Ni-Cr Steel Research Articles

Cyclic deformation behavior of austenitic Cr–Ni-steels in the VHCF regime: Part II – Microstructure-sensitive simulation

In Part I – Experimental study, the cyclic deformation behavior of two austenitic stainless steel grades (AISI 304, AISI 316 L) were experimentally investigated at low stress amplitudes in the very high cycle fatigue (VHCF) regime. The observations indicate that during VHCF the metastable austenitic stainless steel (304 grade) performs a pronounced localization of plastic deformation in shear bands followed by a deformation-induced martensitic phase transformation. The 316 grade undergoes only a very limited local plastic deformation in shear bands with almost no phase transformation. Consequently, both materials exhibit distinctly different cyclic softening and hardening characteristics during VHCF. In order to provide a more detailed knowledge about the individual deformation mechanisms and their effect on the cyclic softening and hardening behavior the experimental study is extended by microstructure-sensitive modeling and simulation. Two-dimensional (2-D) microstructures consisting of several grains are represented using the boundary element method and plastic deformation within the microstructure is considered by a mechanism-based approach. Specific mechanisms of cyclic plastic deformation in shear bands and deformation-induced martensitic phase transformation – as documented by experimental results and based on well-known model approaches – are defined and implemented into the simulation. The fatigue behavior at low stress amplitudes observed in experiments can be well represented in simulations so that the underlying model helps to understand the cyclic deformation behavior of austenitic stainless steels at low stress amplitudes in the regime of VHCF strength. In a comparative study based on the resonant behavior the effect of certain deformation mechanisms on the global cyclic softening and hardening characteristics is pointed out for both materials.

Grain Refinement in Lightweight Advanced High-Strength Steel Castings

A method has been developed for producing grain refinement in lightweight high manganese and aluminum steels. Many researchers have recently reported that cerium addition produces cerium oxides that serve as heterogeneous nucleation sites for austenite during solidification of Cr–Ni steels. Until now, the use of cerium as a grain refining agent during casting of fully austenitic Fe–Mn–Al–C steels has not been evaluated. In the following study, a Ce-based inoculant in levels of 0, 0.05, and 0.1 wt% Ce was added during the tap and also in-mold to determine the effect of an increasing amount of Ce on reduction in the primary austenite grain size in a Fe-30.5 % Mn-7.55 % Al-0.76 % Si-1.11 % C-0.51 % Mo steel. Addition of 0.05 % Ce during the tap produced only a slight reduction in the grain size. However, in-mold inoculation with 0.1 % Ce produced an order of magnitude reduction in the grain size when compared to the base heat without Ce addition, from 10 to 12 mm to an average of 100 μm. Cerium is very reactive in the melt and readily combines with sulfur and oxygen as well as any residual phosphorus. Inclusion analysis showed that the inclusions in the 0.05 % Ce steel were mainly cerium sulfides while inclusions in the 0.1 % Ce steel were mainly complex cerium oxides, sulfides, and phosphides. Adding cerium greatly increased the nonmetallic inclusion density from 183 to 571 inclusions/mm2 and generally decreased the solution-treated notch toughness from 295 to 141 J. In the as-cast condition and for steels aged for 10 h at 530 °C, toughness slightly increased with 0.05 % Ce addition and this is likely the result of the cerium removal of phosphorus from the melt during solidification. Toughness decreased with increasing volume fraction of inclusions and decreasing inclusion spacing regardless of the grain refining effect. It is therefore essential to eliminate sulfur and phosphorus from the melt as much as possible so that cerium will not form sulfides and complex phosphides instead of effective oxide nuclei. This may be achieved with more vigorous calcium addition for desulfurization prior to inoculation with cerium and with the use of nonphosphate bonded refractories to eliminate phosphorus pickup.

THE DEVELOPMENT OF NEW CASTING ALLOYS INTENDED FOR OPERATION UNDER EXTREME CONDITIONS AND SOME TECHNIQUES OF MAKING CASTINGS FROM THEM

The article studies new heat-resistant and wear resistant materials for operation under extreme conditions, especially in the power industry. The methods that improve the quality of a metal in metal castings through the influence of alloying elements on its structure and properties have been considered. These methods are very effective for reducing the tendency of a metal to form a coarse–grained structure. The paper describes optimal techniques for melting special alloys in induction and electric furnaces. A set of rules for the selection of a melting temperature before pouring a metal into the casting forms depending on the dimensions, wall thickness, geometry of castings have been determined. The behavior of new alloys under the conditions of high temperatures, aggressive environments has been studied. It has been established that heat–resistant Cr–Al steels exhibit high heat resistance and wear resistance properties; they 6–8 times surpass Cr–Ni steels in oxidation resistance. The proposed Cr–Mn cast iron processed in an integrated manner with REM (rare earth metals) and Ti is superior to a basic cast iron in conditions of a heavy wear. Numerous industrial trials confirm the usefulness of recommended new casting materials for use under extreme conditions.

Effects of Various Post-Weld Heat Treatments on Austenite and Carbide Formation in a 13Cr4Ni Steel Multipass Weld

Multipass welding procedures are common methods for 13Cr4Ni steels' fabrication and repairs. Compared to a single-pass weld procedure, the weld microstructure in a multipass weld is more heterogeneous due to the complex local thermal cycles imposed by adjacent weld passes. Furthermore, the final microstructure and mechanical properties of these steels are very sensitive to their thermal history which increases the microstructure heterogeneities. Thus, post-weld heat treatments are performed to reduce heterogeneities and produce a relatively homogenous weld. It has been found that the best option to improve mechanical properties of 13Cr4Ni steels is forming a “room temperature stable austenite” phase by heat treatments. This study focuses on the effects of these post-weld heat treatments on the austenite phase and carbide formations and the related evolutions of microhardness distribution. The study shows that nanometer-size carbides form at martensite lath interfaces and sub-block boundaries, and then at higher temperatures austenite lamellae appear at these locations. Results also show that the highest percentage of stable austenite achievable by a single-stage tempering was obtained at 610 °C. When the heat treatment temperature is lower than 610 °C, longer holding time produces softer steel while longer heat treatments at temperatures higher than 610 °C, produces harder steel. Still, double-stage heat treatments are more effective and produce the highest percentage of austenite and the lowest hardness of all heat treatments.

Microestructura y resistencia adhesivo-cohesiva de recubrimientos de níquel, carburo de tungsteno y óxido de cromo aplicados por aspersión térmica

Se aplicaron cuatro recubrimientos por aspersión térmica por combustión con material de aporte en polvo: dos aleaciones ricas en níquel, un recubrimiento de óxido de cromo y un recubrimiento rico en carburos de tungsteno y partículas de Ni-Cr, sobre acero inoxidable ASTM A743 grado CA6NM. Se estudió la microestructura de los depósitos y la variación en la resistencia adhesivo-cohesiva de las capas de acuerdo con la norma ASTM C633, en función de los parámetros de preparación de la superficie (temperatura de precalentamiento y rugosidad superficial). La caracterización microestructural fue realizada utilizando difracción de rayos X (DRX) y microscopía óptica (MO) y electrónica de barrido (MEB), las mediciones de dureza fueron realizadas de acuerdo con la norma ASTM E384. Los ensayos de resistencia adhesivo-cohesiva fueron realizados bajo norma ASTM C633. Los recubrimientos presentaron microestructuras con niveles de defectos del orden de 8% para capas base y entre 15 y 30% para capas cerámicas, las cuales son aceptables para la técnica empleada. En todos los casos se obtuvieron espesores de capas homogéneos del orden de 0.5 mm. La resistencia adhesivo-cohesiva alcanzó entre 10 y 19 MPa para la mayoría de las capas. Los valores alcanzados de adherencia fueron satisfactorios en la mayoría de los casos y, en términos generales, la resistencia adhesivo-cohesiva incrementó significativamente (mayor al 25%) al modificar los parámetros de preparación de las superficies especialmente para el recubrimiento WC/Co-Ni.

Crevice Corrosion Resistance and Structure of Passive Film on Fe–Mn–Si–Cr–Ni Steel

Crevice Corrosion Resistance and Structure of Passive Film on Fe–Mn–Si–Cr–Ni Steel

Effect of neutron irradiation on the microstructure and the mechanical and corrosion properties of the ultrafine-grained stainless Cr–Ni steel

It has been revealed that the neutron irradiation of ultrafine-grained (UFG) 08Kh18N10T steel after severe plastic deformation (SPD) does not lead to the appearance of defects of radiation origin up to a fluence of 2 × 1020 n/cm2 (~0.05 dpa) and that the strength properties of the material are retained after irradiation. At the same time, this irradiation reduces the corrosion resistance of the steel in a chlorine-containing medium, especially after heating at 550°C with a holding for 1 h after SPD.

Multiscale thermodynamic analysis on hydrogen-induced intergranular cracking in an alloy steel with segregated solutes

Abstract A multiscale analysis has been conducted on hydrogen-induced intergranular cracking at ambient temperature in medium strength (840 MPa) Ni-Cr steel with antimony, tin, and phosphorous segregation. Combining first-principles calculations and fracture mechanics experiments, a multiscale relationship between threshold stress intensity factor (K th) and cohesive energy of grain boundary (the ideal work of interfacial separation, 2γ int) was revealed. The K th was found to decrease rapidly under a certain threshold of 2γ int, where the 2γ int decreases mainly by mobile hydrogen segregation on fracture surfaces. This segregation is considered to arise during formation of the fracture surfaces under thermodynamic equilibrium in slow crack growth. The resulting strong decohesion probably makes it difficult to emit dislocations at the microcrack tip region, leading to a large reduction in stress intensity factor. Our analysis based on this mobile hydrogen decohesion demonstrates that the K th decreases dramatically within a low and narrow range of hydrogen content in iron lattice in high-strength steels.

Evaluation of Combined Quantification of Cr-Ni Steel using EDS and WDS

Evaluation of Combined Quantification of Cr-Ni Steel using EDS and WDS

Corrosion behaviors of steels under supercritical CO2 conditions

AbstractCarbon dioxide (CO2) corrosion at low partial pressure has been widely recognized, but research on supercritical CO2 (SC CO2) corrosion is very limited. By far, investigations on steel corrosion under SC CO2 conditions have mainly focused on the corrosion rate, structure, morphology, and composition of the corrosion scales as well as the electrochemical behaviors. It was found in aqueous SC CO2 environment, that the corrosion rate of carbon steel was very high, and even stainless steels (13Cr and high-alloy CrNi steels) were subjected to some corrosion. Inhibitor could reduce the corrosion rate of carbon steels and stainless steels, but none of the tested inhibitors could reduce the corrosion rate of carbon steel to an acceptable value. Impurities such as O2, SO2, and NO2 and their mixtures in SC CO2 increased the corrosion rate of carbon steel. However, the existing studies so far were very limited on the corrosion mechanism of steels in SC CO2 conditions. Thus, this paper first reviews the finding on the corrosion behaviors of steels under SC CO2 conditions, points out the shortcomings in the present investigations and finally looks forward to the research prospects on SC CO2 corrosion.

Factors influencing the color laser marking

<p>In recent years, conventional techniques of marking on some parts of different work pieces, as well as on packages with color printing are increasingly being displaced by laser color marking. Colored marking of stainless steel could be realized by the process annealing. The advantages offered by the new technology are in greater accuracy, speed, flexibility and high amount of recorded information per unit area (bar and matrix codes).</p><p>In the report are discussed and analyzed the factors influencing on the specific to the process of laser color marking at the products of CrNi steel. The study was conducted using a commercially available industrial pulsed fiber laser. Presents the results of the measurements and analysis of the influence of laser process parameters on the color contrasting obtained. In this case, the relevant parameter, the field of high frequencies and low pulse energy were examined. The present thesis describes studies a properties of the laser radiation, such as, pulse width, average power, the intensity and beam diameter.<strong></strong></p>

Corrosion Behavior of High Performance Offshore Platform Steel with Chromium and Nickel Addition in the Environment Containing Chloride Ions

The characterization of corrosion products formed on a high performance offshore platform steel in the environment containing chloride ions has been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA) and electrochemical impedance spectroscopy (EIS). The results reveal that the corrosion process can be divided into the initial stage and the later stage. The main constituents of rust layers are α-FeOOH, β-FeOOH, γ-FeOOH, Fe3O4 and large amounts of amorphous compounds. With increasing corrosion time, the mass fraction of α-FeOOH and Fe3O4 increased, while that of γ-FeOOH and β-FeOOH changed slightly. The enrichment of Cr and Ni at the inner/outer interface, especially the side of inner rust, can be observed in the later corrosion stage of Cr-Ni steel, which can promote the formation of compact inner rust layer, impeding the transmission of corrosion mediums and slowing down the electrochemical reaction process.

Fatigue Crack Deflection-Induced Retardation Based on the Principle of the Minimum Potential Energy

Fatigue crack growth retardation due to tensile overload-induced crack deflection is analyzed. The minimum potential energy principle is implemented to estimate the crack geometry change during the transition from the mode I to mode I+II. An effective stress intensity factor amplitude is derived to approximate the subsequent reduction of the fatigue crack growth rate due to an overload. The proposed model is applied to certain loading cases of CrNi steel, yielding encouraging results.

Crack propagation behavior of solution annealed austenitic high interstitial steels

Austenitic stainless steels provide a beneficial combination of chemical and mechanical properties and have been used in a wide field of applications for over 100years. Further improvement of the chemical and mechanical properties was achieved by alloying nitrogen. But the solubility of N within the melt is limited and can be increased in substituting Ni by Mn and melting under increased pressure. In order to avoid melting under pressure and decrease production costs, a part of N can also be substituted by C. This leads to austenitic high interstitial steels (AHIS). Within the solution annealed state strength and ductility of AHIS is comparable or even higher of those of AHNS and can be further improved by cold working. Unfortunately the endurance limit does not follow this trend as it is known from cold-worked austenitic CrNi steels. This is due to the differences of the slip behavior which is governed by the stacking fault energy as well as other near field effects. Construction components operating under cyclic loads over long periods of time cannot be considered being free of voids or even cracks. Thus the crack propagation behavior is of strong interest as well. This contribution presents the tensile, fatigue, crack propagation and fracture toughness properties of AHNS and AHIS in comparison to those of CrNi-steels. The differences are discussed in relation to microstructural characteristic as well as their alterations under cyclic loading.

Determination of retained austenite content in Fe–Cr–Ni weld metal

Several techniques, including dilatometry, X-ray diffraction, electron backscattering diffraction and magnetisation measurement, were applied and compared in order to reliably determine the retained austenite content of Fe–Cr–Ni steel weld metal. In this work, based on a proposed novel numeric solution for martensite transformation kinetics, it was found that the dilatometric method presented consistent results along with the magnetisation method in the quantification of mechanically unstable or stable retained austenite. By contrast, the X-ray diffraction method was inaccurate and time-consuming for the measurement of mechanically unstable retained austenite. However, the X-ray diffraction method was relatively successful when the retained austenite was mechanically stable. In addition, the magnetisation method seemed to be the only reliable way to detect small amounts (less than 5 vol.-%) of retained austenite in Fe–Cr–Ni weld metal.

Microstructure Characterization of Single and Multipass 13Cr4Ni Steel Welded Joints

13Cr4Ni martensitic stainless steels are frequently used in hydroelectric industries. Considering the size and geometry of the turbine runners manufactured in hydroelectric industries, multipass welding procedures are common methods for fabrication and repair. In this research, the microstructures and crystallographic textures of single-pass and double-pass welds have been studied as a first approach to understand a multipass weld. The highest hardness has been measured in the high-temperature heat-affected zone (HAZ) inside the base metal. Similarly, it has been found that the heat of the second pass increases the hardness of the previous pass and produces a finer martensite microstructure. In areas of the HAZ, 3–6 mm from the fusion line, a tempering-like effect is reported; traces of austenite have also been found in these areas documenting the complexity of the microstructure found in the multipass welds.

Understanding Fatigue Crack Growth Behavior at Low Frequencies for a Mn–Ni–Cr Steel in 3.5 % NaCl Solution Under Controlled Cathodic Potential

Abstract Fatigue crack growth behavior at low loading frequencies for a Mn–Ni–Cr steel immersed in 3.5 % NaCl solution, with and without cathodic polarization, is investigated and presented in this paper. Frequency shedding method is used to estimate fatigue crack growth rate over a range of frequencies between 0.01 and 5 Hz at a constant stress intensity factor range of 15 MPa √m. The effectiveness of cathodic potential of −900 mV SCE in containing corrosion contribution to crack growth is estimated by comparing with published data on fatigue crack growth rate in lab air and 3.5 % NaCl solution without cathodic polarization. It is noted that there are three regions of crack growth rate as a function of applied frequencies when the data is plotted in log–log scale: linear crack growth rate, plateau crack growth rate, and high crack growth rate. The crack growth rate of steel in 3.5 % NaCl solution at 15 MPa √m is scanned for different cathodic potentials between −760 mV SCE and 1150 mV SCE at 0.01 and 0.1 Hz. The potentials at which the crack growth rates are the maximum and the minimum are found to be −760 and −950 mV, respectively. The optimum cathodic protection potential for the minimum corrosion fatigue crack growth rate ranges between −900 and −950 mV. This optimum potential for the minimum corrosion crack growth rate is more negative than the cathodic potential required for restraining the corrosion effects on fatigue strength of steel to normal ambient air behavior.

Impact Strength of Austenitic and Ferritic-Austenitic Cr-Ni Stainless Cast Steel in -40 and +20°C Temperature

Abstract Studies described in this paper relate to common grades of cast corrosion resistant Cr-Ni steel with different matrix. The test materials were subjected to heat treatment, which consisted in the solution annealing at 1060°C followed by cooling in water. The conducted investigations, besides the microstructural characteristics of selected cast steel grades, included the evaluation of hardness, toughness (at a temperature of -40 and +20oC) and type of fracture obtained after breaking the specimens on a Charpy impact testing machine. Based on the results of the measured volume fraction of ferrite, it has been found that the content of this phase in cast austenitic steel is 1.9%, while in the two-phase ferritic-austenitic grades it ranges from 50 to 58%. It has been demonstrated that within the scope of conducted studies, the cast steel of an austenitic structure is characterised by higher impact strength than the two-phase ferritic-austenitic (F-A) grade. The changing appearance of the fractures of the specimens reflected the impact strength values obtained in the tested materials. Fractures of the cast austenitic Cr-Ni steel obtained in these studies were of a ductile character, while fractures of the cast ferritic-austenitic grade were mostly of a mixed character with the predominance of brittle phase and well visible cleavage planes.

Study Accompanying Phenomenas at the Cutting Zone during Drilling Austenitic Stainless Steel X02Cr20Ni8TiMo

The The basic hypothesis of this article focuses on the study of accompanying phenomenas in the cutting zone of the stainless steels, with regard to the elimination of occurrence of poor-quality holes when drilling into new austenitic ELC (Extra Low Carbon) stainless steels. The problem of drilling holes with diameter D=1 to 9 mm resides in the fact that 20 to 28 % of these holes do not comply with prescribed requested requirements. The result of the deformation is very often the unforeseen destruction of the cutting tools; therefore their operational tool life is reduced. This article presents the results of experiments focusing on the study of the plastic deformation of the chips, at drilling with diameter d=5 mm when drilling into a new austenitic ELC stainless steels. This study also includes an analysis of accompanying phenomena in the cutting zone by measuring some selected parameters. The results of the experiments were compared with Cr18Ni8 steel and then verified when drilling holes into specific products.

Effect of low cyclic frequency on fatigue crack growth behavior of a Mn–Ni–Cr steel in air and 3.5% NaCl solution

Corrosion fatigue phenomenon involves the time dependent corrosion and cycle dependent fatigue loading. The intention of this study is to develop a test method to evaluate the crack growth rate of a material in a corrosive environment at low frequencies. The effect of cyclic frequency on crack growth rate of a Mn–Ni–Cr steel in lab air and 3.5% NaCl solution is evaluated using frequency shedding method where the cyclic frequency is decreased exponentially as a function of crack length at a constant stress intensity factor range. A Zn sacrificial anode coupled to the specimen slows down the rate of crack growth.