Modeling of white layer formation under thermally dominant conditions in orthogonal machining of hardened AISI 52100 steel

This paper presents a finite element model for white layer formation in orthogonal machining of hardened AISI 52100 steel under thermally dominant cutting conditions that promote martensitic phase transformations. The model explicitly accounts for the effects of stress and strain, transformation plasticity and the effect of volume expansion accompanying phase transformation on the transformation temperature. Model predictions of white layer depth are found to be in agreement with experimental values. The paper also analyzes the effect of white layer formation on residual stress evolution in orthogonal cutting of AISI 52100 hardened steel. Model simulations show that white layer formation does have a significant impact on the magnitude of surface residual stress and on the location of the peak compressive residual stress.     

The effects of cryogenic cooling on surface integrity in hard machining: A comparison with dry machining

This paper presents results of an experimental study of cryogenic machining of hardened AISI 52100 steel, focusing on surface integrity. Experiments were performed under dry and cryogenic cooling conditions using CBN tools varying cutting speeds, workpiece hardness and tool geometry. Surface integrity parameters (surface roughness, white layer thickness, residual stresses, metallurgical conditions including grain size, phase transformation, etc.) were investigated to establish the effects of cryogenic cooling on the surface integrity of the machined component, and results were compared with those from dry hard machining. Overall, cryogenic cooling provides improved surface integrity leading to extended product life and performance.     

Modification of Low-Alloy Steel Surface by Plasma Electrolytic Nitriding

The structure of the low-alloy steel after plasma electrolytic nitriding (PEN) in electrolyte containing ammonium nitrate was investigated. The cross-sectional microstructure, composition, and phase constituents of modified layer under different processing conditions were characterized. It is shown that anode PEN provides the saturation of steel with nitrogen and formation of α-Fe₂O₃, FeO, and Fe₃O₄ oxides, Fe_2-3N nitride, and martensite. The aqueous solution that contained 15 wt.% NH₄Cl and 5 wt.% NH₄NO₃ allows one to obtain the hardened layer with a thickness of 80 μm and a microhardness up to 740 HV during 5 min at 850 °C. Surface roughness decreases from 1.5 to 0.8 μm after 5-min PEN at 650 °C. The proposed electrolyte and processing mode (750 °C, 10 min) enable to obtain the decrease in the weight loss after lubricate wear testing by a factor of 2.7. The base-nitrate electrolyte conditioned a decrease in the corrosion current density by a factor of 9 due to passivating effect of the oxide and nitride of iron.     

Fatigue crack retardation by silicon carbide powder paste infiltration under different cyclic stress conditions*

Fatigue crack retardation with infiltrated SiC paste into a crack is examined in low carbon structural steel. Two different sizes of SiC powders, whose average diameters are 15 and 53 μm, are used. The SiC powder mixed with oil is infiltrated into a through thickness fatigue crack from the crack mouth. Fatigue crack growth retardation is examined by the ΔK increasing test of R = 0.1, comparing with the base plate property, where ΔK is stress intensity factor range and R is stress ratio. Crack growth is retarded just after infiltrating SiC paste into the crack mouth, and the deceleration of crack growth rate to 1/50 of the base plate appears in the maximum. It is revealed that this crack retardation behaviour results from the crack closure induced by the wedge effect of the SiC particle into a crack. The crack retardation effect is investigated with several combinations of SiC particle size and cyclic stress conditions. The crack growth rate, da/dn and stress intensity factor, K_cl for the crack closure depend on both the maximum stress intensity factor, K_max, and the stress ratio, R. While the better retardation effect can appear in the higher K_max and the higher R ratio, it disappears in the R ratio over 0.7. The SiC paste with 15 μm powder brings the crack retardation effect in the wider cyclic stress condition more stable than in the SiC paste with 53 μm powder.     

The influence of the microstructure of hardened tool steel workpiece on the wear of PCBN cutting tools

Due to the recent developments of advanced cutting tool materials in the superbarasive family, such as cubic boron nitride (CBN) tools, the interest in cutting hardened steels has increased significantly. High flexibility and ability to manufacture complex workpiece geometry in one set up is the main advantage of hard turning compared to grinding. The focus of this study is to investigate the performance and wear behavior of CBN tools in finish, dry turning of four different hardened steels, treated to the same hardness R_c = 54. The following four materials were machined: X155CrMoV 12 cold work steel (AISI D2), X38CrMoV5 (AISI H11) hot work steel, 35NiCrMo16 hot work steel and 100Cr6 bearing steel (AISI 52100). A large variation in tool wear rate was observed in the machining of these steels. The tool flank grooves have been correlated to the microstructure of these steels, namely the presence of various carbides. The chip study reveals that there is presence of different amounts of white layers in machining these steels.     

Ultrasonic assisted magnetic abrasive finishing of hardened AISI 52100 steel using unbonded SiC abrasives

Ultrasonic assisted magnetic abrasive finishing (UAMAF) integrates the use of ultrasonic vibrations and magnetic abrasive finishing (MAF) process to finish surfaces to nanometer order in a relatively short time. The present study emphasizes on the fabrication of UAMAF setup. Using this experimental setup, experimental studies have been carried out with respect to five important process parameters namely supply voltage, abrasive mesh number, rotation of magnet, abrasive weight percentage, and pulse on time (T_on) of ultrasonic vibrations selected based on literature available in the area of MAF process and ultrasonic generator controls. Percentage change in surface roughness (?Ra) for AISI 52100 steel workpiece has been considered as response and unbonded SiC abrasives are used in the work. The experimental results showed that the UAMAF process has better finishing potential as compared to those obtainable by using MAF process for similar processing conditions. The surface roughness value obtained by UAMAF was as low as 22 nm within 80 s on hardened AISI 52100 steel workpiece using unbonded SiC abrasives. Scanning electron microscopy and atomic force microscopy studies were carried out to feel the surface texture produced and to identify finishing mechanism.     

Supersonic Plasma Spray Deposition of CoNiCrAlY Coatings on Ti-6Al-4V Alloy

Plasma spray is a versatile technology used for production of environmental and thermal barrier coatings, mainly in the aerospace, gas turbine, and automotive industries, with potential application in the renewable energy industry. New plasma spray technologies have been developed recently to produce high-quality coatings as an alternative to the costly low-pressure plasma-spray process. In this work, we studied the properties of as-sprayed CoNiCrAlY coatings deposited on Ti-6Al-4V substrate with smooth surface (R _a = 0.8 μm) by means of a plasma torch operating in supersonic regime at atmospheric pressure. The CoNiCrAlY coatings were evaluated in terms of their surface roughness, microstructure, instrumented indentation, and phase content. Static and dynamic depositions were investigated to examine their effect on coating characteristics. Results show that the substrate surface velocity has a major influence on the coating properties. The sprayed CoNiCrAlY coatings exhibit low roughness (R _a of 5.7 μm), low porosity (0.8%), excellent mechanical properties (H _it = 6.1 GPa, E _it = 155 GPa), and elevated interface toughness (2.4 MPa m^1/2).     

Modifying the steel surface by laser heating

Methods of increasing the service properties of steel components by producing hardened modified layers on the surface using laser heating are described. It is proposed to use a combined technology based on laser alloying the steel surface with nitride-forming elements and nitriding. It is shown that laser alloying in the continuous mode results in the formation of a layer with a uniform fine-grained structure with a thickness of 600 μm in the surface layer. Subsequent nitriding eliminates the unfavourable residual stresses and increases the microhardness of low-carbon steels to 20,000 MPa, cracking resistance 1.5–1.8 times and wear resistance 1.5–3 times.     

Influence of Plasma Nitriding on the Microstructure, Wear, and Corrosion Properties of Quenched 30CrMnSiA Steel

The oil-quenched 30CrMnSiA steel specimens have been pulse plasma-nitrided for 4 h using a constant 25% N₂-75% H₂ gaseous mixture. Different nitriding temperatures varying from 400 to 560 °C have been used to investigate the effects of treatment temperature on the microstructure, microhardness, wear, and corrosion resistances of the surface layers of the nitrided specimens. The results show that significant surface-hardened layer consisting of compound and diffusion layers can be obtained when the oil-quenched steel (α′-Fe) are plasma-nitrided at these experimental conditions, and the compound layer mainly consists of ε-Fe_2-3N and γ′-Fe₄N phases. Lower temperature (400-500 °C) nitriding favors the formation of ε-Fe_2-3N phase in surface layer, while a monophase γ′-Fe₄N layer can be obtained when the nitriding is carried out at a higher temperature (560 °C). With increasing nitriding temperature, the compound layer thickness increases firstly from 2-3 μm (400 °C) to 8 μm (500 °C) and then decreases to 4.5 μm (560 °C). The surface roughness increases remarkably, and both the surface and inner microhardness of the nitrided samples decrease as increasing the temperature. The compact compound layers with more ε-Fe_2-3N phase can be obtained at lower temperature and have much higher wear and corrosion resistances than those compound layers formed employing 500-560 °C plasma nitriding.     

Assessment of Fatigue Resistance of Aluminide Layers on MAR 247 Nickel Super Alloy with Full-Field Optical Strain Measurements

This work presents the results of fatigue tests of MAR 247 alloy flat specimens with aluminides layers of 20 or 40 µm thickness obtained in CVD process. Fatigue test was conducted at amplitude equal to half of maximum load and ranging between 300 and 650 MPa (stress asymmetry ratio R = 0, frequency f = 20 Hz). Additionally, 4 of the tests, characterized by the highest amplitude, were accompanied with non-contact strain field measurements by means of electronic speckle pattern interferometry and digital image correlation. Results of these measurements allowed to localize the areas of deformation concentration identified as the damage points of the surface layer or advanced crack presence in core material. Identification and observation of the development of deformation in localization areas allowed to assess fatigue-related phenomena in both layer and substrate materials.     

Surface alloying of Al films/Ti substrate based on high-current pulsed electron beams irradiation

Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis(EPMA),grazing incidence X-ray diffraction analysis(GIXRD),transmission electron microscopy(TEM), and nanoindentation were used to investigate the characterization of Ti–Al surface alloy. The experimental results show that the thickness of alloy layer is *3 lm, and the content of Al in the *1 lm thickness surface layer is *60 at%. The tetragonal TiAl and TiAl2intermetallics were synthesized at the top surface, which have nanocrystalline structure.The main phase formed in the *2.5 lm thick surface is TiAl, and there are few TiAl2and Ti3Al phase for the alloy.Dislocation is enhanced in the alloyed layer. The nanohardness of Ti–Al surface alloy increased significantly compared with a-Ti substrate due to the nanostructure and enhanced dislocation. Since the e-beam remelted repeatedly, the Ti–Al surface alloy mixed sufficiently with Ti substrate. Moreover, there is no obvious boundary between the alloyed layer and substrate.     

Properties and Tribological Performance of Vanadium Carbide Coatings on AISI 52100 Steel Deposited by Thermoreactive Diffusion

Vanadium carbide coatings were formed on AISI 52100 steel specimens by thermoreactive diffusion and characterized using nanoindentation, x-ray diffraction, and chemical analysis. The deposition process formed a 4-µm coating of vanadium carbide (V₄C₃) with an average grain size of 33 nm and a [200] crystallographic texture. The hardness and elastic modulus of the coatings were determined to be 35 ± 7.5 GPa and 334 ± 67 GPa, respectively. Friction and wear of the coatings were examined in reciprocating sliding contact against tungsten carbide (WC) balls in dry and in an abrasive environment. It was determined that in the abrasive environment, the V₄C₃ coating provided wear protection comparable to WC.     

Features of nitroquenching of medium-carbon steel during anodic electrolyte–plasma processing

The research described in this paper is devoted to short-term anodic nitriding of grade 45 steel with postquenching (nitroquenching) in the aqueous solution of ammonia and ammonia chloride. The modified layer structure, as revealed, is composed of alternate layers: a surface oxide layer composed of FeO and Fe₃O₄; a layer of dispersed nitrides Fe₄N and Fe_2–3N with retained austenite; next, a martensitic zone composed of nitrogen and carbon; and the initial nitrogen-enriched ferrite–pearlitic structure. It is found that concentrations of electrolyte components and processing conditions affect the formation character and properties of diffusion layers. The possibility is shown for obtaining a nitroquenched layer 130 µm in thickness with a surface microhardness of to 1200 HV with a decrease in roughness R_a from 0.57 to 0.55 µm, R_z from 1.75 to 1.62 µm, and R_max from 5.74 to 4.00 µm.     

Hot rolling of AISI 304 tailored strips produced by twin roll strip casting

A process for the production of steel strips with an optimized cross section by means of twin-roll strip casting has recently been developed at the Institute of Metal Forming and offers considerable technical and commercial potentials. This production concept is based on the use of profiled casting rolls which continuously transfer the profile geometry to the solidified strip. In order to reduce the internal porosity and improve the surface finish the cast strip was hot rolled using profiled rolls. Offline and inline rolling experiments were performed to prove the effectiveness of this combined forming process. This paper describes the design of a proper rolling tool and the effect of this forming step on the final profile geometry, surface quality, internal porosity and mechanical properties of the strip. The experiments showed that a rolling step with 15 % thickness reduction already allows the global internal porosity to be reduced by 48 % and the strip surface roughness to reach a minimum value of R_a = 2.3 µm. The tensile strength is improved after the hot rolling operation and the obtained values are within the 500–700 MPa range specified by the norm EN 10088-3 for the stainless steel AISI 304. The prescribed ultimate elongation of 45 % is also reached.     

Investigation of corrosion behaviors at different solutions of boronized AISI 316L stainless steel

In this study, corrosion behaviors of boronized and non-boronized AISI 316L stainless steel (AISI 316L SS) were investigated with Tafel extrapolation and linear polarization methods in different solutions (1 mol dm^?3 HCl, 1 mol dm^?3 NaOH and 0.9% NaCl) and in different immersion times. AISI 316L SS were boronized by using pack boronizing method for 2 and 6 hours at 800 and 900°C within commercial Ekabor®-2 powder. Surface morphologies and phase analyses of boride layers on the surface of AISI 316L SS were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. SEM-EDS analyses show that boride layer on AISI 316L SS surface had a flat and smooth morphology. It was detected by XRD analyses that boride layer contained FeB, Fe₂B, CrB, Cr₂B, NiB and Ni₂B phases. Boride layer thickness increases with increased boronizing temperature and time. The corrosion experiments show that boride layer significantly increased the corrosion resistance of the AISI 316L SS in 1 mol dm^?3 HCl solution. While no positive effect of the boride layer was observed in the other solutions the corrosion resistance of the borid layer on AISI 316L SS was increased in all solution with the increase of the waiting periods.     

Improvement of the Electrochemical Behavior of Steel Surfaces Using a [Ti-Al/Ti-Al-N] n Multilayer System

The aim of this work is to improve the corrosion resistance of AISI D3 steel surfaces using a [Ti-Al/Ti-Al-N] _n multilayer system deposited with different periods (Λ) and bilayer numbers (n), via magnetron co-sputtering pulsed d.c. procedure, from a metallic (Ti-Al) binary target. The multilayer coatings were characterized by cross-sectional scanning electron microscopy that showed the modulation and microstructure of the [Ti-Al/Ti-Al-N] _n multilayer system. The composition of the single Ti-Al and Ti-Al-N layer films was studied via x-ray photoelectron spectroscopy, where typical signals for Ti_2p1/2, Ti_2p, N_1s, and Al_2p3/2 were detected. The electrochemical properties were evaluated by electrochemical impedance spectroscopy and Tafel polarization curves. The optimal electrochemical behavior was obtained for the [Ti-Al/Ti-Al-N] _n multilayered period of Λ = 25 nm (100 bilayers). At these conditions, the maximum polarization resistance (1719.32 kΩ cm²) and corrosion rate (0.7 μmy) were 300 and 35 times higher than that of uncoated AISI D3 steel substrate (5.61 kΩ cm² and 25 μmy, respectively). Finally, scanning electron microscopy was used to analyze the [Ti-Al/Ti-Al-N] _n multilayered surface after the corrosive attack. The improvement effects in the electrochemical behavior of the AISI D3 coated with the [Ti-Al/Ti-Al-N] _n multilayered coatings could be attributed to the number of interfaces that act as obstacles for the inward and outward diffusions of Cl^? ions, generating an increment in the energy or potential required for translating the corrosive ions across the coating/substrate interface.     

AISI 316L奥氏体不锈钢低温离子-气体渗碳工艺优化

目的将低温离子-气体乙炔渗碳应用于AISI 316L奥氏体不锈钢表面硬化处理,同时探讨其硬化处理的最优工艺参数及优化效果。方法采用离子轰击去除不锈钢表面钝化膜并活化其表面,再进行低温气体乙炔渗碳,实验过程使用脉冲式供气循环处理方式。进行温度梯度实验,寻找渗碳处理的临界温度。并采用正交试验法设计3因素3水平共9组实验,分析气体比例、离子轰击时间、保温压强3个因素对渗碳层硬度和厚度产生的影响,以期得到不锈钢低温离子-气体乙炔渗碳优化工艺。通过对经过最优化工艺处理过后的不锈钢硬化层组织、成分、厚度、硬度、耐磨性、耐蚀性能的研究分析,验证此工艺对AISI 316L奥氏体不锈钢硬化处理的适用性。结果处理温度为540℃时渗碳层有碳的铬化物析出;离子轰击时间对渗碳层硬度影响最大,保温压强对硬化层厚度影响最明显。在硬化处理温度为520℃,V(H2)∶V(C2H2)=1∶1,渗碳压强为-0.02 MPa,离子轰击时间为20 min时,316L奥氏体不锈钢离子-气体乙炔渗碳效果最优。经优化工艺处理后不锈钢硬化层厚度达到30μm左右,表面硬度达到838HV0.05,耐蚀性和耐磨性能等都显著提高。结论低温离子-气体乙炔渗碳硬化处理适用于AISI 316L奥氏体不锈钢,其处理最合适温度为520℃。经优化工艺处理后的不锈钢具有较高的硬度、厚度,良好的硬度梯度,高耐蚀性能及高耐磨性能。     

Cutting temperatures during hard turning—Measurements and effects on white layer formation in AISI 52100

This paper concerns the temperature evolution during white layer formation induced by hard turning of martensitic and bainitic hardened AISI 52100 steel, as well as the effects of cutting temperatures and surface cooling rates on the microstructure and properties of the induced white layers. The cutting temperatures were measured using a high speed two-colour pyrometer, equipped with an optical fibre allowing for temperature measurements at the cutting edge. Depending on the machining conditions, white layers were shown to have formed both above and well below the parent austenitic transformation temperature, A_c1, of about 750 °C. Thus at least two different mechanisms, phase transformation above the A_c1 (thermally) and severe plastic deformation below the A_c1 (mechanically), have been active during white layer formation. In the case of the predominantly thermally induced white layers, the cutting temperatures were above 900 °C, while for the predominantly mechanically induced white layers the cutting temperatures were approximately 550 °C. The surface cooling rates during hard turning were shown to be as high as 10⁴–10⁵ °C/s for cutting speeds between 30 and 260 m/min independent of whether the studied microstructure was martensitic or bainitic. Adding the results from the cutting temperature measurements to previous results on the retained austenite contents and residual stresses of the white layers, it can be summarised that thermally induced white layers contain significantly higher amounts of retained austenite compared to the unaffected material and display high tensile residual stresses. On the contrary, in the case of white layers formed mainly due to severe plastic deformation, no retained austenite could be measured and the surface and subsurface residual stresses were compressive.     

Microstructure and Properties of SAE 2205 Stainless Steel After Salt Bath Nitrocarburizing at 450 °C

Nitrocarburizing of the type SAE 2205 duplex stainless steel was conducted at 450 °C, using a type of salt bath chemical surface treatment, and the microstructure and properties of the nitrided surface were systematically researched. Experimental results revealed that a modified layer transformed on the surface of samples with the thickness ranging from 3 to 28 μm changed with the treatment time. After 2205 duplex stainless steel was subjected to salt bath nitriding at 450 °C for time less than 8 h, the preexisting ferrite zone in the surface transformed into austenite by active nitrogen diffusion. The main phase of the nitrided layer was the expanded austenite. When the treatment time was extended to 16 h, the preexisting ferrite zone in the expanded austenite was decomposed and transformed partially into ε-nitride precipitate. When the treatment time extended to 40 h, the preexisting ferrite zone in the expanded austenite was transformed into ε-nitride and CrN precipitate. Further, a large amount of nitride precipitated from preexisting austenite zone. The nitrided layer depth thickness changed intensively with the increasing nitriding time. The growth of the nitride layer takes place mainly by nitrogen diffusion according to the expected parabolic rate law. The salt bath nitriding can effectively improve the surface hardness. The maximum values measured from the treated surface are observed to be approximately 1400 HV_0.1 after 8 h, which is about 3.5 times as hard as the untreated material (396 HV_0.1). Low-temperature nitriding can improve the erosion/corrosion resistance. After nitriding for 4 h, the sample has the best corrosion resistance.     

A multivariate robust parameter design approach for optimization of AISI 52100 hardened steel turning with wiper mixed ceramic tool

This paper presents an experimental study of AISI 52100 hardened steel turned with wiper mixed ceramic (Al₂O₃ + TiC) inserts coated with TiN, using Multivariate Robust Parameter Design (MRPD). The main characteristic of this new optimization approach consists of considering both controllable (x_i) and noise (z_i) variables of the hard turning process to find out the parameter levels which minimize the distance of each response (y_i) from its respective targets (T_i) while keeps each variance caused by the noise variables as low as possible. Using a crossed array, a response surface design formed by cutting speed (Vc), feed rate (f) and depth of cut (d) is submitted to the influence of four scenarios built with an 2² full factorial design of two noise factors — workpiece hardness decreasing (Z₁) and tool flank wear (Z₂). This experimental arrangement allows the generating of mean, variance and mean square error (MSE) of five surface roughness parameters (Ra, Rz, Ry, Rt and Rq). As these responses are highly correlated, to extract and employ this information, Principal Component Analysis (PCA) was used. Adopting the Multivariate Mean Square Error (MMSE) as optimization criteria, a robust solution could be found. Theoretical and experimental results were convergent and confirmed. With Vc = 199.9 m/min, f = 0.191 mm/rev and d = 0.190 mm, the five surface roughness parameters and respective variances were minimal, with better results than those obtained with individual optimization.