Mechanical Properties Of Steel Research Articles

Influence of Hydrogenation on Residual Stresses of Pipeline Steel Welded Joints

Hydrogen embrittlement is a phenomenon that affects the performance of steel used for oil and gas pipelines. This paper presents a study of the effect of hydrogenation on the residual stresses of an API 5L X65 steel pipe. Residual stresses were analyzed by X-ray diffraction technique using the sin2Ψ method. The hydrogenation of base metal and welded joint specimens was performed by electrochemical tests in a simulated soil solution NS4. Results show that the hydrogenation led to significant changes in residual stress configuration and in the mechanical properties of steel. The hydrogenation increased the magnitude of the longitudinal residual stress of base metal and fusion zone, without changing the tensile/compressive nature. On the other hand, the hydrogenation increased the intensity of the tangential stress of base metal, and changed from compressive to tensile the residual stress of the fusion zone. The microstructural characterization by optical and scanning electron microscopy was used to complement this study.

Effect of Strain History of Steel Sheets on the Mechanical Characteristics of Individual Microstructural Components by Depth Sensing Indentation

The macroscopic mechanical properties of steel are highly dependent upon microstructure, crystallographic orientation of grains and distribution of each phase present, etc. Nanomechanical testing using depth sensing indentation (DSI) provides a straightforward solution for quantitatively characterizing each of phases in microstructure because it is very powerful technique for characterization of materials in small volumes. Measuring the local properties of each microstructure component separately in multiphase materials gives information that is valuable for the development of new materials and for modelling. The work experimentally analyses the effect of strain history on the mechanical properties of individual components in steel sheets by depth sensing indentation. The measurements were carried out on broken tensile specimens.

Controlled Phase Transformation Simulations to Design Microstructure for Tailored Mechanical Properties in Steel

Advanced materials with light weight but having high strength and ductility are required to decrease the weight of automobiles. Hereby, advanced high-strength steels like dual-phase steels and multiphase steels are vital as they possess good strength in conjunction with good formability. Several methods have been used for the processing of multiphase steels but very limited research has been reported on their processing through controlled cooling and by using a lean composition. The present research reports on methods of production of dual-phase/ multiphase microstructures in a steel of lean chemical composition (0.11C, 1.8Mn, and 0.325Si), making the steel multifunctional. Annealing parameters were determined using Thermo-Calc and JMat-Pro software. Software predictions were validated through experiments in a muffle furnace, followed by actual annealing experiments in an annealing simulator. Multiphase microstructures were obtained from the initial ferrite-pearlite structure by inter-critical annealing involving controlled cooling in the annealing simulator. Dual-phase structures were produced by inter-critical annealing, followed by rapid cooling to room temperature, whereas multiphase microstructures were produced by holding in the bainitic and martensitic ranges, respectively. The steel exhibited good combinations of strength–ductility, with tensile strength and ductility in the range of 550–705 MPa and 11–33%, respectively.

Artificial Intelligence in the AHSS Steel Mechanical Properties and Microstructure Analysis

Artificial Intelligence in the AHSS Steel Mechanical Properties and Microstructure Analysis

Effect of Rare Earth Cerium Addition on Microstructures and Mechanical Properties of Low Carbon High Manganese Steels

AbstractLow carbon high manganese steels with different Ce contents were melted in medium frequency vacuum induction furnace. The microstructures and mechanical properties of steels were studied by OM, SEM, EDS and mechanical property testing. The results showed that the microstructures of experimental steels were refined remarkably, inclusions distributed more finely and uniformly, the tensile strength and impact toughness of tested steels both improved greatly after the addition of Ce. Thermodynamic calculation results demonstrated that Ce contained inclusions were Ce2O3and Ce3S4, which agreed well with the results observed by SEM and EDS. By analysis of two-dimensional lattice disregistry, it was shown that the lattice misfit parameter between δ-Fe and Ce2O3, Ce3S4are less than 6 %, which indicated that Ce2O3and Ce3S4could effectively act as the heterogeneous nuclei of initial δ-Fe. Therefore, the microstructures were refined significantly and the mechanical properties were improved correspondingly in Ce-added low carbon high manganese steels.

Investigation of acoustic properties of Russian grade 1Cr18Ni10Ti steel

This article presents results of experimental study of the acoustic properties (speed and coefficient of attenuation of ultrasound) and relative temperature expansion of Russian grade 1Cr18Ni10Ti steel in the temprature range of 20–1100°C. The approximating equations for temperature dependences between experimental and calculated thermophysical and mechanical properties of steel are obtained.

Effect of the rolling temperature on the structure and the mechanical properties of high-nitrogen austenitic steels 05Kh21G9N7AMF and 04Kh22G12N4AMF

The structure and the mechanical properties of high-nitrogen austenitic 05Kh21G9N7AMF (0.56% N) and 04Kh22G12N4AMF (0.49% N) steels have been studied after hot rolling. It is found that the temperatures of the onset and end of hot deformation influence the structure and the mechanical properties of these steels. The higher set of mechanical properties of steel 05Kh21G9N7AMF after rolling in the temperature range 1100–900°C is due to the formation of a lamellar and equiaxed fragmented structure.

High-strength economically alloyed corrosion-resistant steels with the structure of nitrogen martensite

The use of nitrogen as the main alloying element allowing one both to increase the corrosion resistance and mechanical properties of steels and to improve their processability is a new trend in physical metallurgy of high-strength corrosion resistant steels. The principles of alloying, which are developed for high-nitrogen steel in IMET RAS, ensure the formation of the structure, which contains predetermined amounts of martensite (70-80%) and austenite (20-30%) and is free from δ-ferrite, σ-phase, and Cr23C6 carbide. These principles were used as the base for the creation of new high-strength corrosion-resistant weldable and deformable 0Kh16AN5B, 06Kh16AN4FD, 08Kh14AN4MDB, 09Kh16AN3MF, 27Kh15AN3MD2, 40Kh13AN3M2, and 19Kh14AMB steels, which are operative at temperatures ranging from - 70 to 400°C. The developed nitrogen-containing steels compared with similar carbon steels are characterized by a higher resistance to pitting and crevice corrosion and are resistant to stress corrosion cracking. The new steels successfully passed trial tests as heavy duty articles.

Effects of extended heat treatment on carbide evolution in Cr-Mo steels

Cr and Mo are known to be effective steel alloying elements for high-temperature applications, and they affect steel mechanical properties via carbide formation. Mechanical properties of Cr-Mo steels affected by the carbide evolution were investigated by performing heat treatments, and the treatment duration was determined by the Larson-Miller parameter fitting. The hardness value decreased after heat treatment at 690°C for 10h with the decomposition of the bainitic microstructure. The quantified chemical composition results for the carbides were plotted on the Fe-Cr-Mo ternary and Fe-Cr binary composition diagrams to classify the types of carbides formed. Most of the carbides were identified as Fe-rich M3C-type carbides at the initial stage of heat treatment. The Fe fraction in the carbides decreased with time while the Cr and Mo fractions increased. The Cr- and Mo-rich carbides were identified as M23C6- and M2C-type, respectively. An increase in the Cr and Mo fractions in the carbides resulted in the decrease in the alloying element concentration in the matrix, which in turn resulted in the deterioration of the solid solution strengthening. Further, it was determined that coarse carbides, observed on the grain boundaries after extended heat treatment, deteriorated the mechanical properties of the alloy.

Design Exploration to Determine Process Parameters of Ladle Refining for an Industrial Application

Due to increasing competition and the demand for light-weight steel, manufacturers strive to produce new grades of steel to meet stringent sets of property specifications. The authors are informed by engineers at a major steel-making plant that for them to determine the set-points for the ladle, tundish, and caster to make a new grade of steel it takes between 20 and 25 physical plant trials. These plant trials are expensive and very difficult to schedule. In this paper, the authors focus on explicating the method for one unit operation in the steel-making process, namely, ladle refining, which is a key operation for maintaining cleanliness and controlling composition; these have a significant bearing on the steel's mechanical properties. The challenge is to determine set points for ladle refining using computational models. In this paper, the authors present a method for visualizing and exploring the solution space using the compromise Decision Support Problem (cDSP). To illustrate the efficacy of the method, the authors determine the set points of the ladle operation in an industrial setting. The focus of the paper is to elucidate the utility of method and not on the analysis models used in the framework.

EFFECTS OF Mn ON MULTI-PRECIPITATES EVOLUTION OF Cu-RICH AND NiAl PHASE IN STEELS

Precipitation hardened steels are widely used in various engineering fields due to their high strength, high fracture toughness, good ductility and ease of machinability. As two kinds of common precipitates, Cu-rich and NiAl phases play an important role on the mechanical properties of steels. The obvious effects of Mn on the precipitate evolution of Cu-rich phase and NiAl phase in steel have been observed respectively. However, the effect of Mn is complex, when Cu-rich phase and NiAl phase exist at the same time. This work aims to reveal the effects of Mn on the co-precipitation of Cu-rich phase and NiAl phase in steel. Fe-Cu-Ni-Al and Fe-Cu-Ni-AlMn steels were aged at 500 °C for different times after solution treatment at 900 °C for 2 h. Hardness testing indicates that by adding 2.17%Mn, Fe-Cu-Ni-Al-Mn steel shows a peak hardness of 420 HV which is 80 HV higher than Fe-Cu-Ni-Al steel (about 340 HV). And Fe-Cu-Ni-Al-Mn steel reaches the peak hardness at 1 h which is 1 h earlier as compared with Fe-Cu-Ni-Al steel at 2 h. Moreover, the peak hardness plateau of Fe-Cu-Ni-Al-Mn steel only lasts for 7 h which is far less than that of Fe-Cu-Ni-Al steel. All in all, the addition of Mn enhances the effect of precipitation hardening at early aging, and accelerates the whole process of precipitation hardening. Atom probe *国家自然科学基金钢铁联合基金培育项目U1460103和新金属材料国家重点实验室开放基金项目 2014-Z08资助 收到初稿日期: 2015-06-30,收到修改稿日期: 2016-03-01 作者简介:沈琴,女, 1992年生,硕士生 DOI: 10.11900/0412.1961.2015.00343 第513-518页 pp.513-518

Effects of Ultra-Fast Cooling Technology on Microstructure and Properties of Low Carbon Steel

The cooling technology after hot-rolling influences the microstructure and mechanical properties of steels. Combined with dynamic continuous cooling transformation (CCT) curve by the thermal simulation experiments of Q235B steel, the effects of ultra-fast cooling technology on microstructure and properties of Q235B steel were investigated by optical microscope, scanning electron microscope, tensile and impact tests. Also, the fracture morphology analysis was conducted by scanning electron microscope. The results show that both yield and tensile strength are enhanced by ultra-fast cooling technology. Moreover, the yield and tensile strength increase with the increase of cooling rate of ultra-fast cooling process, while the ductility has no significant change. Furthermore, the yield and tensile strength increase with the decrease of final cooling temperature of ultra-fast cooling process with a little reduction in ductility. The impact tests show that all samples possess excellent impact toughness varying within a small range. The yield strength, tensile strength, and impact toughness of Q235B steel could increase to 395, 516 MPa, and 143 J, respectively, using ultra-fast cooling technology. The study provides theoretical guidance for industrial application of ultra-fast cooling technology.

Influencing the arc and the mechanical properties of the weld metal in GMA-welding processes by additive elements on the wire electrode surface

Under the premise of an increasing scarcity of raw materials and increasing demands on construction materials, the mechanical properties of steels and its joints are gaining highly important. In particular high- and highest-strength steels are getting in the focus of the research and the manufacturing industry. To the same extent, the requirements for filler metals are increasing as well. At present, these low-alloy materials are protected by a copper coating (<1μm) against corrosion. In addition, the coating realizes a good ohmic contact and good sliding properties between the welding machine and the wire during the welding process. By exchanging the copper with other elements it should be possible to change the mechanical properties of the weld metal and the arc stability during gas metal arc welding processes and keep the basic functions of the coating nearly untouched. On a laboratory scale solid wire electrodes with coatings of various elements and compounds such as titanium oxide were made and processed with a Gas Metal Arc Welding process. During the processing a different process behavior between the wire electrodes, coated and original, could be observed. The influences ranges from greater/shorter arc-length over increasing/decreasing droplets to larger/smaller arc foot point. Furthermore, the weld metal of the coated electrodes has significantly different mechanical and technological characteristics as the weld metal from the copper coated ground wire. The yield strength and tensile strength can be increased by up to 50%. In addition, the chemical composition of the weld metal was influenced by the application of coatings with layer thicknesses to 15 microns in the lower percentage range (up to about 3%). Another effect of the coating is a modified penetration. The normally occurring “argon finger” can be suppressed or enhanced by the choice of the coating. With the help of the presented studies it will be shown that Gas Metal Arc Welding processes are significantly affected by thin film coatings on solid wire electrodes for Gas Metal Arc welding. The influences are regarding the stability of the arc, the properties of the weld metal in terms of geometric expression, chemical composition and mechanical properties, the composition of the arc-plasma and the dynamics of the molten metal.

Three-dimensional finite element simulation and application of high-strength bolts

High-strength structural bolts have been utilized for beam-to-column connections in steel-framed structural buildings. Failure of these components may be caused by the bolt shank fracture or threads stripping-off, documented in the literature. Furthermore, these structural bolts are galvanized for corrosion resistance or quenched-and-tempered in the manufacturing process. This paper adopted the finite element simulation to demonstrate discrete mechanical performance for these bolts under tensile loading conditions, the coated and uncoated numerical model has been built up for two numerical integration methods: explicit and implicit. Experimental testing and numerical methods can fully approach the failure mechanism of these bolts and their ultimate load capacities. Comparison has also been conducted for two numerical integration methods, demonstrating that the explicit integration procedure is also suitable for solving quasi-static problems. Furthermore, by using precise bolt models in T-Stub, more accurately simulate the mechanical behavior of T-Stub, which will lay the foundation of the mechanical properties of steel bolted joints.

Study of Electrolytic Dissolution in Steels and Rare Earth Oxide Stability

Improving the mechanical properties of steels requires an accurate knowledge of inclusions’ shape and size. This work examined the dissolution rate of 1030 steel for two electrolytic solutions and the stability of several oxides. The dissolution rate was compared between two electrolytes (2 % TEA and 10 % AA) for up to 16 h. Also, the study of oxide stability in 2 % TEA was performed. Standard pure oxide powders such as Al2O3, NbO, NbO2, La2O3, and CeO2 were tested by adding 1 g each in 2 % TEA, while it was dissolving a test steel sample for 24 h. In this study, the actual weight of oxides was analyzed by the difference in weight before and after the electrolytic test run. It was observed that NbO and Al2O3 weighed 0.95 and 0.97 g after the electrolytic test, whereas other oxides were more stable during the electrolytic extraction. The stability test indicates that rare earth oxides are stable enough without dissolving and this helps in studying the rare earth inclusions morphology after extracting steel samples.

Tests and design of short steel tubes filled with rubberised concrete

An experimental investigation on the strength and ductility of short steel tubes filled with rubberised concrete (RuC), sourced from recycled scrap tyres, is presented in this paper. Firstly, a brief literature review on (i) concrete-filled steel tubes (CFST) and (ii) mechanical characterisation of rubberised concrete is presented. Then, the experimental investigation is described and test results are shown and discussed, namely, the assessment of (i) RuC and steel mechanical properties and (ii) RuCFST column structural properties. The influence of various parameters, such as the cross-section shape (square, rectangular, circular), steel grade, and concrete mix (standard concrete versus RuC), on the short column strength and ductility is analysed and discussed. Eurocode 4 is considered (i) to determine the strength of the tested columns and, in particular, (ii) to assess its applicability to RuCFST columns based on a comparison with the experimental results. The main conclusion of this research is that RuCFST short columns present higher ductility than those made of standard concrete, even though they also show lower strength. This improved ductility is noticeable in columns with circular sections, rather than in square and rectangular sections. From a practical viewpoint, this could be a major benefit for structures in seismic areas where energy dissipation is needed.

Effects of Various Post-Weld Heat Treatments on Austenite and Carbide Formation in a 13Cr4Ni Steel Multipass Weld

Multipass welding procedures are common methods for 13Cr4Ni steels' fabrication and repairs. Compared to a single-pass weld procedure, the weld microstructure in a multipass weld is more heterogeneous due to the complex local thermal cycles imposed by adjacent weld passes. Furthermore, the final microstructure and mechanical properties of these steels are very sensitive to their thermal history which increases the microstructure heterogeneities. Thus, post-weld heat treatments are performed to reduce heterogeneities and produce a relatively homogenous weld. It has been found that the best option to improve mechanical properties of 13Cr4Ni steels is forming a “room temperature stable austenite” phase by heat treatments. This study focuses on the effects of these post-weld heat treatments on the austenite phase and carbide formations and the related evolutions of microhardness distribution. The study shows that nanometer-size carbides form at martensite lath interfaces and sub-block boundaries, and then at higher temperatures austenite lamellae appear at these locations. Results also show that the highest percentage of stable austenite achievable by a single-stage tempering was obtained at 610 °C. When the heat treatment temperature is lower than 610 °C, longer holding time produces softer steel while longer heat treatments at temperatures higher than 610 °C, produces harder steel. Still, double-stage heat treatments are more effective and produce the highest percentage of austenite and the lowest hardness of all heat treatments.

New Medium-Carbon Free-Machining Steels Containing Bismuth and Calcium

The paper describes the properties of two new medium-carbon free-machining alloy structural steels. These steels are environmentally friendly since lead in them is replaced with much less harmful elements bismuth and calcium. Bismuth and calcium are rather uniformly distributed in the ingot, though there are two zones of bismuth heterogeneity in the bottom and in the head part of the ingot. Mechanical properties of steels are at the same level as for steels without bismuth and calcium. Non-metallic inclusion content is typical for structural steels melted in open electric arc furnaces with basic lining and is not changed by the presence of bismuth and calcium. Machinability of the steels with bismuth and calcium is at the same or higher level than that of lead-bearing steels. Melting, casting, forging and rolling of steel containing bismuth and calcium is not associated with working area air-pollution with harmful substances in amounts exceeding maximum permissible concentrations. During rolling of the lead-free steels harmful emissions are almost absent, unlike the lead-bearing steels.

MODIFICATION OF STEEL BY BARIUM AND STRONTIUM

The article is devoted to the steel modification process with natural materials containing barium and strontium. Using the methods of thermodynamic simulation, the authors considered the reduction process of barium and strontium with silicon and aluminum. The influence of steel treatment with barium-strontium modifiers on the structure formation and mechanical properties of steel has been studied. The research results have been implemented when smelting of steel of 25G2S and G13 grades in electric arc furnace at casting shop of OJSC “EVRAZ ZSMK”, as well as at OJSC “Yurginskii MachineEngineering Plant” when smelting of steel of 35CrGSL, 30CrGSLFL, 12ND2FCr grades using the two-slag technology. The results analysis of the production experiments has shown that a barium-strontium modifier influences the microstructure and non-metallic inclusions, as well as provides the supply increase of structural strength of steel estimated by the values of yield point, strength and impact strength at the positive and negative temperatures. To reveal the presence of barium and strontium in steel the analysis of steel structure has been done, when using the extraction replica method with the usage of transmission electron diffraction microscopy. The presence of barium and strontium in the grain capacity indicates the interaction of these elements with metallic melt having a certain influence on the structure formation of a metallic matrix.

MODELLING OF FIRE IN AN OPEN CAR PARK

Steel car parks exhibit high vulnerability to fire, as a consequence of the degradation of the steel mechanical properties at high temperatures and of the combustible type and amount. Real fire accidents in open car parks demonstrated a much faster and extended fire spread than predictions, assuming that a fire spread rate of 12 min and consider at most 3-4 vehicles on fire at the same time. Fire Dynamic Simulator (FDS) is applied in this current paper to study fire spread between cars. The outcomes of the investigations show that the fire spread is strongly influenced by the geometrical layout and that the distance between cars plays a determinant role on the fire spread rate and ignition of adjacent cars. In particular it was found that the fire spread can be faster than 12 minutes in the case of the cars parked 40 and 60 cm from each other.