Porous Steel Research Articles

Influence of inhomogeneities in chemical composition and porosity of sintered steel on development of martensitic transformation

The article is devoted to the study of martensitic transformation in porous sintered steels. When analyzing the process of development of marten­sitic transformation in porous sintered steel, the influence of two factors was assessed: depletion of carbon in the near-surface layers of pores and a change in the energy balance due to relaxation of transformation stresses on free surfaces of the pores. The martensitic transformation was studied in porous steel with a carbon content of 1.56 wt. % obtained after pressing and sintering of a mixture of PZhRV iron powders and GK-3 graphite in hydrogen atmosphere at 1200 °C. Gas carburizing at 1100 °C and homogenization helped to achieve the specified carbon content. The samples were quenched in a sodium chloride solution at a temperature of 27 °C. Pre-cooling was used from temperatures Ast to 800 °C at a rate of 62 °C/s. X-ray microanaly­sis of carbon distribution was carried out using the installation CAMECA Microsonde M.S. 46 with a probe diameter of two microns. The martensite plates predominantly formed on the pores’ surfaces and their cross section had shape close to rhomboidal. The data obtained on the morphology of α′-phase crystals growing from pores and the study by X-ray spectral microanalysis of carbon distribution along the largest martensite plates convince us of the absence of any significant changes in carbon content and, as a consequence, their influence on development of martensitic transformation in the area of pores is not the leader. For sintered porous steels, an irremovable factor in the increase in temperature is the presence of porosity, in contrast to a removable factor – inhomogeneity of the chemical composition, which is caused by incompleteness of the alloy homogenization processes, both during sintering and during the austenitization process that precedes quenching.

Correction to: Fabrication of superhydrophobic, permeable, and anti-reflective porous steel surfaces using laser ablation and heat treatment

Correction to: Fabrication of superhydrophobic, permeable, and anti-reflective porous steel surfaces using laser ablation and heat treatment

Achieving underwater stable drag reduction on superhydrophobic porous steel via active injection of small amounts of air

Over the years, numerous researchers have proposed air lubrication methods to reduce drag in underwater vehicles. This method is challenged by buoyancy and water flow, which facilitate air escape from solid surfaces, necessitating substantial air to achieve significant drag reduction. The adherence of hydrophobic interfaces to submerged air bubbles reduces air escape, stabilizing it on solid surfaces for effective drag reduction. However, high flow velocities or pressure conditions can destabilize the drag reduction effect by disrupting the air-water interface. To address this issue, the paper proposes a method that integrates superhydrophobic surfaces with active air injection. This approach involves preparing stable superhydrophobic surfaces by combining laser ablation, heat treatment, and spraying hydrophobic coatings on porous steel surfaces, and using active air injection to maintain the stability of the air layer. Flow field analysis revealed that active air injection into superhydrophobic porous steel sustains a stable air layer, even at high flow velocities, reaching a drag reduction exceeding 25%. Moreover, at high Reynolds numbers, high drag reduction can be achieved at significantly low flow rates compared to smooth surface. This approach shows promise for maintaining a stable air-water interface on superhydrophobic surfaces and sustaining drag reduction in engineering applications.

Fabrication of superhydrophobic, permeable, and anti-reflective porous steel surfaces using laser ablation and heat treatment

Fabrication of superhydrophobic, permeable, and anti-reflective porous steel surfaces using laser ablation and heat treatment

Laser-induced fluorescence detection of nitroxyl (HNO) formed from the thermal decomposition of hydroxylammonium nitrate vapor

The decomposition of the ionic liquid hydroxylammonium nitrate (HAN) produces gas phase products which have utility in spacecraft propulsion systems. Among the various gas phase species generated from HAN decomposition is the nitroxyl (HNO) radical, a highly reactive molecule with implications in both chemical and electric propulsion applications. The work described here used a laser-induced fluorescence platform to directly detect the relative density of the HNO radical formed by passing HAN vapor through heated porous disks of varying composition. The use of heated porous 316-stainless steel and aluminum disks showed significant HNO density production and is attributed to a surface hydrogen abstraction mechanism. There was also evidence of surface modification to the metal disks which resulted in a shift in the HNO density temperature profiles. The results reported demonstrate that use of a heated porous material can easily generate a molecular vapor at moderate temperatures for combustion and electric propulsion applications.

Numerical simulation of void elimination in the billet during hot shape rolling processes based on the Gurson–Tvergaard–Needleman model

The presence of voids can compromise the strength and continuity of downstream products. The Gurson–Tvergaard–Needleman model was utilized to obtain the relevant parameters. A 3D finite element model was then employed to investigate the elimination of voids in a porous free-cutting steel 1215MS during the hot shape rolling process. The center distribution of voids in the billet was considered in the finite element model, and the relationships between the void elimination and the pressure stress in the billet were analyzed. The influences of rolling reduction, rotation speed, and friction between the work roller and billet on the void elimination were also discussed. The results revealed that the pass reduction has a significant influence on the ultimate value of void volume fraction, which is beneficial for better material self-healing during the shape-rolling process. These findings suggest that accurate predictions of void elimination in the workpiece can be achieved using the finite element method for successful simulation of the hot shape rolling process.

Quantitative characterization and evaluation of key physicochemical characteristics of steel slag

Steel slag is considered to improve the road performance of cold mixed asphalt (CMA) due to its superior physicochemical characteristics. To realize the potential application of steel slag in CMA pavement, the alkalinity, hydration activity, pore characteristics, and three-dimensional (3D) morphology were quantitatively characterized and evaluated based on the X-ray fluorescence (XRF), mercury intrusion porosimetry (MIP), 3D laser scanning, and 3D structured light measurement, respectively. The results show that the alkalinity of steel slag can not fully reflect its hydration activity. Most steel slag has high alkalinity with an alkalinity value greater than 2.5, while the activity index (AI) is generally less than 1.0. The pores of steel slag are mostly "ink-bottle" shaped, in which macropores are the most developed, and small pores and micropores are the least developed. The total pore volume of macropores is the largest, while the total pore area of small pores is the largest. The porosity of porous, less porous, and dense steel slag is 12.05%, 6.88%, and 1.28%, respectively. The adsorption and accommodation capacity of porous steel slag for fluids is the largest, followed by less porous and dense steel slag. All three steel slags have good 3D shapes, and their shape factor (SF), sphericity (S), needle degree (ND), and flake degree (FD) have distribution intervals of 0.81–1.19, 0.70–0.99, 1.01–1.90, and 1.01–1.51, respectively. Porous steel slag shows richer apparent morphology than less porous and dense steel slag. Their apparent morphology characterization indicators Ra, Rq, Rp, Rv, and Rt show a good linear positive correlation with porosity, which can be regarded as the classification criterion for apparent morphology. This study will help enrich the theoretical basis and control indicator system for applying steel slag in CMA pavement.

Preparation of highly dewetted porous steel for shallow water AUV based on laser ablation method

Over the past two decades, autonomous underwater vehicles (AUVs) have been developed for various marine, commercial, and military applications. Porous metals, known for their lightweight high performance, suit AUV hulls, especially in shallow waters. However, because of their inherent hydrophilicity and porous structure, high humidity causes corrosion. In this study, a novel solution involving laser ablation and subsequent heat treatment of porous steel is proposed to improve the waterproofing performance both above and below water. By analyzing the surface structures, wetting attributes, and droplet behavior, the optimal laser and heat treatment parameters for superior performance are revealed. The porous nested structures created by laser ablation effectively reduce fog accumulation and, enhance the anti-fogging capabilities. Furthermore, the underwater stability ofsuperhydrophobic porous steels at different depths is systematically investigated. A method involving air injection into porous steel is proposed to address the limited air-pocket lifespan and instability of dehumidified surfaces. Experimental results confirm rapid and complete restoration of superhydrophobicity at a 0.9-meter depth. Thus, this study presents a practical corrosion-resistant surface material for AUVs in shallow-water environments and a new approach for achieving corrosion resistance in porous metals exposed to long-term aquatic conditions.

Numerical study of effect porous media on heat transfer in a horizontal annular tube

In the current study, to enhance the characteristics and forced convection performance in the horizontal annular in the case of the presence of porous material and without porous material, energy analyses were performed. Many types of porous material, porosities, and diameters were used. Computational fluid dynamics was used to simulate an annuli tube in case of the presence of porous material and without porous material by utilization of ANSYS FLUENT software 17.2. The working fluid utilized was water with Reynolds number from 100-500 and constant wall heat flux at 150 kW/m2. Two types of porous media glass and steel balls, two different porosities (0.6 and 0.7), and two different porous material diameters (12 and 24mm) were utilized. Investigations occurred under the study state for studying heat transfer properties and flow of fluid in the annuli tube. The energy analysis outcomes showed that there is a relationship between Nu and Reynolds number. The highest enhancement of Nu number happened at 12mm diameter and 0.6 porosity for bolls of glass and 0.7 for bolls of steel. The pressure drop rising occurs with the rising of Re for all cases and the diameter of 12mm gives the maximum pressure drop for both steel and glass pellets and the uppermost pressure drop occurs at a porosity of 0.6. As compared with those in the annulus in the absence of a glass sphere as porous material at the same ball volumes.

The Formation of a Flame Front in a Hydrogen–Air Mixture during Spark Ignition in a Semi-Open Channel with a Porous Coating

An experimental study of ignition and flame front propagation during spark initiation in a hydrogen–air mixture in a semi-open channel with a porous coating is reported. The bottom surface of the channel was covered with a porous layer made of porous polyurethane or steel wool. The measurements were carried out for a stoichiometric mixture (equivalence ratio ER = 1.0) and for a lean mixture (ER = 0.4) of hydrogen with air, where ER is the molar excess of hydrogen. The flame front was recorded with a high-speed camera using the shadow method. Depending on the pore size, the velocity of the flame front and the sizes of disturbances generated on the surface of the flame front were determined. Qualitative features of the deflagration flame front at ER = 0.4, consisting of disturbances resembling small balls of flame, were discovered. The sizes of these disturbances significantly exceed the analytical values for the Darrieus–Landau instability. The effect of coatings made of porous polyurethane or steel wool is compared with the results obtained for an empty smooth channel. Depending on the hydrogen concentration in the hydrogen–air mixture, the velocity of the flame front compared to a smooth channel was three times higher when the channel was covered with steel wool and five times higher when the channel was covered with porous polyurethane.

Effect of Al Content on the Microstructure and Mechanical Properties of the Sintered Fe–Mn–Al Porous Steel

Al content is of great importance for the evolution of the microstructure and compressive performance of the high‐Mn and high‐Al porous steels. Herein, Fe–Mn–Al porous steels with different Al contents are prepared via powder sintering at different temperatures. The results show that the main phases of the sintered samples at 640 °C are α‐Fe, α‐Mn, and Al, while a small amount of Fe2Al5 and Al8Mn5 exists in the samples with 15 and 20 wt% Al. At 1200 °C, the sintered sample with 5 wt% Al is composed of γ‐Fe, while those with 15 and 20 wt% Al are mainly α‐Fe. The length of Mn depletion region and porosity of the samples increase with the increase of Al content. The largest total and open porosity are observed in the 1200 °C‐sintered sample with 20 wt% Al, which are 63.1 and 60.7 vol%, respectively. The compressive strength decreases sharply from 770 MPa for the sample with 5 wt% Al to 7.5 MPa with 15 wt% Al, after sintering at 1200 °C. Ductile fracture occurs in the sample with 5 wt% Al, while brittle fracture is the main fracture mode in those with 15 and 20 wt% Al.

Evolution mechanism of freezing in porous media at the pore scale: Numerical and experimental study

The phase change problem in porous media has attracted extensive attention due to its complexity of both the heat transfer process and pore structure. This study investigates the mechanisms governing the freezing of water at the pore scale in a porous model, employing a combination of experimental and numerical approaches. Mathematical-physical model is used to simulate the phase change process in porous structures. Experiments are conducted on water freezing in porous resin and steel, with a pore distance of 500 μm. The evolutions of the phase interface and temperature field during the freezing process are analyzed. Results demonstrate good agreement between the simulations and experiments. Moreover, when the thermal conductivity of the solid skeleton is lower than that of the fluid (porous resin), the phase interface in the pore evolves from concave to convex, with a non-linear change in relative curvature. The temperature gradient of the fluid and skeleton within the pore channels first decreases and then increases. However, when solid skeletons have higher thermal conductivities than the fluid (porous steel), the evolution of the phase interface and its relative curvature, as well as the temperature gradient in the pore are different from the other case.

Plastron restoration for underwater superhydrophobic surface by porous material and gas injection

Restoring and maintaining the gas layer (plastron) on underwater superhydrophobic surface (SHS) is critical for the real-world application of SHS, such as reducing friction drag in high-Reynolds number turbulent flows. In this work, we experimentally investigated the capability of a technology based on porous material and gas injection to restore the plastron on an underwater SHS from a fully wetted state. The SHS was created by sprayed coating a commercial superhydrophobic coating on a porous steel plate. In the experiments, the SHS was immersed in stationary liquid, the gas injection pressure and gas injection duration were independently controlled. The status of gas layer on SHS was examined by a high-speed camera. We found that the surface area being restored with a plastron increased with increasing gas injection pressure and gas injection duration, and that the plastron restoration process involved bubble formation, merging and detachment. A layer of gas was left on the surface after bubble detachment. The size of the detached bubble increased with time due to bubble merging, and became stable when there was no more bubble merging. Increasing gas injection pressure led to higher gas flow rates, larger detached bubble sizes and faster plastron restorations. A plastron restoration within 0.3 s was achieved at the highest pressure, faster than the in-situ gas generation methods. Furthermore, we found that the gas flow rate through the underwater SHS can be described by a modified Darcy’s law. Our results highlighted the potential of using porous material and gas injection to restore the plastron and made possible the real-world implementation of SHS.

Study Effect of HIP & Heat Treatment on MIM Porous Tool Steel SKD11

Hard tool steel SKD11 had a lot of industrial practical applications because it had super mechanical properties such as wear resistance and toughness. There is a trend to manufacture components with competitive costs. The wear resistance and hardness of the sintered components are insufficient to meet the cutter and dies’ strict requirements. The HIP process can further reduce pore size, quantity, and even distribution of pores of as-sinter blanks. As a result, the higher density, lower porosity, and high hardness of components can be obtained without obvious growing of grain size. After heat-treatment and subzero treatment, hardness increased up to HRC58-61, and wear resistance significantly improved.

Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

Oxidation inhibition of 3D printed porous steel by ceria-activated multilayers

A 3D-printed porous 410 L steel support with a novel ceramic multi-coating is fabricated to improve the oxidation resistance of porous metal components for extreme conditions. Simplified support´s morphology with straight channels fabricated by laser powder bed fusion enhances the applicability of wet-chemical coating methods. A multi-coating method combining electrophoretic deposition and infiltration improves the ceramic/steel interface. Ceria-based coatings with catalytic activity towards H2O and O2 provide both physical and dynamic chemical protection mechanisms. Excellent electro-chemo-mechanical stability and superior corrosion resistance (0.26 ×10-15 g2 cm4 s-1) are shown at 750 °C in air-3 % H2O for 122 h.

Effect of ball milling time on the microstructure and compressive properties of the Fe-Mn-Al porous steel

Effect of ball milling time on the microstructure and compressive properties of the Fe-Mn-Al porous steel

Analysis of Unstable Plastic Flow in the Porous 316L Samples Manufactured with a Laser 3D Printer

The study of unstable plastic flow in porous steel 316L samples after compression deformation at room temperature with different strain rates was carried out. The samples were obtained from ASTM F3184 medical grade steel powder by digital metallurgy using a Renishaw AM 400 laser 3D printer. Serrations on the stress-strain curves and strain localization bends were found, which were associated with the Portevin-Le Chatelier effect and testified instability of the plastic flow of the material under the deformation process. Deformation twins were observed in the structure of deformed samples.

Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

3D Printing of Hierarchical Porous Steel and Iron‐Based Materials

AbstractIron is a cheap and environmentally friendly metal that is produced at the gigaton scale every year. While porous metals have long been used as filters in chemical processes and electrodes in functional devices, steel and iron‐based structures with highly tunable porosity have only recently been explored as sustainable, lightweight materials for a variety of structural, biomedical, and energy‐related applications. Here, an extrusion‐based 3D printing process is reported to manufacture steel‐ and iron‐based structures with ultrahigh porosity distributed over three hierarchical levels. Using particle‐stabilized foams as printing inks, pores are generated at multiple length scales by controlling the print path, the concentration of air bubbles in the ink, and the thermal reduction and sintering process of the metal oxide precursor particles. This enables the manufacturing of iron and iron‐based alloys with an elastic modulus above 300 MPa and a density below 1 g cm−3 while keeping the mechanical efficiency expected for porous structures. The potential applications of such hierarchical porous iron and iron alloys are illustrated by printing structures with tunable chemical compositions that are ultra‐lightweight, magnetoresponsive, and capable of spontaneously absorbing oil spills and of vaporizing liquids using low electric power.