18Cr-8Ni Stainless Steel Research Articles

Dynamic constitutive model of Fe–Cr–Ni stainless steel based on isothermal true stress-strain curves

Austenitic Fe–Cr–Ni stainless steel is widely used in aviation, chemistry, energy, due to its excellent properties of high-temperature performance. In this study, the splitting Hopkinson pressure bar with high-temperature system was employed to evaluate the dynamic mechanical properties of Fe–Cr–Ni stainless steel. The true stress-strain curves were obtained under varying conditions, including variable strains, strain rates and temperatures. The true stress increases and levels off as the true strain increases, while increases as the strain rate increases, but decreases sharply as the deformation temperature rises. The deformation temperature is consist of healing temperature and adiabatic temperature. The adiabatic temperature rise related to the specific heat capacity was calculated. The actual deformation temperatures were calculated under different strains by combining the true stress-strain curves. The true stress-strain curve under variable temperature was corrected to the stress-strain curve under isothermal state by using the thermal softening rate, which decoupled the strain and temperature. The Power-Law and Johnson-Cook constitutive models were fitted based on the real stress-strain isothermal curve. The fitting accuracy of Power-Law model was 1.61% for different strain rates at room temperature in average, 3.51% for fixed strain rate at different temperatures. While the fitting accuracy of Johnson-Cook model was 2.94% for different strain rates at room temperature in average, 6.18% for fixed strain rate at different temperatures.

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.

Analysis of Biocompatible Metallic Materials used in Medicine

The paper presents the results of the analysis of two biocompatible materials, Kirschner wires of different thicknesses. Kirschner wires (K-wires) are stainless steel pins used in surgery to fix bone fragments and to provide an anchor for skeletal traction. The K-wires are produced in different diameters. In the present work, a scanning electron microscopy and light microscopy were employed to document the microstructure of two K-wires with different thicknesses. Before observation, the wires were prepared by a standard metallographic procedure (grinding and polishing) followed by electrolytic etching. The chemical composition was determined by studying the wires using quantitative energy-dispersive X-ray spectrometry. It has been found that the chemical composition of the materials corresponds to Cr-Ni stainless steel. In the thick Kirschner wire (sample no. 1) a deformed microstructure after drawing was observed. Sample no. 2 (thin Kirschner wire), on the other hand, consisted of polyhedral austenitic grains, which were formed after recrystallization annealing. Furthermore, isolated microparticles were observed and assigned to titanium nitride. A Vickers hardness test was also performed on the samples. It has been found that the hardness of sample no. 1 was 428.8 HV 0.5. The average hardness of sample no. 2 was 213.4 HV 0.5. It can be concluded that recrystallization annealing decreases the hardness of the material. The K-wires with smaller diameter are thus easier to bend which facilitates their fixation in human body.

Processing an 18Cr-8Ni Austenitic Stainless Steel Without the Dilemma of the Strength and Ductility Trade-Off

Processing an 18Cr-8Ni Austenitic Stainless Steel Without the Dilemma of the Strength and Ductility Trade-Off

Effect of Annealing Temperature on Mechanical Properties and Work Hardening of Nickel-Saving Stainless Steel.

Compared to Cr-Ni stainless steel, nickel-saving stainless steel is a low-cost austenitic stainless steel. We studied the deformation mechanism of stainless steel at various annealing temperatures (850 °C, 950 °C, and 1050 °C). The grain size of the specimen increases with increasing annealing temperature while the yield strength decreases, which follows the Hall-Petch equation. When plastic deformation occurs, dislocation increases. However, the deformation mechanisms can vary between different specimens. Stainless steel with smaller grains is more likely to transform into martensite when deformed. While twinning occurs when the grains are more prominent, the deformation results in twinning. The phase transformation during plastic deformation relies on the shear, so the orientation of the grains is relevant before and after plastic deformation.

Corrosion Inhibition by Sulfate after Surface Preparation

Electropolishing as a surface preparation technique is increasing in popularity in industrial applications and for corrosion studies. Electropolished surfaces have shown a better resistance to pitting corrosion over mechanical polishing, however, the fundamental reason governing the change in corrosion behaviour remains unclear. This study examined the corrosion behaviour of 13Cr4Ni stainless steel (UNS S41500) after five surface preparation techniques and shows that sulfate is incorporated in the oxide film when it is present in the electropolishing solution. Even after removal from the sulfate-containing solution, the sulfate incorporation increases the material’s pitting resistance by lowering the number of sites available for chloride to induce pitting. This work also demonstrates that, when used as a counter electrode, Pt can dissolve and reprecipitate on the working electrode surface during electropolishing. The deposits result in a more noble open circuit potential, indicating an artificial increase in passivity. These artificial changes to corrosion behaviour due to surface preparation method may result in erroneous conclusions. To establish fair comparisons between surface preparation methods, the counter electrode and the sulfate effect should be strictly considered.

Strain-rate dependent deformation behavior of additively manufactured stainless steel with different fractions of δ-ferrite

The effect of strain rate on the tensile deformation behavior of additively manufactured CrNi stainless steel with different fractions of δ-ferrite (14 % in the as-built material and 6 % after the post-built solid-solution treatment) was revealed with the focus on the deformation stage of macroscopic strain-induced γ → α' martensitic transformation. Tension tests were performed with the initial strain rates of 5 ×10−4, 5 ×10−3, and 5 ×10−2 s−1 at two different temperatures, at which slow (300 K) and fast (183 K) kinetics of martensitic transformation were realized. Post-built solid-solution treatment provided a partial dissolution of the δ-ferrite in the additively manufactured steel specimens and assisted higher strain hardening at the stage associated with γ → α' martensitic transformation. Independently on δ-ferrite fraction and test temperature, an increase in the strain rate weakly influences the stress and strain, at which the stage of macroscopic strain-induced transformation starts, but visibly decreases the strain hardening rate at this deformation stage. The latter testifies the slower kinetics of strain-induced martensitic transformation at higher strain rates.

Comparative Study on Microstructure and Properties of the Cr–Mn–Ni Stainless Steel and the Cr–Ni Stainless Steel

Comparative Study on Microstructure and Properties of the Cr–Mn–Ni Stainless Steel and the Cr–Ni Stainless Steel

A new morphology of retained austenite obtained by intercritical tempering of 13Cr-4Ni martensitic stainless steel

This research investigates the effect of various intercritical tempering in a 13Cr-4Ni stainless steel on the morphology, size, and γ-stabilizer elements enrichment of the retained austenite, i.e. the austenite retained at room temperature after intercritical heat treatments. A comparative microstructural and chemical composition study was conducted on AISI415 steel using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro hardness measurements for three tempering conditions giving the same retained austenite volume fraction (10%). These tempering conditions were: 620 °C 1 h, 600 °C 4 h, and 580 °C 10 h. The intercritical tempering at low temperature does not provide greater γ-stabilizer elements enrichment of the austenite. In this condition, the morphology of the formed retained austenite can be described as thin hollow particles with short lamellae shapes, which is significantly different than the morphology obtained at higher temperatures; the latter being characterised by thick and long lamellae. The retained austenite produced by tempering at low temperature is surrounded from both internal and external sides by martensite phases. Furthermore, it increases the austenite-martensite interfacial area that contributes to increase the barrier energy to martensitic transformation induced plasticity (TRIP).

Heat treatment optimization of 13Cr4Ni stainless alloy used as hydro turbine materials

In Nepal and the regions along with the Andes, sediment erosion is one of the major causes of the failure of hydro turbines. Every year lots of the components of turbines exposed to sediment-laden water got eroded resulting unexpected shutdown of the power plants. The cheapest method of repairing these eroded runners and other components of turbines are welding which may induce residual stress, embrittlement, and increase carbide content. Therefore, post welding heat treatment especially stress relieving annealing is always carried out to reduce the induced residual stresses, enhance strength and other mechanical properties as well as reduce the risk of cracking. As heating time is relative of low importance, great care should be taken during heat treatment to maintain the soaking time and cooling rate. Holding time for heat treatment will vary with the thickness of casting sections involved, but should be sufficiently long enough to heat all sections to a uniform temperature throughout. The cooling rate determines the material properties at room temperature and rapid cooling avoids the formation of chromium carbide. In this paper, the post-weld heat treatment used for repair and maintenance of turbines in Nepal is studied along with the investigation of heat treatment conditions on mechanical properties and microstructures of 13Cr4Ni stainless steel used as turbine materials to optimize the heat treatment itself. First of all relative analysis of five different heat treatment conditions with respect to ‘no heat treatment’ regarding mechanical properties i.e. toughness, hardness, and fatigue life was carried out. Heat treatments of the specimen were done in a muffle furnace. Hardness, toughness, and fatigue strength of the specimen using the Rockwell Hardness Test, Charpy Impact Test, and Fatigue Life Test were conducted respectively. Subsequently, microstructures of all the heat treatment conditions are closely examined using the metallurgical microscope. It was observed that holding time plays a great impact on improving mechanical properties.

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.

ATI 201L HP

Abstract ATI 201L HP is a 200-series, Cr-Mn-Ni austenitic stainless steel. It is comparable to the Cr-Ni stainless steel types 301, 304, and 304L in many respects, and can even provide some advantages versus the 18-8 grades in certain applications. Since it possess a very desirable combination of economy plus good mechanical properties and corrosion resistance, it has been used in a wide variety of consumer and transportation applications. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1346. Producer or source: ATI.

Effects of temperature and load during hot impression behavior of Cr-Ni stainless steel

Austenitic Stainless steels are majorly used because of their high resistance to aqueous corrosion and high temperature properties. Some major applications of stainless steels at high temperatures include engine and exhaust components in aircrafts, recuperators in steel mills, and pulverized coal injection lances for blast furnaces. In all the above said applications, the components are constantly subjected to loads and high temperatures. This makes the study of their creep behavior very important to decide the life of the component. Cr-Ni stainless steel was used as a starting material, and hot impression creep test was performed on cylindrical samples of 10 mm height and 15 mm diameter for a dwell time of 150 min at two different loads of 84 and 98 MPa and at two different temperatures 450 and 500 °C. The time vs. indentation depth was plotted, and creep rate was calculated in each case. It was observed that with an increase in time, creep rate increased in the primary creep region and remained almost constant in the secondary creep region irrespective of temperature and load. The indentation depth and creep rate increased with an increase in load and temperature.

Persistent homology on electron backscatter diffraction data in nano/ultrafine-grained 18Cr–8Ni stainless steel

Nano/ultrafine-grained 18Cr–8Ni stainless steel was produced by severe cold deformation followed by annealing. The effect of annealing temperature on the fraction of high-angle grain boundaries (HAGBs), the kernel average misorientation (KAM), and Schmid factor of steels are revealed through electron backscatter diffraction analysis. The analysis on HAGB, KAM values and Schmid factor frequency provide a mechanistic understanding of the impact of structure on mechanical properties, including hardness, strength, toughness and ductility. In this study, a novel application of persistent homology (PH) was employed to reduce the dimensionality of the information describing the complex processing-structure-property relationship. PH emphasizes the relationship between processing (annealing temperature), structure (distribution of the Schmid factor) and property (strength). Specifically, the PH formalism translates multidimensional data sets into clusters, distinguished by common PH features. In this analysis, two clusters emerge. First, at low annealing temperature, incomplete reversion of austenite in austenitic stainless steels results in materials with a greater fraction of grain boundaries, resulting in high strength and low ductility. Second, at high annealing temperature, fully reversed austenite results in lower, though still acceptable strength and superior ductility. The PH approach is applicable for identifying salient features in complex processing-structure-property relationships and is amenable to analysis of large data sets based on machine learning.

Dynamic recrystallization's role in strength-ductility trade-off in polycrystalline Fe–Cr–Ni stainless steels produced by laser powder bed fusion

Abstract The deformation mechanisms and reasons for excellent ductility in additively manufactured Fe–Cr–Ni stainless steels by laser powder bed fusion (L-PBF) were disclosed by an interrupted tensile test at room temperature, electron backscattered diffraction, and transmission electron microscopy. The results showed dislocation (DL) slip starts at low strain values, resulting in a rearrangement of DLs and reorientation of low angle grain boundaries along with shear bands. At higher strain values, deformation twins intersect with other twins, DLs, stacking faults, and grain boundaries. In addition to planar slip and twining-induced plasticity (TWIP), dynamic recrystallization (DRX) was observed during deformation due to the formation of a high density of DLs during L-PBF. Different deformation and DRX mechanisms are disclosed in detail, including their origin, sequences, and interplay. The results presented in this paper opens a new operation window for the other types of TWIP steels, such as medium and high Mn steels to be manufactured by the L-PBF to maximize their energy impact.

Post-treatment of additively manufactured Fe–Cr–Ni stainless steels by high pressure torsion: TRIP effect

High pressure torsion (HPT) at room temperature was used for post-treatment of additively manufactured Fe–Cr–Ni stainless steel with 12.9 wt % Ni as a very strong austenite stabilizer. The results showed that HPT caused a considerable increase in nanohardness of the additively manufactured samples. In contrast with thermodynamic equilibrium-state modeling, a phase transformation from FCC to HCP structure occurred, leading to the formation of ε-martensite during HPT on high angle boundaries, low angle boundaries, and dislocation cells with no detection of deformation twins. It was demonstrated that the combination of additive manufacturing thanks to the high density of dislocations after solidification and HPT process expands the opportunities of both methods to control deformation mechanisms in stainless steels leading to different phase and microstructural features. Thus, the outcome of this study provides a fundamental basis to design advanced structural materials.

ATI 201 HP

Abstract ATI 201 HP is a 200-series, Cr-Mn-Ni austenitic stainless steel. It is comparable to the Cr-Ni stainless steel types 301, 304, and 304L in many respects, and can even provide some advantages over the 18-8 grades in certain applications. Because it possess a very desirable combination of economy plus good mechanical properties and corrosion resistance, it has been used in a wide variety of consumer and transportation applications. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1332. Producer or source: ATI.

Effect of calcium treatment on inclusions in Si-Mn-killed 304 stainless steels

In the current study, two plant trials for the ladle refining process without and with the calcium treatment were compared to investigate the effect of the calcium treatment on the inclusion deformation in Si-Mn-killed 18Cr-8Ni stainless steels. The total aluminum rose from 10ppm to 25ppm due to the slag and steel reaction, increasing the Al2O3 in inclusions during the ladle refining process. Without the calcium treatment, inclusions changed from Al2O3-SiO2-MnO-CaO with about 20% MnO to Al2O3-MgO-SiO2-CaO with about 10% MnO. The calcium treatment obviously lowered Al2O3 and MnO in inclusions and led to the formation of CaO-rich inclusions. Inclusions changed from Al2O3-SiO2-CaO-MnO to SiO2-CaO-Al2O3 after the calcium treatment of Si-Mn-killed stainless steels. Calculations showed that the calcium treatment of 15−25ppm lowered the melting temperature of inclusions but further additions increased the melting temperature. Calculations also showed that calcium addition lowered Young’s modulus. Calcium treatment was an effective method to improve the deformability of inclusions in Si-Mn-killed stainless steel during the cold rolling process.

Stabilization of austenitic structure in transition zone of “austenitic stainless steel/NiCr alloy” joint fabricated by wire-feed electron beam melting

The gradient material “stainless steel/NiCr alloy” has been designed using the additive manufacturing method – double wire-feed electron-beam melting. The effect of gradual addition of Ni-based alloy on phase transformation and microstructure in additively-fabricated “stainless steel/NiCr alloy” joint has been revealed. Despite the abrupt change in wire composition during the fabrication of the joint, the wide transition zone is formed between two parts of the additively-manufactured billet: γ-austenitic matrix and dendritic δ-ferrite in steel part gradually passing into Fe-based austenite, then into Ni-based austenite, and, finally, into γ-(Ni,Cr) austenite with cellular-shape dendrites in NiCr part. The steel-based transition zone of the as-built joint possesses pure austenitic structure stabilized by nickel in comparison with two-phase dendritic microstructure typical for additively-manufactured CrNi stainless steel. The increased microhardness (2.3–2.4 GPa) corresponds to stable austenitic steel structure of the joint.

Temperature-dependent evolution of oxide inclusions during heat treatment of stainless steel with yttrium addition

The evolution of oxide inclusions during isothermal heating of 18Cr-8Ni stainless steel with yttrium addition at temperatures of 1273 to 1573 K was investigated systematically. Homogeneous spherical Al-Y-Si(-Mn-Cr) oxide inclusions were observed in as-cast steel. After heating, most of the homogeneous inclusions were transformed into heterogeneous inclusions with Y-rich and Al-rich parts, even though some homogeneous oxide particles were still observed at 1273 and 1573 K. With the increase in heating temperature, more large-sized inclusions were formed. The shape of the inclusions also changed from spherical to irregular. The maximum transformation temperature of inclusions was determined to be 1373 K. The evolution mechanism of inclusions during heating was proposed to be the combined effect of the (i) internal transformation of inclusions due to the crystallization of glassy oxide and (ii) interfacial reaction between inclusions and steel matrix. Meanwhile, the internal transformation of inclusions was considered to be the main factor at heating temperatures less than 1473 K.