LARGE-SIZE ARTICLE HEAT TREATMENT PROCESS Russian patent published in 2006 - IPC C21D1/25 C21D1/56 

FIELD: heat treatment of large size articles such as connection parts of pipelines or thick-wall large-diameter tubes of low carbon steels.

SUBSTANCE: process comprises steps of hating, soaking, cooling for several stages and tempering. First-stage cooling is realized by immersing article into circulating quenching fluid for cooling it till temperature of metal surface not lower than 180°C. Then articles are warmed and subjected to isothermal soaking and(or) slow cooling at metal temperature providing crossing of cooling curve of zone of structural conversion of austenite to beinite at least along 2/3 of said zone length. After that articles are cooled till metal temperature not lower than 200°C at rate preventing for given kind of steel separation of embedded atoms of super-saturated solid solution. Articles are warmed till temperature that is no higher than temperature of isothermal soaking and (or) slow cooling. Last-stage cooling is realized in air. Warming of articles, isothermal soaking and (or) slow cooling and cooling after isothermal soaking and (or) slow cooling may be realized by bathing in stagnant or in circulating quenching fluid. Circulation speed of quenching fluid during bathing may be constant or it may be slowed to end of bathing process. Circulation speed of quenching fluid may be varied due to controlling power of motor creating directed flow of quenching fluid. First -stage cooling may be realized at maximum power of motor. Warming may be realized at motor power consisting of 0.1 - 0.7 of maximum power value. Isothermal soaking and(or) slow cooling may be realized at motor power consisting of 0.1 -0.9 of its maximum power. Cooling after isothermal soaking and (or) slow cooling may be performed at motor power consisting of 0.1 - 0.7 of its maximum power.

EFFECT: possibility for providing optimal parameters of heat treatment process.

3 cl, 2 dwg, 2 tbl