High Strength Cold Research Articles

Laser Assisted Cold Spray of Aluminum Alloy 6061: Experimental Results

Laser-assisted cold spray (LACS) is investigated for its potential to improve the mechanical properties of cold spray deposits made by using nitrogen as the gas that carries the powder. High strength cold spray deposits are typically achieved by using the more expensive and resource limited helium. In this work, a laser collocated with the spray spot was used in nitrogen CS operations and the porosity, adhesion strength, tensile strength, and fatigue performance of aluminum alloy 6061 (Al6061) were examined. Using the laser improved all the performance metrics. By increasing the spray spot temperature from 180°C to 455°C, the porosity of the deposit reduced to 0.24% from 1.73%. The adhesion strength was increased from 18.4MPa to 76.6MPa. The tensile strength was increased from 34.3MPa to 167.6MPa, and the elongation was increased from 0.07% to 15.58%. It was shown that using laser heating during deposition increases the residual stress in the deposit, but its effects can be counteracted by using a hotplate beneath the substrate. Fatigue testing showed that fatigue performance was largely driven by tensile strength. These results are discussed in the context of in-situ temperature data and metallographic analysis. Analysis indicates these improvements are due to the combined effects of material softening, improved bonding between particles, and various heat treatment modalities.

Study of phase and structural transformations in overcooled austenite for high-strength cold resistant steel during continuous cooling

Study of phase and structural transformations in overcooled austenite for high-strength cold resistant steel during continuous cooling

Spheroidization Heat Treatment Conditions with Data Analysis in Medium Carbon Cr-Mo Steel for Ultra High Strength Cold Heading

The degree to which parameters affect the spheroidization heat treatment of steel was calculated by setting the spheroidization heat treatment conditions of Cr-Mo steel and using data analysis such as S/N ratio and ANOVA. After analyzing the transformation temperatures of the steel, A<sub>c1</sub> and A<sub>c3</sub> , using a DSC, the conditions were set accordingly. The surface hardness was measured for the conditions and used as an evaluation index. The correlation was analyzed by comparing the spheroidized volume fraction and the surface hardness, and the Pearson correlation coefficient was -0.88, proving that a correlation existed between the two values. Using S/N ratio and ANOVA, the degree to which each control parameter affects the decrease in the surface hardness was analyzed, qualitatively and quantitatively. For the S/N ratio, priority affecting the surface hardness for each control parameter was analyzed. The 1<sup>st</sup> heating temperature was found to have a more preferential effect on the surface hardness than the 1<sup>st</sup> heating time and the 2<sup>nd</sup> heating temperature. Using ANOVA, the 1<sup>st</sup> heating temperature was determined to be a very significant factor with the greatest influence, contributing 73.2% to the surface hardness. Intercritical annealing is a suitable spheroidization heat treatment condition, so if the surface hardness of the steel needs to be reduced using Intercritical annealing, the 1<sup>st</sup> heating temperature and time should be designed as the priority.

Preparation and properties of alkali and sulfate coactivated ternary cementitious matrix and its application in high-strength cold bonded lightweight aggregates

In this study, a novel alkali and sulfate coactivated ternary cementitious matrix (ASAM) was produced using sulfur-aluminum low-carbon cementitious material (LCM), red mud (RM), and blast furnace slag (SG). The mechanical properties, mineral components, hydration characteristics, microstructures and pore size distributions of ASAM were systematically investigated, and the results indicated that the compressive strength of ASAM was apparently higher than that of the LCM–RM binary matrix. Based on the alkali and sulfate coactivation effect, the ettringite formed by sulfate-activated SG and the C(N)–A–S–H generated by alkali-activated SG, as well as the U-phase products were the main mineral components of ASAM, which jointly contributed to the compressive strength of ASAM. The maximum compressive strength of ASAM was 34.5 MPa at a curing age of 56 d, when the mass ratio of SCM:RM:SG was 3:5:2. Furthermore, the leaching behaviors and solidification mechanism of Na+ in ASAM were analyzed. The results illustrated that the Na+ could be effectively solidified by C(N)–A–S–H and U-phase, through physical encapsulation and chemical adsorption. The maximum solidification ratio of Na+ was up to 44.3%, when the mass ratio of LCM:RM:SG was 3:5:2. Finally, the optimal ASAM was employed to prepare cold bonded lightweight aggregates (CBLA), and high-strength CBLA with a crushing strength of 11.6 MPa, loose bulk density of 1180 kg/m3 and water absorption of 5% were obtained. Hence, this work provides a new approach for the preparation of a novel ASAM using 100% solid waste, and also verified its potential application in CBLA production.

Hot Workability and Dynamic Recrystallization Behaviors of Medium-Carbon Cr-Mo Alloys for High Strength Cold Heading Quality Wire Rod

The hot deformation behavior of medium-carbon Cr-Mo alloy, which has been developed for high strength cold-heading quality wire rod, was investigated to evaluate its hot workability. A flow curve was derived using the hot torsion test, under conditions with temperatures of 1173-1273 K and strain rates of 0.1-1.0 s-1. At lower deformation temperature and higher strain rate, the overall stress of the flow curve increased, and the flow curve showed a three-stage variation related to the offset of dynamic recrystallization and dynamic recovery. First, as the strain increased, the stress also increased due to work hardening, and reached peak stress. After that, the stress decreased due to softening of the dynamic recrystallization. And when the effect of the dynamic recrystallization and the dynamic recovery reached equilibrium, the stress became steady state. In this paper, the constitutive equation of the peak stress was established using a form of a hyperbolic sine function, and here the thermal activation energy for deformation of the specimen was 244.90 kJ/mol. The peak stresses calculated from the constitutive equation were in good agreement with the experimental results. The dynamic-recrystallized grains were observed using electron backscatter diffraction (EBSD). It showed that the volume fraction of dynamic recrystallization increased as the strain increased under hot deformation. Based on the Avrami kinetic equation, a dynamic recrystallization kinetic model was established. The volume fraction of dynamic recrystallization was predicted from the kinetic model, and can be applied at arbitrary deformation temperatures and strain rates.

Разработка технологии электронно-лучевой сварки рабочих колес центробежных насосов для судов и морских сооружений, эксплуатируемых в Арктике

Object and purpose of research. Centrifugal equipment is widely used in various sectors of industry. One of the main part of centrifugal equipment is the impeller. Application of impellers in shipbuilding is a promising field, in particular for fail-free operation in harsh Arctic environment. The purpose of this study is development of manufacturing processes for impellers involving electro-beam welding (EBW) without soldering alloys and final thermal treatment. Materials and methods. The main material chosen for the impeller is the high-strength cold-resistant steel 10ХН3МД. Main results. In the process of technology development, the impeller design was chosen. Welding conditions were optimized on mock-up samples modeling the T-joint of cover plate with vane. Sample tests and investigation were done. Conclusions were made regarding the follow-on work and EBW introduction. Conclusion. EBW technology for manufacturing of impellers was developed making it possible to fabricate impellers of high-strength cold resistant materials, including difficult-to-weld materials.

Experimental Behavior of Composite Beam using Hot Rolled Channel and Cold Formed Lipped Channel Section under Flexure

Cold formed construction has widely recognized as an important contribution of saving in weight of steel as well as it can be formed according to strength requirements.Cold formed sections may have higher moment of inertia as compare to same weight hot rolled sections. Composite construction is usually associated with hot rolled sections especially I section, double C channel section considering high strength to weight ratio. The traditional hot rolled sections can be replaced by high strength cold formed sections considering its strength properties, less weight, easy fabrication and to fit demands of optimized design. This paper deals with experimental study of flexural behavior of composite beam using hot rolled as well as cold formed steel section. Two composite beams were casted using hot rolled ISMC 100 (back to back with spacing 50 mm) and Cold formed lipped channel section (back to back with spacing 50 mm). Experimental study conducted with simply supported loading conditions under two-point loading. Cold formed lipped channel section is pre- fabricated considering cold formed sectional properties given by EN 1993-1-3. Loading is given with load increment of 50 kN.Values of mid span deflection and slip at interface were recorded. The test strength of composite beam compared with design strength predicted by Eurocode standard.

Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength TRIP-Aided Martensitic Steels

To develop ultra high-strength cold stamping steels for automobile frame parts, the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly, 1.0 mass% chromium added TM steel indicated excellent hydrogen embrittlement resistance. This effect was attributed to (1) the decrease in the diffusible hydrogen concentration at the uniform and fine prior austenite grain and packet, block, and lath boundaries; (2) the suppression of hydrogen trapping at martensite matrix/cementite interfaces owing to the suppression of precipitation of cementite at the coarse martensite lath matrix; and (3) the suppression of the hydrogen diffusion to the crack initiation sites owing to the high stability of retained austenite because of the existence of retained austenite in a large amount of the martensite–austenite constituent (M–A) phase in the TM steels containing 1.0 mass% chromium.

Properties of Longitudinal Welded Steel Pipes for Piled Foundations Built under Cryolithic Zone Conditions

The mechanical properties of the base metal and the welded joints are estimated during tension, impact bending, drop weight tearing, static bending, flattening tests, and the Vickers hardness and the residual tangential stresses in them are determined for the longitudinal welded pipes 219–1020 mm in diameter and 8–12 mm in wall thickness manufactured by the AO Vyksunskii Metallurgical Plant. The hardness distribution over the pipe perimeter and the cross section is uniform and the cracking resistance of the pipes at negative temperatures up to –60°C is high. Local heat treatment of the welded seam and high-temperature tempering of the entire pipe ensure a high strength and high cold resistance of the pipes. The longitudinal pipes subjected to local and bulk heat treatment can be used like seamless pipes and as piles for the bases of buildings and structures erected in the cryolithic zone.

Fatigue cracking in high-strength cold-drawn pearlitic steel wires for anchorage in rocks

This paper analyzes the fatigue crack path in two pearlitic steels with very different microstructural arrangement: a hot rolled pearlitic steel bar and a commercial high-strength cold drawn prestressing steel wire frequently used for anchorage in rocks. In both materials, fatigue cracks are mostly transcollonial and tend to fracture pearlitic lamellae, so that many different micro-phenomena appear such as non-uniform crack opening displacement, micro-discontinuities, branchings, bifurcations and frequent local deflections, all of them creating a sort of microstructural roughness with regard to the fatigue crack path which is different in hot rolled bar and in the cold drawn wire.

Experimental study on innovative sections for cold formed steel beams

Cold Formed Steel members are widely used in today's construction industry. However the structural behavior of light gauge high strength cold formed steel sections characterized by various buckling modes are not yet fully understood. Because of their simple forming and easy connections, the commonly used cold formed sections for beams are C and Z. However both these sections suffer from certain buckling modes. To achieve much improved structural performance of cold formed sections for beams both in terms of strength and stiffness, it is important to either delay or completely eliminate their various modes of buckling. This paper presents various innovative sectional profiles and stiffening arrangements for cold formed steel beams which would successfully contribute in delaying or eliminating various modes of premature buckling, thus considerably improving the load carrying capacity as well as stiffness characteristics of such innovative cold formed sections compared to conventional cold formed steel sections commonly used for beams.

Effect of Hot Rolled Microstructure on Mechanical Properties of High Strength Cold Rolled TRIP Steel

Effect of Hot Rolled Microstructure on Mechanical Properties of High Strength Cold Rolled TRIP Steel

Testing of New Materials and Computer Aided Optimization of Laser Beam Welding of High-Strength Steels

The objective of this research is to investigate the performance and potential high power laser beam welding of high strength cold resistant low carbon quenched and tempered steel F620W with the use of new computer aided optimization methods. The research was divided into three parts. First, in order to identify the optimal thermal cycle, dilatometric and thermokinetic investigations were performed using a Bahr Thermoanalise DIL 805 dilatometer. To achieve recommended cycle during laser beam welding, the process was simulated using LaserCAD software resulting in optimal process parameters. Based on the simulation results an experiment was performed in bead on plate setup with use of continuous wave fiber laser IPG YLS-10000. Mechanical properties of the weld were studied by subjecting the specimens to a number of destructive tests, namely hardness, tensile strength and impact toughness testing at -40°C and -60°C.

Thermodynamics Analysis of Microalloying Technology for Developing High Strength Cold Rolled Structural Steel Sheet

According to thermodynamics of materials, selection of microalloying composition for developing cold rolled structural steel sheet with different strength levels was investigated, by comparing and analyzing the solid solubility and lattice constant of microalloying elements V, Nb and Ti, ideal microalloying composition-niobium and titanium compound additives was obtained, and then process parameters including reheating temperature and annealing process were discussed.

Effect of Thermal-Mechanical Treatment on Texture and Properties of Cold-Drawn Steel Wire

Thermal–mechanical treatment is widely utilized by steelmakers to optimize the properties of high–strength cold drawing eutectoid steel wires. This paper presents the influence of industrial thermal–mechanical treatment utilized in practical manufacturing on microstructure and mechanical properties of drawn pearlitic steels. After post thermal–mechanical processing, drawn pearlitic steel features lower residual stress and improved yield/ultimate tensile strengths, and exhibits a more perfect fiber texture characteristic. Nevertheless, the torsion test of treated steel wire demonstrates that delamination occurs during torsional deformation, which implicates that the studied thermal–mechanical treatment is whereas not the optimum process for manufacturing the high–performance steel wires. The sequential TEM observation shows the remarkable different structure of pearlite lamellae in drawn and treated wires. The local stress concentration resulting from the separately granular cementite precipitation may attribute to the delamination of steel wire after post drawing.

Correlation between microstructure and yield strength of a high-strength cold rolled enameling steel

To develop strategies for modifying the enameling steel chemical composition and processing to minimize yield strength reduction during the enamel-fire anneal (EFA), the reasons for yield strength reduction of a high strength cold rolled enameling steel were studied by combining experiments and thermodynamic calculations. The yield strength reductions were evaluated from the primary strengthening mechanism using existing empirical relationships that relate microstructural parameters to yield strength. The results show that yield strength reductions resulted primarily from an increase in grain size and a decrease in dislocation density. The EFA appeared to have a negligible effect on the solubilities of Mn, Si, and P, and the solubilities are nearly equal to the bulk concentrations. On the other hand, the elements C and N are nearly completely tied up as precipitates in the form of cementite and AlN. Thus, they have a negligible contribution to solid solution strengthening.

Microstructure, Properties and Work Hardening Behavior of High Strength Cold Rolled Dual-Phase Steel

Two kinds of high strength cold rolled dual-phase steel with different Si content were trial-produced in the laboratory. Tensile strength and elongation of the two steels exceed 1000MPa and 15%, respectively. The phase transformation behaviors of both steels were compared and investigated in continuous cooling process by thermal dilatometer. The effects of Si on the mechanical properties and microstructures of dual-phase steel were studied by tensile testing, OM and SEM observation. The results show that the two phase region (α+γ) is enlarged, the precipitation and growth of pro-eutectoid ferrite is promoted, and the morphology and distribution patterns of martensite are improved for high Si steel. Both steels show two-stage strain hardening characteristics. StageⅠ (ε<0.05), the solution of Si hinder the movement of dislocations, make the work hardening exponent of high Si steel is higher than that low Si steel. At stage Ⅱ (ε>0.05), the compatibility and delivery between hard phase and soft phase eliminate the differences between the two steels.

Adhesive prepregs and composite materials on their basis

The properties of high-strength and high-elasticity film-forming adhesives, high-strength cold- and hot-setting adhesive pastes, functional adhesives for metals, and various nonmetal and composite materials are reviewed. The properties of self-adhesive materials of different grades used for temporary repair of airframe surfaces are also described.

Adhesives for aviation equipment

The properties of high-strength and high-elastic film adhesives, high-strength cold- and hot-setting adhesive pastes, adhesives intended for bonding of metals, different nonmetallic and composite materials are overviewed. The properties of self-adhesive materials of different grades used for temporary repair of airframe surfaces are also described.

Effect of thermomechanical processing on mechanical behavior and microstructure evolution of C–Mn multiphase high strength cold rolled steel

Multiphase (MP) steels have complex microstructures containing polygonal ferrite, martensite, bainite, carbide, and small amounts of retained austenite. This mixture of phases and constituents is responsible for a good combination of strength and ductility in this class of steels. The present work shows how different annealing parameters can be used to create the suitable microstructure to improve mechanical properties of MP steels. Samples were first heated to 740, 760, or 780 °C, held for 300 s, and then quickly cooled to 600 or 500 °C. They were then soaked for another 300 s and finally accelerated cooled in the range of 10–30 °C s−1. The microstructures were examined at the end of each processing route using optical, scanning, and transmission electron microscopy. Hardness values were determined for all conditions. Analysis of the available data allowed to establish the simple and yet useful quantitative relationship between the microstructural parameters, cooling rates, and hardness of the steel.