Hardened Surface Layer Research Articles

The laser-plasma cementation as a method of increasing the abrasive resistance of medium-alloy tool steels

The paper is devoted to the study of resistance of medium alloy tool steels after laser-plasma cementation. The authors propose a method of increasing abrasive resistance by means of the combined effect of DC electric arc of reverse polarity and laser radiation. The increased concentration of carbon in the near-surface layer is provided by the erosion of the carbon electrode and melting due to the combined energy effect of laser radiation and electric arc. The formation regularities of the diffusion hardened layer are established. The modes of laser-plasma cementation and test results of the studied materials are presented. The reasons of resistance increase are revealed. The mechanical characteristics of the hardened surface layer are shown. The influence of the energy regimes of the technological process on the depth of the diffusion hardened layer is given.

The structure of composite rollers with iron or nickel-iron base and hard surface layer of WC or TiC based hard alloy produced by the method of hot vacuum pressing with a liquid phase

Abstract In this work the structure and properties of composite rollers with surface layer made of hard alloy were studied. The rollers were made by the powder metallurgy method with sintering during pressing and the presence of a certain liquid phase during sintering (semi-liquid sintering). WC-Co and TiC-Ni-Fe materials were used as hard alloys. Iron-carbon and iron-nickel materials were used as soft base. All of the composite layers were formed in one process. The structure of base materials and border layer of these composites were studied. Investigations of thermocycling sustainability of these composite samples were carried out.

Modeling the hardness of the titanium alloy subjected to laser processing

The article considers the influence of the radiation power W, the longitudinal feed Spr of the laser beam and the distance L from the protective glass of the laser focusing head to the workpiece on the hardness Hv of the titanium alloy TiTaN. A multi-factor model is established that relates the surface layer hardness to the input factors of laser processing and allows you to quickly assign a laser treatment mode and to control it in order to improve the quality of the processed layer. The power W has the greatest effect on the hardness of the surface layer. With increasing W, the hardness increases. Increasing the feed Spr leads to a decrease in the Hv parameter. The effect of the distance L is similar to the radiation power, but the degree of influence of L is more than half as small as W. The developed method of operational assignment of the laser processing mode allows to reduce the auxiliary time for performing the technological operation. The research results are relevant for manufacturing enterprises that implement laser processing processes, as well as for design organizations that develop modern laser equipment.

Non-Destructive Characterization of Subsurface Plastic Deformation in Case Carburized Steel Using Magnetic Barkhausen Noise Technique

The effect of extreme loading in bending was investigated by magnetic Barkhausen Noise (MBN) and X-ray diffraction (XRD) in two types of inhomogeneous steels that widely used in gear industry. EN 36 and H8620 steels in the carburized, tempered and ground condition were investigated after unloading from high stress levels. The inhomogeneity arising from the variation in carbon content showed up clearly by double peaks MBN profiles before loading. The first MBN peak at low field revealed the soft subsurface region and the second peak at higher field revealed the hard surface layer. Residual stresses profiles were produced by XRD before and after loading to probe plasticity in the cross sections of both specimens. Barkhausen noise measurements showed a considerable change in the first peak height in both steels as a response to plastic deformation in tension and compression in the subsurface material. The height of the second peak remained unchanged in EN 36 specimen but increased slightly in the H8620 specimen. The residual stress measurements after unloading indicated that the subsurface materials after a depth of 0.4 mm in both specimens were yielded. The surface layer of the H8620 steel was also affected slightly by bending as revealed by an increase in the second MBN peak height and confirmed by XRD as indication of yielding. The experiment confirmed that the magnetic Barkhausen noise can be used to characterize yielding in inhomogeneous steels non-destructively.

Non-Destructive Characterization of Subsurface Plastic Deformation in Case Carburized Steel Using Magnetic Barkhausen Noise Technique

The effect of extreme loading in bending was investigated by magnetic Barkhausen Noise (MBN) and X-ray diffraction (XRD) in two types of inhomogeneous steels that widely used in gear industry. EN 36 and H8620 steels in the carburized, tempered and ground condition were investigated after unloading from high stress levels. The inhomogeneity arising from the variation in carbon content showed up clearly by double peaks MBN profiles before loading. The first MBN peak at low field revealed the soft subsurface region and the second peak at higher field revealed the hard surface layer. Residual stresses profiles were produced by XRD before and after loading to probe plasticity in the cross sections of both specimens. Barkhausen noise measurements showed a considerable change in the first peak height in both steels as a response to plastic deformation in tension and compression in the subsurface material. The height of the second peak remained unchanged in EN 36 specimen but increased slightly in the H8620 specimen. The residual stress measurements after unloading indicated that the subsurface materials after a depth of 0.4 mm in both specimens were yielded. The surface layer of the H8620 steel was also affected slightly by bending as revealed by an increase in the second MBN peak height and confirmed by XRD as indication of yielding. The experiment confirmed that the magnetic Barkhausen noise can be used to characterize yielding in inhomogeneous steels non-destructively.

Effective methods for optimal design of induction coils on example of surface hardening

Purpose This paper aims to describe main ideas and demonstrates results of the research activities carried out by the authors in the field of optimal design concepts for induction heater for surface hardening. The main goal of the research studies is the application of different optimization methods and numerical finite element method (FEM) codes for field analysis to solve the optimal design problem that is mathematically formulated in terms of the one of the most important optimization criteria for surface hardening technology, e.g. maximum temperature uniformity within the hardening surface layer. Design/methodology/approach Evolutionary algorithm based on Adaptive Gaussian Process-Assisted Differential Evolution for MEMS Design Optimization (AGDEMO) and alternance method of parametric optimization based on optimal control theory are applied as effective tools for the practice-oriented problem for optimization of induction heater design based on non-linear coupled electromagnetic and temperature field analysis. Different approaches are used for combining FEM codes for interconnected field analysis and optimization algorithms into automated optimization procedure. Findings Optimization procedures are tested and investigated for optimal design problem solution on the examples of induction hardening of steel cylindrical billet. Practical implications Solved problems are based on the design of practical industrial applications. The developed optimization procedures are planned to be applied to the wide range of real-life problems of the optimal design of different electromagnetic devices and systems. Originality/value This paper describes main ideas and results of the research activities carried out by the authors in the field of optimal design of induction heaters for hardening based on numerical coupled electromagnetic and temperature field analysis. The implementation of the automated procedure that combines a numerical FEM code for coupled field analysis with an optimization algorithm and its subsequent application for designing induction heaters makes the proposed approach specific and original. This paper also demonstrates that different optimization strategies used (evolutionary algorithm based on AGDEMO and alternance method of optimal control theory) are effective for real-life industrial applications for optimization of induction heaters design.

THE ESTIMATION OF ROLLER STRENGTHENING INFLUENCE ON THE ENDURANCE LIMIT OF SHAFTS WITH PRESSURIZED HUB

The influence of roller strengthening on endurance limit under bending of the 25 mm and 50 mm diameter shafts made of steel 20 and 25 mm diameter shafts made of steel 40X with a pressurized hub has been examined. Its been stated that the endurance limit of roller strengthened shafts with a pressurized hub depends not only on a value of compressive residual stresses in their dangerous section but on the character of its distribution. The valuation of a surface hardening influence on the endurance limit of shafts by the surface residual stresses criterion and the average integral residual stresses criterion has been shown that the average integral residual stresses criterion calculated through the parts dangerous section surface layer thickness equal the critical depth of the non-propagating fatigue crack can be recommended for the hardened shafts with a pressurized hub endurance limit increase prediction. Its been shown that on a diameter of a shaft with a pressurized hub raising it is necessary to increase a thickness of a hardened surface layer with compressive residual stresses.

Surface Texture Analysis after Hydrostatic Burnishing on X38CrMoV5-1 Steel

Ball burnishing is a plastic deformation process used as a surface smoothing and surface improvement finishing treatment after turning or milling processes. This process changes the surface stereometrics of the previously machining surface. Burnishing with hydrostatic tools can be easily and effectively used on both conventional and Computer Numeric Control (CNC) machines. The existing research of the burnishing process mainly focuses on the functional surface characterization, for example, surface roughness, wear resistance, surface layer hardness, etc. There is a lack of references reporting a detailed analysis of 3D parameters calculation with a mathematical model to evaluate the results of the ball burnishing. This paper presents the effect of ball burnishing process parameters with hydrostatic tools on the resulting surface structure geometry. The surface topography parameters were calculated using the TalyMap software. Studies were conducted based on Hartley’s static, determined plan. Such a plan can be built on a hypersphere or hypercube. In this work, a hypercube was used. In the case of Hartley’s plan makes it possible to define the regression equation in the form of a polynomial of the second degree. The input process parameters considered in this study include the burnishing rate, applied pressure, and line-to-line pitch. The significant influence of these parameters was confirmed and described as a mathematical power model. The results also showed a positive effect of hydrostatic burnishing on the roughness and geometric structure of the surface.

Improvement of AISI 1018 Carbon Steel Gr 1018 mechanical properties by liquid carburizing in salt bath

Abstract Liquid carburizing is considered as one of surface heat treatment techniques of steel, where it is possible to produce surface layers with high hardness and good corrosion-wear resistance. In this study, the use of carbonate in a liquid medium of AISI 1018 Gr 1018 medium carbon steel has been investigated in term of the surface layer hardness and surface mechanical properties of low carbon steel AISI 1018 Gr 1018. The sample was prepared in a cylindrical shape of 20 mm height and 15 mm diameter by a laminating machine and then smoothed. The microstructure of the specimens was tested to investigate the phase transformations that occur during the carburizing process. The results obtained showed that the use of liquid carburizing for steel (AISI 1018 Gr 1018) leads to an increase in the value of the surface layer hardness of the samples. It is found that the thickness of the carburized layer increases more with an increasing period that the samples remain in the salt bath. This leads to an increase in the effective and overall depth carburized layer formed on the surface. It is obvious that the change in the microstructure of samples occurs gradually between the surface and the heart of the specimens.

Robotic Fiber Laser Cladding of Steel Substrate with Iron-Based Metallic Powder

Abstract The investigations of robotized laser cladding of mild steel by iron-based powder and the study of process parameters on quality and properties of the test surface layers are described. The test surface layers were produced as single stringer beads by means of a laser head coupled with powder-delivering nozzles and mounted on a welding robot arm. The fiber laser emitting at 1.06÷1.07 µm with maximum output power 3.0 kW was used in the study. As the substrate for cladding, the mild steel was chosen, while the experimental powder was composed of 7.0 wt. % of molybdenum, 4.0 wt. % of chromium, 2.0 wt. % of tungsten and vanadium, and also 0.8÷1.0 wt. % of carbon. The surface layers were produced at different laser powers and different scanning speeds. The area of the melt pool and the surrounding regions were protected by argon flow. The detailed influence of the heat input of cladding on the geometry of single stringer beads of surface layers was determined. Results of the investigations showed that the microstructure of surface layers is homogeneous and fine-grained with dispersive precipitation of very fine carbides. Hardness of the mild steel substrate is in the range of 120 to 150 HV1, while the hardness in surface layer is significantly increased up to 800 HV1. The produced surface layers are characterized by high quality. No significant imperfections or discontinuity such pores or cracks were found.

Corrosion Resistance of the Surface Layer of Steel 45 Components Subjected to Combined Strengthening Treatment

Corrosion breakdown of the surface layer of components made of steel 45 subjected to combined strengthening (electromechanical treatment (EMT) + surface plastic deformation (SPD)) and operating under the influence of corrosive media is investigated. It is established that hardness and corrosion resistance of a hardened surface layer is influenced by the amount of tool feeding during EMT, which determines the distribution of structural components (white layer, original material), as well as the degree of medium corrosivity and interaction time with this medium.

Effect of Heat Input on Micro-Hardness and Shear Strength of Inconel 625 Hardfacing onto AISI 347 Steel pipes by GMAW Process

Inconel 625 is one of the most accepted hardfacing material having good corrosion resistance properties at high temperature applications. Hardfacing is the deposition of a hard surface layer to the base metal by means of welding. The benefit of hardfacing is resistance to environmental stresses mainly corrosion at elevated temperatures. Thermal input plays a critical role for manufacturing good hardfaced components with respect to weld bead geometry, cooling rate, etc. In the present study, an L9 orthogonal array of input parameters were carried out with different heat input combinations using 98% Argon + 2% CO2 as shielding gas. Single layer hardfacing was done. The bead-on-pipe welding trials and macroscopic analysis were carried out to find the optimal welding parameters that yielded minimum dilution. The hardfaced layer thickness varies from 1.88mm to 2.58mm on substrate following optimum welding parameters. Visual inspection results reveal that most of welds of higher heat input conditions possess good quality. It is visually observed that width of weld increases with increase in welding heat input. It is noticed that in the range of 200-250 mm/min welding speed and 150A of welding current, good reinforcement and weld bead width at optimum penetration is observed in the experiments. Shear strength test and micro-hardness test were performed over test samples prepared from hardfaced part. Results revealed that both micro-hardness and shear strength of the hardfaced layer were more than that of base metal and values of both increased with increase in heat input. The Inconel 625 hardfaced layer exhibited 32 % higher hardness than the substrate material AISI 347.

Weld deposition of nickel on titanium for surface hardening with Ti-Ni-based intermetallic compounds

Despite its excellent bulk mechanical properties, titanium performs poorly in tribological applications. Efforts to overcome this shortcoming have focused mainly surface modification using laser cladding with ceramic additives or intermetallic compounds (IMCs) formed during cladding. We present an alternative method using weld deposition for the production of IMC-based hard surface layer on titanium using gas metal arc welding (GMAW) with nickel as the filler wire. We observe formation of different Ti-Ni based IMCs (Ti2Ni, NiTi and Ni3Ti) in the fusion zone which results in considerable hardening of the surface. Microstructural characterization of the deposited samples give insight into the formation of IMCs.

Numerical study of optimized processing condition in rolling strike ultrasonic nanocrystalline surface modification of copper

Ultrasonic nanocrystalline surface modification (UNSM) is state-of-art surface modification technique in which both the static and dynamic loads are contributed in work hardening of surface layer and amount of residual stress. The former performance causes microstructure refining while the later results to enhanced fatigue life. However, contribution of too many parameters in the process makes finding optimal parameter setting in which the process reaches to desired performance complex. In the present study, an attempt is made to find optimal combination of static force, tool tip diameter, tool tip material, linear velocity and vibration amplitude regarding the maximum plastic equivalent strain and the maximum affecting depth. The process is firstly modeled through finite element simulation in ABAQUS/EXPILICT software, and the results are further verified considering the residual stress distribution. Hereafter, a series of simulation runs are derived based on design of experiment to generate required data for optimization. In this stage, the run data are associated with response surface methodology to find optimal parameter setting regarding maximum PEEQ and maximum effective depth. The results showed that selection of 300 N static force, 9 mm tungsten carbide ball, 10 μm vibration amplitude and 1000 mm/min feed rate is optimum solution causes achieving maximum PEEQ of 3.44 at the depth of 200 μm. By finding optimal results, a series of USAT experiments have been carried out with optimum parameter setting and its hardness distribution, residual tress and microstructure has been compared with as received sample. It is found that the surface residual stress of the sample reaches from +40 MPa and reaches to –60 MPa after UNSM. On the other hand, the hardness of the sample enhances up to 50% after performing process under optimal setting.

Underwater laser hardening of bearing steels

Water can act as an effective cooling agent during processing of materials. This can be beneficial especially for surface hardening of steels whereby a rapid quenching rate is desired to generate a hard martensitic surface layer. In this study, the underwater laser hardening of bearing steels is experimentally investigated using a fiber laser. The study found that underwater laser hardening increases surface hardness by about 3.5 times than that of the base material which is higher than in conventional laser hardening. Surface hardness as high as 900 HV is achieved when processed with a thin layer of water above the steel surface. However, the depth and width of the laser hardened zone are found to be significantly smaller than in conventional laser hardening. Further analysis revealed that irregular hardened track formed at slower scanning speed due to the convective motion of water and shock wave generation.

Very High-Cycle Fatigue Properties and Residual Stress Relaxation of Micro-shot-Peened EA4T Axle Steel

In this paper, EA4T alloy railway axle steel was shot peened with steel balls and ceramic balls with a diameter of 50 μm, and 109-cycle fatigue tests of unpeened and peened specimens were carried out. The fatigue properties and the surface compression residual stress relaxation processes were investigated. The results of surface fracture observation indicated that all the cracks initiated from the surface, and both peened and unpeened specimens have conventional fatigue limits in the very high-cycle fatigue regime. Moreover, compared with unpeened (UP) specimens, the fatigue limits were improved by 31 and 28% for ceramic shot-peened (CSP) and steel shot-peened (SSP) specimens, respectively. The improvement of fatigue limit is related to the surface compressive residual stresses (SCRS) and the surface-hardened layer. The SCRS and full-width half-maximum (FWHM) values during the relaxation processes have been analyzed. At stress amplitudes lower than the cyclic yield strength, the residual stress of SSP specimens relaxed quickly in the first loading cycle and then remained stable, while the residual stress of CSP specimens relaxed quickly in the first loading cycle and relaxed slowly afterward, then remained stable. For all SSP and CSP specimens with applied stress amplitudes larger than the cyclic yield strength, the residual stress relaxed quickly in the initial cycles, and then remained stable after the first loading cycle.

Effect of Nitriding on the Microstructure and Mechanical Properties of Stainless Steels

Austenitic stainless steels are common spread in many industries. Plasma nitriding is one of the few technologies that allows surface modification of austenitic stainless steels. In this study, a plasma nitriding method to form a hard surface layer at two different austenitic steels AISI 302 and AISI 316L. The surface morphology, chemical composition and mechanical properties of the formed layers were described and the results were compared with each other. The formed nitrided layers on both steels created a uniform multi-phase layer which was characterized by high hardness and very good abrasion resistance.

The Right Signature for Every Process

AbstractThe hardness, residual stress and other properties of a component's surface layers are crucial to its functionality and durability. To achieve specific improvements to the component's “skin”, engineers need a more detailed understanding of the physical and chemical processes at work during manufacturing processes and how these can be exploited to modify the material properties.

Combination of cold drawing and cryogenic turning for modifying surface morphology of metastable austenitic AISI 347\xa0steel

The application of components often depends to a large extent on the properties of the surface layer. A novel process chain for the production of components with a hardened surface layer from metastable austenitic steel was presented. The investigated metastable austenitic AISI 347 steel was cold-drawn in solution annealed condition at cryogenic temperatures for pre-hardening, followed by post-hardening via cryogenic turning. The increase in hardness in both processes was due to strain hardening and deformation-induced phase transformation from γ-austenite to α′-martensite. Cryogenic turning experiments were carried out with solution annealed AISI 347 steel as well as with solution annealed and subsequently cold-drawn AISI 347 steel. The thermomechanical load of the workpiece surface layer during the turning process as well as the resulting surface morphology was characterized. The forces and temperatures were higher in turning the cold-drawn AISI 347 steel than turning the solution annealed AISI 347 steel. After cryogenic turning of the solution annealed material, deformation-induced phase transformation and a significant increase in hardness were detected in the near-surface layer. In contrast, no additional phase transformation was observed after cryogenic turning of the cold-drawn AISI 347 steel. The maximum hardness in the surface layer was similar, whereas the hardness in the core of the cold-drawn AISI 347 steel was higher compared to that in the solution annealed AISI 347 steel.

Influence of Shot Peening Treatment in Erosion Wear Behavior of High Chromium White Cast Iron

High alloy white cast irons (WCI) play an important role in many industrial fields such as mining, cement industry, or grinding due to their high hardness and wear resistance. In all these processes, white cast iron components must work under erosion and abrasion conditions. Many investigations have been carried out with the aim of improving the mechanical properties of this type of alloys. Wear resistance depends on the mechanical properties, mainly hardness. Thus, the WCI are typically heat treated in order to modify its microstructure, improving its tribological and wear behavior. The aim of this study is to propose a mechanical surface treatment, shot peening, as an alternative to global heat treatments, due to its capacity to induce phase transformation and microstructural modification, at the same time that it improves the mechanical properties of materials. Characterization of different treated samples was performed by means of microstructural characterization, X-ray diffraction analysis, SEM observation, hardness and roughness measurements, and erosion tests. The results show that shot peening treatment is able to transform residual austenite and increase hardness in the top surface layer of the material. Both effects contribute to improve the erosion wear behavior of the WCI.