Stainless Steel Melt Research Articles

Melting of SiC powders preplaced duplex stainless steel using TIG welding

TIG torch welding technique is a conventional melting technique for the cladding of metallic materials. Duplex stainless steels (DSS) show decrease in performance under aggressive environment which may lead to unanticipated failure due to poor surface properties. In this research, surface modification is done by using TIG torch method where silicon carbide (SiC) particles are fused into DSS substrate in order to form a new intermetallic compound at the surface. The effect of particle size, feed rate of SiC preplacement, energy input and shielding gas flow rate on surface topography, microstructure, microstructure and hardness are investigated. Deepest melt pool (1.237 mm) is produced via TIG torch with highest energy input of 1080 J/mm. Observations of surface topography shows rippling marks which confirms that re-solidification process has taken place. Melt microstructure consist of dendritic and globular carbides precipitate as well as partially melted silicon carbides (SiC) particles. Micro hardness recorded at value ranging from 316 HV0.5 to 1277 HV0.5 which shows increment from base hardness of 260 HV0.5kgf. The analyzed result showed that incorporation of silicon carbide particles via TIG Torch method increase the hardness of DSS.

Numerical and experimental investigation into the subsequent thermal cycling during selective laser melting of multi-layer 316L stainless steel

Subsequent thermal cycling (STC), as the unique thermal behavior during the multi-layer manufacturing process of selective laser melting (SLM), brings about unique microstructure of the as-produced parts. A multi-layer finite element (FE) model was proposed to study the STC along with a contrast experiment. The FE simulational results show that as layer increases, the maximum temperature, dimensions and liquid lifetime of the molten pool increase, while the heating and cooling rates decrease. The maximum temperature point shifts into the molten pool, and central of molten pool shifts backward. The neighborly underlying layer can be remelted thoroughly when laser irradiates a powder layer, thus forming an excellent bonding between neighbor layers. The contrast experimental results between the single-layer and triple-layer samples show that grains in of latter become coarsen and tabular along the height direction compared with those of the former. Moreover, this effect become more serious in 2nd and 1st layers in the triple-layer sample. All the above illustrate that the STC has an significant influence on the thermal behavior during SLM process, and thus affects the microstructure of SLMed parts.

Corium melt researches at VESTA test facility

VESTA (Verification of Ex-vessel corium STAbilization) and VESTA-S (-small) test facilities were constructed at the Korea Atomic Energy Research Institute in 2010 to perform various corium melt experiments. Since then, several tests have been performed for the verification of an ex-vessel core catcher design for the EU-APR1400. Ablation tests of an impinging ZrO2 melt jet on a sacrificial material were performed to investigate the ablation characteristics. ZrO2 melt in an amount of 65–70 kg was discharged onto a sacrificial material through a well-designed nozzle, after which the ablation depths were measured. Interaction tests between the metallic melt and sacrificial material were performed to investigate the interaction kinetics of the sacrificial material. Two types of melt were used: one is a metallic corium melt with Fe 46%, U 31%, Zr 16%, and Cr 7% (maximum possible content of U and Zr for C-40), and the other is a stainless steel (SUS304) melt. Metallic melt in an amount of 1.5–2.0 kg was delivered onto the sacrificial material, and the ablation depths were measured. Penetration tube failure tests were performed for an APR1400 equipped with 61 in-core instrumentation penetration nozzles and extended tubes at the reactor lower vessel. ZrO2 melt was generated in a melting crucible and delivered down into an interaction crucible where the test specimen is installed. To evaluate the tube ejection mechanism, temperature distributions of the reactor bottom head and in-core instrumentation penetration were measured by a series of thermocouples embedded along the specimen. In addition, lower vessel failure tests for the Fukushima Daiichi nuclear power plant are being performed. As a first step, the configuration of the molten core in the plant was investigated by a melting and solidification experiment. Approximately 5 kg of a mixture, whose composition in terms of weight is UO2 60%, Zr 10%, ZrO2 15%, SUS304 14%, and B4C 1%, was melted in a cold crucible using an induction heating technique.

A Novel Heat Treatment Process for Surface Hardening of Steel: Metal Melt Surface Hardening

A novel heat treatment process for surface hardening of steel has been demonstrated and named as “metal melt surface hardening (MMSH).” A surface layer with a thickness of about 400 μm and a hardness of about 700 HV has been achieved by ejecting AISI 304 stainless steel melt at a temperature of about 1783 K (1510 °C) onto the 40Cr steel surface. This proposed MMSH provides a very promising application for surface hardening of steel.

Forming Mechanism of Bump Shape in Pulsed Laser Melting of Stainless Steel

Laser surface topography has great applications in mechanical, medical, and electrical industries. This paper proposes a mechanism for the shape formation of stainless steel by pulsed laser melting. A 2D axisymmetric finite element model considering the temperature-dependent surface tension is developed, in which the melt flow and free surface deformation are analyzed by using the normal and shear surface forces. The numerical results show that the molten flows toward the place of the greatest surface tension and the free surface deformation are dominated by the shear force (Marangoni effects), generated by the surface tension gradient during heating phase, and the normal stress, generated by the surface tension at the curved surface during the cooling period.

Reduction of Surface Roughness by Means of Laser Processing over Additive Manufacturing Metal Parts.

Optimization of processing parameters and exposure strategies is usually performed in additive manufacturing to set up the process; nevertheless, standards for roughness may not be evenly matched on a single complex part, since surface features depend on the building direction of the part. This paper aims to evaluate post processing treating via laser surface modification by means of scanning optics and beam wobbling to process metal parts resulting from selective laser melting of stainless steel in order to improve surface topography. The results are discussed in terms of roughness, geometry of the fusion zone in the cross-section, microstructural modification, and microhardness so as to assess the effects of laser post processing. The benefits of beam wobbling over linear scanning processing are shown, as heat effects in the base metal are proven to be lower.

The application of a SMARTTECH 3D scanner for the production of additional parts / industry: motorcycle accessories

Enduro-Tech is the best known suppliers of parts in the off-road racing motorcycle industry. The company uses 3D printing technology based on melting stainless steel powder in order to design dedicated, additional or replacement parts. Application of the 3D digitization of an object has enabled optimization and accelerated the process of creating prototypes. The article presents an example process of design and manufacturing of dedicated engine casing.

Experimental investigation on selective laser melting of 17-4PH stainless steel

Selective laser melting (SLM) is an additive manufacturing (AM) technique that uses powders to fabricate 3Dparts directly. The objective of this paper is to perform an experimental investigation of selective laser melted 17-4PH stainless steel. The investigation involved the influence of separate processing parameters on the density, defect, microhardness and the influence of heat-treatment on the mechanical properties. The outcomes of this study show that scan velocity and slice thickness have significant effects on the density and the characteristics of pores of the SLMed parts. The effect of hatch spacing depends on scan velocity. The processing parameters, such as scan velocity, hatch spacing and slice thickness, have effect on microhardness. Compared to the samples with no heat-treatment, the yield strength of the heat-treated sample increases significantly and the elongation decreases due to the transformation of microstructure and the changes in the precipitation strengthening phases. By a combination of changes in composition and precipitation strengthening, microhardness improved.

Metallic 3-D Printed Antennas for Millimeter- and Submillimeter Wave Applications

This paper presents a study to use the metallic three dimensional (3-D) printing technology for antenna implementations up to 325 GHz. Two different printing technologies and materials are used, namely binder jetting/sintering on 316L stainless steel and selective laser melting (SLM) on Cu–15Sn. Phases, microstructure, and surface roughness are investigated on different materials. Balancing between the cost and performance, the manually polished Cu–15Sn is selected to develop a series of conical horn antennas at the E-(60–90 GHz), D- (110–170 GHz), and H-band (220–325 GHz). Good agreement is observed between the simulated and measured antenna performance. The antennas’ impedance bandwidth ( $\vert S_{11}\vert ) cover the whole operational band, with in-band gain of >22.5, >22, and >21.5 dBi for the E-, D-, and H-band antennas, respectively. Compared with the traditional injection molding and micromachining for metallic horn antenna implementation, the 3-D printed metallic horn antenna features environmental friendliness, low cost, and short turn-around time. Compared with the nonmetallic 3-D printed antennas, they feature process simplicity and mechanical robustness. It proves great potential of the metallic 3-D printing technology for both industrial mass production and prototyping.

Characterization of particle exposure in ferrochromium and stainless steel production

ABSTRACT This study describes workers’ exposure to fine and ultrafine particles in the production chain of ferrochromium and stainless steel during sintering, ferrochromium smelting, stainless steel melting, and hot and cold rolling operations. Workers’ personal exposure to inhalable dust was assessed using IOM sampler with a cellulose acetate filter (AAWP, diameter 25 mm; Millipore, Bedford, MA). Filter sampling methods were used to measure particle mass concentrations in fixed locations. Particle number concentrations and size distributions were examined using an SMPS+C sequential mobile particle sizer and counter (series 5.400, Grimm Aerosol Technik, Ainring, Germany), and a hand-held condensation particle counter (CPC, model 3007, TSI Incorporated, MN). The structure and elemental composition of particles were analyzed using TEM-EDXA (TEM: JEM-1220, JEOL, Tokyo, Japan; EDXA: Noran System Six, Thermo Fisher Scientific Inc., Madison,WI). Workers’ personal exposure to inhalable dust averaged 1.87, 1.40, 2.34, 0.30, and 0.17 mg m−3 in sintering plant, ferrochromium smelter, stainless steel melting shop, hot rolling mill, and the cold rolling mill, respectively. Particle number concentrations measured using SMPS+C varied from 58 × 103 to 662 × 103 cm−3 in the production areas, whereas concentrations measured using SMPS+C and CPC3007 in control rooms ranged from 24 × 103 to 243 × 103 cm−3 and 5.1 × 103 to 97 × 103 cm−3, respectively. The elemental composition and the structure of particles in different production phases varied. In the cold-rolling mill non-process particles were abundant. In other sites, chromium and iron originating from ore and recycled steel scrap were the most common elements in the particles studied. Particle mass concentrations were at the same level as that reported earlier. However, particle number measurements showed a high amount of ultrafine particles, especially in sintering, alloy smelting and melting, and tapping operations. Particle number concentration and size distribution measurements provide important information regarding exposure to ultrafine particles, which cannot be seen in particle mass measurements.

Механизм и причины образования глубоких поверхностных дефектов на слябах при непрерывной разливке нержавеющих сталей, легированных титаном

The paper considers the structure of metal losses in melting stainless steel with titanium and casting the steel in curved-type continuous casting machine. A hypothesis on the mechanism of surface defect formation on continously cast slabs is described and recommendations to decrease the amount of trimming of defects are given. In other authors’ works it was supposed that this defect is caused by rippled surface like in ingot casting of stainless steel by uphill teeming; by sinking into liquid metal of raw slag-metal shells formed by interaction of dissolved titanium with oxygen and chamotte refractory lining of tundish; that there is relation between surface defects and the quality of slag mix for continuous casting machine mould and the character of distribution of metal streams in the mould. Arguments to criticize the versions that decreasing the amount of dissolved nitrogen is the key factor in obtaining better slab surface quality are also presented. Effect of dissolved nitrogen and titanium on trimming level of continuously cast slabs is shown, the ways to decrease this defect are proposed and the factors affecting its appearance are described.

Reinforced perovskite hollow fiber membranes with stainless steel as the reactive sintering aid for oxygen separation

Unlike polymeric hollow fiber membrane which has been successfully used in industrial applications, ceramic hollow fiber membrane has not been widely applied due to their brittle nature of ceramic materials. In this work, La0.6Sr0.4CoO3−δ (LSC) hollow fiber membrane was fabricated for oxygen permeation using a combined phase inversion/sintering technique. As expected, the mechanical strength of LSC hollow fiber is very low, only 72.76MPa from three-point-bending test. In order to improve the mechanical strength of perovskite hollow fibers, stainless steel powder was added in the perovskite for the starting membrane material. During high temperature sintering, the stainless steel phase was transferred to iron oxide phase. The mechanical strength of the resultant hollow fiber membranes has been significantly improved due to the enhanced densification by the melting stainless steel at high temperature which played a role as the sintering aid, and the volume expansion caused by the iron oxide formation from the metal phase. There is a balance between the enhanced mechanical strength and the lowered oxygen flux due to the addition of non-oxygen permeable material. Experimental results demonstrate that the optimal weight percentage of stainless steel powder mixed in the perovskite is 10%. Compared to the pristine membrane, the mechanical strength of the resultant composite membrane was improved by 80% although the flux was lowered by 18% relative to the original flux.

Cause-specific mortality in Finnish ferrochromium and stainless steel production workers.

BackgroundAlthough stainless steel has been produced for more than a hundred years, exposure-related mortality data for production workers are limited.AimsTo describe cause-specific mortality in Finnish ferrochromium and stainless steel workers.MethodsWe studied Finnish stainless steel production chain workers employed between 1967 and 2004, from chromite mining to cold rolling of stainless steel, divided into sub-cohorts by production units with specific exposure patterns. We obtained causes of death for the years 1971–2012 from Statistics Finland. We calculated standardized mortality ratios (SMRs) as ratios of observed and expected numbers of deaths based on population mortality rates of the same region.ResultsAmong 8088 workers studied, overall mortality was significantly decreased (SMR 0.77; 95% confidence interval [CI] 0.70–0.84), largely due to low mortality from diseases of the circulatory system (SMR 0.71; 95% CI 0.61–0.81). In chromite mine, stainless steel melting shop and metallurgical laboratory workers, the SMR for circulatory disease was below 0.4 (SMR 0.33; 95% CI 0.07–0.95, SMR 0.22; 95% CI 0.05–0.65 and SMR 0.16; 95% CI 0.00–0.90, respectively). Mortality from accidents (SMR 0.84; 95% CI 0.67–1.04) and suicides (SMR 0.72; 95% CI 0.56–0.91) was also lower than in the reference population.ConclusionsWorking in the Finnish ferrochromium and stainless steel industry appears not to be associated with increased mortality.

Boundary Geometric Control of a Nonlinear Diffusion System with Time‐Dependent Spatial Domain

AbstractA Stefan problem represents a distributed parameter system with a time‐dependent spatial domain. This paper addresses the boundary control of the position of the moving liquid–solid interface in the case of nonlinear Stefan problem with Neumann actuation. The main idea consists in deriving an equivalent linear model by means of Cole‐Hopf tangent transformation, i.e. under a certain physical assumption, the original nonlinear Stefan problem is converted to a linear one. Then, the geometric control law is deduced directly from that developed, by the authors of the present paper, for the linear Stefan problem. Based on the fact that the Cole‐Hopf transformation is bijective, it is shown that the developed control law yields a stable closed‐loop system. The performance of the controller is evaluated through numerical simulation in the case of stainless steel melting characterized by a temperature‐dependent thermal conductivity, which is nonlinear. The objective is to control the position of the liquid–solid interface by manipulating a heat flux at the boundary.

The effect of ultrasonic processing on solidification microstructure and heat transfer in stainless steel melt

The heat transfer in the ultrasonic processing of stainless steel melt is studied in this thesis. The temperature field is simulated when the metal melt is treated with and without ultrasound. In order to avoid the erosion of high temperature melt, ultrasound was introduced from the bottom of melt. It is found that the temperature of melt apparently increases when processed with ultrasound, and the greater the ultrasonic power is, the higher the melt temperature will be; ultrasonic processing can reduce the temperature gradient, leading to more uniform temperature distribution in the melt. The solidification speed is obviously brought down due to the introduction of ultrasound during solidification, with the increasing of ultrasonic power, the melt temperature rises and the solidification speed decreases; as without ultrasound, the interface of solid and mushy zone is arc-shaped, so is the interface of liquid and mushy zone, with ultrasound, the interface of solid and mushy zone is still arc-shaped, but the interface of liquid and mushy zone is almost flat. The simulation results of temperature field are verified in experiment, which also indicates that the dendrite growth direction is in accord with thermal flux direction. The effect of ultrasonic treatment, which improves with the increase of treating power, is in a limited area due to the attenuation of ultrasound.

A Study on the Laser Spatter and the Oxidation Reactions During Selective Laser Melting of 316L Stainless Steel, Al-Si10-Mg, and Ti-6Al-4V

The creation of an object by selective laser melting (SLM) occurs by melting contiguous areas of a powder bed according to a corresponding digital model. It is therefore clear that the success of this metal Additive Manufacturing (AM) technology relies on the comprehension of the events that take place during the melting and solidification of the powder bed. This study was designed to understand the generation of the laser spatter that is commonly observed during SLM and the potential effects that the spatter has on the processing of 316L stainless steel, Al-Si10-Mg, and Ti-6Al-4V. With the exception of Ti-6Al-4V, the characterization of the laser spatter revealed the presence of surface oxides enriched in the most volatile alloying elements of the materials. The study will discuss the implication of this finding on the material quality of the built parts.

Experimental Investigation of the Interaction Kinetics between Metallic Melt and Special Concrete

The ablation kinetics of special concrete, which has been developed as one of the candidate protecting materials for the EU-APR1400 ex-vessel core catcher, was investigated experimentally. Metallic corium and stainless steel melts were generated using an induction heating technique in a cold crucible and used for the interaction tests with the special concrete. The melt delivery system was designed to prevent the melt impingement effect and chemical changes of the concrete specimen owing to preheating during the melt generation process. The metallic corium melts above the activation temperature interacted with the concrete specimens very intensively, which led to an abrupt increase of concrete ablation. However, in the interactions with the steel melts, the concrete specimens were ablated slowly even though the melt temperatures were higher than the metallic corium melts. A postanalysis of the chemical compositions and microstructures of the ingot with the ablated concrete was performed to understand the ablation phenomena. It was found that the U and Zr contained in the metallic corium melt reacted with the oxygen released by the dissociation of ferric oxides in the special concrete above the activation temperature. As a result of the exothermic reaction, both the ablation rate and the reaction layer coefficient were increased with a higher melt temperature and exhibited higher values than those in the interactions with the steel melt. Moreover, it was verified that the oxidation quotients of U and Zr are higher than those of Fe and Cr.

Melt expulsion during ultrasonic vibration-assisted laser surface processing of austenitic stainless steel

Simultaneous application of ultrasonic vibrations during conventional materials processing (casting, welding) and material removal processes (machining) has recently been gaining widespread attention due to improvement in metallurgical quality and efficient material removal, respectively. In this paper, ultrasonic vibration-assisted laser surface melting of austenitic stainless steel (AISI 316) is reported. While the application of ultrasonic vibrations during laser processing delays the laser interaction with material due to enhancement of surface convection, it resulted in expulsion of melt from the irradiated region (forming craters) and transition from columnar to equiaxed dendritic grain structure in the resolidified melt films. Systematic investigations on the effect of ultrasonic vibrations (with vibrations frequency of 20kHz and power output in the range of 20–40%) on the development of microstructure during laser surface melting (with laser power of 900W and irradiation time in the range of 0.30–0.45s) are reported. The results indicate that the proposed ultrasonic vibration-assisted laser processing can be designed for efficient material removal (laser machining) and improved equiaxed microstructure (laser surface modifications) during materials processing.

Blasting and Passivation Treatments for ASTM F139 Stainless Steel for Biomedical Applications: Effects on Surface Roughness, Hardening, and Localized Corrosion

Due to the combination of good biofunctionality and biocompatibility at low cost, AISI 316 low carbon vacuum melting (LVM) stainless steel, as considered in ASTM F139 standard, is often the first choice for medical implants, particularly for use in orthopedic surgery. Proper surface finish must be provided to ensure adequate interactions of the alloy with human body tissues that in turn allows the material to deliver the desired performance. Preliminary studies performed in our laboratory on AISI 316LVM stainless steel surfaces modified by glass bead blasting (from industrial supplier) followed by different nitric acid passivation conditions disclosed the necessity to extend parameters of the surface treatments and to further consider roughness, pitting corrosion resistance, and surface and subsurface hardening measurements, all in one, as the most effective characterization strategy. This was the approach adopted in the present work. Roughness assessment was performed by means of amplitude parameters, functional parameters, and an estimator of the fractal dimension that characterizes surface topography. We clearly demonstrate that the blasting treatment should be carried out under controlled conditions in order to obtain similar surface and subsurface properties. Otherwise, a variation in one of the parameters could modify the surface properties, exerting a profound impact on its application as biomaterial. A passivation step is necessary to offset the detrimental effect of blasting on pitting corrosion resistance.

Effect of Al deoxidation on the formation behavior of inclusions in Ce-added stainless steel melts

The effect of Al deoxidation on the oxygen content and the inclusion properties (composition, size and morphology) of Ce-added stainless steel melts at 1873 K was investigated. The total oxygen content was about 310(±40) ppm before Al addition and slightly decreases with holding time when Al content was lower than 0.01%, whereas the oxygen content drastically decreased when Al content was greater than about 0.05%. Al content initially decreased, followed by an increase by addition of Ce, which originates from the reduction of Al2O3 in the refractory and/or inclusions by added Ce. The initial inclusions before Al addition were mainly Mn(Cr)-silicates. When Ce was added without Al deoxidation, small amounts of Ce oxide were detected after Ce addition. However, the content of Ce oxide decreased with holding time, and the inclusion composition reverted to the MnO-SiO2-Cr2O3 system. The initial Mn(Cr)-silicate inclusions transformed to Al2O3-rich inclusions by Al addition, and then Ce2O3 was enriched by Ce addition due to local enrichment of Ce around Al2O3 particles, resulting in the formation of AlCeO3-type inclusions. However, the Ce2O3 in the inclusions was continuously reduced by Al due to higher chemical potential of Al than Ce, finally forming the Al2O3-CeAl11O18 complex inclusions.