Ni-Cr Steel Research Articles

Influence of strain rate on the tensile properties of metastable austenitic stainless CrNi and CrMnNi spring steels

Austenitic stainless steels have a wide area of applications, including spring steels in their hardened condition. A preceding forming process mainly achieves the necessary high yield strength (YS) for spring steel. During strain hardening, strain-induced α′-martensite formation results in high strength characteristics. The driving forces behind this transformation include low stacking fault energy of austenitic base material and high chemical driving force of α′-martensite formation. Both parameters are strongly dependent on temperature. This research represents the temperature dependent mechanical properties in a temperature range between −40 °C and 200 °C of a) nickel reduced manganese and nitrogen alloyed stainless steel X5CrMnNiMoN16-4-4 (4Mn) and b) CrNi steel X10CrNi18-8 (1.4310) at a strain rate of 4.6 × 10−4 s−1. Additionally, the effect of a moderate increase in strain rate to 9.2 × 10−4 s−1 and 6.7 × 10−3 s−1 on quasi-adiabatic heating of the steels was investigated. For both steels, by increasing the strain rate, the adiabatic temperature increases and subsequently decreases the strain-induced α′-martensite formation. The increase in the strain rate results in a strong drop of ultimate tensile strength (UTS) for both steels. Nevertheless, the uniform elongation (UE) remains almost constant at a high level for 4Mn. The UE decrease sharply in case of 1.4310. Independent of strain rate value, a larger strain-induced α′-martensite fraction generated in 4Mn compared with 1.4310. Consequently, under all experimental conditions, higher UTS values were achieved for 4Mn. The strain-induced α′-martensite was quantified by magnetic saturation analysis (MSAT). Subsequently, it was characterised by scanning electron microscopy (SEM) using electron channelling contrast imaging (ECCI) and electron backscatter diffraction technique (EBSD).

Insight on corrosion behavior of a Cu–P–Cr–Ni steel with different Ni contents by electrochemical and periodic immersion corrosion experiments

Insight on corrosion behavior of a Cu–P–Cr–Ni steel with different Ni contents by electrochemical and periodic immersion corrosion experiments

Constitutive modelling of the deformation‐induced martensite transformation observed in metastable austenitic CrNi steels

AbstractMetastable austenitic CrNi steels undergo phase transformation when loaded or deformed plastically. In the current work a macroscopic and phenomenological constitutive model is presented to model the strain induced transformation of austenite to martensite. The approach is based on the previous works of Olsen and Cohen [1] & Stringfellow et al. [2]. The kinetics of the phase transformation is modelled based on the assumption that the intersections of the shear bands in the austenitic phase, act as potential martensite nucleation locations. Evolution of the shear band density and their intersections are modelled using the plastic strain in the austenitic phase. The probability of the intersection creating martensite is given by a Gaussian cumulative distribution, which in turn depends on the temperature and stress triaxiality. The resulting stress‐ strain behavior considers the volume fraction, plastic strains and the strain hardening parameters of the individual phases as internal variables. An explicit formulation of the material model is implemented as a user subroutine in a bi‐linear element formulation of FEM. Some of the required material parameters are estimated by fitting experimental stress‐strain and martensite volume evolution curves. For the purpose of illustrating the model's behavior, boundary value problems of components with structured surfaces are presented.

Fractographic Analysis of GTAW Robotic Welded Joints Fractured under Stress in Experimental HSLA Cr-Ni Steel

The welding current (A), arc voltage (V) preheating (°C), travel speed (mm·min-1) and net heat input (Qnet) were evaluated, on the strength and morphology of the fracture in experimental HSLA Cr-Ni steel welded joints, with commercial (ERS70S-6) filler metal and robotic GTAW technique. The samples were characterized by uniaxial stress tests, stereoscopy and Digital Image Processing (DIP). The results showed that the resistance to fracture of the experimental steel was exceeded by 18.39% by applying Qnet 0.520 (kJ·mm-1) and the combination of: 200 A, 12.7 V, 25 °C and 180 mm min-1, which influenced the ductile fracture morphology and topology. While the low Qnet (0.200-0.208 kJ·mm-1) favors instantaneous deformation of the welded joints with fracture in the weld bead as the major defect.

Fractographic Analysis of GTAW Robotic Welded Joints Fractured under Stress in Experimental HSLA Cr-Ni Steel

The welding current (A), arc voltage (V) preheating (°C), travel speed (mm·min-1) and net heat input (Qnet) were evaluated, on the strength and morphology of the fracture in experimental HSLA Cr-Ni steel welded joints, with commercial (ERS70S-6) filler metal and robotic GTAW technique. The samples were characterized by uniaxial stress tests, stereoscopy and Digital Image Processing (DIP). The results showed that the resistance to fracture of the experimental steel was exceeded by 18.39% by applying Qnet 0.520 (kJ·mm-1) and the combination of: 200 A, 12.7 V, 25 °C and 180 mm min-1, which influenced the ductile fracture morphology and topology. While the low Qnet (0.200-0.208 kJ·mm-1) favors instantaneous deformation of the welded joints with fracture in the weld bead as the major defect.

Measurement of welding fume production in welding with high-alloy electrodes

Due to their good structural properties, stainless Cr-Ni steels have a very wide application in various branches of technology. During the welding of stainless Cr-Ni steels with high-alloy coated electrodes, welding fumes of complex chemical composition are generated, which is very harmful for welders and the environment. For the purposes of this experiment, two variants of one rutile Cr-Ni commercial electrode, designated E 23 12 2 LR 12, were designed and fabricated. Higher production of welding fume particles also means greater danger to humans and the environment. In order to show the influence of the base material on the production of welding fume particles, an experiment for measuring the production of welding fume particles was performed in which two different steels were used as the base material, general structural steel S235JRG2 and stainless steel X6CrNiTi18.10.

Effect of shot peening on the surface properties, corrosion and wear performance of 17-4PH steel produced by DMLS additive manufacturing

Components produced by additive manufacturing (AM) via direct metal laser sintering (DMLS) have typical as-fabricated surface defects. As a result, surface properties of AM products should be modified to increase their strength, anti-wear behaviour, and at the same time to ensure their high corrosion resistance. Surface modification via shot peening is considered suitable for additive manufacturing of medical devices made of 17-4PH stainless steel. The objective of this study was to determine the effect of shot peening pressures (0.3 MPa and 0.6 MPa) and three types of blasting media (CrNi steel shot, nutshell granules and ceramic beads) on the tribological characteristics and corrosion resistance of specimens of DMLS 17-4PH stainless steel. Results demonstrated that shot peening caused steel microstructure refinement and—except for the nutshell shot-peened specimens—induced both martensite (α) formation and retained austenite (γ) reduction. 17-4PH specimens peened with steel and ceramic shots showed the highest increase in surface hardening by approx. ~ 119% (from 247 to 542 HV), which significantly improved their wear resistance. The highest mechanical properties (hardness and wear resistance) and corrosion resistance were obtained for the surfaces modified using the following media: ceramic beads > CrNi steel shot > nutshell granules. Adhesive and fatigue wear were two predominant mechanisms of tribological deterioration. Results demonstrated that the application of shot peening using ceramic beads led to grain size refinement from 22.0 to 14.6 nm and surface roughness reduction, which in turn resulted in higher corrosion resistance of the material. DMLS 17-4PH specimens modified by shot peening using ceramic beads and a pressure of 0.6 MPa exhibited the optimum surface morphology, hardness and microstructure, and thus improved wear and corrosion performance.

Stacking Fault Energy in Relation to Hydrogen Environment Embrittlement of Metastable Austenitic Stainless CrNi-Steels

Metastable austenitic steels react to plastic deformation with a thermally and/or mechanically induced martensitic phase transformation. The martensitic transformation to α’-martensite can take place directly or indirectly via the intermediate stage of ε-martensite from the single-phase austenite. This effect is influenced by the stacking fault energy (SFE) of austenitic steels. An SFE < 20 mJ/m2 is known to promote indirect conversion, while an SFE > 20 mJ/m2 promotes the direct conversion of austenite into α’-martensite. This relationship has thus far not been considered in relation to the hydrogen environment embrittlement (HEE) of metastable austenitic CrNi steels. To gain new insights into HEE under consideration of the SFE and martensite formation of metastable CrNi steels, tensile tests were carried out in this study at room temperature in an air environment and in a hydrogen gas atmosphere with a pressure of p = 10 MPa. These tests were conducted on a conventionally produced alloy AISI 304L and a laboratory-scale modification of this alloy. In terms of metal physics, the steels under consideration differed in the value of the experimentally determined SFE. The SFE of the AISI 304L was 22.7 ± 0.8 mJ/m2 and the SFE of the 304 mod alloy was 18.7 ± 0.4 mJ/m2. The tensile specimens tested in air revealed a direct γ → α’ conversion for AISI 304L and an indirect γ → ε → α’ conversion for 304 mod. From the results it could be deduced that the indirect phase transformation is responsible for a significant increase in the content of deformation-induced α’-martensite due to a reduction of the SFE value below 20 mJ/m2 in hydrogen gas atmosphere.

Study on Mechanical Properties of Carburized Layer Based on Nano-Indentation

The work aims to obtain the local mechanical parameters of carburized layer of CiNi steel. Tensile test and nano-indentation test were carried out for CrNi steel, stress-strain curve and load-displacement curve were then obtained. The finite element model of nano-indentation was built, and a model for obtaining the local mechanical parameters of carburized layer from load-displacement curve was established combined with dimension analysis. The mechanical parameters of pure iron and carburized layer of CrNi steel were calculated. The results show that, the dimension analysis model is accurate for predicting the mechanical properties of pure iron, the model accuracy is verified. The local mechanical parameters of carburized layer are predicted by the model, the simulated load-replacement curve based on the predicted mechanical parameters is in good agreement with the experimental result, it shows that the prediction result of the model is reasonable.

Phase Composition of Austenitic Stainless Steels in Additive Manufacturing: A Review

Additive manufacturing (AM) is among the novel industrial technologies for fast prototyping of complex parts made from different constructional and functional materials. This review is focused on phase composition of additively manufactured chromium-nickel austenitic stainless steels. Being produced by conventional methods, they typically have single-phase austenitic structure, but phase composition of the steels could vary in AM. Comprehensive analysis of recent studies shows that, depending on AM technique, chemical composition, and AM process parameters, additively manufactured austenitic stainless steels could be characterized by both single-phase austenitic and multiphase structures (austenite, ferrite, σ-phase, and segregations of alloying elements). Presence of ferrite and other phases in AM steels strongly influences their properties, in particular, could increase strength characteristics and decrease ductility and corrosion resistance of the steels. Data in review give a state-of-art in mutual connection of AM method, chemical composition of raw material, and resultant phase composition of AM-fabricated Cr-Ni steels of 300-series. The possible directions for future investigations are discussed as well.

The microstructure, phase composition and tensile properties of austenitic stainless steel in a wire-feed electron beam melting combined with ultrasonic vibration

The growth of coarse columnar grains and dendritic ferrite is a common problem peculiar for Cr–Ni steels produced by electron beam additive manufacturing. For these heterophase additively fabricated steels, the oriented dendritic microstructure in such columnar grains provides the anisotropy of the mechanical properties. Herein, we study the effect of ultrasonic (US) vibrations during wire-feed electron beam additive manufacturing (WEBAM) on microstructure, phase composition and tensile properties of AISI 304L steel. US vibrations during WEBAM processing provide the refinement of the austenitic grains, partially suppress the directional solidification of austenite and reduce δ-ferrite volume fraction (in 1.5–2%). The regular elongated austenitic grains with long and straight dendritic colonies of δ-ferrite are typical of WEBAM-specimens. Austenitic grains are visibly more spherical in WEBAM-US specimens, and their mean grain size (256 ± 17 μm) is smaller than that of WEBAM-fabricated steel (433 ± 145 μm). The δ-ferritic arms are broken and partially dissolved in WEBAM-US specimens and the most pronounced changes are observed in the middle part of the billets. US-assisted grain refinement, partial columnar-to-equiaxed transition and reducing δ-ferrite content – all positively affect the resultant properties of WEBAM-fabricated steel. The results of present study clearly show that application of US during WEBAM is an effective way to obtain a positive influence in additive manufacturing of austenitic Cr–Ni steel.

Effects of rare earth modifying inclusions on the pitting corrosion of 13Cr4Ni martensitic stainless steel

• ASPEX PSEM, SKP, SEM, TEM and electrochemical methods are employed to study corrosion behavior of 13Cr4Ni steel modified with rare earth metals. • Rare earth metals change the composition, size and quantity of inclusions in steel. • The addition of rare earth metals has a significant effect on both metastable and stable pitting processes, the optimum content of rare earth elements (La, Ce) added is 0.021%. • The mechanism of pitting corrosion induced by rare earth inclusions is revealed. In this study, the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel (BASE) and that modified with rare earth (REM) in 0.1 mol/L NaCl solution were characterized. Techniques such as automatic secondary electron microscope (ASPEX PSEM detector), scanning electron microscope (SEM), transmission electron microscope (TEM), scanning Kelvin probe force microscope (SKP), potentiodynamic and potentiostatic polarizations were employed. The results obtained indicate that BASE steel contains Al 2 O 3 /MnS, Al 2 O 3 and MnS inclusions, while REM steels contain (La, Ce, Cr, Fe)-O and (La, Ce, Cr, Fe)-O-S inclusions. Compared with BASE steel, REM steel is more susceptible to induce the metastable pitting nucleation and repassivation, whereas it restrains the transition from metastable pitting to stable pitting. Adding 0.021% rare earth element to BASE steel can reduce the number and area of inclusions, while that of 0.058% can increase the number and enlarged the size of inclusions, which is also the reason that pitting corrosion resistance of 58REM steel is slightly lower than that of 21REM steel. In the process of pitting corrosion induced by Al 2 O 3 /MnS inclusions, MnS is preferentially anodic dissolved, and also the matrix contacted with Al 2 O 3 is subsequently anodic dissolved. For REM steels, anodic dissolution preferentially occurs at the boundary between inclusions and matrix, while (La, Ce, Cr, Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix. The chemically dissolved substance (La 3+ and Ce 3+ ) of (La, Ce, Cr, Fe)-O inclusions are concentrated in pitting pits, which inhibits its continuous growth.

Neural network prediction of slurry erosion of heavy-duty pump impeller/casing materials 18Cr-8Ni, 16Cr-10Ni-2Mo, super duplex 24Cr-6Ni-3Mo-N, and grey cast iron

The aim of the present study is to develop a neural network model for the prediction of slurry erosion (SE) of heavy-duty pump impeller steels and casing material. The heavy-duty pump impeller has a wide range of applications like slurry transportation system and coal conveying system of thermal power stations, and various other industries like mining, chemical and marine industry. In the present study, the slurry erosion performance of three different pump impeller steels namely 18Cr-8Ni, 16Cr-10Ni-2Mo and super duplex 24Cr-6Ni-3Mo-N, and one pump casing material namely Grey cast iron was tested. The SE experiments were carried out on a laboratory scale pot tester using the sand as an erodent. A data set was produced to develop a prediction-based neural network (NN) model and 70% of this data set was used as input to NN model. The learning of NN model was based on an artificial neural network (ANN) and used to build a prediction model that can predict the results while the input data was supplied to it. Firstly, the data were divided into training, validation, and testing. The NN model was trained on 70% of the original dataset and validated by another 15% data. A total of 30 training epochs were performed for training, testing, and validation of the model. The validation of the model indicates that the build NN model was the best fit and comprises no over-fitting and under-fitting issues. In the end, the prepared NN model was given the remaining 15% data for testing. It outputs the corresponding values for each input. These predicted values are then compared with the actual ground truth to check the robustness of the designed model. The various measures used for evaluating the model were R2 (coefficient of determination), Root mean square error, etc. Results show that 18Cr-8Ni steel exhibits the best SE performance followed by 16Cr-10Ni-2Mo, 24Cr-6Ni-3Mo-N, and Grey cast iron.

The Effect of Hydrogen-Charging on Mechanical Properties of Austenitic CrNi Steel Fabricated by Wire-Feed Electron Beam Additive Manufacturing

A comparative study of the mechanical properties, fracture mechanisms and hydrogen embrittlement peculiarities was carried out using the specimens of austenitic CrNi steel produced by two different methods: wire-feed electron beam additive manufacturing and conventional casting followed by solid-solution treatment. Hydrogen-induced reduction of ductility and the increase in the yield strength are observed in steel specimens produced by both methods. Despite hydrogen embrittlement index is comparable in them, the increase in the yield strength after hydrogen-charging is different: 25 MPa for cast steel and 175 MPa for additively manufactured steel. This difference is associated with the peculiarities of phase composition and phase distribution in steels produced by different methods.

Effects of pre-creep on dislocation and tensile property of Cr-Ni steel

Pre-creep experiments were performed on chromium-nickel (Cr-Ni) stainless steel in the early stage of creep. The temperature was held for 500–2000 h under high-temperature load conditions (873 K and 150 MPa), and various analysis methods, including optical microscopy, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and X-ray diffraction, were used to determine the pattern of dislocation evolution under different temperature-holding times. The results showed that the slip bands intersected at the initial stage of pre-creep, and a quadrilateral network structure was formed by the dislocation pinning. As the temperature-holding time increased, the dislocation network began to climb to form dislocation walls, dislocation cells, and other substructures. At 2000 h, the grain boundaries widened considerably; creep holes were found at the grain boundaries; and dislocation pairs with oscillating contrast occurred, which indicates nitrogen diffusion. The yield and tensile strengths of the Cr-Ni steel samples subjected to pre-creep at holding times of above 1000 h decreased after they were subjected to room-temperature tensile tests.

A Study on the Shrink Fit of Cr-Ni Steel Shaft Using SM20C Insert Ring

The torque and shear strength of shaft materials fabricated using Cr-Ni steel, with an SM20C insert ring and SM45C roller ring, were analyzed in the temperature range from 20°C to 400°C. The number of slits in the SM20C insert ring was set to three to maintain appropriate strength and circumvent the effect of the temperature relationship. The life span of this retractor was less than that of a single retractor at high temperatures. In terms of the shear strength and thermal expansion coefficient, the shrinking of the insert ring and roller ring increased the shear strength, while the shear strength of the axial expansion material decreased. The reduction in the life span of the shrinking bonding material of the SM45C roller ring and SM20C insert ring is due to plastic deformation resulting from the extension of the outer ring during heating.

A Numerical and Experimental Study on the Solidification Structure of Fe–Cr–Ni Steel Slab Casting by Roller Electromagnetic Stirring

We present a segmented coupling model for slab casting by roller electromagnetic stirring (R-EMS) of electromagnetic, flow, heat transfer, and solidification behavior based on magnetohydrodynamics and solidification theory. A three-dimensional (3-D) segmented coupling model that included electromagnetic, flow, and heat transfer elements was established using Ansoft Maxwell and ANSYS Fluent software. The effects of the roller sleeve, magnetic shielding ring, coil, core, molten steel, and air domain on the electromagnetic, thermal and flow fields were studied numerically. The accuracy of the model was verified by measuring the magnetic flux density at the centerline in a pair of rollers and the electromagnetic force of the copper plate. Based on the numerical results of the optimal technical parameters, the effect of the R-EMS on the solidification of Fe–17 wt% Cr–0.6 wt% Ni stainless steel was explored. The results indicated that with each additional pair of electromagnetic rollers, the average electromagnetic force increased by 2969 N/m3 in the casting direction, and 5600 N/m3 in the central section of the rollers. With increasing number of pairs of rollers, the effective stirring region increased, and the velocity of molten steel at the solidification front first increased but then decreased. The strong electromagnetic swirling washing effect reduced the solidification rate of the slab shell and promoted the superheated dissipation of molten steel in the center of the strand. The center equiaxed crystal ratio of the slab was improved to 69% with two pairs of R-EMS rollers and electromagnetic parameters of 400 A/7 Hz, which was beneficial for obtaining a uniform and dense solidified structure to improve the subsequent hot working performance and product quality.

Changes of cytotoxicity of Ti-6Al-4V alloy made by DMLS technology as effect of the shot peening.

The aim the study was to investigate the impact of the shot peening process on the condition of the surface layer and biological properties of titanium alloy produced by means of the Direct Metal Laser Sintering (DMLS) method. Specimens were prepared by the EOSINT M280 metal sintering laser system. The surfaces were subjected to the shot peening process using three different media, i.e. steel shot, nutshell granules and ceramic beads, after which they were subjected to profilometric analysis, scanning electron microscopic (SEM) observations and energy dispersive X-ray spectroscopy (EDS) tests, as well as to assessment of biological compatibility in terms of cytotoxicity (SH-SY5Y cell lines). The general results obtained from the tests indicate satisfactory biocompatibility of the examined surfaces and that the impact of the shot peening process on the titanium alloy cytotoxicity is acceptable. The lowest cytotoxicity was demonstrated by the surfaces modified by ceramic beads than the nutshells and the biggest steel shot correspondingly. Moreover, the shot peening process carried out by means of CrNi steel and ceramic shot caused the reduction of surface roughness when, for the surface processing by means of nutshell granules, the increase of surface roughness was observed compared with the unmodified surface of titanium alloy samples.

Optimization of Model and Structural Analysis Hypoid Gear

The purpose of this work is to analyze structural behaviour of differential hypoid gear. For the studying of the structural analysis of the gear is made up of the different composite materials & as well as alloy materials compared with conventional metallic materials. As, composite materials provide enough strength and emerged as a good alternative for replacing metallic gears which is Ni-Cr steel. The alloy materials considered here is Aluminium alloy, Grey cast iron, and the composite material is Epoxy E-Glass unidirectional and compare with existing gear material Ni-Cr steel. This work makes an attempt to replace the metallic gears of Ni-Cr steel with alloy & composite materials based on static structural analysis results. For the analysis purpose the solid model is created by using CATIAV5R20 design software and ANSYS 17.1 is used to determine the Total deformation, Von-Mises stress and the equivalent elastic strain for the different selected materials at three different speeds.

Corrosion Resistance Properties of a Nickel–Chromium Steel Bar in Marine Atmosphere

The corrosion behaviors of Ni–Cr and 20MnSi steel bars in a simulated marine atmosphere are compared using alternate immersion corrosion tests and electrochemical techniques. The microstructure features are characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical measurements and alternate immersion corrosion tests demonstrate that the Ni–Cr steel bar has a more positive potential (– 0.397 V), lower corrosion current density (28.19 μA/cm2), and better corrosion resistance at a corrosion rate of 3.81 g/(m2· h) and corrosion depth of 4.27 mm/g. There are inner and outer rust layers on the Ni–Cr steel bar, the inner layer being dense and bonded to the steel substrate. The α -FeO(OH)/γ -FeO(OH) ratio of the rust layer on the Ni–Cr steel bar is greater, which contributes to a more denser rust layer enhancing corrosion resistance.