Surface Hardening Process Research Articles

Complexity Modeling of Steel-Laser-Hardened Surface Microstructures

Nowadays, laser hardening is a consolidated process in many industrial sectors. One of the most interesting aspects to be considered when treating the surface-hardening process in steel materials by means of laser devices is undoubtedly the evaluation of the heat treatment quality and surface finish. In the present study, an innovative method based on fractal geometry was proposed to evaluate the quality of surface-steel-laser-hardened treatment. A suitable genetic programming study of SEM images (1280 × 950 pixels) was developed in order to predict the effect of the main laser process parameters on the microstructural geometry, assuming the microstructure of laser-hardened steel to be of a structurally complex geometrical nature. Specimens hardened by anthropomorphic laser robots were studied to determine an accurate measure of the process parameters investigated (surface temperature, laser beam velocity, laser beam impact angle). In the range of variation studied for these parameters, the genetic programming model obtained was in line with the complexity index calculated following the fractal theory. In particular, a percentage error less than 1% was calculated. Finally, a preliminary study of the surface roughness was carried out, resulting in its strong correlation with complex surface microstructures. Three-dimensional voxel maps that reproduce the surface roughness were developed by automating a routine in Python virtual environment.

Battery on Carburization ST 37 Steel

A surface hardening process by adding carbon to its surface without changing the core properties of the material is called the carburization process. This process is carried out at the austenite temperature so that the carbon can diffuse into the phase. This process can only be done on low carbon steels with a content of below 0.25%. This research uses ST 37 steel which is a low content steel with a carbon content of 0.18%. This type of steel is surface hardened with a carburizing temperature of 850°C for a long lasting time of 1 hour, then it is carried out under moderate cooling with outside air media. This research produces a carburizing method with carbon battery media that easily breaks down into steel, which occurs in carbon batteries at temperatures below 723°C. And change its mechanical properties from the comparison of the initial mechanical properties of the specimen. Carburizing with battery rock media is more efficient at temperatures below 723°C. Because of at temperatures below austenite or below the carburizing temperature of carbon from the batteries, it can absorb the surface of the steel even though the amount is still very small. Because the temperature is below the austenite temperature, the absorbed carbons cannot diffuse as happened in the carburization process, but the absorbed carbons can bind the grain boundaries so that they change their hardness by 4%. The microstructure in the research that occurs in this process has nothing to change its phase because the temperature does not reach the austenite temperature.

Improvement Corrosion Behaviour of Lean Duplex Stainless Steel 2101 alloy in Ringer solution by Plasma Nitriding for Biomedical applications

“Plasma nitriding” is a surface hardening process that involves diffusion of the atoms of nitrogen onto the surface of metal under different plasma nitriding conditions. The new alloys used in the field of Biomedical applications are Lean Duplex Stainless Steel. The alloys of Lean DSS are corrosion resistant, lightweight, and have good mechanical properties such as fatigue strength, but in aggressive environments, they lack “wear resistance”. In a vacuum chamber of air (3 mbar), 400 V, and 30 mA, a lean duplex stainless steel (2101) alloy rod was plasma nitrided. The procedure of plasma nitriding was carried out at various times. The effect of plasma nitriding at different times (5, 10, 15, 20, 25) hrs on the chemical structure of LDX 2101 DSS alloy and the form of phases was investigated using OM, FESEM with EDS, XRD, and antibacterial test, tafel potential polarizaton and cyclic polarization for Orthopedic application. The results show that layers and phases S, Fe3N, and Fe2-3N were formed on the alloy’s surface, which would improve mechanical properties and corrosion resistance in Ringer solution at 37 °C.

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.

Simulation of Diffusion Processes in Chemical and Thermal Processing of Machine Parts

To solve a number of technological issues, it is advisable to use mathematical modeling, which will allow us to obtain the dependences of the influence of the technological parameters of chemical and thermal treatment processes on forming the depth of the diffusion layers of steels and alloys. The paper presents mathematical modeling of diffusion processes based on the existing chemical and thermal treatment of steel parts. Mathematical modeling is considered on the example of 38Cr2MoAl steel after gas nitriding. The gas nitriding technology was carried out at different temperatures for a duration of 20, 50, and 80 h in the SSHAM-12.12/7 electric furnace. When modeling the diffusion processes of surface hardening of parts in general, providing a specifically given distribution of nitrogen concentration over the diffusion layer’s depth from the product’s surface was solved. The model of the diffusion stage is used under the following assumptions: The diffusion coefficient of the saturating element primarily depends on temperature changes; the metal surface is instantly saturated to equilibrium concentrations with the saturating atmosphere; the surface layer and the entire product are heated unevenly, that is, the product temperature is a function of time and coordinates. Having satisfied the limit, initial, and boundary conditions, the temperature distribution equations over the diffusion layer’s depth were obtained. The final determination of the temperature was solved by an iterative method. Mathematical modeling allowed us to get functional dependencies for calculating the temperature distribution over the depth of the layer and studying the influence of various factors on the body’s temperature state of the body.

ST37 Steel Carburization with Coconut Charcoal

The carburization process is a surface hardening process where carbon is added to the surface without changing the core properties of the material. This process is carried out at the austenite temperature so that the carbon can diffuse into the phase. This process can only be done on low carbon steels with content below 0.25%. This research was conducted on ST37 steel, which is steel with low carbon content with 0.18% carbon content. This type of steel is surface hardened with a carburizing temperature of 850 C with a long lasting time of 1 hour, then it is carried out under moderate cooling with outside air media. And change its mechanical properties from the comparison of the initial mechanical properties of the specimen. The highest hardness value occurs in the carburizing process of coconut shell charcoal, but this hardness value occurs not because of the carburization process but because of the enlarged grain size caused by heating at temperatures below 723⁰ C, thus reducing the elongation properties of the material. Carburizing with battery stone media is more efficient than coconut shell charcoal at temperatures below 723 C. Because the temperature is below the austenite temperature, the absorbed carbons cannot diffuse as happened in the carburization process, but the absorbed carbons can bind the grain boundaries and change their hardness by 4%. In the microstructure research that occurs in this process nothing can change its phase because the temperature does not reach the austenite temperature. However, there are differences in the microstructure between the carburization process with coconut shell charcoal media.

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.

Some aspects of the nitriding process of parts in machine construction

Nitriding is the most common and effective surface hardening method. Such chemical-thermal treatment is capable of increasing surface hardness, contact endurance, wear and seizure resistance, as well as heat resistance and corrosion resistance of a wide range of machine parts. This process of surface hardening has found its application in many branches of modern mechanical engineering. The operational requirements for the parts led to the need to replace high-temperature methods of chemical-thermal treatment (carburizing, high-temperature nitrocarburizing, etc.) for hardening processes at lower temperatures (500-650° C), namely nitriding. This replacement was facilitated by the latest technological developments in the field of various nitriding methods. The scientific developments obtained to date make it possible to gradually eliminate such disadvantages of nitriding as a significant duration of the process, increased fragility of the surface layer, insufficient values of contact endurance, and labor intensity of the process [1, 2].

Evaluation of microstructural complex geometry of robot laser hardened materials through a genetic programming model

Surface-hardening process of steel materials by robot laser technologies can involve the challenge of modeling the determining process parameters through non-conventional tools in order to evaluate the quality of the heat treatment. In the current study a new method based on fractal geometry, used to determine the microstructural properties of laser hardened steels manufactured by anthropomorphic robots, is presented. The assumptions were that the microstructure of laser hardened steel can be studied as a complex structural geometry and the modeling of the analyzed complex geometries can be made through genetic programming for prediction purposes. The effect of process parameters and their joint combination on the final microstructures geometry of the heat treated steel was investigated. In particular, the influence of temperature, laser beam velocity, and impact angle were studied since they were showed in a preliminary study to be the process parameters that most significantly influenced the quality of the heat treated steel. The developed model reached a precision of the prediction equal to 98.59 %.

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.

Shotblasting process for surface hardening

The results of studies of shot blasting as one of the methods of mechanical cleaning for surface hardening (peening) of parts are presented. The simulation in the QForm-3D (VX) software environment of high-speed impact of spherical particles on the metal was carried out and the stress–strain state of the metal in the impact hardening zone was revealed. It was shown that friction losses are proportional to the squared velocity of the particles of the shot blasting machine, and a decrease in the value of the contact friction coefficient will accordingly reduce the frictional work and increase the blades resource. Calculations and studies have established the basic laws of the shot blasting process conditions influence on the surface geometry and the metal surface layer properties.

Effect of boronizing composition on hardness of boronized AISI 1045 steel

Surface hardening process of cam shafts manufactured from AISI-1045 Steel was provided by boronizing in liquid and solid media. To boronize in liquid and solid medium, various chemical agents were used. At this study, research was conducted on hardness and thickness of the layers obtained according to the boronizing composition. The effects of boronizing bath compound on the quality of the layers obtained are being disputed. It is understood that 70% Borax (Na2B4O7) + 30% B4C is the most suitable boronizing compositions in the liquid medium to obtain the hardest and thickest borid layer on AISI-1045 steel samples. For solid media boronizing, the combination was determined as 5% B4C + 90% SiC + 5% KBF4.

Tailored bainitic-martensitic microstructures by means of inductive surface hardening for AISI4140

Inductive surface hardening processes are widely used in the manufacturing of automotive parts. They combine short process times with high economic and energy efficiency. Because of their high surface hardness, induction hardened steel parts feature beneficial wear resistance and also good fatigue properties due to the induced compressive residual stresses in the surface. Considering the positive effects on the mechanical properties by creating a bainitic-martensitic microstructure, outlined by severel authors, this study includes the implementation of a temperature controlled inductive surface hardening process on a conventional hardening machine. Therefore an innovative inductor design, which allows a controlled sample cooling is presented. Supported by dilatometric studies as well as different heat treatment strategies, limitations are identified to gain a profund process understanding. Hereby an accelerated bainite formation after short time austenitization is detected. By using different heat treatment strategies, the fraction of the bainitic phase can be adjusted in the surface of the part made of AISI 4140. The results of this innovative heat treatment method are compared to short time inductive hardening and tempering processes regarding microstructure, hardness and residual stresses. The generated surface layer states, including mixed microstructures, show promising properties resulting in a possible enhancement of the fatigue strength of induction hardened parts.

The cathodic electrolytic plasma hardening of the 20Cr2Ni4A chromium-nickel steel

In order to obtain the modified surface structure of the 20Cr2Ni4A steel plasma electrolytic hardening (PEH) method was used. The surface hardening process was conducted in the aqueous electrolyte solution of 20% sodium carbonate and 20% urea. The sample consists of a ferritic-pearlitic structure, i.e. the part retains its viscous core, and the surface layer contains carbide particles. Hardening process induces martensite transformation and creation of carbide particles in the surface layer. The presence of carbide particles in the surface layers has a positive effect on the tribo-mechanical performance. Hardened structure 600μm long was obtained with hardness increase up to 520 HV and 2.5 times higher wear resistance. Tribological test results showed the difference of the coefficient of friction as a function of surface roughness determined by plasma-electrolytic hardening process.

Laminar plasma jet surface hardening of the U75V rail steel: Insight into the hardening mechanism and control scheme

Insight into the mechanism of laminar plasma jet (LPJ) surface hardening is critical for the controllable preparation of ideal hardened layer to improve the wear and fatigue resistance of U75V rail steel. To reveal the surface hardening mechanism, a series of surface hardening experiments on the U75V rail steel surface were performed under different working parameters using a self-designed laminar plasma generator. Results showed that the geometrical dimension, microstructure and hardness distribution of the hardened layer can be adjusted by changing the arc current, the scanning velocity and the anode nozzle diameter. Further characterization and numerical simulation suggested that the geometrical dimension of the hardened layer is determined by the heat affected zone over the critical austenitizing temperature (730 °C), while its microstructure and hardness distribution depend on the local cooling rate below the critical austenitizing temperature. By changing the working parameters, the heat flux density applied on the workpiece surface and the heating time can be controlled to obtain the desired temperature field within the heat affected zone. Not only a full hardened layer but also a transition layer consisting of martensite, pearlite, ferrite and carbides can be achieved. This configuration of LPJ surface hardening process for U75V rail steel indicates that the LPJ surface hardening with the ability of producing hardness gradient is promising for reducing the risk of crack generation on the rail.

The effect of laser surface hardening on the surface hardness of mild steel

Laser surface hardening (LSH) has become the most vital process in order to increase the hardness of a mild steel surface, especially to overcome the wear issues in machining parts, where mild steel was hugely applied. This is due to its advantages such as less air pollution, low cost of maintenance and easy to handle compared to other conventional surface hardening process. The laser surface hardening of mild steel has been performed using fibre laser machine which is having a maximum peak power of 30 Watt, with 1060 nm of wavelength above the surface of mild steel having dimension of 15 × 15 × 6 mm. The Vickers hardness test on the laser hardened surface of this metal were measured by a load of 0.5 kgf and 10 seconds dwell time for ten indention points, randomly. It was found that the highest average microhardness value was 281.72 HV on the surface of sample hardened by a laser power of 21 Watt and 40 mm/s scanning speed. Across the cross sectional area, the affected hardened depth was measured at 19 ± 2.5 µm from the surface. In this region, the fine martensitic grain structure was observed, which contributes to the higher microhardness value. Higher laser power produced higher surface hardness, meanwhile higher scanning speed lead to lower surface hardness.

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.

The effect of temperature and volume fraction of mahoni (<i>Swietenia mahogani</i>) wood charcoal on SS400 steel using pack carburizing method: Study of hardness and microstructure characteristics

Surface hardening process is one of the final steps to improve the product quality especially in toughness of the steel core. In this study, the SS400 steel was investigated as the potential steel core to be used as a sprocket. However, this material is categorized in low hardness due to its low carbon content. Improving SS400 steel by using surface hardening was carried out by pack carburizing with Mahoni Wood Charcoal (MWC) powder as carburizing. The volume fraction of MWC was varied at 60, 70, and 80% with ratio mixing of BaCO3 activator for 40, 30 and 20%, respectively. The pack carburizing process was conducted at 850 and 900 ℃ with holding time for 1 h followed by quenching. The hardness test showed that the highest hardness value was 677.4 HV at variation of 60% MWC + 40% BaCO3 on 900 ℃ (holding time 1 h). This hardness value number of the sample (60% MWC + 40% BaCO3 on 900 ℃) was higher than raw materials for 452% of raw material. The microstructures also display a martensite structure in this sample.

Analytical Study of the Effect of NaCl Solution on Fatigue Resistance of Rotating Shafts

Dynamic shafts subjecting to salty rain water, especially in places with no rain water drainage networks, is undesirable because this media causes corrosion of the parts of shaft that increases as increasing of shaft immersion in a salty media (NaCl) also, increasing of concentration which in turns reducing number of operation runs. Increasing salt concentration from 3% to 6% NaCl results in decreasing of operation runs from 25600 to 17100 runs. Also, increasing salt concentration leads to raise the effect of alternating stress that makes strain hardening factor drop to 0.45 and ratio of dynamic shear stress to static one raise to 2.44 that affects shaft metal performance to resist fatigue. Samples were also, treated by oxy acetylene surface hardening and were cooled by immersion in oil then immersion in 6% NaCl salty solution, the results showed that number of operation runs before failure had increased up to 71022, the effect of alternating stress had decreased down to 6100 N/m2, surface strain hardening factor had increased up to , also ratio of dynamic shear stress to static one had decreased down to 0.839. This is a good indicator of the effectiveness of surface hardening process of shaft parts that subject to salty rain water during maintenance operations.