TUBULAR ARTICLE HEAT TREATMENT PROCESS Russian patent published in 2006 - IPC C21D8/10 B21C37/08 

FIELD: heat treatment of welded large-size articles such as connecting parts of pipelines or thick-wall large-diameter tubes of low carbon complex-alloy steel.

SUBSTANCE: tubular article is welded of shaped sheet blanks. Before hot shaping sheet blank is heated up to temperature Ac3 +(80 - 190)°C. Ready welded article is finally bulk heated up to Ac3 +(50 -100)°C , then it is cooled and subjected to tempering. Before final bulk heating of ready article it is preliminarily bulk heated up to temperature Ac3 +(80 - 190)°C. After preliminary heating article is cooled in air or it is subjected to accelerated cooling till metal temperature M - 600°C for further cooling in air. After preliminary bulk heating and(or) preliminary final bulk heating cooling may be performed by three stages. At first stage cooling is realized at rate providing crossing of cooling curve with line of starting structural conversion of austenite to ferrite in thermal kinetic diagram. At second stage cooling is realized at less rate or isothermal soaking is performed in temperature range M_n -_{550°C till complete austenite decomposition according to said diagram. At third stage cooling is realized at rate preventing separation of interstitial atoms from supersaturated solid solution till temperature no less than 180°C. Then during preliminary bulk heating article is loaded in furnace for final bulk heating. If only final bulk heating is realized, article cooling is going on at rate no more than 3°C/s. Before preliminary or final bulk heating, additional local heating up to temperature Ac3 +(80 -190)°C may be realized. Accelerated cooling of welded seam metal and adjacent zone whose width does not exceed five thickness values of article wall at each side from center of welded seam till temperature of metal no less than 450°C at rate providing ferrite-bainite or bainite metal structure also may be realized.}

EFFECT: optimized parameters of heat treatment of tubular articles.

5 cl, 1 tbl