High Strength Steel Welds Research Articles

Numerical modeling and prediction of weld microstructure in high-strength steel welding (Review)

Numerical modeling and prediction of weld microstructure in high-strength steel welding (Review)

Residual Stress Distributions at High Strength Steel Welds Prepared by Low Transformation Temperature (LTT) and Conventional Welding Consumables

Residual stress distributions in fillet welds in 8 mm 900 MPa steel have been mapped perpendicular and parallel to the weld line and also through the thickness in the vicinity of weld toe position. Measurements were carried out on four welds when two of them were performed with conventional and two with the so called LTT (low transformation temperature) filler materials. Both neutron and X-ray diffractions were used for determination of the residual stress distribution. Fatigue properties have also been evaluated for all test welds. Neutron diffraction measurements showed that the stress profiles perpendicular to the weld toe qualitatively did not depend on filler material type although the absolute stress levels differed. Trends were similar for positions 2, 4 and 6 millimetres below the surface for all three stress components; σx (direction perpendicular to the weld), σy (parallel to the weld) and σz (through the thickness). X-ray diffraction showed difference in residual stress level at the weld toe. Lower residual stress levels have been identified for LTT filler material when compared to the conventional consumable compositions. The effect of residual stress is discussed in relation to fatigue properties of all four welds. Remarkable higher fatigue strength has been measured for welds prepared by the LTT filler materials.

Microcrack Formation During Gas Metal Arc Welding of High-Strength Fine-Grained Structural Steel

The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc, which results in higher penetration depths and welding speed. However, microcracks occurred in the weld metal while approaching the process limits of the modified spray arc, represented by a 20-mm double layer DV-groove butt-weld. These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself. The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks. The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment. However, these microcracks do not impact the design specification for toughness in the Charpy V-notch test (absorbed energy at −40 °C for the present material is 30 J).

Modeling flux chemistry for submerged arc weldments of high-strength low-alloy steel

Chemical and mechanical properties of the welded joint are greatly affected by flux composition. The resulting chemical compositions of C, Si, Mn, P and S in the weld metal have been studied using formulated fluxes. The constrained mixture design, extreme vertices design, has been used to formulate fluxes to study the effect of flux constituents. Regression models were developed for weld metal content in terms of individual flux constituents and their binary mixtures for submerged arc welding of high-strength low-alloy steel. From the results, it is found that CaF2 is the most significant flux constituent and Al2O3 is the second most significant constituent among individual mixtures. CaO–MgO and CaO–Al2O3 binary mixtures are the most effective to change weld metal content. Regression mathematical models have been checked for adequacy using t-test and analysis of variance (F-test). Flux mixtures’ composition has been provided for optimum chemical composition of weld metal.

ガスメタルアーク溶接プロセスモデルの溶接力学シミュレーションへの応用

In this study, a new integrated simulation methodology has been proposed for the more accurate numerical simulation of weld distortion generated by gas metal arc welding. The integrated simulation model of gas metal arc welding was constructed by coupling between welding process and mechanics. The welding process models consist of arc plasma (heat source) model and bead formation (process) model. In the arc plasma (heat source) model, computational simulation based on mathematical modeling of the heat transfer from arc plasma to a welded plate is performed to obtain a more precise properties of heat source from welding heat input conditions. In the bead formation (process) model, computational simulation based on a coupling analysis between weld bead balance and thermal conduction is performed to obtain a more precise temperature distribution and weld bead configuration during welding from the properties of heat source obtained. In the stress and distortion (mechanics) model, computational simulation based on a large deformation thermal elastic-plastic analysis is performed to obtain a more precise weld distortion from the temperature distribution and weld bead configuration obtained. Through the developed simulation technique, weld distortion becomes to be available almost exclusively from welding heat input and process conditions. A bead-on-plate welding of high strength steel was performed under the same welding heat input and process conditions to compare the simulation results with the experimental results. It was concluded that both results of angular distortion were in extremely good agreement and thus the developed simulation technique has the potential to become useful for a highly accurate predictive simulation of weld distortion.

GMA-laser Hybrid Welding of High-strength Fine-grain Structural Steel with an Inductive Preheating

The industrial useof GMA-laser hybrid welding has increased in the last 10 years, due to the brilliant quality of the laser beam radiation, and higher laser output powers. GMA-laser hybrid welding processes operate in a common molten pool. The combination of the laser beam and the arc results in improved welding speed, penetration depth, heat affected zone and gap bridgeability. Single-layer, GMA-laser hybrid welding processes have been developed for high-strength fine-grain structural steels with a grade of S690QL and a thickness of 15 mm and 20 mm. In addition, the welding process is assisted by an integrated, inductive preheating process to improve the mechanical properties of the welding seam. By using the determined parameters regarding the energy per unit length, and the preheating temperature, welding seams with high quality can be achieved.

Assimilation of Production of High-Strength Wear-Resistant Weldable Steel with Yield Strength of more than 950 N/mm2 for Supporting Metal Structures

A technology is developed under MMK conditions for industrial production of steel 18KhGNMFTR plate 9–25 mm thick for platforms of heavy-duty quarry dump trucks and mining equipment. The set of mechanical properties is achieved by thermal improvement (double quenching and tempering) by which property stability is achieved with the formation of a uniform fine-grained martensitic microstructure.

Influence of Ti on non-metallic inclusion formation and acicular ferrite nucleation in high-strength low-alloy steel weld metals

The phase transition behaviors of non-metallic inclusions as a function of Ti content were investigated by monitoring changes in the microstructure and mechanical properties of high-strength low-alloy steel multipass weld metals. Weld metals with Ti contents ranging from 0.007 to 0.17 wt% were prepared using a gas metal arc welding process. The inclusion analysis was performed based on thermodynamic calculations and transmission electron microscopy, accompanied by energy-dispersive spectrometry and selected area electron diffraction. With increase in the Ti content of weld metals, the chaotic arrangement of ferrite laths in the columnar zone was transited to a well aligned arrangement and the impact toughness of the weld metals drastically deteriorated in response to the decrease in the Mn content of the inclusion. The effective inclusion phase for intragranular nucleation contained considerable amounts of Mn and a Mn depleted zone was observed around the effective nucleant.

DP1000高强钢激光焊接接头组织性能研究

DP1000高强钢激光焊接接头组织性能研究

The effect of galvanizing on the mechanical resistance and fatigue toughness of a spot welded assembly made of AISI410 martensite

Welding of high strength steels containing martensite is difficult due to the appearance of brittle grains after fast cooling. Galvanizing spot-welded specimens made of AISI410 solves this problem, and strongly improves the performances of spot welds. The mechanisms responsible for these achievements are presently analyzed. The changes of the mechanical strength and fatigue toughness of spot-welded samples made of AISI410 after galvanizing have been studied. AISI410 is a chromium-rich martensite. Tensile tests on normalized specimens indicate that the yield stress is close to 1010MPa and the UTS at ~1270MPa. The fatigue limit of raw AISI410 is at 690MPa (ΔσL at R=0.1). Specimens were cut following the rolling direction and spot-welded. Metallography reveals that spot welding produces: – hard martensite at the center of the nugget; – a heat affected zone, which has been forged by the welding electrodes and recrystallized at high temperature; – and finally, a ring of grains tempered in a subcritical temperature range. Spot welds were tested in tensile–shear mode. Both overload failure and fatigue toughness were evaluated. Annealing and galvanizing post-treatment have been used to improve the mechanical properties of the spot-welded specimens. The improvement of the mechanical performances of spot-welded specimens after post-treatments are reported as follows. First, we observed significant changes in the modes of rupture both in overload failure and fatigue tests. The mechanical strength of untreated spot welds is controlled by the brittleness of the nugget and the forged heat affected zone. After post-treatment, the ultimate tensile strength is increased, and rupture results from fissures propagating exclusively into the zone recrystallized in the subcritical range of temperature. This mode is genuine to spot welds in martensite because of the high strength of the base metal. Second, three modes of rupture depending on the force range control the fatigue toughness. Annealing and galvanizing modify the ranges. Galvanizing increases the endurance, and the fatigue limit by a factor ~3.5. This effect is attributed to zinc brazing that strongly changes the distribution of stresses under tensile–shear solicitation. Hardness measurements and tensile test on specific samples clarify the mechanical behavior of the layers around the spot, and shed some light on the mechanisms of rupture. Lifetimes are controlled by the initiation of fatigue cracks.

Effect of welding speed on microstructure, hardness and tensile properties in laser welding of advanced high strength steel

The increasing demand of lightweight and durability makes advanced high strength steel attractive for future automotive applications. In this study, 0·8 mm thick bare 600, 800 and 1000 MPa grade dual phase steel and 1500 MPa grade martensitic steel were laser welded, and the effect of welding speed on weld bead geometry, microhardness, microstructure and tensile properties was investigated. The steels exhibited similar weldability, and a critical welding speed for acceptable joint was determined as 25 mm s−1. A linear relationship of the hardness at fusion zone with carbon equivalent was observed, while carbon content showed a poorer linear fit. Heat affected zone (HAZ) softening increased with the steel grades due to the higher martensite volume fraction of the base metal in stronger steels. In addition, decrease of welding speed led to longer tempering time and consequently higher degree of HAZ softening. Correlations between tensile strength and hardness were also investigated.

Effect of Activating Hot Dipping Aluminum Process on High Strength Steel and Aluminum Alloy Welding Properties

Technology of activating hot-dipped aluminum on high strength steel was studied, activating time and aluminizing time was also analyzed, and the optimal activating time and aluminizing time was concluded in the end. The results showed that the optimum activating treating time was 14s in this paper. At this time the degree of corrosion on steel plate surface is the most suitable for aluminizing. The proper aluminizing treating time was 14s in this experiment. In this condition, the strength of the joint could reach up to 136N/mm. Welding between activated hot-dip aluminizing steel and aluminum alloy can be got good weld joint appearance and metallurgical bonding.

Welding of VNS-72 high-strength stainless steel

The conditions of automatic and manual argon-arc welding and filler materials are selected. The results of investigation of the technological and mechanical properties and also of the structure of the welded joints are presented.

Role of inclusions in formation of high strength steel weld metal microstructures

A series of high strength weld metals with varying Al content are studied. The inclusions are characterised using energy dispersive X-ray analysis and electron diffraction. The tendency for alignment of the microstructure is characterised quantitatively using electron backscatter diffraction and a recently developed post-processing technique. Correlation is found between the inclusion phases present and the amount of aligned neighbouring grains in the microstructure. It is shown that amorphous Si–Al oxides form at low Al weld metal contents and an Mg–Al spinel at higher contents. The former is associated with less alignment of the microstructure and therefore higher impact toughness. The effect of these inclusions on the formation of the microstructure is discussed.

Avaliação da perfuração na soldagem em operação pelo processo MIG/MAG de dutos de alta resistência e baixa espessura

O objetivo deste trabalho foi o desenvolvimento de reparo em dutos com pequena espessura (3,0 e 3,2 mm), fabricados em aços de alta resistência (API 5L X70) e em tubo ASTM 106 Grau B de forma a minimizar o risco de perfuração. Para o experimento, foi construída uma bancada de testes com ajuste variável de vazão e pressão do fluido, a saber, vazões de 20 l/min, 40 l/min e 80 l/min e pressões de 2 bar e 5 bar. Foram realizadas soldagens na direção longitudinal sobre tubos contendo água como fluido interno, utilizando-se o processo semiautomático MIG/MAG (GMAW) com posterior avaliação do aspecto da menor penetração do cordão. Desta forma, foram empregadas duas técnicas de soldagem, puxando e empurrando a poça de fusão, assim como os modos de transferência metálica em curto circuito ou em corrente pulsada. No estudo das condições limites para a ocorrência de perfuração foram pesquisados parâmetros de soldagem em função de condições específicas de vazão e de pressão. A temperatura interna da parede da tubulação foi determinada através de uma solução analítica para a transferência de calor na soldagem. Os resultados mostraram que para o processo MIG/MAG com corrente pulsada e com a técnica empurrando a poça de fusão, mantidas todas as outras variáveis de soldagem fixas, há pequena penetração do cordão de solda. Além disso, os níveis de energia de soldagem para a ocorrência da perfuração revelaram-se superiores aos obtidos na literatura para o processo SMAW, indicando o processo como robusto e apropriado para soldagem de reparo em operação.

Identification of Weld Residual Stresses Using Diffraction Methods and their Effect on Fatigue Strength of High Strength Steels Welds

It is well known that fatigue strength of welded joints does not depend on steel strength. Better fatigue strength of welded joints, e.g. longer life time of fatigue loaded weld structures, can be achieved with a smooth transition between the weld and the base material to minimize stress concentration. It has also been recognized that residual stresses play a critical role in the fatigue behaviour of welds. In the last decade an extensive research has been performed in order to increase the fatigue strength of high strength steel weldments. The martensite and bainite transformation start temperatures of weld metals have been shown to have a large effect on fatigue life time of high strength steel welds. This is of particular importance if the full potential of high strength steels is to be used in fatigue loaded constructions. A detailed investigation of the effect of phase transformation temperature on residual stress distribution in the vicinity high strength steel welds and its effect on fatigue life time has been performed. The transformation temperature of the weld metal was varied by changing the chemical composition of the filler material. Residual stress distributions have been measured by neutron as well as by X-ray diffraction and fatigue tests have been performed on the fillet welds. A strong effect of weld metal phase transformation temperature on residual stress level was observed. Fatigue strength increased approximately three times when an optimised low transformation temperature filler material was used in comparison to the application of conventional filler material.

전기저항 점용접한 자동차 강판의 강도특성평가

The resistance spot welding of high strength steel degrades the weldability because of its high strength with rich chemical composition and coating layer to protect from corrosion. And the weld Expulsion is prone to occur and severely affect the nugget guality when the initial gap between automatic borrowing galvanied steel sheets(SGARC35) and Zn-coateel trip steels(GA580TRIP and GA980 TRIP) exist in resistance spot welding(RSW). RSW is one of the most popular welding processes used to join sheet metals. but weld guality sometimes do creases due to welding condition. in this paper to verity tue weldability using spot welding with the hemispherically concaved electrode, tensile shear strength and cross-tensile strength were measured by a universal test machine. in addition, the nugget size on cross-sectional area of the weld was observed by optical and electron microscopy. As a result, the nugget size of this specimen is increased with increasing welding current and Max load of tensile-shear strength is increased with welding current is increasing.

Effect of welding parameters on bead profile, microhardness and H2 content in submerged arc welding of high-strength low-alloy steel

In oil and gas industries, submerged arc welding is the only primarily used process to weld high thickness, large distance structural oil pipes. Welding process parameters play a significant role in determining the quality of a weld joint in submerged arc welding. In the present work, an attempt has been made to optimize the weld bead parameters: weld bead form factor, dilution, microhardness and diffusible hydrogen content for welding of structural pipe steel (API 5L X65 grade) by desirability function approach used by Derringer and Harrington. For design of experiments, response surface methodology had been used. Mathematical models for output responses had been developed in terms of welding parameters and checked for adequacy using t-test and analysis of variance (F-test). It was found that welding current was the most significant parameter controlling all the responses, and arc voltage had increasing effect on all the responses except microhardness.

Finite Element Modeling of the Inertia Friction Welding of Dissimilar High-Strength Steels

Finite element (FE) process modeling of inertia friction welding between dissimilar high-strength steels, AerMet® 100 and SCMV, has been carried out using the DEFORM™-2D (v10.0) software. This model was validated against experimental data collected for a test weld performed between the materials; this included process data such as upset and rotational velocities as well as thermal data collected during the process using embedded thermocouples. The as-welded hoop residual stress from the FE model was also compared with experimental measurements taken on the welded component using synchrotron X-ray and neutron diffraction techniques. The modeling work considered the solid-state phase transformations which occur in the steels, and the trends in the residual stress data were well replicated by the model.

Effect of titanium on the solidification and postsolidification microstructure of high-strength steel welds

The present study describes for the characterization of the microstructure of dipping test samples with different Ti content. Over several years, an experimental test rig for fundamental metallurgical investigations of continuous casting processes has been further developed to facilitate higher cooling rates. This experiment is based on the principle of a dipping test under inert gas atmosphere inside a vacuum induction furnace. Recently, this apparatus has been equipped with a pyrometer in order to measure the temperature of the solidified sample during the subsequent cooling phase and also with a furnace in order to simulate different cooling strategies. The introduced dipping test simulator is a competitive possibility to reproduce casting parameters of the strip casting process as well as welding parameters of gas metal arc welding. The results indicate a significant change of the microstructure at different Ti contents, in the range 20 to 555 ppm, and a good comparability of the microstructure of dipping test samples and weld samples. These results are finally compared with results from literature and discussed with respect to the expected influence of titanium on the microstructure of the welded joint.