High Strength Steel Welds Research Articles

Numerical modeling of liquid metal embrittlement initiation during resistance spot welding of third generation advanced high strength steel – Effect of welding schedule and electrode alignment

Third generation (GEN3) advanced high-strength steels are increasingly used to reduce vehicle body structure weight for improved fuel economy. Zinc-induced liquid metal embrittlement (LME) has become a prevalent challenge when these steels are welded by resistance spot welding (RSW). In the literature, various numerical models have been developed to study LME during RSW of GEN3 steels. Those models tend to have a limited utility in predicting how various factors such as RSW parameters affect LME cracking. In this study, a novel LME calculation method has been developed by integrating an electro-thermo-mechanical finite element model of RSW process with an LME ratio for crack initiation established from hot tensile testing data. The onset of different types of LME cracking is tracked throughout the weld region over the entire course of RSW including the final cooling stage after electrode retraction. The model is validated using an existing set of literature data that involves different welding schedules, electrode geometries and electrode misalignments. The local temperature and stress conditions during RSW are calculated and used to understand how different welding parameters affect the severity of LME cracking. It is found that electrode misalignment exacerbates crack initiation on outer surfaces of the spot weld due to the tensile stress arisen from the off-centered squeeze force as well as the reduced surface cooling to electrodes. Initiation of cracks between the steel sheets, taking place mainly after electrode retraction, is not significantly affected by the welding schedule and the electrode tip diameter.

Research on the Causes and Treatment of Weld Zone Fracture in Cold Rolled High Strength Steel Rolling Process

In response to the poor quality of laser welding of cold-rolled advanced high-strength steel and the problem of easy fracture at the weld seam during the rolling process, the reasons for the fracture at the weld seam were first analysed using scanning electron microscopy and other equipment, to clarify the fracture characteristics and organizational distribution. Combined with the characterization results of mechanical properties, the reasons for the fracture at the weld seam during the rolling process were elucidated; Then, the influence of welding process on weld quality is studied from four aspects: laser power, welding speed, pre heat power, and post heat power; Based on the above analysis, a typical cold rolled advanced high-strength steel laser welding technology has been developed. By optimizing welding parameters such as welding power, speed, and preheating before and after, the quality of the weld seam and the cup protrusion effect have been ensured. At the same time, a reasonable rolling process optimization plan has been proposed; After applying the research results to the site, the quality of the weld seam has been significantly improved, and the occurrence rate of band breakage at the high-strength steel weld seam has decreased from an average of 3.6% per month to 0.13%. The band breakage defect at the weld seam has been effectively treated.

Effect of microstructure on hydrogen embrittlement and hydrogen-induced cracking behaviour of a high-strength pipeline steel weldment

Hydrogen embrittlement (HE) and hydrogen-induced cracking (HIC) behaviour of a X65 steel pipeline weldment were investigated using slow strain rate tensile (SSRT) testing of specimens that were specifically extracted from different zones of the weldment (i.e., weld metal (WM), heat-affected zone (HAZ), and base metal (BM)). The WM was found to be the most susceptible zone to HE and HIC, while BM the least. Analysis of microstructure, fracture surface, secondary crack formation, and mechanical behaviour revealed that the high HE susceptibility of WM is correlated to microstructural features including Ti-rich inclusions, martensite/austenite (M/A) constituents, and prior austenite grain boundaries (PAGBs).

Micro-Alloying Effect on the Inter-Critical Grain Coarsened Heat Affected Zone of a S355 Steel Welded Joint

The inter-critical heat affected zone (ICHAZ) appears to be one of the most brittle sections in the welding of high-strength micro-alloyed steels (HSLA). Following repeated heating cycles in in with temperature ranging Ac1 /Ac3, the ICHAZ will face with an evident toughness and fatigue behavior reduction especially due to martensite-austenite constituent (MA) formation. Microalloying in high strength steels causes the generation of some phases in the matrix able to increase the mechanical properties of the joint. In this paper we report an investigation related to 1000 ppm vanadium addition in the welded joint of a structural S355 steel. The inter-critical zone of ta double pass welded joint is here reproduced by dilatometer, with second peak temperature ranging 720°C-790°C. The residual austenite dependence on inter-critical temperature is analyzed and related to the hardness behavior.

Numerical design calculation of the high-strength steel welds

This study focused on the design of fillet welds fabricated using high-strength steel (HSS). Herein, we present a numerical design calculation (NDC) method for assessing weld strength using the regular inclined shell element model (RISEM) in the finite element method (FEM). The NDC uses the FEM to design joints according to standardised procedures. The inclined shell element in the RISEM represents the geometry and stiffness of the welds, which controls the stresses in the plane. We recommend using a common inclined shell element with rigid links to accurately represent the geometry and rigidity of fillet welds. A new strength criterion is proposed based on the stresses on the inclined shell element, using the maximum equivalent stress as an indicator. An experiment was conducted on the transverse fillet lap-welded connection from the S700 MC Plus steel plate and OK AristoRod 13.12 electrode at room temperature. The deformation capacity of the welded connection was measured via a non-contact process using the digital image correlation (DIC) technique. This method was validated by comparing the RISEM and test results using finite element (FE) simulations. Additionally, the weld resistance computed from the analytical model of prEN 1993–1–8:2020 was in good agreement.

Influence of shielding gas on filler wire mixing at laser hybrid welding of thick high strength steels

The laser hybrid welding process offers many advantages during welding of thick-walled steels, such as the increased penetration depth and, thus, reduced number of layers, reduced heat input and decreased distortion compared to arc-based welding processes. Especially, when welding high-strength steels (HSS), the reduced heat input plays an essential role. However, a major challenge when laser hybrid welding of thick-walled steels is the limited filler wire mixing over the entire seam thickness, which can lead to changed mechanical properties over the depth. To overcome this issue, the add of oxygen into the shielding gas and its influence on the filler wire mixing and finally to the mechanical properties were investigated within this work. Therefore, 20 mm thick S690QL steels were laser hybrid welded in a single-pass. A contactless electromagnetic backing was used to avoid sagging. The admixture of oxygen was performed by a gas mixer, where the oxygen content was varied between 0 % and 7.2 %. The experiments were also accompanied by laser beam welding tests in steel/glass configuration, where the melt pool geometry as well as the melt flow characteristics were captured by a high-speed camera. It can be concluded, that adding of approx. 4 % oxygen into the shielding gas had a positive effect on the filler wire mixing, were up to a depth of 18 mm elements of the filler wire could be observed.

Solute Enrichment in the Fusion Zone during Resistance Spot Welding of a Third Generation Advanced High Strength Steel

Resistance spot welding is a critical joining technique in automobile assembly. The load carrying properties of spot welds are generally accepted to correlate with weld diameter, which increases with increasing weld current or duration. The formation of a softened layer, or weld halo, surrounding the fusion zone in a spot-welded third generation (Gen3) advanced high strength steel (AHSS) was recently reported in the literature. To optimize weld performance by schedule design, it is necessary to understand the halo formation characteristics and potential impacts. Accordingly, welding of a Gen3 AHSS was performed using weld times between 130 – 1300 ms. Microhardness mapping characterized weld microhardness and the evolution of the halo during welding. Electron probe microanalysis and timeof-flight secondary ion mass spectrometry enabled measurement of solute distributions through the weld halo, while scanning electron microscopy was used for microstructural characterization. The solidified structure was examined using light-optical microscopy, and with the microhardness and compositional data, used to infer the mechanism by which the halo forms during welding. It was found that the halo develops due to solute rejection from a cellular solidification front that advances towards the center of the fusion zone while weld current is applied. Extended weld times increase the size of the weld halo and the solute content of the inner fusion zone. The decrease in weld halo microhardness and the increase in inner fusion zone microhardness is largely explained by the changes in local carbon content associated with halo formation.

Numerical investigation of sidewall penetration in narrow gap oscillating laser welding process

The lack of sidewall fusion is one of the process challenges in narrow gap laser welding. To solve this problem, beam oscillation has been applied to narrow gap laser welding. Because the laser oscillation behavior had a great influence on the sidewall penetration, a 3D heat transfer model of narrow gap oscillating laser welding of high-strength steel was established for numerical simulation. The effect of oscillation parameters on sidewall penetration was investigated by quantitatively analyzing the sidewall penetration under different oscillation parameters. The results showed that the high-temperature region of the molten pool changed periodically with the laser oscillation. As the oscillation amplitude increased from 0 mm to 1.5 mm, the molten pool cross-section shape changed from tip shape to arc shape, the peak temperature of the sidewall increased from 1857℃ to 2115℃, and the sidewall penetration also increased from 0.82 mm to 0.96 mm. As the oscillation frequency increased from 20 Hz to 100 Hz, the peak temperature of the sidewall decreased from 2036℃ to 1936℃. However, more heat was accumulated in the high frequency mode, and the value of sidewall penetration increased from 0.9 mm to 0.94 mm.

Study on the Influence of Repair Welding Process on the Microstructure and Mechanical Properties About 30CrMnSiNi2A High-Strength Steel Weld Joints

Study on the Influence of Repair Welding Process on the Microstructure and Mechanical Properties About 30CrMnSiNi2A High-Strength Steel Weld Joints

Experimental and numerical study on fatigue damage evolution of Q690D welding details

Steel structures are widely used in various types of structures, and welding details, which are fatigue-prone constructions, are typically utilized in steel constructions. In this study, regarding the high cycle fatigue performance and fatigue damage evolution behaviors of high strength steel welding details, experimental and numerical studies have been carried out on two typical types of Q690D high strength steel welding details, including butt-weld connections and cruciform load-carrying fillet weld (CLFW) connections. High cycle fatigue tests have been conducted, SN curves based on effective notch stress have been established and compared with the suggested curves in IIW specification, showing that FAT200 is more suitable for fatigue evaluation of high strength steel welding details. Fatigue damage evolution model and numerical simulation methods for Q690D welding details based on effective notch stress and continuum damage mechanic have been established and validated. Damage evolution analysis of welding details has been conducted based on the proposed numerical simulation method. The simulation method enables accurate characterization of fatigue damage locations.

Experimental investigations on composite columns: round hollow sections with embedded solid core section made of high‐strength steel

AbstractDue to price developments, steel composite columns have lost significant market shares to prefabricated reinforced concrete columns in recent years. Using high‐strength steel (HSS) in composite columns may offer a way of reviving the market for these kinds of columns. There are different ways of using HSS for composite columns, however, many are associated with the use of welds. Welding of HSS can lead to cold and hot cracks, while also causing high residual stresses which can lead to a decrease of the load bearing capacity. Hollow section composite columns with embedded solid core cross‐sections and using HSS may offer a way to solve this problem.Round hollow sections with embedded solid core as a composite column have so far only been investigated for steel grades up to S460. Within the scope of German FOSTA research project P1501, a concept for a test setup is derived to investigate hollow sections with embedded solid core as a composite column made of HSS. The experimental results will be used as the basis for further numerical studies, which will be discussed within the scope of this paper. Based on these models, parametric studies will be conducted in the future to validate design concepts.

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

Fatigue crack propagation performance of Q690 high-strength steel and butt welds

The fatigue performance of high-strength steels is an important issue in bridge engineering. In this study, fatigue crack propagation rate tests and theoretical studies of high-strength steel Q690 base material and butt welds were conducted. Two types of compact tensile (CT) specimens—one for the Q690 compact tensile specimens and the other for the butt welds—were used for the test under stress ratios of R = 0.1, 0.3, and 0.5, with a loading frequency of 15 Hz. The fatigue crack length was measured using the flexural method with an extensometer, and the load value and the corresponding cycle number in the tests were also obtained. These results were processed using the seven-point polynomial method to obtain the fitting curve of log (da/dN) to log ΔK. Finally, the modified Paris formula of Q690 was presented, and the corrected values of the material parameters C and m were determined. The test results show that the fatigue crack propagation rate of Q690, both for the compact tensile specimens and those with butt welds, increased with the stress ratio R. The fatigue crack propagation rate of Q345qD was 1.8 times higher than that of Q690 high-strength steel. In addition, the fatigue resistance of Q690 was significantly higher than that of other standard steels. The fatigue crack propagation rate of the Q690 specimens with butt welds at a low-stress amplitude was lower than that of the Q690 compact tensile specimen. At a high-stress amplitude, the fatigue crack propagation rate of Q690 is greater than that of the Q690 compact tensile specimen.

On Welding of High-Strength Steels Using Laser Beam Welding and Resistance Spot Weld Bonding with Emphasis on Seam Leak Tightness

The design of most electric vehicles provides for the positioning of the heavy energy storage units in the underbody of the cars. In addition to crash safety, the battery housing has to meet high requirements for gas tightness. In order to test the use of high-strength steels for this sub-assembly, this paper examines welded joints utilizing resistance spot weld bonding and laser remote welding, with special regard to the gas tightness of the welds. For this purpose, the pressure difference test and helium sniffer leak detection are presented and applied. The combination of both leak test methods has proven ideal in experimental investigations. For laser remote welding, gas-tight seams can be achieved with an inter-sheet gap of 0.1 mm, even if occasionally leaking samples cannot be prevented. Resistance spot welding suits gas-tight joining with both one- and two-component adhesives. Against the background of leak tightness, process fluctuations that lead to weld spatter and defects in the adhesive layer must be prevented with high priority.

Study on the Microstructure and Properties of Welded Joints of Laser Shock Peening on HC420LA Low-Alloy High-Tensile Steel.

Laser shock peening is a promising surface strengthening technology that can effectively improve the mechanical properties of materials. This paper is based on the laser shock peening process for HC420LA low-alloy high-strength steel weldments. Contrast analysis of the evolution of the microstructure, residual stress distribution and mechanical properties of the welded joints before and after the laser shock peening on each region is carried out; a combination of tensile fracture and impact toughness fracture morphology analyses of laser shock peening on the welded joint strength and toughness regulation mechanism are also completed. The results show that the laser shock peening can refine the microstructure of the welded joint effectively, the microhardness of all areas of the joint increases and the weld residual tensile stresses are transformed into beneficial residual compressive stresses, affecting a layer depth of 600 μm. In addition, the strength and impact toughness of welded joints of HC420LA low-alloy high-strength steel are improved.

Improvements in welding continuous cooling transformation diagram of high-strength low-alloy steel weld

The welding continuous cooling transformation (CCT) diagram concerning microstructure evolution in a fine zone of the weld joint provides essential data for microstructure control in practice. In this study, a welding CCT diagram was improved to be elaborate by using the expanded lever rule. Processes for obtaining pieces of phase information are explained in detail. Improvements are: (i) phase areas are clearly presented, (ii) phase volume percentages are given, and (iii) overlapped phase areas are revealed. To meet high-strength requirement, a heat input of 21 kJ cm−1 was referenced from the welding CCT diagram, for achieving acicular ferrite and lath-like martensite. Transformed phase volume fractions are estimated and high strength and good toughness are obtained due to the elaborate phase information.

Investigations on the thermal conditions during laser beam welding of high-strength steel 100Cr6

This study examines the thermal conditions during laser beam welding of 100Cr6 high-strength steel using a TruDisk5000 disc laser with a continuous adjustable power range of 100–5000 W. Two parameter sets, characterized by laser power and welding speeds, were analyzed by thermal-metallurgical FE simulations to determine their impact on the thermal conditions during welding. The results show a significant shift in heat coupling, with conduction transitioning to deep penetration welding. As a result of the high welding speeds and reduced energy input, extremely high heating rates up to 2∙104 K s−1 (set A) respectively 4∙105 K s−1 (set B) occur. Both welds thus concern a range of temperature state values for which conventional Time-Temperature-Austenitization (TTA) diagrams are currently not defined, requiring calibration of the material models through general assumptions. Also, the change in energy input and welding speed causes significantly steep temperature gradients with a slope of approximately 5∙103 K mm−1 and strong drops in the temperature rates, particularly in the heat affected zone. The temperature cycles also show very different cooling rates for the respective parameter sets, although in both cases they are well below a cooling time t8/5 of 1 s, so that the phase transformation always leads to the formation of martensite. Since the investigated parameters are known to cause a loss of technological strength and conditionally result in cold cracks, these results will be used for further detailed experimental and numerical investigation of microstructure, hydrogen distribution, and stress-strain development at different restraint conditions.

Fracture performance study on Q460D steel and ER55-G welds after high temperature

Uniaxial tensile tests were conducted on smooth round bar specimens made of Q460D high-strength steel base metal and ER55-G welds after a high temperature of 900 °C and natural cooling. Counterpart specimens at room temperature were also examined for comparison. The basic mechanical properties of each specimen were obtained, enabling quantification of the true stress-plastic strain curve of the material required for finite element analysis (FEA) in ABAQUS. The notched round bar specimens were heated up to high temperature of 900 °C, and then naturally cooled to room temperature. Uniaxial tensile tests were carried out on the notched round bar specimens. By combining test results with ABAQUS FEA and scanning electron microscope tests, the void growth model (VGM) parameters of Q460D high-strength steel and ER55-G welds after high temperature of 900 °C and natural cooling were calibrated. Finally, the calibrated VGM model was adopted as a fracture criterion in the ABAQUS subroutine VUMAT to simulate the uniaxial tensile tests on notched round bar specimens of Q460D steel base metal and ER55-G welds after high temperature of 900 °C and natural cooling. It is indicated that in most cases, the post-fracture path and the whole force-deformation curve can be simulated through the FEA with subroutine VUMAT with reasonable accuracy.

Analysis of Residual Stresses for Underwater Wet Welding of High Strength Steel

This study describes a perspective using non-destructive testing of stress-strain state joints in underwater wet welding and air. High residual stresses after underwater wet welding may be a possible cause of arising corrosion processes and cold cracking in structures. Assessing residual stresses can introduce additional changes in the technological welding process and subsequent reducing stresses. Analysis of application magnetic anisotropy and X-ray diffraction methods are shown for discovering residual tensile stresses after surfacing on high strength steel. Two complementary methods make it possible to determine the magnitude and features of the distribution of residual welding stresses after underwater wet surfacing and air surfacing.