Influence Of Laser Welding Research Articles

Research on Microstructure Characteristics of Welded Joint by Magneto-Optical Imaging Method

This paper proposes an approach for analyzing the microstructure evolution of laser welding seam by magneto-optical imaging (MOI). The Faraday magneto-optical effect and magnetic domain theory are used to account for the MOI mechanism. The influence of laser welding on the welded joint was inspected by the analysis of color, grayscale and brightness of magneto-optical images. The relation between the brightness of magneto-optical image and grain size of microstructure is discussed as well, and the characteristics of magneto-optical images of weld microstructure were compared with those of scanning electron microscope (SEM) images. Experimental results show that three regions, including the weld zone (WZ), the heat-affected zone (HAZ), and the base metal (BM) are distributed in the magneto-optical image of the welded joint. The MOI method can investigate the microstructure evolution of welded joints and provide a theory and experimental basis for detecting weld defects.

The Performance of CR180IF and DP600 Laser Welded Steel Sheets under Different Strain Rates.

The presented research background is a car body manufacturer’s request to test the car body’s components welded from dissimilar steel sheets. In view of the vehicle crew’s protection, it is necessary to study the static and dynamic behavior of welded steels. Therefore, the influence of laser welding on the mechanical and dynamical properties, microstructure, microhardness, and welded joint surface roughness of interstitial free CR180IF and dual-phase DP600 steels were investigated. Static tensile tests were carried out by using testing machine Zwick 1387, and dynamic test used rotary hammer machine RSO. Sheet steel was tested at different strain rates ranging from 10−3 to 103 s−1. The laser welds’ microstructure and microhardness were evaluated in the base metal, heat-affected zone, and fusion zone. The comprehensive analysis also included chemical analysis, fracture surface analysis, and roughness measurement. The research results showed that the strain rate had an influence on the mechanical properties of base materials and welded joints. The dynamic loading increases the yield stress more than the ultimate tensile strength for the monitored steels, while the most significant increase was recorded for the welded material.

Analysis of vapor plume and keyhole dynamics in laser welding stainless steel with beam oscillation

The influence of laser welding with beam oscillation on dynamic behavior of vapor plume, melt pool and keyhole was investigated. The stability of plume morphology is improved with a little fluctuation, and the height and area of plasma plume are decreased as the oscillation frequencies increased. The melt pool morphologies and flowing feature under beam oscillation conditions are also regulated due to the resultant energy deposition, which has an influence on weld solidification process. The re-melting effect of circular beam oscillation can eliminate pores formation and improve weld quality.

Influence of Laser-Welding on Microstructure and Corrosion Properties of Twinning-Induced Plasticity (TWIP) Steel.

The effect of welding speed on microstructure, mechanical properties, and corrosion properties of laser-assisted welded joints of a twinning-induced plasticity (TWIP) steel was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) analysis, electrochemical test, and micro-area scanning Kelvin probe test (SKP). The results reveal that the welded joints, with a fully austenitic structure, are obtained by laser welding. In addition, the preferred orientation of grains in fusion zone (FZ) increased with the increase of welding speed. Additionally, the coincidence site lattice (CSL) grain boundaries of FZ decreased with increasing welding speed. However, potentiodynamic polarization and SKP results demonstrated that the welding speed of 1.5 m/min renders superior corrosion resistance. It can also be inferred that the corrosion properties of the welded joints are related to the grain size and frequency of CSL grain boundary in FZ.

Analysis of properties laser welded RAK 40/70 steel sheets

Both, the ecological production and operation of vehicles demand using such materials for deformation zones’ structural parts, which show some specific properties and use innovative technologies to process them. Specific requirements for functionality (strength, stiffness, deformation work, fatigue properties) are closely linked to processability (formability). In the paper are presented results for multiphase TRIP steel RAK40/70 when welded by pulse solid-state fiber laser YLS-5000. Based on microstructure analysis in the fusion zone and heat affected zone the welding parameters were optimised. The influence of laser welding on the strength and deformation properties was verified by characteristics of strength, stiffness and deformation work, as they were calculated from mechanical properties measured by tensile test and three-point bending test. The knowledge gathered in the field of laser welding influence on the strength and deformation properties of multiphase TRIP steel RAK40/70 should help designers when design the lightweight structural parts of the car body.

The Influence of Laser Welding on the Mechanical Properties of Dual Phase and Trip Steels

Nowadays, a wide range of materials is used for car body structures in order to improve both the passengers’ safety and fuel consumption. These are joined by laser welding and solid state fiber lasers being used more and more in present. The article is focused on the research of laser welding influence on the mechanical and deformation properties, microstructure and microhardness of advanced high-strength steels: high-strength low-alloyed steel HC340LA, dual phase steel HCT600X and multi-phase residual austenite steel RAK40/70. The proper welding parameters have been found based on weld quality evaluation. The specimens for tensile test with longitudinal laser weld were used to measure mechanical and deformation properties. Microstructure and microhardness of laser welds were evaluated in the base metal, heat affected zone and fusion zone. The higher values of strength and lower ones for deformation properties of laser-welded materials have been found for dual and multi-phase steel. The microhardness strongly depends on the carbon equivalent of steel. Deformation properties are more sensitive than strength properties to the change of microstructure in the fusion zone and heat affected zone.

Analysis of the Influence of Laser Welding on Fatigue Crack Growth Behavior in a Newly Developed Nickel-Base Superalloy

The influence of laser welding on fatigue crack growth (FCG) behavior of a newly developed nickel-base superalloy, Haynes 282 was studied. Laser welding resulted in cracking in the heat affected zone (HAZ) of the alloy during welding and FCG test results show that this produces deleterious effect on the fatigue crack growth behavior of Haynes 282. However, two post weld heat treatments, including a new thermal treatment schedule developed in this work, are used to significantly improve the resistance of the Haynes 282 fatigue crack growth after laser welding. The effects of laser welding and thermal treatments are discussed in terms of HAZ cracking and heterogeneity of slip, respectively.

Influence of welding process on Type IV cracking behavior of P91 steel

Influence of laser welding (LW) and shielded metal arc welding (SMAW) processes on Type IV cracking behavior of modified 9Cr–1Mo (P91) steel has been investigated in this paper. The study involved comparison of stress rupture lives of modified 9Cr–1Mo steel weldments prepared by SMAW and continuous wave CO2 laser welding processes. Width of the heat affected zone (HAZ) in laser weldment was found to be 1.0mm, whereas it was ~2.5mm in SMAW weldment. The rupture lives of laser weldment were found to be higher than SMAW weldment at higher stress level and comparable at lower stress level. Under similar stress levels, the creep rupture lives of 875°C heat treated specimens were found to be lower than that of the base metal and cross weld specimen. These results clearly suggest that the instability of microstructure in the intercritical heat affected zone (ICHAZ) is responsible for lower creep rupture lives of P91 steel weldment than the base metal. The experimentally observed variations in creep cavitation have been corroborated with the results of finite element (FE) analysis.

Influence of Laser Welding on the Alumina Growth on a Thin FeCrAl-RE Foil at High Temperature

We study isothermal oxidation of laser welded FeCrAl-RE samples containing specific fractions of seams in a bead-on-plate configuration at approximately 900°C using thermogravimetric analysis (TGA), field emission scanning electron microscope (FEG-SEM), transmission electron microscope (TEM), electron probe microanalysis (EPMA) techniques. An important reduction in the alumina-growth rate over the fusion zone compared to the base material occurs at 900°C, thereby, suppressing the discontinuous increase in mass gain commonly observed for alumina-forming alloys when the temperature decreases from 1000°C to 900°C. This phenomenon is mainly related to the concomitant dramatic chromium carbide precipitation at the fusion zone/oxide film interface and possible earlier injection of the rare earth elements into the oxide layer. On one hand, chromium carbide precipitation, which is linked to the laser melting-induced high free carbon, contributes to improve the effectiveness of the diffusion barrier provided by the thermally growing scale. On the other hand, due to their initial high enrichment at the fusion zone surfaces, rare earth elements can penetrate in the oxide layer and promote the elimination of detrimental phase transformation of metastable platelets (γ,θ-Al2O3) to α-Al2O3 during the initial stages of oxidation.

Property of Laser Welded Bake-Hardening Steel in Tailored Blanks for Automobile

The behavior of bake-hardening of the laser weldment was investigated. The bake-hardening steel(BH steel) was welded with Nd:YAG laser followed by plastic deformation and subsequent heat-treatment. Then the influence of laser welding on the behavior of bake-hardening was investigated. The hardness of the laser weld metal significantly increased after welding. After the plastic deformation, both the base metal and weld metal became harder by work-hardening. The heat treatment resulted in more increment of hardness in both the base metal and weld metal by bake-hardening. The amount of bake-hardening reached a maximum value at the plastic strain of 5% or more. We modified a kinetic equation proposed for predicting the strength of a low-carbon bake-hardening steel and applied to the estimation of hardness of the base metal and weld metal. The calculated hardness values agree with the experimental data. The calculated activation energy for bake-hardenig was that for diffusion of carbon and nitrogen atoms in α-Fe. Thus the hardening is thought to be governed by diffusion of these solute atoms.

実機プラントの経年劣化度診断のための超小型試験法の提案

This paper describes a procedure proposed for fracture toughness evaluation of pressure vessels in use. A small-size specimen of thickness B=2.5 to 5.0 mm with a couple of hard zones enclosing a notch is presented. Main attention is focused on how to create the hard zone in the small-size specimen. Preliminary FE-analysis indicates that the distance e from the hard zone to notch plane and the strength ratio Sr=σYH/σYB are major controlling factors of the near notch-tip constraint, where σYH and σYB are the yield stresses of the hard zone and base material, respectively. In order to obtain a sufficient plastic constraint, the e and Sr should be e 2. The CO2 laser welding is effective to realize such constrained state of specimens. The laser welds are hard enough and a rectangular hard zone can be created under a selected welding condition. The peak temperature in the region sandwiched by the laser welds is less than 200°C, and the level of welding residual stress is at most ± 100 MPa. Accordingly, the influence of laser welding on the mechanical and metallurgical properties of the test region is very marginal. The fracture toughness test verifies the validity of the small-size specimen with the laser welds. The fracture toughness measured by the small-size specimen is almost identical with the toughness of the full-thick specimen of base metal.

Laser-beam weld microstructures and properties of aluminum-lithium alloy 2090

The influence of laser welding on the microstructure and mechanical properties of aluminum-lithium alloy 2090 is presented. The quality of the laser-welded 2090 material was evaluated through microscopical observations and mechanical tests. Microscopical observations of the laser welds revealed a low degree of degradation of the weld surface coupled with an absence of porosity and cracking in the weld zone. Mechanical tests revealed that the laser-welded material had attractive joint efficiencies. The results reveal an overall superiority of the laser-welded 2090 material compared to conventional arc-welded material.