High-strength AISI Research Articles

Effect of machining parameters on average surface roughness during computer numerical controlled dry milling of high strength AISI 420 martensitic stainless steel

This study focuses on developing an empirical model for average surface roughness during computer numerical controlled (CNC) dry milling of AISI 420 martensitic stainless steel, utilizing response surface methodology (RSM). Experiments were designed with three levels of axial depth of cut, feed rate, and spindle speed to quantify their impact on surface roughness. The RSM-Box-Behnken design was employed to construct the empirical model. Model adequacy was validated through residual analysis and analysis of variance (ANOVA). Analysis of the main effects and interaction effects revealed that the primary influences on average surface roughness were the feed rate, spindle speed, and axial depth of cut, while interaction effects were less significant. Optimal cutting conditions were determined to be a spindle speed of 1500 rpm, a feed rate of 30 mm min−1, and an axial depth of cut of 0.3 mm. The model’s validity was further confirmed through additional validation tests.

Additive manufacturing of high-strength low-alloy AISI 4340 steel with an optimal strength-ductility-toughness trade-off

Additive manufacturing (AM) has revolutionised steel part fabrication, yet not all steels are amenable to its unique solidification features, characterised by cyclic and rapid heating/cooling, and directional solidification. These conditions often result in challenges such as columnar grain formation, microstructural heterogeneity, and consequently, inferior mechanical performance, brittleness and severe anisotropy in particular. Recent studies have adopted inoculation or post-fabrication treatments to address this issue, but often entailing extra cost and processing time. This study aims to verify that some steels such as AISI 4340 steel are inherently compatible to AM, producing components that are innately robust and ready for use in the as-built state. The medium carbon content and low alloying element concentration enable AM processing to produce a uniform and refined bainite microstructure with minimal elemental segregation, avoiding the formation of unstable retained austenite. The high AM-processability of this steel is demonstrated by achieving high densification (>99.9 %) across a broad processing window, which allows precise microstructural control via proper tunning the processing parameter modifications, inducing a transition from upper bainite to lower bainite dominance, to tailor mechanical properties for specific applications. The as AM-fabricated AISI 4340 steel exhibits a good combination of strength, ductility, and toughness, manifested by a yield strength range from 1240 to 1370 MPa, an ultimate tensile strength from 1360 to 1740 MPa, an elongation from 7 % to 14 %, and an impact toughness range of 11–44 J. The mechanical properties of the AM-fabricated 4340 steel are comparable to those of the wrought counterpart and superior to the majority of other AM-fabricated steels. This research reveals the high potential of AM to process high-strength low-alloy steels.

Fracture prediction on hydrogen-charge notched samples using a stress-state-dependent phenomenological model

There is a consensus for transitioning to clean energy sources to meet the world’s energy demands. Hydrogen is a candidate to supply green energy. However, hydrogen embrittlement (HE) in materials is an issue that needs to be assessed. Based on the damage concept, a straightforward and robust computational framework is presented to predict the harmful effects on material resistance caused by the HE phenomenon. The adopted model framework builds upon dealing with the coupled mechanical diffusion problem in a simplified approach by considering the local equilibrium between hydrogen concentration at interstitial sites and Cauchy stresses. A modified version of the Mohr–Coulomb criterion dependent on the stress triaxiality and Lode angle introduces a damage indicator parameter. The proposed model is applied to study the brittle intergranular fracture of a high-strength AISI 4135 steel. A detailed description of the stress state and hydrogen-driven failure parameters are presented for two specimens with different notch radii. The proposed model is implemented in a VUMAT subroutine and made available for download to the technical community for research and educational use. After calibrating the model parameters, the numerical results yield good agreements of the predicted fracture strength of notched hydrogen-charged samples compared to the experimental ones. Maximum differences of around 10% among experimental and numerical tests are observed.

Comparison of Tool Wear, Surface Roughness, Cutting Forces, Tool Tip Temperature, and Chip Shape during Sustainable Turning of Bearing Steel.

In this study, a comparison of measured cutting parameters is discussed while machining AISI 52100 low-alloy hardened steel under two different sustainable cutting environments, those in which a dry and minimum quantity lubrication (MQL) medium are used. A two-level full factorial design method has been utilized to specify the effect of different experimental inputs on the turning trials. Experiments were carried out to investigate the effects of three basic defining parameters of turning operation which are namely cutting speed, cutting depth, feed rate effects and also the effects of the cutting environment. The trials were repeated for the combination of different cutting input parameters. The scanning electron microscopy imaging method was used to characterize the tool wear phenomenon. The macro-morphology of chips was analyzed to define the influence of cutting conditions. The optimum cutting condition for high-strength AISI 52100 bearing steel was obtained using the MQL medium. The results were evaluated with graphical representations and they indicated the superiority of the pulverized oil particles on tribological performance of the cutting process with application of the MQL system.

In-situ generation of high-strength AISI 1045 steel with SiO2 nano-precipitation by selective laser melting (SLM)

High-strength AISI 1045 steel with SiO2 nano-precipitated particles is prepared via selective laser melting (SLM). The microstructure and mechanical properties of the as-built samples were studied and characterized by Scanning electron microscope (SEM), X-Ray Diffraction (XRD), Electron backscatter diffraction (EBSD) and Transmission electron microscope (TEM). XRD analysis shows that the powder mainly contains α-Fe phase, while γ-Fe phase appears in the SLMed specimen. The peak intensity increases slightly with the increasing of the processing energy density. In addition, ultra-fine martensite and SiO2 nano-precipitated particles were found in the as-built samples. Moreover, excellent mechanical performances were achieved by SLM-AISI 1045 (Vickers hardness: 502 ± 25 HV0.1, yield strength: and 1250 MPa), which are 1.63 times and 3.29 times higher than those of traditional commercial AISI 1045 respectively. Finally, the strengthening mechanism of the SLM-AISI 1045 was analyzed and discussed.

Effects of ER308L buttering and post-buttering heat treatment on the microstructure and mechanical properties of API 5L X65/AISI304 dissimilar joint

This study investigates the effects of ER308L butter layer on the microstructure and mechanical properties of API 5L X65/dissimilar joint. High strength low alloy API 5L X65 and AISI 304 steel grades are widely used in a wide range of industrial applications, and more specifically in the oil and gas sector. Dissimilar welds between API 5L X65 pipeline and austenitic stainless steel joints have long been used in the oil/gas and petrochemical sectors. Using buttering layer to improve properties of these types of dissimilar joints has lately received significant attentions. In the present work, the ER308L butter layer was applied on the API 5L X65 side through gas tungsten arc welding, followed by a stress-relief heat treatment at 600 °C. Buttered API 5L X65 samples were welded to AISI 304 samples through gas tungsten arc welding in 5 passes. Microstructures of joints were evaluated by scanning electron microscope (SEM) and optical microscope (OM). Mechanical properties were also assessed by tensile, impact, and Vickers micro-hardness tests. Fractography and phase identifications were carried out using SEM and energy dispersive spectroscopy (EDS). Results showed that a martensite layer on the fusion zone with a thickness of about 30 μm was observed at the interface of API 5L X65/butter layer. It appears that compositional changes played a significant role in the formation of martensitic structures and type-II grain boundaries. Results also showed that the fracture positions in both heat treated and as-welded samples were in the heat affected zone (HAZ) of API 5L X65. The implications of buttering and post-buttering stress-relief heat treatment for the microstructure and mechanical properties are comprehensively discussed.

Dissimilar welding of Inconel 713 superalloy and AISI 4140 steel using Nd:YAG pulse laser: An investigation on the microstructure and mechanical properties

In the present research, welding of Inconel 713 superalloy and high strength AISI 4140 steel was successfully implemented by using pulsed Nd:YAG laser. The effect of heat input on the microstructural and mechanical properties of the weld was studied to find the best conditions for achieving a high quality weld. The microstructure characteristics of different weld regions including weld metal and heat affected zone were examined using the optical and scanning electron microscopies. It was observed that a columnar dendritic structure was formed at the edge of weld metal due to higher gradient temperature, while the reduction of gradient at the center of weld metal produced a cellular dendritic structure. The increase of heat input encouraged the formation of coarse dendritic structure which resulted in a reduction in the hardness of weld metal. The HAZ of 4140 steel side showed the maximum hardness for different values of heat inputs due to formation of martensitic microstructure, while the hardness in HAZ of Inconel 713 side was not showed a significant change. The higher value of heat input led to the segregation of Nb, Mo and Ti elements in the inter-dendritic regions and formation of brittle laves phase which resulted in a reduction in the tensile strength. However, the weld joint indicated a maximum tensile strength of 1068 MPa at lower heat input (1875 J/mm). The fracture surface of the tensile specimens showed a brittle fracture in the weld metal at different heat inputs.

Effect of Selected Cooling and Deformation Parameters on the Structure and Properties of AISI 4340 Steel.

The paper is focused on investigation of the high-strength AISI 4340 steel at various temperature and deformation conditions. The article is divided into two specific analyses. The first is to examine the dilatation behavior of the steel at eight different cooling rates, namely, 100, 10, 5, 1, 0.5, 0.1, 0.05 and 0.01 °C·s−1. The mapping of the phase transformations due to varying cooling rates from the austenitizing temperature of 850 °C allows the construction of the CCT diagram for a given high-strength steel. These dilatation curves were also compared with the metallography of the selected samples for the proper construction of the CCT diagram. A further analysis of the high temperature deformation of high strength steel AISI 4340 was performed in the range of temperature 900–1200 °C, and the strain rate was in the range from 0.001 to 10 s−1 with maximum value of the true strain 0.9. Changes in the microstructure were observed using light optical microscopy (LOM). The effect of hot deformation temperature on true stress, peak stress and true strain was investigated. The hardness of all deformed samples, depending on the temperature, the deformation rate and the peak stress σp overall together related with hardness, has also been evaluated.

Effects of Homoacetogenic Bacteria on the Corrosion Behaviour and Cathodic Protection of AISI 4135 Steel

The corrosion behaviour of high-strength low-alloy AISI 4135 steel was studied in the presence of homoacetogenic bacteria (Blautia coccoides GA-1), which catalyse the formation of acetate from H-2 plus CO2 in their energy metabolism. In addition, the effects of cathodic protection were studied. The chronoamperometry curves showed a negative current density. The minimum current density was approximately -1.5 mu A.cm(-2). The results revealed that the strain GA-1 could consume 'cathodic hydrogen' and promote the cathodic reaction of AISI 4135 steel, but the hydrogen consumption of strain GA-1 was not the main reason leading to the increase in the corrosion current density.

Analysis and characterisation of WC-10Co and AISI 4340 steel bimetal composite produced by powder–solid diffusion bonding

Cermet and steel material bonding is a challenging task, due to their large difference of physical properties, e.g. coefficient of thermal expansion. In this study, a hot compaction diffusion bonding method was employed to fabricate a small-dimensional bimetallic composite of WC-10Co and high strength AISI 4340 steel, where the cermet was used in powder form and the steel as solid. The bimetal composite was characterised by microstructural analysis and mechanical properties evaluation. The interface microstructure reveals a successful metallurgical bonding between the cermet and steel materials. The influence of sintering temperature (1050–1250 °C) was examined at intervals of 50 °C. This study shows that the properties of sintered powder and the bonding quality with the steel improve with an increase in sintering temperature. A bonding beneficiary reaction layer was observed to grow at the joining interface by mutual diffusion of the alloying elements, which increases with the increasing temperature. The maximum width of the reaction layer observed was 4.13 μm and consists mainly of intermetallic ternary carbides. The bonding shear strength of the interface is found to be slightly higher than claimed in previous studies. The developed bimetal composite could be used in applications where a combination of high strength and hardness is required.

Microstructure and mechanical properties of laser-welded high-strength AISI 301LN steel in reversion-treated and temper-rolled conditions

Reversion treatment is an efficient method to refine the grain size of metastable austenitic stainless steels and enhance their mechanical properties. A piece of an AISI 301LN 56% cold-rolled 3.4 mm thick sheet was annealed at 790 °C for 80 s on a 600 kW pilot induction heating line resulting in the grain size of 0.9 μm. A commercial 3.0 mm thick temper-rolled 301LN (+CP700 / C1000) sheet together with data for a hot-rolled steel from a previous study were used for comparisons. The sheets were bead-on plate autogenously welded using a diode pumped Yb:YAG laser at a constant power of 4 kW. Microstructure examinations were performed employing optical microscopy and electron backscatter diffraction. Hardness and tensile tests as well as strain-controlled fatigue tests were carried out to determine the mechanical properties. Microstructure evolution revealed that only slight grain growth occurred in a very narrow zone in the heat-affected zone (HAZ) in the reversion-treated sheet during welding. In the HAZ of the temper-rolled sheet both recrystallization and grain growth took place. The HAZ was also narrower in the reversion-treated sheet. The minimum hardness level was about 240 HV in the both welds. The yield strengths of the weld seams of the reversion-treated and temper-rolled sheets were equal but twice as high as the yield strength of hot-rolled steel without welding. The fatigue strength was identical in the both structures, impaired by welding, but about the same as that of the hot-rolled steel without welding. The welded specimens failed in the weld metal either along the fusion line between the HAZ and the weld metal or inside the weld metal. It can be assumed that the microsegregation and/or the grain structure provide some weaker sites for crack nucleation, but also the grain size and structure are different from those of the base metals.

Atom probe tomographic observation of hydrogen trapping at carbides/ferrite interfaces for a high strength steel

A three-dimensional atom probe (3DAP) technique has been used to characterize the hydrogen distribution on carbides for a high strength AISI 4140 steel. Direct evidence of H atoms trapped at the carbide/ferrite interfaces has been revealed by 3DAP mapping. Hydrogen is mainly trapped on carbide/ferrite interfaces along the grain boundaries. Slow strain rate tensile (SSRT) testing shows that the AISI 4140 steel is highly sensitive to hydrogen embrittlement. The corresponding fractographic morphologies of hydrogen charged specimen exhibit brittle fracture feature. Combined with these results, it is proposed that the hydrogen trapping sites present in the grain boundaries are responsible for the hydrogen-induced intergranular fracture of AISI 4140. The direct observation of hydrogen distribution contributes to a better understanding of the mechanism of hydrogen embrittlement.

Microstructural evolution in adiabatic shear band in the ultrafine-grained austenitic stainless steel processed by multi-axial compression

Adiabatic shear bands play the most important role in the deformation and failure of high strength AISI 201 austenitic stainless steel. The microstructure and microtexture of the adiabatic shear band in ultrafine-grained stainless steel are investigated by means of optical microscopy, TEM and EBSD. The shear bands can be generated at about 54μs after the true flow stress reaches the peak value of about 1135MPa. The width of the shear bands is about 9μm, and the grains sizes 50–200nm in the boundary of the shear band are elongated along the shear direction; the grain subdivision on approaching the shear band can be observed, and the core of the shear band consists of recrystallized equiaxed grains (sizes 30–80nm) with new microtextures and the ultrafine grains with deformed microtextures and with high dislocation density. The grain boundaries in the adiabatic shear band are geometrical necessary boundaries with high-angles. The calculated temperature in the shear band is estimated to reach 0.58 Tm (968K). It takes 7μs for the shear band to cool down from 968K to the room temperature when the shear localization ceases, and the cooling strain rate is calculated as high as 9.6×107K/s. Kinetic calculations indicate that during the deformation process, the recrystallized nanosized grains can be formed in the shear band by way of the subgrain boundaries rotation when the subgrains׳ sizes are lower than 80nm or the temperature in the shear band is higher than 0.5 Tm (834K), and they do not undergo significant growth by grain boundary migration at the cooling stage. These results indicate that the microstructure development within shear band is controlled by both dynamic recovery and rotational dynamic recrystallization.

A Microstructural Investigation of Roll Formed Austenitic Stainless Steel

Due to high production rates and the possibility to form complex geometries roll forming has become an increasingly popular forming process for sheet metal. Increasing quantities of high strength steels are used today but can be difficult to form due to their low ductility. One way to partly overcome this problem is to heat the steel in the forming area thus locally increasing the ductility. In the present study partially heated cold rolled high strength AISI 301 type austenitic stainless steel was investigated using electron backscattered diffraction (EBSD), and the results were compared to microhardness measurements. The results show that partial heating will give an almost complete reverse martensite transformation, i.e. martensite (α ́) transforms to austenite (γ), close to the surfaces and grain growth in the middle of the steel sheet. The extension of the heat affected zone can be determined using either microhardness or EBSD measurements. Both these measurements can be used to determine the position of the neutral layer after roll forming. The hardness measurement cannot distinguish between microstructural features but the results are in good agreement with the EBSD results for volume fraction of α ́-martensite. A major advantage of using EBSD is the possibility to characterize and follow the microstructural development when heating and roll forming.

Effect of Hydrogen and Magnetic Field on the Mechanical Behavior of High Strength AISI 4340 Steel

Presence of hydrogen in materials is known to affect their mechanical properties due to hydrogen embrittlement problem. Steels used in various applications are prone to be exposed to aqueous electrochemical environments, which may introduce hydrogen into the alloy. These alloys are also prone to be simultaneously exposed to magnetic field, which may affect the hydrogen embrittlement susceptibility of these alloys. Therefore, it is important to examine the effect of hydrogen and magnetic field on the mechanical behavior of iron-based alloys. In this work, the effect of hydrogen and magnetic field on the fracture behavior of high strength AISI 4340 steel was examined. Three-point bend test was used to study the fracture behavior. In all the cases, the samples tested with hydrogen charging show a drastic reduction in ductility and fracture stress values. The effect of magnetic field was seen to be negligible. The hydrogen embrittlement was characterized by a change in the fracture surface from a ductile-type fracture to a brittle cleavage-type fracture. Acoustic emission signals collected during the test corresponds to the fracture behavior.

Fatigue Strength Improvement of AISI E52100 Bearing Steel by Induction Heating and Repeated Quenching

Martensitic high-carbon high-strength AISI E52100 steel (JIS SUJ2) is one of the main alloys used in rolling contact applications when high wear and fatigue resistance are required. In this work, repeated induction heating and quenching of AISI E52100 is proposed, and the refinement of the martensite structure and consequent improvement of the fatigue properties measured by rotating bending fatigue tests of steel parts is reported.

Hydrogen embrittlement of 4340 steel due to condensation during vaporized hydrogen peroxide treatment

Hydrogen peroxide vapor has been proposed as a sterilant/decontaminant for usage in buildings and transportation vehicles including emergency vehicles, buses, trains and aircraft. Although the efficacy of the process has been demonstrated, questions regarding the compatibility of vaporized hydrogen peroxide treatments with the many diverse materials of construction have been raised. This paper presents results on the embrittlement of high strength AISI 4340 steel as a result of condensation of the vapor during exposure to vaporized hydrogen peroxide. Notched four point bending samples of AISI 4340 steel were tested using the standard test methods of ASTM F519-06 to quantify susceptibility to hydrogen embrittlement in this aggressive service environment. No embrittlement effects were observed for samples exposed to strictly vapor phase hydrogen peroxide for concentrations up to 1000 ppm H 2O 2 and exposure times of 4.8 h. Higher concentrations of 1300 and 1600 ppm H 2O 2 led to the condensation of the vapor throughout the process chamber and brittle fracture of samples. These results were confirmed by examination of the fracture surfaces of samples using scanning electron microscopy. Samples that were not considered embrittled possessed dimpled fracture surfaces consistent with ductile failure. Embrittled samples exhibited inter-granular fractures along prior austenitic grain boundaries near the root of the notch – a common characteristic of hydrogen embrittlement.

Evaluation on fatigue strength of AISI 4340 steel aluminum coated by electroplating and IVD processes

In spite of toxicity, hydrogen embrittlement susceptibility, and environmental issues, cadmium electroplating is usually applied on high strength AISI 4340 aeronautical steel due to its efficient protection against electrochemical corrosion. Ion vapor deposition (IVD) process with pure aluminum also offers good protection against corrosion with the advantages of decreasing hydrogen embrittlement susceptibility and improving the fatigue strength of metallic components. In this research, the effects of aluminum electroplating and IVD aluminum coating on the rotating bending fatigue strength of AISI 4340 steel were evaluated in comparison with cadmium electroplated specimens. Experimental fatigue results showed that both aluminum electroplating and IVD aluminum coatings are possible alternatives to cadmium electroplating.

Evaluation of delayed fracture property of outdoor-exposed high strength AISI 4135 steels

Delayed fracture properties of AISI 4135 high strength steels with 1490 and 1310 MPa of tensile strength, represented as B15 and B13, respectively, have been studied by means of slow strain rate test (SSRT) of notched bar specimens after outdoor exposure at rural and coastal areas. The exposed specimens were kept at humid medium before SSRT to reproduce active hydrogen entry influenced by the rust layer and to homogenize hydrogen distribution. The influences of exposure site and exposure time on fracture stress have been investigated. The susceptibility of B15 to delayed fracture was obviously higher than that of B13.

Effect of Hydrogen on the Fracture Behavior of High-Strength Cr-Mo Steel

We examine the hydrogen embrittlement susceptibility of a high-strength AISI 4135 steel by means of a slow strain-rate test (SSRT) using notched round bar specimens. Hydrogen was introduced into the specimens by electrochemical charging and its content was measured by thermal desorption spectrometry (TDS). It was found that the maximum tensile stress decreased in a power law manner with increasing diffusible hydrogen content. Finite element method (FEM) calculations demonstrated that the peak value of the maximum principal stress and the peak value of the locally accumulated hydrogen concentration at the maximum tensile stress were in good agreement with one power law relationship for the specimens with different stress concentration factors.