At present the quality of steel is often improved by thermomechanical treatment (TMT). It is of interest to establish the effect of the state of austenite in strain caused by TMT on the properties of steels. This paper is devoted to the effect of various thermal-strain treatment regimes on the properties and structure of steels 25GSR and 20 with different stabilities of austenite.The technological process of thermomechanical strengthening of rolled steel permits substantial savings in power resources because the strengthening is conducted using the rolling heating after the strain treatment of the steel is finished. TMT also makes it possible to save alloying elements because it ensures a high level of properties (both strength and toughness) of the steel. Use of roiled stock with elevated strength properties creates conditions for the production of mechanisms, machines, and metal and ferroconcrete structures with a diminished consumption of metal [1].Another factor affecting the efficiency of such treatment of steel consists in that it can eliminate the negative effect of the processes of high-speed rolling in modem continuous mills characterized by an elevated temperature at the end of the process, which worsens the properties of the metal and especially the toughness characteristics.In the process of hot plastic strain of steel the elements are uniformly distributed over austenite grains and the harmful impurities positioned in near-boundary zones dissolve. As a result of dynamic and static recrystallization austenite grains are fractured. The high cooling rate of the rolled stock after it leaves the mill causes formation of highly dispersed products of decomposition of austenite and diminishes the size of austenite grains [2][3][4].The structural state that results after TMT increases the strength and fatigue resistance of the metal with a simultaneous substantial growth of the impact toughness even at negative temperatures (which is especially important). For example, low-alloy steels (09G2-14G2, 09G2S, and other grades) strengthened to o r = 520 and 600 N/mm 2 have an impact toughness a I > 35 J/cm 2 at -70~Institute of Ferrous Metallurgy of the National Academy of Sciences of Ukraine. 19It should be noted that the parameters of the thermalstrain treatment of steel in the process of the TMT can be varied in order to form a favorable structural state and obtain a high set of properties [5 -6].For this purpose we studied various temperature and strain regimes for treating steels 20 and 25GSR characterized by different stabilities of austenite. The specimens were rolled in a mill at the Institute of Ferrous Metallurgy of the National Academy of Sciences of Ukraine with a 30% reduction. The furnace heating for rolling was conducted by the following regime: the specimens were heated to 1100~ then placed in the furnace heated to various temperatures, and strained (see Table l). The rolled specimens were cooled in water in a special device at a mean flow rate of the water equal to 45-50 deg/sec. The accelerated co...

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The strength and the operational properties of low-alloy thick-sheet steels is increased by heat treatment m the line of the mill with the use of the rolling or furnace heat. The present work concerns the special features of structure formation and the mechanical properties of rolled stock from sheet structural steel 09G2S with a strength level C345 (er> = 325 -345 MPa) in a hot-rolled and a normalized state after accelerated cooling from the normalizing furnace and after rolling behind the finishing stand. As a result of the rapid cooling in the line of the mill the sheet acquires properties corresponding to steels with a C390-C440 strength level (o> = 390 -440 MPa).We studied the microstructure and the properties of rolled sheets 10 mm thick from steel 09G2S (0.1% C, 1.43% Mn, 0.62% Si, 0.02% S, 0.016% P) after various kinds of heat treatment under industrial conditions. The steel was melted in a 300-ton converter of the Azovstal' Plant and cast in continuous casting machines. The slabs were rolled for sheets 10 mm thick and heat treated in the line of a 3600 mill using the regimes presented below. -30Notations: l fr IS the final rolling temperature, vc,., I is the cooling rate in the 900 600~ range (regimes 1 -3 ) and 890 -590~162 range (regime 4 ); then in air. Notes. I. The number of the treatment regime is given in parentheses. 2. The accelerated cooling by regime 3 was conducted in a noz_zle installation; the cooling by' regime 4 was conducted in an LIOVT tank installation.After treatment by various regimes we studied the structure of the specimens and evaluated its effect on the set of strength, ductile, and toughness characteristics of the given steel.