Laser Surface Hardening Research Articles

A Predictive Modeling Based on Regression and Artificial Neural Network Analysis of Laser Transformation Hardening for Cylindrical Steel Workpieces

Laser surface hardening is a very promising hardening process for ferrous alloys where transformations occur during cooling after laser heating in the solid state. The characteristics of the hardened surface depend on the physicochemical properties of the material as well as the heating system parameters. To exploit the benefits presented by the laser hardening process, it is necessary to develop an integrated strategy to control the process parameters in order to produce desired hardened surface attributes without being forced to use the traditional and fastidious trial and error procedures. This study presents a comprehensive modelling approach for predicting the hardened surface physical and geometrical attributes. The laser surface transformation hardening of cylindrical AISI 4340 steel workpieces is modeled using the conventional regression equation method as well as artificial neural network method. The process parameters included in the study are laser power, beam scanning speed, and the workpiece rotational speed. The upper and the lower limits for each parameter are chosen considering the start of the transformation hardening and the maximum hardened zone without surface melting. The resulting models are able to predict the depths representing the maximum hardness zone, the hardness drop zone, and the overheated zone without martensite transformation. Because of its ability to model highly nonlinear problems, the ANN based model presents the best modelling results and can predict the hardness profile with good accuracy.

Hardness Profile Prediction for a 4340 Steel Spline Shaft Heat Treated by Laser Using a 3D Modeling and Experimental Validation

Laser surface transformation hardening becomes one of the most effective processes used to improve wear and fatigue resistance of mechanical parts. In this process, the material physicochemical properties and the heating system parameters have significant effects on the characteristics of the hardened surface. To appropriately exploit the benefits presented by the laser surface hardening, it is necessary to develop a comprehensive strategy to control the process variables in order to produce desired hardened surface attributes without being forced to use the traditional and fastidious trial and error procedures. The paper presents a study of hardness profile predictive modeling and experimental validation for spline shafts using a 3D model. The proposed approach is based on thermal and metallurgical simulations, experimental investigations and statistical analysis to build the prediction model. The simulation of the hardening process is carried out using 3D finite element model on commercial software. The model is used to estimate the temperature distribution and the hardness profile attributes for various hardening parameters, such as laser power, shaft rotation speed and scanning speed. The experimental calibration and validation of the model are performed on a 3 kW Nd:Yag laser system using a structured experimental design and confirmed statistical analysis tools. The results reveal that the model can provide not only a consistent and accurate prediction of temperature distribution and hardness profile characteristics under variable hardening parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects. The modelling results show a great concordance between predicted and measured values for the dimensions of hardened zones.

Optimization of Process Parameters for High Efficiency Laser Forming of Advanced High Strength Steels within Metallurgical Constraints

Laser forming (LF) has been shown to be a viable alternative to form automotive grade advanced high strength steels (AHSS). Due to their high strength, heat sensitivity and low conventional formability show early fractures, larger springback, batch-to-batch inconsistency and high tool wear.In this paper, optimisation of the LF process parameters has been conducted to further understand the impact of a surface heat treatment on DP1000. A FE numerical simulation has been developed to analyse the dynamic thermo-mechanical effects. This has been verified against empirical data. The goal of the optimisation has been to develop a usable process window for the LF of AHSS within strict metallurgical constraints. Results indicate it is possible to LF this material, however a complex relationship has been found between the generation and maintenance of hardness values in the heated zone. A laser surface hardening effect has been observed that could be beneficial to the efficiency of the process.

A Study on Laser Surface Hardening of Cylindrical Components in Manufacturing Process

Continuous improvement in the manufacturing sector advances the comfort of our society. The selected moving pattern of the laser hardening system was a spiral, in which the bottom roller rotates and moves axially by keeping laser head fixed. The different sizes of specimens made according to the requirement of studies like microstructure, hardness and depth, wear resistance. The properties investigated are microstructure, hardness, depth of hardness, temperature distribution and trial run of the bottom roller for yarn test. Finite element analysis conducted for temperature distribution in the model using ANSYS software. The laser treated bottom roller was fitted on the textile machine for a trial run. Performance study made for fitment and productivity. The yarn produced by the laser treated bottom roller were tested and compared with the existing yarn results and the yarn standards.. The process parameters, laser power, scanning speed and pulse width, which are influencing the hardness and depth are selected. Pre-tests are made to fix the range of the parameters. The combination of the parameters in their range was arrived from the design matrix of central composite rotatable design. The regression equations have been developed from the design matrix and responses using MINITAB 14 software. The models have been checked for adequacy using ANOVA technique.

A sequential method to determine the surface absorptivity in the process of laser surface hardening

A sequential method is adopted to estimate the surface absorptivity in the process of laser surface hardening in this paper. The experimental temperature data given by Wang et al. [8] is used to verify the applicability of the proposed method. The results indicated that the proposed method is able to estimate the surface absorptivity accurately in the process of laser surface hardening.

Numerical-experimental analysis of the effect of surface oxidation on the laser transformation hardening of Cr–Mo steels

Laser surface hardening is a technology that enables important advantages to be obtained in comparison with conventional techniques in terms of accuracy of the heat affected zone and productivity. Nevertheless, the development of realistic and flexible models has to be fulfilled in order to control the effects of every set of process conditions. Despite many different models having been developed, very few of them deal with the increment of absorption related with the instantaneous value of the layer of oxide growth during the process in a non-protective atmosphere. This work analyzes the problem of oxide formation at the external surface using kinetic relations, whose parameters have been related with the process variables, considering non-equilibrium conditions. Then, the oxide thickness was associated with a value of absorption through an innovative formula that considers the path of the laser radiation in the interface oxide-base material. The thermal calculations obtained by this method have allowed phase changes to be predicted using Avrami law. Both thermal and metallurgical results for different process conditions have been compared with experimental data showing an excellent agreement.

Surface microrelief and hardness of laser hardened and ultrasonically peened AISI D2 tool steel

This paper is focused on experimental analysis of the effects of laser surface hardening (LSH) combined with subsequent ultrasonic impact treatment (UIT) on the surface microrelief, hardness and microstructure in near-surface layers of AISI D2 high-chromium, cold worked tool steel. The LSH provides fast heating of the near-surface layers to the temperature above that of the phase transformation and temperature then rapidly cools by a self-quenching process. The formed heat affected zone is hardened thanks to the rapid heating/cooling process affecting microstructure, phase composition and carbide formation. Conversely, the UIT induces multiple impact loads providing severe plastic deformation of near-surface layers, and the hardening occurs by a dislocation mediated process. The optimal parameters of each process were determined to obtain maximum hardness and regular surface microrelief. Further, complete analysis of the effect of combined treatment (LSH+UIT) on the surface hardness, microhardness depth profile and surface microrelief was performed. Results show that the combined LSH+UIT process provides almost triple, double and a 10% increase in hardness in comparison with those of the initial, UIT-processed and LSH-treated states, respectively. The surface microrelief, waviness and roughness parameters were respectively diminished after LSH+UIT by approx. 50, 65, and 90%. XRD analysis was carried out after LSH and LSH+UIT processes, which showed essential α-Fe peak broadening due to the formation of microstrains (0.27% and 0.47%, respectively) and reduction in crystallite size (84nm after LSH+UIT). Favorable compressive residual stresses (−205MPa and −409MPa, respectively) were also observed in the near-surface layers of ~350 and 80μm thick, respectively. The obtained results demonstrate that the combined LSH+UIT process is a feasible surface treatment for the quality improvement of the tool steel components including both the surface microrelief and hardness characteristics.

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.

Time-Resolved X-Ray Diffraction Stress Analysis during Laser Surface Hardening of Steel

Abstract The time- and temperature-dependent phase specific stress evolution, the residual stress distribution as well as the resulting microstructure of the heat treatable steel AISI 4140, generated by laser surface hardening was investigated. Using a measuring approach presented in [1] fast in-situ synchrotron X-ray stress analysis with sampling rates up to 10 Hz were carried out during laser surface hardening. Tests were carried out with maximum process temperatures of 850 °C, 1150 °C and 1300 °C. The results show that compressive stresses are induced inside the laser spot during the heating-up step. During the subsequent self-quenching step, these compressive stresses are reduced and tensile stresses develop. As martensite transformation starts, the tendency is reversed again and finally compressive residual stresses are obtained at room temperature. The in-situ stress analyses give a deep insight into the stress evolutions for the three maximum process temperatures. Results also show that, the higher the maximum process temperature, the smaller are the resulting compressive residual stresses.

Wear and corrosion behavior of laser surface engineered AISI H13 hot working tool steel

The present study reports the effect of laser parameters on the microstructure, and consequently, the wear resistance of laser surface engineered (hardening and melting) AISI H13 tool steel (in hardened and tempered condition) substrate. The microstructure of the laser surface hardened zone consists of ultrafine mixed carbides (M23C6, M7C3, MC or M2C) dispersed between martensite laths. On the other hand, a laser surface melted microstructure comprises retained austenite, martensite, transformed ledeburite and fine carbides precipitated in the inter-dendritic zone. Microhardness of the laser surface engineered zone is significantly enhanced to as high as 670–810 VHN as compared to 480–500 VHN of the as received quenched and tempered substrate and decreases along vertical depth from the surface until a narrow soft zone at the interface with a typical hardness of 440 VHN. Laser surface melting yields a higher hardness level (770±10 VHN) as compared to that after laser surface hardening (660±10 VHN). Wear resistance of laser surface engineered samples (evaluated both by ball-on-disk and fretting wear testing equipments) shows a significant improvement as compared to that in hardened and tempered condition. Due to an increased hardness, surface melting shows superior resistance to wear both under fretting as well as ball on disk wear testing conditions. A marginal improvement in corrosion resistance was also recorded in laser surface engineered samples due to microstructural/compositional homogenization introduced by laser surface engineering.

Laser Surface Treatment of SAE 4340 and 300M Steels

The 300M steel has emerged from the high strength SAE 4340 steel, which had been developed in order to obtain increased toughness and weldability in applications requiring better mechanical properties; some minor changes in the alloy elements were introduced: addition of vanadium, and raise in the silicon content. The laser surface hardening is a process in which the steel surface is heated below the melting point, in order to produce solid state phase transformations whithout changing the bulk. This work has evaluated which would be the best parameters for the laser carburizing heat treatment using a low power (50W) CO2 laser, comparing and contrasting the resulting microstructure and hardness of both steels. The following CO2 laser parameters were varied: speed, resolution and number of passes; power was kept constant. Carbon black was used as coating. After the surface laser treatment, the samples were cooled in air and the formation of a hardened layer and heat affected zone in both materials was observed. Samples were prepared for metallographic analysis, followed by optical and scanning electron microscopy observation. Layers presented a Vickers hardness value higher than the base metal and the hardened layer had a higher hardness value compared to the heat affect zone. The formation of martensite in the heat affected zone in both steels was observed, although not to the full extension, making this a multiphasic zone.

The Research for Control of the Laser Beam Trajectory on Surface Hardening Using NC

Laser surface hardening is widely used. The complexity of the surface restricts its application. To solve this problem, it is necessary to study the path of the laser spot. By comparison the difference of CNC cutting machine and laser processing machines, the control system of laser spot is built. And the method of alignment for work coordinate system is obtained. NC programming model of the laser beam is established using CAM software. The change of area of spot when laser beam projected to the different normal angles surface was analyzed, and it is get the relationship of normal angles and feed rate. The complex surface laser surface hardening is realized.

Effect of Preloading on Local Residual Stresses Induced by Laser Surface Hardening of Steel

The effect of defined preloading in the tensile and compressive regime on the near surface (residual) stress distributions, which result from laser surface hardening, is systematically studied in-situ, i.e. under the applied preload and after unloading. Samples made of steel grade AISI 4140 are defined surface hardened by means of a high-power diode laser (HPDL) system during uniaxial compressive elastic loading at-300 MPa as well as during uniaxial elastic tensile loading at 300 MPa using a custom designed 4-point-bending device, which can be mounted on an X-ray diffractometer. The results of X-ray stress analysis were compared to data derived for a sample state unaffected by any preload. Without external loading compressive residual stresses are induced inside the process zone that are balanced by tensile residual stresses outside this zone. The investigations show that external loading in the tensile and compressive regime has a strong impact on the resulting lateral residual stress distribution in loading direction. The results further indicate that undesirable tensile residual stresses outside the process zone can even be suppressed by using a defined appropriate preloading in the tensile regime.

A Comparative Study of High-Power Diode Laser and CO2 Laser Surface Hardening of AISI 1045 Steel

The study investigates laser surface hardening in the AISI 1045 steel using two different types of industrial laser: a high-power diode laser (HPDL) and a CO2 laser, respectively. The effect of process parameters such as beam power, travel speed on structure, case depth, and microhardness was examined. In most cases, a heat-affected zone (HAZ) formed below the surface; a substantial increase in surface hardness was achieved. In addition, big differences were found between the hardened specimens after HPDL surface hardening and CO2 laser surface hardening. For HPDL, depths of the HAZ were almost equal in total HAZ o, without surface melting. For CO2 laser, the depths changed a lot in the HAZ, with surface melting in the center. To better understand the difference of laser hardening results when use these two types of laser, numerical (ANSYS) analysis of the heat conduction involved in the process was also studied. For HPDL method, a rectangular beam spot and uniform energy distribution across the spot were assumed, while for CO2 laser, a circular beam spot and Gaussian energy distribution were assumed. The results showed that the energy distribution variety altered the thermal cycles of the HAZ dramatically. The rectangular HPDL laser beam spot with uniform energy distribution is much more feasible for laser surface hardening.

Lasers in Green Manufacturing Processes

A safe and healthy work piece is important for sustainable manufacturing process. Green laser surface hardening is a heat treatment process on a part of its application does not use water or oil as quenching media, because it is self-quenching and less detrimental to the environment. Since it is an energy saving process it is fast being adopted by manufacturing industries. Quenching media used in conventional heat treatment process for a sudden cooling of the heated work piece to get hard structure transformation. Unfortunately the reactions of quenchant with hot working also have several negative health, production cost, and environmental impact.This paper focuses the experimental investigation into the roller of green surface hardening on energy saving, the production cost of the industrial components. A comparative study of surface hardening under conventional and laser sources was conducted using similar components. The results show that the quality of hardening improved in laser hardening but the process time increased marginally at one stage and reduced at other shapes of manufacturing. In analyzing the process cost laser hardening show cast saving notably.

Selective surface hardening by laser melting of alloying powder

Microlayer surface hardening process by laser melting of Fe–Ni–Cr powder with AISI D2 tool steel surface has been investigated in this study. In distinction from the conventional processes of laser surface hardening, laser microlayer hardening involves hardening of target surface to a shallow depth. The melted powder to a depth required for hardening is subsequently self-quenched at a high rate of cooling by heat conduction into the substrate. In this study, parametric study for surface hardening is performed by 200 W fiber laser system. The single line bead was fabricated with various laser parameters and the quadrangle shape was analysed by optimised process parameters. The effects of laser power, scan rate and layer number on the hardness profile are investigated. From the analysis results, operational guide for laser surface hardening with metal powder will be suggested to get surface of target depth with desired hardness.

Structural Relaxation and Nanocrystallization-Induced Laser Surface Hardening of Fe-Based Bulk Amorphous Alloys

Amorphous metallic alloys or bulk metallic glasses are emerging as promising materials for a range of structural, microelectromechanical systems, and biomedical applications. With the recent developments in spark plasma sintering and superplastic forming of the amorphous alloys, it is likely that the amorphous alloys will find a place in new applications. In this article, surface hardening of spark plasma sintered Fe48Cr15Mo14Y2C15B6 bulk amorphous alloys using a continuous-wave Nd:YAG laser is reported. Depending on the processing parameters, the laser surface irradiation causes structural relaxation (enhanced medium-range ordering and/or annihilation of excess free volume) and nanocrystallization of hard carbides (M23C6 and M7C3), resulting in surface hardening. Detailed investigations on the thermal effects, microstructural modifications, and hardness improvements due to laser surface irradiation with laser fluence in the range of 1.77–2.36 J/mm2 are presented. An increase in hardness in the range of 1360–1560 HV for laser surface-treated alloys compared to 1200 HV for as-sintered alloys over a hardening depth of about 50–80 µm is observed.

A dual weighted residual method for an optimal control problem of laser surface hardening of steel

The main focus of this article is on analyzing and implementing a dual weighted residual (DWR) approach for an optimal control problem of laser surface hardening of steel. The problem which is governed by a dynamical system consisting of a semi-linear parabolic equation and an ordinary differential equation is discretized using the finite element method. A posteriori error estimates are derived and an adaptive algorithm is formulated. The numerical experiments justify the theoretical results obtained.

Unconventional Metallographic Methods for the Structural Characterization of Laser Hardened Al-Zn-Si Cast Alloy

The laser surface hardening is method which provides increased mechanical properties of secondary (recycled) Al-Si cast alloys for automotive industry. Improvement of mechanical properties and structure of secondary aluminium alloys can often significantly increase the lifetime of casting and reduce costs for fuel and reduction of environmental loading. For study was used a laser beam Nd: YAG lasers, BLS 720, on the test samples of secondary cast alloy AlZn10Si8Mg. AlZn10Si8Mg cast alloy are used for engine and vehicle constructions, hydraulic unit and mould making without the need of heat treatment because this alloy is self-hardened. The effect of laser beam was evaluated with the laser power 50 W and 80 W on the surface of samples. The final microstructure of Al-alloys depend on the laser process parameters. The changes of microstructure after laser surface hardening was observed by using classical techniques of etching (standard black-white contrast - etching by 0.5 % HF, 10 % H3PO4and colour contrast - etching by Weck-Al) and deep etching with HCl. Due to the action of laser beam on the surface of the secondary alloy AlZn10Si8Mg there have been changes in the microstructure of the material. Melting area is alpha-phase with much fine columnar dendrites morphology without the presence of Si-particles and intermetallic phases. In the transition area were observed grain refinement of eutectic Si (finer and rounder Si particles) as the modify action of the laser. By increasing the laser power the microhardness of surface layers decreases. In the surface layer (80 W) were observed cracks due to uneven heat transfer of the material.

Laser Hardening Parameters Influencing Component Lifetime and Residual Stresses

Laser surface hardening is an advanced method of surface treatment of structural steels with a great potential for wide industrial applications. The technology is quite new and so, investigations have to be performed in order to gain a comprehensive knowledge about effects on microstructure, hardness, surface properties of treated materials, but also mechanical an particularly fatigue properties. Concerning fatigue resistance of material treated with this technology, results and knowledge recently published in the literature indicate that fatigue resistance can be either reduced or increased, even considerably, depending on numerous parameters of basic material, laser hardening parameters etc. This contribution contains results of a partial study of effect of laser hardening of relatively small specimens on fatigue resistance of 42CrMo4 steel. Two different parameters of the treatment were used, namely two speeds of laser beam on the material surface at constant beam energy. Unlike the lower speed, when fatigue resistance was slightly reduced, higher speed of laser beam resulted in a slight increase of fatigue resistance and fatigue limit. The results are discussed considering an occurrence of residuals stresses. Key words: Laser hardening, residual stress, lifetime, fatigue, fracture, microstructure, surface