Research of phase and structural transformations and properties in high-strength cold resistant steels for machine-building

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

The effect of nickel content in a high-strength medium-carbon complexly alloyed steel on the structural and phase transformations, location of critical points, quantitative parameters of microstructure and critical quenching rate is studied. Thermokinetic diagrams of decomposition of supercooled austenite in the steel with original composition are plotted and the characteristic types of microstructure forming under cooling at different rates are described. The effect of nickel on the combination of mechanical properties of thick rolled sheets after quenching and low-temperature tempering is determined. The results obtained may be used for development of high-strength cold-resistant steels and modes of their heat hardening.

Mechanical properties of high-strength Q960 steel at elevated temperature

The effect of high-temperature thermomechanical treatment on the structural transformations and mechanical properties of metastable austenitic steel of the AISI 321 type is investigated. The features of the grain and defect microstructure of steel were studied by scanning electron microscopy with electron back-scatter diffraction (SEM EBSD) and transmission electron microscopy (TEM). It is shown that in the initial state after solution treatment the average grain size is 18 μm. A high (≈50%) fraction of twin boundaries (annealing twins) was found. In the course of hot (with heating up to 1100 °C) plastic deformation by rolling to moderate strain (e = 1.6, where e is true strain) the grain structure undergoes fragmentation, which gives rise to grain refining (the average grain size is 8 μm). Partial recovery and recrystallization also occur. The fraction of low-angle misorientation boundaries increases up to ≈46%, and that of twin boundaries decreases to ≈25%, compared to the initial state. The yield strength after this treatment reaches up to 477 MPa with elongation-to-failure of 26%. The combination of plastic deformation with heating up to 1100 °C (e = 0.8) and subsequent deformation with heating up to 600 °C (e = 0.7) reduces the average grain size to 1.4 μm and forms submicrocrystalline fragments. The fraction of low-angle misorientation boundaries is ≈60%, and that of twin boundaries is ≈3%. The structural states formed after this treatment provide an increase in the strength properties of steel (yield strength reaches up to 677 MPa) with ductility values of 12%. The mechanisms of plastic deformation and strengthening of metastable austenitic steel under the above high-temperature thermomechanical treatments are discussed.

Study on dynamic mechanical behavior of Q460JSC and HQ600 high strength steel

Analysis of shear localization in viscoplastic solids with pressure-sensitive structural transformations

This paper presents the effect of temperature on the mechanical properties of high-strength alloy structural Q460 steel. The strength and stiffness properties of steel degrade with temperature and this deterioration has to be properly accounted for in the fire resistant design of steel structures. The strength and stiffness degradation is also influenced by the composition of steel. Because of a lack of data specific to high-strength Q460 steel, design standards assume the high temperature strength variation of Q460 steel to be same as that of conventional mild steel. To overcome this drawback, strength and stiffness properties of Q460 steel were measured at various temperatures in the range of 20–800°C. A relative comparison of measured data indicates that high-strength steel experiences a slower loss of strength and stiffness with temperature than conventional steel. Data generated from the experiments, namely, load-displacement relationships and vibration frequency, were utilized to develop rel...

Mechanical properties of very high strength steel at elevated temperatures

In many alloy steels, the reverse α → γ transformation occurs upon heating under conditions when complete structural inheritance is realized, and it is accompanied by formation of phase cold-worked austenite. The phase cold-working effect is a type of uniform and significant plastic deformation of the austenite, and so can actively affect structure formation processes in steels during austenitizing. Accordingly, it is of interest to use phase cold-working of austenite to improve the structure and properties of high-strength structural steels. We present the results of investigations of the effect of the quench heating conditions on structural transformations in phase cold-worked austenite and the properties of 25N12M6K10 steel with carbideintermetallide hardening.

In recent years, high-strength steel (HSS) is finding increasing applications in building construction due to its excellent strength and durability properties. However, structures, incorporating HSS, exhibit lower fire resistance due to rapid deterioration of their mechanical properties at elevated temperatures. For evaluating the fire resistance of steel structures, high-temperature properties of steel are to be specified as input data. The properties of steel not only vary with temperature but also the extent of variation is influenced by the type and grade of steel. This paper presents a state-of-the-art review on temperature-dependent properties of HSS. The available data and relations for thermal, mechanical, and deformation properties of HSS are compiled. Using these data, the variations in the elevated properties of HSS are established and the reasoning for such variation is explained. Finally, the critical properties to be considered for evaluating the fire resistance of structures, incorporating HSS, are discussed.

The structural and phase transformations and the strengthening of nitrogen-containing steels resulting from alloying and thermomechanical treatment have been investigated using X-ray diffraction analysis, optical microscopy, hardness measurements and tensile testing. For the modeling of thermomechanical treatment processes, a DIL 805A/D dilatometer with a deformation capability and a Gleeble 3800 simulator were used. Rational nitrogen or nitrogen plus carbon concentrations are determined by basic composition of an alloy. They are limited by the processes of precipitation of excess phases during crystallization and their dissolution during heating stage of the thermal or thermomechanical treatment. Combined alloying by carbon and nitrogen leads to significant complication of phase and structural transformations in steels, including hot deformation that manifests itself in changes of strain-stress diagram parameters. Effectiveness of increasing of a hot deformation resistance under alloying by nitrogen and carbon depends on a basic composition of steel, C/N ratio and temperature-strain rate deformation conditions.

Results of investigations of structural and phase transformations that occur in the titanium-nickelide-based alloy Ti49.5Ni50.5 with a shape memory effect during severe plastic deformation by torsion under high pressure (HPT) are reported. The studies were performed using transmission and scanning electron microscopy, neutron and X-ray diffraction, and measurements of temperature dependences of electrical resistivity. The martensitic B2 → B19′ transformation was found to be induced in the alloy when applying a high pressure. After unloading, the martensitic B19′ phase is retained in the alloy. The fine structure of the B19′ martensite and its evolution into nanocrystalline and, subsequently, amorphous state during HPT with 1/4, 1/2, 1, 5, and 10 rev have been studied. It was shown that, after HPT, all nanosized crystallites whose sizes are less than 30–50 nm have a B2-type structure and, therefore, the reverse martensitic B19′ → B2 transformation is realized in the alloy at room temperature after unloading.

Phase and structural transformations in annealed copper coatings in relation to oxide whisker growth

A systematic study of structural and phase transformations in Ti-Ta quenched alloys in a wide concentration range has been carried out. Boundaries of the concentration ranges of the hexagonal α′ and orthorhombic α″ phases have been determined. Morphological forms of the transformation products have been studied. Distribution of diffuse scattering in the space of the reciprocal lattice of the β phase and its dependence on the Ta concentration have been analyzed.

The features of structural and phase transformations during the processing of alloyed metallurgical wastes using reduction smelting are determined herein. This is necessary in order to determine the technological parameters of the melting process that ensure the reduction in the losses of alloying components. The use of X-ray phase analysis in combination with the methods of raster electron microscopy and X-ray microanalysis ensured the identification of the microstructure features and the chemical composition of individual phases and inclusions in the metal. Our study identified new technological aspects of high-alloyed technogenic waste processing using reduction smelting. The obtained parameters of the resource-saving alloying compound provide the possibility to replace parts of the standard ferroalloys in steelmaking processes.