Nickel-free Austenitic Stainless Steel Research Articles

Achieving Homogeneous Microstructure and Superior Properties in High-N Austenitic Stainless Steel via a Novel Atmosphere-Switching Method

Powder metallurgy is widely used to fabricate high-nitrogen, nickel-free austenitic stainless steel. However, after sintering and nitriding, additional solution treatment is typically required to achieve uniform nitrogen distribution and a homogeneous austenite phase. This work proposes a novel method to eliminate the need for lengthy and high-temperature solution treatment by switching the nitrogen atmosphere to argon during the cooling process. The effects of different N2-Ar atmosphere-switching temperatures (750–1320 °C) on the phase composition, element distribution, microstructure, mechanical properties, and corrosion resistance of the studied steels were systematically investigated. Results show that cooling in the N2 atmosphere initially transforms the matrix to a fully austenitic structure enriched with nitrogen. Excessive nitrogen infiltration leads to Cr2N precipitation, inducing partial austenite decomposition and forming a multiphase structure comprising austenite, α-Fe, and Cr2N. Strategic switching from N2 to Ar reverses this reaction, yielding a high-nitrogen, chemically uniform austenitic structure. Specifically, switching at 1150 °C, the steel exhibits excellent mechanical properties and corrosion resistance, with a yield strength of 749 MPa, an ultimate tensile strength of 1030 MPa, an elongation of 38.7%, and a corrosion current of 0.06 mA/cm2, outperforming the steels cooled solely in N2 and subsequently solution-treated. This novel method offers advantages in cost reduction, energy saving, and operational effectiveness, highlighting its potential for broad industrial application.

Influence of Thermal Aging Treatments on Intergranular Corrosion and Cyclic Oxidation Behavior of Low Nickel and Nickel-Free Austenitic Stainless Steels

Influence of Thermal Aging Treatments on Intergranular Corrosion and Cyclic Oxidation Behavior of Low Nickel and Nickel-Free Austenitic Stainless Steels

Bioactivity, Cytotoxicity, and Tribological Studies of Nickel-Free Austenitic Stainless Steel Obtained via Powder Metallurgy Route.

In the present study, the bioactivity, cytotoxicity, and tribological properties of a nickel-free austenitic stainless steel produced via the mechanical alloying of elemental iron, chromium, and manganese nitride powders following by hot isostatic pressing was investigated. Powders after 90 h of mechanical alloying were consolidated via hot isostatic pressing at 1150 °C (1425 K) and heat treated at 1175 °C (1448 K) for 1 h in a vacuum with furnace cooling. Tribological tests were performed to determine the resistance of the as-received nickel-free steel. It was noticed that applying heat treatment after hot isostatic pressing decreases the average friction coefficient and wear rate of the austenitic steel. An immersion test in a simulated body fluid for 28 days at 37 ± 1 °C has been used to determine the biocompatibility of the tested material. The SEM-EDS analysis allowed us to characterise the morphology of the films and the elements of the steel on the thin-film layer. Elements typical of apatite (calcium and phosphorus) were detected on the surface of the sample. Cellular toxicity tests showed no significant toxic side effects for Saos-2 human osteosarcoma cells and the number of Saos-2 human osteosarcoma cells on the nickel-free steel was greater than on the 316LV grade steel.

Experimental Investigations of Nano Finishing Process on Nickel-Free Austenitic Stainless Steel by Grey Relational and Principal Component Analysis

The nano surface roughness of metallic materials is important in engineering and medical fields for specific applications. Magneto rheological abrasive flow finishing (MRAFF) process was performed on nickel-free austenitic stainless workpieces in order to obtain surface roughness at the nano level and also to forecast the performance of the MRAFF process in terms of responses such as surface roughness (SR) and material removal rate (MRR). These two responses are affected by process factors such as hydraulic pressure, current to the electromagnet, and the number of cycles performed during the machining process. The design of experiments (DOE) was used to determine the contributions of process parameters to output responses. The techniques of grey relational analysis (GRA) and principal component analysis (PCA) were used in these experimental investigations to discover the process factors that minimise the final Ra and maximise MRR. Through the DOE, a minimum SR of 63.24 nm and a maximum MRR of 2.34 mg/sec were obtained on the samples for the combination of 30 bar pressure, 6 A current, and 300 number of cycles.

Microstructure, mechanical and magnetic properties of a nickel-free austenitic stainless steel fabricated by hot powder forging

Nickel-free high nitrogen austenitic stainless steel, with a composition according to ASTM F 2581, was produced by hot powder forging (HPF). To improve the sintering behavior and increase the density of this alloy, a biocompatible additive of Mn-11.5 wt% Si at 3, and 6 wt% was added to the alloying powder, and the effect of the additives on the physical and mechanical properties of the alloy was investigated. The structure of the specimens was examined by X-ray diffraction (XRD), metallography, optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy(TEM), selected area diffraction (SAD) and magnetometer. The densities of the samples were analyzed by the Archimedes and image analysis methods and the mechanical properties of the samples were determined by microhardness, hardness, compression and tensile tests. The XRD results demonstrate that the forged samples contain austenitic nanocrystalline and amorphous phases with no ferrite and martensitic phases in the structure. Densitometry proves that the sample with a 6 wt% additive consolidated to near 96% theoretical density. Hardness, microhardness, tensile and compression tests show that this alloy composition also has better mechanical properties than alloys containing 0 and 3 wt% additive. The results show that stainless steel 316L and forged nickel-free high nitrogen austenitic stainless steel behave similarly to soft magnetic materials, although the magnetic saturation of nickel-free steel is lower than that of 316L steel. This study proves that the alloy made by HPF has significantly better mechanical properties than conventional commercial 316L. The effect of the additive on the microstructure and other features is discussed in detail.

Sintering optimization of high nitrogen nickel free austenitic stainless steel prepared by Metal Injection Molding

High nitrogen and nickel free austenitic (HNNFA) stainless steel prepared by powder metallurgy has become a research hotspot because of solving nickel precipitation and saving cost. In this paper, metal injection molding (MIM)method was used to prepare such kinds of steel. The effect of sintering parameters such as sintering temperature, holding time, and nitriding pressure on the density, shrinkage rate, and nitrogen content of austenitic stainless steel was systematically evaluated by an orthogonal experiment to obtain the optimum sintering parameters. When the sintering temperature is 1200°C, the holding time is 6 h, and the nitriding pressure is 1100 mbar, the sample possesses a higher density (7.52g/cm3) and nitrogen content (0.76%). The matrix of stainless steel is austenite after nitriding sintering.

Effects of Nitrogen Content and Strain Rate on the Tensile Behavior of High-Nitrogen and Nickel-Free Austenitic Stainless Steel

The uniaxial tensile behaviors of Fe-19Cr-16Mn-2Mo-0.49N and Fe-18Cr-16Mn-2Mo-0.85N high-nitrogen and nickel-free austenitic stainless steels at two strain rates of 10−2 s−1 and 10−4 s−1 were comparatively investigated. The related deformation microstructure was characterized and fracture mechanism was analyzed. The results show that the nitrogen content and strain rate both have significant effects on the tensile properties of the tested steels. As the strain rate is the same, the tested steel containing a higher nitrogen content has higher Rm and Rp0.2. However, Rm is higher at a lower strain rate and Rp0.2 is higher at a higher strain rate in the case of the same nitrogen content. The tested steel with a lower nitrogen content (0.49 wt.%N) tensioned at a lower strain rate of 10−4 s−1 obtains the highest elongation, while the tested steel with a higher nitrogen content (0.85 wt.%N) tensioned at a higher strain rate of 10−2 s−1 has the lowest elongation. The tensile plastic deformation is mainly governed by slip and twinning, affected jointly by stacking fault energy and short-range order. Dislocation slip featured by planar slip bands and twin-like bands is the main deformation structure in the tested steel containing a higher nitrogen content (0.85 wt.%N) tensioned at a lower strain rate of 10−4 s−1, whereas twinning deformation becomes more prominent with decreasing nitrogen content and increasing strain rate.

Nickel-free austenitic stainless steel alloys as a sodium-cooled fast reactor fuel cladding

ABSTRACT Nickel-free austenitic stainless steel alloys Fe-Cr-Mn (SSMn) and Fe-Cr-Mn-N (SSMnN) were successfully developed to be used as sodium-cooled fast reactor fuel cladding. An austenite phase was observed through microstructure examination for both SSMn and SSMnN. The effect of Mn and Mn-N as an alternative to Ni on tensile properties was studied at room temperature. Subsequently, the effect of temperature was studied through tensile testing of the alloys produced at 300 ºC and 500 ºC. Mn and Mn-N enhance the room temperature yield strength (YS) and ultimate tensile strength (UTS). Mn caused a small reduction in elongation (El%) but Mn-N caused its deterioration. The YS, UTS, and El% of both SSMn and SSMnN alloys are strongly temperature dependent. Both the SSMn and SSMnN alloys showed better mechanical properties than the standard AISI304 at elevated temperatures. So, the SSMn and SSMnN alloys could be considered strong candidates as fuel cladding for sodium-cooled fast reactors.

Correlative Analysis of Morphology–Mechanical–Corrosion Behavior of Conventional Nickel-Based and Nitrogen-Alloyed Nickel-Free Austenitic Stainless Steels

Correlative Analysis of Morphology–Mechanical–Corrosion Behavior of Conventional Nickel-Based and Nitrogen-Alloyed Nickel-Free Austenitic Stainless Steels

Wear and Electrochemical Behavior of High-Nitrogen, Nickel-Free Austenitic Stainless Steel Produced by Hot Powder Forging

Wear and Electrochemical Behavior of High-Nitrogen, Nickel-Free Austenitic Stainless Steel Produced by Hot Powder Forging

Surface Modification of a Nickel-Free Austenitic Stainless Steel by Low-Temperature Nitriding

Low-temperature nitriding allows to improve surface hardening of austenitic stainless steels, maintaining or even increasing their corrosion resistance. The treatment conditions to be used in order to avoid the precipitation of large amounts of nitrides are strictly related to alloy composition. When nickel is substituted by manganese as an austenite forming element, the production of nitride-free modified surface layers becomes a challenge, since manganese is a nitride forming element while nickel is not. In this study, the effects of nitriding conditions on the characteristics of the modified surface layers obtained on an austenitic stainless steel having a high manganese content and a negligible nickel one, a so-called nickel-free austenitic stainless steel, were investigated. Microstructure, phase composition, surface microhardness, and corrosion behavior in 5% NaCl were evaluated. The obtained results suggest that the precipitation of a large volume fraction of nitrides can be avoided using treatment temperatures lower than those usually employed for nickel-containing austenitic stainless steels. Nitriding at 360 and 380 °C for duration up to 5 h allows to produce modified surface layers, consisting mainly of the so-called expanded austenite or γN, which increase surface hardness in comparison with the untreated steel. Using selected conditions, corrosion resistance can also be significantly improved.

Effect of recrystallization on degree of sensitization in nickel free austenitic stainless steel

PurposeEffect of grain size on degree of sensitization (DOS) was been evaluated in Nickel free steel. Manganese and nitrogen contained alloy is a Ni-free austenitic stainless steels (ASS) having type 202 grade. The main purpose of this investigation is to find the effect of recrystallization on the DOS of stainless steel after the thermo-mechanical processing (cold work and thermal aging).Design/methodology/approachIn the present investigation, the deformation of 202 grade analyzed using X-ray diffraction (XRD) and microstructural testing. Optical microstructure of Ni-free ASS has been done for cold worked samples with thermally aged at 900°C_6 h. Double loop electrochemical potentiodynamic reactivation test used for findings of degree of sensitization.FindingsNi-free ASS appears to be deformed more rapidly due to its higher stacking fault energy which gave results in rapid transformation from strain induced martensite to austenite in form of recrystallized grains, i.e. it concluded that as cold work percentage increases more rapidly recrystallization occurs. XRD results also indicate that more fraction of martensite formed as percentage of CW increases but as thermal aging reverted those all martensite to austenite. So investigation gives the conclusion which suggests that with high deformation at higher temperature and duration gives very less DOS.Originality/valueVarious literatures available for 300 series steel related to the effect of cold work on mechanical properties and sensitization mechanism. However, no one has investigated the effect of recrystallization through thermomechanical processing on the sensitization of nickel-free steel.

Corrosion behavior of high nitrogen nickel-free austenitic stainless steel in the presence of artificial saliva and Streptococcus mutans

High nitrogen nickel-free austenitic stainless steels (HNSs) have great potentials to be used in dentistry owing to its exceptional mechanical properties, high corrosion resistance, and biocompatibility. In this study, HNSs with nitrogen of 0.88 wt% and 1.08 wt% displayed much lower maximum pit depths than 316L stainless steel (SS) after 21 d of immersion in abiotic artificial saliva (2.2 μm and 1.7 μm vs. 4.5 μm). Microbiologically influenced corrosion (MIC) evaluations revealed that Streptococcus mutans biofilms led to much severer corrosion of 316L SS than HNSs. Corrosion current densities of HNSs were two orders of magnitude lower than that of 316L SS after incubation of 7 d (37.5 nA/cm2 and 29.9 nA/cm2 vs. 5.63 μA/cm2). The pitting potentials of HNSs were at least 550 mV higher than that of 316L SS in the presence of S. mutans, confirming the better MIC resistance of HNSs. Cytotoxicity assay confirmed that HNSs were not toxic to MC3T3-E1 cells and allowed better sessile cell growth on them than on 316L SS. It can be concluded that HNSs are more suitable dental materials than the conventional 316L SS.

Electrochemical Behavior and Passive Film Composition of a High-Nitrogen Nickel-Free Austenitic Stainless Steel

Electrochemical Behavior and Passive Film Composition of a High-Nitrogen Nickel-Free Austenitic Stainless Steel

Inhibition of Nitride Precipitation in a Fe-Cr-Mn-Mo-N High-Nitrogen Austenitic Stainless Steel through Grain Boundary Character Distribution Optimization

The precipitation behavior of the second phase in Fe-18Cr-17Mn-2Mo-0.85N high nitrogen and nickel-free austenitic stainless steel after grain boundary character distribution (GBCD) optimization was investigated. The results show that the fraction of low Σ coincidence site lattice (CSL) boundaries increases from 47.9% for the solid solution treated specimen to 82.25% for the specimen cold-rolled by 5% and then annealed at 1423 K for 72 h (r5%-a1423 K/72 h). Compared with the solution treated sample, nitride precipitation is obviously restrained and the fraction of precipitates is the least in r5%-a1423 K/72 h sample with the highest proportion of SBs. The appearance of a high proportion of CSL boundaries with low energy inhibits the nitrides precipitation through GBCD optimization.

Hydroxyapatite/titania nanocomposite coating on nickel-free austenitic stainless steel

In this research, a series of biocompatible coatings are applied to nickel-free austenitic stainless steel via the electrophoretic method. Hydroxyapatite (nHA) and titania (nTiO2) nanoparticles are utilized as primary materials, while polycaprolactone (PCL) is employed as a binder for production of the electrolyte suspensions. Optimum concentration of binder is achieved and suspensions with different amounts of nHA-nTiO2 are fabricated and investigated. The suspensions are characterized by particle size distribution, zeta potential, and viscometer measurements. The results show that PCL is protonated via an electrostatic stabilization mechanism absorbed on the nHA-nTiO2 surface, which stabilizes the suspension. Microstructural of coated layers is characterized using x-ray diffraction (XRD), optical microscopy, and scanning electronic microscopy. Mechanical properties of the coating are measured by microhardness, thickness measurements, pin-on-disk sliding, and pull-off adhesion tests. Moreover, the electrochemical behavior of the coated layers is investigated via Tafel polarization tests in simulated body fluid (SBF). It is found that the coated layer containing PCL (2 g/l) has the highest adhesion strength and a smoother surface with minimal or no cracks or pores. Mechanical characterization indicated that the hardness and wear resistance of the coating can improve by increasing the TiO2 concentration, while increased TiO2 enhances the electrochemical behavior of the coating too.

Application of Grain Boundary Engineering to Improve Intergranular Corrosion Resistance in a Fe–Cr–Mn–Mo–N High-Nitrogen and Nickel-Free Austenitic Stainless Steel

Optimization of grain boundary engineering (GBE) process is explored in a Fe–20Cr–19Mn–2Mo–0.82 N high-nitrogen and nickel-free austenitic stainless steel, and its intergranular corrosion (IGC) property after GBE treatment is experimentally evaluated. The proportion of low Σ coincidence site lattice (CSL) boundaries reaches 79.4% in the sample processed with 5% cold rolling and annealing at 1423 K for 72 h; there is an increase of 32.1% compared with the solution-treated sample. After grain boundary character distribution optimization, IGC performance is noticeably improved. Only Σ3 boundaries in the special boundaries are resistant to IGC under the experimental condition. The size of grain cluster enlarges with increasing fraction of low ΣCSL boundaries, and the amount of Σ3 boundaries interrupting the random boundary network increases during growth of the clusters, which is the essential reason for the improvement of IGC resistance.

Microstructure, Mechanical, and Corrosion Properties of Ni-Free Austenitic Stainless Steel Prepared by Mechanical Alloying and HIPping.

An influence of the powder metallurgy route on the phase structure, mechanical properties, and corrosion resistance of Fe–18%Cr–12%Mn–N nickel-free austenitic stainless steel as a potential material for medical applications were studied. The powder was mechanically alloyed in a high purity nitrogen atmosphere for 90 h followed by Hot Isostatic Pressing at 1150 °C (1423 K) and heat treatment at 1175 °C (1423 K) for 1 h in a vacuum with furnace cooling and water quenching. More than 96% of theoretical density was obtained for the samples after Hot Isostatic Pressing that had a direct influence on the tensile strength of the tested samples (Ultimate Tensile Strength is 935 MPa) with the total elongation of 0.5%. Heat treatment did not affect the tensile strength of the tested material, however, an elongation was improved by up to 3.5%. Corrosion properties of the tested austenitic stainless steel in various stages of the manufacturing process were evaluated applying the anodic polarization measurements and compared with the austenitic 316LV stainless steel. In general, the heat treatment applied after Hot Isostatic Pressing improved the corrosion resistance. The Hot Isostatic Pressing sample shows dissolution, while heat treatment causes a passivity range, the noblest corrosion potential, and lower current density of this sample.

Nanoindentation creep deformation behaviour of high nitrogen nickel-free austenitic stainless steel

ABSTRACTNanoindentation tests of the high nitrogen nickel-free austenitic stainless steel (HNS) were performed with peak load in a wide range of 100–600 mN to investigate the nanoindentation creep deformation behaviours. The results of the nanoindentation creep tests have demonstrated that the load plateaus, creep strain rate and creep stress of the cold-rolled HNS are larger and its creep stress exponent is smaller than the solution-treated HNS. The analysis reveals that the obvious creep deformation behaviour in the cold-rolled HNS arises from the rapidly relaxed dislocation structures in the initial transition regime, while the small creep deformation behaviour of the solution-treatedHNS is mainly attributed to that the stable dislocation structures for the intensive interactions between dislocations.

Experimental Investigation of the PMEDM of Nickel Free Austenitic Stainless Steel: A Promising Coronary Stent Material

A new composition of Taguchi and the technique for order preference by similarity to ideal solution (TOPSIS) in combination with principal component analysis (PCA) has been explored. A series of experiments were performed in order to acquire an optimal parametric combination during powder mixed electro-discharge machining (PMEDM) of nickel free austenitic stainless steel. Peak current, pulse on time and powder concentration were selected as three process variables, whereas the material removal rate (MRR), tool wear rate (TWR) and over cut (OC) were the major attention. Domain of the investigation was adopted from Taguchi based L16 orthogonal array. The outcomes of the experiment were optimized using TOPSIS method whereas PCA technique was employed to determine the weightage of each response. Response table for S/N ratio was drawn to identify the most influencing machining parameter. Results of the investigation indicated that, peak current was the most effective machining variable followed by pulse on time and powder concentration. The proposed amalgamation of PCA-TOPSIS method was observed to be robust, easily understandable, time saving and modest approach which can help the decision maker to identify an optimal parametric combination with desirable accuracy.