Steel AISI Research Articles

Evaluation of the fatigue life of AISI 347 specimens with small notches based on local strain considerations

The use of materials data for cyclic loading determined on unnotched specimens to predict the fatigue life of notched components has a long tradition, specifically when it comes to nuclear engineering. The basic principle is that the material behaviour of the unnotched specimens can be transferred to what the material is exposed to be in a notch root. This principle has been proven for large notches. However, what happens when the notch is relatively small? Can the fatigue life still be predicted on the grounds of what has been considered as the local strain or Neuber approach? A key reference in that regard is the Neuber equation or generally the load versus notch stress, notch strain – or any combination of those – relationship. In a larger study, unnotched and notched specimens from the metastable austenitic steel AISI 347 have been tested and characterized providing a database that may give some answers to the question raised above.The unnotched specimens considered here had a cross-section diameter of 10 mm while the notch radii of the notched components were only 0.5 and 0.35 mm, respectively. Notch radii of such dimensions will easily reach a fully plastic condition once the material has exceeded the yield limit, because the difference in load between yield start in the notch and full plastification is relatively small. This fully plastic state exceeds the validity of the Neuber equation and requires respective corrections. In this paper it is shown how such corrections can be obtained through a finite element analysis and how this applies to the cases mentioned above.

Determining of the effect of reinforcing microrelief guides on the efficiency of folding integrated covers

The object of research is the processes of strengthening the working surfaces of profile folding strips made of stainless steel AISI 347 and carbon steel AISI 1005 using laser formation of microrelief guides. The analytical and experimental studies are based on the technique of laser microrelief formation by pulsed laser effects. The main assumption of the study is that the use of laser microrelief formation could increase the hardness and wear resistance of the folding strips, improving the process of folding integrated covers. Analyzing the effect of different hardening methods on the mechanical properties and wear resistance of the working surfaces of folding strips is necessary to achieve this goal. A methodology for assessing microstructural changes and their impact on the mechanical properties of folding strips during laser hardening has been proposed. It has been shown that the formation of microrelief guides by laser pulse exposure reduces the thermal load on the material, increases the uniformity of hardening and wear resistance. The revealed wear rates calculated for carbon steel AISI 1005 are 0.875, and for stainless steel AISI 347 – 0.345. To improve the accuracy and efficiency of the folding process, a methodology has been devised for calculating the quantitative formation of microrelief guides on the working surface of profile folding strips. This will not only improve the wear resistance and mechanical properties of the strips but also optimize production processes. Differences in the results of hardening for stainless steel AISI 347 and carbon steel AISI 1005 were found: the hardness values for AISI 347 are 3,088–4,904 MPa at a load of 50–350 g with a deviation of 37.1 %, and for AISI 1005 – 2141–1665 MPa with a deviation of 22.3 %

Electropolishing study of metastable austenitic steel AISI 347 for EBSD analyses

Abstract For the metastable austenitic steel AISI 347 (X6CrNiNb18-10), various electropolishing parameters were evaluated by means of hardness testing, electron backscatter diffraction (EBSD), and atomic force microscopy. Depending on the chosen parameters, different surface characteristics could be achieved simply by only varying voltage, flow rate, and polishing time, although EBSD indexing was always possible. Differences in hardness of up to 20 HV0.5 and in microscopic roughness could be detected on otherwise comparable samples. Finally, the microstructure distribution of a hot rolled bar material with a diameter of 153 mm made from AISI 347 was characterized over the cross section using the previously determined parameter set. Here, insights about recrystallization during forming were concluded and δ-ferrite was differentiated from α’-martensite by kernel average misorientation and morphology.

Design and Development of Combined Mechanical and Pneumatic Valve Spring Remover

A combined mechanical and pneumatic valve spring remover is used to remove or install valve springs from an engine while the cylinder head is mounted on the engine or supported on a workbench (off the head). The designed tool was adjustable and mounted over the cylinder head by a stud. It can operate manually to depress the spring or by using an air compressor for a pneumatic actuator. The model of the tools is done by SOLIDWORK 2021 and we selected the stainless steel AISI grade-304(12) material. Tools were made following the calculations that have been done on valve springs. From the data calculation, the force required to depress the valve spring is 1350 N but the tools were designed to produce 1962.5 N by considering some friction loss. The analysis of the pneumatic system done by ANSYS software shows acceptable results like, Von Mises stress (20.036 MPa), maximum principal stress (26.426 MPa), and the total deformation becomes 1.6029×10-3. The prototype was built, and the test was carried out in time efficiently during the removal or installation of the valve spring on Engine YaMZ-238. The test result shows that to remove 4 springs, the designed tool is very effective to use by optimizing the difference in time savings of an average of 1 minute and 17 seconds when removing the spring valve, and 1 minute and 26 seconds when installing the valve, even when we use it mechanically. The developed valve spring remover has several advantages over the standard C-clamp tools, such as greater precision and accuracy in removing valve springs, reduced labor and time required for the task, and Increased safety with minimal human force.

On the effect of salt bath nitrocarburizing on the cavitation erosion behavior of AISI 304L stainless steel

In this study, salt bath nitrocarburizing was applied on austenitic stainless steel AISI 304L to stabilize austenite at the surface exposed to cavitation attack. Samples were treated at 470 °C and 500 °C for 6 h, giving an average thickness of the nitrocarburized layer of 6 µm and 26 µm, respectively. The thickness of the nitrocarburized layer is found to influence the formation of deformation-induced martensite (DIM) in the material and, thereby, the cavitation erosion resistance. The mass loss vs. time plot shows that the nitrocarburized specimens performed significantly better than the base material under ultrasonic vibratory cavitation erosion test (ASTM G32). Cross-sectional micrographs show that the phenomenon responsible for the failure in the base material is the formation of DIM. The specimen, nitrocarburized at 470 °C, showed a reduction of about 90 % in mass loss when compared to the base material (AISI 304L SS), owing to a higher yield strength (/resilience) after the formation of more stable austenite.

Pre-stress effect of metal bars in low-stress separation technology

This paper proposes a low-stress separation technology based on pre-stress effect. It connects notching and loading to take advantage of the rotating bending fatigue to achieve the cropping of metal bars. The real-time positions of the notching tool and loading hammer are calculated based on energy equivalence theory. Compared to the conventional notching method, it achieves 25.1 % reduction of cutting force in the case of AISI1045 steel bars. A testing platform is set up and the loading curve is designed to meet the requirements of deflection law and fatigue cyclic loading law. The bending stress for the minimum cutting force, crack angle and deviation under different notch parameters, and the reasonable pre-loading of different materials are determined through cropping tests and finite element simulation. Cropping results indicate that the optimized notch angle and depth are 60° and 1.5 mm, respectively.

Sustainable machining of AISI4140 steel: a Taguchi-ANN perspective on eco-friendly metal cutting parameters

This work explores environmentally conscious machining practices for AISI4140 steel through Taguchi analysis. The study employs a design of experiments (DOE) approach, focusing on cutting speed, depth of cut, and coolant type as parameters. Taguchi’s L9 orthogonal array facilitates systematic experimentation, and the results are analyzed using MINITAB 17 software. Signal-to-noise ratios (SNR) are utilized to establish optimum operating conditions, evaluate individual parameter influences, and create linear regression models. The experiments reveal neem oil with graphene coolant as an eco-friendly solution, addressing health and environmental concerns. Main effects plots visually represent the impact of parameters on machining quality. Additionally, regression and artificial neural network (ANN) models are compared for surface roughness prediction, with ANN showing superior performance. The findings advocate for optimized cutting conditions, emphasizing material conservation, enhanced productivity, and eco-friendly practices in AISI4140 steel machining. This research contributes valuable insights for industries seeking sustainable machining solutions.

Characterization and erosion wear behavior of Ni-13%WC8Co microwave clad on AISI-316 steel

Characterization and erosion wear behavior of Ni-13%WC8Co microwave clad on AISI-316 steel

Evaluation of scale invariance in fatigue crack growth in metallic materials

The length-scale dependence of fatigue crack growth is evaluated for a set of metallic materials, namely titanium Ti-6Al-4V, ductile iron EN-GJS-500-7 and tool steel AISI H13, by performing fatigue crack growth tests on geometrically similar compact C(T) specimens of different sizes. With references to length-scale-invariant variables, notably the crack growth rate normalised by the specimen width, it is demonstrated that fatigue crack growth is not a length-scale-invariant process for the tested conditions. In particular, the length-scale dependence is less significant for larger specimens and at longer crack lengths. The test results also contradict the hypothesis of similitude, i.e., that the growth rate is uniquely related to the stress-intensity-factor range, as smaller specimens manifest a higher growth rate when compared at the same stress-intensity-factor range. The observations are in line with presented fracture-mechanical demonstrations, which show that the Paris–Erdogan law depends on the length scale whenever fatigue crack growth is anticipated to be scale invariant.

Microstructural characterization of AISI 440C stainless tool steel fabricated by laser powder bed fusion

Abstract The microstructure of a stainless tool steel AISI 440C fabricated by laser powder bed fusion (L-PBF) without pre-heating of the build plate was characterized by multi-scale experimental methods. In combination with thermodynamic calculations, the solidification and cooling-down procedures were analyzed with the intention to understand the cracking behavior of high carbon tool steels processed by L-PBF. The results showed a fully austenitic structure in the as-built sample with sub-micro cellular structures and nano-sized carbides decorating the cell walls. Significant segregation exists merely at the intersection of cell walls while it is absent along high angle grain boundaries. Factors contributing to crack-free AISI 440C are discussed, providing guidelines for future L-PBF fabrication of high-carbon tool steels.

Microstructure, mechanical, and tribological properties of transition metal (Nb, V, W) nitride coating on AISI-1045 steel by cathodic cage plasma deposition

AISI-1045 steel is a medium-carbon, medium-strength steel that usually requires surface engineering to be usable in industrial applications. Using the cathodic cage plasma deposition technique, transition metal (Nb, V, W) nitride coating is deposited on this steel using cathodic cage lids of these metals. The hardness of untreated steel (1.8 GPa) is upgraded to 11.2, 12.2, and 9.7 GPa for niobium nitride, vanadium nitride, and tungsten nitride coating, respectively. The elastic modulus, the ratio of hardness-elastic modulus (H/E, H2/E, and H3/E2), and the plasticity factor depict the improvement in mechanical and elastic properties. The sample treated with a niobium cage lid exhibits the Nb4N5 phase, the vanadium cage lid shows the VN phase (along with the Fe4N phase), and the tungsten cage lid consists of W2N3, WFeN2, and Fe4N phases. Among these coatings, the thickness of niobium nitride coating is maximum (1.87 μm), and a low deposition rate is obtained for tungsten nitride coating (0.83 μm). In addition to this coating, a nitrogen diffusion zone (∼60 μm) is also formed beneath the coating, which creates a hardness gradient between the coating and the substrate. The ball-on-disc wear tester shows that niobium nitride coating deposition reduces the wear rate from 19.5 × 10−3 to 8.8 × 10−3 mm3/N m and exhibits excellent wear performance.

Understanding the machined material’s behaviour in electro-discharge machining (EDM) using a multi-phase smoothed particle hydrodynamics (SPH) modelling

Electro-discharge machining (EDM) has been extensively employed for machining hard alloys, and its simulations have been widely conducted using finite element analysis (FEA). However, the majority of mesh-based models depended on forecasting the crater profile only based on the temperature gradient, without offering detailed data regarding the machined material properties. It is crucial to understand the behaviour of the machined material in order to accurately assess the flushing efficiency, analyse the wear on the electrode, and examine the interaction between the debris generated during machining and the remaining workpiece. This is done to ensure that no recast material is left behind after the EDM process. For the first time, a meshless smoothed particle hydrodynamics multi-phase model was implemented to gain practical insights and comprehensively understand a very intricate phenomenon that occurs within a very short time. Additionally, this approach is utilised to investigate the characteristics of the materials being machined. We utilised our SPH model to simulate both the capacitance- and transistor-based EDM of Ti–6Al–4V and AISI304 steel. Our simulation considered the temperature-dependent thermal properties and latent heats of the materials. The accuracy of our model was confirmed by comparing its results with experimental, analytical, and finite element analysis (FEA) results. The machined material was observed during its removal from the surface, and the dimensions of the resulting crater, as well as its aspect ratio and the rate at which the material was removed, were predicted with an error ranging from 2 to 22%. This error is far lower than that of the typical finite element (FE) prediction. This model lays the groundwork for a more complex model that will more accurately represent EDM and other similar manufacturing processes.

Machinability study of stainless steel AISI 304 under the influence of copper oxide nanoparticles dispersed emulsifier cutting fluid

Machinability study of stainless steel AISI 304 under the influence of copper oxide nanoparticles dispersed emulsifier cutting fluid

Surface segregation phenomena encountered during solid carbon active screen plasma nitrocarburizing of AISI 316L

Plasma nitrocarburizing of an austenitic stainless steel AISI 316L was performed in an N2-H2 atmosphere (50 % H2 and 50 % N2) with a carbon-fiber reinforced carbon (CFC) active screen. The experimental concept of a plasma-discharged CFC active screen in conjunction with a substrate holder at floating potential ensures that no charged particles are present on the sample surface and no sputtering occurs. As a result, carbon contaminations are formed on the surface which were studied in detail with a combination of scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). The results indicate that a layer of about 25–50 nm of carbon is formed. At the same time, a strong segregation of Mn, Ni and Cr is observed below the coating within the steel substrate. Both effects progress with treatment time and there exists a clear correlation between the formation of the carbon layer and the segregation effect.

Design and testing of novel three-dimensional modular negative stiffness honeycomb structures as reusable crash absorbers

Conventional crash absorbers dissipate kinetic energy of impacts into plastic irreversible deformation, needing an immediate replacement to restore safety of the structure, highly increasing cost and inconvenience of the system. Aim of the present work was to develop innovative prototypes of reusable crash absorbers, able to withstand multiple collisions . A novel design was proposed, based on a modified Negative Stiffness Honeycomb (NSH) approach, using a three-dimensional modular layout with the objective of improving performance, reliability, and functionality of the device in repeated impacts. Two prototypes were manufactured to prove the concept. The first was produced in Nylon PA 6/66 by fused deposition modelling, while the second was obtained from laser-cut plates of stainless steel AISI 304. The nylon prototype was evaluated in cyclic static compression and dynamic impact tests, while the performance of the steel prototype was assessed only in impact tests. Results show improved values of energy absorption with respect to previous studies using bidimensional NSH energy absorbers and a highly reliable behaviour in multiple dynamic compression tests. Moreover, the nylon prototype featured a novel behaviour during impact tests, with autonomous delayed recovery of deformation after the collision. Our data show that three-dimensional modular NSH approach is effective in obtaining a reusable crash absorber, with improved performance and functionality compared to previously proposed design. This work can be considered a step forward in the search for alternative crash absorbers able to sustain multiple impactsbefore substitution, with potential advantages when their replacement is either impossible or too expensive.

Analysis of the effect of cryogenic cooling during drawing on AISI-316 steel wire properties

Analysis of the effect of cryogenic cooling during drawing on AISI-316 steel wire properties

Gradient microstructure formation in carbon steel bars

In recent years, severe plastic deformation has been one of the most popular methods of increasing the mechanical properties of bars. Obtaining an ultra or nanostructure in such bars provides high strength properties, but also reduces plasticity. This paper shows that gradient structure formation in carbon steel bars gives a simultaneous increase in strength properties and some decrease in plastic properties. A new combined technology is proposed for obtaining gradient microstructure. This technology consists of drawing medium carbon steel bars on a radial-shear broaching mill and subsequent drawing. Bars with 30 mm diameter were strained at room temperature to a diameter of 16 mm in 3 passes. As a result, during three straining cycles, the average value of microhardness in the central zone was 2085 MPa, in the neutral zone was 2505 MPa, and in the surface zone was 2915 MPa. This variation of microhardness confirms gradient microstructure availability. Also there was an increase in strength characteristics almost 2 times, plastic characteristics undergo reduction due to gradient microstructure obtained during straining, but remain at a fairly good level for steel AISI 1045. The validity of the results is confirmed by a large number of experiments using a set of standard and modern research methods, such as optical, scanning and transmission microscopy, EBSD analysis, microhardness changes, fractographic method and tensile tests of mechanical properties, as well as by the results reproduction in the joint use of methods.

The Effect of Cryogenic Treatment on Wear Resistance and Hardness of Tool Steel AISI “D2”

The purpose of this paper intended to study different heat treatments in conjunction with a special Cryogenic treatment process and its effect on the wear behavior, and hardness of AISI D2 tool steel. An experimental demonstration of this study was first carried out by a set of specimens left for one week in air after conventional treatment to make stabilization and the other set conditioned at 60°C for one hour before shallow and deep cryogenic treatment. This investigation has shown that an improvement of hardness and wear resistance in deep cryogenic (DCT) process compared to shallow cryogenic treatment (SCT) for different soaking time which was approved by micro-structural examination especially in the stabilized specimens. This finding is in agreement with other results found in the research using similar tool steel and other specific cryogenic processes.

A robust method for assessing the macroscale tribological behaviour of solid lubricant nanoparticles

Reducing friction and wear is crucial for efficiency and longevity in tribological systems. Solid lubricant nanoparticles show great potential in this context but lack deposition control methods and tribological performance investigations under conditions closer to real systems. The present study used drop-casting to deposit multi-layer graphene (MLG) and carbide-derived carbon (CDC) nanoparticles on AISI1020 steel substrates. Tribological performance was evaluated using a ball on flat tests with an incremental load increase in a reciprocating motion. Results indicate a minimum coverage threshold for effective lubrication and highlight substrate topography's critical role. This research enhances understanding of nanoparticle deposition process optimization and control, showing an excellent tribological performance of MLG and CDC nanoparticles in solid lubricated systems.

Experimental investigation of fracture mechanism in organically modified silica-based coating applied on austenitic stainless steel AISI 904L under monotonic and very high cycle fatigue loading

Surface morphology significantly influences the fatigue life of the metallic materials. Therefore, improving surface performance is important for economic and safety applications. Silica-based coatings are anticipated to protect the metallic materials under synergistic operating conditions, such as fatigue and corrosion. However, pure inorganic silica-based coatings are brittle and fail to protect metallic materials. The properties of the sol–gel coatings can be determined by optimizing synthesis factors, such as synthesis steps, precursors, solvents, and catalysts. Organically modified silica-based sol–gel coatings were synthesized using 3-glycidoxypropyl trimethoxysilane and 3-aminopropyltriethoxysilane as precursors, with ethanol as the solvent. The resulting coating was named EtOH. This coating was applied on the surface of stable austenitic stainless steel AISI 904L with the dip coating method. The fracture behavior of the coating during monotonic loading has been studied by interrupted tensile tests at different load steps and examined closely with scanning electron microscopy. On the other hand, very high cycle fatigue experiments were conducted using an ultrasonic fatigue testing system at load frequency of 20 kHz on coated specimens to investigate the fracture behavior of the coating during cyclic loading. Three different kinds of fracture due to stress relaxation in the coating and at its interface with substrate were observed in monotonic loading. The same kinds of stress relaxation were observed in cyclic loading with the difference being that the range of experienced elongation in cyclic tests was significantly smaller. Therefore, the fracture in cyclic loading were concentrated in the vicinity of macro crack. The application of organically modified coatings could suppress the persistent slip bands and result in increased fatigue life for coated specimens.