimental investigation using gas metal arc welding (GMAW) process with fully austenite filler wire were applied to developed thermal cycle and evaluate residual stress in the heat-affected zone of both materials. The experimental data were recorded using a thermal-cycle sensor (TCS) and x-ray diffraction technique. A microstructural investigation was done using Scanning electron microscopy (SEM) and Energy-Dispersive x-ray Spectroscopy (EDS). The thermal cycle showed the maximum temperature (T max) in the HAZ of 316L side (850 °C) at a distance of 7 mm away from the centreline of the weld compare to S690QT side. The magnitude of tensile residual stresses in the 316L side decreased as welding heat input increased. The maximum residual stresses were observed on the S690QT side (700 MPa). Microstructural investigations revealed the formation of Bainite, and some retained of austenite at the temperature of 800 °C in the coarse grain heat-affected zone (CGHAZ) of S690QT. On 316L side, some grain boundary austenite (GBA), intragranular austenite (IGA), and carbides were observed in the CGHAZ. Compared to the initial microstructure of both materials, a slightly increase of Mn, Cr, and Si were observed at the respective values of 1.90%, 1.25%, and 0.40% on the S690QT side compared to the BM. For 316L side, it indicated an increase of Cr (26%), Mo (5.69%), and Ni (17%) in the alloying element composition compared to the BM. Applying 10 kJ cm−1 of heat input produced an excellent mechanical property and reduced the formation of carbide, inter-granular corrosion in the microstructure of 316L side.

Effect of the Welding Thermal Cycles Based on Simulated Heat Affected Zone of S1300 Ultrahigh Strength Steel

In the automotive industry there is an increasing demand for the wider application of high strength steels due to their favourable mechanical properties. The steel producers continuously developing new generations of high strength steels to insure higher strength and toughness properties. Since in most cases these steels are joined in welded structures, great attention must be taken to their weldability. The weldability of high strength steels has still challenges which are as follows: cold cracking sensitivity; reduction of strength and toughness of heat affected zone (HAZ); filler metal selection. Because the mechanical properties of ultrahigh strength steels are provided by using various alloying elements, micro alloys, and by different metallurgical methods, the steels may lose their outstanding properties during welding. In real welded joints the critical parts of the HAZ have small extent so their properties can be limitedly analysed by conventional material testing methods. With the help of physical simulators, the different parts of the heat affected zone can be produced in an adequate size for subsequent tests. In our research work the weldability, especially the HAZ properties of an ultrahigh strength structural steel (Rp0.2 = 1300 MPa) were investigated on thermal simulated samples with the help of Gleeble 3500 physical simulator. Three relevant technological variants for gas metal arc welding (GMAW), t8/5 = 5 s, 15 s and 30 s were applied during the HAZ simulations in the selected coarse-grained (CGHAZ), intercritical (ICHAZ) and intercritically reheated coarse-grained (ICCGHAZ) zones. Both the microstructure was studied by optical microscope and the mechanical properties were analysed by Vickers hardness tests and Charpy V-notch impact tests at -40 °C. According to the results the investigated ultrahigh strength steel was softened on account of the welding heat cycles, besides that the strength of the investigated ultrahigh strength steel can be better with the application of shorter t8/5 cooling time.

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

Hydrogen-Assisted Cracking in GMA Welding of High-Strength Structural Steel—A New Look into This Issue at Narrow Groove

Modern arc processes, such as the modified spray arc (Mod. SA), have been developed for gas metal arc welding of high-strength structural steels with which even narrow weld seams can be welded. High-strength joints are subjected to increasingly stringent requirements in terms of welding processing and the resulting component performance. In the present work, this challenge is to be met by clarifying the influences on hydrogen-assisted cracking (HAC) in a high-strength structural steel S960QL. Adapted samples analogous to the self-restraint TEKKEN test are used and analyzed with respect to crack formation, microstructure, diffusible hydrogen concentration and residual stresses. The variation of the seam opening angle of the test seams is between 30° and 60°. To prevent HAC, the effectiveness of a dehydrogenation heat treatment (DHT) from the welding heat is investigated. As a result, the weld metals produced at reduced weld opening angle show slightly higher hydrogen concentrations on average. In addition, increased micro- as well as macro-crack formation can be observed on these weld metal samples. On all samples without DHT, cracks in the root notch occur due to HAC, which can be prevented by DHT immediately after welding.

A study on the stress corrosion mechanism of microstructures in a heat-affected zone of high-strength steel weldment in artificial seawater

This short communication investigate the relationship of mechanical properties and stress corrosion cracking (SCC) behavior of microstructures in a heat-affected zone of high strength low-alloy steel in artificial seawater. It showed that SCC susceptibilities of different microstructure were controlled by electrochemical corrosion behavior and grain size, which is decided by the SCC mechanism.

Hydrogen permeation and distribution at a high-strength X80 steel weld under stressing conditions and the implication on pipeline failure

Hydrogen permeation and distribution at pipeline welds is critical to integrity maintenance of the pipelines, especially for those made of high-strength steels. The situation becomes even more important under stressing conditions. In this work, metallographic characterization and micro-hardness measurements were conducted at an X80 steel weld. Potentiodynamic polarization and electrochemical hydrogen permeation testing were performance at various zones at the weld, along with numerical modeling of hydrogen distribution at the zones. The X80 steel contains a microstructure of bainite bundles and polygonal ferrite. There are more polygonal ferrite, fewer bainite and some segregated cementite at heat-affected zone (HAZ). The weld metal is featured with acicular ferrite and some grain boundary ferrite. HAZ softening occurs at the weld. The hardness of the weld metal, HAZ and base steel is about 290, 248 and 261 HV0.2, respectively. There is the greatest corrosion current density, i.e., corrosion rate, at HAZ under both elastic and plastic stresses. An applied stress further increases the corrosion current density. Under the plastic stress of 1.1σys (σys is yield strength), the corrosion current densities of HAZ, base steel and weld metal are 41.04, 17.03 and 25.49 μA/cm2, respectively. There are always the greatest hydrogen trapping density and the smallest hydrogen diffusivity at HAZ. Hydrogen, once penetrating the welded steel, tends to accumulate at the HAZ, compared with other two zones. When the welded steel is under stresses, especially a plastic stress (i.e., 1.1σys), the hydrogen diffusivity and permeability decrease, while the subsurface hydrogen concentration and hydrogen trapping density increase remarkably. Plastic deformation favors the hydrogen permeation and trapping at weld, especially the HAZ, to elevate the susceptibility to hydrogen damage. The hydrogen distribution at different welding zones can be evaluated and determined by a developed modeling method.

Multiaxial low cycle fatigue of notched 10CrNi3MoV steel and its undermatched welds

It is a fundamental step to quantify the multiaxial fatigue damage considering the complex service conditions for notched components or welded structures. In our study, multiaxial Low Cycle Fatigue (LCF) tests of notched specimens were conducted on 10CrNi3MoV high strength steel and related undermatched welds under proportional and non-proportional cyclic loadings. The characteristic states of normal/shear stress, strain and energy around notch roots are analyzed considering the elasto-plastic material behavior under low cyclic loadings by the cyclic plasticity model. The predicted fatigue life curves of the test data were constructed by five strain-based and energy-based parameters combining with the critical plane approach and notch Theory of Critical Distance (TCD). According to Smith-Watson-Topper (SWT) damage parameters definitions, the paper proposed a simplified SWT model incorporating the effect of non-proportional loading, notch energy concentration characteristics and cyclic hardening behaviors for the LCF assessment of notch specimens. The proposed model shows good agreements between predictions and test data by comparing different multiaxial fatigue damage models for notch specimens.

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.

Mechanical Properties and Structural State of Rolled Sheets from High-Strength Wear-Resistant Weldable Steel H500 Magstrong®

A process of manufacturing of rolled sheets from a new high-strength wear-resistant weldable steel H500 MAGSTRONG® with wear resistance, strength and impact toughness parameters at negative temperatures not inferior to those of the best world counterparts is described. Transmission electron microscopy is used to study the structure of a sheet with a thickness of 12 mm formed as a result of hot rolling and quenching.

Effect of chemical composition of welding consumable on slag formation and corrosion resistance

In the automotive industry, it is essential to reduce the weight of the car body to improve fuel efficiency and reduce CO2 gas emissions. As such, the application of advanced high-strength steels is rapidly increasing. However, in the case of gas metal arc (GMA) welding of advanced high-strength steels (AHSS), slag particles are observed to form on the weld surface resulting in poor corrosion resistance. The presence of slag particles on the weld also affects mechanical performance. This paper focuses on the degradation of corrosion resistance due to these slag particles. Current methods to decrease slag islands are costly as they attempt (1) to better protect the weld pool by decreasing the content of oxygen-containing ingredients or increasing argon in the shielding gas and (2) to mechanically clean the weld surface using processes such as shot blasting after gas metal arc welding (GMAW). In this study, the amount of slag was reduced by adjusting the chemical composition of welding consumables. Silicon was decreased to minimize silica/silicate formation, and sulfur was adjusted to affect the surface tension balance of the molten pool. Slag particles were observed to flow along the welding direction to solidify into a large particle in the weld crater that could be removed easily. In a separate consumable, Si and Mn contents were adjusted to form Mn3O4 and SiO2 slag. The use of these two welding consumables reduced the amount of slags, which improved the corrosion resistance. It is not the intent of this paper to compare the performance of these two experimental consumables, however.

Dynamic Compression Properties of the Resistance Spot Welding of High Strength Steels under Varying Temperature Conditions

In this paper, we have studied the dynamic compression performance of the RSW of QP980 steel and TRIP800 steel by using a split Hopkinson pressure bar (SHPB), and we have also examined the fracture mode of the two research objects. It is found that the spot welding zone is primarily composed of the martensite structure, and there is a sparse defect of crystal structure adjacent to the center of nugget. In addition, there are evident gaps between the plates on both sides of the spot welding zone. Through the measurement of the microhardness of the two grade steel, it is found that the average hardness of the RSW of QP980 steel is higher than that of TRIP800 steel. There is a softening region in the interface of the heat affected zone and the substrate zone. The dynamic compression experiments are carried out on the RSW of QP980 steel and TRIP800 steel under 200°C and 300°C conditions, and it is found that the strain rate would increase with the rising temperature, but the compressive strength would experience declines. Furthermore, the sparse defects of crystal structure adjacent to the center of nugget would lead to stress rebound when the specimen is compressed. Moreover, through the observation of the fracture surface of the recovered specimens, it is found that the fracture of the nugget is brittle, whereas the fracture mode of the sample is more complicated. In addition, the fracture surface features a number of “river pattern” cleavage facets, and there are very few dimples of ductile tearing. This study is expected to have huge implications to the safety of vehicle body under high‐speed impact.