Laser-assisted removal of weld heat tints from stainless steel surface

ISIJ International, 2006

Microstructure and high temperature oxidation behaviour of laser weldments of 316L and 316LN steels have been found to influence by the variation in welding speed. Ferrite content and ferrite morphology change for both type 316L and 316LN laser weld with welding speed. Laser weldments consisting mainly of weld metal and base metal region of two austenitic stainless steels (ASS) were oxidized in dry air at 973 K for 240 h. Steel weldment was found to have a higher oxidation rate when joined with lower welding speed of 11.66 mm/s as compared to 25 mm/s speed. On the other hand, 316LN steel weldments have indicated much superior oxidation resistance property under similar condition. Oxidation behaviour of two ASS weldments has been correlated with microstructure and oxide scales formed over the different regions have been characterized by scanning electron microscopy (SEM/EDXA).

Optics & Laser Technology, 2011

Surface modification of AISI316 stainless steel by laser melting was investigated experimentally using 2 and 4 kW laser power emitted from a continuous wave CO 2 laser at different specimen scanning speeds ranged from 300 to 1500 mm/min. Also, an investigation is reported of the introduction of carbon into the same material by means of laser surface alloying, which involves pre-coating the specimen surfaces with graphite powder followed by laser melting. The aim of these treatments is to enhance corrosion resistance by the rapid solidification associated with laser melting and also to increase surface hardness without affecting the bulk properties by increasing the carbon concentration near the surface. Different metallurgical techniques such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the microstructure of the treated zone. The microstructures of the laser melted zones exhibited a dendritic morphology with a very fine scale with a slight increase in hardness from 200 to 230 Hv. However, the laser alloyed samples with carbon showed microstructure consisting of g dendrite surrounded by a network of eutectic structures (g +carbide). A significant increase in hardness from 200 to 500 Hv is obtained. Corrosion resistance was improved after laser melting, especially in the samples processed at high laser power (4 kW). There was shift in I corr and E corr toward more noble values and a lower passive current density than that of the untreated materials. These improvements in corrosion resistance were attributed to the fine and homogeneous dendritic structure, which was found throughout the melted zones. The corrosion resistance of the carburized sample was lower than the laser melted sample.

Electrochimica Acta, 2007

Martensitic high nitrogen stainless steels offer a combination of wear-, corrosion-and fatigue properties. But for some applications a higher surface hardness is required. A laser hardening with rapid heating (without smelting) and cooling (quenching) rates can improve the surface hardness with compressive residual stresses in the near surface layer. Yet, some cases of pitting corrosion in chloride media are reported.

Crystals

Small differences in the contents of surface active elements can change flow direction and thus heat transfer, even for different batches of a given alloy. This study aims to determine the effects of sulfur on weld bead morphology in the laser process. The paper presents the results related to the weld bead shape of two thin AISI 304 industrial stainless steel casts. One cast contains 80 ppm (0.008%) of sulfur, considered as a high sulfur content, and the other one contains 30 ppm (0.003%) sulfur, which can be considered low sulfur. The welds were executed using a CO2 laser. The effects of laser power (3.75, 3.67, 6 kW), welding speed (1.25, 2.40, 2.45, 3.6 m/min), focus point position (2, 7, 12 mm), and shield gas (Helium, mixed 40% helium + 60% argon and mixed 70% helium + 30% argon) with a flow rate of 10 L/min on the depth of the weld (D) and the aspect ratio (R = D/W) were investigated using RSM (response surface methodology). The experimental results show that the transfer of ...

Materials & Design, 2000

Laser surface melting (LSM) were carried out in three types of stainless steels — austenitic, martensitic and ferritic — in order to improve pitting corrosion resistance. After the LSM, most of the steels present a shift in the pitting potential to more noble values, a longer passivity stage and lower passive current density than the substrate. These improvements are achieved by means of a modified surface layer, more homogeneous with a fine cellular dendritic structure free of large precipitates. Nevertheless, the corrosion resistance depends critically on the laser processing parameters, particularly for the cases of ferritic and martensitic stainless steels. Therefore, care must be taken in the choice of the laser-processing parameters that leads to optimal properties in each material.

An der Hochschule Mittweida wurde das Hochgeschwindigkeits-Scannerschweißen als neue Methode zum verschweißen von Blechen größerer Dicke untersucht. Die Versuche wurden 2 Stählen, einem austenitischen Edelstahl X1 NiCrMoCuN 25-20-6 (1.4529) und dem Super-Duplex Edelstahl X2CrNiMoCuWN25-7-4 (1.4501), in den Materialstärken von 6 mm, 8 mm und 10 mm durchgeführt. Die Versuchsauswertung umfasste die mechanische Prüfung, die optische Mikroskopie sowie die elektrochemische Korrosionsprüfung. Die jeweils 3 Materialdicken wurden in der mechanischen Prüfung sowie in der Schweißkornausbildung verglichen. Die Optische Mikroskopie deckte Typ A-Verfestigung im 1.4529 und deutliche Mikrostrukturänderungen innerhalb des Duplex Edelstahls sowie viele Schweißdefekte auf. Die Härteprüfung ergab eine Härtezunahme zur Schweißnahtmitte hin und Unterschiede bezüglich der Härte bei den verschiedenen Dicken artgleicher Materialien. Die Zugprüfung ergab, dass die Schweißnaht fast so hohe Festigkeiten wie das Grundmaterial erreichen kann, wenn sie fehlerfrei geschweißt ist. Bei der Korrosionsrate zeigte sich, dass geschweißtes Material empfindlicher gegen Korrosion und Lochfraß ist. High-speed remote scanner laser-welding is a relatively new technique that is being tried out at the Mittweida Laser institute for welding stainless steel sheets of high thicknesses. The used materials were 6, 8 and 10 mm thick. Two different materials were tested: X1 NiCrMoCuN 25-20-6 (1.4529) super-austenitic stainless steel (ASS) and X2CrNiMoCuWN25-7-4 (1.4501) duplex stainless steel (DSS). The work involved mechanical testing using (tensile and hardness). Optical microscopy was employed to investigate the phase changes and weld defects inside the materials. Electrochemical corrosion testing was used to evaluate the corrosion behaviour of the weld zone. The three different thicknesses were compared during mechanical testing and weld bead examination. Microstructure investigation revealed the formation of finer microstructures with different grain boundaries due to the melting and the resolidification of the base metal and extensive microstructure changes inside the materials. Many weld defects were also observed. Hardness measurements revealed that hardness increases towards the centre and differences in the hardness are observed in similar materials with different thicknesses. Tensile testing revealed that the weld has the potential to have very high strength approaching that of the original material. Measuring corrosion rates shows that the welded material is more susceptible to corrosion and to pitting in all cases, due to the formation of ferrite as the primary phase in duplex stainless steel and compositional variations due to melting and resolidification.

Materials & Design, 2012

The pitting corrosion and sensitization in laser rapid manufactured specimens of type 316L stainless steel are studied and compared with its wrought and weld deposit (by plasma transferred arc welding-PTAW) counterparts. With respect to wrought specimens, the laser rapid manufactured specimens exhibited lower pitting corrosion resistance as well as higher degree of sensitization. However, pitting corrosion resistance of laser rapid manufactured specimens is largely similar to that of PTAW-deposited specimens. Relatively lower pitting corrosion resistance of laser rapid manufactured and PTAW-deposited specimens are attributed to their cast microstructure and associated micro-segregation effects as expected. Repeated exposure to sensitization temperature range (773-1073 K) during multiple layer deposition coupled with slower rate of cooling during later part of laser rapid manufacturing resulted in sensitization, giving rise to continuous corrosion attack along the grain boundaries. Solution annealing is found to be helpful in healing the associated chromium depletion and decreasing the degree of sensitization with modest improvement in pitting resistance. Primary mode of solidification in laser rapid manufactured specimens of type 316L stainless steel influenced potential sites for initiation of pitting corrosion. In primary ferrite solidified regions, initiation of pitting corrosion occurred preferentially at d-ferrite/austenite boundaries whereas core of austenite cells/dendrites and grain boundaries were the preferred sites for initiation of pitting corrosion in primary austenite solidified regions. These studies provide insight into the basic corrosion mechanisms of laser rapid manufactured specimens of type 316L stainless steel.

Optical and Quantum Electronics, 1995

Laser surface treatment is a promising technique for improving the wear and corrosion resistance of materials. In the case of tool steels, laser surface treatment is preferably carried out in the liquid state to allow for complete dissolution of carbides. This paper concerns the application of laser melting to the surface treatment of AISI 420 and 440C martensitic stainless steels and sintered AISI T15 high-speed steel. Usually, lasermelted tool steels contain martensite, retained austenite and carbides. In steels containing large proportions of ferrite-forming alloying elements, 6-ferrite may also be observed. When applied to sintered steels, laser treatment leads to the elimination of residual porosity. The proportion of retained austenite in laser-melted steels is much higher than in conventionally treated steels. However, the hardness is high because austenite is strengthened by solid solution, dislocations and small grain size. The high volume fraction of retained austenite usually prohibits the application of tool steels in the laser-treated condition. Austenite may be eliminated by multiple tempering treatments at temperatures in the range 550-650~

Applied Surface Science, 2006

Marking is of prime importance in the field of biomaterials to allow the identification of surgical tools as well as prostheses. Nowadays, marking is often achieved by means of laser beam, which may modify the characteristics of the treated surfaces. The use of laser devices delivering nanosecond pulses is known to induce dramatic corrosion degradations during sterilization or decontamination processes of the biomaterials. The aim of the present study is to investigate the ability of femtosecond (pulse duration in the 10 À15 s range) laser treatments to avoid preferential corrosion processes of the marked areas, in order to extend the durability and the reliability of biomaterials. Experiments have been performed on martensitic Z30C13 and austenitic 316L stainless steels. Electrochemical measurements (cyclic polarization curves) were carried out to determine the passive state of samples before and after engraving, their corrosion rate and their susceptibility to localized corrosion. Further protracted immersion tests were also carried out to evaluate the natural long-term degradation of engraved parts. The electrochemical behavior is then explained on the basis of surface characterizations. Femtosecond laser marking is shown to provide an electrochemical ennoblement. Moreover, the chemical composition is not affected so that the passive character of both stainless steels is maintained, even improved if we consider the susceptibility to localized corrosion.

Corrosion Science, 2001

This paper studies the efficiency of high-power laser methods for modifying the AISI 304 steel surface in order to increase its corrosion resistance. The surface of SS 304 was melted in argon and nitrogen atmospheres using different laser beam scan rates and gas flows. The results obtained show that in both cases the laser surface melting (LSM) induced improvements in pitting resistance with respect to the base steel. Electrochemical studies showed that the improvements are greater when the LSM is carried out in a nitrogen environment because of the incorporation of nitrogen into solid solution. As a result, the corrosion and pitting potential shift to more noble values while the passive current density decreases by nearly two orders of magnitude. The presence of chromium oxides and nitrogen compounds on the surface of the specimens seem to indicate that nitrogen may help the reconstruction of the passive layer as well as act as a barrier for the electrolyte.

The advanced methods for treatment of materials with concentrated energy fluxes provide major opportunity for obtaining wear, fatigue, corrosion resistant and hard surfaces or persistently engraved ones with bitmaps in the form of texts or images. Today, we are aware of many methods of treatment but the laser technology is known to be highly accurate in positioning. In this respect, the laser treatment together with additionally applied combustible particulate substances (like magnesium paste, black powder, REX-C100-C900, etc.) on the treated surface enables obtaining of enhanced tribological properties while guaranteeing a certain depth of the treatment. The present study aims at determining a regime for obtaining lasting traces with fiber laser for decorative purposes on an austenitic AISI 301 sheet steel. The result of the applied treatment is evaluated by means of microstructure, XRD analysis and tribological examinations. They show that the use of the concentrated power-controlled light beam that transmits the energy to the active magnesium paste produces qualitative and process-controlled surface treatments.

Applied Surface Science, 2020

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Journal of Achievements in Materials and Manufacturing Engineering

Purpose: of this paper was to examine the corrosion resistance of laser surface alloyed (LSA) stainless steels using electrochemical methods in 1M NaCl solution and 1M H2SO4 solution. The LSA conditions and alloying powder placement strategies on the material's corrosion resistance were evaluated. Design/methodology/approach: In the present work the sintered stainless steels of different microstructures (austenitic, ferritic and duplex) where laser surface alloyed (LSA) with elemental alloying powders (Cr, FeCr, Ni, FeNi) and hard powders (SiC, Si3N4) to obtain a complex steel microstructure of improved properties. Findings: The corrosion resistance of LSA stainless steels is related to process parameters, powder placing strategy, that determines dilution rate of alloying powders and resulting steel microstructure. The duplex stainless steel microstructure formed on the surface layer of austenitic stainless steel during LSA with Cr and FeCr reveal high corrosion resistance in 1M...

2015

The oxidation behaviour of laser welded of TP347HFG and VM12-SHC stainless steels in air atmosphere were investigated. The temperature was changed from 25 to 1400 0 C. The stainless steels butt were welded. Materials were examined by the thermogravimetric method. The surface and microstructure of the sample were observed in an optical microscope (OM) and a scanning electron microscope (SEM). The X-ray fluorescence spectrometer (XRF) was used to observation change in chemical composition along the cross-section of specimen. The results showed the substantial intermixing of both substrates within the fusion zone. The thermogravimetric data indicate that the investigated materials undergo chemical corrosion. The thermodynamic parameters formation oxides on substrates were calculated and discussed. The CO2 laser welding technique was suggested as a good method for joining dissimilar steels.