Laser Hardening Process Research Articles

Effects of low-power laser hardening on the mechanical and metallurgical properties of biocompatible SAE 420 steel

The present experimental work is carried out on SAE 420 steel to optimize process parameters of low-power laser hardening to improve surface micro-hardness and wear resistance for dry sliding for bio-medical applications. Laser power is the most significant factor for micro-hardening and wear resistance. Rank two for scanning speed and three for standoff distance, respectively. The experiments show that the surface micro-hardness of treated samples varies from 711 to 833 Vickers Pyramid Number by optimized process parameters such as laser beam power of 300 W, laser scan speed of 1.0 mm/s, and standoff distance of 225 mm. In comparison, the base material micro-hardness is 208 Vickers Pyramid Number as the predictive equation generated for finding micro-hardness value for the above three laser hardening process parameters. The dry sliding wear test is conducted on all laser-treated samples and a comparison is made with the untreated sample. A significant improvement in wear resistance was observed for treated as compared to untreated samples. The wear of laser hardened sample of SAE 420 steel was 3.67 x10-9 g/cm compared to untreated base metal wear rate of 139.00 x 10-9 g/cm at an applied load of 30 N and sliding speed of 300 revolutions per minute. The scanning electron microscopy analysis of wear samples (untreated, treated maximum, and minimum hardness) is observed for investigating material removal patterns.

Effect of laser hardening and post hardening shot peening on residual stress evolution in X5CrNiCuNb16-4 steel for steam turbine blade applications

Laser-hardening process produces higher surface hardness and provides deeper hardness profile into the material. This increment in hardness reduces water-droplet erosion on steam turbine blades. In the present study, a steam turbine blade profile was subjected to laser-hardening process primarily on the suction side of the profile. This hardening process transformed tempered martensite structure of the unaffected material to a fine martensite structure at the processed zone with an intermediate transition zone being present in between them. The fine martensite was responsible for spike in hardness profile at the surface. When the laser-hardened blade was subjected to operational stresses, a number of parallel cracks formed on the blade profile in the direction perpendicular to the blade axis. Detailed investigations in the form of residual stress mapping revealed that a narrow interfacial region beside laser-hardened zone over the profile of the processed blade material, indicated presence of tensile residual stresses. This region was responsible for the formation of parallel cracks over the blade profile. A shot peening process was introduced post laser-hardening which resulted in the elimination of the tensile residual stress, thus, mitigating crack formation over the blade profiles upon application of operational stresses.

Influence of Texture Effects on the Laser-Irradiated Tool Performance

Introduction. Laser surface treatment of mechanical engineering products makes it possible to increase their durability. However, the laser hardening process is not good at the consistency of results, since choosing the irradiation modes and schemes of specific products, texture effects in the zones of laser exposure are not taken into account. This leads to premature wearing and even destructing the working surfaces of irradiated products. Therefore, the work objective is to study the mechanism of influence of the structure of the laser-hardened layer on the operational properties of the tool.Materials and Methods. The materials for this study were tool steels: R6M5 and R18 (according to the EN 10027 standard tool steels: 1.3355, 1.3343). Pulsed laser irradiation was carried out at the technological device Kvant-16 with a radiation power density of 70–250 MW/m2. Scanning probe and optical microscopy, X-ray diffraction and durometric methods for analyzing the steels structure were used. The values of steel strength in bending and impact strength were determined before and after laser treatment.Results. It has been experimentally proven that it is necessary to strengthen the sections of the products working surfaces that are subject to maximum wear and are under the action of compressive stresses during operation. It is shown that textural effects in the laser treatment zones lead to a decrease in the friction coefficients and contribute to an increase in the wear and adhesion resistance of the steels surface layers.Discussion and Conclusion. The results of the research carried out make it possible to rationally select the surface laser processing modes and schemes of products for various functional purposes and ensure their operability with a guarantee. The possibilities increasing the structural strength and properties of the tool due to laser alloying the surface layers of powder-coated steels and stabilizing tempering after laser irradiation are determined.

Comparing the surface hardness of mild steel processed with CO₂ and fibre lasers

The microhardness of low carbon mild steel was analysed after surface treatment by using carbon dioxide CO₂ and Fibre laser for comparison. Identical input parameters were used to compare the increase between the as-supplied material hardness and the treated surface. Microhardness testing was used to measure the surface hardness and a scanning electron microscope (SEM) was used to investigate the microstructural changes in the substrate. It was found that the laser scanning speed had a significant effect on the increased surface hardness, while the laser power was a less significant factor. The samples processed with the lower laser fluence of the Fibre laser exhibited a hardness increase of 38% with maximum depth of 200 μm, while those processed by the CO₂ laser exhibited a hardness increase of 41% with a maximum depth of 50 μm. A full design of experiment (DoE) model was modified for the optimization and prediction of the laser hardening process. The processing parameters applied were the laser beam power and the scanning speed.

Microstructure and wear behavior of arc-shaped 40CrNiMo steel after laser hardening

This study focuses on arc-shaped 40CrNiMo steel; the microstructure characteristics and formation mechanism of the hardened layer at different positions were investigated after laser hardening. Moreover, sliding friction experiments were conducted against GCr15 steel after the conventional heat treatment under dry friction conditions, and the wear characteristics of 40CrNiMo steel hardened after different laser process parameters was analyzed, the wear mechanism in different wear stages was studied. The results show that the martensite reliefs within different austenite grains have no effect on each other. The martensite relief within each individual austenite grain is closely related to the martensite growth in that grain. The laser hardening process parameters for obtaining the effective wear resistance performance of arc-shaped 40CrNiMo steel are as follows: the power was 2010 W, the spot size was 1 × 14 mm2 and the scanning speed was 800 mm/min. At the beginning of the friction wear tests, the wear type of arc-shaped 40CrNiMo steel is mainly abrasive wear. Abrasive wear causes spalling, and oxidation wear can easily occur at the peeling sites. As the dry friction wear tests continued, both oxidation wear and adhesive wear increased, and fatigue wear gradually occurred. The wear mechanism of the grinding plate with a similar hardness at different stages is similar to that of the circular-arc specimen.

SELECTIVE SURFACE HARDENING OF GEAR MECHANISM SHAFT BY ROBOTIC LASER 3D SYSTEM

A robot-based laser 3D hardening method is proposed as a finishing operation to increase the wear resistance of the metal end-products. The laser hardening process of the surface layer of the products by changing its structure is one of the most effective methods of selective surface hardening. Thermal hardening of metals and alloys by laser radiation is based on local heating of a surface area under the influence of radiation and subsequent cooling of this surface area at a supercritical speed due to heat removal into the inner layers of the metal. The used robot-based laser 3D system (FANUC industrial robot and SCANLAB scanning optics) allows processing the surfaces of any complexity and geometry, including the shafts of the gear mechanism of the seed drill. It was found that the development and improvement of the technological process of manufacturing steel shafts of the gearbox of the seed drill is an urgent technological problem due to the rapid retirement of the shaft, which leads to the expenditure of time and money for its replacement. The most heavily loaded sections of the shaft were pre-estimated using the SolidWorks Simulation software package. A high-power TruDisk 8002 solid-state disk laser with a maximum laser power of 8 kW and a wavelength of laser radiation of 1030 nm is used for high-quality laser surface treatment of the AISI 1066 steel shaft of the gear mechanism. The laser surface heat treatment was carried out using a constant power strategy (continuous mode), varying the laser power in the range of 1.35–2.25 kW. Based on the Fe-Mn two-component state diagram, the critical points of the temperature of complete austenization of the studied steel were previously predicted taking into account the chemical composition of the material. Additionally, the energy density values of the laser beam with a diameter of 1 mm on the working surface was estimated. The results showed that the surface hardness of the shaft was about 2.5 times higher compared to the untreated surface. The working ranges of laser heat treatment parameters of the gearbox shaft were established to increase the hardening intensity (100–150%) of the responsible areas.

Improvement in the graphite electrode wear characteristic of electrical discharge machined Nimonic 90 through plasma nitriding, laser hardening and duplex process

Improvement in the graphite electrode wear characteristic of electrical discharge machined Nimonic 90 through plasma nitriding, laser hardening and duplex process

Studying and Improving the Hardness Properties of Gray Cast Iron

This research focuses on the hardness of gray cast iron. Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. The machinability cannot set a specific definition. However, several indicators and directories give a clear image, the most important of which is the factors that affect the machinability of gray cast iron according to the metallurgies and the metal cutting and cutting conditions. The main goal of this research is to improve the hardness of gray cast iron. Many experiments on several samples to get different results and then compare these results to get the best which is the goal of the research. The conclusions through the practical side of this research are the different values of hardness through the different hardening processes. As the hardening processes gave a sample of grey cast iron a hardness value that differs in each type of hardening. The notes through the graph that the hardness reaches its peak in the traditional hardening, where its value is (370.6), followed by the laser hardening process, which reaches (321.6) The amount of increase between the hardness of the laser and the traditional hardness takes the value of (15.24 %) The work on samples in the form of aggregates, and each group will be treated in a specific way and then subject to tests.

Stress sensitivity analysis of laser quenching based on regression model

In the laser quenching process, quantitative evaluation of the influence of different process parameters on quenching stress is the key to achieve quenching process optimization. A variety of different process parameters are selected as research objects, and a parameterized thermomechanical coupling model of the disk laser hardening process for 45 steel is established. Through the calculation of the model, the instantaneous change law of stress field and the phase change field under different process parameters are obtained, and the response surface equation between the multiphysics solution results and process parameters is established. The Monte Carlo method is used to randomly sample the response equation repeated times, and the sensitivity of quenching process parameters is calculated through sampling results. The calculation result shows that hollow teardroplike stress distribution is formed in the center of the spot during quenching, and the stress around the spot is larger. Thermal stress concentration appears in the reverse direction of quenching scanning, with a maximum value of 850 MPa, and a cometlike stress zone appears in the reverse direction of quenching scanning. The diameter of the laser spot is negatively correlated with quenching stress and has the greatest influence on it. The laser incidence angle has a great influence on the depth and width of the phase change layer and is positively correlated. This model can reveal the mechanism of multifield coupling changes in the material during quenching and provide technical and theoretical support for the reasonable selection of process parameters.

Numerical simulation of two-track laser hardening process of 42CrMo steel

ABSTRACT In this study, a thermal–phase–mechanical coupled numerical model was presented for the prediction of the distribution of temperature, phase and residual stress of 42CrMo steel during two-track laser hardening process. Austenite and tempering transformation were simulated based on the isoconversional method. K-M equation was used to calculate the fraction of martensite. Residual stress was calculated considering the thermal strain, transformation strain and transformation plasticity. The accuracy of the numerical model was verified according to the comparison with experimental results. The stress distribution of two-track laser hardening process was studied according to numerical simulation results. And the effect of the second track on the residual stress produced by the first track in two-track laser hardening was also analyzed by using this numerical model.

Improvement of laser hardening technology with oscillating beam using multiphysics simulation

A simulation approach was used to improve the results of the laser hardening process of a thin-walled medium manganese steel specimen using oscillating beam technology. During the analysis of the material hardness results, it was found that the hardened zone had an irregular shape, which was the result of different thermal cycles varying with the process progress and heating of the sample. A simulation model of the laser hardening process was built to determine the proper power values to compensate for the effect of thermal inertia of the cool part. The simulation approach, in addition to the development of the master model, included the definition of the proper beam power distribution and the virtual determination of the necessary oscillation frequency that allows the equivalent linear beam distribution to be used in the calculations. The main model considered the dependence of the material properties on the phase composition of the material and was calibrated based on the results of experimental thermocouple measurements. This enabled the determination of the required power course. Using the simulation-calculated beam power, a hardening process was carried out, the results of which confirmed the successful modification of the shape of the hardened zone.

Experimental validation of workpiece deformation simulations by means of rigorous boundary condition analysis

The new concept of process signatures allows the targeted adjustment of workpiece surface integrity in various manufacturing processes. Since the process signature is often identified by means of numerical simulations, its experimental validation is an important research aspect. While the mechanical workpiece load required to determine the process signature can be measured in the process using speckle photography, the boundary conditions assumed for the simulation usually do not match with the experiment. The reason for this is, for example, the uncontrollable thermal drift movements of the workpiece in the clamping. Using the example of a laser hardening process, a method for reducing clamping influences is proposed. The force-free single-point fixture of the workpiece, which is used in this context, ensures defined process conditions in the center of the measuring field and, with its fixed point, simultaneously specifies the boundary conditions for the simulation. As a result, consistent agreement between measurement and simulation is achieved with deviations of less than one percent and validation of the process simulation is enabled.

A comparative investigation of different overlaps of the diode laser hardening in low-carbon steel and stainless steel

In this paper, the effect of laser overlap on the low-carbon and stainless steel are investigated. The analyzed samples are made of AISI 4130 low-Carbon steel and AISI 410 stainless steel with 50% overlap. The used laser is an industrial high-power diode laser with a continuous wave and a maximum power of 2 kW. Samples are fabricated using optimized levels for laser power, focal plane position, and laser scanning speed, and the heat-treatment process is done after that. The parameters and conditions for the laser hardening process of both samples are the same situation. Then, the microstructure analysis is done using OM and SEM. Besides, the hardness of the samples is tested in the hardening depth and width. The study shows that the hardness is improved for both samples at the overlap area, up to 762 hv for AISI 4130 and 675 hv for AISI 410. Also, in both samples the amount of ferrite phase has decreased.

Numerical simulation and experimental study on laser hardening process of the 42CrMo4 steel

The large diameter pitch bearing was made of steel 42CrMo4 and the laser hardening process was used to improve its surface properties. In this paper, a numerical approach which can predict the temperature field and the hardened depth is provided for the laser hardening process of the 42CrMo4 steel. According to the simplification of the raceway structure of pitch bearing, the finite element model was constructed using ABAQUS software. Based on the actual process parameters, the transient thermal analysis was accomplished and the distribution of temperature field is analyzed. The hardened depth is determined according to the proposed temperature range. Laser power, laser scanning speed, and spot diameter were considered as input parameters, the experimental studies were performed based on orthogonal design in order to study the effects of process parameters. The finite element model is validated. The surface roughness and microstructure studies on treated surfaces were conducted. Also the micro-hardness testing was performed. The results show that the laser hardening increases surface hardness by about 3.8 times than that of the base material. The three parameters of laser power, laser scanning speed, and spot diameter have a coupling effect on the surface treatment. The input laser power density is more important.

Hybrid processing of bearing steel by combining Direct Laser Interference Patterning and laser hardening for wear resistance applications

In this study, a hybrid process for increasing the hardness and thus resistance of laser-generated surface textures by a laser heat treatment for functional surfaces is proposed. The process chain involves the fabrication of well-defined periodic surface features on bearing steel using Direct Laser Interference Patterning in conjunction with a laser-hardening process. The fabricated laser hardened layer exhibits a laser feed rate dependent thickness between 500 and 800 µm which additionally enhances the hardness of the patterned surface from 210 to 827 HV 0.1. The increased surface hardness directly translates into a significantly improved wear-resistance of the surface patterns, which exhibit up to ~200% of that of non-hardened patterns. The proposed hybrid laser texturing-hardening approach allows the generation of wear-resistant and at the same time intact surface patterns for harsh environmentssuch in tribological applications.

Real-time stress evolution during laser surface line hardening at varying maximum surface temperatures using synchrotron X-ray diffraction

Multiple laser surface line hardening experiments on flat samples, made of tempering steel SAE 4140, were carried out under variation of the maximum control temperature in the range of 850 °C to 1150 °C at the sample surface. For each temperature, time resolved X-ray diffraction measurements using synchrotron radiation were performed at beamline P05@PETRA III at DESY (Deutsches Elektronen Synchrotron) in Hamburg, Germany. The samples were line hardened using a 4 kW High Power Diode Laser unit at a constant laser feed of 800 mm/min with a specific laser optics under pyrometer control of the maximum surface temperature. A special designed process chamber with 4 symmetrically attached fast silicon micro strip line detectors allows for stress analysis during the process according to the sin2ψ method in single exposure mode with a measurement frequency of 50 Hz. As a result of the time resolved analyses the elastic strains were separated from thermal ones and near surface local stress evolutions, longitudinal and transverse to the laser track direction in the center of the processed zone, were determined. The in situ experiments were complemented by high spatially resolved post-process residual stress analyses using conventionally generated X-rays and by metallographic investigations. The results are carefully discussed regarding mechanisms of local stress formation during the laser hardening process and their dependence on the maximum control temperature. The temporal stress course during laser surface line hardening is presented for the first time in both surface parallel directions, where temperature differences in the process zone lead to significant differences in the resulting residual stress profiles. In addition to the common validation of process simulations by comparison with experimentally determined data from the final state after processing, e.g. the resulting local residual stresses, the current work provides real-time data from in situ experiments during laser surface hardening for the validation of temporal stress courses of numerical process simulations.

Phase transformation of austempered and quench-tempered gray cast irons under laser surface hardening treatment

ABSTRACT In this research, the effects of laser surface hardening treatment on the phase transformation of austempered and quench-tempered grey cast irons were investigated. It was found that there were four zones in the matrix of austempered grey cast iron and three zones in the matrix of quench-tempered grey cast iron produced by the laser hardening process. Both cast irons had central laser-hardened zones containing ledeburite (Zone 1) and heat-affected zones (Zone 2) containing martensite. For austempering, an additional heat-affected zone (Zone 3) consisting of tempered ausferrite and a substrate (Zone 4) consisting of ausferrite was formed in the matrix, the dimensions of the laser-hardened and heat-affected regions were independent of the austempering and tempering temperatures. The results reported in this work could be used as a valuable reference for future research on laser-hardened grey cast iron applications. For quench tempering, the substrate (Zone 4) consisted of tempered martensite. Additionally

Study of the influence of the oscillation frequency on the surface hardening process of the 42CrMo4 alloy using an oscillating laser beam

A study of the surface hardening process of the 42CrMo4 steel alloy by means of an oscillating laser beam has been carried out. For this purpose, a fiber coupled high power diode laser source and a galvanometric mirror scanner have been used. The study is focused on determining the influence of the oscillation frequency parameter on the temperature, geometry, microstructure, microhardness and stress state of the treated region, as well as its relationship with the key parameters of the laser hardening process. The results confirm that the surface hardening process of the 42CrMo4 alloy by means of an oscillating laser beam is an alternative technique to the conventional laser surface hardening methods based on fixed optical guidance systems. On the other hand, the selected frequency of oscillation has a significant influence on the treated region, mainly on the temperature, and, consequently, on the geometry, microstructure and stress state of the same. The selection of a high oscillation frequency, able to maintain the material temperature above that of austenization and below that of melting, is decisive to ensure the stability and uniformity of the treatment.

The choice of pulse laser radiation modes for hardening a metal cutting saw

Increasing production rates of parts, toughening of operation modes and load increasing, reduce the service life of equipment. The destruction of the tool usually begins with the surface, so its strengthening is one of the main factors of improving the resource and reliability. Hardening the working surfaces with laser radiation is the most effective and promising method of hardening tools that are used under friction conditions. This article presents the results of experimental study of the laser hardening process of a band saw made of 9CrV tool steel; a mathematical model based on these experiments was made to show the connection of the parameters of pulse laser radiation and the depth of the resulting hardened area. It shows that the pulse energy and the movement speed for pulse laser hardening with the chosen parameters have a decisive influence on the depth of the hardened area.

Effects of Laser Hardening Process Parameters on Hardness Profile of 4340 Steel Spline—An Experimental Approach

This study displays the effect of laser surface hardening parameters on the hardness profile (case depth) of a splined shaft made of AISI 4340 steel. The approach is mainly based on experimental tests wherein the hardness profile of laser hardened splines is acquired using micro-hardness measurements. These results are then evaluated with statistical analysis (ANOVA) to determine the principal effect and the contributions of each parameter in the laser hardening process. Using empirical correlations, the case depth of splined shaft at tip and root of spline’s teeth is also estimated and verified with measured data. The obtained results were then used to study the sensitivity of the measured case depths according to the evolution of laser process parameters and geometrical factors. The feasibility and efficiency of the proposed approach lead to a reliable statistical model in which the hardness profile of the spline is estimated with respect to its specific geometry.