METHOD OF THERMAL TREATMENT OF ITEMS Russian patent published in 2005 - IPC

FIELD: thermal treatment of pipelines coupling pieces made out of alloyed or low-alloy steels.

SUBSTANCE: the invention is pertaining to the field of thermal treatment of pipelines coupling pieces made out of alloyed or low-carbon steels. The technical result is optimization of the treatment parameters. The method of the thermal treatment of items provides for their heating up to the temperature of _{AC3 + (50-190°C), aging, cooling in some stages and tempering. At that at the first stage the cooling is conducted at the speed ensuring interception of the cooling curve with the line of the beginning of the structural transformation of austenitic into ferrite on the thermalkinetic diagram below the point Ar1; at the second stage corresponding to the field of formation of ferrite the cooling is conducted at a lower speed or conduct an isothermal aging; and at the third stage the cooling is conducted at the speed ensuring formation of a bainite up to temperature of 250-180°C; then prolong the cooling at the speed of no more than 3°C/s. The temperature increase at tempering may be conducted at least in two stages, after each of which conduct an isothermal aging. At that the first aging is conducted at the temperature of no less than 180°C and the final aging - at the temperature of no more than AC1-20°C. After the isothermal aging conducted after the first and-or one or several subsequent stages of temperature increase may be conducted a cooling till termination of the stage of boiling in the water at the temperature of no less than 80°C.}

EFFECT: the invention ensures optimization of the thermal treatment parameters.

3 cl, 1 dwg, 2 tbl