Metal Science and Heat Treatment最新文献

The digital image correlation method is used to determine the structural and deformation factors at the meso- and macro-levels responsible for the low ductility of steel 08G2B (08Mn2Nb), which exhibits the effect of strain aging after heating at 250°C. The factors include a small scale of plastic deformation by the banded mechanism localized in about 1/3 of the sample, where only two strain bands are formed on a short yield plateau and form a strain source when they intersect. The other two strain sources arise in the linear and exponential stages of the tension, when dislocations are unlocked during the distributed deformation.

The effect of technological parameters of gas metal arc welding with SG2 electrode wire and subsequent tempering on the structure and mechanical properties of multi-pass welded joints from dissimilar sheet steels St37-2 and St52-3 with a thickness of 10 mm has been studied. To optimize the technological conditions of welding and heat treatment during the experiments, a systematic approach with three level variables of parameters for the Taguchi orthogonal array was used, where mechanical properties (tensile tests, hardness and impact strength) and microstructural characteristics (optical metallography, SEM, XRD) are investigated. The contribution of each welding and tempering variable was evaluated, and optimized with Grey relational analysis. It was found that that changing the arc voltage during welding has the greatest impact on the mechanical properties, and the tempering process after welding increases the plastic characteristics of welded joints.

A comparative study of the effect of quenching temperature from the austenitic and intercritical temperature ranges on the microstructure, hardness, phase composition and abrasive wear resistance of medium-carbon engineering steels 45, 34KhN1M (34CrNi1Mo), and 38KhN3MFA(38CrNi3MoW) is carried out. It is shown that after the quenching with heating above Ac₃ , alloyed steels 34KhN1M and 38KhN3MFA are inferior to steel 45 with respect to the abrasive wear resistance. However, after the quenching from the intercritical temperature range, the abrasive wear resistance of these steels exceeds that of steel 45 by 10% due to the presence of a heterophase structure represented by high-carbon martensite, metastable austenite, which transforms on the working surface into friction-induced martensite during wear, and ferrite, capable for friction twinning.

The microrelief of samples of pure titanium and aluminum in single-crystal, coarse-grained and ultrafine- grained states subjected to tension accompanied by different modes of pulse current is studied using scanning electron microscopy. It is shown that the metals in all the states studied fracture by a ductile mechanism characterized by a dimple-cup fracture pattern. A common feature of the single-crystal and coarse-grained states is a microrelief bearing shear bands and large cups, while the ultrafine-grained state is characterized by dimples on the fracture surface. The dimple size does not correlate with the grain size but depends on the intensity of the pulse current and on the microporosity arising during the refinement of the structure.

The microstructure, phase composition and distribution of chemical components in two-layer coatings obtained by the method electrospark deposition (ESD) on steel 45 (cathode) are studied. It is shown that the lower layer formed by Ni or Cu acts as a damper preventing penetration of microcracks into the cathode from the upper layers of the coatings obtained from alloys based on the Ni – Al system. The two-layer coatings in all the cases have a gradient structure constituted by columnar crystallites, the concentration of components in which varies gradually over the thickness.

A review and comparison of methods for measuring stresses in situ in oxide scale, including x-ray diffraction, Raman spectroscopy, piezospectroscopy, and deflection methods, is presented. An analysis of the principles and procedures of testing has shown that each of them has both advantages and limitations. The results of measuring stresses in various oxides are considered: NiO, Zr₂O, Cr₂O₃, Al₂O₃, etc., studied by different methods. The deflection method is superior to others in measuring stresses in thick oxide scales. However, the coating process brings more errors. In order to eliminate the adverse impacts of coating process, a novel method — Archimedes curve slice moment technique is developed to detect stresses in thick oxide scales on metals for long-term service at high temperature. The experimental principal is illustrated, and the stress formula is derived. Without coating before oxidation, the Archimedes curve slice specimen is oxidized freely at high temperature, and the stresses in oxide scales could be calculated by observing the slice crimping displacement in situ real time during oxidation. A set of the experimental equipment is established, expecting to test the growth stress and thermal stress separately with higher precision.

The choice of the chemical composition of new sparingly alloyed high-strength cold-resistant steels with strength level of at least 950 MPa for heavily loaded equipment is substantiated. Thermokinetic diagrams of decomposition of supercooled austenite are plotted for the steels with selected chemical compositions. Heat treatment modes are suggested. The mechanical properties during the heat treatment are determined to develop recommendations for the use of the research results under industrial conditions.

The effect of microadditions of transition metals Zr, Hf, Ti, V on the kinetics of solid solution decomposition, recrystallization and strengthening characteristics of an ingot with diameter 92 mm, extruded strip, and cold-rolled sheets from alloy Al – 0.17 wt.% Sc is studied. It is shown that microalloying with zirconium is the most effective. The best combination of mechanical properties is obtained in the alloy when the content of zirconium is equal to that scandium, i.e. it is necessary to observe a 1-to-1 proportion of Sc to Zr. The addition of zirconium, which dissolves in the solid solution together with scandium, inhibits the decomposition of the solid solution in the ingots and increases the recrystallization temperature and significantly raises the strength in the deformed semiproducts.

The structure, phase composition and fracture behavior of samples of steel 1.45.40 (15-5 PH) obtained using an EOSINT 280M laser printer are studied by x-ray diffraction analysis and magnetic force microscopy after cyclic cantilever bending tests at room temperature. The mechanism of crack propagation during cyclic bending in the martensitic-ferritic steels obtained by laser 3D printing is considered. It is shown that under cyclic deformation of such samples, fracture occurs over martensite regions, and the fracture pattern is brittle. The content of the martensitic phase in the steel structure is higher than after casting.

Ajoint of two titanium plates is created using magnetic pulse welding. The structure of the welded joint is examined using light microscopy, scanning electron microscopy and energy dispersive x-ray microanalysis. The collision speed of the plates during the welding process is increased progressively from 450 m/sec to 650 m/sec producing the corresponding rise in the deformation and thermal effects. The hardness in local melting zones at the interlayer boundary increases substantially. Numerical simulation employing the method of smooth particle hydrodynamics reflects effectively the key features typical for magnetic pulse welding, including the formation of a jet and local melting at the layer interface.