Cast Stainless Steel Research Articles

Impact of substrate material and chlorine/chloramine on the composition and function of a young biofilm microbial community as revealed by high-throughput 16S rRNA sequencing.

The bacterial composition of biofilms in drinking water distribution systems is significantly impacted by the disinfection regime and substrate material. However, studies that have addressed the changes in the biofilm community during the early stage of formation (less than 10 weeks) were not yet adequate. Here, we explore the effects of the substrate materials (cast iron, stainless steel, copper, polyvinyl chloride, and high density polyethylene) and different disinfectants (chlorine and chloramine) on the community composition and function of young biofilm by using 16S rDNA sequencing. The results showed that Alphaproteobacteria (39.14%-80.87%) and Actinobacteria (5.90%-40.03%) were the dominant classes in chlorine-disinfection samples, while Alphaproteobacteria (17.46%-74.18%) and Betaproteobacteria (3.79%-68.50%) became dominant in a chloraminated group. The infrequently discussed genus Phreatobacter became predominant in the chlorinated samples, but it was inhibited by chloramine and copper ions. The key driver of the community composition was indicated as different disinfectants according to principle coordination analysis (PCoA) and Permutational multivariate analysis of variance (Adonis test), and the bacterial community changed significantly over time. Communities of biofilms grown on cast iron showed a great distance from the other materials according to Bray-Curtis dissimilarity, and they had a unique dominant genus, Dechloromonas. A metagenomics prediction based on 16S rDNA was used to detect the functional pathways of antibiotic biosynthesis and beta-lactam resistance, and it revealed that several pathways were significantly different in terms of their chlorinated and chloraminated groups.

The High-Temperature Mechanical Properties of EN 1.4509 Stainless Steel Cast Using Investment Casting

The high-temperature (600-900 °C) mechanical properties of EN 1.4509 stainless steel made by investment casting were studied by changing the Nb content based on this stainless steel composition standard. The results indicate that with an increase in tensile temperature, the high-temperature strength shows a downward trend and the high-temperature plasticity increases. The results also indicate that with an increase in Nb content, the high-temperature strength rises continually and the high-temperature plasticity decreases; for example, the tensile strengths at 900 °C of Steel A, Steel B and Steel C are 21, 25 and 31 MPa, respectively, and the yield strengths are 15, 20 and 22 MPa, respectively, and the elongations are 97.7, 85.3 and 73.7%, respectively. The high-temperature tensile strength of the investment casting EN 1.4509 stainless steel sample is closely related to the bulk (Ti, Nb) (C, N) and the Laves phase (Fe2Nb) at the ferritic grain boundaries and in the ferritic grains. These are the main factors for improvement in the high-temperature strength of the tested steels; additionally, the coarse ferritic grains also play a certain role in improving the mechanical properties. The Nb content of the investment casting EN 1.4509 stainless steel can be reduced to 0.25 wt.%, and at this content, a combination of good high-temperature mechanical properties and higher room-temperature plasticity is obtained.

Effect of cracking feedstock on carburization mechanism of cracking furnace tubes

In the present research, one of the primary problems which often arises in cracking furnaces of ethylene plants was pioneered. This problem is associated with high failure rate of heat resistant cast stainless steel tubes used in pyrolysis furnaces. The interaction between feed types and tubes which is accompanied by carburization is considered as the main origin of such a high failure rate. Hence, in this study three samples of tube (a heat resistant alloy of HP40 + Nb) involving as-cast sample (without exposure to feed), the sample exposed to liquid feed and the sample exposed to gaseous feed were studied. In this respect, two types of feed including liquid phase (i.e., naphtha), and gas phase (ethane) were selected to be compered in terms of their influence on the tube structure. In order to evaluate the interaction between the feed type and the tube destruction, microstructural changes were studied using SEM, EDS and microhardness analyses. The results revealed that higher values of hardness were obtained for the gas feedstock tubes compared to the liquid feedstock ones and as-cast sample. This can be attributed to easier carbon diffusion and more sever growth of carbide in the tube structure that makes it more brittle. Moreover, in inner surfaces of tubes, spalling of oxide layers in addition to reformation of chromium oxide on the surface cause chromium to diffuse into the metal surface, leading to reduction of the chromium content to 5 wt%. The results showed that generally the gas feedstock caused more microstructural changes and damages on the tube structure compared with the liquid feedstock with identical life services.

Study on Properties of Hyper-duplex Stainless Steel 7A of ASTM A-890 (CD3MWN)

Hyper-duplex stainless steel castings of grade 7A of ASTM A-890 are comparatively new in duplex series, and their regular production has not yet been started like other super-duplex grades 5A and 6A. In view of this, a study has been undertaken to find out the properties of this grade under different experimental conditions. Tensile properties and hardness are found to be higher than other super-duplex grades; however, impact values at − 50 °C are lower than grade 6A. Pitting corrosion, critical pitting temperature and intergranular corrosion tests were carried out as per ASTM standard. Potentiodynamic polarization scan was carried out and compared with 6A. Deleterious phases were formed by holding samples for a shorter time at 1000 °C with a corresponding increase in hardness and drop in ferrite content. 475 °C embrittlement effect was studied and compared with other duplex grades. Re-dissolution of harmful precipitates was carried out at 550 °C by varying time to study any change in properties. Some of the properties of grade 7A were compared with wrought product of hyper-duplex grade, UNS S32707. Low-temperature impact values of hot-worked cast 7A test block were improved considerably in both longitudinal and transverse direction. Dry sliding wear resistance test was carried out as per ASTM standard, and values were found to be better than grade 6A.

Numerical simulation of bimetallic casting cooling during the process of lost foam casting

The authors consider cooling process of a “gray cast iron–austenitic stainless steel” bimetallic casting in the lost foam casting conditions. They provide a mathematical model of coupled heat transfer between the molten gray cast iron, stainless steel, nonstick coating and dry quartz sand during the process of bimetallic casting cooling, taking into account phase transitions in gray cast iron and quartz sand. The article shares calculated data on casting crystallization time and a solid-phase fraction formed in gray cast iron with temperature field changes with time and cooling rates of the bimetallic casting. The data have been obtained for stainless steel thicknesses of 1.5 mm, 5 mm and 10 mm (volume ratio of 20:1, 6:1 and 3:1, respectively) and two pouring temperatures of 1350 °C and 1500 °C. The calculated values of the bimetallic casting solidification time are summarized as a polynomial. Formation of shrink holes near the left wall of the casting proves to be possible with a stainless steel thickness of 1.5 mm.

Applicability of nonlinear ultrasonic technique to evaluation of thermally aged CF8M cast stainless steel

Abstract Cast austenitic stainless steel (CASS) is used for fabricating different components of the primary reactor coolant system of pressurized water reactors. However, the thermal embrittlement of CASS resulting from long-term operation causes structural safety problems. Ultrasonic testing for flaw detection has been used to assess the thermal embrittlement of CASS; however, the high scattering and attenuation of the ultrasonic wave propagating through CASS make it difficult to accurately quantify the flaw size. In this paper, we present a different approach for evaluating the thermal embrittlement of CASS by assessing changes in the material properties of CASS using a nonlinear ultrasonic technique, which is a potential nondestructive method. For the evaluation, we prepared CF8M specimens that were thermally aged under four different heating conditions. Nonlinear ultrasonic measurements were performed using a contact piezoelectric method to obtain the relative ultrasonic nonlinearity parameter, and a mini-sized tensile test was performed to investigate the correlation of the parameter with material properties. Experimental results showed that the ultrasonic nonlinearity parameter had a correlation with tensile properties such as the tensile strength and elongation. Consequently, we could confirm the applicability of the nonlinear ultrasonic technique to the evaluation of the thermal embrittlement of CASS.

Formation Mechanism of Large Inclusions in 80t 20Cr–8Ni Stainless Steel Casting for Nuclear Power

80t 20Cr–8Ni stainless steel castings are used to manufacture pump casing for nuclear power. However, large inclusions are usually observed on an ingot surface, which cause failure in penetrant testing. To clarify the formation mechanism of large inclusions, the evolution, growth, and aggregation of inclusions during the argon oxygen decarburization furnace (AOD) refining–Ca treatment–ingot casting process are investigated. The results show that Al2O3 clusters >50 μm and single Al2O3 particles >10 μm are typical large inclusions on ingot surface. After aluminum addition in AOD, typical inclusions are spinel or dual‐phase CaO–MgO–Al2O3. After Ca treatment, typical inclusions are liquid or dual‐phase CaO–MgO–Al2O3. With temperature decreasing during casting process, the mass fraction of Al2O3 keeps on increasing due to decreasing oxygen and aluminum solubility. It is concluded that Al2O3 is formed during casting process. Single Al2O3 particles grow up to ≥7.5 μm or more. With the size of single Al2O3 particles increasing, Al2O3 clusters are formed mainly through Stokes and turbulent collision. In addition, the aggregation area of single Al2O3 particles and Al2O3 clusters is formed on the surface of ingot.

Electrochemical Impedance Study of Cast and ALM Stainless Steel Electropolishing in Acids Media and Deep Eutectic Solvents

Electropolishing (EP) process is now extensively used as a post-treatment particularly for additive manufacturing parts. This electrolytic dissolution process consists in a controlled dissolution of metallic surfaces leading to both surface roughness decrease and brightness increase, and is usually performed in concentrated acidic media. Interestingly, alternatives eco-friendly electrolytes depending on the metal type have been developed during the last years such as Deep Eutectic Solvents 1,2. Four distinct regions appear on a typical electropolishing polarization curve,3–5namely the active dissolution of the substrate after the oxide layer breakdown, a viscous film formation at the interface electrolyte/substrate (not always present), a limiting current plateau ascribed to a diffusion controlled mechanism (this corresponds to the electropolishing zone), and the solvent oxidation and oxygen evolution domain. Given the complexity of the electropolishing process, many mechanisms have been proposed. Among them, the most commonly accepted explanations consists in the presence of a resistive layer due to dehydratation, oxide formation or saturation of dissolved metal ions at the electrode interface. In this respect, the electropolishing mechanism was investigated by Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS) for 316L Stainless Steel in phosphoric and sulfuric acid media and choline chloride-ethylene glycol mixtures. Then an extended study has concerned additive manufacturing parts. The control of the dissolution reaction by diffusion was confirmed with the linear dependence of the limiting current density vs.electrode rotation rate as described by the Levich’s law. Nevertheless, varying the viscosities by changing temperature from 35°C to 70°, show a direct relationship between the diffusion coefficient and the kinematic viscosities, irrespective of the cation concentration at the interface, which suggest a minor role in the diffusion limiting step. This limitation is therefore provided by the diffusion of an acceptor specie from the electrolyte toward the anode surface. To discriminate the role of water or mineral anion, a full descriptive model of the electrochemical behaviour of interface was developed, based on the corresponding hypotheses. This model found its roots in iron corrosion and electropolishing considerations.6Additionally, EIS measurements were carried out in acidic and DES media. This enable to confront experimental results with the theoretical model for the dissolution reaction. In the first case, water was assumed to be the limiting specie, whereas and in the second case an acceptor specie (as phosphates or chlorides) was considered. A similar study has been conducted for both cast and additive manufacturing 316L Stainless Steel in both acidic and DES media. In all cases, the proposed model allows to predict the electrochemical behaviour of the system. A. P. Abbott, G. Capper, K. J. McKenzie, A. Glidle, and K. S. Ryder, Phys. Chem. Chem. Phys., 8, 4214 (2006). C. Rotty, M.-L. Doche, A. Mandroyan, and J.-Y. Hihn, ECS Trans., 77, 1199–1207 (2017). C. Rotty, A. Mandroyan, M.-L. Doche, and J. Y. Hihn, Surf. Coat. Technol., 307, Part A, 125–135 (2016). C. A. Huang, J. H. Chang, W. J. Zhao, and S. Y. Huang, Mater. Chem. Phys., 146, 230–239 (2014). A. M. Awad, N. A. A. Ghany, and T. M. Dahy, Appl. Surf. Sci., 256, 4370–4375 (2010).J.-P. Diard, P. Landaud, J.-M. Le Canut, and B. Le Gorrec, in, 6ème Forum sur les Impédances Electrochimiques - Montrouge - France (1992). Figure 1

Numerical prediction of thermal aging and cyclic loading effects on fracture toughness of cast stainless steel CF8A: Experimental and numerical study

This paper presents a FE simulation method to predict the thermal aging effect on fracture behavior of cast stainless steel CF8A under monotonic and very low-cyclic fatigue loading conditions. A multi-axial fracture strain energy damage model is determined from tensile and C(T) test data of un-aged CF8A under the monotonic loading condition. To simulate fracture behavior of aged CF8A, the multi-axial fracture strain energy of aged CF8A is obtained by multiplying the thermal aging constant determined from tensile test data by the multi-axial fracture strain energy of the unaged CF8A. The model is then extended to predict fracture behaviours of unaged and aged CF8A under fully-reversed cyclic loading. For the damage model, the model determined for the monotonic loading is applied to simulate fracture behavior under cyclic loading, based on the assumption that fracture energy is not dependent on the loading mode. It is shown that simulation results can capture the thermal aging effect on fracture behavior under monotonic and cyclic loading well.

Design of wear and corrosion resistant FeNi-graphite composites by laser cladding

Friction and wear can cause severe surface damage of machine elements and result in their complete failure. Of the several ways to limit/control friction and wear, a measure to counter the potential damage is to apply a layer of a material with more desirable surface properties, which also provides the flexibility to use cost-efficient bulk materials. In systems under dry sliding conditions, such as railway switches, replacing the components cost considerable time and money. In the current study, laser cladding, a well-known powerful process for repair engineering, was used to fabricate new innovative low friction materials for dry sliding contacts that are exposed to corrosive attacks. The successful implementation of graphite as a solid lubricant in dry sliding conditions is well-known. A homogenous coating with an austenitic FeNi-based alloy containing different percentages of graphite was applied by means of laser cladding using preplaced powder method. The effect of graphite content and its lateral distribution on the friction and wear properties is investigated using a modified ASTM G65 test rig in two-body sliding configuration. Tribological results showed that increasing graphite content in the clads significantly reduces wear, but the level of the coefficient of friction appears to be determined mainly by the composition of the matrix. The wear resistance can be further increased by maximising the inter-particle distances. On the whole, clads of all compositions had superior wear resistance compared to reference materials such as stainless steel XNi22 and cast iron GJL250. The clads were further classified in terms of corrosion resistance against synthetic sea water in a modified potentiodynamic setup. The resistance to wear and corrosion improve with graphite content.

Three-Dimensional (3D) Microstructure-Based Modeling of a Thermally-Aged Cast Duplex Stainless Steel Based on X-ray Microtomography, Nanoindentation and Micropillar Compression

Finite element analysis was conducted on a thermally-aged cast duplex stainless steel based on the true three-dimensional (3D) microstructure obtained from X-ray microtomography experiments and using the constitutive behavior of each individual phase extracted from nanoindentation on single-crystal and bicrystal micropillar compression tests. The evolution of the phase morphology, the mechanical properties and the boundary deformation behavior during the aging process are highlighted. Quantitative analysis in terms of the distribution and evolution of the stress and strain in both the as received and aged conditions was performed. The experimental results show that aging at an intermediate temperature has a negligible influence on the morphology of the two phases in cast duplex stainless steel (CDSS). Results from simulations reveal that the mechanical behavior of this material were seriously affected by the microstructure and the mechanical properties of the individual phase and the necking deformation tend to form in the area with less large ferrite grains after aging. In addition, stress localization tends to form at the austenite/ferrite interface, in the narrow region of ferrite grains and in the small ferrite grains.

Effects of thermal aging on the fracture toughness of cast stainless steel CF8

Cast stainless steels are widely used in the primary coolant systems of nuclear power plants because of their high strength, toughness, and corrosion resistance. Mechanical property degradation due to thermal embrittlement of the ferrite phase is of major concern in long-term operations. To investigate the aging-induced loss of fracture resistance in cast stainless steels, static fracture resistance (J-R) testing was performed for three different CF8 stainless steels with significantly different δ-ferrite contents. The materials were thermally aged at 290–400 °C for up to 10,000 h and tested in static fracture at 25–400 °C. It was found that the fracture toughness in high-ferrite materials generally decreased with thermal aging, while the relationship between aging and fracture toughness in low-ferrite materials was complicated, showing non-monotonic variation with the degree of aging. While significant degradation was observed for long-term aged high-ferrite materials, no material tested showed a K0.2mm value less than 100 MPa√m.

Electrochemical investigation of in-service thermal aging in two CF8M cast stainless steels

In-service thermal aging of CF8M cast austenitic stainless steel was investigated in materials removed from the steam generator inlet and crossover elbows of the Ringhals 2 pressurized water reactor nuclear power plant unit after approximately 92kh of full operating time. The thermal aging of these materials was investigated using the double loop electrochemical potentiokinetic reactivation method, coupled with indentation hardness measurements and microstructural characterizations, to identify correlations between the electrochemical behavior and traditional methods of investigating thermal aging embrittlement effects in cast stainless steels. While this electrochemical method can be easily employed to quantify thermal aging effects in materials aged at higher temperatures (e.g. greater than 350∘C), this study highlights the difficulties encountered when electrochemically evaluating the aging of materials exposed to nuclear power plant operating conditions.

Designing for Turbine Housing Weight Reduction Using Thermal Fatigue Crack Propagation Prediction Technology

<div class="section abstract"><div class="htmlview paragraph">Turbine housings in car engine turbochargers, which use costly stainless steel castings, account for nearly 50% of the parts cost of a turbocharger. They are also the component which controls the competitiveness of the turbocharger, in terms of both function and cost. In this research, focusing on thermal fatigue resistance which is one of the main functions demanded of a turbine housing, achieving reduction in wall thickness while securing sufficient thermal fatigue resistance, it is possible to reduce the amount of material used in the turbine housing and aimed for cost reduction. Therefore, we built a method to quantitatively predict, using 3D FEM, the lifespan from the initiation of thermal fatigue cracking to the formation of a penetrating crack which leads to gas leakage. This prediction method uses the Abaqus general-purpose nonlinear analysis software from Dassault Systèmes, and produced a low-cycle fatigue analysis by the direct cyclic algorithm, by identifying the parameters for analysis from the results of RIG tests, which applied hot-cold cycle loads. In addition, we reduced the analysis time by using submodel analysis with only the model near the evaluation part cut out. By combining the crack propagation prediction technology using CAE, which was built in this research, with existing shape optimization software, we were able to produce designs which reduced turbine housing mass by 10% or more, while maintaining thermal fatigue resistance.</div></div>

Influences of sputtering process factors on wear resistance of TiN coated on a machine component

In this work, effects of sputtering process factors including DC current, pressure and Ar to N2 flow rate ratio on wear resistance of TiN coated on cast stainless steel of a fishing net-weaving machine part namely, an upper hook were systematically investigated using 2k factorial design, analysis of variance (ANOVA) and other statistical tools. Wear testing experiments of the TiN coated upper hooks were carried out on the real fishing net weaving machine. A normal probability of effects and main and interaction effect plots of process factors were constructed in order to identify the statistically significant process factors and to determine an appropriate operating condition of the process factors with the lowest weight loss. The Ar to N2 flow rate ratio and the interaction between the pressure and the Ar to N2 flow rate ratio were found to be statistically significant while pressure and sputtering DC current were not statistically important.

Influence of Nonmetallic Inclusions on the Failure of Cast Stainless Steels

The structure of high-strength 09Kh16N4BL and 14Kh17N2L stainless steels produced by casting on fusible models is studied. The influence of the steel composition on the content of nonmetallic inclusions in the cast steel is of considerable interest. The morphology of the nonmetallic inclusions is studied, and they are identified. Fractographic analysis shows that the nonmetallic inclusions affect the failure of the stainless steels. Two methods are used for quantitative assessment of that influence. Besides the classical methods, multifractal parameterization of the structure is employed to study the structure of the stainless steels. On that basis, correlations are established between the main multifractal parameters and the mechanical properties of the steel.

Influence of Cooling Rate on the Ferrite Prediction Diagram of Duplex Stainless Steel Castings

Six different composition steels were designed based on CD3MWCuN, a common industrial alloy formulated to have a microstructure consisting of 50 pct ferrite and 50 pct austenite. The steels were designed to have ± 10 pct Cr, Ni, and Mo over the nominal composition of CD3MWCuN and were obtained by remelting a keel bar of the base alloy and adjusting the composition. The + compositions variations were achieved simply by adding additional Cr, Ni, or Mo, while the − variations were obtained by adding additional amounts of the remaining major elements to the nominal composition of the keel bar. In this way it was possible to produce a series of alloys where the Cr/Ni equivalent ratio, Creq/Nieq, as calculated using the equations first employed by Schoffler varied from ≈ 1.35 to 1.65. A series of homogenization temperatures ranging from 1000 °C to 1250 °C were used to produce a uniform starting microstructure and the alloys were cooled at rates ranging from 500 °C to 1000 °C/hour from these homogenization temperatures. Air-cooled and water-quenched samples were examined as well. Based on observations of the microstructure a generalized ferrite prediction diagram was developed that takes into account homogenization temperature, cooling rate, and chromium-to-nickel equivalence ratio (Creq/Nieq) to predict the amount of ferrite that can be expected in the alloy. This diagram represents the first major evaluation of ferrite content as a function of homogenization temperature and cooling rate specifically for cast duplex alloys.

Fracture toughness prediction of thermally-aged welded stainless steels using multi-axial fracture strain FE damage model

Thermal ageing constant “C” concept was applied with multi-axial fracture strain FE damage model to predict the fracture toughness of aged gas tungsten arc weld (GTAW) type 316L stainless steel (SS). Although the model was developed for cast stainless steel (CASS), it showed good agreement with GTAW SS. Then, a study was conducted to find the relationship between the fracture toughness of aged GTAW SS and ductility-related variables such as reduction of area (R.A), multi-axial fracture strain or thermal ageing constant “C”. And it was found out that the thermal ageing constant “C” has a linear relation with the fracture toughness of aged GTAW SS.

Electrochemical Superfinishing of Cast and ALM 316L Stainless Steels in Deep Eutectic Solvents: Surface Microroughness Evolution and Corrosion Resistance

Significant weight and cost savings are provided by Additive Laser Manufacturing (ALM) compared to mechanical machining, particularly for complex shape parts. However, ALM as-printed parts are affected by surface defects and roughness and require a post-treatment, which can be done with an electrochemical polishing performed in harmful solutions, sometimes following another processes such as chemical etching. The same possibilities still exists for ALM parts in applications that require a mirror-like finishing which can be obtained after a mechanical polishing step. This paper focuses on ALM 316 L pre-polished parts, successfully electropolished in a Deep Eutectic Solvent composed of choline chloride + ethylene glycol mixture. A typical electropolishing behavior, characterized by the presence of a large current density plateau on polarization curves was observed. In situ Atomic Force Microscopy measurements allowed surface modifications and film formation during the polishing process to be followed. After electropolishing, both Cast and ALM samples exhibit bright and smooth aspects, revealing a high roughness reduction. The pitting corrosion resistance of both materials is also enhanced by this process.

Modeling and Analysis of Exhaust Manifold using CFD

This project goals in re-designing an exhaust manifold by means of determining the thermal stresses and deflections exhibited underneath various operating situations with distinctive materials and temperatures. The objective is to make certain the suitability of the design for two diffrent fabric from the view point of reliability and serviceability. Defects in present manifold are cracks normally occur because of prolonged publicity to severe temperatures, defects in casting and repeated warmness cycling. Welded regions and the curved profiles are the essential regions of failureA methodology is developed to ensure the best suited design and material for the given operating conditions, Manifold behaviour is analysed on two different materials such as stainless steel and grey cast iron. Redesigning the curved profiles can reduce the turbulence effect of the exhaust gases on the welds. High-end CAD/CAM software such as SOLIDWORKS 2016 and ANSYS 16.0 are used for modelling and analysis. Exhaust manifold is design by using solidworks software and transfer to ansys software, Computational fluid dynamic analysis is performed to study flow characteristics such as pressure velocity and temperature to study its performance and back pressure factors, and temperature after convection by surrounding air, than the same temperature after CFD analysis is applied on body in static structural analysis module to study its strength on thermal load that is to find out its stresses and deformation on working thermal load conditions, the material which give good strength to weight ratio will conclude the best material.