Cold Strength Research Articles

Synergistic strengthening effects of precipitation and work hardening in cold-rolled Cu-0.4 wt%Cr alloy

Given the limitation of the precipitation strengthening effect in high strength and high conductivity Cu-Cr alloy, work hardening emerges as a practical and effective means to further enhance its strength. The Cu-0.4 wt%Cr alloy underwent varying degrees of cold rolling between the solution and aging treatments. The results of TEM characterization indicate that plastic deformation enhances precipitation, which occurs earlier than recrystallization in the deformed Cu-0.4 wt%Cr alloy. Thermodynamic calculations indicate that the driving force for precipitation is several orders of magnitude higher than that for recrystallization, while the nucleation barrier for precipitation is several orders of magnitude lower than that for recrystallization. Thus, the delayed recrystallization relative to precipitation theoretically allows for the coexistence of precipitates and deformed microstructures. In the peak aging state, despite the presence of numerous deformed microstructures, conductivity is almost fully restored. After aging for 1 h, the synergistic strengthening effects of precipitation and work hardening result in the yield strength and tensile strength of the sample cold rolled 64 % reaching 384.6 MPa and 422.0 MPa, respectively.

Understanding the lower fracture resistance of cold sintered ceramics

The cold sintering process (CSP) enables densification of ceramics at unprecedented low temperatures, unlocking unique opportunities in microstructural design. However, the mechanical behaviour of cold sintered ceramics remains unexplored. This study aims to compare the mechanical strength and fracture resistance of cold sintered (140°C) with conventionally sintered (1000°C) ZnO. The effect of grain size is investigated in samples sintered using conventional, cold and rapid sintering. It was found that cold sintered ZnO exhibits ∼50 % lower strength compared to conventionally sintered parts (∼120 vs. ∼240 MPa). This is explained by the lower fracture toughness of the former (0.57 vs. 1.15 MPa·m1/2), resulting from a grain size effect that favours intergranular fracture along nanometric grains. This grain size effect is supported by the higher hardness measured on cold vs. conventionally sintered ZnO (4.5 vs. 1.8 GPa). The lower toughness of cold sintered ceramics is demonstrated to be related to their nanocrystalline nature.

Factors influencing the wetting performance of asphalt emulsion on RAP surface

The wetting performance of asphalt emulsion on reclaimed asphalt pavement (RAP) strongly affects the physical bonding ability of asphalt emulsion-RAP interface. For a more comprehensive understanding on the wetting performance of asphalt emulsion on RAP, many factors affecting the wetting performance of asphalt emulsion on RAP are studied, including the asphalt and emulsifier dosage in asphalt emulsion, RAP asphalt aged degree, and some additives (such as wetting agent, hydrated lime and silane coupling agent). The contact angle of asphalt emulsion on RAP asphalt surface and the other wetting parameters calculated by the surface wetting theory were used to comprehensively analyze the wetting performance. The results show that all of the tested factors have influence on the wetting performance of asphalt emulsions. The grey relational analysis indicates that the wetting agent, hydrated lime and silane coupling agent have significant effects on the wetting performance of asphalt emulsion on RAP. A suitable dosage of wetting agent, hydrated lime modified with silane coupling agent (HL-SCA) can decrease the contact angle and improve the wetting speed of asphalt emulsion on RAP. Meanwhile, the addition of both wetting agent and hydrated lime modified with silane coupling agent can greatly decrease the volume of air voids and improve the indirect tensile strength of cold recycled mixture with asphalt emulsion. Therefore, the wetting agent and the HL-SCA are recommended to improve the wetting performance of asphalt emulsion on RAP and the mechanical performance of cold recycled mixture with asphalt emulsion.

Microstructural and mechanical properties analysis of SS 316L structure fabricated using CMT-wire arc additive manufacturing

Integrating robotic arm technology with cold metal transfer (CMT) has revolutionized wire arc additive manufacturing (WAAM). The research work consists of the fabrication of SS 316L WAAM using the CMT technique. Investigations of mechanical and microstructural properties, i.e. residual stress measurement (RSM), microhardness (MH), ultimate tensile strength (UTS), percentage elongation (PE), and microstructure of WAAM sample and cold rolled (CR) plate, results were compared. WAAM attained an UTS of 590 MPa, with an average yield strength (YS) of around 302 MPa, exceeding the CR plate’s UTS of 557 MPa while maintaining a similar YS of 305 MPa. WAAM and the CR plate exhibited nearly identical PE, with 64% and 62% values, respectively. Residual stress analysis revealed that the WAAM sample showed an average compressive residual stress of 124 MPa, accounting for 87% of the average residual stress observed in the CR plate, which measured 142 MPa. The MH profile of WAAM revealed an average value of 230 HV0.5, accounting for 88% of the MH observed in the CR plate at 260 HV0.5. The performance of WAAM closely matched that of the CR plate in terms of residual stress and MH.

Effects of Alumina Bubble Addition on the Properties of Corundum-Spinel Castables Containing Cr2O3.

Purging plugs made of corundum-spinel castables containing Cr2O3 have been widely utilized in secondary refining process. However, their poor thermal shock resistance has greatly limited the improvement of their service life. Aiming to enhance their properties, we introduced alumina bubbles (ABs) to corundum-spinel castables, and the effects of the AB addition on the properties of the castables are studied in this manuscript. The results indicate that the apparent porosity, permanent linear change, cold strength, and hot strength all increased with an increasing AB amount. The thermal shock resistance of the samples with the AB addition was improved; the residual strength and residual strength ratio of the sample with 4 wt% ABs was the best. The effects of ABs on the tabular alumina aggregate distribution and relationship between the cold strength of the samples and the AB content was evaluated via the box dimension method. With the increments of AB content, the box dimension value of the tabular alumina within the samples significantly decreased, indicating that the tabular alumina aggregate distribution was related to the amount of ABs. In addition, the relationship between the box dimension and the strength was also established.

Flexural Strength of Cold Formed Section with Laterally Restrained Tension Flange

Flexural Strength of Cold Formed Section with Laterally Restrained Tension Flange

Prediction of stress corrosion crack growth rate of cold worked stainless steels in BWR conditions by the slip oxidation model

Stress corrosion cracking (SCC) is a critical issue for boiling water reactor (BWR) components, and their cold working is considered to be an accelerating factor for SCC crack growth rates (CGRs). However, no method has been proposed to quantitatively evaluate the SCC CGRs of cold worked stainless steels. In this study, the changes in material properties due to cold working were reflected in the input parameters of the Hashimoto-Koshiishi model, a mechanistic model of SCC growth based on the slip oxidation mechanism, to enable a quantitative evaluation of the SCC crack growth rate (CGR) of cold worked SSs. In addition, a simplified equation as a function of the yield strength of cold worked 316LSSs was developed for ease of practical use in the integrity assessment of components. The CGRs calculated by the model and/or the simplified equation were in good agreement with the experimentally obtained CGRs for cold worked SSs and the heat affected zone (HAZ) of Type 316L SSs.

Improving the comprehensive properties of ZrO2–C materials with aid of TiO2 addition

Owing to the harsh working condition, the ZrO2–C materials used in the slag line in the submerged entry nozzle are confronted with serious slag erosion. In order to solve this issue, different amounts of TiO2 addition ranging from 0 to 6 wt% are added and their effects on the erosion resistance of ZrO2–C materials in addition to phase composition, microstructure, physical properties and high-temperature mechanical properties are investigated in this work. When the sintering temperature is above 1400 °C, fine TiC grains and SiC whiskers are in-situ formed and distributed around ZrO2 particles, which can reinforce the matrix and improve the strength of ZrO2–C materials. With the amount of TiO2 addition increasing, the cold strength of ZrO2–C materials increases while the high-temperature strength slightly decreases. Combining with the erosion resistance, the optimum amount of TiO2 in ZrO2–C materials is determined to be 4 wt%, in which the cold compressive strength (46.13 MPa), the cold modulus of rupture (35.12 MPa) and the residual strength after thermal shock (15.01 MPa) reach the maximum. Based on this, the promotion mechanism of erosion resistance is further discussed with aid of molecular dynamics simulation.

The Influence of Strain Aging at Different Temperatures on the Mechanical Properties of Cold-Drawn 10B21 Steel Combined with an Electron Microscope Study of the Structures.

The effect of aging treatments at various temperatures on the mechanical properties and microstructure of 10B21 cold heading steel with a 20% reduction in area (ε = 0.1) was investigated. The mechanical properties were evaluated based on tensile tests and hardness tests, while the evolution of microstructure was observed by using an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results reveal that aging treatment enhance the strength and hardness of 10B21 cold heading steel after drawing, and the highest values of strength and hardness are attained at an aging temperature of 300 °C. Specifically, the yield and ultrahigh tensile strength after aging at 300 °C are measured at 620 MPa and 685 MPa, respectively, which are 30 MPa and 50 MPa higher than the cold-drawn sample. Moreover, the hardness after aging at 300 °C reaches 293 HV, which has an increase of 30 HV compared to the cold-drawn state. The improvement in mechanical properties may be related to the strain-aging mechanism and the increased density of dislocations. In addition, the analysis of the TEM results reveal that the presence of the second-phase Ti(C,N) contributes to pinning the dislocations, whereas the dislocations are pinned between the cementite (Fe3C) lamellar and stacked at the grain boundaries, leading to strain hardening of the material.

Improvement of the deposition efficiency and adhesion strength of cold sprayed fluoropolymer coating by laser surface texturing of the substrate

High-performance polymer cold-spraying is attracting the interest of many for its economical, time-saving, and environmentally safe features in comparison to traditional thermal spraying processes. The cold spray process allows applying functional polymer coatings on a similar or dissimilar material surface for protective measures or additional functionalities. However, its practical use has been restricted by inherently low deposition efficiency associated with a weak interfacial adhesion strength.In this study, fluoropolymer powder mixed with 5 wt% of nano-alumina was cold-sprayed on laser-textured carbon steel substrates. A thorough analysis of the particle deposition as a function of the spray parameters (gas temperature, pressure, pass number, traverse speed) was performed to highlight the effect of the laser-texturing (groove geometry, laser pitch, pattern) on the deposition efficiency and adhesion strength. By laser-texturing the substrate, the deposition efficiency increases up to 60 %, and the adhesion strength reaches 1.25 MPa. Thus, while the addition of nano-alumina enhances the interparticle cohesion, a laser-textured substrate promotes the mechanical interlocking at the particle/substrate interface.

Numerical evaluation of shear strength of CFS shear wall panel with OSB sheathing

Outside of the American Iron and Steel Institute AISI S400-15 limitations of Shear Wall Panel (SWP) height-to-width (h/w) aspect ratio, the present paper puts forward a sufficiently detailed Finite Element Modeling (FEM) using “Abaqus” software, capable to evaluate with a reasonable precision the shear strength of Cold Formed Steel (CFS) SWP with Oriented Strand Board (OSB), under lateral load. In terms of nonlinear response, shear strength and failure modes, the numerical results of the SWP with and without an opening are validated against available experimental data, accounting for nonlinear mechanical and geometrics characteristics, as well as the nonlinear behavior of connection. Subsequently, the conducted comprehensive parametric studies have revealed that the variation of the screw spacing, from 50.8 mm up to 152.4 mm, provides a nonlinear variation of shear strength that cannot be extrapolated for different screw spacings. In addition, the shear strength of a two-sided OSB-sheathed SWP is less than twice one-sided OSB-sheathed SWP. Furthermore, the door’s and window’s openings’ position between the center and the edge of the SWP provide the best performance in terms of shear strength up to 33 % and 24 % than the center and edge openings’ positions respectively.

Improvement of technology and technique for the production of sinter at the SP EVRAZ KGOK. Report 1. Loading and ignition of the mix.

A brief literature review of theoretical and applied works on charging and ignition of sinter mix has been made. The review considers experimental data on the influence of the distribution of the particle size of the mix and the fuel content over the height and width of the bed, and its bulk density on the consumption of solid fuel, height and gas permeability, on the productivity of sinter machines and sinter strength. The problems of sinter mix ignition, the influ-ence of throttling of the first vacuum chambers of sinter machines on the quality of sinter and gas consumption for ignition are discussed. The results of industrial studies of mix loading and ignition modes on EVRAZ KGOK sinter ma-chines are presented, which provide an increase in the bed height, an increase in the cold strength of the sinter, and a decrease in natural gas consumption for mix ignition. As a result of increasing the rotational speed of the drum feeder, the discrete descent of the mix from the mix flow stabilizer was eliminated. It has been established that due to the ex-pansion of the sinter pallets and the negative slope of their sides, there is no need to form a mix bed profile variable in height and width. The operation of sinter machines with and without separation of the loading chute from the bed has been studied. The presence of critical fluctuations of the grain size composition of the mix and the content of fuel car-bon in it along the width and height of the bed for both options of operation, due to the mode of operation of the shuttle mix distributor and fluctuations the height of the bed in the intermediate hopper, has been established. The important role of the design and mass of the mix smoother has been experimentally confirmed. The design of the throttling device of the vacuum chambers legs with manual change of the free section only as it wears out has been developed and implemented. The rational free section of the legs of the vacuum chambers is determined, which provides a minimum suction (1–2 Pa) in the chamber of the ignition hearth, and equal to 10–12%. As a result of the introduction of new technical solutions, an increase in the cold strength of the sinter by 1.09%, a decrease in natural gas consumption by 29%, and an increase in the height of the sintered charge layer up to 30 mm were achieved without reducing the productivity of sinter machines

High performance tin-based Babbitt coatings deposited by high-pressure cold spraying

Tin-based Babbitt alloys are widely used as sliding bearing materials due to their excellent tribological properties such as good friction reduction, friction resistance and embeddedness. In this study, for the first time, tin-based Babbitt coatings (SnSb11Cu6) were deposited on 40Cr steel substrates by a high-pressure cold spraying system with dual downstream injection as a preliminary investigation of anti-friction coatings for sliding bearings. The effects of process parameters on deposition efficiency, microstructure, microhardness, bond strength and tribological properties of cold sprayed SnSb11Cu6 coatings were systematically investigated. Results showed that with the optimization of process parameters, deposition efficiency tends to increase first and then decrease, and the optimal deposition efficiency achieved is 53 %. The coating prepared at the gas pressure of 1.5 MPa and gas temperature of 450 °C has the highest density, and the best overall mechanical and tribological properties. XRD results showed that no phase change and oxidation occurred for coatings under all cold spraying conditions. The highest microhardness of cold sprayed SnSb11Cu6 coatings is 28.8 HV0.05, higher than that of as-cast alloy (~22.5 HV0.05). The bond strength between SnSb11Cu6 coatings and the steel was significantly increased by using bond coat and is highest as 21 ± 3 MPa. The lowest coefficient of friction and wear rate of the SnSb11Cu6 coatings is 0.23 and 7.99 × 10−5 mm3/N·m, respectively (pair: GCr15 ball, 3 N). The deposition mechanisms and wear mechanisms of cold sprayed SnSb11Cu6 coatings were also analyzed. With the optimization of process parameters, the particle physical state transits from semi-molten to fully-molten, and the bonding mechanism is mainly mechanical interlocking. The wear mechanisms of cold sprayed SnSb11Cu6 coatings are abrasive wear and adhesive wear, and abrasive wear dominates.

Study on the Adhesion Characteristics of Asphalt-Aggregate Interface in Cold Recycled Asphalt Mixtures

The reclaimed asphalt pavement materials have been used for sustainable cold-recycling, significantly benefiting air quality and resource conservation, while its microscale interface properties greatly affected road performance during the cold-recycling processes. In this investigation, the cold recycled asphalt mixtures were prepared with different mixing proportions, considering the effects of cement content and mixing water amount. The adhesion characteristics of the asphalt-aggregate interface in different cold recycled asphalt mixtures have been comprehensively investigated based on the atomic force microscopic (AFM). The microscale morphology and the adhesion properties, including roughness, inclination angle, adhesion force, Derjaguin–Muller–Toporov (DMT) modulus, and dissipated energy were evaluated at the interface and noninterface regions. The micromorphology results showed that the addition of cement could enhance the roughness and inclination in interface regions. In addition, the content of mixed water showed the most significant effect when the water amount was 80%. The results showed that the adhesion force, DMT modulus, and dissipated energy increased with the addition of cement, indicating that the cement could improve the microscale mechanical properties of cold recycled asphalt mixtures. With the increase of mixing water content, the adhesion characteristics showed varied results, and the optimum water content of 80% contributed to the adhesive properties. In addition, the adhesion force, DMT modulus, and dissipated energy were all higher in the interface region by comparing with the noninterface region. The correlations between the macroscale splitting tensile strength and microscale adhesion characteristics of cold recycled asphalt mixtures were established.

Large-Scale Fabrication of SiC-TiC@C Powders via Modified Molten Salt Shielding Synthesis Technique and Their Effect on the Properties of Al2O3-MgO Castables.

Graphite flakes are commonly used to fabricate carbon-based refractories owing to their superior properties, including better corrosion resistance and thermal shock resistance (TSR); unfortunately, their insufficient water-wettability has remarkably hindered their application in castables. Aiming to enhance their water-wettability, a facile and low-cost technique for fabricating carbides coated in graphite was proposed in this work. Firstly, SiC-TiC coated graphite (SiC-TiC@C) powders were prepared via modified molten salt shielding synthesis in an air atmosphere using graphite flake, Si and Ti powders as raw materials and NaCl-KCl as the molten salt shielding medium. Water-wettability and oxidation resistance of SiC-TiC@C powders were significantly improved. Compared to the Al2O3-MgO castables with graphite flakes, the water demand of the castables with SiC-TiC@C was noticeably decreased from 6.85% to 4.89%, thereby decreasing the apparent porosity of the castables with 5% SiC-TiC@C (from 20.3% to 13%), enhancing the cold strength, hot strength and oxidation resistance of the castables. Such enhancements are ascribed to continuous and crack-free SiC-TiC coatings on graphite surfaces ensuring that the castables have outstanding properties.

HRTEM analysis of carbon structure evolution during the formation of metallurgical coke and impacts on coke quality

The coke quality influences the performance of the blast furnace, and the coal properties and coke structure play important roles in affecting the ultimate coke quality. The evolution of the physical and chemical structures during the plastic layer formation is generally accompanied by the modification of the carbon structure, which influences the strength and reactivity of coke, e.g., mechanical strength (micum indices-M40/M25, M10) and hot strength (coke strength after reaction with CO2-CSR and coke reactivity index-CRI). This paper reports the evolution and transformation of carbon structures during the coking processes of six Australian coking coals, aiming to draw correlations between the carbon structures of coke and coal properties as well as coke strength. Results indicate that cokes contain various proportions of turbostratic structures and graphitized structures derived from the transformation of carbon structures in terms of coal properties. After the chemical structural transformation of coals during the coking process, the heteroatoms are removed, and the carbon structures of the cokes consist of more ordered stacked structures. The cross-links and oxygen-containing functional groups in low-rank coals evolved to form more tortuous stacked structures. Cokes made from higher-rank coals formed fringes with longer average lengths and lower tortuosity in a more tightly stacked structure, leading to the formation of anisotropic structures. The carbon structure of coke was found to be closely correlated with the cold strength parameters.

Large‐scale fabrication of TiC@C powders and its effect on the properties of Al2O3‐MgO‐C castables

AbstractHigh performance carbon containing castables have always been pursued by researchers and steelmaking producers, unfortunately, poor water‐wettability of graphite flakes was greatly limited their application in castables. To respond this, we proposed a large‐scale and low‐cost modified molten salt shielding synthesis technique for fabricating TiC coated graphite in air atmosphere using graphite flake and Ti powder as raw materials. Microstructure, wettability and oxidation resistance of TiC@C powders, and effect of TiC@C powders on the properties of Al2O3‐MgO‐C castables were investigated. The results demonstrate that TiC coated graphite was synthesized via modified molten salt shielding synthesis route in air atmosphere. A uniform and continuous TiC layer was formed on the surface of graphite, thereby significantly improving the water‐wettability and oxidation resistance of graphite flakes. The castables with 5% TiC@C powders possessed lower apparent porosity, higher cold strength, good oxidation resistance, and slag resistance in comparison with the castables with graphite flakes, and slag resistance were also better than Al2O3‐MgO castables. The as‐fabricated TiC@C powders have good water‐wettability and oxidation resistance, making them as a prime carbon source for producing carbon containing castables for steel ladle linings.

Early Strength of Cold Recycled Emulsified Asphalt Mixtures

In order to study the influence of different factors on the early strength of the cold recycled emulsified asphalt mixtures, 16 different types of cold recycled mixtures were designed and produced, which were combined with different cement content, water content, and cement-water ratio. The indirect tensile strength (IDT), compressive strength (UCS), tensile strength at 15°C (TS), and indirect tensile strength ratio (ITSR) tests were used to test the early strength of the cold recycled mixture. The variance analysis method was utilized to analyze the influence of the single factor on the early strength of the cold recycled mixture. The results show that appropriate cement-water ratio content can effectively improve the early strength of cold recycled mixtures. According to the Spearman correlation coefficient and comparison of each evaluation indicator, IDT and ITSR are significantly affected by various factors, and the results are relatively stable and well-differentiated, which is recommended as indicators of early strength evaluation. Cement-water ratio is recommended as the main control factor to control the early strength of the cold recycled emulsified asphalt mixtures. The optimal cement-water ratio ranges from 0.6 to 1.0, while the cement content is controlled from 1.2% to 1.5% and the water content from 3.8% to 4.3%. This study is of great significance for promoting the design of emulsified asphalt cold regenerative mixture with cement-water ratio and improving and accelerating its early strength development.

Influence of Irregular Al2O3 Content on Electrical Conductivity, Adhesion Strength, and Tribological Properties of Cold Sprayed Al-Al2O3 Coatings on Polyether Ether Ketone Substrate

Influence of Irregular Al2O3 Content on Electrical Conductivity, Adhesion Strength, and Tribological Properties of Cold Sprayed Al-Al2O3 Coatings on Polyether Ether Ketone Substrate

Scientific and technical support for the devel-opment of sinter plant no. 5 of PJSC MMK

The design characteristics of the sinter plant No. 5 of PJSC MMK, commissioned in 2019, are presented. The results of studies of the processes of homogenization, mixing, moistening and pelletizing of the burden, its burdening on the sintering machine, ignition, sintering and cooling of the sinter cake are presented. The erroneousness of the design solutions for installing the pelletizing drum at the zero level and the charge bunker with a volume of 60 m3 in the sintering body without an intermediate bunker is shown. Technical solutions are presented to prevent a discrete charge descent of the charge from the drum feeder of the loading unit and to form the profile of the charge layer on the sintering machine, which increases the uniformity of the process of its sintering along the width of the pallets. The operation of a multi-roll charge stacker, first used at sinter plants in the CIS, was studied. Industrial experiments were carried out on sintering a conditionally “dense” and loosened by a special device batch layer, the advantage of the latter in terms of the speed of the sintering process was established. A technical solution has been developed and accepted for implementation to reduce the length of the hearth by 40%, which will increase the sintering area of the sintering machine by 3%. The operation of the energy-consuming exhaust gas recirculation system based on their selection from eight vacuum chambers of the sinter machine out of twenty with the installation of a smoke exhauster with a drive capacity of 3.1 MW and gas cleaning from dust was stopped. Vacuum chambers of the recirculation system are connected to two parallel collectors of the sintering machine; an analysis of the impact of these measures on the operation of the sintering machines has been carried out. The possibility of using gas recirculation with the installation of a smoke exhauster with a drive power of 400 kW without additional purification of gases from dust is shown. In the future, it is proposed to increase the open section of the collectors by making them from three sections of different sections. It was found that the area of linear coolers was overestimated due to the use of “direct” loading of sinter on them, in which the cooling of the material is limited by its large lumps located in the upper part of the layer. A sinter back loading system was proposed and implemented in the project, which allows to reduce the cooling area by 30% (turn off two of the six blowers), it was decided to implement it. As a result of development of AF-5, for the first time in the practice of sintering plants in the CIS, the height of sintered charge layer of 700 mm was established. The specific productivity of sintering machines during the sintering of the charge based on the Sokolovsko-Sarbaisky concentrate was achieved, equal to 1.10 t/(m2•h); the cold strength of the sinter according to GOST 15137–77 for impact is on average 82.5%, for abrasion ‒ 4.5%.