Laser Surface Hardening Process Research Articles

Research on microstructure evolution of laser surface quenching of ductile cast iron

Abstract Ductile cast iron is widely used in the manufacturing of components and dies due to its excellent performance and low cost. Laser surface quenching can further improve its performance and extend its service life. This article uses scanning electron microscopy, electron backscattered scattering detection and microhardness tester to systematically analyse the microstructure evolution of the melted zone, hardened zone, and matrix of ductile cast iron with laser surface quenching. The hardening zone can be divided into two layers: one layer contains a large amount of martensite, graphite, and bits of residual austenite, and the other layer contains a composite structure of graphite, ferrite, layered martensite+austenite+Fe3C. On the basis of microstructure research, the determination and optimization methods of the depth of the laser surface hardening zone and the process are formed, providing a basis for the selection and optimization of the laser surface hardening process for ductile cast iron.

AN ENHANCEMENT IN THE COPPER ELECTRODE WEAR CHARACTERISTIC ELECTRICAL DISCHARGE MACHINED INCONEL 718 THROUGH ION NITRIDING, LASER SURFACE HARDENING AND HYBRID PROCESS

The virgin copper electrode has limited application due to its wear and mechanical properties using Electrical Discharge Machined (EDMed) on Inconel 718 superalloys. In order to enhance the performance of copper electrodes, in this work, Ion Nitriding (IN), Surface Hardening by Laser (LSH) and Hybrid Process ([Formula: see text]) are performed on copper electrodes to reduce the electrode wear in frontal and lateral. The electrode wear in the frontal and lateral of virgin copper electrode is processed and studied using EDM with varying pulse durations, current and Silicon Carbide (SiC) mixed EDM oil. The surface hardness in virgin and processed electrodes is also investigated. Overall analysis found that the hybrid technique produced a 59% higher hardness than that of virgin copper. The hardness in the EDMed surface was higher than that of the processed copper surface. A 1000[Formula: see text][Formula: see text]s pulse duration, 2 A current and 15 g/l SiC powder mixing EDM oil produced a low frontal wear in both virgin and processed copper electrodes. The electrode wear was reduced by 30% for frontal and 76% for lateral using a hybrid method.

State of art: Review on laser surface hardening of alloy metals

Surface hardening treatments are performed to increase the hardness, wear resistance, durability and their micro structural properties. After the development of High-Powered Diode Lasers (HPDL), the laser surface hardening process is widely applied due to their non-contact treatment process, rapid cooling without any medium, controlled method of heat treatment and depth with automation and precision with relatively minimum energy input. Laser surface hardening of steels, carbon alloys, iron and other metals in manufacturing of components, stamping and forging dies, tools and other components in the field of mechanical, automotive and metallurgical have shown a positive progression in hardness and wear resistance with controlled phase changes. The factors of laser power density and travel speed plays key roles in phase changes and the surface transformation hardening. The surface hardening of heavily loaded components under motion should possess good surface roughness, tribological characteristics of wear resistance, hardness and temperature coefficients. Thus, laser surface hardening is optimum, controlled and economic way of surface treatment processes in manufacturing of mechanical components.

Feasibility of using graphene as a substitute to graphite in the laser surface hardening of ferritic stainless steel

The broad potential applications of ferritic stainless steel in industry can be increased with the addition of protective elements such as carbon for surface hardening. Laser surface hardening (LSH) using carbon elements, such as graphite, has received widespread attention. However, to obtain high quality results, the use of graphite slurry, a specific environment, or remelting are required. To overcome this challenge, the LSH using graphene as an alternative to graphite was comparatively studied in this work. Accordingly, the stability of hardened layers, which depicts their sustainability in actual environmental conditions, was compared in graphene, graphite, and their slurries to improve the evaluation of graphene in the LSH process. The stability of hardened layers predominantly depends on the hardness, crack susceptibility, interfacial stress, hardness depth (or aspect ratio), and interfacial hardness. Under suitable process conditions, graphene exhibits good stability, with the highest hardness and low stress fluctuation without crack formation at the interface. Moreover, the powder layer thickness and laser power can be adjusted to achieve maximum improvements in the aspect ratio and microhardness in the area near the interface. Thus, high microhardness and a crack-free hardened layer without additional remelting or the use of a slurry were obtained.

A comparative analysis of the effect of laser surface treatment on the dry sliding wear behavior of ductile cast irons with different microstructures

In this study, the wear behavior of ferritic (GJS 400) and pearlitic (GJS 700) ductile cast iron (DCI) specimens after laser surface hardening were investigated comparatively. In general, multi-pass laser applications are inevitable in a laser surface treatment (LST) applied for surface hardening because the laser spot diameter is quite small compared to the applied surface area. This situation may cause a decrease in wear resistance due to residual stress formation because of the thermal gradient and softening effect due to the overlap ratio. In this study, a single-pass laser surface hardening (LSH) process with a laser pulse area of 20 × 5 mm2 compatible with the laser energy density (6.28 J/mm3) used in the literature, was applied to overcome these limitations. Thus, it is aimed to make it possible to evaluate the comparative analysis more reliably. After LSH processes, hardness values of DCI samples increased approximately 4.3 times compared to untreated ones due to the transformation hardening effect. In the microstructure of the laser-treated pearlitic DCI samples, martensite was present as the dominant phase in addition to a small amount of residual austenite. As for the ferritic DCI samples, the ledeburite and martensite phases were detected. Dry sliding wear tests were performed using different loads (5 N, 10 N) and sliding speeds (10 mm/s, 20 mm/s, 30 mm/s). As a result, the wear volume loss values of laser-treated ferritic and pearlitic DCI samples could be reduced by approximately 26.6% and 30.7%, respectively, compared to untreated ones. The COF values of the untreated samples increased with increasing load, while those of LSHed decreased. Severe plastic deformation and delamination were observed for untreated samples, while mild plastic deformation and micro-grooves were observed for samples with LSHed.

Combining the Finite Element Analysis and Kriging Model for Study on Laser Surface Hardening Parameters of Pitch Bearing Raceway.

Laser surface hardening is used to improve the fatigue performance of the large diameter pitch bearing. Determination of the process parameters by a trial and error method, depending on the experience of the technician, by changing the parameters repeatedly for each laser surface hardening process is time-consuming and costly. In this paper, a method of analyzing the maximum temperature and depth of a hardened layer during the laser surface hardening process for a pitch bearing raceway of a wind turbine is proposed, which combines finite element simulation and the Kriging model. A three-dimensional finite element model of a pitch bearing ring was established using ABAQUS. The temperature field analysis was performed. The effects of process parameters including laser power, scanning speed, and laser spot radius on the depth of the hardening layer were investigated. Then, taking into account the interactional effects of different process parameters, Kriging models were constructed to reflect the relationship between input process parameters and output responses. The results show that the Kriging approximation model has a small relative error compared with the simulated results and can be used to predict the hardened layer depth.

Numerical and statistical modelling of high speed rotating diode laser surface hardening process on a steel rod

The present study aims to develop an integrated statistical mathematical model utilizing response surface methodology (RSM) coupled with finite element method (FEM) for optimizing laser surface hardening process on a cylindrical steel solid rod. The proposed quasi-stationary laser beam processing technique utilizing high-speed rotation facilitates to obtain a uniform hardened layer along the entire work piece surface with complete elimination of deleterious inter-pass tempering effects in overlapped regions. The developed model validated with experimental results conducted by changing laser power (2500–3500 W), linear speed (8–12 mm/s) and rotary axis speed (1600–2000 RPM) on a 12 mm thick En-31 steel cylindrical rod employing a 4 mm X 4 mm square laser spot. The setup constitutes a 1.0 mm fiber-coupled diode laser integrated to 6-axis Robot and a high-speed rotating lathe. The three-factor three-level Box-Behnken design available in RSM used to develop the regression model. A multi-objective optimization technique used to optimize the process parameters on attaining maximum case depth, maximum mean hardness along hardened layer depth and minimum differential hardness across the treated layer. Good agreement realized between actual experimental values to optimized values obtained from the RSM model with desirability approach resulting in complete elimination of tempering effects in overlapped regions. Indeed, the optimal processing parameter combination obtained from RSM methodology desirability approach constituted 3500 W laser power, 8 mm/s linear speed and 2000 RPM that facilitated in validation of hardened layer in terms of 330–350 µm case depth with minimal differential hardness of 56–58 HV within the treated layer throughout its length processed. Apparently, optimum parameters obtained with a desirability approach found to be in good agreement with thermal profiles obtained from FEM analysis with an error difference of 3–5%.

Finite element analysis and experimental validation of high-speed laser surface hardening process

In this study, a finite element method is presented with an aim to predict the temperature distribution for optimizing laser surface hardening process on a cylindrical steel solid rod. The proposed quasi-stationary laser beam processing technique utilizing high-speed rotation was employed to obtain a uniform hardened layer along the entire workpiece surface with complete elimination of deleterious inter-pass softening effects in the overlapped regions and melting. The simulated model has been validated with actual experimentation on En-31 steel rod employing a fiber-coupled diode laser and high-speed rotating mini-lathe. Two principal quality-determining factors of laser surface hardened layer, namely, total hardened case depth and hardness distribution, across and along its depth and length of the rod are correlated and compared. The most important output factor—differential hardness—a measure of variation in hardness distribution obtained longitudinally along the processed rod length—was analyzed in terms of its variation with processing parameters such as laser power, linear speed, and rotary axis speed. The simulated thermal history with temperature distribution and thermal contours simulated facilitated in correlating the hardened surface profile with hardness distribution. Indeed, the temperature distribution profiles simulated along the treated layer longitudinally and through thickness, processed with high rotary axis speed and appropriate linear speed, exhibited uniform treated layer with complete elimination of inter-pass tracking softening effects with surface temperature being above critical temperature throughout the processed length. A good agreement could be realized between actual experimental values and that of optimized values using the finite element model.

Sliding wear behavior of laser surface hardened austempered ductile iron

This study describes the laser surface hardening process effect on microstructures produced and their wear behavior. Ductile iron samples were austempered at three different austempering temperatures: 232 °C/288 °C/398 °C respectively. Then, the laser surface hardening process was applied on each sample. Different laser gaps were designed: 1.5mm/3mm/4 mm. The microstructures were observed using optical microscopy and tribo-tests were run using a UMT-3 tribo tester. A Rockwell hardness tester was used to measure the hardness after heat-treatment. Optical microscopy and SEM were used to observe the different microstructures and their distribution on the worn surface. The results showed that the laser processing generated ledeburite, martensite, or tempered bainite microstructures. Vickers hardness tests were carried out on these microstructures. The original needle-like microstructures were observed on the samples with 4 mm laser gap but not with 1.5 mm or 3 mm laser gap. This is because part of the 4 mm laser gap is beyond the laser heat effected zone. Generally, severe ploughing wear and smearing wear were observed on the tempered bainite zone but not the bainite zone. Debris was generated during the tribo-tests and led to three body abrasive wear which not only resulted in higher wear loss, but also polished the worn surface.

Experimental investigation and effects of laser hardening process parameters on microhardness of En24 steel

In presented paper through experimental investigation is carried out with fiber laser system so as to evaluate the effects of laser surface hardening process parameters on the microhardness (width and depth) of the laser treated En24 steel using a Taguchi method. The optical microscope and microhardness tester is used to examine the microstructure, microhardness (width and depth) of the laser hardened samples across the heat affected zone. The selected process parameters were laser beam power (210, 225 and 300 W), laser scanning speed (1.0, 5.5 and 10.0 mm/s) and standoff distance (175, 200 and 225 mm) respectively. The laser treated hardened surface layer has a microhardness of 728.1 HV0.3 and reached a microhardness depth of 2471.44 µm, which is twice as high as untreated samples of En24 steel. From this study, it can be summarized that the microhardness of laser treated samples is maximized by controlling laser beam power, laser scanning speed and standoff distance, which improves the service life of laser-treated En24 steel components. The percentage error within the acceptable range was found to be small and was obtained by comparing the microhardness values obtained from the experimental results and predicted microhardness values obtained by using nonlinear regression equation.

Laser surface hardening of engine camshaft cams

The publication describes research into the laser hardening process of the camshaft cams surface. Samples of camshaft cams made of structural bearing steel were hardened using a powerful fiber laser LS-15. The effect of altering the laser surface hardening process parameters on the microstructure and microhardness of the surface was investigated. Also, the influence of low-temperature tempering after laser surface hardening was shown.

Multi-objective optimization of high power diode laser surface hardening process of AISI 410 by means of RSM and desirability approach

In this research, laser surface hardening of AISI 410 was carried out by a high power diode laser based on Response Surface Method (RSM). Laser power, scanning speed, and focal plane position were evaluated as input process changeable while geometry dimensions of hardened zone (i.e., Depth and width of hardness), maximum hardness, Microhardness deviation (MHD) from base material in depth, and ferrite phase percentage in the microstructure were evaluated as process output Results. The effect of input parameters on the response variations were studied by statistical investigation. Results indicated that by increasing the laser power and decreasing other parameters, higher surface hardness with significant penetration, and least ferrite percentage would be reached by means of the desirability function approach. By using experimental tests, validation of optimized results was performed. In this research in the optimum conditions, the maximum hardness, maximum depth of hardness and minimum ferrite percentage were achieved 670 Vickers, 2.2 mm and 0.45%, respectively.

Profile characterisation and response surface modelling of laser surface hardened Cr12 mould steel

Abstract For laser surface hardening (LSH) process, it is of great significance to obtain bead information from hardened layer as it is closely related to mechanical properties of hardened area. Correlating process parameters to fewer geometry features would greatly reduce the modeling complexity. In this paper, a three-factor-five-level central composite design (CCD) is proposed, based on response surface methodology (RSM), to model, analyse and optimize the influences of three process parameters, namely: laser power (LP), scanning speed (SS), and defocusing distance (DD) on the bead profile of laser surface hardened of Cr12 mould steel. Transverse cross-sectional profiles were firstly modelled by parabola function, in contrast to sine function, ellipse function and Gaussian function. The profile focal length (FL) as well as the hardened depth (HD) were selected as characteristic lengths for the bead profile. The results show that the response models interpret the hardened depth and focal length successfully and satisfactorily. It is observed that both responses are determined by three input variables with quadratic correlations. The predicted results are in good agreement with experimental counterparts. Validation experiment was finally conducted for testing the generalisation of fitted regression models. As the maximum relative prediction errors for both responses are respectively 3.91% and -7.35%, good generalisation of developed models has been accomplished.

A comparative study of laser surface hardening of AISI 410 and 420 martensitic stainless steels by using diode laser

Laser surface hardening process is one of the new technologies for improving the surface of metals, especially steels, which in recent decades has received a lot of attention. This paper surveys the capability of laser surface hardening of AISI 410 and AISI 420 martensitic stainless steel by using continues wave diode laser with a maximum power of 1600 W, experimentally. Microstructure of the laser treated area by using optical microscope (OM), Field emission Scanning Electron Microscope (FESEM), and XRD were investigated and compared. Geometrical dimension, micro-hardness deviation (MHD) from the micro-hardness of the base metal, ferrite percentage, and the grain size of the hardened zone are the other considered responses. The results indicate that in the same input parameters the AISI 420 has higher surface hardness and less penetration depth and width than the AISI 410 stainless steel. Observations showed that a laser surface hardened layer of AISI 410 is about 620 HV with 1.8 mm depth and while for AISI 410 is about 720 HV with 1.2 mm depth is obtained. Comparing the results with the furnace hardening heat treatment show that the laser hardening process is more effective and precise than conventional processes.

Improved laser surface hardening of AISI 4130 low alloy steel with electrophoretically deposited carbon coating

In the present study, the laser surface hardening of AISI 4130 was conducted using a continues wave diode laser with a maximum power of 1600 W. To improve the laser surface hardening process, carbon powder is deposited on the sample surface by electrophoretic method. By conducting laser surface hardening at the same input parameters and same heat input, the quality of the hardening is compared; cross sectional geometry of the hardened area (width, depth and entry angle of hardened), micro-hardness and the ferrite phase percentage of hardened layer. Microstructure evaluation of the laser hardened area was performed using optical microscopy. Results indicate that because of increasing the laser absorption in carbon coated samples, hardened area is larger (deeper and wider) and the value of the hardness is more than laser hardening of bare samples. Microstructure analysis indicates that transformation of the retained austenite into martensite due to the fast quenching, lead to the lower ferrite phase in martensitic structure in laser hardened layer and causes higher microhardness. Observations reveal that depth, width, and maximum hardness of laser hardening carbon coated sample without surface melting are 1.150 mm, 9.980 mm, and 762 Vickers, respectively, while for bare sample these values are 0.957 mm, 9.451 mm, and 707 Vickers, respectively. Comparing the results with the furnace hardening heat treatment show that the laser hardening process especially with carbon coated, is more effective and precise than conventional processes.

EFFECT OF LASER HARDENING OF STEEL ON THE WEAR PROCESS IN AN ABRASIVE SOIL MASS

This paper presents the results of tests for the effects of laser hardening on the course and intensity of wear of 38GSA (38MnSi4) and Hardox 600 steels in an abrasive soil mass. The tests were carried out under laboratory conditions, using a “rotating bowl” type machine. Two types of soil, i.e. light and medium, were used as the abrasive mass. Based on the obtained test results, it was found that hardness decreased (in relation to asdelivered condition). The performed laser surface hardening process significantly increased the abrasive wear resistance only for 38GSA (38MnSi4) steel. As regards to Hardox steel, the hardening treatment reduced the abrasive wear resistance index compared to the as-delivered condition of the steel.

Feasibility Studies on Underwater Laser Surface Hardening Process

Laser surface hardening process is a very promising hardening method for ferrous and nonferrous alloys where transformations occur during cooling after laser melting in the solid state. This study experimentally characterizes laser surface hardening of tool steel in both water and air. For the underwater operation, laser surface scanning is performed over the tool steel surface which is immersed in water. The laser surface hardening tests are performed with a maximum 200 W fiber laser with a Gaussian distribution of energy in the beam. For the surface hardening, single-track melting experiment which sequentially scans elongated path of single line has been performed. As the hardened depth depends on the thermal conductivity of the material, the surface temperature and the penetration depth may be varied by underwater laser processing. The feasibility of underwater laser surface hardening process is discussed on the basis of average hardness level and hardened bead shape.

A Crank–Nicolson Scheme with ADI to Compute Heat Conduction in Laser Surface Hardening

In this article, a two‐dimensional (2D) numerical model of a Crank–Nicolson scheme with alternating‐direction implicit (ADI) is developed for a heat conduction model in the laser surface hardening process. A numerical solution is compared to the analytical solution and shows a better suitability. Numerical experiment of the repetitive heating is carried out using the present model in order to investigate influences of processing parameters on temperature profiles. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(6): 522–541, 2014; Published online 11 November 2013 in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21085

Numerical evaluation of the reflectivity coefficient in laser surface hardening simulation

This paper reports the results concerning the simulation of a laser surface hardening process of a cylindrical surface. In particular it focuses on the problems related to the definition of the physical parameter values necessary in order to achieve an accurate and reliable simulation. The strict dependency of laser process simulation results on the physical parameters describing the target material is, in fact, a well known matter, especially considering that the values of these parameters change during the process dependently on temperature and time. Moreover in laser surface hardening this problem is even more important because melting of the target material should be avoided, surface roughness plays an important role and, sometimes, the surface is coated with absorbent layers. These factors increase the complexity of the simulations and make the evaluation of the physical parameters more difficult and critical. The results presented in this paper are obtained on AISI420B steel, coated with graphite and treated with a direct diode laser. Considering the above mentioned conditions, a plausible temperature dependent reflectivity coefficient was evaluated and its robustness was investigated. This reflectivity coefficient can be used with a good approximation for the simulation of laser hardening treatments of many carbon steels.

금형재료용 주철의 다이오드 레이저 표면경화처리에 관한 연구(II) - 표면경화의 적용 부위에 따른 열처리 특성의 차이 -

레이저 표면경화처리는 고밀도 에너지 열원에 의해 레이저 조사부위만 급속 가열한 후 표면의 열이 내부로 전도되어 급속히 자기냉각 됨으로써 표면을 경화시키는 방법이다. 이 표면처리 방법은 열처리에 의한 열변형이 거의 없고, 표면경화처리 이후 다른 공정을 수반하지 않는다. 또한 국부적인 가공이 가능하기 때문에 복잡한 형상을 가지는 금형에는 적합한 표면처리 방법이다. <BR> 본 연구에서는 열처리에 적합한 빔 프로파일을 가진 고출력 다이오드 레이저를 이용하여 금형재료용 주철의 표면처리를 실시하였다. 프레스 금형 공정에 따른 금형의 형상이 다르기 때문에 적용부위에 따라 시험편을 평면과 모서리부로 나누어 열처리를 실시하였다. 이때 모서리부의 열처리는 광학헤드를 10° 기 울인 상태에서 진행하였다. 그 결과, 모서리부의 열처리는 평면부와 비교하여 형상에 따른 열전달 루트가 제한되므로, 입열이 집중되기 쉬워 평면 열처리보다 빠른 이송속도에서 경화가 이루어졌다.