High-chromium Alloys Research Articles

Corrosion Behavior of High-Chromium Alloys in Molten LiCl–KCl Eutectic

Corrosion Behavior of High-Chromium Alloys in Molten LiCl–KCl Eutectic

ОЦІНКА НАПРУЖЕНОГО СТАНУ РОБОЧОГО ШАРУ ВАЛКІВ КОЕРЦИТИМЕТРИЧНИМ ЕКСПРЕС-МЕТОДОМ

The purpose of the work is the problem of researching the influence of chemical composition and structure on the indicators of operational stability of centrifugal two-layer rolling rolls made of high chromium cast iron by the coercimetric express method. In order to ensure the achievement of this goal, the following tasks were set and solved: conducting an analysis of the causes of the destruction of the surface layer of rolls; building a mathematical model for studying the influence of the chemical composition and structure of cast iron on the level of hardness and coercive force; using the coercimetric method to analyze the quality of rolled rolls. Conclusions. Forecasting the behavior of the rolls during operation is inextricably linked to the analysis of the main factors on which the level of properties and operational stability of the working layer depend. The properties of high-chromium alloys are closely related to the type of phases formed and their ratio. The amount of residual austenite and martensite in the structure of the alloy has the greatest influence on the properties of the alloy (in the studied interval of changes in the proportion of phases). The operational layer of two-layer high-chromium rolls is characterized by a high level of residual stresses. Exceeding the permissible level of stresses or their unfavorable distribution can cause premature destruction during the operation of the roll. With the help of the coercimetric express method, it is possible to solve a fairly wide range of tasks of quality control of rolls, related to the determination of the level and distribution of residual stresses in the working layer of the rolls. This is because the intensity of the process of formation of thermal cracks under conditions of thermo-cyclic loading largely depends on the level of residual compressive stresses. Too high a level of stresses or their unfavorable distribution can cause premature destruction of the working layer of the roll, because the typical type of destruction due to an unbalanced distribution of stresses is cracking. A local increase in the level of coercive force can be the basis of the prediction of crack formation.

Electrochemical dealloying of a high-chromium alloy at oxygen evolution potential

We first investigate the electrochemical dealloying effect and mechanism of a high-chromium alloy in alkaline NaNO3 solution at oxygen evolution potential.

Studies on the Corrosion Resistance of High Chromium Alloy Steels

Abstract The paper studies the corrosion resistance of 40Cr130 in different structural states. The material is thus characterized in the annealed, normalized, quenched, tempered state and, respectively, following a thermochemical treatment. Good corrosion resistance was found in all states, and substantial improvements were noted following the thermochemical nitriding treatment.

О МЕХАНИЗМАХ ОБРАЗОВАНИЯ НАНОСТРУКТУРНЫХ ЭЛЕКТРОЛИТИЧЕСКИХ ПОКРЫТИЙ Fe-Ni, Co-Mn, Ni-Cr С ФУНКЦИОНАЛЬНЫМИ СВОЙСТВАМИ

The evolution of modern industry is impossible without the development of new materials and technologies. Nanostructured coatings, in particular electrolytic coatings, are among the most demanded in mechanical engineering. The purpose of this work was to study the different mechanisms of obtaining Fe-Ni, CoMn, Ni-Cr galvanic alloys and their relationship with the specified universal physical and mechanical properties. Fe-Ni alloy is characterized by high microhardness and corrosion resistance in sea water, low cold brittleness; Co-Mn – by a specified phase composition (α-Co >> α-Mn, amorphous and metastable phase Co(OH)2); Ni-Cr – by high coating microhardness, specified phase composition. The main methods of production: high-frequency alternating current for Fe-Ni and Co-Mn alloys; introduction of a special additive (carbamide or H-acid) for Ni-Cr alloy. The main mechanisms are: Fe-Ni due to phase transition α-Fe ε-Fe; Co-Mn by means of high-frequency alternating current and carbamide addition, providing a specified phase composition; Ni-Cr by means of stationary method of addition of H-acid (high-chromium alloy of 68 mass percent of Cr) and carbamide (low-chromium alloy of 25 mass percent of Cr). Recommended uses for electroplating: Fe-Ni – for protection of oil and gas production equipment in the Arctic; CoMn – in modulation systems and as a nanocatalyst in the Fischer-Tropsch synthesis reaction; Ni-Cr – for corrosion-resistant protective coatings in petrochemistry and for resistive elements.

Development of a hardbanding material for drill pipes based on high-manganese steel reinforced with complex carbides

In the present study the new “casing-friendly” hardbanding alloy based on high-manganese steel reinforced with complex carbide particles was developed by combining thermodynamic modelling within the CALPHAD approach and first-principles calculations. The alloy, deposited by flux cored arc welding on a steel substrate, has a composite structure consisting of manganese-austenite with the ability to work hardening, fine (up to 5 µm) inclusions of the multicomponent carbide (Nb, Ti, Mo, V) and C the thin layers of (Mo,V)C at the austenite grain boundaries. The comparative wear tests carried out with commercially available hardfacing materials of the Fe-W-C and Fe-Cr-C systems showed that the proposed alloy has the best combination of properties preventing the wear of the drill casing, while its abrasion resistance as well as wear resistance in sliding friction conditions by steel counterbody is close to hypereutectic high chromium alloys. The microhardness tests performed on deformed specimen areas after the friction tests show the presence of a significant hardness gradient in the range of 800-450 HV at a distance of about 300 µm when moving perpendicularly away from the zone of friction contact. During the microscopic observation of the layer deposited with the developed alloy and the interfaces between the deposit and the base steel no cracks, pores delamination were detected indicating a strong metallurgical bonding. The hardbanding process was performed for drill pipe joints with the worn Fe-based high chromium alloy hardbanding after exploitation, which allows the drill pipe to be reused with the same durability.

Effect of Lost-Foam Casting Process on Properties of Spiral Blade

The wear failure mode of a paver spiral blade was simulated by EDEM software. High-manganese steel, medium chromium alloy steel, and high chromium alloy steel were selected as matrix materials; SiC particles and WC particles were selected as surface particle reinforcement materials; and the spiral blade was prepared by the EPC process. The performance and wear mechanism of the spiral blade prepared by EPC were analyzed by microstructure, hardness, impact, pin disk, erosion wear test, and wear morphology. Modeling with EDEM software and applying the discrete element analysis method of particle system could simulate the actual working situation of the spiral blade of the paver well. Through the simulation, it was found that the wear amount of the spiral blade of the paver from the spiral shaft to the outside of the spiral blade was increasing. SiC and WC particle-reinforced wear-resistant coatings were prepared on the surfaces of high-manganese steel, medium chromium alloy steel, and high chromium alloy steel by the EPC method. The wear-resistant coating of high-manganese steel was 5.05 mm, the coating of medium chromium alloy steel was 5.98 mm, and the coating of high chromium alloy steel was 7.02 mm. The higher the chromium content, the better the diffusion with SiC and WC particles. In the process of the wear test, the soft phase in the coating was first worn away and concaved, and the hard phase protruded to bear the wear. After wear, it was found that the sample with high chromium alloy steel as matrix and SiC and WC particles as wear-resistant coating had the best wear resistance.

Investigation of the influence of the parameters of selective laser fusion of metal powders and cold isostatic pressing on the structure and mechanical properties of a nickel-based heat-resistant alloy

The influence of the parameters of selective laser melting (SLM) of metal powders and cold isostatic pressing (CIP) of samples from a high-chromium heat-resistant alloy on the microstructure of the processed alloy, the size and number of formed pores is investigated. The use of HIP for SLM alloys makes it possible to reduce the number and size of pores. The strengthening effect of deformation (increase in hardness) at normal temperature is established. Keywords: selective laser melting, additive manufacturing, track, pores, cold isostatic pressing, mechanical properties, microstructure. remshev@mail.ru, Galina@mail.ru, grisha.afimin@mail.ru, gulyarenko@mail.ru

КИНЕТИКА ПРЕВРАЩЕНИЙ АУСТЕНИТА В ВЫСОКОХРОМИСТЫХ СПЛАВАХ ЖЕЛЕЗА ПРИ НЕПРЕРЫВНОМ ОХЛАЖДЕНИИ

The work develops the models of two principal diffusional transformations in high-chromium iron alloys on continuous cooling, viz. precipitation of secondary carbides (Cr, Fe)7C3 from aus-tenite and pearlitic decomposition of the latter. Literature experimental data for alloys of various composi-tion were used for analysis. Chemical composition of austenite by the end of austenitizing holding was de-termined using previously developed models, and then the exact expression describing isothermal precipita-tion of carbides from supercooled austenite was found based on the general equation following from the ki-netic theory of phase transformations. It was found out that the time exponent n in that expression equals to 3/2, which corresponds to the case of preferred precipitation of very fine carbide particles. For transition to the continuous cooling condition the C-curve of isothermal carbide precipitation was approximated by a square parabola. This permitted to find the relation between cooling rate and the amount of precipitated car-bide phase by means of the Scheil–Steinberg integral. Further comparison with the experimentally observed increase of martensitic point allowed to determine the numerical parameters of the model and their depend-ence on carbide composition of a given alloy. For the pearlitic transformation, a previously developed mod-el describing the parameters of temperature dependence of the Avrami equation coefficients on austenite composition was employed. That model was generalized for the continuous cooling case in the same was as above. As a result, CCT diagrams of diffusional austenite transformations in high-chromium alloys were calculated, that in general corresponded well the experimental ones.

Studies on the Wear Behaviour of High Chromium Alloy Steels

Studies on the Wear Behaviour of High Chromium Alloy Steels

STUDY OF HIGH CHROME WHITE SHEEP DEPENDENCE ON CARBONE QUANTITY AND ABRAZIVE CONDITIONS

In addition to studying the properties of abrasive corrosion-resistant alloys, the article considers it important to study the abrasive corrosion-based effect of abrasive corrosion resistance of high-chromium white cast iron on the amount of carbon and the dependence of abrasive particles on carbide and particle dependence. At the same time, the spread of white cast iron with 1.5 - 30% Mo is higher, which makes it easier to spread the processed martensite cast iron. Açar sözlər: oil drilling equipment high chromium alloy, abrasive particle, diffusion resistance, hardness, erosion coefficient, abrasive conditions.

Effects of Cooling Parameter and Cryogenic Treatment on Microstructure and Fracture Toughness of AISI D2 Tool Steel

The application of cryogenic treatments is gradually increasing in tool steels. In this sense, these heat treatments can modify the mechanical properties of high chromium alloy steels. However, the influence of the cooling parameter (during quenching) is often neglected. This investigation aims at evaluating the effects of cooling parameter and cryogenic treatment on microstructure and fracture toughness of AISI D2 tool steel. The cooling parameter (λ) was defined as the cooling time from 800 to 500 °C divided by 100. During quenching, different cooling parameters (λ1 = 2.8 and λ2 = 1.8) were employed, and the samples were tempered three times or, besides, cryogenically treated by a single tempering. Later, the samples were evaluated through phase analyses and their proportions, sizes, and distribution of carbides by optical and scanning electronic microscopy, hardness measurements, x-ray diffraction, and fracture toughness tests. For the λ2 cooling parameter followed by cryogenic treatment, the results presented an increase of 51% over the initial condition of secondary carbides. However, the higher hardness values were found in the λ1 cooling parameter followed by cryogenic treatment. In the fracture toughness evaluation, a reduction of 8% in KIC was observed for samples with cryogenic cycles compared to the samples without it.

Electrochemical Mechanism of Microporous Autocatalytic Surface Formation on a High-Chromium Alloy in an Alkaline Solution

Electrochemical Mechanism of Microporous Autocatalytic Surface Formation on a High-Chromium Alloy in an Alkaline Solution

In situ formation of molybdenum borides at hardfacing by arc welding with flux-cored wires containing a reaction mixture of B4C/Mo

This paper reports a study into the formation of the phase composition, structure, and properties of arc welding coatings by the flux-cored electrode materials from the Fe-Mo-B-C system. The welding alloys were applied using the flux-cored arc welding (FCAW) electrodes, which consisted of a shell made from the low-carbon steel filled with a reaction powder mixture that contained boron carbide and molybdenum in a ratio of 1:1. The calculation of the phase composition of alloys that correspond to the surfaced layers by a CALPHAD method using the Thermo-Calc OpenCalphad software shows that under the equilibrium conditions the boride phases of molybdenum and ferrite cannot co-exist. The main phase of such alloys is a FeMo 2 B 2 compound, which forms the eutectics with austenite. Given that the eutectic structures with borides are characterized by high brittleness, the introduction of components was conducted in the form of a reaction mixture in order to obtain the in situ formed boride phases in the form of separate structural components. Analysis of the results of studying the microstructure and phase composition of coatings reveals that they consist of three main structural components: the eutectic (FeMo 2 B 2 +ferrite) and the grains of molybdenum tetraboride MoB 4 . Thus, under the conditions of arc welding using the reaction mixture, an irregular structure is formed, which is favorable in terms of ensuring wear resistance due to the high microhardness of MoB 4 >27 GPa. The hardness of the coatings obtained is at the level of 63–65 HRC, and the wear resistance is higher compared to standard high-chromium alloys (grades Т620 and Т590) by 2‒2.5 times. This makes it possible to recommend the coating of a given system for hardfacing the working surfaces of equipment in the coal, processing, woodworking industries, etc., where abrasive wear is the dominant type of surface wear

Alternative materials for grey cast iron corn-mill plates by computer-aided selection and weighted property methods: the case of Ghana

Most locally-manufactured corn-mill plates in tropical countries are made of grey cast iron due to its relatively low cost, good wear resistance, good hardness and other mechanical properties in general. However, these corn-mill plates are prone to corrosion and abrasive wear resulting to contamination of milled corn which is consumed by humans. This work focuses on the use of computer-aided selection and weighted property methods to identify alternative materials for grey cast iron corn-mill plates. Requirements such as non-toxicity, good corrosion resistance, good wear resistance, low friction coefficient, high thermal conductivity, low specific gravity, high compressive strength and low cost were used in the initial material selection stages. The derivation of material performance index in addition to Ashby’s materials selection chart are used to find suitable materials to replace grey cast iron. The decision method showed that white cast iron with high-chromium alloy had the highest weighted performance index (93.75%), while nodular graphite cast iron had the least weighted performance index (65.55%). High-chromium alloyed white cast iron was therefore considered as substitute for the grey cast iron corn-mill plates.

Argon localizing by concentration method for GTAW welding process of high chromium alloy steel pipes

The present invention relates to a novel argon purging device in butt joint welding for high chromium alloy steel pipes or more predominantly relates to a device which can be used for focusing of argon at root area of welding and also an approach for purging out the atmospheric air through the inert gas argon at butt welding of high thickness pipes of high pressure steam generators. The butt joint root welding of high chromium alloy steel pipes carried out by manual Gas Tungsten Arc Welding (GTAW) requires shielding from atmospheric oxygen. Otherwise, Chromium reacts with oxygen and forms Chromium Oxide (CrO2) which is termed as oxidation. In the conventional method of purging, the argon gas is fed into both ends of the pipe using two argon cylinders. The ends are closed with metallic end covers which have many inherent limitations like ineffective purging at the butt joint, more wastage of the inert gas argon, incomplete fusion, lack of penetration, root oxidation and formation of weak brittle structures etc. Present invention is to provide a device for argon supply in butt welding of high chromium alloy steel pipe which ensure substantially better shielding and thereby avoiding the root oxidation. The developed argon purging device has resulted in elimination of root oxidation in high chrome high alloy steel pipe butt joint welding, improved weld quality as well as reduced process time. Argon gas savings up to 87.5%, as only one fourth of an argon cylinder is used in place of 2 argon cylinders for purging one butt joint and the overall cycle time is reduced by 40%.

Study on grinding damage of high chromium alloy based on molecular dynamics

The new cast high chromium alloy is the conventional material of the nuclear main pump thrust-bearing with good wear and corrosion resistance. According to the structural characteristics of high chromium alloy, the simulation model and the coupling potential function were constructed to study the grinding damage layer using molecular dynamics method. The simulation results show that the crystal lattice distortion caused by carbon atoms in the formation of interstitial solid solution leads to the occurrence of amorphous structure after full relaxation. The break and recombination of metal bond and non-metal bond between atoms in the alloy result in the occurrence of damaged layer under grinding. And the bond angles between the atoms in the damage layer are less than that in the alloy matrix. The damage layer is mainly composed of atoms in front of the abrasive particle and the atoms of extrusion deformation in the bottom. Moreover, with the increase of grinding depth, the cutting force and the damage layer thickness increase. The study is conducive to understand the damage formation mechanism of high-chromium alloy materials in micro-nano processing, and provides a theoretical reference value for the actual processing.

A NEW WELDING MATERIAL FOR REGENERATION IN THE WELDING TECHNOLOGY BASED ON NICKEL. ANALYSIS OF THE PROCESSABILITY OF APPLICATION OF THE EXPERIMENTAL FILLER IN THE REGENERATION OF SUPERALLOY CASTINGS VIA TIG WELDING AND OTHER TECHNOLOGIES

This work involves an analysis of high-chromium high-temperature deformable wieldable nickel alloys for use in GTE repair assemblies. It is shown that the alloys EP868 (VZh98) and Haynes 230 can be used in welded assemblies with an operating temperature of 800-1100 °C. The alloys Nimonic 81, Nimonic 91, IN 935, IN 939, and Nicrotan 2100 GT also have a high potential for use in welded assemblies. They are characterized by a combination of good weldability, high-temperature strength, and resistance to scaling. There have been conducted studies on high-temperature salt corrosion of model nickel alloys. They allowed establishing the patterns of the impact of base metal alloying with chromium, aluminum, titanium, cobalt, tungsten, molybdenum, niobium, tantalum and rare earth metals on the critical temperature of the start of salt corrosion Tcor and the alloy mass loss. It has been established that alloys with a moderate concentration (13-16%) of chromium can possess satisfactory hightemperature corrosion resistance (HTC resistance) under the operating conditions of ship GTE. The HTC resistance of CrAl-Ti alloys improves upon reaching the ratio Ti/Al ˃ 1. Meanwhile, the ratio Ti/Al ˂ 1 promotes the formation of corrosion products with low protective properties. The positive effect of tantalum on the HTC resistance of alloys is manifested at higher test temperatures than that of titanium, and the total content of molybdenum and tungsten in alloys is limited by the condition 8Mo2 – 2W2 = 89. The presence of refractory elements stabilizes the strengthening phase and prevents formation of the ɳ-phase. However, their excess promotes formation of the embrittling topologically close packed (TCP) phases and boundary carbides of an unfavorable morphology. Based on the studies of the HTC resistance, there has been identified a class of model high-temperature corrosionresistant nickel alloys with a moderate or high chromium content (30%), Ti/Al ˃ 1, and a balanced content of refractory and rare-earth elements.

Effect of stoichiometry on the evolution of thermally annealed long-range ordering in Ni–Cr alloys

Ni-based alloys, such as alloys 690 and 625, are widely used in the nuclear industry as structural components, because of their desirable mechanical properties and resistance to stress corrosion cracking. However, in some high chromium alloys, a disorder-order phase transformation near 33 at% Cr, is known to decrease ductility and fracture toughness. In this study, the ordering transformation is investigated in Ni–Cr binary model alloys to better understand the effects of composition. Model alloys with different stoichiometries (Ni/Cr = 1.8, 2.0, 2.2, 2.4) were isothermally aged up to 10,000 h at three temperatures (373 °C, 418 °C, and 475 °C) and characterized by transmission electron microscopy (TEM), microhardness, and synchrotron-based X-ray diffraction (XRD). TEM results show the evolution of the Ni2Cr (MoPt2-type) ordered precipitates between 3000 h and 10,000 h with corresponding size of ∼10–20 nm. Microhardness testing results show that off-stoichiometry (Ni/Cr ≠ 2.0) alloys exhibit a smaller change with ordering compared to the stoichiometric (Ni/Cr = 2.0) alloy at all temperatures. XRD quantifies ordering induced lattice contraction in the matrix structure and the size of the ordered precipitates. No BCC Cr was detected by XRD or TEM during characterization in the range of 29.83–35.66 at% Cr after 10,000 h of aging, confirming that all of the hardening can be attributed to the development of Ni2Cr in alloys ranging from Ni/Cr of 1.8 to Ni/Cr of 2.4.

Modeling and Simulating of High Chromium Alloy Based on Molecular Dynamics.

High chromium alloy is a kind of metal material with high corrosion resistance and high hardness. It is used in the thrust bearing bush of nuclear main pump in a severe environment. Based on the content of elements in high chromium alloy and the manufacturing preparation process of the alloy, a method for constructing the molecular dynamics (MD) model was proposed to study the machinability of the alloy. The MD simulation model of high chromium alloy was established based on alloy structure with the atomic random permutation and two bubble algorithms. Then, according to the actual manufacturing process of the high chromium alloy, a quenching process was introduced to simulate the actual manufacturing process of the high chromium alloy, so the property of the high chromium alloy model was improved and it was more suitable for precision machining. The accuracy of the model was verified by the internal structure and by calculating the nanohardness and density of the high chromium alloy model after adequate relaxation to studying the nanomachining performance. The coordination number of the high chromium alloy is about 4.3 calculated by integrating the radial distribution function. And there is not a perfect crystal structure in the alloy model. The density of the alloy model is about 7.549 g/cm₂, which agreed with the results of actual experimental measurement. A series of MD simulations were performed to investigate the nanomechanical property of the high chromium alloy by using the MD model. The maximum depth of 2 nm, 2.5 nm and 3 nm indentation simulations were carried out with 3 nm indenter. The results showed that the nanohardness is about 6.951 GPa-8.095 GPa, these properties are very close to the real measured results. The material and the deformation property of the high chromium alloy were stable during the indentation process.