Laser Surface Transformation Hardening Research Articles

Laser Surface Transformation Hardening for Automotive Metals: Recent Progress

This article discusses recent advancements in the Laser Surface Transformation Hardening (LSTH) process applied to industrial metals. It focuses on examining the microstructure of the metal surface layer and explores different methods of performing LSTH to evaluate mechanical and surface properties. The study also investigates the utilization of various industrial lasers and simulation software for the LSTH process. The careful analysis of heat transfer and temperature control during LSTH aims to prevent the generation of surface defects like micro-cracks and surface melting. Finite element method (FEM) software effectively simulates the LSTH process. The research provides a comprehensive overview of recent developments in LSTH, categorized based on different metals and subsequent testing, highlighting its applications in the automotive industry. Electrochemical, wear, and microhardness tests are investigated to assess the potential applications of automotive metals.

How the laser beam energy distribution effect on laser surface transformation hardening process; Diode and Nd:YAG lasers

The laser surface transformation hardening (LSTH) of AISI 4130 steel by 1600 W high power diode laser (HPDL) and 700 W Nd:YAG lasers were investigated in this present study. The distribution influence, and the lasers beam shape; Top-hat in the HPDL and Gaussian distribution in the Nd:YAG laser, have been studied on the geometrical dimensions, and micro-hardness in hardened area (i.e.; depth, width, and angle of entry of hardened profile), micro-hardness deviation (MHD) from the row steel in geometric dimensions, and the ferrite’s percentage in hardened layer center. Microstructure evaluation of the laser hardened areas were performed by FE-SEM and optical microscopy. Based on the results, maximum hardness was created with the HPDL, and the geometrical dimension was more than the Nd:YAG laser. Also, MHD, and minor phase of ferrite in the HPDL laser surface hardening than the hardened layer in Nd:YAG laser, which is related to the higher laser absorption. Results show that, the hardened zone of HPDL is about 698 HV0.1 with 1.02 mm depth, while for Nd:YAG laser is about 698 HV0.1 with 0.98 mm depth. Comparing the results with the furnace hardening heat treatment (FHT) demonstrated that the hardness in diode laser and Nd:YAG laser hardening are 1.38 and 1.22 times of the hardness in FHT, respectively.

Experimental and Numerical Study of AISI 4130 Steel Surface Hardening by Pulsed Nd:YAG Laser.

Laser surface transformation hardening (LSTH) of AISI 4130 was investigated by a Nd:YAG pulsed laser. Laser focal height (LFH), pulse width (LPW), scanning speed (LSS), and power (LP) varied during the experiments. The microstructure of the treated zone was characterized by optical (OM) and field emission scanning electron microscopy (FESEM). Micro-hardness was measured in the width and depth directions. Results showed that the hardness and depth of hardened layer increased by decreasing the LSS and the laser focal position (LFP), and by increasing the LPW. The results were compared with those obtained by furnace heat treatment of the same steel. Eventually, a finite element model was employed for the simulation of the LSTH of AISI 4130 steel and calculation of the heat-treated zone. The results showed that the model can predict with accuracy the temperature profile and the size and the shape of the laser hardened region.

Experimental Investigation of Laser Surface Transformation Hardening of 4340 Steel Spur Gears

This paper presents an experimental investigation of laser surface transformation hardening (LSTH) of 4340 steel spur gears using regression analysis. The experimental work is focused on the effects of various LSTH parameters on the hardness profile shape and the hardened depth variation. The investigations are based on a structured design of experiments and improved statistical analysis tools. The experimentations are carried out on AISI 4340 steel spur gears using a commercial 3 kW Nd:YAG laser system. Laser power, scanning speed, and rotation speed are used as process parameters to evaluate the variation of the hardened depth and to identify the possible relationship between the process parameters and the hardened zone physical and geometrical characteristics. Based on the experimental data and analysis of variance, the direct and interactive contributions of the process parameters on the variation of the hardness profile shape and the hardened depth are analyzed. The main effects and the interaction effects are also evaluated. The results reveal that all the process parameters are relevant. The cumulative contribution of the three parameters in the hardened depth variation represents more than 80% with a clear predominance of laser power. The contribution of the interactions between the parameters represents 12% to 16%. The resulting hardness values are relatively similar for all the experimental tests with about 60 HRC. The evaluation of the produced regression models for hardened depth prediction shows limited performance suggesting that the predictive modeling process can be improved.

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.

탄소강 환봉의 레이저 표면변태경화 특성에 관한 연구 (II) - 빔 프로파일 차이에 따른 레이저 표면변태경화 특성 비교 -

The conventional study on the laser surface transformation hardening has been carried out with a beam of the specified shape and uniform power-intensity distribution in order to ensure the uniformity of the hardening depth. Two types of beams - the circular gaussian beam and rectangular beam of the uniform power-intensity distribution were used in this study. we were supposed to optimize the process parameters and to compare the hardening results with two optics respectively. As a result, the hardness distribution of the hardened zone was similar in both cases and the hardened phase by the rectangular beam was denser than that by the circular gaussian beam.

Thermal analysis of laser surface transformation hardening?optimization of process parameters

This paper deals with the optimization of process parameters for maximum productivity (given by the product of scanning velocity and cross feed) in laser transformation hardening. The process parameters considered are laser beam power, P; laser beam diameter, Db; and the heat intensity distribution, namely, normal, bimodal, or uniform. A thermal analysis of the laser surface transformation hardening of gears was conducted (based on Jaeger’s classical moving heat source method) by considering the laser beam as a moving plane (disc) heat source to establish the temperature rise distribution in the workpiece (gear) of finite width. In a recent investigation [Int. J. Heat Mass Transfer 44 (2001) 2845], the authors considered the case of a heat source with a pseudo-Gaussian (or normal) distribution of heat intensity. The analytical results were compared with the experimental results published in the literature. In laser heat treatment of steel, it is generally considered preferable to use a wider heat intensity distribution, such as uniform or bimodal, for it enables more uniform case hardening depth. In this paper, this model is extended to cover bimodal and uniform distributions and compared with the normal distribution. Scanning velocities for no surface melting and for a case hardening depth of 0.1 mm were determined for surface transformation hardening of AISI 1036 (EN 8) steel for a range of laser beam powers, P, laser beam diameters, Db, and various heat intensity distributions. Since diffusion during the heat treatment (surface transformation hardening) process is a time dependent phenomenon, based on the literature review, an interaction time of 15 ms was taken as a basis. It is hoped that laser industry with adequate facilities available can validate the thermal analysis and subsequent optimization presented in this paper.

Thermal analysis of laser surface transformation hardening—optimization of process parameters

This paper deals with the optimization of process parameters for maximum productivity (given by the product of scanning velocity and cross feed) in laser transformation hardening. The process parameters considered are laser beam power, P; laser beam diameter, Db; and the heat intensity distribution, namely, normal, bimodal, or uniform. A thermal analysis of the laser surface transformation hardening of gears was conducted (based on Jaeger’s classical moving heat source method) by considering the laser beam as a moving plane (disc) heat source to establish the temperature rise distribution in the workpiece (gear) of finite width. In a recent investigation [Int. J. Heat Mass Transfer 44 (2001) 2845], the authors considered the case of a heat source with a pseudo-Gaussian (or normal) distribution of heat intensity. The analytical results were compared with the experimental results published in the literature. In laser heat treatment of steel, it is generally considered preferable to use a wider heat intensity distribution, such as uniform or bimodal, for it enables more uniform case hardening depth. In this paper, this model is extended to cover bimodal and uniform distributions and compared with the normal distribution. Scanning velocities for no surface melting and for a case hardening depth of 0.1 mm were determined for surface transformation hardening of AISI 1036 (EN 8) steel for a range of laser beam powers, P, laser beam diameters, Db, and various heat intensity distributions. Since diffusion during the heat treatment (surface transformation hardening) process is a time dependent phenomenon, based on the literature review, an interaction time of 15 ms was taken as a basis. It is hoped that laser industry with adequate facilities available can validate the thermal analysis and subsequent optimization presented in this paper.

Thermal analysis of the laser surface transformation hardening process

An analytical solution for the temperature rise distribution in laser surface transformation hardening of a steel workpiece of finite width is developed based on Jaeger's classical moving heat source method [Proc. Roy. Soc. NSW 76 (1942) 203] and Carlsaw and Jaeger [Conduction of heat in solids, Oxford University Press, Oxford, UK, 1959] to predict the optimal operational parameters. The laser beam is considered as a moving plane (disc) heat source with a pseudo-Gaussian distribution of heat intensity. It is a general solution in that it is applicable for both transient and quasi-steady state conditions. The effect from two boundaries of the workpiece of finite width is included in the analysis. The solution can be used to determine the temperature rise distribution in and around the laser beam heat source on the work surface as well as with respect to depth at all points including those very close to the heat source. The width and depth of the melt pool (MP) and the hardening zone near the surface of the workpiece with finite width can also be calculated under transient and quasi-stationary conditions. The analytical model developed here can be used to determine the time required for reaching the quasi-steady state. Steen and Courtney [Metals Technol. (December 1979) 456] reported a five level, full factorial experiments of laser surface transformation hardening. They considered the surface temperatures and the depth of hardening as approximate functions of the laser input parameters, namely, the laser beam power, P, the laser beam diameter, D e, and the traverse velocity of the beam, v. A comparative study is made on the analytical approach presented here with the multi-parameter experimental and the semi-empirical approach by Steen and Courtney. While good agreement was found between the results of the analytical work and the semi-empirical approach for the case of scanning velocity for no surface melting, significant differences were found for the laser transformation hardening for a depth of hardening of 0.1 mm. This was due to the nature of the semi-empirical relationships considered by Steen and Courtney for each case. For example, the traverse velocity was assumed to be proportional to P/ D b 2 (i.e., power intensity) for no surface melting which has some physical significance, while it was assumed to be proportional to P 2/ D b for laser transformation hardening for a depth of hardening of 0.1 mm, for which there is no physical or analytical basis. Steen and Courtney developed semi-empirical equations based on the regression analysis of the experimental data, while the analytical solutions presented here are exact. The analytical solutions provide a better appreciation of the physical relationships between the relevant laser parameters and the width of the workpiece. The analysis facilitates the prediction and optimization of the process parameters for practical applications.

Surface properties of laser processed ductile iron

On laser melt treatment, Sliding Wear of pearlitic ductile iron reduced from severe metallic wear to oxidative mild wear by nearly two orders of magnitude at $7.5 ms^{-1}$ over a load range of $14-31 kg cm^{-2}$; resistance to Cavitation Erosion improved by a factor of seven in corrosive media and surface hardness increased from 20-22 to 40-58 $HR_c$. Laser melting could effectively reduce Corrosion rates in dilute acids by nearly 40%. These improvements were caused by the ultrafine microstructure $(1-4 \mu, DAS)$, microhardness $(700-900, HV_{0,1})$ and the consequent high resistance to plastic flow and subsurface crack initiation. In this investigation, pin-on-disc adhesive wear, ultrasonic vibratory cavitation erosion and potentiodynamic corrosion in synthetic sea water and 0.01 $NH_2SO_4$, were assessed after laser surface melting or transformation hardening of hyper-eutectic ductile iron, typically employed in automotive and marine engine components by using $CO_2$ CW or Nd-YAG pulsed high power laser. Also the processing parameters viz, beam power (P), scan rate (U), and specific energy intensity $(P/UD_b^2)$ for threshold and specific depth of transformation hardening or melting have been determined.

Engineering Applications and Analysis of Hardining Data for Laser Heat Treated Ferrous Alloys

Published information on the wide range of industrial applications in which laser surface transformation hardening has been used on ferrous alloys is reviewed. The effect of operational parameters on the heat treatment response (case depth, coverage rate, distortion, and hardness) is surveyed and illustrated from the results of a study of laser heat treatment of ASTM class 40 grey and class 80–55–06 ductile cast irons. Attempts are made to establish the relationship between the case depths obtained and the applied laser and material variables, on the basis of experimental data and heat flow models, and the available published data in this field are tabulated.