Stainless Alloys Research Articles

Design and Assessment of an Austenitic Stainless Alloy for Laser Powder Bed Additive Manufacturing

Recent developments in metallic additive manufacturing (AM) processes for the production of high-performance industrial pieces have been hampered by the limited availability of reliably processable or printable alloys. To date, most of the alloys used in AM are commercial grades that have been previously optimized for different manufacturing techniques. This study aims to design new alloys specifically tailored for AM processes, to minimize defects in the final products and to optimize their properties. A computational approach is proposed to design novel and optimized austenitic alloy compositions. This method integrates a suite of predictive tools, including machine learning, calculation of phase diagrams (CALPHAD) and physical models, all piloted by a multi-objective genetic algorithm. Within this framework, several material-dependent criteria are examined and their impact on properties and on the occurrence of defects is identified. To validate our approach, experimental tests are performed on a selected alloy composition: powder is produced by gas atomization and samples are fabricated by laser powder bed fusion. The microstructure and mechanical properties of the alloys are evaluated and its printability is compared with a commercial 316L stainless steel taken as a reference. The optimized alloy performs similarly to 316L in terms of coefficient of thermal expansion, hardness and elongation, but has a 17% lower yield strength and ultimate tensile strength (UTS), indicating that further optimization is required.

Algorithm for optimization of cold‑rolled pipe rolling routes

The relevance of the work is justified by the need to refine the methodology for calculating cold rolling routes, associated with the expansion of factors that need to be taken into account in conducting such calculations. The aim of the work is to develop an algorithm for optimizing the routes of cold rolling of pipes using CRP and CRPR type mills, convenient for implementation in a software product. The paper analyzes the main parameters for optimizing the routes of cold rolling of pipes, factors limiting the field of optimal values of the geometric parameters of the billet‑pipe in each pass. Among the latter, the maximum possible reduction in the cross‑sectional area, the required reduction in the cross‑sectional area in the last pass, the requirement for the nature of the distribution of the reduction value in the cross‑sectional area, in the wall thickness and in the pipe diameter from pass to pass and other parameters are highlighted. The importance of minimizing the number of passes is noted. The main dependencies included in the method for calculating the deformation parameters of the cold rolling route using CRP and CRPR mills are analyzed and highlighted. An algorithm for calculating the route of cold rolling of pipes, with several iteration operations, has been developed. The proposed algorithm allows optimizing the rolling route of pipes made of any grades of steels and alloys, and allows optimizing most parameters, including those affecting the economic parameters of production. Depending on the grade of steel or alloy, some iteration operations can be excluded. The algorithm has been tested in the practice of calculating rolling routes for pipes made of carbon and stainless steels and alloys.

Comparative analysis of microstructure and corrosion resistance in laser-clad austenitic and martensitic stainless-steel coatings

Post-casting austenite often possesses better corrosion resistance than martensite. In order to compare the difference of corrosion resistance between austenitic stainless steel coating (ASSC) and martensitic stainless steel coating (MSSC) in the powder metallurgical state, two stainless steel Fe-based alloy coatings of the same process parameter were prepared on the surface of 40Cr steel by using laser cladding technology. Through SEM, EBSD, XRD and electrochemical tests, the microstructure, phase and cross-section metallurgical bonding condition of the coating were studied, and the difference in corrosion resistance between the two was comprehensively analyzed. The results showed that the main phase structure of ASSC was the FCC phase, and the main phase structure of MSSC was the BCC phase. The average self-corrosion current (9.92 × 10−8 A/cm2) and average self-corrosion rate (1.04 × 10−3 g/m2·h) of MSSC were 4.77 % and 5.62 % of ASSC, respectively. In addition, the polarization resistance, impedance value, and passivation film density of MSSC are higher than ASSC, MSSC has less damage from corrosion. The combination of factors, such as fabric refinement and passivation film density, makes the corrosion resistance of MSSC better than ASSC.

Strengthening CrFeNi multi-principal element alloy through grain refinement, introducing partially recrystallized structure, and constructing fine heterostructures

The excellent corrosion resistance exhibited by CrFeNi multi-principal element alloys makes them highly desirable for the development of novel stainless alloys, but they exhibit a low strength. This work explores a simple processing route to enhance the strength by cold-rolling and annealing a CrFeNi alloy to introduce a partially recrystallized structure, refine its grain, and construct fine heterostructures. These changes increased the yield strength from 402 MPa to 1025 MPa while maintaining acceptable ductility. Dislocation strengthening, grain boundary strengthening, and hetero-deformation-induced strengthening were responsible for the strength enhancement. A smaller soft phase in the heterostructure enhanced the effectiveness of hetero-deformation-induced strengthening. The findings presented in this article offer additional strengthening methods for CrFeNi multi-principal element alloys.

A Comparative Evaluation of Surface and Elemental Changes in Stainless Steel and Titanium Orthodontic Mini-screw Implants: A Multi-arm Randomized Control Trial.

The present study aimed to compare and quantify the surface changes seen in two most commonly used orthodontic miniscrew implants (MSI) materials; titanium and stainless steel after their clinical use. 40 MSIs (20 titanium and 20 stainless steel) were retrieved from the maxillary arch of 20 subjects (13 females and 7 males) in the age group of 18 - 27 years (mean age=22.4 ± 3.83 years) after their intended use. 40 (20 titanium and 20 stainless steel) asreceived MSIs were used as control. All the MSIs were analyzed under a Scanning Electron Microscope (SEM) for the characterization of their morphological condition (blunting of tip, surface defects and corrosion). Furthermore, Energy Dispersive X-ray (EDX) microanalysis was carried out to study the changes in surface characterization. When imaged using SEM, as-received Titanium and Stainless Steel MSIs demonstrated a relatively smooth surface with no surface defects. However, the retrieved titanium and stainless-steel implants showed increased surface defects (both corrosion and cracks) with the difference being statistically significant. The retrieved Titanium MSIs (115.31±24.38μm) showed 4 times more blunting compared to the retrieved Stainless-steel MSIs (29.74±8.56 μm), with the latter showing 2-3 times more surface corrosion. Clinical usage had pronounced effects on both Titanium and Stainless steel MSI alloys in terms of changes in the surface characteristics. While stainless steel MSIs are more susceptible to surface corrosion, Titanium MSIs exhibit greater alterations in the form of tipblunting and cracks in screw threads.

Smelting characteristics of nickel‑chromium‑manganese bearing prereduced pellets for the preparation of nickel saving austenite stainless steel master alloys

Nickel saving austenite crude stainless steel master alloys were innovatively produced by smelting of nickel‑chromium‑manganese bearing prereduced pellets in an effective and economical way. The thermodynamics analysis and systematic process mineralogy were also conducted to further reveal the smelting characteristics of prereduced pellets and the related enhanced mechanism. The results showed that the preferable stainless steel master alloys with 66.29% Fe, 4.21% Ni, 17.28% Cr, 6.53% Mn and 4.76% C can be prepared from the nickel‑chromium‑manganese bearing prereduced pellets with a corresponding recovery of valuable metals more than 95%. Furthermore, during the enhanced smelting process, the optimization of slag types can further realize the phases transformation from high-melting-point enstatite and forsterite to low-melting-point diopside and monticellite to obtain a decreased smelting temperature and viscosity of slag. The smelting duration and the alloy grain included in the smelting slag were both obviously decreased, resulting in an improved smelting performance.

High-strength corrosion-resistant FeMnCr-based composite damping alloys fabricated by vacuum annealing

High-strength high manganese FeMn-based damping alloys suffer from lower damping capacity at low strain amplitudes and poor corrosion resistance, while the strength is lower in stainless ferromagnetic FeCr-based alloys with high damping capacity at low strain amplitudes. By simple vacuum annealing, we fabricated high-strength, high-manganese FeMnCr-based alloys coated with ferromagnetic FeCr-based stainless damping alloys. Compared to the FeMn-based alloys, the FeMnCr-based composite alloys showed not only higher damping capacity at low strain amplitudes and higher tensile strength but also much better corrosion resistance. Stress relief annealing could further improve their damping capacity. The vacuum annealing will offer a new technique for fabricating composite alloys with unique properties.

Investigation of the microstructure obtained following joining stainless and medium carbon alloy steel by wire arc additive manufacturing

Investigation of the microstructure obtained following joining stainless and medium carbon alloy steel by wire arc additive manufacturing

An investigation of non-noble metal electrodes for carbon dioxide electrolysis in molten lithium carbonate

Carbon dioxide (CO2) emissions are a known cause of global warming, but at the same time, they constitute a potentially valuable source of carbon. Using a high-temperature electrolysis process in molten carbonate, CO2 can be transformed into carbon and oxygen. However, the corrosive ambient in molten carbonate necessitates resilient electrode material. To lower the cost, it is also important to select affordable electrodes. This study aimed to investigate the performance of non-noble metal electrodes specifically nickel, stainless steel, and Alloy X (a Ni-Cr-Fe-Mo alloy) in molten lithium carbonate (Li2CO3) at 750∘C. Electrochemical performance was measured using step-wise constant current and cyclic voltammetry, and the yield was examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The investigation revealed that nickel has a lower sum of cathodic and anodic overpotential and OER onset potential than stainless steel and Alloy X. Nickel electrodes produced spherical amorphous carbon; stainless steel electrodes generated amorphous carbon along with nanotubes; and Alloy X electrodes yielded amorphous carbon. The EDS confirmed the formation of carbon with metal contamination from Ni, Fe, and Cr. These results provide insight into the utilization of non-noble metal electrodes for CO2 electrolysis in Li2CO3.

Effect of laser shock peening on fretting wear behaviour of AISI 304 stainless alloy

Unlike many other surface treatment techniques, such as shot peening (SP), low plasticity burnishing (LPB), ultrasonic surface rolling process (USRP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP) is a non-contact process. This means that LSP achieves surface modification without direct physical contact, thereby eliminating the risk of media contamination and undesired wear on the peening equipment. As a surface hardening technology, LSP tends to produce a hardened layer with a high gradient of residual stress (RS) in the near-surface, significantly enhancing wear resistance. The well-known wear theories applied for numerical prediction, whether Archard model or dissipated frictional-energy model, contain a multiplier for contact pressure and relative slip amplitude p·ds or shear stress and relative slip amplitude q·ds, respectively. These multipliers are sensitive to the mechanical properties near the surface. Additionally, the wear profile is governed not only by the wear effect but also by the deformation of materials. Therefore, to accurately evaluate the wear performance for surface-hardened materials, the influence of RS is hard to be overlooked. In this work, the finite element method (FEM) is utilised to construct a 3D numerical model, which ignores and considers RS, for both as-received and LSP-treated samples. Two distinct RS distributions induced by different scanning strategies (one- and five-time), are introduced in the finite element (FE) model. The numerical simulation results are then compared with the experimental data to verify the accuracy of the fretting wear model built in this study. On this basis, the impact of different RS distributions on fretting wear characteristics, including wear profile and volume, is extensively investigated. The findings reveal that higher amplitude RS can reduce the degree of fretting wear to a greater extent, highlighting the beneficial role of RS in enhancing wear resistance. Furthermore, the numerical models incorporating RS demonstrate superior predictive accuracy compared to those that omit RS. This naturally underscores the importance of integrating RS in numerical simulations of LSP and other surface-hardened materials.

Mathematical Methods of Observation of Wave Processes During Deformation of 3D Technology Products

The purpose of this work is to develop and apply mathematical methods (Fourier interpolation) to fix the presence and evaluation of the mechanisms of wave processes developing in products made of powder stainless and heat-resistant alloys of additive technologies (SLM) during their deformation.Methods. To fix the presence of wave processes of plastic deformation in loaded 3d technology products, samples of powder stainless steel 03X18H12M2 (analog AISI 316L) and powder heat-resistant alloy 08ХN53BMTU (analog Inconel 718), manufactured using SLM technology on a 3d printer SLM280 2.0HL, were used. The samples were subjected to uniaxial stretching (GOST 1497-84) with a constant rate of capture in air at room temperature. The lengths of the marked sections were measured using digital video recording of the loading process of the marked surface of the samples. Graphs of the dependences of local relative deformation along the length of the sample and at selected test moments were constructed. The mathematical substantiation of the existence of the wave character of the fixed functions as periodic was carried out by decomposing them into a Fourier series with subsequent interpolation.Results. It has been experimentally established that in the volume of the studied samples of powder stainless steel type 316L and heat-resistant alloy type Inconel 718, obtained by SLM technology, when they are stretched, there is a multistage character of wave deformation reflecting the development and movement of local micro-volumes of increased plasticity (foci of localized deformation). The Fourier interpolation procedure of a complex of experimentally obtained piecewise linear functions of the dimensions of the marking grid and their local deformations confirmed their apparent periodicity, i.e. the presence of a wave character.Conclusion. The developed technique of fixing and mathematical processing of wave deformation spectra can be used to analyze the changing parameters of the surface marking (rolling grid) of 3d products both along their length and at fixed loading times, as well as when constructing multidimensional dependencies of the marking parameters on the geometry of samples and test time.

Evaluation of shielding and interaction properties of different stainless steel alloys for nuclear power plant shielding

This study evaluated the gamma and neutron-shielding parameters, electron and charge particles’ interaction properties of three different stainless steel-based alloys (2507SS, 304SS and AISI1018) with densities of 7.82, 7.81 and 7.82, respectively for deployment in nuclear reactor construction. Gamma shielding parameters were evaluated with Phy-X/PSD, Py-MLBUF and GRASP computer programs within the energy range of 0.2 MeV to 15 MeV. The relative deviations (RD %) between two of these computational platforms were calculated. Fast Neutrons Effective Removal Cross-Sections (FNRCS) and Macroscopic Removal cross-section (MRCS) values for fast neutrons were calculated with Phy-X/PSD and MRCS software, while thermal/fast neutron attenuation factors were calculated with NGCals software. The continuous-slowing-down approximation (CSDA) range and total stopping power (TSP) values of H+ and He++ ions were estimated with SRIM Monte Carlo code in a wide energy range of 1–20 MeV. The projectile range of electrons was computed with ESTAR NIST software within the kinetic energy of 0.01–1000 MeV. Gamma-ray, thermal neutron and fast neutron transmission factors (TFs) values were calculated for all samples for a range of well-known energies. From the obtained results, all evaluated parameters were dependent on the composition of shielding materials, the type of radiation and the photon energy of the radiation. The maximum MAC values obtained from the three alloy samples are 0.1505 cm2/g for 2507SS, 0.1453 cm2/g for 304SS and 0.1459 cm2/g for AISI1018 at 0.02 MeV. These results projected 2507SS as a better shielding alloy when compared with other investigated alloy samples. Considering the closeness of densities of investigated alloy samples the shielding and interaction properties of all alloy samples gave excellent and similar results implying that all investigated alloys will effectively serve as a radiation-shielding material in a nuclear reactor.

ELIMINATION OF THE DEFECTIVE LAYER AND STRESS CONCENTRATORS DURING MICROMACHINING OF HOLES IN THIN SHEET BLANKS OF METAL CELLULAR PANELS

Thin-sheet blanks made of aluminum (in particular, AMg2-N), titanium (VT-15, VT-19) or stainless (12X17) alloys are widely used in the production of honeycomb panels in the aviation and space industries. Foil (thickness 0.025-0.055 mm) is used for the production of fillers for cellular sandwich panels; it is pre-perforated with holes of 0.05-0.18 mm and laid out in a corrugated box with adhesive strips. The possibility of making holes by the laser jet method is considered, as it precedes the occurrence of mechanical damage and thermal defects of the surface adjacent to the treatment zone. It is shown that the Water Jet Guided Laser (WJGL) is an effective and efficient method of obtaining profile holes in the fillers of cellular panels and in the panels themselves, which is characterized by high productivity and allows obtaining holes without thermal and mechanical defects. The method can be used both for foil fillers and for metal panels made of stainless steel up to 1.5 mm thick.

Increasing ductility via Cu addition in AlxCrFeMnNi: Towards a scrap-based high entropy alloy

Alloys comprising common alloying elements are more amenable to accepting high fractions of scrap. The present study examines the effect of Cu and Al addition on common element containing multiple principal element alloy (CE-MPEA): AlxCuyCrFeMnNi (x = 0, 0.15, 0.3, 0.6, 0.9 and y = 0, 0.07, 0 = 0.14). Alloys were fabricated by arc casting. As expected, after quenching, the microstructures displayed FCC A1, Cr-rich BCC A2 and B2 precipitate phases in varying amounts. Adding small amounts of Cu to low and medium Al alloy groups increased the FCC phase fraction and refined the FCC grains. It is proposed that these microstructural changes account for the increased ductility seen to accompany Cu addition. A hybrid model was successfully employed to predict the hardness of the FCC phase. In contrast to high Cu-containing HEAs from prior studies, Cu additions in the studied alloys did not detrimentally affect the corrosion resistance in idealised polarization corrosion tests in salt solution. This can be ascribed to the absence of a Cu-rich FCC phase at the low Cu levels employed in the present work. The current alloys show promise as a base composition for further development into a tough fine-grained stainless alloy able to be produced using high fractions of scrap input.

Tolerance of several construction materials and polycrystalline SiC to blistering and flecking due to ion implantation and annealing

The results on the tolerance of several construction materials (D16T alloy, Zr, ЭИ-847, 12Х18Н9Т steels) and polycrystаlline SiC to blistering and flecking after irradiation with 500 keV He+ ions and following annealing have been high-lighted. Samples of stainless steels, zirconium, D16T alloy and silicon carbide were irradiated with helium ions in the range from 1016 to 3 · 1018 ion/cm2. Immediately after irradiation and annealing under temperatures from 300 to 750 °C, the optical microscopy was used to study the structure of surface layers. Temperature and fluence ranges of tolerance to blistering and flecking were determined for all examined materials. Primary types of material structure distortions were reviewed.

Comprehensive microstructural and mechanical characterization of transient liquid phase bonded austenitic stainless steel by Ni–Cr–Si–B amorphous interlayer

In this research, along with the joining of the gas turbine fuel nozzle part from austenitic stainless steel 316L alloy with BNi-2 interlayer by the transient liquid phase bonding process, microstructure test, shear strength and tensile strength tests have been placed. Bonding at a temperature of 1080 °C and a holding time of 45 min has led to the completion of isothermal solidification in the bonding zone. Microstructural and phase investigations showed that austenitic stainless steel 316L undergoes phase transformation after exposure to temperature conditions and the δ ferrite phase is formed as separate areas due to the diffusion of the solid state of ferrite-forming elements, and the grains of the base metal are 32 μm have reached 43 μm, which has caused a decrease in the shear strength of the base metal from 362 MPa to 347 MPa. Despite the completion of isothermal solidification in the joint centerline due to the boron diffusion of the solid state into the base metal and achieving the maximum shear strength of the joint (402 MPa), two generations of boride deposits have been formed. The first-generation borides based on nickel-iron-chromium-molybdenum are formed during heating up to the bonding temperature, and the second-generation boride deposits are based on iron-chromium-molybdenum, which were deposited in situ during the isothermal solidification stage. The microhardness test confirms the uniform distribution of hardness in each of the bonding zones, which feedback was determined in the tensile strength test. The tensile strength of the bonded sample was 485 MPa, which is approximately 82 % of stainless steel 316L. In both shear and tensile tests, the presence of small dimples indicates the ductile failure of the joint samples in base metal.

Insights into the stress corrosion cracking propagation behavior of Alloy 690 and 316 L stainless steel in KOH versus LiOH oxygenated water

The stress corrosion cracking (SCC) propagation behavior of 20% cold worked 316 L stainless steel (SS) and Alloy 690 was investigated in high-temperature oxygenated water. No discernable effect was observed at the same pH level for LiOH or KOH. Increasing pH could dramatically enhance the crack growth rates (CGRs) due to the dissolution of Cr-rich oxide film and the weakening of passivity in high pH regimes. The similarities in SCC behavior and cracking characteristics indicate that the cracking mechanism of both austenite alloys occurs by a slip-dissolution model.

Dehalococcoides mccartyi strain NIT01 grows more stably in vessels made of pure titanium rather than the stainless alloy SUS304.

Advances in many isolation studies have revealed that pure Dehalococcoides grow stably, although the large-scale pure cultivation of Dehalococcoides has yet to be established. In this study, 7 L-culturing of Dehalococcoides mccartyi strain NIT01 was first performed using vessels made of glass and stainless alloy SUS304. All batches cultured in the glass vessel successfully dechlorinated >95% of 1 mM trichloroethene (TCE) to ethene (ETH), whereas only 5 out of 13 batches cultured in the SUS304 vessel did the same. The difference in dechlorination efficiency suggested the possible inhibition of dechlorination by SUS304. Also, the strain NIT01 showed long delays in dechlorination with pieces of SUS316, steel, and a repeatedly used SUS304, but not with titanium. The repeatedly used SUS304 cracked and increased the Fe2+ concentration to ≥76 μM. Dechlorination by this strain was also inhibited with ≥1000 μM Fe2+ and ≥23 μM Cr3+ but not with ≤100 μM Ni2+ , suggesting that Cr3+ eluted from solid stainless alloys inhibited the dechlorination. Culturing in a titanium vessel instead of a stainless alloy showed the complete dechlorination of 1 mM TCE within 12-28 days with a growth yield of 2.7 × 107 cells/μmol-released Cl- , even after repeating use of the vessels six times.

A slow positron beam study of the oxidation behaviour of 310S stainless steel and alloy 800HT exposed to supercritical water

This paper reports a variable-energy slow positron beam characterisation of the surface oxide films in 310 S stainless steel and 800HT nickel-based alloy exposed to 550 °C supercritical water for 1000–4392 h. The evolution of the oxide layer was depth-profiled using positron beam energies from 0.5 to 20 keV, which enabled a probe of up to 2 mm of the near-surface region. SEM/EDS was used as a complementary characterisation tool to support and comprehend the positron annihilation spectroscopy data. A strong dependency on the positron trapping rate and the effective positron diffusion length on the microstructure of the studied materials enabled us to identify up to three non-bulk layers, which were preliminarily attributed to different oxide layers and Fe/Cr depletion regions. By calculating the effective positron diffusion length in the given multi-layer systems, we obtained the thicknesses of individual layers, which are in good agreement with the EDS analysis.

Microstructure and corrosion resistance of ultrahigh pressure Mg-8Li based alloys

High anti-corrosion Mg alloys is desirable to expand their industrial applications. Herein we report an outstanding corrosion resistance of dual-phase Mg-8Li-Y alloy using ultrahigh pressure (UHP) technology. The average corrosion rate is ∼0.47 mm/y, overwhelming the majority of Mg-Li alloys reported hitherto. In-situ X-ray diffraction and scanning electron microscope observation demonstrate that a unique multiple-film on UHPed Mg-8Li-Y alloy attributes to the excellent corrosion resistance, which origins from the dynamic dissolution/regeneration of Li2CO3-rich composite film, thus effectively prohibiting corrosion solution permeation. These results provide some implications to design good anti-corrosion coating for Mg, ever stainless Mg alloys.