Ni-Cr Steel Research Articles

Development of a Flow Rule Based on a Unified Plasticity Model for 13Cr-4Ni Low-Carbon Martensitic Stainless Steel Subject to Post-Weld Heat Treatment

This study aims to develop a flow rule for evaluating the relaxation and redistribution of residual stresses during the post-weld heat treatment (PWHT) of hydroelectric runners made from low-carbon martensitic stainless steel (13Cr-4Ni composition). During the PWHT, austenite reforms in the filler metal and surrounding areas of the base metal near welded joints. The evolving inelastic strain rate with reformed austenite led to defining two distinct flow rules in the pure martensitic (α′) and austenitic (γ) phases. A linear rule of mixture was then applied to assess global effective stress based on the inelastic strain rate and current austenite fraction during the PWHT. A unified constitutive model incorporating drag stress and back stress, evolving with creep and plastic deformation mechanisms during the PWHT, described the stress–strain behavior. To validate this analysis, a third flow rule was determined in the 18% tempered austenitic microstructure, compared with the rule of mixture’s effective stress contribution from each phase on the inelastic strain rate. Isothermal constant strain rate tests in stabilized crystalline microstructures evaluated constants specific to their respective flow rules. This study demonstrates the stability of reformed austenite at elevated temperatures during slow cooling and its significant influence on the mechanical properties of 13Cr-4Ni steels. The effectiveness of estimating yield stress using the rule of mixture based on individual phase behaviors is also confirmed.

Stainless steels as a solution for corrosion and erosion problems involving grains in agribusiness sector applications

Agricultural activities such as grain processing play a crucial role in Brazil's economy, contributing significantly to its gross domestic product (27.4% in 2021). The use of carbon steel equipment leads to considerable environmental and economic losses in agribusiness due to corrosion. This study explores the erosion-corrosion behavior of a dual-phase 11Cr and an 18Cr8Ni stainless steel (SS), compared to a mild (ASTM A36) and a high-strength carbon (AHSS) steel under conditions close to the agribusiness reality. The impact of corn particles as erosive component associated to pure water and chloride-containing environments was studied using a fog chamber, a topic until now unexplored in the literature. The methodology adopted is novel and explores the erosion-corrosion synergy in cumulative steps, aiming to shed light on the mechanisms of corrosion and wear that affect the materials in the agribusiness industry. The findings reveal that corn particles, despite their soft nature, can easily remove non-adherent corrosion products from the steel surface. In the deionized water medium, the impact of the soft particles can also shift the corrosion pattern of advanced high-strength steels from general corrosion to localized pitting damage reduzing the corrosion rates. The carbon and 11Cr steels showed the highest corrosion rates under the pure corrosion condition in both media. The erosion-corrosion process considerably reduced the corrosion rate, mainly in the deionized water medium for the carbon steels. An exception to this behavior was 18Cr8Ni steel, whose corrosion rates, however, were the lowest among the materials. Low-chromium stainless steel emerges as a cost-effective solution to erosion-corrosion challenges in the agribusiness segment.

Shot Peening Effect on Sliding Wear in 0.9% NaCl of Additively Manufactured 17-4PH Steel.

The growing demand for modern steels showing corrosion and tribological resistance has led to their increased use in the production of medical devices. This study analyzed the effect of shot peening on wear resistance in 0.9% NaCl solution of 17-4PH steel produced by direct laser metal sintering (DMLS) technology. The study's novelty relies on revealing the effect of shot peening (SP) surface treatment on the wet sliding wear resistance of 17-4PH steel produced with DMLS. Moreover, in the context of 17-4PH steel application for medical devices, the 0.9% NaCl tribological environment were selected, and SP processes were conducted using steel CrNi shot and ceramic (ZrO2) beads. The up-to-date scientific literature has not identified these gaps in the research. DMLS technology makes it possible to obtain products with complex architectures, but it also faces various challenges, including imperfections in the surface layer of products due to the use of 3D printing technology itself. The chemical and phase composition of the materials obtained, Vickers hardness, surface roughness, and microscopic and SEM imaging were investigated. Tribological tests were carried out using the ball-on-disc method, and the surfaces that showed traces of abrasion to identify wear mechanisms were subjected to SEM analysis. The XRD phase analysis indicates that austenite and martensite were found in the post-production state, while a higher martensitic phase content was found in peened samples due to phase transformations. The surface hardness of the peened samples increased by more than double, and the post-treatment roughness increased by 12.8% after peening CrNi steels and decreased by 7.8% after peening ZrO2 relative to the reference surfaces. Roughness has an identifiable effect on sliding wear resistance. Higher roughness promotes material loss. After the SP process, the coefficient of friction increased by 15.5% and 20.7%, while the wear factor (K) decreased by 25.9% and 32.7% for the samples peened with CrNi steels and ZrO2, respectively. Abrasive and adhesive mechanisms were dominant, featured with slight fatigue. The investigation showed a positive effect of SP on the tribological properties of DMSL 17-4PH.

Developing the optimal chemical composition of heat-resistant Cr-Ni steel for aerospace equipment

The object of research in this work is the processes of forming the microstructure and mechanical properties of heat-resistant steels depending on their chemical composition. The microstructure and high-temperature mechanical properties of austenitic heat-resistant chrome-nickel steels of the proposed chemical composition were investigated in the work. The microstructure study determined the grain size and topography of inclusions in steels. Based on the results of mechanical tests, a multifactorial experiment was planned, which made it possible to establish the relationship between the mechanical properties of steels with alloying elements selected as factors. The obtained regression equations were used to estimate the quantitative influence of each alloying element on the corresponding mechanical properties. Analysis of the results of the experiment made it possible to determine the optimal chemical composition of steel for gas turbine engines used in the aerospace industry, as well as in the metallurgy of titanium production. It is shown that the state of solid solution and heat-resistant niobium and molybdenum carbides (chromium carbides dissolve at a temperature of 950 °C) are an important factor that significantly affects the structure, mechanical, and service properties of heat-resistant steel. The austenite structure is provided by the required amount of nickel. The resulting indicators of heat resistance of steels of different compositions, tested at temperatures of 850 °C, 950 °C, and 1050 °C, proved the superiority of steel with a higher content of carbon and chromium and a lower content of nickel. The mechanism of steel strengthening and the influence of alloying with carbon, chromium, and nickel on it have been determined. The optimal chemical composition of heat-resistant steel on an iron-nickel basis for operation at a temperature of 950 °C has been established

Atomistic characterization of multi nano-crystal formation process in Fe–Cr–Ni alloy during directional solidification: Perspective to the additive manufacturing

The directional solidification phenomenon has been observed in conventional castings and state-of-the-art manufacturing processes like additive manufacturing of steel. Precise control of temperature gradient during directional solidification in the additive manufactured components is essential to get growth and evolution of various crystalline structures, which enhance the properties. In this study, we have used molecular dynamics simulation to investigate the directional solidification of Fe–Cr–Ni steel under a wide range of temperature gradients. It is observed that multiple crystal morphology such as single crystal, nano-grains, multiple stacking faults, twins etc. Form during directional solidification depending on the temperature gradient. Evolution of various crystalline structures characterized by adaptive common neighbour analysis, surface area, volume and corresponding dimensionless aspect ratio. The current investigation adds to the pedagogical understanding of the effects of thermal gradients on the evolution characteristics of crystal morphology evolved during modern additive manufacturing processes.

Numerical modelling of stress‐strain response and deformation‐induced martensite in metastable austenitic stainless steels under monotonic tensile loading

AbstractA constitutive model describing the deformation‐induced martensite transformation in metastable austenitic CrNi steels is presented. In line with the previous work of Stringfellow et al. [1], the material is considered to have a composite response of the underlying austenite and the evolving martensite phases. The stresses and strains in the individual phases are described using viscoplastic models. The effective properties of the material are then computed by a homogenization method. Strain hardening in the individual phases is represented using separate flow rules. Furthermore, based on the plastic strain in the austenitic phase, a transformation kinetics model describes the evolution of the martensite volume, in the two‐phase composite.A numerical implementation of the model is done in the finite element program FEAP [2]. The parameters in model are identified by experimental data using the least‐squares optimization. Finally, some results are presented using an illustrative boundary value problem of a structured surface.

Changes in Abrasion Resistance of Cast Cr-Ni Steel as a Result of the Formation of Niobium Carbides in Alloy Matrix

Cast austenitic chromium-nickel steel is commonly used for the manufacture of machine parts and components, which are exposed to the attack of corrosive media and abrasive wear during operation. The most commonly used grades include GX2CrNi18-9 and X10CrNi18-8 as well as GX2CrNiMo17-12-2 and X6CrNiMoNb17-12-2. To improve the abrasion resistance of cast chromium-nickel steel, primary niobium carbides were produced in the metallurgical process by increasing the carbon content and adding Fe-Nb. The microstructure of the obtained test castings consisted of an austenitic matrix and primary niobium carbides evenly distributed in this matrix. The measured hardness of the samples after heat treatment ranged from 215 to 240 HV and was higher by about 60 units than the hardness of the reference cast GX10CrNi18-9 steel, which had a hardness of about 180 HV. Compared to the reference cast steel, the abrasive wear resistance of the tested cast chromium-nickel steel (measured in Miller test) with contents of 4.4 and 5.4 wt% Nb increased only slightly, i.e., by 5% for the lower niobium content and 11% for the higher niobium content. Compared to ordinary cast GX10CrNi18-9 steel, the addition of 9.2 wt% Nb reduced the abrasive wear by almost 2.5 times.

Fracture mechanisms and properties for irradiated austenitic chromium-nickel steel over elevated temperature range and formulation of intergranular fracture criterion

The fracture mechanisms of austenitic 18Cr-9Ni steel have been investigated over the temperature range from 200° to 600 °C using the following states: (1) after neutron irradiation at temperature of 400 °C up to damage dose of 30 dpa; (2) after neutron irradiation and subsequent aging at 550 °C for 3000 h. The fracture properties and mechanisms have been determined under uniaxial tension of smooth round and notched round bars, i.e. for various stress triaxialities. Sharp decrease in the fracture strain and transition to intergranular fracture have been revealed for smooth round bars over high temperature range that indicates high temperature radiation embrittlement. Over the same temperature range the fracture strain is larger for notched round bars than for smooth round bars, moreover a portion of intergranular fracture is also larger. This finding is rather abnormal as the fracture strain usually decreases when stress triaxiality and intergranular fracture portion increase. On the basis of the obtained experimental results, for the first time, the fracture stress-controlled criterion and fracture model have been developed over temperature range of high temperature radiation embrittlement. The proposed model allows one to explain larger value of the fracture strain for notched round bars as compared with smooth round bars and also to predict fracture toughness over range of high temperature radiation embrittlement. The formulated criterion and model have been verified by comparison of the calculated and experimental values of fracture toughness for 18Cr-9Ni steel irradiated up to damage dose of (24–30) dpa. Experimental values of fracture toughness have been obtained from compact tension CT-0.5 specimens tested at 200 °C and 600 °C.

Temperature-Dependent Deformation Behavior of “γ-austenite/δ-ferrite” Composite Obtained through Electron Beam Additive Manufacturing with Austenitic Stainless-Steel Wire

Temperature dependence of tensile deformation behavior and mechanical properties (yield strength, ultimate tensile strength, and an elongation-to-failure) of the dual-phase (γ-austenite/δ-ferrite) specimens, obtained through electron-beam additive manufacturing, has been explored for the first time in a wide temperature range T = (77–300) K. The dual-phase structures with a dendritic morphology of δ-ferrite (γ + 14%δ) and with a coarse globular δ-phase (γ + 6%δ) are typical of the as-built specimens and those subjected to a post-production solid–solution treatment, respectively. In material with lower δ-ferrite content, the lower values of the yield strength in the whole temperature range and the higher elongation of the specimens at T > 250 K have been revealed. Tensile strength and stages of plastic flow of the materials do not depend on the δ-ferrite fraction and its morphology, but the characteristics of strain-induced γ→α′ and γ→ε→α′ martensitic transformations and strain-hardening values are different for two types of the specimens. A new approach has been applied for the analysis of deformation behavior of additively fabricated Cr-Ni steels. Mechanical properties and plastic deformation of the dual-phase (γ + δ) steels produced through electron beam additive manufacturing have been described from the point of view of composite materials. Both types of the δ-ferrite inclusions, dendritic lamellae and globular coarse particles, change the stress distribution in the bulk of the materials during tensile testing, assist the defect accumulation and partially suppress strain-induced martensitic transformation.

Influence of the grain orientation and δ-ferrite on the cyclic deformation behavior of an austenitic CrNi steel manufactured by wire and arc additive manufacturing

In contrast to most additive manufacturing processes, Wire and Arc Additive Manufacturing enables the production of big metallic components, as it offers sufficient building rates and dimension limits. As the larger dimensions and higher building rates lead to other thermal conditions compared to other, more frequently used additive manufacturing processes, a sound analysis of the resulting microstructure and the corresponding mechanical properties is required. As shown in the presented work for the austenitic stainless steel X1CrNi19-9 (AISI 308L; DIN EN-ISO: 1.4316), the process-induced microstructure features textured austenite grains with intragranular δ-ferrite dendrites, both arranged in dependency with the building direction. Thus, the monotonic and cyclic deformation behavior was analyzed for three different orientations of the loading direction to the building direction, i.e., parallel (vertical), 45° and perpendicular (horizontal). The presented results reveal a strong anisotropy in elastic and plastic deformation behavior. Due to the preferential orientation of the austenite grains, the 45° orientation led to a higher stiffness, a more pronounced plastic deformability and a higher cyclic hardening potential, when compared to the other orientations. Because of this, at lower stress amplitudes the 45° orientation shows a higher fatigue life than the vertical and horizontal orientation. However, besides the texture also the grain elongation and the orientation of the δ-ferrite dendrites towards the loading direction influence the plastic deformation processes. This results in higher monotonic strength for the horizontal orientation in relation to the vertically oriented specimens.

Effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel

The effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel (HSLAs) were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, electrochemical tests, X-ray photoelectron spectroscopy and Raman spectroscopy. The results showed that the grain size and microstructure of the steel were optimized due to the increase of crystallinity and Cr3C2 relative content by adding Cr and Ni. The tensile strength was enhanced because of the refined crystalline strengthening, phase transformation strengthening and solution strengthening. Electrochemical tests displayed that the self-corrosion current density of steel and the total anode current density as well as the number of total anodes of the WBE decreased significantly by adding Cr and Ni during immersion in 3.5 wt% NaCl solutions for 24 h. During the corrosion process, the composition and phase structure of the rust layers changed for the existence of Cr and Ni in the Cr–Ni steel, and the formation of NiFe2O4 and FeCr2O4 promoted the increase of the Fe2+/Fe3+ ratio and the relative content of α-FeOOH in the rust layers enhancing the compactness and protectiveness of the corrosion products. Besides, the microstructure of the steel containing Cr and Ni had significant effects on the mechanical strength and corrosion resistance.

Assessment of Corrosion Resistance and Hardness of Shot Peened X5CrNi18-10 Steel.

Although the application of shot peening facilitates increasing hardness and corrosion resistance of stainless steel, the inappropriate peening parameters result in overestimated hardening and exaggerated surface roughness, which deteriorate the surface morphology and negatively affect the corrosive behavior of treated steel. Therefore it is crucial to select the peening parameters that allow obtaining both high hardness and elevated corrosion resistance. This study aims to determine the effect of X5CrNi18-10 stainless steel samples shot peening on the surface morphology, hardness, and corrosion resistance. Samples were shot peened with a CrNi steel shot, applying 0.3 MPa and 0.4 MPa peening pressures and treatment times of 60 s and 120 s. Roughness analysis and microscopic and SEM-EDS examination were employed to state the effect of peening parameters on the sample's corrosive behavior in a 3.5% NaCl solution. The most promising shot peening parameters for Vickers hardness and electrochemical corrosion resistance were selected. It is revealed that the surface roughness increase has a detrimental effect on the corrosion behavior. Overall, high corrosion resistance and the high hardness of stainless steel samples were noted for the peening pressure of 0.4 MPa and time treatment of 60 s.

Fracture properties and mechanisms for irradiated austenitic steels over high temperature range and formulation of fracture criterion. Part 1. Experimental results

The experimental study results of the fracture properties and mechanisms are represented over temperature range from 200 up to 600°С for austenitic 304 steel (18Cr–9Ni steel) in the following conditions: (1) after neutron irradiation at temperature of 400°С up to damage dose of 30 dpa; (2) after neutron irradiation and subsequent aging at 550°С for 3000 hours. The fracture properties and mechanisms are determined under uniaxial tension of standard smooth cylindrical specimens and notched cylindrical specimens, i.e. for various stress triaxialities. Sharp decrease in the fracture strain and transition to intergranular fracture are revealed over high temperature range forstandard smooth cylindrical specimens. Over the same temperature range the fracture strain is larger for notched cylindrical specimens than for smooth cylindrical specimens, moreover a portion of intergranular fracture is also larger. This finding is rather abnormal as the fracture strain usually decreases when stress triaxiality and intergranular fracture portion increase. The obtained results are used for formulation of fracture criterion and elaboration of fracture model for high temperature radiation embrittlement that is considered in the second part of the paper.

Fracture properties and mechanisms for irradiated austenitic steels over high temperature range and formulation of fracture criterion. Part 2. Fracture criterion and model

On the basis of experimental data considered in the first part of the paper the fracture criterion and fracture model are represented for high temperature radiation embrittlement of irradiated austenitic steels. The proposed model allows one to explain larger value of the fracture strain for notched cylindrical specimens as compared with smooth specimens as it has been found in the first part of the paper and also to predict fracture toughness over range of high temperature radiation embrittlement. The formulated criterion and model are verified by comparison of the calculated and experimental values of fracture toughness for 18Cr-9Ni steel irradiated up to damage dose of (24–30) dpa. Experimental values of fracture toughness are obtained from compact tension CT-0.5 specimens tested at 200°С and 600°С. The fracture toughness data for irradiated steel are represented also over temperature range from 20°С and 600°С.

Effect of Stress Ratio and Evaluation of Crack Sizes on Very-High-Cycle-Fatigue Crack Propagation Life Prediction of Carburized Cr-Ni Steel

Carburized Cr-Ni steel is widely used in the manufacture of components in many fields due to excellent performance, of which the service life has been a concern. In order to investigate the high-cycle-fatigue and very-high-cycle-fatigue properties of carburized Cr-Ni gear steel, axial loading fatigue tests were performed by QBG-100 with stress ratios of −1, 0 and 0.3. The Generalized Pareto distribution was used to evaluate the inclusion size of carburized Cr-Ni gear steel. Based on the stress ratio and the evaluated crack size, a new fatigue life prediction model for carburized Cr-Ni gear steels was constructed. The results show that the S–N characteristics of carburized Cr-Ni gear steel represent the continuously descending tendency. Based on the long crack propagation threshold and the instability propagation threshold of carburized Cr-Ni gear steel, the sizes of FGA, fisheye and surface smooth area (SSA) can be evaluated, respectively. In addition, the maximum size of surface and interior inclusion of carburized Cr-Ni gear steel are 17.50 μm and 6.46 μm with a cumulative probability of 99.9%. By validating the new established model, the prediction result is acceptable according to the good consistency between the predicted life and the experimental life.

Effect of shot peening on corrosion resistance of additive manufactured 17-4PH steel

AbstractComponents 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 behavior, and at the same time ensure their high corrosion resistance. Surface modification via shot peening (SP) is considered suitable for AM of engineering devices made of 17-4PH (X5CrNiCuNb16-4) stainless steel. The objective of this study was to determine the effect of three types of peening media (CrNi steel shot, glass, and ceramic beads) on the corrosion resistance of specimens of DMLS 17-4PH stainless steel. Results demonstrated that SP caused steel microstructure refinement and induced both martensite (α) formation and retained austenite (γ) reduction. 17-4PH specimens peened showed the increase in surface hardness of 255, 281, and 260 HV0.2for ceramic, glass, and steel, respectively. DMLS 17-4PH specimens modified by SP exhibited different surface morphology, hardness, and microstructure and thus, these properties affect corrosion performance. The results implied that steel shot peened with steel shot showed the highest resistance to corrosion processes (Icorr= 0.019 μA/cm2), slightly worse with glass (Icorr= 0.227 μA/cm2) and ceramics (Icorr= 0.660 μA/cm2) peened. In the case of ceramic and glass beads, it was possible to confirm the presence of the above-mentioned particles in the surface layer after SP.

Failure analysis of stainless and heat resisting steels, documented on selected examples

Abstract Failures of stainless and heat-resistant austenitic CrNi steels frequently occur in practice due to incorrect material selection, improper processing or unforeseeable factors under operating conditions. Selected examples will be used to illustrate various of these factors influencing the development of failure.

Size effects in stress propagation and dynamics of dislocations: Fe–Ni–Cr steel

Movement of line dislocations in fcc steel 310S is found to depend on the size of nanometer sized structures, based on modeling within molecular dynamics (MD). The effect is attributed to time (and size) dependencies of pressure propagation into the medium interior. The observation is crucial in interpreting any MD studies of pressure effects since these are governed by time-dependent internal virial stresses. In particular, velocity of dislocations scales better with value of local internal shear component of virial stress S xy than with external shear pressure applied. Dynamics of stress penetration is described well within the model of damped harmonic oscillator, where characteristic oscillation frequency depends on number of crystallographic layers in direction along the wave propagation while the speed of stress propagation is the speed of sound. The minimal stress required for dislocation movement (Peierls stress) is determined to be 0.75 GPa. Pressure and temperature effects on dislocation movement are systematically investigated.

Phase Transformation after Heat Treatment of Cr-Ni Stainless Steel Powder for 3D Printing.

Today, Ni-Cr steel is used for advanced applications in the high-temperature and electrical industries, medical equipment, food industry, agriculture and is applied in food and beverage packaging and kitchenware, automotive or mesh. A study of input steel powder from various stages of the recycling process intended for 3D printing was conducted. In addition to the precise evaluation of the morphology, particle size and composition of the powders used for laser 3D printing, special testing and evaluation of the heat-treated powders were carried out. Heat treatment up to 950 °C in an air atmosphere revealed the properties of powders that can appear during laser sintering. The powders in the oxidizing atmosphere change the phase composition and the original FeNiCr stainless steel changes to a two-phase system of Fe3Ni and Cr2O3, as evaluated by X-ray diffraction analysis. Observation of the morphology showed the separation of the oxidic phase in the sense of a brittle shell. The inner part of the powder particle is a porous compact core. The particle size is generally reduced due to the peeling of the oxide shell. This effect can be critical to 3D printing processing, causing defects on the printed parts, as well as reducing the usability of the precursor powder and can also change the properties of the printed part.

Microstructure and mechanical properties of Nb-alloyed austenitic CrNi steel fabricated by wire-feed electron beam additive manufacturing

We investigated the phase composition, microstructure, mechanical properties, and fracture mechanisms of Nb-alloyed austenitic stainless steel, produced by electron beam additive manufacturing (EBAM), after different regimes of the post-EBAM solid-solution treatments. As-build EBAM-produced steel has a predominantly austenitic structure, contains vermicular δ-ferrite (Vδ = 5–7%) and Nb-enriched precipitates (Laves phase Fe2Nb, FeNb and NbC). Niobium-alloying assists the stabilization of austenitic phase but does not suppress the columnar grain growth during EBAM-fabrication of austenitic stainless steels. Solid-solution treatments provide a change in morphology of δ-ferrite, a decrease in the ferrite volume fraction and the dissolution of intermetallic phases (Fe2Nb, FeNb), which all affect the tensile properties. Post-EBAM treatments contribute a decrease in the yield strength of the steel and improve the elongation-to-failure. All EBAM-produced specimens have good mechanical properties, which are comparable with those for steels produced by conventional methods. Irrespective of treatment regime, EBAM-fabricated specimens exhibit ductile transgranular fracture. For the EBAM-produced Nb-alloyed steel, the phase composition is described from the point of view solidification mode, and the effects of the precipitate hardening and solid-solution strengthening on the mechanical properties and fracture mechanisms were discussed.