High Nitrogen Austenitic Steel Research Articles

Calculations of phase composition of austenitic high-nitrogen welding wire and study of a welded joint made from it

The processability of a material is directly related to the possibility of its production, operation and maintainability. One of the most important indicators of the processability of any metal is weldability. Austenitic steels with a high nitrogen content proved themselves as high-strength, corrosion- and cold-resistant materials, but the issue of their weldability is still not fully understood. The lack of welding filler materials on the market specifically designed for welding high-nitrogen steels is the primary obstacle to solving this problem. Thus, the goal of the work was to develop and obtain a laboratory sample of high-nitrogen welding wire. Based on calculations of nitrogen solubility and the phase composition of the weld metal, the chemical composition of Cr – Mn – Ni – Mo – V, N steel was selected for this wire. A defect-free ingot with 0.57 % N was obtained, and wire with a nitrogen content of 0.57 wt. % was produced using hot plastic deformation and drawing methods. Testing of this wire to obtain a welded joint of austenitic cast steel, close to it in chemical composition, with the welding process carried out according to the developed technological recommendations, made it possible to obtain a defect-free welded joint without loss of nitrogen in the weld metal. With a microhardness of the base metal of 252 HV50 , due to the alloying of the welding wire steel with nitrogen and vanadium, the metal of the weld and fusion line had a high microhardness (278 and 273 HV50 , respectively), significantly exceeding the microhardness of Cr – Ni cast austenite. The metal of the welded joint has high strength (0.9 of the base metal strength) and high impact toughness. The fracture of impact samples is characterized by a dimple structure characteristic of viscous materials. According to the obtained results, the new welding wire showed itself to be a promising material for welding austenitic high-nitrogen steels.

Isothermal aging treatment and its effect on the mechanical properties of Fe-Cr-Mn high-nitrogen austenitic steel

The high-temperature solution nitriding process is a suitable treatment for producing high-nitrogen steels by the diffusion of nitrogen from the surface to the center of steels under high nitrogen pressure at high temperatures. On the other hand, long-term solution nitriding at high temperatures can cause the formation of coarse-grained austenite. This study focused on the grain size, strength, and elongation properties of Fe-Cr-Mn high-nitrogen austenitic steels by isothermal aging. For this purpose, we produced high-nitrogen steels by three-step phase transformations: (i) high-temperature solution nitriding, (ii) isothermal aging, and (iii) reaustenitization. After solution nitriding, high-nitrogen austenitic steel was treated with isothermal aging to induce austenite decomposition. Supersaturated austenite (ϒ) transformed to less nitrogen-saturated austenite (ϒ′) and discontinuous cellular precipitation (DCP) during the isothermal aging treatment. Subsequently, the decomposed structure was reversed into austenite through reaustenitization. The results suggested that austenite grain refinement and increasing hardness were achieved by nucleating reversed austenite grains after reaustenitization treatment. On the other hand, a noticeable increase in elongation appeared after reaustenitization treatment for 30 min.

Performance of Austenitic High-Nitrogen Steels under Gross Slip Fretting Corrosion in Bovine Serum.

Modular artificial hip joints are a clinical standard today. However, the release of wear products from the head-taper interface, which includes wear particles in the nm size range, as well as metal ions, have raised concerns. Depending on the loading of such taper joints, a wide variety of different mechanisms have been found by retrieval analyses. From these, this paper concentrates on analyzing the contribution of gross slip fretting corrosion at ultra-mild wear rates using a bovine calf serum solution (BCS) as the lubricant. The parameters were chosen based on biomechanical considerations, producing wear rates of some ng/m wear path. In parallel, the evolution of tribomaterial (third bodies) was analyzed as to its constituents and generation rates. It has already been shown earlier that, by an advantageous combination of wear mechanisms and submechanisms, certain constituents of the tribomaterial remain inside the contact area and act like extreme-pressure lubricant additives. For the known wear and corrosion resistance of austenitic high-nitrogen steels (AHNSs), which outperform CoCrMo alloys even under inflammatory conditions, we hypothesized that such steels will generate ultra-mild wear rates under gross slip fretting. While testing AHNSs against commercially available biomedical-grade materials of CoCrMo and TiAlV alloys, as well as zirconia-toughened alumina (ZTA) and against itself, it was found that AHNSs in combination with a Ti6Al4V alloy generated the smallest wear rate under gross slip fretting corrosion. This paper then discusses the wear behavior on the basis of ex situ analyses of the worn surfaces as to the acting wear mechanisms and submechanisms, as well as to the tribological reaction products.

Effects of Annealing Temperature on Microstructural Evolution and Mechanical Properties in Cold-Rolled High-Nitrogen Austenitic Steel

High-nitrogen austenitic steel (HNS) cold-rolled with a reduction rate of 25% was subjected to an investigation of the effect of annealing temperature on microstructural evolution, tensile properties and the variation in fracture surface morphology. In cold-rolled HNS, matrix recovery occurred at an annealing temperature of 600 °C, and recrystallization was locally initiated at an annealing temperature of 800 °C. The 0.2% offset yield strength (0.2% YS) and ultimate tensile strength (UTS) were almost constant up to an annealing temperature of 500 °C, and these values gradually decreased above the annealing temperature of 600 °C, while a sharp reduction in the percentage reduction in area (RA) occurred at the annealing temperatures of 600 and 700 °C due to Cr2N precipitation along the grain and twin boundaries. The ratio of 0.2% offset yield strength to ultimate tensile strength (0.2% YS/UTS) remained constant until matrix recovery took place; however, once recrystallization occurred, the ratio decreased significantly. Furthermore, the variation in the morphology of Cr2N along the grain boundaries in the annealing temperature range from 600 to 800 °C influenced the intergranular fracture morphology, resulting in a transition from dimple to ledge and back to dimple.

Additive manufacturing of high nitrogen austenitic steel using shell-core strategy

Laser Powder Bed Fusion/Metal (PBF-LB/M) is a promising technology for industrial applications, but challenges such as long process times remain. Innovations such as the shell-core approach aim to address this by creating a dense shell around a minimally exposed powder core, significantly reducing processing times, with full densification and property adjustments achieved by subsequent hot isostatic pressing (HIP). This study focuses on the fabrication of shell-core samples using a powder mixture of austenitic steel and Si3N4 to produce high nitrogen steel PBF-LB/M components, which are otherwise difficult to produce due to the limited nitrogen solubility in the melt. PBF-LB/M induces Si3N4 decomposition, resulting in Si and N loss through laser-powder interaction. Si3N4 particles in the still powdered regions serve as a source of N enrichment during HIP, circumventing the limitations of nitrogen solubility in the melt and exploiting the higher solubility in the solid. After HIP, energy dispersive spectrometry and electron backscatter diffraction reveal a fully austenitic matrix with Si diffusion seams mainly in non-laser-exposed areas. The Si3N4 dissolution during HIP contributes to an interstitial dissolved N content of about 0.189 mass%, which, together with the higher Si content, increases hardness. Wavelength dispersive spectrometry (WDS) and nanoindentation line scans show decreasing Si and N concentrations from core to shell, resulting in reduced (nano)hardness in the shell. This innovative approach demonstrates the potential to produce AM components with enhanced properties by overcoming the limitations of nitrogen solubility in the steel melt during PBF-LB/M.

Welding of High-Nitrogen Austenitic Steels (Review)

Welding of High-Nitrogen Austenitic Steels (Review)

STRUCTURAL CHANGES OF SURFACE LAYERS DURING WEAR TESTING OF HIGH-STRENGTH AUSTENITIC STEEL VNS-53

Tribotechnical characteristics of high nitrogen austenitic steel VNS-53 under conditions of dry sliding friction in contact with steel ShH15-ShD have been studied. It was found that in a thin surface layer the work hardening occurs without martensitic transformation, as a result the hardness increases by more than 90 %. It is established that this steel has a lower coefficient of friction and a greater increase in hardness in the contact zone of the surfaces compared to the steel 08H18N10T

Effect of Warm Multidirectional Forging on the Microstructure and Mechanical Properties of a High-Nitrogen Austenitic Steel

Effect of Warm Multidirectional Forging on the Microstructure and Mechanical Properties of a High-Nitrogen Austenitic Steel

First-principles study of the effect of N on the ∑5 (210) [001] grain boundary of γ-Fe

High-nitrogen austenitic steels possess excellent properties owing to the solid solution strengthening of nitrogen, which is widely used in many fields. So it’s significant to investigate the effect of nitrogen on the properties of high austenitic nitrogen steels. In order to get atomic scale understanding of the influence of nitrogen, the first principles method was used to investigate the energetics, site preference, and segregation of nitrogen at γ-Fe ∑5 (210) [001] grain boundary (GB) and different atomic layers near GB plane. It is found that the nitrogen atom prefers to occupy the octahedral site. As nitrogen locates at different atomic layers away from the GB plane, the segregation energy presents increase first and then decrease. The mechanical properties were analyzed by Rice-Wang theory and theoretical tensile stress test, which shows that nitrogen at ∑5 (210) [001] GB has an embrittling effect on GB cohesion, while nitrogen located away from the GB plane presents a strengthening effect. The underlying mechanism was analyzed by bond length, charge density, and density of states (DOS). The segregation of nitrogen at ∑5(210) [001] grain boundary has negative effect on grain boundary cohesion, while nitrogen locating away from grain boundary plane presents strengthening effect on grain boundary.

Surface Hardening of High-Nitrogen Austenitic Steel by Severe Deformation–Heat Treatment

Surface Hardening of High-Nitrogen Austenitic Steel by Severe Deformation–Heat Treatment

Structure and Properties of the Welded Joints of Rolled Austenitic High-Nitrogen Steel Fabricated by Manual Consumable-Electrode Arc Welding

Structure and Properties of the Welded Joints of Rolled Austenitic High-Nitrogen Steel Fabricated by Manual Consumable-Electrode Arc Welding

Precipitation behavior of M23C6 in high nitrogen austenitic heat-resistant steel

The precipitation behavior of M23C6 carbides in LF25 high nitrogen austenitic heat-resistant steel was investigated from 700 °C to 850 °C. The results demonstrated that the precipitates in LF25 steel included Nb (C, N) and M23C6 during the aging treatment. M23C6 carbides with four morphologies formed during aging followed a sequence of intergranular precipitates, parallel plate-like precipitates, cellular precipitates, and intragranular precipitates with increasing aging temperature. The four types of morphologies of M23C6 retained a cube-on-cube crystallographic relation with the matrix. Firstly, the M23C6 precipitated as discontinuous particles along the grain boundaries due to the faster diffusion rate of the elements. With the aging temperature increasing, intergranular M23C6 grew and connected to form a film-like morphology. The partial dislocations slipped out from the non-coherent twin boundaries due to the stresses resulting from quenching and elastic modulus together with atomic volume difference between the M23C6 and austenite matrix. M23C6 nucleated at the slipped dislocations and grew along the (111) or (110) planes to form a parallel plate-like morphology. Cellular precipitates were precipitated from supersaturated austenite matrix and then formed an alternating morphology of lamellae M23C6 and austenite during the discontinuous precipitation reaction. Due to high resistance to intracrystalline growth, the intragranular precipitates were short rods or granules with small sizes.

ВЛИЯНИЕ СТАРЕНИЯ НА ФАЗОВЫЙ СОСТАВ И МЕХАНИЧЕСКИЕ СВОЙСТВА ВАНАДИЙСОДЕРЖАЩЕЙ ВЫСОКОАЗОТИСТОЙ СТАЛИ

Complex solid solution hardening of austenitic chrome-manganese steels by nitrogen and carbon is one of the most effective ways of production of high-nitrogen austenitic steels (HNS) without using special casting methods. To enhance the solubility of interstitials in the metal liquid state and suppress undesired secondary phases of Cr2N and Cr23C6, the carbide-forming elements (for instance, vanadium) are added to the HNS composition. By now, there are no experimental works on the age-hardening of ultrahigh-interstitial vanadium steels (more than 1 % wt.). In the present work, the authors used the X-ray structure analysis method, electron microscopy, and the uniaxial static tensile tests to study the effect of temperature (600 °С and 700 °С) and duration (0.5 h, 5 h) of age-hardening on the structure and mechanical properties of ultrahigh-interstitial vanadium-containing Cr–Mn steel (Fe–22Cr–26Mn–1.3V–0.7C–1.2N, N+C=1.9 % wt.). The experiments demonstrated that due to the complex decomposition (by intermittent and continuous mechanisms) of austenite saturated by interstitials, the aging at 600 °С and 700 °С is accompanied by a solid-solution hardening of the austenitic phase by carbonitrides Cr2(N, С) and (V,Cr)(N,С). The study identified that the increased temperature and prolongation of age-hardening stimulate the movement of intermittent decomposition front from the boundaries to the center of austenitic grains. (V,Cr)(N,С) particles formed by the continuous decomposition in the austenitic grains hinder the propagation of the reaction front, meanwhile, the large spherical (V,Cr)(N,C) and Cr2(N,C) particles, not dissolved after quenching, have little effect on its movement. At the chosen age-hardening modes, the yield strength of steel increases, and the fracture elongation decreases.

Effect of ultrasonic forging strain processing on the surface layer microstructure and temperature-dependent mechanical properties of high nitrogen austenitic steel

The paper presents the research results on the effect of ultrasonic forging strain (UFS) processing of the high-nitrogen Cr–Mn–N austenitic stainless steel on the surface layer microstructure and tensile properties in the temperature range from −80 up to 20 °C. The high dispersion microstructure, strain aging with the formation of both CrN and Fe2N nitrides, as well as twinning were revealed in the surface layer 2–3 μm thick using a transmission electron microscope (TEM). In addition, ε-martensite with the hcp lattice was observed at a depth of more than 80 μm from the surface after UFS processing. Tensile tests showed that UFS processing had increased the yield strength. Elongation level of about 40% did not differ over the entire test temperature range. A ductile type of the fracture surfaces was observed for all test temperatures down to −80 °C.

Nickel-free high-nitrogen austenitic steel outperforms CoCrMo alloy regarding tribocorrosion in simulated inflammatory synovial fluids.

CoCrMo alloys are well-established biomaterials used for orthopedic joint replacement implants. However, such alloys have been associated with clinical problems related to wear and corrosion. A new generation of austenitic high-nitrogen steels(AHNSs) has been developed for biomedical applications. Here, we have addressed influences of hyaluronic acid, combined with inflammatory (oxidizing) conditions, on tribocorrosion of the high-nitrogen FeCrMnMoN0.9 steel (DIN/EN X13CrMnMoN18-14-3, 1.4452), and of the low carbon CoCrMo0.03 alloy (ISO 5832-12). We aimed to elucidate critical and clinically relevant conditions affecting the implant's performance in certain orthopedic applications. Tribocorrosion tests were conducted in triplicate, with discs under reciprocating sliding wear against a ceramic ball. Different lubricants were prepared from standardized bovine serum solution (ISO 14242-1), with variable additions of hyaluronic acid (HA) and hydrogen peroxide (H2 O2 ). Test conditions were: 37°C, 86,400 cycles, 37 N load (20-40 MPa after run-in phase). Volumetric wear was quantified; surfaces were evaluated by electrochemical parameters and microscopy/spectroscopy analyses (SEM/EDS). Factorial analysis of variancetests was conducted to examine the effects of HA, H2 O2 , and test material on wear- and corrosion-related dependent variables. Tribocorrosion performances of CoCrMo0.03 and FeCrMnMoN0.9 were comparable in fluids without H2 O2 . With higher H2 O2 concentrations, tribocorrosion increased for CoCrMo0.03 , while this was not the case for FeCrMnMoN0.9 . HA significantly enhanced wear of CoCrMo0.03 in the absence of H2 O2 , while it mitigated the tribocorrosive action of 3 mM H2 O2 ; HA had no impact on FeCrMnMoN0.9 . These results indicate a favorable performance of FeCrMnMoN0.9 compared to CoCrMo0.03 , and encourage further research on AHNS for certain orthopedic applications.

Влияние фазовых превращений в процессе электронно-лучевой 3D-печати и последующей термической обработки на закономерности пластической деформации и разрушение образцов высокоазотистой Cr-Mn-стали

We investigated the phase composition, plastic deformation and fracture micromechanisms of Fe-(25-26)Cr-(5-12)Mn-0.15C-0.55N (wt. %) high-nitrogen chromium-manganese steel. Obtained by the method of electron-beam 3D-printing (additive manufacturing) and subjected to a heat treatment (at a temperature of 1150°C following by quenching). To establish the effect of the electron-beam 3D-printing process on the phase composition, microstructure and mechanical properties of high-nitrogen steel, a comparison was made with the data for Fe-21Cr-22Mn-0.15C-0.53N austenitic steel (wt. %) obtained by traditional methods (casting and heat treatment) and used as a raw material for additive manufacturing. It was experimentally established that in the specimens obtained by additive manufacturing method, depletion of the steel composition by manganese in the electron-beam 3D-printing and post-built heat treatment contributes to the formation of a macroscopically and microscopically inhomogeneous two-phase structure. In the steel specimens, macroscopic regions of irregular shape with large ferrite grains or a two-phase austenite-ferrite structure (microscopic inhomogeneity) were observed. Despite the change in the concentration of the basic elements (chromium and manganese) in additive manufacturing, a high concentration of interstitial atoms (nitrogen and carbon) remains in steel. This contributes to the macroscopically heterogeneous distribution of interstitial atoms in the specimens - the formation of a supersaturated interstitial solid solution in the austenitic regions due to the low solubility of nitrogen and carbon in the ferrite regions. This inhomogeneous heterophase (ferrite-austenite) structure has high strength properties, good ductility and work hardening, which are close to those of the specimens of the initial high-nitrogen austenitic steel used as the raw material for additive manufacturing.

Structure, Phase Composition, and Mechanical Properties of a Boron-Containing High-Nitrogen Austenitic Steel Made by Induction Melting

The structure and the mechanical properties of a cast high-nitrogen austenitic steel are studied after hot and cold deformation. The as-cast steel contains the FeCrB and BN phases. During hot deformation, the B13N13C74 phase forms. This phase has a layered structure and is easily deformed during hot or cold rolling. The existence of the B13N13C74 phase only slightly changes the strength and the ductility, but it substantially decreases the impact toughness of the steel as compared to that of similar boron-free Cr–Mn–Ni high-nitrogen austenitic steels.

Corrosion resistance of the nickel-free high-nitrogen steel FeCrMnMoN0.9 under simulated inflammatory conditions.

Nickel-free, high-nitrogen austenitic steels (AHNS) have been introduced for biomedical applications, with encouraging results in terms of mechanical and corrosion properties. Here, we tested the corrosion resistance of a nickel-free high nitrogen steel (FeCrMnMoN0.9) in bovine serum solutions containing 0 or 3 g/L hyaluronic acid (HA), and 0, 3, or 30 mM hydrogen peroxide (H2 O2 ) simulating no, moderate, or strong inflammatory conditions, respectively. Nondestructive electrochemical measurements (open circuit potential [OCP], linear polarization resistance "RP ", and electrochemical impedance spectroscopy) were run in triplicate over 10 hr. The presence of HA had no significant effect either on the stabilized OCP values, or on the corrosion resistance of FeCrMnMoN0.9. Increasing H2 O2 concentrations shifted the OCP to more electropositive values; the corrosion resistance decreased only at a 30 mM H2 O2 . Final RP values at 0, 3, and 30 mM H2 O2 resulted in 1598 ± 276, 1746 ± 308, and 439 ± 47 kΩ cm2 , respectively. These values were 4-14 times higher, than the RP values measured on LC-CoCrMo in our previous study, conducted under identical conditions. While these findings are encouraging, future studies need to focus on tribocorrosive properties of the AHNS to evaluate its applicability in joint replacement.

Effect of Alloying on the Volume Effect of the γ → α Transformation in High-Nitrogen Steels

The influence of alloying on the magnitude and the sign of the volume effect of the strain-induced martensitic transformation in high-nitrogen austenitic steel is analyzed. The volume effect of the martensitic transformation in such steels as a result of plastic deformation is shown to be dependent on the nitrogen and manganese contents and to be negative, leading to the formation of tensile stresses. This fact distinguishes high-nitrogen austenitic steels from traditional austenitic steels, for which this volume effect is always positive and determines the formation of compressive stresses which compensate the tensile stresses of a thermal origin.

Correction to: Structural Features and Application Prospects for High-Nitrogen Austenitic Steels

To the article “Structural Features and Application Prospects for High-Nitrogen Austenitic Steels,” by O. A. Bannykh, Vol. 61, Nos. 5 – 6, pp. 287 – 294, September, 2019.