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Specimens of armco iron and steels 09GS and 37G2S possessing strongly different load-extension diagrams are studied. The σ = f (δ) curves are divided into regularly alternating periods, i.e., linear, power within the uniform stage, and I, II, III in the lumped stage. Each period is characterized by the yielding parameter (YP), plasticity components (elongation δi), initial stress σi, and rate of growth/decrease of the stress (∆σ/δ∆)i. Analysis of the YP is used to compare the periods in differently hardened specimens. It is shown that the combination of these periods is responsible for the standard mechanical properties of the specimens. The values of the YP are used to trace the relation between the ductility and the crack resistance and to show that the stress σII and the elongation $$ {\updelta}_{\mathrm{l}}^{\mathrm{IIs}} $$ at the start of period II of the concentrated stage may be treated as criteria of crack resistance.

The structure, the dynamic crack resistance, and the characteristics of mechanical properties of quenched and tempered structural steel 09G2S are studied. Special features of structure in the zones of plastic strain (ZPS) under fracture surfaces are considered after a single dynamic test. The structural features of bands of adiabatic shear formed in the starting region of the zone of plastic strain and in the region of the force action of the hammer are studied. The influence of formation of bands of adiabatic shear on the level of dynamic crack resistance is assessed. The temperatures arising in the material in the process of three-point dynamic bending are calculated.

Special features of structure formation in steel 40Kh2N2MA are studied after a high-temperature thermomechanical treatment with martensitic-bainitic transformation of austenite. It is shown that the treatment produces a mixed structure represented by alternating extended regions of tempered martensite and lower bainite. The treatment raises substantially the impact toughness and the crack resistance of the steel. The process is the most effective for hardening alloy steels with enhanced stability of supercooled austenite.

The crack resistance of welded joints of pipe steels of strength class K60 and different alloying systems is studied. The parameter of the crack tip opening displacement (CTOD) is shown to be dependent on the size of the austenite grains and on the morphology of bainite in the superheated region of the heat-affected zone of the weld. The crack resistance is shown to be controllable due to optimization of the alloying system.

The crack resistance of railroad rails with transverse internal and external cracks in the head formed in operation is determined. The ultimate crack resistance Ic, the values of which coincide with the critical values of the stress intensity factor KIc under the brittle fracture typical for rails, is determined.

The characteristics of strength, static crack resistance, rate of growth of fatigue cracks and cyclic endurance of annealed sheets from weldable alloys of the Al – Mg – Sc system are studied as compared to annealed sheets from alloy AMg6. The compositions of aluminum alloys with scandium (01545 and 1570S) with characteristics substantially superior to those of AMg6 and level of properties comparable to that of the base aircraft not weldable alloy 1163 in state T6 are determined.

The structure and the dynamic crack resistance of steel 09G2S tubular billets are compared after a heat treatment and different versions of deformation and heat treatment, including cold plastic deformation by radial forging and subsequent annealing. Radial forging followed by annealing has a favorable effect on strength and dynamic crack resistance, which confirms the possibility of industrial use of tubular billets from steel 09G2S after cold radial forging.

The structure, dynamic crack resistance, strength and micromechanisms of crack growth are studied in tubular billets from steel 35Kh after different variants of deformation and heat treatment including cold plastic deformation by radial forging followed by annealing. The radial forging with subsequent post-deformation annealing is shown to affect positively the strength and the dynamic crack resistance of the metal. Quantitative analysis of the micromechanism of crack growth is made after tests for dynamic crack resistance. Special features of the formation of macro-splits are determined.

Relations between the parameters of dynamic crack resistance, impact toughness, sizes of zones of plastic strain in the start region, hardness of the unstrained material, strength characteristics, and tempering temperature of steel 09G2S are determined. The linear regression equations are used to construct mathematical and graphical models for predicting the level of properties in quenched and tempered steel 09G2S. The method is used to predict the properties of a tubular billet from steel 09G2S with composition somewhat different from the rated one after quenching and high tempering at 570°C.

Results of a comparative evaluation of the fracture toughness parameters K c of cladding pipes from zirconium alloys of type E110 after tests simulating loss-of-coolant accidents at a nuclear power plant are presented. The effect of the content of impurities, alloying elements and structure on the fracture toughness of the zirconium pipes after high-temperature oxidation at 1100°C is analyzed.

The structure of steels 09G2S, 25 and 40 after quenching and tempering at from 200 to 650°C is studied. An own method of the authors is used to estimate the impact toughness and the dynamic crack resistance of structural steels in various structural states. The micromechanisms of crack growth are studied in steels with various structures.

The effect of welding and heat treatment modes on mechanical properties and corrosion resistance of welded joints of oil line pipes is studied. It is shown that high-frequency welding followed by high-temperature annealing provides strength and corrosion properties in welds of pipes from low-carbon low-alloy steels at the level of the welded metal.

The structure and mechanical properties of structural steels 35KhMA and 40KhMFA are studied after various kinds of heat treatment. Regression equations of the dependence of the crack resistance, the hardness, and the toughness on the temperature of hardening and tempering are obtained.

Comparative analysis of the properties of semiproducts from aluminum alloys with recrystallized and nonrecrystallized structures is performed. New data showing the importance of preservation of nonrecrystallized structure (the main feature of structural strengthening) for elevation of the characteristics of strength and static and cyclic crack resistance of aluminum alloys are presented. Special features of structural strengthening of aluminum-lithium alloys are considered.

The structure and properties of welds of titanium alloys VT6ch and VT22 after thermocycling performed in various modes are studied. The structure of the welds is studied by the methods of metallographic and x-ray diffraction analysis. The mechanical characteristics of the welds are determined by testing them for tensile strength, impact toughness, and crack resistance.

Statistical processing of the results of a study of cast casing parts from steels 15Kh1M1FL and 20KhMFL is preformed. The specimens were taken from over 100 turbines that had operated for 30 years. The tendencies in the variation of short-term mechanical properties at room and service temperatures, of long-term strength, and of structural parameters are studied, and the values of these characteristics after service for 350,000 h are predicted. Structure models are developed and used for predicting the crack resistance and the remaining life of casing parts.

The microstructure and mechanical properties of welded joints of cuts from Du 300 and Du 500 pipelines of the Leningradskaya and Novovoronezhskaya nuclear power plants are studied after 70 and 100 thousand hours of operation. The effects of thermal aging simulating operational impact on the microstructure and properties of welded joints of the cuts and of a model coil are determined. It is shown that long-term operation can be accompanied by embrittlement and decrease in the crack resistance of the metal of welds in Du 300 and Du 500 pipelines produced from steels 08Kh18N10T and 08Kh18N12T. The discovered changes in the microstructure can lead to deterioration of the mechanical properties of the metal of welded joints in operation of Du 300 and Du 500 pipelines.

The presented complex methods for analyzing the processes of deformation and fracture, including the evaluation of process ductility and measurement of crack resistance characteristics, are based on joint analysis of loading diagrams, acoustic emission signals, and fractures of articles fabricated from low-strength alloys. The possibilities of the methods in evaluation of fracture resistance of thin-walled parts from zirconium alloys are shown.

The effect of structure on the processes of deformation and fracture of zirconium alloys and on the characteristics of crack resistance and resistance to stress corrosion cracking of articles produced from them is studied. Methods for controlling fracture resistance by changing the structure of the alloys are considered.

Corrosion, mechanical (under static and dynamic loads), and fatigue characteristics, crack resistance, and high temperature strength of sheets from alloy V1341 with controlled recrystallized structure in state T1 are presented. The properties of the sheets are also studied after operational heating to 100 – 150°C with holds for 10 – 500 h. Sheets from alloy V1341T1 are compared with sheets from alloy AMg6M used for articles serving at medium loads.

Regular features of variation of the characteristics of strength and cyclic crack resistance are determined as a function of stage decomposition of solid solution in tempering of hardened maraging steels. Results obtained for sparingly alloyed maraging steels 03Kh11N10M2T and 03Kh11N10M2T1 are used for considering the probable mechanisms of the effect dispersion and nature of intermetallic segregations on the growth of fatigue crack at different levels of the amplitude of the stress intensity factor ΔK.

The main factors influencing the structural strength of high-strength reinforcing wire serving for a long period under the conditions of preliminarily stressed structures of reinforced concrete bridges are considered. The processes of local corrosion of reinforcing wire, softening due to relaxation in the metal, and lowering of the crack resistance due to hydrogen saturation of the steel are considered.

Comparison of the characteristics of static strength and crack resistance of pressed and rolled semiproducts from series-produced high-temperature aluminum alloys in state T1 shows that sheets of alloys AK4-2ch, VD17, and 1215 have the best combination of properties.

A standard regime of heat treatment has been developed for semifinished products of VT22 alloy manufactured by the conventional technology (casting + deformation). However, it gives a comparatively low level of crack resistance in the case of granular technology (hot isostatic pressing + deformation). In this connection it became necessary to refine the regime of heat treatment of the granulated VT22 alloy. The present work concerns the effect of different regimes of heat treatment on the size and shape of segregations of the ct-phase, investigated with the aim of improving the crack resistance characteristics of granulated VT22.

Aluminum alloys used in the aircraft industry have to satisfy the requirements of high strength at low density, appropriate resistance to different kinds of corrosion, maximum possible rigidity, good adaptability to manufacturing in the metallurgical and machine-building industries, etc. A new requirement on aircraft materials imposed in the last twenty years is an elevated resistance to crack propagation, because it is impossible so far to completely eliminate cracks in industrial materials. Therefore, aircraft builders have developed the concept of “safe vulnerability to damage,” which permits the presence of cracks in aircraft structures but requires knowledge of the laws of their propagation, The present work is devoted to a direction in the development of aluminum alloys that provides elevated crack resistance parameters.

Aluminum-lithium alloys with diminished density and high crack resistance characteristics are widely used in aircraft. Scandium additives to this alloy improve the strength properties and considerably enhance the weldability.

Characteristics of mechanical strength of maraging steel N18K9M5T after various variants of heat treatment are studied. The treatment mode providing a structure with retained austenite and two types of reverted austenite is determined. An optimum structure ensuring enough strength at high impact toughness and static and cyclic crack resistances is chosen.

In high-temperature deformation of steel slippage is observed along the inclusion-matrix interphase boundaries for different types of nonmetallic inclusions. Slippage along inclusion-matrix boundaries causes an increase in crack resistance of the steel at high temperatures.

1. The newly devised criteria and method of preliminary choice of structural steel make it possible to take into account, in addition to the properties of the material, also the dimensions and special traits of the structure, the existance of cracks, the conditions of loading. 2. We plotted experimental generalized dependences of the crack resistance (K*c/σu)2 on the reduced temperature under static and dynamic loading for low and medium-strength structural steels. 3. The newly devised method was experimentally substantiated, limitations were established for the applicability of the criteria contained in it and for the method as a whole connected with the thickness of the product and the structure of the steel.

This investigation is a continuation of these works. The proposed method of determination of Kic and Kid is applicable to alloys with a body-centered cubic lattice in the 0 5 T ! 0.2Tmelt temperature range. A clearly expressed temperature-rate relationship of yield strength is characteristic of alloys with a body-centered cubic lattice. In addition, at a certain temperature a sharp change in the energy, force, and deformation characteristics of such alloys occurs as the result of the presence in them of the ductile-to-brittle transformation.

The optimal thermomechanical treatment of dual-phase titanium alloys, which contributes to their improved crack resistance, consists of deformation in the lower portion of the β-region+deformation in superplasticity regimes+quenching from the deformation temperature+aging. In this case, maximum hardening is also achieved.

The pure 50 steel has a lower hardenability, higher fatigue life and impact strength, and lower ductile-to-brittle transition temperature (T50) and crack resistance in the hardened layer and possess a lower tendency toward the formation of hardening cracks than the steel melted from scrap.

1. It is recommended to use as parameters for calculating crack resistance the nominal stress intensity factors: KJ, determined by the method of the J-integral, taking crack growth into account, and Kδ, calculated according to the critical crack opening δc using the theoretical values of the rotational factor. The use of Kδ is preferable because of the conservativeness of the evaluation in the range of operating temperatures of heavy-duty hot-forging dies. 2. In regard to crack resistance in the range of the operating temperatures of forging dies, steel 5KhNM is better than steel 4Kh5V2FS.

1. The use of the method of Latin squares, and specifying or excluding those alloying elements whose optimum content is known and is largely independent of the concentrations of the principal alloying elements makes it possible to reduce the number of investigated experimental melts in working out the composition of steel with the required properties. 2. We obtained multiple regression equations type "chemical composition-properties" for weldable low carbon alloy steel, heat-treated to the same strength (σ0 · 2 ⩾ 750 MPa). 3. The simplex method of linear programming as used to optimize the composition of steel with σ0 · 2 ⩾ 750 MPa according to the criteria of ductility, impact toughness, and crack resistance, with constraints on the chemical composition for obtaining satisfactory weldability. The devised weldable steel in sections up to 250 mm after hardening in water and temnering has good ductility, impact toughness, and crack resistance.

1. An increase of the volume fraction of particles of excess phase from 1 to 2.7\2-3.5% leads to a decrease of Kcy by 5\2-10% and an increase of the growth rate of the fatigue crack by a factor of 1.5\2-2 for \gDK=850\2-1000 N/mm3/2. When the volume fraction of excess phases is 4.5%, the growth rate of the fatigue crack increases even with low values of ΔK. 2. In comparison with natural aging, artificial aging leads to reduced characteristics of static crack resistance and increased growth rate of the fatigue crack in the entire investigated range of \gDK. 3. The use of thermomechanical treatment in the production of rolled plates makes it possible to increase the strength properties approximately by 10% while the rupture work of the specimen with crack is reduced and the growth rate of the fatigue crack increases.

1. After normalizing, 20GFL steel possesses higher fatigue-crack propagation resistance the 10−9–10−7 m/cycle range of rates than normalized 20GL stee. 2. After hardening and tempering, 20GL and 20GFL steels have better cyclic crack resistance than after normalizing. 3. The relationship of the fatigue-crack propagation resistance to mechanical properties is nonlinear and has an extreme. The maximum crack propagation resistance is observed in 20GL steel after hardening and tempering at 500°C.