We present the results of development of the technology of thermal hardening and thermal straightening of shaped rolled St3 steel (structural angles) based on the mathematical and physical simulation ...of the process of heat transfer with accelerated water cooling of the metal. For this purpose, we used the DEFORM 3D + HEAT TREATMENT software environment of the finite-element method and carried out laboratory experiments in three furnaces for different temperatures and holding times varying within broad ranges in order to simulate the modes of accelerated water cooling of shaped rolled products. The characteristics of mathematical simulation of the technology of thermal treatment of equal-section rolled structural angles 63 × 63 × 4 mm in size made of St3sp steel are presented with an aim to evaluate the structure and mechanical properties of the rolled metal. It is confirmed that the diffusion phase transformation is accompanied by the heat release (the so-called phenomenon of recalescence). We also present the temperature distributions over the sections and areas of the rolled steel showing that the less massive areas of the profile (edges of the structural angles) are cooled much more intensely than the massive sections (the top of the profile angle). However, the areas accumulating more heat transfer their heat to less massive and hardened areas. As a result, we observe the self-tempering of the martensitic areas accompanied by the formation of tempering pearlitic structure quite efficient for the purposes of operation. The laboratory investigations were carried out on three shaped profiles (equal-leg structural angles 40 × 40 × 4 and 75 × 75 × 8 mm in sizes and channel No. 5). The efficiency of thermal treatment was proved for shaped profiles made of unalloyed ordinary St3sp steel hardened within the range of tempering temperatures 200–650°C, with attainment of the hardening coefficient within the range 1.4–2.6 (according to the temporal rupture resistance). This guarantees the possibility of the production of angled rolled products of elevated strength classes within the range 440–1130 MPa instead of the original hot-rolled strength class of 320 MPa (by the yield strength). The obtained results of modeling of the technology of thermal treatment of structural angles made of St3sp steel can be extended (after the required experiments) to other types of steel (e.g., 09G2, 09G2S, 10KhSND, etc.) with the exception of expensive microalloying with vanadium, niobium, titanium, and other elements.
The contribution of separations into the impact toughness of steels of strength class X80 is studied. Tests for impact bending are preformed in the range from +20 to –90°C, and analysis of fracture ...surfaces of Charpy specimens is performed. It is shown that the length
L
h
of the high-energy zone of homogeneous ductile fracture is directly correlated with the level of the impact toughness
KCV
. The evolution of the form and number of separations upon lowering of the test temperature is considered. The conditions of attainment of a high level of impact toughness (
KCV
– 60
≥ 250 J/cm
2
) are determined.
Tempcore and Thermex technologies for the thermal strengthening of rebar in the bar-rolling line are analyzed. New Thermtime technology is proposed. The dependence of the cooling rate on the water ...flow rate is determined. The temperature distribution over the bar cross section in thermal strengthening is presented.
The evolution of mechanical properties of two steels of strength class K65 (X80) is studied under heating in the intercritical temperature range and from 150°C to the lower boundary of the ...intercritical range.
The influence of nitrogen as a microalloying element in steel for metallic structures is investigated. The use of nitrogen to improve the mechanical properties and low-temperature strength of rolled ...steel in various strength classes is very promising and permits reduction in the steel’s manganese content.
The effect of welded joint heat-affected zone (HAZ) cooling rate on structure, mechanical properties and brittle failure resistance of pipe steels of strength class X100 is studied by simulating ...welding thermal cycles in a Gleeble-3180 test unit. These properties are compared with results obtained with pipe welding, and good correlation of data obtained in a laboratory and for an actual pipe is demonstrated. It is also shown that the method for simulating thermal cycles makes it possible to evaluate properties of the heataffected zone without associated processing factors during actual pipe welding. Research results make it possible to establish the range of HAZ cooling rates providing preparation of the required values of longitudinal weld properties for pipe of considerable diameter made from steel of strength class X100.
Fibers are added to concrete to bridge cracks, in order to improve mechanical behavior from brittle to pseudo-plastic. Uniform dispersion of fibers is known to be critical, to avoid weak planes and ...the influence of self-compacting ability of fiber-reinforced concrete (FRC) on fiber dispersion has been studied and reported in the literature to some extent. A self-compacting (SCFRC) and a normal workability FRC (NFRC) was designed and tested systematically. Indirect assessment of fiber dispersion and orientation was performed by mechanical testing on small specimens, to study the influence on mechanical performance. The results show superiority of SCFRC in flexure.
Structural steels used in the production of welded metal structures in contemporary domestic and overseas practice are analyzed. Common tendencies and differences from strength classes used most ...frequently are revealed in steel alloy systems used in the production of thick rolled sheet. Simulation of normalizing and thermomechanical rolling, and also normalizing for steel of the alloy system C–Mn–Si–Nb, is performed under laboratory conditions. The possibility is demonstrated of preparing rolled product of strength class 390 with an increased level of brittle failure resistance from economically alloyed steel using thermomechanical (normalizing) rolling technology.
The material traditionally used for the structures of oil storage tanks – hot-rolled low-alloy plate steel 09G2S – rapidly decreases in strength with an increase in the thickness of the plates and ...becomes more susceptible to brittle fracture. The material does not provide the necessary resistance to the initiation of hydrogen-induced corrosion cracking and is not reliable or safe enough for use in storage tanks. The low strength of this steel makes it impossible to blast-proof these structures. The solution to these problems is the development and use of new rolled plates with excellent service properties. One steel that meets these needs is steel 08G2NMFB, of strength class 390. This steel has good weldability and is highly resistant to brittle fracture. Its use will ensure a high degree of reliability and safety in the operation of large storage tanks and provide significant technical-economic benefits.
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