Steel Laser Research Articles

Benefits of interfacial regulation with interlayers in laser welding Ti6Al4V/316L steel

Laser welding of Ti6Al4V and 316L stainless steel is performed using single Cu interlayer and composite Cu-Nb interlayer. The microstructural characterization and mechanical properties of Ti6Al4V/316L steel laser welded joints at various laser offsets were investigated. Proper laser offset distance to 316L steel side ensured weld integrity and restrained mass production of intermetallic compounds for single Cu interlayer. Energy dispersive spectroscopy showed that Cu solid solution and discontinuous Ti-Fe and Ti-Cu intermetallics were formed due to the dissolution and diffusion of atoms. The joint had a lower tensile strength and fractured along Ti6Al4V/Cu weld interface with obvious cleavage steps and tongue pattern. The inserting of Nb interlayer with high-melting point was conducive to prevent atomic diffusion and suppress the formation of brittle intermetallics. Similarly, the laser energy distribution was crucial to the weld formation and metallurgical reaction in fusion zone. The Cu sheet and 316L steel was mainly connected by heat conduction. The weld fusion zone consisted of (Cu, Nb) and (Ti, Nb) solid solution with no intermetallics. Compared to the welded joints with single Cu interlayer, the microhardness of fusion zone was reduced and tensile strength was improved because no brittle IMCs were formed with composite Cu-Nb interlayer. The maximum tensile strength reached 215 MPa and ductile fracture mode occurred with composite Cu-Nb interlayer, which was approximately 160% greater than that found with single Cu interlayer.

Microstructure of intercritical heat affected zone and toughness of microalloyed steel laser welds

Microstructure of laser welds of the X70 low-carbon pipe steel was studied. High cooling rates after laser welding and non-uniform distribution of carbon in the ferrite-pearlite base metal caused formation of regions with increased microhardness (up to 650 НV) in inter-critical heat affected zone (ICHAZ). These regions consisted of finely dispersed degenerate upper bainite and martensite-austenite constituents of a slender shape and small fraction of a massive shape along the boundaries of bainite laths, as well as twinned martensite. High concentration of martensite-austenite constituents (10–16%) and residual stresses in ICHAZ, as well as a dendritic martensitic structure with carbide interlayers along the boundaries of martensite laths in fusion zone were the main reasons of sharp decrease in charpy impact energy of the welded samples. High microhardness of the laser welds was decreased down to 320 HV and their brittleness was improved by annealing. Also, in ICHAZ, degenerate upper bainite and the regions of martensite-austenite constituents decayed forming tempered sorbite and Fe2C and Fe3C carbides, respectively. Charpy impact energy of the welds doubled after annealing compared to the welds without annealing, and ductile-brittle transition temperature decreased down to –60°С.

Effect of laser process an inclined surface cutting of mild steel then analysis data statistically by RSM

The regression analysis process is used to study and predicate the surface response by using the design of experiment (DOE) as well as roughness calculation through developing a mathematical model. In this study; response surface methodology and the particular solution technique are used. Design of experiment used a series of the structured statistical analytic approach to investigate the relationship between some parameters and their responses. Surface roughness is one of the important parameters which play an important role. Also, its found that the cutting speed can result in small effects on surface roughness. This work is focusing on all considerations to make interaction between the parameters (position of influence) because laser power directly depends on cutting speed with high gas pressure and vice versa to obtain a less surface roughness. Data analysis showed that the lower value for roughness was (0.68) µm and the high roughness was (8.56) µm. The model values for considered fit are suggested to be as (R2) = 51.76%. The selected coefficient is referred to the amount of model variation in the response. The adjusted value of (R2) = 8.34% will calculate the number of forecasting model and is normally useful for comparing models with different numbers of predictions. The (F) test is used to determine whether interaction and major effects are significant. The p-value is the probability of obtaining a statistic test which is considered as the extreme of actual calculated values if the null hypothesis is true. A commonly cut-off value that used for the p-value is (0.05). This value is used to be the active contribution to investigate the correlation between laser machining parameter with the surface roughness. Also the goal of this research highlights the experimental control parameters of mild steel laser processing with their responses.
 

Process stability analysis and weld formation evaluation during disk laser–mag hybrid welding

For monitoring process stability and evaluating weld formation in laser–metal active gas arc welding (MAG) hybrid welding, this work proposes a new method that combines instantaneous status analysis and continuous stability analysis with a double high-speed photography system. Instantaneous physical phenomena were extracted from the top and bottom surfaces, which included information on arc light, metallic vapour, spatter, and the flow of the bottom molten pool. These features were used to evaluate the instantaneous status by analysing the keyhole status and droplet transition status in 316 stainless steel laser–MAG hybrid welding. The grey-level co-occurrence matrix (GLCM) and Gabor wavelet were used to measure the instantaneous status of the bottom molten pool in the spatial and frequency domains, respectively. Multiple physical phenomena of the top surface were obtained by morphological methods. The process stability mechanism was analysed based on visual features, and the time–frequency distributions of the process features were investigated for the stability analysis and formation evaluation. Unstable frequencies in the laser–MAG hybrid welding process and their influence factors were presented. Additionally, the relationship between the stability of the welding process and the weld formation was analysed by a continuous analysis method. The experimental results showed that the instantaneous analysis method effectively evaluated the instantaneous status of laser–MAG hybrid welding process, and the global stability of the continuous analysis method directly reflected the weld formation. The proposed method could be used to monitor the stability and weld formation of the laser–MAG hybrid welding process.

EDS X-ray Characterization of S7 Tool Steel Laser Alloyed with Boron and Silicon

EDS X-ray Characterization of S7 Tool Steel Laser Alloyed with Boron and Silicon

Benchmarking of premium rail material wear

Railway steel that offers a greater quality and extended life is described by the industry as premium rail. It is mainly used on areas of rail networks where accelerated wear, rolling contact fatigue or other rail related damage phenomena prevail. However, little performance data exists for these materials and where it does it is limited to a narrow set of contact conditions. The aim of this work was therefore to map premium rail performance across a range of Tγ contact conditions to benchmark against standard grade R260 rail. Laboratory tests using a twin disc machine were performed to determine the wear performance of four premium rail grades against R8 wheel material, at various slip conditions of 1–20%. Comparison with Martensitic Stainless Steel (MSS) laser clad material was made as a further benchmark. The results are shown in terms of Tγ and wear rate for both the rail and wheel discs. Material hardness maps were obtained of the full rail and the laboratory small scale specimen materials in order to correlate hardness with their wear behaviour. The purpose of this work is to understand the likelihood and rate of wear in different wheel/rail contact conditions and to produce enough wear information for the premium rail that could be used in prediction tools for comparison with other materials and contact conditions.

Effect of laser shock peening on corrosion resistance of 316L stainless steel laser welded joint

This paper describes the testing of laser shock peening (LSP) on the corrosion resistance of a 316L stainless steel laser welded joint. The objective of this research is to explore the changes in corrosion resistance when a laser shocks weldments under the same laser line energy (50 J/mm). The research shows that LSP can increase the corrosion resistance of weldments, produce grain refinement, generate high magnitude compressive residual stress and increase microhardness. Moreover, this research also provides theoretical evidence for optimizing parameters which have the same line energy.

Semiconductor properties of passive film and corrosion resistance of 2205 duplex stainless steel joint welded by laser hybrid welding

Purpose There are obvious differences in corrosion resistance of different 2205 welding joints with different ratios of austenite and ferrite, from the top to the bottom, the austenite content decreased gradually while the ferrite increased. In each region of welded joint, the pitting resistance number of ferrite is higher than that of austenite; pitting corrosion is more likely to occur in austenite phase first on the top region of the weld and in the secondary phase precipitates on the other regions of the weld. The fluctuation of the ratio of austenite and ferrite has a great influence on performance of passive film in 3.5 per cent NaCl solution. Design/methodology/approach To study the corrosion behavior of welded joint, the samples were obtained by laser hybrid welding. Pitting corrosion was studied in different area of welded joint. The Mott–Schottky curves of welded joints were measured to study the passive film on the different welded joint area. Findings Due to the difference of heat input and the limit of filler depth of the wire, the microstructure of duplex stainless steel laser welding joint has obvious difference in the thickness direction. In addition, there will be harmful secondary phase (such as chromium nitride and σphase) precipitates in the lower part of the joint. For the welded joint, the corrosion resistance decreases with the increase in the difference of the microstructure. Pitting corrosion usually takes the two phases as the nucleation point and grows up. The surface of 2205 duplex stainless steel laser hybrid welding joint cannot form a complete passive film in 3.5 per cent NaCl solution, and the more the ratios of austenite and ferrite deviate from equilibrium position (50:50), the worse the performance of passive film is. Originality/value In this paper, the authors attempt to establish the correlation between the semiconductor electronic properties of passive film and the difference of microstructures and the component in a joint welded by laser hybrid welding. The effect of passive film on the corrosion resistance of the weld was further investigated.

Identification and characterization of spatter particles and their effect on surface roughness, density and mechanical response of 17-4 PH stainless steel laser powder-bed fusion parts

As an emerging additive manufacturing (AM) process, laser powder-bed fusion (LPBF) provides a new prospect for production of complex metallic parts. Laser-material interaction and melt pool dynamics govern the physics behind the LPBF process. However, instabilities in melt pool dynamics lead to the formation and ejection of spatter particles, which are known to change the powder-bed characteristics thus affecting the quality of printed parts. In this work, a comparative study is performed on the virgin and spatter powder particles where two types of spatter particles so-called: under-size (US) and over-size (OS) spatters are studied. Chemical composition, crystallographic phases, microstructure and morphology of the virgin powder as well as the US and OS spatters of 17-4 martensitic/precipitation hardened (PH) stainless steel (SS) powders are studied in detail. Particle analysis results show a significant morphology and size difference between the virgin (D90 – 60 μm) powder, US (D90 – 80 μm) and OS (D90 – 130 μm) spatters. Effect of spatter particles on the surface roughness, density and tensile response of printed parts is also studied. Compared to the parts printed in the non-spatter rich (NSR) region, parts printed in the spatter rich (SR) zone show a 15% and 28% increase in surface roughness for tensile and cylindrical samples, respectively. In addition, higher porosity is observed in these parts with larger pores. Moreover, tensile response shows an abrupt failure resulting in a reduction in ductility due to the presence of large pores (∼100 μm) observed on the fracture surface and x-ray computed tomography results.

Influence of wire feed rate on mechanical and microstructure characteristics of aluminum to galvanized steel laser brazed joint

Laser brazing technique was employed to weld-braze 2 mm thick galvanized steel to 5083 aluminum alloy in flange joint configuration using 2 mm diameter solid AlSi12 (AA4047) filler wire. Experiments were performed at various wire feed rates (2.0–3.6 m/min) with constant laser power (3.5 kW), scan speed (2.5 m/min) and spot size (1.7 mm). The microstructural observation of the etched specimens under SEM showed cast structure at the brazed zone and a two-layered (planar and needle structured) interface towards the galvanized steel. HAZ was observed at the aluminum side. The selective Energy-dispersive X-ray spectroscopy (EDS) point analysis and X-ray diffraction technique were used to study the interface and the results confirmed that the planar and needle structures are comprised of ternary Alx-Fey-Siz and binary Alx-Fey intermetallic phases respectively. From hardness testing, both the base material, i.e., AA5083and galvanized steel are found to be harder than brazed zone. In case of nano-indentation testing, intermetallics have shown higher hardness values compared to base materials. The joint strength increased with increasing wire feed rate and recorded interfacial failure. Fatigue life of the laser brazed joints at lower stain amplitude is better with increasing wire feed rate and are in close range to the aluminum base material (AA5083) value. Fatigue tested specimens recorded brazed zone failure and revealed flow lines, intergranular cracking and typical fatigue striations.

Suppression of δ-ferrite formation on Al-Si coated press-hardened steel during laser welding

Mechanical properties of Al-Si coated press-hardened steel laser welded joint can not meet requirement due to the presence of δ-ferrite. This study investigated the suppression mechanism of δ-ferrite using a nickel interlayer during fiber laser welding. The fraction of primary solidification δ-ferrite was reduced to 57% with a 5.85% Ni in welding pool, and completely transformed into austenite during peritectic reaction (L + δ → γ) and solid phase transformation (δ → γ). Full martensite microstructure was obtained in welded seam and fusion line without Al-segregation. Tensile strength of welded joint had a ∼17.1% improvement compared to as-received welded, similar to that of removing Al-Si coating.

Microstructure and fracture performance of 304 stainless steel laser repairs with Al2O3 nano-particles

Abstract Pre-cracked 304 stainless steel compact tension specimens were repaired by a CO2 laser at the crack tips with the addition of different weight fractions of nano-Al2O3. Crack opening displacements were measured by a digital image correlation system for the evaluation of fracture performance. Microstructures of the repaired areas were examined by scanning electron microscopy equipped with an energy dispersive spectrometer. Results indicated that laser repair with the addition of 1.0 wt.-% nano-Al2O3 resulted in metallurgical bonding at the interface and fine columnar crystal in the repair layer. The addition of nano-Al2O3 increases sites of heterogeneous nucleation, which acts as a fine-grain strengthener. In addition, the uniform distribution of nano-Al2O3 plays a role in dispersion strengthening, resulting in improved fracture performance by approximately 10 % to 30 % as applied loads varied from 1 to 20 kN. However, the excessive addition of nano-Al2O3 gives rise to the agglomeration and micro-cracks in the repair layers and clear detachment are observed at the interface.

Investigation on microstructure, surface and corrosion characteristics of heat treated AISI 420 martensitic stainless steel laser welds in simulated body fluid (SBF)

Investigation on microstructure, surface and corrosion characteristics of heat treated AISI 420 martensitic stainless steel laser welds in simulated body fluid (SBF)

Research on carbon fiber reinforced thermal polymer/stainless steel laser direct joining

To improve the numerical simulation accuracy of carbon fiber reinforced thermal polymer (CFRTP)/stainless steel laser direct joining (LDJ), a fitting formula of thermal contact conductance was established based on experiments in this paper. Taking into account the thermal contact resistance, a three-dimensional finite element thermal contact model of LDJ was established, and the theoretical simulation and experimental results were compared and analyzed. The result showed that the thermal contact model was more consistent with the reality compared with the traditional model. This thermal contact model could be used to characterize the influence of clamping pressure on the laser joining quality. When the laser power was 318 W and the clamping pressure was 0.1 MPa, the relative error of the melting width was 17.8% for the traditional model and 6.7% for the thermal contact model considering the thermal conductivity. The numerical simulation accuracy could be improved in the process of LDJ. With this numerical model, relationships between the thermal behaviors and the joining parameters were studied numerically. The CFRTP/stainless steel laser joining experiments were also carried out, and the result showed that the joint width measured agreed well with the numerical result.

Tensile–Shear Fracture Behavior Prediction of High-Strength Steel Laser Overlap Welds

A wider interface bead width is required for laser overlap welding by increasing the strength of the base material (BM) because the strength difference between the weld metal (WM) and the BM decreases. An insufficient interface bead width leads to interface fracturing rather than to the fracture of the BM and heat-affected zone (HAZ) during a tensile–shear test. An analytic model was developed to predict the tensile–shear fracture location without destructive testing. The model estimated the hardness of the WM and HAZ by using information such as the chemical composition and tensile strength of the BM provided by the steel makers. The strength of the weldments was calculated from the estimated hardness. The developed model considered overlap weldments with similar and dissimilar material combinations of various steel grades from 590 to 1500 MPa. The critical interface bead width for avoiding interface fracturing was suggested with an accuracy higher than 90%. Under all the experimental conditions, a bead width that was only 5% larger than the calculated value could prevent the fracture of the interface.

Tensile Property of ANSI 304 Stainless Steel Weldments Subjected to Cavitation Erosion Based on Treatment of Laser Shock Processing.

Tensile property was one important index of mechanical properties of ANSI 304 stainless steel laser weldments subjected to cavitation erosion (CE). Laser shock processing (LSP) was utilized to strengthen the CE resistance, and the tensile property and fracture morphology were analyzed through three replicated experiment times. Results showed tensile process of treated weldments was composed of elastic deformation, plastic deformation, and fracture. The elastic limit, elastic modulus, elongation, area reduction, and ultimate tensile strength of tensile sample after CE were higher in view of LSP. In the fracture surface, the fiber zone, radiation zone and shear lip zone were generated, and those were more obvious through LSP. The number and size of pores in the fracture surface were smaller, and the fracture surface was smoother and more uniform. The dimples were elongated along the unified direction due to effects of LSP, and the elongated direction was in agreement with the crack propagation direction. Their distribution and shape were uniform with deeper depth. It could be reflected that the tensile property was improved by LSP and the CE resistance was also enhanced.

A study on plasma plume fluctuation characteristic during A304 stainless steel laser welding

A passive electrical probe device is employed to detect the electrical signals of the plasma in the experiments of YAG laser welding on 304 stainless steels. The high-speed CCD camera device is synchronously triggered to record the plasma plume shape. The corresponding relation between plasma plume shape and electrical signal is found by analyzing the fluctuation of the plasma plume shape and the change of the detected electrical signal. A shape of the plasma plume expands corresponding to the electrical signal declining while a shape of the plasma plume contracts corresponding to the signal electrical increasing. This indicates that the voltage fluctuation of the electrical signal can be used to characterize the expansion and contraction of the plasma plume shape, so the electrical signal can be used to analyze the fluctuation characteristic of the plasma plume. The electrical signals are processed by FFT. A characteristic peak occur on the frequency spectrum of the electrical signal in the deep penetration laser welding. In contrast, the frequency spectrum of the electrical signals did not show a characteristic peak in the heat conduction welding. A method named spectral intensity is proposed to compare the difference between deep penetration laser welding and heat conduction welding. The result demonstrates that the spectral intensities of deep penetration laser welding are larger than those of heat conduction welding.

Microstructure-property relationship for AISI 304/308L stainless steel laser weldment

Laser welding is attractive for numerous applications requiring materials joining, due to its low energy input. However, it is unknown how the laser welding process influences the microstructure-property relationship across the weldment. The objective of this study is to determine the strengthening mechanisms in the weld metal, base metal, and heat affected zone (HAZ) of an AISI 304/308L stainless steel (SS) laser weldment. Scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD) scanning and transmission electron microscopy (TEM) was used to evaluate the microstructure, and static nanoindentation was used to evaluate strength across the weldment. Although the HAZ has a finer dendritic grain structure, its higher hardness compared to the base and weld metal cannot be explained by the Hall-Petch relationship. Therefore, a new strengthening model for weldments that considers the evolution in grain boundary size and orientation angle, as well as dislocation density, precipitation, and solid solution is proposed. Notably, core-shell Ti-C-N precipitation, which provides Orowan dislocation bypass strengthening, is found to be a major contributor to strengthening in the HAZ. The proposed model predictions fall within 10% of experimentally measured properties for all three regions of the analyzed weldment.

CFRTP and stainless steel laser joining: Thermal defects analysis and joining parameters optimization

Experiments with different joining parameters were carried out on fiber laser welding system to explore the mechanism of CFRTP/stainless steel joining and the influence of the parameters on the joining quality. The thermal defect and the microstructure of the joint was tested by SEM, EDS. The joint strength and the thermal defect zone width was measured by the tensile tester and the laser confocal microscope, respectively. The influence of parameters such as the laser power, the joining speed and the clamper pressure on the stainless steel surface thermal defect and the joint strength was analyzed. The result showed that the thermal defect on the stainless steel surface would change metal’s mechanical properties and reduce its service life. A chemical bonding was found between the CFRTP and the stainless steel besides the physical bonding and the mechanical bonding. The highest shear stress was obtained as the laser power, the joining speed and the clamper pressure is 280 W, 4 mm/s and 0.15 MPa, respectively.

Effect of Al-Si Coating on Microstructure and Properties of 22MnB5 Steel Laser Welded Joint

Effect of Al-Si Coating on Microstructure and Properties of 22MnB5 Steel Laser Welded Joint