Armco Iron Research Articles

On the regularities of electrolytic hydrogenation of ARMCO iron

On the regularities of electrolytic hydrogenation of ARMCO iron

NEW METHODOLOGIES FOR ASSESSING CAVITATION LOAD AND RESISTANCE OF STRUCTURAL MATERIALS AND PROTECTIVE COATINGS IN NUCLEAR POWER INDUSTRY. PART I. MONOFRACTIONAL APPROACH

The paper presents a new method for assessing the cavitation load and durability of structural materials and protective coatings. To determine the cavitation load on a rotating disk or other test rig, a new method for extracting erosion loads based on tests of reference materials on a reference cavitation rig is proposed. Direct measurements of the cavitation load in a cavitation tunnel with a slot cavitator, performed using piezoelectric sensors, made it possible to obtain information on the spatial distribution of the impact load. As an analytical function for modeling cumulative erosion curves in the monofractional approach, the logarithmic formula of L. Sitnik is used, assuming that cavitation erosion is a stochastic process described using fatigue theory. Armco iron is chosen as a reference material, in view of the weak dependence of its erosion rate on cavitation qualitative features. Therefore the local load value could have been extracted from the eroded surface profile of the Armco iron sample. Using the example of TiN coating analysis on stainless steel and VT3-1 titanium alloy, the time dependencies and threshold characteristics of their resistance were determined depending on the parameter of the density of the supplied energy.

Investigation of the Influence of Including or Omitting the Oxide Layer on the Result of Identifying the Local Boundary Condition during Water Spray Cooling

In the case of products made of steel, the presence of an oxide layer, which is formed during the steel production process as a result of high temperature, has a significant impact on the process of heat removal from the surface of the cooled material. For this reason, it is necessary to take into account the presence of the oxide layer in mathematical and numerical models used to simulate the distribution of the temperature field in cooled steel products. These models are based on the boundary conditions identified for given production conditions. This paper presents a comparison of the results of the identification of the boundary condition during water spray cooling of Armco iron with the use of the inverse solution. Numerical calculations were carried out using two models of heat conduction. In the first model, the presence of an oxide layer with different thermophysical properties than the base material (Armco iron) was taken into account. The second model assumed no oxide layer on the cooled Armco iron surface. It was found that the inverse solution obtained in the case of the heat conduction model taking into account the thickness of the oxide layer is correct in time and as a function of temperature. Thus, the boundary condition model obtained as a function of temperature is universal. However, this model requires an additional layer of oxides with different thermophysical properties than the base material to be included in the finite element model (FEM). Based on the conducted uncertainty tests of the inverse solution, it was found that the results of the determined boundary condition in the absence of the oxide layer on the cooled surface are subject to an error higher than 10% in comparison to the maximum reference value of the heat transfer coefficient.

Kinetics of deformation fronts during serrated Lüders deformation in α-iron at high temperature

At room temperature, the deformation of most bcc metals, which contain a small amount of interstitial elements, is accompanied by the formation of a Lüders band and its monotonic propagation over the tensile yield area. Within the framework of the autowave concept, front of the Lüders band is a switching autowave, which realizes the transition from a metastable elastically deformable state to a stable plastically deformable state. However, in the temperature range of blue brittleness of mild steels of 423 – 510 K, when the interaction of atoms of the dissolved substance with mobile dislocations takes place, propagation of the Lüders band is accompanied by a discrete flow. The patterns of propagation of the Chernov-Lüders fronts in ARMCO iron in the temperature range from 296 to 503 K and strain rates from 6.67·10–6 to 3.7·10–2 s–1 are considered in this paper. It was established that under these conditions both monotonic and discrete kinetics of front movement can be realized. Regardless of the movement nature, the Lüders deformation and width of the front remain unchanged throughout the entire process. The local strain rate at the front depends on magnitude of the effective stress, and with monotonic kinetics it increases with stress according to an exponential law, and with discrete kinetics it increases according to a linear law. This difference is due to different autowave modes that are formed in this case. The autowave of localized plasticity switching corresponds to monotonic kinetics, and the autowave of excitation – to discrete kinetics.

Experimental and numerical evaluation of multi-pass scratch on borided ARMCO iron

Thermochemical treatments are used for increasing the surface mechanical properties of iron and steels. The wear on mechanical components caused by sliding contact is an important parameter in the field of tribology. In this study, the wear resistance of ARMCO pure iron hardened by the powder-pack boriding process was evaluated using unidirectional dry sliding. The thermochemical treatment of boriding was carried out at temperatures of 850 °C for 1, 2 and 3 h of exposure time. Surface properties such as hardness and Young's modulus were obtained using the nanoindentation technique. The wear testing was performed by multi-pass scratch using an Al2O3 sphere as counterpart, constant loads of 20 and 30 N and 50, 100 and 150 passes (with a sliding distance of 5 mm for each pass). The Archard's model was used to obtain the wear coefficient for each treatment condition. The finite element method applying mesh nonlinear adaptivity was used to evaluate the stress field in the borided samples under sliding contact. Results showed that borided ARMCO pure iron under unidirectional sliding loading caused both adhesive and abrasive wear. Furthermore, for the boriding conditions established in this work, the wear behavior at loads ≥30 N was governed by both the mechanical properties of the boride layer and its thickness, whereas at lower loads only the mechanical properties of the boride layer influenced the wear resistance.

Review of Fatigue Crack Initiation Mechanisms Development and Monitoring in the Very High Cycle Fatigue Regime

Abstract Fatigue devices working at high frequency (20 kHz) allow now to explore the fatigue domain with a total number of cycles much higher than 107 cycles in reasonable times. In that case, lifetime belongs to the very high cycle fatigue (VHCF) domain. As for low and high cycle fatigue (LCF and HCF), the fracture begins by microstructural damage because of microplasticity, before leading to the initiation stage (stage I), and then the short and long crack propagation stages (stage II). It is now admitted that in VHCF the initiation stage is higher than 90 % of the total life. The main difference with LCF and HCF is the crack initiation location. For materials without internal defects (type I), the initiation is always on the specimen surface, whereas for materials with internal defects (inclusions, porosities, etc.) named type II, the microstructure appears in subsurface on defects leading to a typical “fish eye” on fractographies. If the crack initiation mechanisms on surface are well accepted to be related to dislocations gliding in well-oriented grains, the mechanisms in subsurface are not very clear and many hypotheses on the fish-eye development are suggested by different authors. In the fish-eye center, it appears a fine granular area more or less large, the origin of which is debated. In the first part, this article proposes a review on these crack initiation mechanisms (surface and subsurface). Microplasticity produces a temperature increase in fatigue tests. It has been demonstrated that the temperature recording during tests is a mean to determine the number of cycles corresponding to crack initiation and crack propagation. In the second part, through two examples on Armco iron (surface initiation) and a low alloy steel (subsurface crack initiation), the method to determine the number of cycles during the initiation and propagation stages is exposed.

Momentum enhancement from 3-cm-diameter aluminum sphere impacts into iron and rock at 5 km/s

Utilizing a large two-stage light gas gun and a large pendulum assembly, experiments were performed to measure the momentum enhancement (or increase in momentum transfer due to the ejecta) of an ARMCO iron target, two large hematite rock targets, a target of stones held by concrete, and a concrete block target. The choice of iron and iron rich materials was motivated by interest in the asteroid Psyche and the planned upcoming mission. The target comprised of a collection of stones, to mimic a rubble pile asteroid, was to provide insight into the Double Asteroid Redirection Test (DART) impact. The role of impactor size is important, and these tests were performed at a large scale, with 3-cm-diameter aluminum spheres as the impactor. Save for the concrete block, these impacts were in the vicinity of 5 km/s. There is a distinct difference in the amount of momentum enhancement (measured by β) that occurs with ductile metals vs. brittle materials and this fact shows in these impacts. The momentum enhancement with a relatively brittle aluminum falls in between the two extremes of rock and iron. Computations were performed to compare with the ARMCO iron impacts. Data at a large scale is desirable to quantify momentum enhancement in the context of hypervelocity impactors deflecting celestial bodies such as asteroids or comet nuclei.

The effect of the chemical activity of the implanted element to metal alloy components on the formation of surface layers under ion irradiation

The paper comparatively studies the effect of implanting O+ ions into the Cu50Ni50 and Cu56Mn44 alloys and M0 copper, as well as N+ ions into the VT6 titanium alloy, the 03Kh17N12M2T stainless steel, and Armco iron, on the formation of the chemical composition and changes in the structural and phase state of the surface layers. It is shown that, under conditions of implantation of ions of chemically active elements, the accumulation of the implanted impurity, the formation of chemical compounds, and their precipitation in the form of phase inclusions are determined by the chemical activity of the implanted element to the alloy components. The results obtained will allow the further development of scientific foundations for the formation of the chemical and structural-phase state in materials under nonequilibrium conditions of ion implantation.

Influence of iron oxide layer on intensification of heat dissipation from the surface of a horizontal plate cooled with a water nozzle

The paper presents the changes in the heat transfer coefficient (HTC) and heat flux (HF) during the water spray cooling of the metal plate on the surface of which the thickness of the oxidized layer changed. The experimental investigations consisted in measuring the temperature changes inside the plate during spray cooling with water from 700 °C to the ambient temperature. The plate was made of the material (Armco iron), the surface of which had been oxidized during heating. Three measurements were made for three different thickness of the oxidized layer. The size of the area related with the directed impact of the spray water on the surface (high impingement zone) and the size of the secondary water flow zone (horizontal flow zone) that was placed beyond the high impingement zone were assessed. The distribution of the water flux density over the cooled surface was determined as well as the increase in the thickness of the oxidized layer with the heating time. The experimental investigations allowed identify HTC and HF by using the inverse method. The uncertainty tests that allowed determine the accuracy of the inverse solution were performed. The obtained results shows that the development of the boiling process on the surface covered with the oxidized layer is local. In the high impingement zone, the increase in the thickness of the oxidized layer from 0.018 to 0.035 mm significantly influences the changes of HF and HTC during each boiling phase. The increase in the thickness of the oxidized layer caused a shift of the maximum HF and the beginning of the transition boiling towards a higher surface temperature. Outside the high impingement zone the influence of the increase in the thickness of the oxidized layer is small during film boiling phase. The obtained results were compared with those obtained for the surface characterized by a low oxidation state, obtaining 35% lower maximum values of HF in relation to the oxidized surface.

Micromechanics of small deformations in metal alloys under laser irra­ diation

Development of the nanomaterial science heightened the interest in studying the deformation mechanism accompanied by grain boundary sliding (GBS). However, the experimental study of GBS processes in mi­cro- and nanovolumes of metallic materials faces difficulties attributed to high localization of strains and requires the use of modern methods and tools of high-resolution electron microscopy. Therefore, the avail­able literature data refer mainly to theoretical and model studies in this area. Treatment of metal alloys with concentrated energy flows, for example, laser irradiation, can impart characteristic features to the grain boundary slip. In this regard, we performed the experimental study of the microplastic deformation of Armco iron with a single-phase ferrite structure under pulsed laser processing. To exclude the effect of phase transformations on the deformation process, only the heat-affected zone (HAZ) was studied. The temperature in HAZ was below the temperature of the first critical point and did not exceed 700°C, which made it possible to consider the total deformation an equivalent of the GBS deformation. The microstructure studies by the methods of optical and scanning electron microscopy revealed that in condi­tions of ultrafast heating and cooling during laser processing of metal, deformation occurred with the par­ticipation of the GBS mechanism. The characteristic features of GBS, i.e., the presence of stepped bound­ aries and accommodation zones, as well as the appearance of high-angle grain boundaries were observed. A technique is proposed for measuring the strain value through the GBS mechanism under an assump­tion that the strain vector components for cubic lattices are statistically equal. A statistical analysis of the measurements of the orthogonal component of the strain vector using the secant method was performed, which provided determination of the relative strain values by GBS mechanism in Armco iron within a range of 1.2-5.9%.

Application of the DIC System to Build a Forming Limit Diagram (FLD) of Multilayer Materials

The extraordinary combination of strength and ductility of multilayered materials makes them attractive in the various applications and industries (military, aerospace, energy industry etc.). In the present work, the investigated materials were joined into multilayered sheet using the explosive welding method. The three-layer material was made of two titanium sheets and one Armco iron sheet in between. Materials produced by explosive welding can easily be used in a simple deformation process, but more complex processes that employ a more complex mechanical state are still not sufficiently studied. The presented study analyzes the possibilities of using Ti - Armco - Ti sheet for the deep drawing process. For this purpose, the forming limit diagram (FLD) has been constructed and verified. FLD is one of the most important tools in the analysis of sheet metal forming processes. In the presented work the non-standard method (Erichsen test) coupled with Digital Image Correlation analysis was used. The obtained results confirmed that the method of producing the tested sheet and the morphology of the microstructure created have a direct impact on the deformation mechanisms.

Contribution to the Understanding of Carbon Diffusion in Ferrite: Simulation Modelling

This research is focused on testing how the austenite breakthrough occurs in ferrite at a temperature of 850ºC. For this purpose, an experiment has been designed to deal with this fact at this temperature. A piece of F-114 steel was placed in contact with a piece of ARMCO iron. The F-114 steel at 850ºC transforms into austenite while the ARMCO iron remains as ferrite. The breakthrough takes place by slow diffusion of the carbon from the F-114 steel into the ferritic ARMCO iron matrix. This feed increases the carbon content of the ARMCO iron until it transforms it into austenite. The intimate contact between ARMCO iron and austenite has been carried out by hot forging without exceeding 850ºC. The metallographic study was carried out by scanning electron microscopy.

Influence of Low Prestrain and Initial Temperature on Resistance to High-Strain-Rate Deformation of Armco Iron in Shock and Rarefaction Waves

Influence of Low Prestrain and Initial Temperature on Resistance to High-Strain-Rate Deformation of Armco Iron in Shock and Rarefaction Waves

A new approach for accurately measuring the spectral emissivity via modulating the surrounding radiation

Accurately measuring the spectral emissivity is of significant importance in thermal radiation. In this study, an improved measurement method for determination of spectral emissivity via modulating the surrounding radiation is proposed. A proof-of-concept measuring apparatus is constructed, and the main component parts are described in detail. The temperature uniformity of the isothermal aperture is verified, and the impact of the temperature uniformity on the emissivity measurements is studied. The good linearity and long-term stability of the detector is evaluated to ensure the validity of the improved method. The potential reference materials (silicon carbide and Armco iron) were used to validate the reliability and the accuracy of the measurement apparatus. The excellent data consistency of both two reference materials with the literature data demonstrates the reliability of the improved method and the measurement apparatus. The performance of the measurement apparatus with and without the isothermal aperture is compared, and the necessity of the modulated surrounding radiation is validated. The calculated combined uncertainty for the SiC sample at 1073 K is better than 2.38 %. The superior performance of the emissivity measurement apparatus indicate that the improved method proposed in this work provides a new approach for accurately measuring the spectral emissivity.

The interaction of carbon-bonded ceramics with Armco iron

To investigate the possible reactions between carbon-bonded ceramics and liquid Armco iron, three types of carbon (10 wt% C) bonded ceramics Al2O3 rich spinel (C-AR78), MgO rich spinel (C-MR66), and CaO·6Al2O3 (C-CA6) were put into contact with liquid Armco iron at 1625 °C by using the sessile drop method. During the interaction experiments, the oxygen partial pressure values in the experimental chamber were monitored with an oxygen detector. Thereby, the oxygen partial pressures differed based on the used carbon-bonded ceramic. It was found that the iron samples after interaction experiments were covered by newly formed oxide layers, and oxide whiskers have grown at the interface with the ceramic substrates. The compositions of the newly formed oxide layers and whiskers were related to the applied ceramic substrates. Moreover, Al and C pick-up into the iron sample was observed. The obtained results were discussed with a thermodynamic simulation based on the available Al-Fe-Mg-O-database.

Mechanical Properties of Neutron-Irradiated Armco Iron upon Plastic Deformation at Elevated Temperatures

Mechanical Properties of Neutron-Irradiated Armco Iron upon Plastic Deformation at Elevated Temperatures

Interaction of molten Armco iron with various ceramic substrates at 1600 °C

Ceramic substrates (Al2O3·MgO, CA6, CaZrO3, AZT (Al2O3 based substrates containing ZrO2 and TiO2)) were interacted with liquid Armco iron under a low oxygen partial pressure in the heating microscope. No noticeable dissolution of the ceramic substrates and reaction was observed for most of the substrates. Furthermore, deposition of SiO2 and Fe was found on the cross section between iron and these substrates. However, for the substrate AZT, a reaction layer of complex composition was found on the interface between the iron sample and the AZT substrate. After all experiments, the total number of inclusions in the iron samples greatly decreased. The deposition, agglomeration of inclusions, and the evaporation of some elements were the factors for the inclusions decreasing. Furthermore, the stability of oxides consisted of substrates under low oxygen partial pressure was confirmed by the thermodynamic calculation.

Investigation of the rate dependences of the stress of plastic flow and fracture of Mn2-Si steel at normal and elevated temperatures

The Hugoniot elastic limit and spall strength of reactor Mn2-Si steel under shock compression were measured by recording and subsequent analysis of the wave profiles. The temperature-rate dependences of the resistance to high-strain rate and fracture of steel at normal and elevated temperatures are determined. The results of measurements of the strength characteristics of steel under spall are supplemented by a metallographic analysis of the fracture zone and compared with data for 15Kh2NMFA reactor steel and Armco iron. Keywords: ferrite-pearlite steel, shock waves, deformation, temperature, Hugoniot elastic limit, spall strength.

Impact of the diffusion coefficient calculation on predicting Fe2B boride layer thickness

Abstract In this study, a single-phase boride layer thickness Fe2B is predicted on two different substrates (Armco iron and XC38 steel) by following the integral method. This method is a mathematical model based on a system of differential algebraic equations that help to deduce the diffusion coefficient, which is the key factor on predicting the layer thickness. Literatures cover different diffusion coefficients for each substrate, albeit researchers usually extract from experimental data, variations of growth rate constants within only one time treatment and deduce the diffusion coefficient from them. This deduction is done via an estimation of a frequency factor and an activation energy from the growth rate constants. Therefore, our main aim is to illustrate the impact of the deduction of the diffusion coefficient on predicting the boride layer thickness. Lastly, the impact with and without incubation time on the boriding kinetics of both substrates was also examined.

Dislocation cell walls with high dislocation density as effective hydrogen traps in Armco iron

AbstractThe effect of cold rolling (CR) deformation on the hydrogen permeation and trapping behavior of pure iron was systematically investigated. Increased deformation resulted in a decreased effective hydrogen diffusion coefficient, an extended effective lattice interstitial hydrogen diffusion path length, and increased hydrogen trap densities. However, the proportion of irreversible hydrogen traps to all traps was constant irrespective of the deformation level in the range of 30%–70% CR and increased when the deformation reached 80%. This is because the dislocation cell wall is composed of a central layer with high trap‐binding capacity and an outer layer with low trap‐binding capacity. More importantly, once the dislocation density in the center layer of the dislocation cell walls reached a relatively high value due to the severe plastic deformation, these regions become effective irreversible hydrogen traps.