Conventional Low-carbon Steel Research Articles

Fabrication and Experimental Investigation of Composite Pressure Vessel

Abstract: Composite pressure vessels are an important type of high-pressure containers that are widely used in aerospace industries. The pressure vessels develop hoop stresses that are twice the longitudinal stresses. CFRP (Carbon Fiber Reinforced Polymer) composite materials with their higher specific strength and characteristics will result in reduction of weight of the structure when compared with isotropic materials like steel. The present work is aimed in understanding the behaviour of the Composite Pressure Vessel with variation of internal pressure. In this connection, a pressure vessel using CFRP (Carbon Fiber Reinforced Polymer) is fabricated which can hold liquids or gases under pressure and is tested at various pressures. The FEA tool ANSYS 14.5 is used to determine better fiber angle required for liquid storage, when the conventional low carbon steel cylinder is replaced with CFRP Pressure Vessel.

Effect of alloying (Cr, Mo, and V) on corrosion behaviors of API-grade steel in CO2-saturated aqueous solutions with different pH

The corrosion behaviors of steels alloyed with Cr, Mo, and V were examined in two different solution chemistries: near-neutral (pH 6) and weakly acidic (pH 4.5) solutions saturated with CO2. In near-neutral solutions, Cr alloying hindered the formation of a stable corrosion scale on the surface, reducing the corrosion resistance compared to conventional low-carbon steel. On the other hand, the alloyed steel exhibited higher corrosion resistance in acidic solutions. In contrast to the conventional carbon steel, which had a single scale of crystalline FeCO3 scale on its surface, a more stable bi-layer of corrosion scale consisting of an inner layer of amorphous Cr(OH)3 and an outer layer of crystalline FeCO3 was developed on the alloyed steel. This was attributed primarily to the increased thermodynamic stability of Cr(OH)3 with an increase in Cr contents at this solution pH. Moreover, the increase in Cr with Mo addition resulted in a refinement of FeCO3 on the outer surface through increased hydrolysis reactions leading to a decrease in the local pH on the steel surface. Furthermore, adding V, even in minute quantities contributed to an increase in Cr-enrichment in the inner scale by suppressing M7C3 precipitation and leaving more Cr in the solid solution.

Synergistic enhancement of strength, ductility, and toughness in a low carbon micro-alloy steel with an ultrafine-grained heterogeneous lamellar structure

Structural materials with heterostructure design have emerged as an efficient strategy to address the dilemma of balancing strength and ductility/toughness, resulting in increased interest from the scientific community. In this study, a novel ultrafine-grained heterogeneous lamellar (HL) structure has been architected in a common low-carbon micro-alloyed steel. The heterostructured steel exhibits a lamellar microstructure comprising alternating ultrafine/nano-grained lamellae and micrometer-grained lamellae, with a texture gradient along the thickness. Results show that the HL structure has a tensile strength comparable to quenched and tempered martensite (QTM) steel while retaining similar ductility as coarse-grained dual-phase (CG) steel. Furthermore, the HL specimen exhibits enhanced fracture toughness (KQ = 232.8 MPa m1/2), which is 11.3% and 28.8% higher than that in the CG and QTM specimens, respectively. Extrinsically, the macroscopical heterogeneous lamellar structure and microscopical elongated grain shape in ultrafine/nano-grained lamellae could provide substantial lamellar grain boundaries to hinder the connection of voids and make the crack propagation path more tortuous, which effectively increases the energy release rate to contribute to the exceptional fracture toughness. Intrinsically, not only micrometer-sized CG lamellae with high plastic deformation tolerance capacity can develop coarse (deep) dimples for energy consumption, but also the elongated ultrafine martensite grains can undergo significant plastic deformation together with the coordinated deformation of coarse-grained ferrite. We hope the strategy in this study may provide insights for microstructure optimization and synergistic strength-plasticity/toughness enhancement of conventional low-carbon micro-alloyed steels for structural applications.

Distribution of corrosion products at the steel-concrete interface: Influence of mill scale properties, reinforcing steel type and corrosion inducing method

In this study, corrosion products of a Cr-bearing low-alloy (LA) steel and the conventional low-carbon (LC) steel with intact mill scale at the steel-concrete interface were investigated by means of backscattered electron (BSE) images. Furthermore, the effect of mill scale properties and corrosion inducing methods (long-term natural exposure to chloride solution and accelerated corrosion by chloride electromigration) on the distribution and penetration of corrosion products was compared. Complex interactions were highlighted between the corrosion products and the mill scale of LC and LA steels at the steel-concrete interface. In addition, different corrosion patterns of both steels were evident when subjected to different corrosion inducing methods.

The Effect of Flue Gas Environment on the Corrosion Behavior of the Sulfuric Acid Dew-Point Corrosion Resistant Steel

In order to compare the corrosion resistance of conventional low carbon steel, Cu containing low carbon steel for sulfuric acid dew-point corrosion inhibition, and stainless 409L, immersion tests were carried out in 50 wt.% sulfuric acid. The effects of HCl concentraion on the corrosion behavior in a fixed sulfuric acid concentration (16.9 vol.%) was also investigated by immersion test. In addition to immersion test, field test in a thermal plant was carried out for 10 months. As a result, it was confirmed that Cu-containing dew-point corrosion resistent steel has the highest corrosion resistance compared with other materials. To verify superior corrosion resistence of dew-point corrosion resistant steel, surface morpology after various test was observed by SEM. It was found that surface corroded product of the dew-point corrosion resistant steel was much denser and thicker compared with the other steel.

Electrochemical behaviour of a novel alloy steel in alkali-activated slag mortars

The present paper aims to investigate the passivation capability and accelerated chloride-induced corrosion behaviour of a novel alloy steel (00Cr10MoV) and a conventional low-carbon steel (20MnSiV) in ordinary Portland cement (OPC) and alkali-activated slag (AAS) mortars. Both steels were embedded in mortars with intact mill scale. Compared with OPC mortar, AAS mortar resulted in the formation of less protective passive film for both 20MnSiV and 00Cr10MoV steels after passivation due to the presence of reducing sulphides. Despite this, the initial negative effect of AAS mortar on 20MnSiV steel can be well compensated by its denser interfacial microstructure after the occurrence of active corrosion induced by chlorides. As for 00Cr10MoV steel in AAS mortar, however, this compensating effect was less pronounced. Moreover, unexpected low passivation capability and corrosion resistance can be confirmed for 00Cr10MoV steel in both OPC and AAS mortars due to the presence of defective and Cr-depleted mill scale.

Long-Term Electrochemical Behavior of Low-Alloy Steel in Simulated Concrete Pore Solution with Chlorides

AbstractThe passivation capability and long-term chloride-induced corrosion behavior of a low-cost low-alloy (LA) steel and the conventional low-carbon (LC) steel in a simulated concrete pore solut...

Pitting corrosion resistance of a novel duplex alloy steel in alkali-activated slag extract in the presence of chloride ions

In this study, two types of reinforcing steels (conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions (ordinary Portland cement (OPC) extract and alkali-activated slag (AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various NaCl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.

A Review of Electrically-Assisted Manufacturing With Emphasis on Modeling and Understanding of the Electroplastic Effect

Increasingly strict fuel efficiency standards have driven the aerospace and automotive industries to improve the fuel economy of their fleets. A key method for feasibly improving the fuel economy is by decreasing the weight, which requires the introduction of materials with high strength to weight ratios into airplane and vehicle designs. Many of these materials are not as formable or machinable as conventional low carbon steels, making production difficult when using traditional forming and machining strategies and capital. Electrical augmentation offers a potential solution to this dilemma through enhancing process capabilities and allowing for continued use of existing equipment. The use of electricity to aid in deformation of metallic materials is termed as electrically assisted manufacturing (EAM). The direct effect of electricity on the deformation of metallic materials is termed as electroplastic effect. This paper presents a summary of the current state-of-the-art in using electric current to augment existing manufacturing processes for processing of higher-strength materials. Advantages of this process include flow stress and forming force reduction, increased formability, decreased elastic recovery, fracture mode transformation from brittle to ductile, decreased overall process energy, and decreased cutting forces in machining. There is currently a lack of agreement as to the underlying mechanisms of the electroplastic effect. Therefore, this paper presents the four main existing theories and the experimental understanding of these theories, along with modeling approaches for understanding and predicting the electroplastic effect.

Nanostructured Steel Susceptibility to Sulfide Stress Cracking

The susceptibility of a high strength low alloy nanostructured steel to sulfide cracking resistance (SSCC) is assessed. Notch Tensile Slow Strain Rate (NTSSRT) method is used to evaluate the threshold stress intensity values (KISSCC)). The objective is to understand the effect of the microstructure on the susceptibility to SSCC, the control condition is a conventional low alloy carbon steel with a tempered martensite micro structure. The tests were performed in a brine with 1% NaCl buffered at pH 4.5 with H2S gas with 1% to 100% (mol %) balance N2 at room conditions. The nanostructured steel results of the KISSCC parameter are: 107 Ksi in0.5 at 1% H2S to 42 Ksi in0.5 at 100% H2S. The control condition exhibited 22 Ksi in0.5 at 100% H2S. The evaluation of the relative crack propagation energy suggest that the nanostructured ferrite grains exhibit a much lower susceptibility to SSCC than the tempered martensitic microstructure

Finite Element and Experimental Analyses on the Formability of Steel Sheets Produced by Compact Endless Cast and Rolling

Although the compact endless cast and rolling mill (CEM) is a promising candidate as a next-generation energy-saving steel process, due to its short history, the formability of the steel sheet produced by the CEM process are not known yet. Herein, drawability and stretchability of low-carbon steel sheets produced by the CEM process are investigated and compared with those of conventional hot-rolled low-carbon steel sheets, to estimate its applicability to industrial parts. Finite element analyses using the Gurson-Tvergaard-Needleman damage model were conducted and compared with the experimental results. Homogeneous microstructure and relatively strong textures of {111}||ND γ-fibers and 〈110〉||RD α-fibers were developed in the CEM-processed steel in comparison with the conventional hot-rolled specimen. The drawn cup of the CEM specimen showed weak earing phenomena, while having higher limiting drawing ratios (2.0 and 1.95 in the experimental and numerical simulation, respectively). Furthermore, a difference in limit dome height between the two specimens is negligible. Therefore, it is confirmed that CEM-processed steels have comparable properties of strength and formability, provide an effective manufacturing process, and exhibit good potential as a next-generation energy-saving process.

Influence of mill scale and rust layer on the corrosion resistance of low-alloy steel in simulated concrete pore solution

Electrochemical impedance spectroscopy, cyclic potentiodynamic polarization measurements, and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy were used to investigate the influence of mill scale and rust layer on the passivation capability and chloride-induced corrosion behaviors of conventional low-carbon (LC) steel and low-alloy (LA) steel in simulated concrete pore solution. The results show that mill scale exerts different influences on the corrosion resistance of both steels at various electrochemical stages. We propose that the high long-term corrosion resistance of LA steel is mainly achieved through the synergistic effect of a gradually formed compact, adherent and well-distributed Cr-enriched inner rust layer and the physical barrier protection effect of mill scale.

Influence of chloride concentration and pre-passivation on the pitting corrosion resistance of low-alloy reinforcing steel in simulated concrete pore solution

The effect of chloride concentration and pre-passivation on the pitting corrosion resistance of low-alloy steel and conventional low-carbon steel in simulated concrete pore solution was investigated using electrochemical techniques and surface analysis measurements. The results show that the passive film could enhance the pitting corrosion resistance for both investigated steels. Low-alloy steel exhibits slightly lower pitting corrosion resistance at low chloride concentration compared to low-carbon steel, regardless of the passivation condition. However, at high chloride concentration, low-alloy steel shows higher pitting corrosion resistance due to the formation of Cr-enriched protective rust layer.

Laser Welded Corrugated Steel Panels in Industrial Applications

Corrugated core steel panels are an effective way to reduce weight and increase stiffness of steel structures. In numerous applications, these panels have shown very promising commercial possibilities. This study presents the design, manufacturing and commercializing process for two practical examples: Case 1) a fly wheel cover for a diesel engine and Case 2) rotationally symmetrical panel for an electric motor. Test materials of various kinds were used for corrugated cores and skin plates: conventional low-carbon steel grade EN 10130 and ferritic stainless steel grade 1.4509 with plate the thicknesses of 0.5, 0.6 and 0.75mm. To manufacture different kinds of corrugated core steel panels, flexible manufacturing tools and cost-effective processes are needed. The most important criterion for laser welding panels was the capability of forming tools for producing high quality geometry for the core. Laser welding assembly showed that the quality of the core in both studied cases was good enough for welding the lap joints properly. Developed panels have been tested in industrial applications with excellent feedback. If thickness of a corrugated panel structure is not a limiting issue, these panels are good solution on application where stiffness and lighter weight are required as well as vibrational aspect considered.

Mechanical Properties of a Metal Sandwich Panel Manufactured Using Longitudinally Laminated Forming Tools

Sandwich panel structures are increasingly used in applications where the most important demands are the weight saving and long service life. Utilizing sandwich panels, extremely light-weight, stiff and robust structures can be manufactured. In this study, sandwich panels were produced by specially designed cost-effective forming tools. Various kind of test materials were used for corrugated cores and skin plates: conventional low-carbon steel grade EN 10130 and ferritic stainless steel grade 1.4509 with plate thicknesses of 0.6 and 0.75 mm. A common S355 structural steel was used as a reference for bending strength comparison.For measuring the stiffness, MTS tensile and fatigue testing machine was selected to determine the bending resistance of the sandwich panels. The bending force, needed for yielding and fracture, related to the bending length and intensity was compared with the results from bending of the reference plates. Results showed that the bending force of the panels is significantly higher than that of a plate having similar intensity. The best results were obtained with the stainless steel (SS) panel that had 27% higher bending force at the yield point than 5 mm thick S355 plate having 3 times larger intensity. The carbon steel panel was approximately 40% weaker than the SS-panel and both panel types lost strength when loading direction was changed from transverse to 45 degree and further to 90 degree load (longitudinal).

Microstructure and Mechanical Properties of Ultrafine Lath-Shaped Low Carbon Steel

The mechanical properties of ultrafine lath-shaped low-carbon steel plates were studied. Results indicated that the hardness and tensile strength of the conventional low-carbon steel are HRC 19 and 410 MPa, respectively. With the decreased grain size of the ultrafine lath-shaped steel plates, the hardness and tensile strength of the test samples rapidly increase. Mechanical properties are at their optimum when grain size reaches 90 nm. Furthermore, both the hardness and the tensile strength values reach their maximum, which are HRC 53.5 and 1217 MPa, respectively.

Effect of Electrode Force on Expulsion in Resistance Spot Welding with Initial Gap

Compared with the conventional low carbon steels, the expulsion is more prone to occur in resistance spot welding (RSW) of dual phase (DP) steels. Especially when the initial gap exists between the steel sheets, the weld expulsion would reduce the weld quality of the joint. It is important to decrease or inhibit the occurrence of the weld expulsion in auto-body assembly line in order to guarantee the joint quality. In this study, the experiments of RSW with different initial gaps have been done to study the effect of the electrode force on the expulsion using different thicknesses of dual phase steels. The results show that the increment of the electrode fore would enable to decrease the occurrence of expulsion with the increase of the sheet thickness and gap spacing in resistance spot welding of DP steel sheets.

A Finite Element Modeling for Dilatometric Nonisotropy in Steel

It is well known that nonisotropic volume changes in dilatometry were observed during the phase transformation in steel. In this study, a finite element (FE) model incorporating the transformation plasticity was adopted to describe the nonisotropic dilatometric behavior during the phase transformation in steel. An implicit numerical solution procedure to calculate the deformation during the dilatometric experiment was incorporated into the general purpose implicit FE program. The nonisotropic dilatometric behavior could be successfully reproduced by using the FE simulation considering the transformation plasticity. The transformation plasticity was caused by the small amount of stress that naturally developed in the specimen during the dilatometric experiment. In conventional low carbon steel, the stress in the specimen mainly forms due to the very small external force supplied to support it during the dilatometric experiment. As regards ultralow carbon steel, whose phase transformation occurs within an extraordinarily narrow temperature range, the inhomogeneous phase transformation due to the temperature deviation in the specimen was mainly responsible for the stress field in the specimen during the dilatometric experiment.

Mechanical Properties and Temper Resistance of Deformation Induced Ferrite in a Low Carbon Steel

The microstructures and mechanical properties of deformation induced ferrite (DIF) in the low carbon steel Q235 under different deformation temperatures have been investigated systematically. Through deformation induced ferrite transformation (DIFT), ferrite grain can be refined to 3 mu m and accounts for above 85% of the overall fraction. Yield strength of DIF (>500 MPa) is increased by up to 100% compared with the conventional low carbon steel. Comparison of microstructure and mechanical properties in the Q235 steel with DIF and tempered DIF microstructure illustrates that the strengthening mechanism of DIF microstructure is the combination of grain boundary strengthening and carbon supersaturated strengthening. Electron back-scattered diffraction (EBSD) analysis and high magnification scanning electron microscopy (SEM) observation denote that high-angle grain boundary among ultrafine ferrite grain and the transformation product of retain austenite membrane along ferrite boundaries are responsible for the stability of ferrite grain size during tempering process. Transmission electron microscopy (TEM) analysis demonstrates that the transformation product of retained austenite membrane between ferrite grain boundaries is cementite.

PEM Fuel Cell Separator with Thermally Nitrided Low Carbon Steel

The separator is one of the most important parts in PEM fuel cells. Stainless steels are widely used as separator for its good mechanical properties and mass production. However, for a good chemical compatibility, stainless steels need to have high chromium content or surface treatment, which makes separator high cost. Low cost of separator is important for commercial use. In this study, conventional low carbon steel is used as base metal of separator. Low carbon steel is low at cost, but has poor chemical properties for separator. For a good corrosion resistance, low carbon steel needs to be surface treated. To make a uniform surface treated layer on low carbon steel, chromium is conventionally electroplated on the steel and thermally nitrided. Surface treated low carbon steel is investigated using microstructure and element analysis tools. Interfacial contact resistance and polarization test is applied for the properties of fuel cell separator. The results show that chromium nitrided layer uniformly formed on low carbon steel. And the surface treated steel showed a good corrosion resistance as a separator.